686 results on '"Werner, Douglas H"'
Search Results
2. Terahertz vortex beam generation based on reflective and transmissive graphene metasurfaces
- Author
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Ren, Qiang, Wang, Lin, Wang, Tianrang, Wang, Shuining, Zhou, Yuanguo, Kang, Lei, Werner, Pingjuan L., and Werner, Douglas H.
- Published
- 2024
- Full Text
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3. Zinc oxide (ZnO) hybrid metasurfaces exhibiting broadly tunable topological properties
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Wu Yuhao, Chowdhury Sarah N., Kang Lei, Saha Soham S., Boltasseva Alexandra, Kildishev Alexander V., and Werner Douglas H.
- Subjects
polarization synthesis ,topological photonics ,tunable metasurfaces ,Physics ,QC1-999 - Abstract
Extreme light confinement observed in periodic photonic structures, such as the vortex singularities in momentum (k) space, has been associated with their topological nature. Consequently, by exploiting and tuning their topological properties, optical metasurfaces have been demonstrated as an attractive platform for active photonics. However, given the fact that most active media under external excitations can only provide limited refractive index change, the potential advancements offered by the topological character of active metasurfaces have remained mostly unexplored. Zinc oxide (ZnO), which has recently exhibited optically-induced extraordinarily large permittivity modulations at visible and near-infrared frequencies, is an excellent active material for dynamic metasurfaces exhibiting strong tuning. This work demonstrates that a hybrid metasurface consisting of an array of ZnO nanodisks on a silver backplane displays broadly tunable topological properties. In particular, by performing k-space scattering simulations using measured pump-fluence-dependent material properties of ZnO, we study in detail the light reflection from the hybrid metasurface. Our results validate that the large k-space topology tuning of the metasurface can result in enormously strong polarization manipulation of near-infrared light in the vicinity of the topological features. The observed polarization switching effect is highly sensitive to the polarization and wavelength of an incident wave, owing to the symmetry and dispersion characteristics of the proposed system. Our study indicates that leveraging a combination of the extraordinary material properties and the k-space topology, hybrid metasurfaces based on ZnO may open new avenues for creating all-optical switchable metadevices.
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- 2022
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4. Improved convergence in planar nanophotonic topology optimization via the multigradient
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Jenkins, Ronald P., Whiting, Eric B., Campbell, Sawyer D., and Werner, Douglas H.
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- 2022
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5. Generalized temporal transfer matrix method: a systematic approach to solving electromagnetic wave scattering in temporally stratified structures
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Xu Jingwei, Mai Wending, and Werner Douglas H.
- Subjects
anisotropy ,anti-reflection coating ,multi-layer medium ,polarization conversion ,temporal modulation ,transfer matrix method ,Physics ,QC1-999 - Abstract
Opening a new door to tailoring electromagnetic (EM) waves, temporal boundaries have attracted the attention of researchers in recent years, which have led to many intriguing applications. However, the current theoretical approaches are far from enough to handle the complicated temporal systems. In this paper, we develop universal matrix formalism, paired with a unique coordinate transformation technique. The approach can effectively deal with temporally stratified structures with complicated material anisotropy and arbitrary incidence angles. This formulation is applied to various practical systems, enabling the solution of these temporal boundary related problems in a simple and elegant fashion, and also facilitating a deep insight into the fundamental physics.
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- 2022
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6. Establishing exhaustive metasurface robustness against fabrication uncertainties through deep learning
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Jenkins Ronald P., Campbell Sawyer D., and Werner Douglas H.
- Subjects
deep learning ,fabrication ,robustness ,supercell ,tolerance ,Physics ,QC1-999 - Abstract
Photonic engineered materials have benefitted in recent years from exciting developments in computational electromagnetics and inverse-design tools. However, a commonly encountered issue is that highly performant and structurally complex functional materials found through inverse-design can lose significant performance upon being fabricated. This work introduces a method using deep learning (DL) to exhaustively analyze how structural issues affect the robustness of metasurface supercells, and we show how systems can be designed to guarantee significantly better performance. Moreover, we show that an exhaustive study of structural error is required to make strong guarantees about the performance of engineered materials. The introduction of DL into the inverse-design process makes this problem tractable, enabling optimization runtimes to be measurable in days rather than months and allowing designers to establish exhaustive metasurface robustness guarantees.
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- 2021
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7. An Ultrathin, Fast‐Response, Large‐Scale Liquid‐Crystal‐Facilitated Multi‐Functional Reconfigurable Metasurface for Comprehensive Wavefront Modulation.
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Wu, Xin Yu, Feng, Hong Yuan, Wan, Fengshuo, Wei, Meng, Guo, Chong, Cai, Longzhu, Wu, Fan, Jiang, Zhi Hao, Kang, Lei, Hong, Wei, and Werner, Douglas H.
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- 2024
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8. Flexible terahertz spoof plasmonics based on graphene-assembled films.
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Zhang, Bohan, He, Dapeng, Zhang, Qian, Fang, Jiaxing, Lu, Xueguang, Huang, Wanxia, Chen, Zibo, He, Daping, Kang, Lei, Werner, Douglas H., and Wang, Shengxiang
- Subjects
TERAHERTZ technology ,PLASMONICS ,ELECTRIC conductivity ,THERMAL stability - Abstract
Spoof plasmonics, which can enable strong terahertz (THz) radiation–matter interactions, hold great promise for the advancement of THz science and technology. However, THz spoof plasmonic devices based on micro-structured metals are in general limited by lithography-based fabrication processes as well as metals' mechanical, chemical, and thermal stability, which hinders their applications in, for instance, flexible and wearable THz imaging and communications, molecular sensing, etc. Possessing high electrical conductivity and outstanding mechanical robustness, graphene-assembled films (GAFs) promise many benefits for electronics as an alternative to metals. Here, by studying the resonance-enhanced transmission properties of subwavelength GAF hole arrays, we demonstrate a GAF metasurface as a transformative platform for flexible THz spoof plasmonics. Based on a laser direct writing (LDW) patterning technique, the proposed micro-engineered GAF is expected to pave the way toward large-area, durable, and inexpensive THz metadevices with superior flexibility. [ABSTRACT FROM AUTHOR]
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- 2024
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9. Exploiting plasmons in 2D metals for refractive index sensing: Simulation study.
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Kang, Lei, Robinson, Joshua A., and Werner, Douglas H.
