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Achromatic devices present unique capabilities in efficient manipulation of waves and have wide applications in imaging and communication systems. However, the research of achromatic devices is limited by the narrow bandwidth, low efficiency as well as large configurations. In this paper, we propose a general strategy to design spin-locked achromatic metasurface with broadband and high efficiency properties in microwave region. A multi-resonant model is used to control the dispersion within a wide bandwidth by tuning its resonant intensity, resonance numbers as well as resonant frequency. As a proof of the concept, two achromatic meta-devices with ultra-thin profile at microwave frequency are experimentally investigated. The achromatic deflector can reflect the normal incident waves to the same angle within 9.5 to 11.5 GHz, while the other achromatic lens can focus the excitations at the same focal points. The experimentally working efficiency of the meta-devices fluctuates around 71–82% and 57–65% within the target working bandwidth, respectively. Moreover, our meta-devices can preserve the charity of the excitations. The scheme of this research shows great advances in the design of broadband and high-efficiency achromatic devices which can also be applied to other frequency ranges and inspires the realization of ultrabroadband and high-efficiency metadevices.

Tailoring the wavefronts of spoof surface plasmon polaritons (SSPPs) at will, especially with multifunctional integration, is of great importance in near-field photonics. However, conventional SSPP devices suffer from the issues of bulk configurations, limited functionalities, and single operating modes, which are unfavorable for electromagnetic (EM) integration. Here, a novel scheme is proposed to design bifunctional SSPP meta-devices based on the polarization dependent property via satisfying the comprehensive phase distributions and multi-mode momentum matching in a transmission geometry. As proof of the concept, we experimentally demonstrate a bifunctional SSPP meta-device in the microwave regime that can convert incident x- and y-polarized waves to transverse magnetic (TM)-mode SSPP Bessel beams and transverse electric (TE)-mode SSPP focusing beams, respectively. Our findings open a door to achieve near-field manipulation of SSPPs with multi-function and multi-mode integration, which can stimulate the applications of SSPP functional devices, such as near-field sensing, imaging, and on-chip photonics.

Non-Dispersive InfraRed (NDIR) gas sensor is widely used for gas detection in collieries and the gas chemical industry, etc. The performance of the NDIR gas sensor depends on the volume, optical length and transmittance of the gas chamber. However, the existing gas sensor products have problems of large volume, high cost and incapable of integration, which need to develop towards the miniaturized sensor. This paper first presents the theoretical background of the NDIR gas sensor and the novel structure of a fully integrated infrared gas sensor and its micro-machined gas chamber structure. Then, the light structure and the gas flow of the gas chamber are optimized on Tracepro software and Ansys workbench, respectively, and the technological process for preparing the Micro-Electro-Mechanical System (MEMS) gas chamber is designed. Finally, we produce a gas chamber with a small volume and good transmissivity, which would be the most important part of producing the miniaturized NDIR gas sensor.

Circularly polarized (CP) spoof surface plasmon polariton (SSPP) functional metadevices, especially those with spin decoupling and hybrid modes, play an important role in modern photonics applications. However, currently available SSPP functional metadevices have the defect of restricted functionalities and single‐working modes for a given polarization, as it is a great challenge to simultaneously support SSPPs with hybrid modes and different wavefronts. Herein, a general strategy is proposed for designing CP SSPP functional metadevices with spin decoupling and hybrid modes based on transmissive spin‐decoupled metasurfaces and angle‐insensitive anisotropic SSPP eigenmode plates (EMPs). The metasurface can simultaneously and independently control the resonant and geometrical phases of the CP waves, and the SSPP EMP satisfies the hybrid‐mode (both transverse magnetic [TM] and transverse electric [TE] modes) momentum matching with high angular/momentum stability of the propagating SSPPs. For verification, a CP SSPP beam splitter is designed, fabricated, and experimentally demonstrated, which can convert incident right‐handed (R) and left‐handed (L) CP plane waves to CP hybrid‐mode SSPP deflected beams and decoupled beams, respectively. The work paves the way for the realization of CP SSPP multifunctional‐integration metadevices with hybrid modes and other functionalities, which can find extensive applications in different frequency domains. [ABSTRACT FROM AUTHOR]

