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Developing a millimeter-wave (mm-wave) antenna that enables wide bandwidth with its operating band covering the entire global 5G spectrum is highly desirable but very challenging for achieving both compact size and high-performance antenna. Herein, the mm-wave microstrip patch antenna (MPA) and its multiple-input multiple-output (MIMO) configuration based on the metasurfaces for 5G system applications are proposed and investigated by the simulation method. To improve performance and keep the low-profile and low-cost MPA antenna, square ring resonator (SQRR) metasurface and radiating patch are printed on a single dielectric layer. With the presence of the metasurfaces that acting as a secondary radiator, the performance of the designed antenna is significantly improved with a wide operating band in the range of 23.9-30.7 GHz, high peak gain of 9.4 dBic, and radiation efficiency of above 87%. Based on this design, four-port MIMO antenna configuration is performed for evaluating a MIMO system that realizes the advantage features such as compact size, wide bandwidth covering the entire global mm-wave 5G spectrum band of 24.25-29.5 GHz, and excellent diversity performance characterized by good isolation between the adjacent elements and low envelope correlation coefficient. Thus, the MIMO antenna design is a very promising candidate for 5G MIMO mm-wave applications, specifically in cellular systems.

Silica-coated gold nanorods (AuNRs) exhibit significantly enhanced photothermal effects and photoacoustic (PA) signal intensities, which is beneficial for various nanophotonic applications in materials science. However, the silica shell thickness for optimum enhancement is not fully understood and is even controversial depending on the physical state of the silica shell. This is because of the lack of systematic investigations of the nanoscale silica shell thickness and the photothermal effect. This study provides a robust synthetic method to control the silica shell thickness at the nanoscale and the physical state-dependent heat diffusion property. The selected base and solvent system enabled the production of silica-coated AuNRs (AuNR@SiO2) with silica shell thicknesses of 5, 10, 15, 20, 25, 30, 35, and 40 nm. AuNRs with a 20 nm silica shell showed the highest photothermal effect with a 1.45-times higher photothermal efficiency than that of AuNRs without a silica shell. The low density of the silica shell on the AuNRs showed a low photothermal effect and photostability. It was found that the disruption of cetyltrimethyl ammonium bromide (CTAB) layers on the AuNRs was responsible for the low photostability of the AuNRs. The simulation study for the heat diffusion property showed facilitated heat diffusion in the presence of a 20 nm silica shell. In a cell-based study, AuNRs with a 20 nm silica shell showed the most sensitive photothermal effect for cell death. The results of this robust study can provide conclusive conditions for the optimal silica shell thickness to obtain the highest photothermal effect, which will be useful for the future design of nanomaterials in various fields of application.

Noble metal nanostructures have been widely explored as an effective method to increase photon absorption and charge separation in plasmonic photocatalysis. In this study, we integrated two differe...

A microwave planar resonator sensor design supporting spoof surface plasmon waves is used for wafer dielectric characterization. The proposed circuit guides the microwave as a surface wave across the metal signal line, from port to port of the device. The surface wave effectively interacts with the sample being measured, placed on top of the planar sensor. The proposed planar sensor is fabricated on an RF-35 substrate, resulting in a low-cost implementation. The sensor is used to discriminate between wafers with different dielectric permittivity and thickness. Quartz, borosilicate, BK7 glass, and Silicon wafers have been characterized using the proposed sensor. The sensor resonant frequency and losses change according to the permittivity and the thickness of the samples, with an achieved sensor sensitivity of 60.22 MHz/?r. Simulation and measurements demonstrate that the proposed spoof surface plasmon resonator sensor can be used to create a high sensitivity sensor for dielectric material characterization. The dielectric constant and loss tangent of the samples are inferred from a polynomial fit obtained from sample simulations and confirmed through measurements. © 2017 IEEE.

Silica-coated gold nanorods (AuNRs) exhibit significantly enhanced photothermal effects and photoacoustic (PA) signal intensities, which is beneficial for various nanophotonic applications in materials science. However, the silica shell thickness for optimum enhancement is not fully understood and is even controversial depending on the physical state of the silica shell. This is because of the lack of systematic investigations of the nanoscale silica shell thickness and the photothermal effect. This study provides a robust synthetic method to control the silica shell thickness at the nanoscale and the physical state-dependent heat diffusion property. The selected base and solvent system enabled the production of silica-coated AuNRs (AuNR@SiO