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REFRACTIVE index ,THIN films ,PLASMONICS ,METALS ,NANORIBBONS ,METALLIC films ,SENSES - Abstract
Ultrathin and two-dimensional (2D) metals can support strong plasmons, with concomitant tight field confinement and large field enhancement. Accordingly, 2D-metal nanostructures exhibiting plasmonic resonances are highly sensitive to the environment and intrinsically suitable for optical sensing. Here, based on a proof-of-concept numerical study, nano-engineered ultrathin 2D-metal films that support infrared plasmons are demonstrated to enable highly responsive refractive index (RI) sensing. For 3 nm-Au nanoribbons exhibiting plasmonic resonances at wavelengths around 1600 nm, a RI sensitivity of S
RI > 650 nm per refractive index unit (RIU) is observed for a 100 nm-thick analyte layer. A parametric study of the 2D-Au system indicates the strong dependence of the RI sensitivity on the 2D-metal thickness. Furthermore, for an analyte layer as thin as 1 nm, a RI sensitivity up to 110 (90 nm/RIU) is observed in atomically thin 2D-In (2D-Ga) nanoribbons exhibiting highly localized plasmonic resonances at mid-infrared wavelengths. Our results not only reveal the extraordinary sensing characteristics of 2D-metal systems but also provide insight into the development of 2D-metal-based plasmonic devices for enhanced IR detection. [ABSTRACT FROM AUTHOR]- Published
- 2022
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10. Design for quality: reconfigurable flat optics based on active metasurfaces
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Shalaginov Mikhail Y., Campbell Sawyer D., An Sensong, Zhang Yifei, Ríos Carlos, Whiting Eric B., Wu Yuhao, Kang Lei, Zheng Bowen, Fowler Clayton, Zhang Hualiang, Werner Douglas H., Hu Juejun, and Gu Tian
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deep neural network ,inverse design ,metasurface ,meta-optics ,phase-change material ,reconfigurable ,Physics ,QC1-999 - Abstract
Optical metasurfaces, planar subwavelength nanoantenna arrays with the singular ability to sculpt wavefront in almost arbitrary manners, are poised to become a powerful tool enabling compact and high-performance optics with novel functionalities. A particularly intriguing research direction within this field is active metasurfaces, whose optical response can be dynamically tuned postfabrication, thus allowing a plurality of applications unattainable with traditional bulk optics. Designing reconfigurable optics based on active metasurfaces is, however, presented with a unique challenge, since the optical quality of the devices must be optimized at multiple optical states. In this article, we provide a critical review on the active meta-optics design principles and algorithms that are applied across structural hierarchies ranging from single meta-atoms to full meta-optical devices. The discussed approaches are illustrated by specific examples of reconfigurable metasurfaces based on optical phase-change materials.
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- 2020
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11. Chapter 7 - Task-oriented reconfigurable metasurfaces based on inverse design and temporal meta-systems
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Kang, Lei, Campbell, Sawyer D., Wu, Yuhao, Xu, Jingwei, Mai, Wending, Whiting, Eric B., and Werner, Douglas H.
- Published
- 2024
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12. A metamaterial-enabled design enhancing decades-old short backfire antenna technology for space applications
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Binion, J. Daniel, Lier, Erik, Hand, Thomas H., Jiang, Zhi Hao, and Werner, Douglas H.
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- 2019
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13. Correction to 'Spatial transformation-enabled electromagnetic devices: from radio frequencies to optical wavelengths'
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Jiang, Zhi Hao, Turpin, Jeremy P., Morgan, Kennith, Lu, Bingqian, and Werner, Douglas H.
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- 2016
14. Spatial transformation-enabled electromagnetic devices: from radio frequencies to optical wavelengths
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Jiang, Zhi Hao, Turpin, Jeremy P., Morgan, Kennith, Lu, Bingqian, and Werner, Douglas H.
- Published
- 2015
15. A generalized temporal transfer matrix method and its application to modeling electromagnetic waves in time-varying chiral media.
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Yang, Dongha, Xu, Jingwei, and Werner, Douglas H.
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TRANSFER matrix ,COMPUTATIONAL electromagnetics ,ELECTROMAGNETIC waves ,OPTICAL rotation ,METAMATERIALS - Abstract
Chiral metamaterials have attracted significant attention in recent years due to their unique properties in both the microwave and optics regimes. However, most existing works rely on engineering the desired properties of spatial interfaces, and the concept of time-varying chirality has only recently begun to be explored. As a consequence, there is currently a lack of suitable tools for evaluating the propagation of electromagnetic (EM) waves in time-varying chiral media. As such, this paper presents the theoretical formulation for temporal reflection and transmission of EM waves in time-varying chiral media using the temporal transfer matrix method (TTMM). The developed TTMM tool will then be utilized to explore several application examples including a structure with an arbitrary temporal profile, optical activity generated from time interfaces, and anti-reflection temporal coatings. In addition, we employ a specialized finite-difference time-domain (FDTD) technique, known as BI-FDTD, in all the scenarios to validate the proposed theory. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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16. Nonlinear Chiral Metasurfaces Based on the Optical Kerr Effect.
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Kang, Lei, Wu, Yuhao, and Werner, Douglas H.
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KERR electro-optical effect ,OPTICAL polarization ,OPTICAL materials ,INDUCTIVE effect ,NONLINEAR waves ,CIRCULAR dichroism ,RESONANCE - Abstract
Chiral nanostructures have immense potential for complete polarization control of light. Given the intrinsic 3D structure of circularly polarized light, nanoarchitectures with structural chirality in 3D space are usually required to achieve "full" chiroptical response. On the other hand, due to the lack of available active materials at optical wavelengths, examples of chiral photonic devices that can be tuned in an active manner remain rare. Here, based on the large Kerr nonlinearities of silicon, the nonlinear chiroptical response from a planar Si metasurface supporting high quality (Q)‐factor guided mode resonances (GMRs) at near‐infrared wavelengths, are numerically demonstrated. In the linear regime, the optical anisotropy of the C2‐symmetric structure associated with the observed GMRs leads to a pair of chiral resonance modes, enabling pronounced cross‐polarization transmission circular dichroism and a strong handedness‐dependent field enhancement effect. Owing to the nonlinear Kerr effect, such Si metasurfaces are seen to exhibit prominent chiral‐selective optical nonlinearity. Importantly, a pronounced co‐polarization transmission circular dichroism is observed, suggesting that the circularly polarized waves in the nonlinear regime possess asymmetric Jones matrices. Dielectric chiral metasurfaces with Kerr nonlinearities can be utilized to facilitate polarization‐state modulators with simple planar structures. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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17. System response analysis in wavenumber domain for linear space-invariant time-varying problems
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Mai, Wending, Xu, Jingwei, Das, Arkaprovo, and Werner, Douglas H.
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FOS: Physical sciences ,Optics (physics.optics) ,Physics - Optics - Abstract
Being a powerful tool for linear time-invariant (LTI) systems, system response analysis can also be applied to the so-called linear space-invariant (LSI) but time-varying systems, which is a dual of the conventional LTI problems. In this paper, we propose a system response analysis method for LSI problems by conducting Fourier transform of the field distribution on the space instead of time coordinate. Specifically, input and output signals can be expressed in the wavenumber (spatial frequency) domain. In this way, the system function in wavenumber domain can also be obtained for LSI systems. Given an arbitrary input and temporal profile of the medium, the output can be easily predicted using the system function. Moreover, for a complex temporal system, the proposed method allows for decomposing it into multiple simpler subsystems that appear in sequence in time. The system function of the whole system can be efficiently calculated by multiplying those of the individual subsystems., This article has been withdrawn due to an unresolvable internal author dispute
- Published
- 2022
18. Linear and nonlinear chiroptical response from individual 3D printed plasmonic and dielectric micro-helices.
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Famularo, Nicole R., Kang, Lei, Li, Zehua, Zhao, Tian, Knappenberger, Kenneth L., Keating, Christine D., and Werner, Douglas H.