Achromatic devices present unique capabilities in efficient manipulation of waves and have wide applications in imaging and communication systems. However, the research of achromatic devices is limited by the narrow bandwidth, low efficiency as well as large configurations. In this paper, we propose a general strategy to design spin-locked achromatic metasurface with broadband and high efficiency properties in microwave region. A multi-resonant model is used to control the dispersion within a wide bandwidth by tuning its resonant intensity, resonance numbers as well as resonant frequency. As a proof of the concept, two achromatic meta-devices with ultra-thin profile at microwave frequency are experimentally investigated. The achromatic deflector can reflect the normal incident waves to the same angle within 9.5 to 11.5 GHz, while the other achromatic lens can focus the excitations at the same focal points. The experimentally working efficiency of the meta-devices fluctuates around 71–82% and 57–65% within the target working bandwidth, respectively. Moreover, our meta-devices can preserve the charity of the excitations. The scheme of this research shows great advances in the design of broadband and high-efficiency achromatic devices which can also be applied to other frequency ranges and inspires the realization of ultrabroadband and high-efficiency metadevices. [ABSTRACT FROM AUTHOR]

Optical illusion has always attracted extensive attention, as it provides a superior self‐protection ability for both natural animals and human beings. A decade ago, this motivated the study and application of transformation optics, which provides a universal tool to manipulate light for invisibility cloaking and optical illusion. However, mainstream transformation‐optics‐based optical illusions are inherently hindered by the extreme requirements of metamaterial compositions in practice and unfavorably limited by the very large computational cost caused by their bulky state. To overcome these grand challenges, a novel and intelligent optical illusion supported by form‐free metasurfaces via a deep learning architecture is reported, which can not only render a similar illusion effect but also greatly reduces the parameter space in physics. Illustrative examples of conformal metasurfaces are presented, with a high‐fidelity inverse design from either the near‐ or far‐field in the simulation and experiment. Furthermore, a full set of intelligent systems is developed to benchmark the real‐world optical illusion applicability. The work brings the available illusion strategies closer to a wide range of in situ practical‐oriented applications and lays a foundation for the next generation of intelligent metamaterials. [ABSTRACT FROM AUTHOR]

Spoof surface plasmon polariton (SSPP) antennas are of particular importance in communication and radar systems. Currently available SSPP radiation devices are limited to low performance with high side‐lobes because it is extremely challenging to accurately control the wave vector of SSPP and the inherent momentum mismatch between the SSPP and spatial waves. Inspired by the optical principle of reversibility, high‐performance radiation control of SSPP is proposed to be achieved with transmissive phase gradient metasurface (TPGM). The TPGM, placed a meticulously optimized distance above the SSPP propagation structure, can provide an additional opposite wave vector to match the momentum between the SSPP and spatial waves. When the propagating SSPP transmits on the TPGM, it can be decoupled into the free space accurately and flexibly. Numerical results coincide well with the measurements, indicating that the radiation control of SSPP achieves high‐performance and low side‐lobe within 9 to 10.5 GHz with the measured radiation efficiency higher than 50%. The measured maximum efficiency appears at 9.8 GHz for 69%. Thanks to the flexible and accurate manipulation of the dispersion relation of SSPP provided by TPGM, the findings may open an avenue in achieving larger angle scanning antenna. [ABSTRACT FROM AUTHOR]

In this letter, we report a two-in-one acoustic wave resonator with Rayleigh and Lamb modes for temperature decoupled viscosity-density product sensing. The Lamb mode of the resonator is sensitive to both the viscosity-density product and the ambient temperature, while the Rayleigh mode only responds to the ambient temperature and is not affected by liquid properties. These unique characteristics of the two modes are due to the different spatial distributions of the acoustic energy. Taking advantage of the aforementioned features, a beat frequency strategy is proposed to decouple the temperature influence from the viscosity-density product measurement, thus realizing temperature independent viscosity-density product sensing in a single acoustic wave resonator chip. Experimental results show that the accurate measurement of the viscosity-density product can be achieved in Newtonian liquids with a sensitivity of −0.36 MHz/kg m−2 s−0.5 within a wide temperature range from 20 °C to 80 °C. Our work holds great promise for liquid property measurement occasions with large fluctuations in ambient temperature, such as oil and gas exploration, automobile, and aeronautic applications. [ABSTRACT FROM AUTHOR]

In this letter, we demonstrate a high-temperature dual-resonator Lamb wave tensile strain sensor which can achieve temperature compensation in a wide temperature range and has high strain sensitivities. This sensor consists of two identical AlN-on-SOI Lamb wave resonators (LWRs) adhered on a uniaxial tensile plate, with the wave propagating directions in the two LWRs parallel and perpendicular to the tensile axis, respectively. The most obvious higher-order Lamb wave modes, i.e., the A4, S4, and S5 modes, in the “parallel” LWR present high strain sensitivities of 0.229 ppm/με (196 Hz/με), 0.480 ppm/με (431 Hz/με), and 0.222 ppm/με (205 Hz/με) all with minus signs, whereas in the “perpendicular” LWR, they demonstrate smaller strain sensitivities all with plus signs. The S4 modes in the two LWRs have almost the same temperature coefficients. Based on the experimental results, a generally applicable beat frequency method with these two LWRs is proposed to realize temperature compensation as well as the high-sensitivity strain measurement. [ABSTRACT FROM AUTHOR]