In this paper, a bump-forming method for flip chip bonding using ink-jet printing technology is proposed. A flip chip bonded transmission line using ink-jet printed silver bumps consisting of conductive ink containing silver nanoparticles was fabricated to verify the electrical characteristics after the flip chip bonding process. The transmission line was designed according to microstrip theory for a frequency range of 300 kHz to 3 GHz, with the size of fabricated line being 35 (width) × 8.64 (length) × 0.5 (thickness) mm3. The electrical characteristics of a reference microstrip and the flip chip bonded line were compared with FEM simulation and measurement results. Direct current (DC) resistances of both the reference line and the flip chip bonded line were measured to be 3.1 Ω and 3.2 Ω, respectively. The discrepancy between measured insertion loss and the simulation result was only 0.04 dB at 3 GHz, and the return loss was greater than 15 dB in the measurement frequency range. As a result of the analysis, it was confirmed that the DC resistance of ink-jet printed bumps account for 0.56% of the total DC resistance, and the ink-jet printed bumps hardly affected the radio frequency (RF) characteristics of the RF transmission line at low frequencies. The results demonstrate that ink-jet printed silver bumps can be used for a simple and low-cost flip chip bonding process. We expect that the proposed method can be applied to the packaging of various electronics such as flexible, wearable devices and RF applications.

In this letter, we propose a frequency discriminator design method with uniform frequency sub-bands. Frequency discriminators are designed using an interferometer projected with the proposed formulated phase. For experimental verification that a uniform sub-band is formed using the proposed phase formula, 3-bit frequency discriminators are designed and fabricated to operate in the 2-3 GHz and 2-4 GHz bands, respectively. The frequency discriminator consists of a power divider/combiner, reference line and delay line. RF characteristics of the frequency discriminators are analyzed using RF simulation and measurement results. RF characteristic results show that a 3-bit frequency discriminator designed using the proposed phase formula can identify an unknown signal inside the defined frequency band.

This letter presents a low-cost and compact reconfigurable frequency measurement circuit able to reconfigure bandwidth and resolution, the design uses a varactor loaded phase shifter, a reference delay line, and power divider/combiner to form a 2-bit frequency discriminator with four states for frequency measurement. The reconfigurable discriminator has four bandwidth states of 0.5, 0.9, 1.3, and 1.7 GHz, with uniform subband resolution of 125, 225, 325, and 525 MHz, for each bandwidth state of operation, respectively.

A simple and cost-effective fabrication process of a flexible-based inverse micro-cone array (i-MCA) structure textured on flexible transparent conductive electrodes (TCEs) was successfully demonstrated via a micro-imprinting process. The flexible i-MCA films exhibited an extremely high total transmittance of ∼93% and a haze of ∼95% with reduced reflectance while simultaneously demonstrating water-repellent properties. Introducing i-MCA on the illuminating side of organic solar cells (OSCs)- and perovskite solar cells-rigid glass substrate showed improved power conversion efficiencies (PCEs) due to the light trapping effect by multiple light bounces between cone array structures (forward scattering). This results in an increase of the optical path length in the photoactive layer. Similarly, flexible TCEs embedded with textured i-MCA increased the PCE by 14% for flexible OSCs. More importantly, i-MCA-TCE-based OSCs were highly flexible with 98% retention from the initial PCE at both 0° and at 60° even after 2000 bending cycles at a radius of 2 mm. This finding demonstrates that textured i-MCA is promising for improving: (a) the light harvesting efficiency of solar cells when installed in low-/high-latitude locations and (b) the wearable technology where a flexible device attached on curved objects could retain the PCE, even at an oblique angle, with respect to the normal incidence angle.

Herein, a novel strategy is presented for enhancing light absorption by incorporating gold nanostars (Au NSs) into both the active layer of organic solar cells (OSCs) and the rear-contact hole transport layer of perovskite solar cells (PSCs). We demonstrate that the power conversion efficiencies of OSCs and PSCs with embedded Au NSs are improved by 6 and 14%, respectively. We find that pegylated Au NSs are greatly dispersable in a chlorobenzene solvent, which enabled complete blending of Au NSs with the active layer. The plasmonic contributions and accelerated charge transfer are believed to improve the short-circuit current density and the fill factor. This study demonstrates the roles of plasmonic nanoparticles in the improved optical absorption, where the improvement in OSCs was attributed to surface plasmon resonance (SPR) and in PSCs was attributed to both SPR and the backscattering effect. Additionally, devices including Au NSs exhibited a better charge separation/transfer, reduced charge recombination rate, and efficient charge transport. This work provides a comprehensive understanding of the roles of plasmonic Au NS particles in OSCs and PSCs, including an insightful approach for the further development of high-performance optoelectronic devices.