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SECOND harmonic generation ,CIRCULAR dichroism ,MICROSCOPY ,NONLINEAR optical spectroscopy ,OPTICAL spectroscopy ,DIELECTRICS ,NEAR-field microscopy - Abstract
Sub-wavelength chiral resonators formed from artificial structures exhibit exceedingly large chiroptical responses compared to those observed in natural media. Owing to resonant excitation, chiral near fields can be significantly enhanced for these resonators, holding great promise for developing enantioselective photonic components such as biochemical sensors based on circular dichroism (CD) and spin-dependent nonlinear imaging. In the present work, strong linear and nonlinear chiroptical responses (scattering CD > 0.15 and nonlinear differential CDs > 0.4) at visible and near infrared frequencies are reported for the first time for individual micrometer-scale plasmonic and dielectric helical structures. By leveraging dark-field spectroscopy and nonlinear optical microscopy, the circular-polarization-selective scattering behavior and nonlinear optical responses (e.g., second harmonic generation and two-photon photoluminescence) of 3D printed micro-helices with feature sizes comparable to the wavelength (total length is ∼5λ) are demonstrated. These micro-helices provide potential for readily accessible photonic platforms, facilitating an enantiomeric analysis of chiral materials. One such example is the opportunity to explore ultracompact photonic devices based on single, complex meta-atoms enabled by state-of-the-art 3D fabrication techniques. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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19. Contact tracing Inspired Efficient Computation by Energy Tracing
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Mai, Wending, Jenkins, Ronald P., Chen, Yifan, and Werner, Douglas H.
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Computational Engineering, Finance, and Science (cs.CE) ,FOS: Computer and information sciences ,Computer Science - Computational Engineering, Finance, and Science - Abstract
Inspired by the epidemic contact tracing technique, we propose a method to efficiently solve electromagnetics by tracing the energy distribution. The computational domain is adaptively decomposed, and the available computational resources are focused on those energy-active (infections) and their adjacent (exposed) domains, while avoiding the unnecessary computation of energy-null (unexposed) domains. As an example, we employ this method to solve several optics problems. The proposed method shows high efficiency while maintaining a good accuracy. The energy tracing method is based on the causality principle, and therefore is potentially transformative into other computational physics and associated algorithms., This article has been withdrawn due to an unresolvable internal author dispute
- Published
- 2022
20. Assembled medium: A route to the generation of vortex waves carrying orbital angular momentum with different modes.
- Author
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Yi, Jianjia, Liu, Chenchen, Shi, Zhe, Zhu, Lina, Chen, Xiaoming, Werner, Douglas H., and Nawaz Burokur, Shah
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ANGULAR momentum (Mechanics) ,LAPLACE'S equation ,VECTOR beams ,TRANSFORMATION optics ,TELECOMMUNICATION systems - Abstract
In this letter, a method for the generation of multimodal vortex waves carrying orbital angular momentum (OAM) is proposed based on the transformation optics concept. The device is equally divided into eight sectors assigned by transformed material parameters, which are determined by solving Laplace's equation. Sectors with different phase variations from 0 to 2 π can be judiciously shuffled to generate vortex beams with different modes. Full wave numerical simulations are performed to validate multimodal OAM beam generation functionality and broadband performance of the proposed device. Such an implementation method opens the door to the application of vortex waves carrying OAM in communication systems. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
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21. Fundamental Asymmetries between Spatial and Temporal Boundaries in Electromagnetics.
- Author
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Mai, Wending, Xu, Jingwei, and Werner, Douglas H.
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ELECTROMAGNETISM ,ENERGY conservation ,CONSERVATION laws (Physics) ,OPTICAL reflection ,DEGREES of freedom - Abstract
Time-varying materials bring an extra degree of design freedom compared to their conventional time-invariant counterparts. However, few discussions have focused on the underlying physical difference between spatial and temporal boundaries. In this letter, we thoroughly investigate those differences from the perspective of conservation laws. By doing so, the building blocks of optics and electromagnetics such as the reflection law, Snell's law, and Fresnel's equations can be analogously derived in a temporal context, but with completely different interpretations. Furthermore, we study the unique features of temporal boundaries, such as their nonconformance to energy conservation and causality. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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22. Compact Multifunctional Gain Enhancing GRIN Lens for Widely Separated Frequency Band Shared Aperture Antennas.
- Author
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Whiting, Eric B., Xu, Jingwei, Campbell, Sawyer D., Bossard, Jeremy A., Barrett, John P., Withrow, Joshua W., Weigner, James D., and Werner, Douglas H.
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ELECTROMAGNETIC wave propagation ,TRANSFORMATION optics ,CERAMIC materials ,SYNTHETIC aperture radar - Abstract
Gradient index (GRIN) lenses embody a powerful technology that enables control of electromagnetic wave propagation over wide frequency bands. However, GRIN lenses that achieve multifunctional (i.e., dual broadband) performance have not been realized mainly due to the limitations of conventional techniques such as Transformation Optics (TO). This paper proposes a multi‐objective inverse‐design approach for the optimization of multi‐band GRIN lenses with highly constrained aperture sizes. A candidate lens design is fabricated from a ceramic material using a new additive manufacturing approach allowing for spatially‐varying permittivities between 2–6.5 to be achieved at sub‐cm resolution. Measured results validate the candidate functionalized ceramic GRIN lens's simulated multi‐band performance and demonstrate the efficacy of the proposed inverse‐design procedure. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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23. Adjoint Sensitivity Optimization of Three-Dimensional Directivity-Enhancing, Size-Reducing GRIN Lenses.
- Author
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Whiting, Eric B., Mackertich-Sengerdy, Galestan, Campbell, Sawyer D., Soltani, Saber, Haack, Micah P., Barrett, John P., Withrow, Joshua W., Bossard, Jeremy A., and Werner, Douglas H.
- Abstract
Gradient Index (GRIN) lenses have the potential to tailor the radiation behavior of existing antennas for improved gain performance. Conventional methods such as transformation optics have mainly focused on two-dimensional (2-D) problems (e.g., axisymmetric or sectoral horn lenses), and often produce designs with unrealistic material parameters or poor impedance matching. In this letter, we propose a new method of designing freeform GRIN lenses using adjoint sensitivities to rapidly find optimal solutions within feasible material bounds that achieve desired performance goals. A proof-of-concept 3-D GRIN lens that achieves comparable performance to a larger 20 dB standard gain horn albeit with considerable size reduction is optimized, fabricated, and tested in order to highlight the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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- View/download PDF
24. Contributors
- Author
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Ahmed, Abdelhamed, Alù, Andrea, Barbuto, Mirko, Benoni, Arianna, Bilotti, Filiberto, Budhu, Jordan, Campbell, Sawyer D., Castaldi, Giuseppe, Chazelas, Jean, Díaz-Rubio, Ana, Di Renzo, Marco, Engheta, Nader, Flamini, Roberto, Galdi, Vincenzo, Gradoni, Gabriele, Grbic, Anthony, Hao, Yang, Kang, Lei, Lombardi, Renato, Ma, YiHan, Maci, Stefano, Mai, Wending, Massa, Andrea, Massagrande, Claudio, Mazzucco, Christian, Moccia, Massimo, Monti, Alessio, Oliveri, Giacomo, Ramaccia, Davide, Salucci, Marco, Toscano, Alessandro, Tretyakov, Sergei, Tripon-Canseliet, Charlotte, Vellucci, Stefano, Verní, Francesco, Werner, Douglas H., Whiting, Eric B., Wu, Yuhao, Xu, Jingwei, and Zappone, Alessio
- Published
- 2024
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25. Modal Analysis, Inverse-Design, and Experimental Validation of Bandwidth-Controllable Suspended Patch Antennas Loaded With Cylindrical Anisotropic Impedance Surfaces.