Here, we demonstrate an uncooled, miniaturized, and high resolution infrared (IR) detector based on an aluminum nitride (AlN) film bulk acoustic resonator with dual resonant modes. Due to temperature dependence of the resonance frequency of the resonator and charge carrier generation effect of the AlN piezoelectric material, both the resonant frequency and valley value in reflection coefficient S11 are found responsive to IR irradiation at each resonant mode, thus realizing four IR sensing signal concurrence in a single device. The four sensing signals achieved IR responsivities of 3.32 Hz/nW, 561.21 μdB/nW, 43.17 Hz/nW, and 53.70 μdB/nW, respectively. The second sensing signal even realized a noise equivalent power down to 108 pW/Hz1/2, which is the lowest value among resonant infrared detectors reported in literature studies till now. More importantly, these four sensing signals lie in two separate frequency bands up to GHz, thus enabling the detector to operate normally by the frequency-hopping sensing method when one of the frequency bands suffers from strong electromagnetic interference. The presented device shows a great potential for ultra-sensitive and anti-interference infrared detection in civilian and military fields. [ABSTRACT FROM AUTHOR]

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A piezoelectric AlN-on-SOI structured MEMS Lamb wave resonator (LWR) is presented for high-temperature strain measurement. The LWR has a composite membrane of a 1 μm thick AlN film and a 30 μm thick device silicon layer. The excited acoustic waves include Rayleigh wave and Lamb waves. A tensile strain sensor has been prepared with one LWR mounted on a uniaxial tensile plate, and its temperature characteristics from 15.4°C to 250°C and tensile strain behaviors from 0 με to 400 με of Rayleigh wave and S4 mode Lamb wave were tested. The temperature test verifies the adaptability of the tensile strain sensor to temperature up to 250°C, and S4 mode Lamb wave and Rayleigh wave represent almost the same temperature characteristics. The strain test demonstrates that S4 mode Lamb wave shows much higher strain sensitivity (-0.48 ppm/με) than Rayleigh wave (0.05 ppm/με) and confirms its advantage of strain sensitivity. Finally, for this one-LWR strain sensor, a method of beat frequency between S4 mode Lamb wave and Rayleigh wave is proposed for temperature compensation and high-sensitivity strain readout. [ABSTRACT FROM AUTHOR]

The physical basis of a smart city, the wireless channel, plays an important role in coordinating functions across a variety of systems and disordered environments, with numerous applications in wireless communication. However, conventional wireless channel typically necessitates high-complexity and energy-consuming hardware, and it is hindered by lengthy and iterative optimization strategies. Here, we introduce the concept of homeostatic neuro-metasurfaces to automatically and monolithically manage wireless channel in dynamics. These neuro-metasurfaces relieve the heavy reliance on traditional radio frequency components and embrace two iconic traits: They require no iterative computation and no human participation. In doing so, we develop a flexible deep learning paradigm for the global inverse design of large-scale metasurfaces, reaching an accuracy greater than 90%. In a full perception-decision-action experiment, our concept is demonstrated through a preliminary proof-of-concept verification and an on-demand wireless channel management. Our work provides a key advance for the next generation of electromagnetic smart cities.

Stealth radome (SR), especially with an ultra-broad and nearly transparent window between two absorption bands, plays a crucial role in stealth techniques, antenna radomes, and so on. However, current devices have the defects of narrow transmission bands, high insertion loss, and wide transition bands between the transmission and absorption bands, which are unfavorable for the stealth of broadband radar and communication systems. In this paper, a novel SR with an ultra-broad and high-efficiency inter-absorption band transparent window is proposed by combining broadband resonance lumped circuits with a multi-layer cascaded frequency-selective surface (FSS). The equivalent circuit model (ECM) and transmission line method (TLM) are provided and analyzed as a guideline for the SR design. The SR consists of a resistive lossy layer loaded with wide passband lumped circuits and two stacked lossless FSS layers to collectively achieve the high selectivity and ultra-broad transmission band. Simulated results indicate that the proposed SR exhibits an ultra-broad passband from 8.2 to 11.2 GHz (31%) with transmission amplitude more than 0.85 and two 90% absorption bands over 6.8-7.8 GHz and 12-13 GHz, and the transition bands at both sides are only 0.4 GHz and 0.8 GHz, respectively. Our findings can stimulate the promising applications of SR in broadband stealth devices with integrated ultra-broad communication capability or in other electromagnetic (EM) compatibility facilities.