This paper reviews the application of microwave signal-interference techniques to interferometers for frequency measurement and filters. The microwave interference takes place when the input-signal components pass through two different electrical paths to be then recombined and produce an interference pattern. Path lengths define the interference-based power-transmission maximum and minimum, which are calculated to obtain the desired device frequency response. Reconfigurable interferometers, wide-band, and dual-band filters designed using interference principles are described in this overview paper.

In this paper we propose Otto surface plasmon resonance (SPR) system with tunable air-gap using piezoactuator for the first time. The proposed Otto configuration based SPR system include a piezoactuator for varying an air-gap distance between a prism and gold surface. We verified effects of air-gap variation in Otto SPR system and the measured results show that the Otto SPR sensor can be realized with a metal film and prism by using a microactuator without complex microfabrication process for specific air-gap distance.

This paper presents a reconfigurable frequency measurement circuit that can reconfigure bandwidth and resolution. A compact and inexpensive reconfigurable frequency discriminator is designed with 2-bits for frequency identification. The phase shifter, which is part of the frequency discriminator, employs a varactor diode to have multiple frequency bands of operation and uniform sub-band resolution. The discriminator design has only two ports and one set of electronic components, including a power divider, reference line, phase shifter, and power combiner. The measurement results confirm the use of the circuit for detecting unknown signal with multiple operation bandwidths from 0.5 to 1.7 GHz.

In this study, a micromachined chip in Otto configuration with multiple air-gaps (1.86 µm, 2.42 µm, 3.01 µm, 3.43 µm) was fabricated, and the resonance characteristics for each air-gap was measured with a 980 nm laser source. To verify the variability of the reflectance characteristics of the Otto configuration and its applicability to multiple gas detection, the air-gap between the prism and metal film was adjusted by using a commercial piezoactuator. We experimentally verified that the SPR characteristics of the Otto chip configuration have a dependence on the air-gap distance and wavelength of the incident light. When a light source having a wavelength of 977 nm is used, the minimum reflectance becomes 0.22 when the displacement of the piezoactuator is about 9.3 µm.

In this paper, microstrip lines that are directly patterned by Ag ink-jet printing are discussed and their RF performance is investigated on both rigid and flexible substrates, which are FR-4 and polyimide (PI) film substrates, respectively. Microstrip lines are designed by computational simulation, and the simulated results are compared with the measured RF results of the fabricated microstrip lines. The measured transmission losses of the microstrip lines are 0.24 dB/cm for the FR-4 substrate and 0.66 dB/cm for the PI film substrate at 3 GHz. To measure the RF performance of the printed microstrip lines undergoing bending tests, the distances between the ends of the bended microstrip line are varied from 5 cm to 9.2 cm. The microstrip lines are twisted by torsion angles in the range of 0–40°. The RF performance and characteristics remain nearly unchanged under bending and torsion tests except for negligible variation caused by impedance mismatching occurred during the measurement process. The measured RF performance demonstrates that the printed Ag conductive lines can be utilized in RF application such as wearable and flexible systems, which require low-cost and low-end antennae at low frequencies.

We firstly show the prototype of an ohmic contact Single-Pole Double-Throw Radio Frequency Micro-Electro-Mechanical Systems (SPDT RF MEMS) switch operating at 50-100GHz. The fabricated ohmic contact SPDT RF MEMS silicon switch moves both laterally and vertically, to improve the isolation at high frequencies by initially misaligning the contact part of the switch over a Coplanar Waveguide (CPW) transmission line. The lateral and vertical movement of the switch is operated by using comb and parallel plate actuators, respectively. The proposed switch was fabricated using Silicon-On-Glass (SiOG) bonding process. The insertion loss of the fabricated switch is measured according to the different operation states of the switch, in the range from 50 to 100GHz. The fabricated length of the transmission line is 4.6mm and the measured insertion loss and isolation are 9.13dB and 24.37dB at 70GHz, respectively. Display Omitted A SPDT RF MEMS metal-contact switch for 50-100GHz applications is proposed.The switch is driven by a bidirectional comb actuator and parallel plate actuator.The RF characteristics of the switch are measured in the lateral and vertical movement sequentially.The measurement results show that the isolation can be increased using the proposed design.