- Author
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Peng, Manxin, Zhang, Ke, Yue, Taiwei, Jiang, Zhi Hao, and Werner, Douglas H.
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ANTENNAS (Electronics) ,SURFACE impedance ,OMNIDIRECTIONAL antennas ,IMMUNOCOMPUTERS ,ULTRA-wideband antennas ,MODAL analysis ,BROADBAND communication systems ,GENETIC algorithms - Abstract
In this article, bandwidth-controllable suspended patch antennas (SPAs) loaded by anisotropic impedance surfaces (AISs) are proposed. A highly efficient yet accurate semianalytical modal expansion method (MEM) is developed for calculating the input impedance and radiation properties of the proposed antenna, which greatly reduces the simulation time and consumed memory compared to a commercial full-wave solver. The MEM is further utilized by coupling it with a genetic algorithm for effectively performing inverse-design, i.e., optimizing AIS-loaded SPAs with different predefined frequency responses. Three proof-of-concept antenna examples are designed, fabricated, and characterized, including an ultrawideband (UWB) antenna, a dual-wideband antenna, and a band-notched UWB antenna. The operating principle is illustrated by investigating the resonant modes of the AIS-loaded SPAs. The measured results of the three antennas exhibit good agreement with theoretical predictions, demonstrating that all three antennas have vertically polarized conical patterns in the E-plane and omnidirectional patterns in the H-plane with a cross polarization of smaller than −15 dB in their respective operational frequency band(s). The good performance demonstrates that the proposed AIS-loaded SPAs are promising candidates for broadband and multiband communications. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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26. Generalized Sequential Rotation Arrays With Full Control of Dual-Circularly-Polarized Aperture-Field Distribution Based on Elliptically-Polarized Elements.
- Author
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Wu, Xin Yu, Jiang, Zhi Hao, Zhang, Yan, Yue, Taiwei, Hong, Wei, and Werner, Douglas H.
- Subjects
GEOMETRIC quantum phases ,DEGREES of freedom ,ROTATIONAL motion ,TELECOMMUNICATION satellites ,FORWARD error correction ,DESIGN techniques - Abstract
In this article, the theory, design, and experimental validation of wideband generalized sequential rotation arrays (GSRAs) are reported. In particular, the GSRA has the ability to provide dual-circularly polarized (dual-CP) beams with different handedness using a single feeding network, whose aperture amplitude and phase distributions can both be independently controlled. Such functionality is achieved by jointly utilizing the dynamic phase and Berry phase, as well as exploiting elliptically polarized (EP) array elements with different axial ratio (AR) values. The proposed technique and the design methodology are verified by two proof-of-concept microstrip GSRAs consisting of an $8\times8$ array of EP stacked-patch elements operating in the K-band. The first prototype exhibits a 3 dB gain difference between the two CP beams, while the other offers a 6 dB gain difference and different sidelobe levels (SLLs) for the generated dual-CP beams. Both arrays are fabricated and measured, experimentally achieving a joint $S_{11} < -10$ dB, AR < 3 dB, and 3 dB gain bandwidth of more than 28.4% and 20.1% with a beam squinting of less than 3°. In addition, the two GSRAs enable a bandwidth of about 19% and 3% within which the gain difference between the two CP beams of different handedness deviates from the targeted value by less than 1 dB. With the large degree of freedom in aperture field control, the proposed GSRAs could be potential candidates for use in satellite communications, point-to-multipoint communications, and so on. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
27. Dual-Band Advanced Short Backfire Antenna With 100% Aperture Efficiency Over a Wide Range of Diameters.
- Author
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Binion, J. Daniel, Mussman, Colin A., Lier, Erik, Hand, Thomas H., and Werner, Douglas H.
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APERTURE antennas ,ANTENNAS (Electronics) ,DIAMETER ,SURFACE impedance - Abstract
In this article, we demonstrate that a circular advanced short backfire antenna (A-SBFA) can be optimized for high single- or dual-band aperture efficiency over a range of different aperture sizes. Optimization methods developed previously to utilize anisotropic, dispersive metasurfaces on the cavity walls of the hexagonal A-SBFA are modified and applied to achieve 100% aperture efficiency at two frequency bands for circular aperture diameters spanning a remarkably large range from $1.0\lambda _{0}$ up to $2.13\lambda _{0}$. Furthermore, a single-frequency optimization was able to achieve a design with 100% aperture efficiency for an A-SBFA with a diameter of $2.6\lambda _{0}$ , the highest known achievable efficiency for an antenna of its aperture size, and overall height. Finally, simulations revealed the first compact hard horn or open-ended waveguide design with close to 100% aperture efficiency below $1.6\lambda _{0}$. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
28. Photoconductor-metadevices: an enabling platform for dual-optical/electrical modulation of terahertz waves.
- Author
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Meng, Lingqiang, Lu, Yelong, Sha, Xin, Zhang, Yu, Liu, Wenquan, Kang, Lei, Konishi, Kuniaki, Werner, Douglas H., and Li, Jia
- Abstract
We report a photoconductor-based terahertz metadevice whose transmission characteristics can be comprehensively controlled by a combination of an optical excitation and electrical bias. A metasurface with interdigitated electrodes is proposed to simultaneously support a terahertz resonance and the photoconductive effect, allowing efficient local and global dual-tuning of the carriers in the semiconductor and thus the terahertz wave, based on the simultaneous external optical and electrical stimuli. Experimental results reveal the opposite tuning trend of optical and electrical excitations, leading to the comprehensive transmission modulation of terahertz wave. Our study demonstrates a proof-of-concept device for sophisticated manipulation of terahertz radiation. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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29. Numerical Analysis of Dielectric Post-Wall Waveguides and Its Application to Realization of Bandpass Filters from Millimeter to THz Waves
- Author
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Jandieri, Vakhtang, Erni, Daniel, Werner, Douglas H., and Yasumoto, Kiyotoshi
- Subjects
Elektrotechnik - Published
- 2021
30. Band-Gap Solitons in Nonlinear Photonic Crystal Waveguides and Their Application for Functional All-Optical Logic Gating
- Author
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Jandieri, Vakhtang, Khomeriki, Ramaz, Onoprishvili, Tornike, Erni, Daniel, Chotorlishvili, Levan, Werner, Douglas H., and Berakdar, Jamal
- Subjects
Physics::Optics ,Elektrotechnik - Abstract
This review paper summarizes our previous findings regarding propagation characteristics of band-gap temporal solitons in photonic crystal waveguides with Kerr-type nonlinearity and a realization of functional and easily scalable all-optical NOT, AND and NAND logic gates. The proposed structure consists of a planar air-hole type photonic crystal in crystalline silicon as the nonlinear background material. A main advantage of proposing the gap-soliton as a signal carrier is that, by operating in the true time-domain, the temporal soliton maintains a stable pulse envelope during each logical operation. Hence, multiple concatenated all-optical logic gates can be easily realized paving the way to multiple-input ultrafast full-optical digital signal processing. In the suggested setup, due to the gap-soliton features, there is no need to amplify the output signal after each operation which can be directly used as a new input signal for another logical operation. The efficiency of the proposed logic gates as well as their scalability is validated using our original rigorous theoretical formalism confirmed by full-wave computational electromagnetics. CA Extern
- Published
- 2021
31. Generalized Periodic Boundary Conditions for DGTD Analysis of Arbitrary Skewed Periodic Structures.
- Author
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Bao, Huaguang, Zhang, Tiancheng, Ding, Dazhi, Chen, Rushan, and Werner, Douglas H.