Metasurfaces have provided a novel way on modulating the wavefront of electromagnetic (EM) waves, where phase modulating is an important method to control EM waves. Normally, phase can be continuously modulated by changing the size of a meta-atom. For a broadband device, it is essential that phase changes linearly varying against frequency within a wide frequency interval, which is quite difficult to design, especially for the transmissive scheme. In this paper, we propose a 0-1 coding method by using genetic algorithm (GA) to realize broadband linear transmission phase and high transmission amplitude against frequency. To verify the method, a beam bending metasurface is designed based on array of six meta-atoms with step gap of 60°. Simulation and experimental results show that the metasurface deflector achieves perfect beam refraction from 8 to 12 GHz, which is consistent with theoretical calculations. Moreover, the working efficiency is kept at about 75%, with the variation of the frequency, which demonstrates the good stability of the metasurface. This method offers a new insight into the designing of broadband devices.

Perfect absorbers are highly desired in many engineering and military applications, including radar cross section (RCS) reduction, cloaking devices, and sensor detectors. However, most types of present absorbers can only absorb space propagation waves, but absorption for surface waves has not been researched intensively. Surface waves are easily excited on the interfaces between metal and dielectrics for electronic devices, which decreases their working performances due to the electromagnetic disturbances. Thus, it is of great significance to design appropriate absorbers to dissipate undesirable surface waves. Here, we propose the concept of a surface wave absorber, analyze its working principle, and prove its good performances experimentally. To demonstrate our concept, we design and fabricate a realistic surface wave absorber that is fixed on a metal surface. Experiments are performed to verify its electromagnetic characteristics. The results show that our designed meta-absorber can achieve an excellent surface wave absorption within a wide frequency window (5.8-11.2 GHz) and exhibit a very high efficiency over than 90%, but only with the thickness of 1 mm (0.028 λ). Our device can help to solve the issues of absorption at large angles, and it can find wide applications in large antenna array design and other communication systems.

Absorbers have high potential application values in the military field, such as electronic screening, radar cross-section reduction and invisible cloaking. However, most methods have the defects of narrow bandwidth, low absorptivity, complex three-dimensional structure and fixed polarizations. In this paper, we realize an ultra-broadband and full-polarization planar metamaterial absorber (PMA) with a three-layer composite structure, which exhibits multi-resonant and impedance matching properties by combining the ultra-light foams and indium tin oxide (ITO) films. The bottom two layers achieve a high-efficiency absorption rate at the low and medium spectrum, while the upper layer realizes a absorption property at a high frequency. Also, an equivalent circuit model is extracted to explain its operating mechanism. The experimental results show that our meta-absorber can achieve great absorber performance of better than 90% within 1-18 GHz for full-polarization incident waves, which is in great agreement with the numerical simulations. Moreover, our device is insensitive to oblique incidences and polarizations and possesses the physical characteristics of an ultralight, weighing 0.6 kg for a square meter, which is only 1/85.0-1/126.7 of the conventional absorbers under the same size. All these excellent performances determine that our research can be a good candidate for military stealth materials.

Full-space metasurfaces (MSs) attract significant attention in the field of electromagnetic (EM) wave manipulation due to their advantages of functionality integration, spatial integration and wide applications in modern communication systems. However, almost all reported full-space metasurfaces are realized by multilayer dielectric cascaded structures, which not only has the disadvantages of high cost and complex fabrication but also is inconvenient to device integration. Thus, it is of great interest to achieve high-efficiency full-space metasurfaces through simple design and easy fabrication procedures. Here, we propose a full-space MS that can efficiently manipulate the circularly polarized (CP) waves in dual frequency bands by only using a single substrate layer, the reflection and transmission properties can be independently controlled by rotating the optimized meta-structures on the metasurface. Our full-space metasurface has the potential to design multifunctional devices. To prove the concept, we fabricate the device and measured it in microwave chamber. For the reflection mode, our metasurface can behave as a CP beam splitter at the frequency of f 1  = 8.3 GHz and exhibit high efficiencies in the range of 84.1%-84.9%. For the transmission mode, our metasurface acts as a meta-lens at the frequency of f 2  = 12.8 GHz for the LCP incidence, and the measured relative efficiency of the meta-lens reaches about 82.7%. Our findings provide an alternative way to design full-space metasurfaces and yield many applications in EM integration systems.