- Subjects
MAXWELL equations ,FREQUENCY selective surfaces ,ELECTROMAGNETIC wave scattering ,GOLD films ,UNIT cell ,FINITE element method ,SKEWNESS (Probability theory) - Abstract
An efficient discontinuous Galerkin time-domain (DGTD) method with an implementation of generalized periodic boundary conditions (PBCs) is proposed to analyze the electromagnetic scattering from arbitrary skewed periodic structures. The transformed field variable approach and the discontinuous Galerkin technique with nonconformal mesh are presented to implement the generalized PBCs for arbitrary skewed periodic structures under both normally and obliquely incident illuminations. The arbitrary high-order time-stepping scheme, which retains the DGTD feature of high-order accuracy and breaks the Butcher barrier, is extended to a transformed version of Maxwell’s equations introduced by the generalized PBCs implementation. The proposed method enables an efficient modeling of arbitrary skewed arrays with a fixed unit-cell mesh. Numerical examples for skewed periodic structures, such as an infinite gold film, 1-D and 2-D staggered dipole frequency-selective surfaces (FSSs), mechanically reconfigurable FSSs, and skewed nanohole arrays, are presented to demonstrate the accuracy and applicability of the proposed method. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
32. 3D printed metamaterial absorbers for mid-infrared surface-enhanced spectroscopy.
- Author
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Hendrickson-Stives, Albanie K., Kang, Lei, Donahue, Nicole R., Keating, Christine D., and Werner, Douglas H.
- Subjects
METAMATERIALS ,MOLECULAR vibration ,DNA fingerprinting ,SPECTROMETRY ,INFRARED absorption ,DEGREES of freedom ,INFRARED radiation - Abstract
The resonant nature and geometric scalability make metamaterials an ideal platform for an enhanced light–matter interaction over a broad frequency range. The mid-infrared (IR) spectral range is of great importance for vibrational spectroscopy of molecules, while IR metamaterials created from lithography-based planar nanostructures have been used to demonstrate enhanced molecular detection. Compared with visible and near-infrared, the relative long wavelengths of IR light make it possible to achieve three-dimensional (3D) IR metamaterials via the state-of-the-art 3D fabrication techniques. Here, we design and fabricate a 3D printed plasmonic metamaterial absorber (MMA), and by performing Fourier-transform IR spectroscopy, we demonstrate that a series of molecular fingerprint vibrations of glycine can be significantly enhanced by the high absorption mode supported by the 3D meta-atoms of the MMA. The observed enhanced IR detection can also be partially attributed to the improved accessibility offered by the 3D architecture of the MMA. In particular, due to capillary forces during the drying process, the microscale 3D printed features lead to selective analyte deposition in high-field regions, which provides another degree of freedom in the design of the 3D printed structures for surface-enhanced IR detection. Our study shows the flexibility of metastructures based on advanced 3D printing technology in tailoring the interaction between IR light and materials on a subwavelength scale. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
33. Interleaved ultrawideband antenna arrays based on optimized polyfractal tree structures
- Author
-
Petko, Joshua S. and Werner, Douglas H.
- Subjects
Antenna arrays -- Design and construction ,Ultra wideband technology -- Research ,Tree structures (Computers) -- Evaluation ,Genetic algorithms -- Usage ,Business ,Computers ,Electronics ,Electronics and electrical industries - Published
- 2009
34. Terahertz Chiral Metamaterials Enabled by Textile Manufacturing.
- Author
-
Wang, Peng, Hu, Rui, Huang, Xiaotian, Wang, Teng, Hu, Shulin, Hu, Min, Xu, Huanhuan, Li, Xiaoyu, Liu, Keshuai, Wang, Shengxiang, Kang, Lei, and Werner, Douglas H.
- Published
- 2022
- Full Text
- View/download PDF
35. Broadband Asymmetric Transmission of Linearly Polarized Mid‐Infrared Light Based on Quasi‐3D Metamaterials.
- Author
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Whiting, Eric B., Goldflam, Michael D., Kang, Lei, Sinclair, Michael B., Musick, Katherine M., Campbell, Sawyer D., Burckel, D. Bruce, and Werner, Douglas H.
- Subjects
METAMATERIALS ,MIRROR symmetry ,SYMMETRY breaking ,LIGHT propagation ,GENETIC algorithms ,POLARITONS - Abstract
Metamaterials consisting of subwavelength resonators offer an exciting opportunity for realizing asymmetric transmission (AT) of linearly polarized light. However, to date, only moderate/narrow‐band AT responses have been obtained in metadevices based on stacked planar nanostructures. Here, leveraging a combination of a genetic algorithm (GA) based optimization method and a membrane projection lithography (MPL) fabrication approach, a quasi‐3D metamaterial for broadband AT of linearly polarized mid‐infrared light is demonstrated. Facilitated by the customized GA, an efficient exploration of 3D plasmonic meta‐atoms with broken mirror symmetry in the light propagation direction allows the satisfaction of the rigorous conditions for AT of linearly polarized waves over a broad wavelength range. Confirmed by surface current analysis, the observed AT behavior is attributed to the resonant coupling between the plasmonic nanostructures located on the two orthogonal walls of the MPL cavities. Incorporating an advanced inverse‐design method and a state‐of‐art fabrication technique, the methodology used in the present study provides a promising route for exploiting 3D metamaterials with sophisticated functionalities via effectively exploring the high‐dimensional parametric space offered by true 3D meta‐atoms. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
36. Active quasi-BIC optical vortex generators for ultrafast switching.
- Author
-
Wu, Yuhao, Kang, Lei, and Werner, Douglas H
- Subjects
OPTICAL vortices ,BOUND states ,GEOMETRIC quantum phases ,VECTOR beams ,TOPOLOGICAL property ,VORTEX generators ,VORTEX motion ,BESSEL beams - Abstract
The Pancharatnamâ€"Berry phase induced by the winding topology of polarization around a vortex singularity at bound states in the continuum (BIC) provides a unique approach to optical vortex (OV) generation. The BIC-based OV generators have the potential to outperform their counterparts that rely on spatial variations in terms of design feasibility, fabrication complexity, and robustness. However, given the fact that this class of OV generators originates from the topological property of the photonic bands, their responses are generally fixed and cannot be dynamically altered, which limits their applications to photonic systems. Here, we numerically demonstrate that a silicon photonic crystal slab can be used to realize optically switchable OV generation by simultaneously exploiting the vortex topology in momentum space in conjunction with silicon’s nonlinear dynamics. Picosecond switching of OV beams at near-infrared wavelengths are observed. The demonstrated nontrivial topological nature of the active generators can significantly expand the application of BIC toward ultrafast vortex beam generation, high-capacity optical communication, and mode-division multiplexing. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
37. Tunable frequency selective surfaces and negative-zero-positive index metamaterials based on liquid crystals
- Author
-
Bossard, Jeremy A., Liang, Xiaotao, Li, Ling, Yun, Seokho, Werner, Douglas H., Weiner, Brian, Mayer, Theresa S., Cristman, Paul F., Diaz, Andres, and Khoo, I.C.
- Subjects
Refractive index -- Measurement ,Algorithms -- Methods ,Liquid crystals -- Properties ,Algorithm ,Business ,Computers ,Electronics ,Electronics and electrical industries - Abstract
We utilize the properties of aligned nematic liquid crystal (LC) cells in the design of: (i) a new type of metamaterial whose index of refraction is tunable from negative, through zero, to positive values and (ii) micron-scale metallodielectric and all-dielectric tunable frequency selective surfaces (FSSs). The metamaterial is constructed by randomly doping a liquid crystal substrate with coated dielectric (non-magnetic) spheres and can be utilized over a large spectral range. FSSs with a liquid crystal superstrate are synthesized using conventional and genetic algorithm methods to exhibit broadband tunable filter characteristics at mid-infrared (mid-IR) wavelengths. These LC tunable FSS structures can be used to develop a new class of infrared/optical switches for terahertz applications. Index Terms--Frequency selective surfaces (FSSs), genetic algorithms (GAs), liquid crystals (LCs), metamaterials, negative index materials (NIMs), terahertz, zero index materials (ZIMs).
- Published
- 2008
38. Stub-loaded long-wire monopoles optimized for high gain performance
- Author
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Werner, Pingjuan L., Bayraktar, Zikri, Rybicki, Brian, Werner, Douglas H., Schlager, Kenneth J., and Linden, Derek
- Subjects
Genetic algorithms -- Usage ,Antennas (Electronics) -- Design and construction ,Mobile communication systems -- Research ,Wireless communication systems -- Research ,Wireless technology ,Business ,Computers ,Electronics ,Electronics and electrical industries - Abstract
A technique to realize stub-loaded monopoles with enhanced gain performance is introduced in this paper. The omnidirectional high gain is achieved by combining an electrically long monopole with stubs attached at optimal locations along the antenna. In general, the lengths of the stub-loaded monopoles presented in this paper are significantly longer than conventional quarter-wave monopoles. Long wires alone do not provide the desired gain and VSWR performance; the stubs connected to the long monopole are vital in realizing simultaneous high gain and low VSWR at the intended operating frequency. A genetic algorithm (GA) is employed to optimize the locations and lengths of each of the stubs required to meet the design objectives. The results of this work show that between 11 and 12 dBi of gain can be obtained when the stub-loaded monopoles are placed over an infinite ground plane, whereas 8 dBi is obtained for one example when sited over a finite ground plane. A prototype of an optimized stub-loaded monopole was fabricated and tested. Excellent agreement was achieved between the measured and simulated results. Index Terms--Genetic algorithms (GAs), high-gain, long-wire antennas, monopole antennas, stub-loading, wire antennas.
- Published
- 2008
39. Design of broadband planar arrays based on the optimization of aperiodic tilings
- Author
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Spence, Thomas G. and Werner, Douglas H.
- Subjects
Broadband transmission -- Equipment and supplies ,Genetic algorithms -- Usage ,Antenna arrays -- Design and construction ,Broadband Internet ,Business ,Computers ,Electronics ,Electronics and electrical industries - Abstract
Antenna arrays based on aperiodic tilings have been shown to exhibit low sidelobe levels and modest bandwidths over which grating lobes are suppressed. In addition, compared to conventional periodic arrays, these arrays are naturally thinned (i.e., mean interelement spacing is greater than [lambda]/2). The generation of these arrays involves placing array elements at the locations of the vertices of an aperiodic tiling. To obtain a realizable design, the entire array is then scaled and truncated to achieve a desired minimum element spacing and aperture size. This paper demonstrates that it is possible to greatly extend the bandwidth of these arrays by incorporating a simple perturbation scheme into the basic array generation process. The implementation of this perturbation scheme is straightforward and it lends itself well to being combined with an optimization technique such as the genetic algorithm. It is successfully used to generate arrays that have large bandwidths (peak sidelobe level [less than or equal to] -10 dB with no grating lobes) of up to a minimum element spacing of 5[lambda]. Moreover, the flexibility of this technique will be further demonstrated by introducing a slight variation of the basic scheme that is capable of generating arrays with extremely wide bandwidths. An example will be presented for an array design that has a bandwidth corresponding to a minimum element spacing of up to 11[lambda]. Index Terms--Aperiodic arrays, aperiodic tilings, broadband arrays, genetic algorithms (GAs), tiling theory, wideband arrays.
- Published
- 2008
40. The Pareto optimization of ultrawideband polyfractal arrays
- Author
-
Petko, Joshua S. and Werner, Douglas H.
- Subjects
Genetic algorithms -- Usage ,Ultra wideband technology -- Equipment and supplies ,Antenna arrays -- Design and construction ,Business ,Computers ,Electronics ,Electronics and electrical industries - Abstract
The application of global optimization techniques, such as genetic algorithms, to antenna array layouts can provide versatile design methodologies for highly directive, thinned, frequency agile, and shaped-beam antenna systems. However, these methodologies have their limitations when applied to more demanding design scenarios. Global optimizations are not well equipped to handle the large number of parameters used to describe large-N antenna arrays. To overcome this difficulty, a new class of arrays was recently introduced called polyfractal arrays that possess properties well suited for the optimization of large-N arrays. Polyfractal arrays are uniformly excited with an underlying self-similar geometrical structure that leads to aperiodic element layouts. This paper expands on polyfractal array design methodologies by applying a robust Pareto optimization technique with the goal of reducing the peak sidelobe levels at several frequencies specified over a wide bandwidth. A recursive beamforming algorithm and an autopolyploidy based mutation native to polyfractal geometries are used to dramatically accelerate the genetic algorithm optimization process. This paper also demonstrates that the properties of polyfractal arrays can be exploited to create designs that possess no grating lobes and relatively low sidelobe levels over ultrawide bandwidths. The best example discussed in this paper maintains a -15.97 dB peak sidelobe level with no grating lobes from a 0.5[lambda], to more than a 20[lambda] minimum spacing between elements, which corresponds to at least a 40:1 bandwidth for the array. Index Terms--Antenna array, autopolyploidy, fractal, fractal-random, genetic algorithm (GA), large-N, Pareto, polyfractal, polyploidy, strength Pareto evolutionary algorithm (SPEA), ultrawideband (UWB).
- Published
- 2008
41. Compact Patch Antenna with Vertical Polarization and Omni-Directional Radiation Characteristics
- Author
-
Mao, Chun Xu, Khalily, Mohsen, Zhang, Long, Xiao, Pei, Sun, Yuhang, and Werner, Douglas H.
- Abstract
This communication proposes a compact, low-profile patch antenna with omni-directional radiation pattern and vertical polarization. A pair of shorted patches are excited in-phase to achieve the omni-directivity and the vertical polarization, simultaneously. The principle is to excite two back-to-back arranged shorted patches to generate symmetrical electric field (E-field) distributions normal to the ground plane. Analytical study on how to generate the omni-directional radiation pattern is carried out. Base on this study, we found the spacing in-between the two patches have little influence on the radiation characteristics, which provides another flexibility in the design. In addition, the shape of the patch and the corresponding field distribution are investigated to further improve the omni-directivity. To improve the impedance bandwidth, resonant structures are inserted in-between the patches, producing the 2nd order response in frequency. The antenna has been fabricated and characterized, and the measured results are in a reasonable agreement with the simulations, showing that the proposed antenna is suitable for potential surface-mount wireless applications.
- Published
- 2020
42. Interaction of electromagnetic waves with 3-D arbitrarily shaped homogeneous chiral targets in the presence of a lossy half space
- Author
-
Wang, Xiande, Werner, Douglas H., Li, Le-Wei, and Gan, Yeow-Beng
- Subjects
Integral equations -- Properties ,Finite element method -- Usage ,Electromagnetic waves -- Scattering ,Electromagnetic waves -- Research ,Business ,Computers ,Electronics ,Electronics and electrical industries - Abstract
The interaction of electromagnetic waves with an arbitrarily shaped three-dimensional (3-D) homogeneous chiral object located above a lossy half space is investigated using the method of moments (MoM) via the coupled mixed potential integral equations (MPIEs). Based on the surface equivalence principle, the equivalent surface electric and magnetic currents are used to replace the homogeneous chiral target in the presence of the half space. Two coupled MPIEs are developed for the unknown equivalent surface electric and magnetic currents by utilizing the continuity condition of the tangential total electric and magnetic field components on the chiral body's surface. The well-known Galerkin procedure with Rao-Wilton-Glisson (RWG) basis functions is applied to solve this problem. The spatial domain half-space Green's functions are obtained from the corresponding spectral domain Green's functions via the discrete complex image method (DCIM) combined with the generalized-pencil of function (GPOF) technique. The reciprocity theorem is employed to calculate the far-zone scattered field. Numerical results are presented for characterizing electromagnetic scattering by a 3-D arbitrarily shaped homogenous chiral object located above a lossy half space so as to demonstrate the accuracy and efficiency of the proposed technique. Index Terms--Discrete complex image method, electromagnetic scattering, homogeneous chiral target, integral equations, method of moments (MoM).
- Published
- 2007
43. Wideband dipoles en electromagnetic bandgap ground planes
- Author
-
Akhoondzadeh-Asl, Lida, Kern, Douglas J., Hall, Peter S., and Werner, Douglas H.
- Subjects
Genetic algorithms -- Evaluation ,Ultra wideband technology -- Research ,Dipole antennas -- Design and construction ,Business ,Computers ,Electronics ,Electronics and electrical industries - Abstract
The performance of broadband dipole antennas above electromagnetic bandgap (EBG) structures is investigated. Two different structures are examined. One is a diamond dipole over an EBG with square patch elements optimized by hand and the other an open sleeve dipole over an EBG optimized by a genetic algorithm (GA). Both configurations demonstrate that a low profile dipole antenna over an EBG can have a broad bandwidth. Careful design of both is required and in particular for best results, the antenna-EBG system should be optimized together, rather than as separate components. The performance is compared to an absorber backed wideband dipole antenna and it is found that the gain is significantly increased, whilst the bandwidth is reduced. In general, for the diamond dipole antenna return loss bandwidths of over 2:1 (67%) have been achieved, although radiation pattern control is difficult and reduces the bandwidth to the order of 1.4:1 (33%). The sleeve dipole over an EBG achieved a bandwidth of 1.28:1 (26%). The realized gain, which is power gain reduced by input match loss, of both structures are approximately the same. GA optimization and parametric studies seem to suggest that bandwidths significantly greater than these are difficult to achieve. Index TermsmElectromagnetic bandgap (EBG), genetic algorithm (GA), low profile antenna, wideband dipole antenna.
- Published
- 2007
44. An autopolyploidy-based genetic algorithm for enhanced evolution of linear polyfractal arrays
- Author
-
Petko, Joshua S. and Werner, Douglas H.
- Subjects
Genetic algorithms -- Usage ,Antenna arrays -- Design and construction ,Electromagnetism -- Research ,Business ,Computers ,Electronics ,Electronics and electrical industries - Abstract
There has been considerable recent interest in techniques for the optimization of large-N antenna arrays. Unfortunately, the successful development of such techniques has been hindered by the large number of independent parameters that must be optimized and the complexity of the calculations needed for the electromagnetic evaluation of large-N arrays. One promising new design methodology for large-N arrays which has recently been introduced is based on properties of a subset of fractal-random arrays called polyfractal arrays. Polyfractal arrays have many embedded self-similar structures, thereby allowing very large and seemingly complex array layouts to be described with only a small set of independent parameters. In addition, by effectively utilizing the self-similarity of polyfractal arrays, a considerable reduction can be achieved in the amount of time required to evaluate the radiation patterns of large-N arrays. This paper introduces a type of nature-based design process that applies a specially formulated genetic algorithm (GA) technique to evolve optimal polyfractal array layouts. The most unique aspect of this optimization technique is a new autopolyploidy-based chromosome expansion that maximizes the efficiency of the GAs. Simple polyfractal geometries are used in the initial stage or first epoch of the optimization because the number of independent parameters is small and the computation times are relatively fast. After the optimization converges for the first epoch, more complicated descriptions of these polyfractal arrays are introduced to provide additional independent parameters for the optimizer as it progresses through later epochs of evolution. This process has been shown to be very effective in creating optimized large-N arrays, the largest example considered here being a 1616-element linear array with a -24.30-dB sidelobe level and a 0.056[degrees] half-power beamwidth. Index Terms--Autopolyploidy, fractal arrays, fractal-random arrays, genetic algorithms (GAs), large-N arrays, polyfractal arrays, polyploidy.
- Published
- 2007
45. A Knotted Meta-molecule with 2-D Isotropic Optical Activity Rotating the Incident Polarization by 90{\deg}
- Author
-
Mai, Wending, Kang, Lei, Mao, Chunxu, Jenkins, Ronald, Zhu, Danny, Werner, Pingjuan, Werner, Douglas H., Hu, Jun, Cao, Weiping, and Chen, Yifan
- Subjects
High Energy Physics::Lattice ,Physics - Chemical Physics ,Physics - Classical Physics ,Physics - Optics - Abstract
Optical activity is the ability of chiral materials to rotate linearly-polarized (LP) electromagnetic waves. Because of their intrinsic asymmetry, traditional chiral molecules usually lack isotropic performance, or at best only possess a weak form of chirality. Here we introduce a knotted chiral meta-molecule that exhibits optical activity corresponding to a 90{\deg} polarization rotation of the incident waves. More importantly, arising from the continuous multi-fold rotational symmetry of the chiral torus knot structure, the observed polarization rotation behavior is found to be independent of how the incident wave is polarized. In other words, the proposed chiral knot structure possesses two-dimensional (2-D) isotropic optical activity as illustrated in Fig. 1, which has been experimentally validated in the microwave spectrum. The proposed chiral torus knot represents the most optically active meta-molecule reported to date that is intrinsically isotropic to the incident polarization.
- Published
- 2019
46. A novel miniature broadband/multiband antenna based on an end-loaded planar open-sleeve dipole
- Author
-
Spence, Thomas G. and Werner, Douglas H.
- Subjects
Broadband transmission -- Research ,Dipole antennas -- Research ,Magnetic dipoles -- Research ,Genetic algorithms -- Research ,Genetic algorithms -- Usage ,Broadband Internet ,Business ,Computers ,Electronics ,Electronics and electrical industries - Abstract
Open-sleeve dipoles are versatile antennas primarily because they have several design parameters that can be varied to achieve a wide range of VSWR performance and operating bandwidth. By properly adjusting their parameters, it is possible to create versions of these antennas that have either a broadband or a dual-band response. In this paper, a new variation of the conventional open-sleeve dipole antenna is introduced, which we call an end-loaded planar open-sleeve dipole (ELPOSD). This configuration provides a degree of miniaturization while retaining a comparable bandwidth in terms of the VSWR response to that of conventional open-sleeve dipoles. Several designs are presented for the conventional and end-loaded configurations that demonstrate the VSWR and miniaturization capabilities of this class of antennas. Measured results have been compared with simulations and found to be in good agreement for an end-loaded planar open-sleeve monopole. Index Terms--Broadband antennas, genetic algorithms (GAs), open-sleeve dipole, printed antennas, small antennas.
- Published
- 2006
47. Bezier representations for the multiobjective optimization of conformal array amplitude weights
- Author
-
Boeringer, Daniel W. and Werner, Douglas H.
- Subjects
Antenna arrays -- Design and construction ,Mathematical optimization -- Analysis ,Polynomials -- Usage ,Business ,Computers ,Electronics ,Electronics and electrical industries - Abstract
For conformal phased arrays, generally the excitation amplitude of the array elements must be adjusted in order to maintain low sidelobes as the array is scanned. While the desired phase weights for maximum gain are deterministically set by the array geometry and scan angle, the representation of optimum low sidelobe amplitude weights remains an open problem. Following up on prior work using the efficiency-constrained optimization of a modified Bernstein polynomial for low sidelobe conformal array synthesis, a Bezier surface is shown to provide a good representation of the optimized amplitude weights with a reduced number of parameters, while demonstrating [epsilon]-constraint multi-objective optimization of conformal aperture efficiency versus sidelobe level. These results are extended to include a Bezier volume representation for the multiobjective optimization of conformal aperture efficiency versus both sidelobe level and scan angle. Index Terms--Antenna arrays, antenna radiation patterns, conformal antennas, optimization methods.
- Published
- 2006
48. The design and fabrication of planar multiband metallodielectric frequency selective surfaces for infrared applications
- Author
-
Bossard, Jeremy A., Werner, Douglas H., Mayer, Theresa S., Smith, Jacob A., Tang, Yan U., Drupp, Robert P., and Li, Ling
- Subjects
Far infrared lasers -- Design and construction ,Fractals -- Analysis ,Genetic algorithms -- Analysis ,Business ,Computers ,Electronics ,Electronics and electrical industries - Abstract
In this paper, micron-scale frequency selective surfaces (FSS) are presented for the first time that exhibit multiple strong stopbands (>10dB) in the far-infrared (IR). Fractal and genetic algorithm (GA) synthesis techniques are employed in the design of single-layer, multiband IR FSS. These designs have been fabricated on thin, flexible polyimide substrates and characterized using Fourier transform infrared (FTIR) spectroscopy. Measurements show excellent agreement with predictions from a periodic method of moments (PMoM) analysis technique that takes into account metallic and dielectric losses. Additional design constraints were incorporated into the GA in order to guarantee that the synthesized FSS structures could be accurately fabricated. Index Terms--Fractals, frequency selective surfaces (FSS), genetic algorithms (GAs), infrared filters, metallodielectric photonic crystals.
- Published
- 2006
49. Novel BI-FDTD approach for the analysis of chiral cylinders and spheres
- Author
-
Semichaevsky, Andrey, Akyurtlu, Alkim, Kern, Douglas, Werner, Douglas H., and Bray, Matthew G.
- Subjects
Time-domain analysis -- Usage ,Electromagnetic waves -- Scattering ,Electromagnetic waves -- Analysis ,Business ,Computers ,Electronics ,Electronics and electrical industries - Abstract
A versatile time-domain technique, known as bi-isotropic finite difference time domain (BI-FDTD), has recently been introduced for the numerical analysis of electromagnetic wave interactions with complex bi-isotropic media. However, to date only one-dimensional BI-FDTD schemes have been successfully implemented. This paper presents novel two-dimensional (2-D) and three-dimensional (3-D) dispersive BI-FDTD formulations for the first time. The update equations for these new 2-D and 3-D BI-FDTD approaches are developed and applied to the analysis of electromagnetic wave scattering by chiral cylinders and spheres in free space. The distinctive feature of this technique is the use of two independent sets of wavefields representing the left- and right-polarized waves in the chiral medium. This wave-field decomposition approach allows dispersive models for the chirality parameter as well as the permittivity and permeability of the medium to be readily incorporated into an FDTD scheme. The 2-D and 3-D BI-FDTD simulation results are compared with available analytical solutions for the scattering from a circular chiral cylinder and a chiral sphere respectively. Index Terms--Bi-isotropic finite-difference time-domain (BI-FDTD), chiral cylinder, chiral media, chiral sphere, electromagnetic scattering, finite-difference time-domain (FDTD).
- Published
- 2006
50. A model-based parameter estimation technique for wide-band interpolation of periodic moment method impedance matrices with application to genetic algorithm optimization of frequency selective surfaces
- Author
-
Li, Ling, Werner, Douglas H., Bossard, Jeremy A., and Mayer, Theresa S.
- Subjects
Genetic algorithms -- Usage ,Parameter estimation -- Methods ,Interpolation -- Analysis ,Frequency estimation -- Analysis ,Business ,Computers ,Electronics ,Electronics and electrical industries - Abstract
A model-based parameter estimation (MBPE) technique is introduced in this paper for efficiently interpolating periodic moment method (PMM) impedance matrices over a wide frequency band. In the model, only the Floquet harmonics that strongly affect the frequency band of interest are employed to approximate the matrix elements, while the contributions from all other higher-order harmonics are compactly represented by two additional terms. The derivation of the model is physics-based, and the objective is to find the coefficients of the terms in the model by utilizing the values of the impedance matrix elements calculated via PMM at only a few frequency points. The number and position of these fitting points can be pre-determined from the cutoff frequencies of the Floquet harmonics, which allows the MBPE interpolation process in this case to be completely automated. In other words, the number and position of the sampling points are only dictated by the periodicity of the frequency selective surface (FSS) structure and the frequency range of interest. Unlike many of the other scattering parameter-based techniques, the shape and the resonances in the response of the FSS do not have any impact on the construction of the interpolation model. This makes it particularly useful in genetic algorithm (GA) aided FSS design, since for a fixed periodicity and frequency range the MBPE interpolation is independent of the scattering response of candidate FSS designs. Several examples of the new PMM-MBPE approach are presented including one in which it is used to considerably speed up the GA-based design process for a reconfigurable FSS. Index Terms--Frequency selective surfaces (FSS), genetic algorithms (GAs), impedance matrix interpolation, model-based parameter estimation (MBPE), periodic moment methods (PMM).
- Published
- 2006
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