This paper presents a building block approach to design a reconfigurable discriminator (RD), which is the core circuit in frequency identification receivers. The RD is used to identify an unknown signal; the output of the circuit determines a frequency subband where the unknown signal falls into. The proposed building block design approach is scalable and can be used to produce any multibit RD. This design approach can be used to produce RD circuits with more or less resolution for a fixed band of operation, according to the number of bits used for a given design. The building block approach is demonstrated through the design of a 4-bit RD. This design is a two-port device that provides a series readout and can produce 4 bits for frequency identification. The device operates from 1 to 4 GHz, implemented by microstrip lines and PIN diode switches. Simulated and measured responses are in agreement.

In this paper, we report an X-band 3D printed two-way rectangular waveguide power divider made up of electroless plated non-conductive material. In contrast to conventional metal machining fabrication processes, such as computerized numerically controlled (CNC) milling and laser beam machining (LBM), it is verified that 3D printing methods can be used to fabricate rectangular waveguide power dividers with low cost and low weight in short time.

This paper reports an experimental study focused on the characterization of the Otto chip device. These devices are structures sealed with a glass window, having a gold film, which is separated from the window surface by a well-defined gap. The gap is designed for the surface plasmon resonance effect. In this study, gap profiles were scanned by optical reflectometry. A preliminary analysis of reflectance curve patterns allows mapping the topography of the different regions of the chip. The results of the study can be used to optimize the manufacturing process of this type of structure.

In this study, a MEMS acceleration switch using mechanical hooked latch is designed, fabricated, and measured. A mechanical latching mechanism and switching characteristic are analyzed using FEM simulation. The acceleration switch with a size of 1.8×3.2×0.55mm3 was fabricated using a Silicon-on-Glass (SiOG) process. A resonance frequency of the fabricated switch and an acceleration threshold are measured to be 1.022kHz and 43.7g, respectively. The fabricated switch is latched when an applied external acceleration is higher than the threshold value of 43.7g. After latching "on", the "on" state of the switch is reliably sustained regardless of the applied external acceleration. Display Omitted We analyze switching characteristic of a MEMS acceleration switch with latching function.Fabricated switch is latched by applied acceleration which is higher than 43.7g.Measurement result agrees well with simulation result based on fabricated switch.After latching on, the "on" state is reliably sustained regardless of the applied acceleration.

We studied the effects of various plasma etching gases on a silver nanoparticle (AgNP) layer to find the proper etching conditions compatible with the AgNP printing process. An AgNP layer with thickness of 1.4 μm was prepared by spin-coating a AgNP suspension on a glass wafer; O2, CF4, and SF6 plasma were then individually treated on the AgNP layer for 1 min and for 10 min. The surface properties, elemental composition, and sheet resistance were measured in order to study the effects of plasma exposure on AgNP layer. Small particles and deposited materials were observed on the surface after treating with O2 and CF4 plasma, respectively, while large particles were grown by re-crystallization after SF6 plasma exposure. In summary, O2 plasma has the least damage to the AgNP layer, showing good surface properties and sheet resistance. CF4 plasma showed moderate results, and the SF6 plasma severely damaged the AgNP layer.

In this study, we suggested a method to fabricate a coplanar waveguide with high resolution using an inkjet printing process. A glass substrate was selectively coated with fluorocarbon film, which makes the coated region hydrophobic. Silver nanoparticle colloid ink was printed on the hydrophilic region using an inkjet printer, where the fluorocarbon film effectively hindered the ink from dispersing onto the film. As a result, a coplanar waveguide with a uniform gap of 16.1 μm was fabricated, where the thickness of the structure was higher than 2 μm. The conductivity of the printed structure was about eight times lower than that of bulk silver. The transmission loss of the coplanar waveguide was measured to be 0.61 dB/cm and 2.01 dB/cm at 1 GHz and 10 GHz, respectively, and the return loss was mostly better than 15 dB at the frequency ranging from 100 MHz to 40 GHz. The measurement results show that the proposed method is not only cost-effective and simpler than conventional processes, but is also suitable for the fabrication of microstructures with high-resolution and high-thickness.

We report DNA-mediated simple synthetic methods to obtain anisotropic plasmonic nanostructures with a tailorable intra-nanogap distance ranging from 0.9 to 4.0 nm. Anisotropic half-shell structures with sub-1.0 nm intra-nanogaps showed a wavelength-independent surface-enhanced Raman scattering (SERS) intensity and a highly sensitive SERS response to NIR light. We found that the reaction conditions such as pH and NaCl concentration are responsible for the resulting shell structures and intra-nanogap distances. Three noticeable plasmonic nanostructures [i.e., half-shell with sub-1.0 nm nanogaps, closed-shell with a wide nanogap (2.1 nm) and star-shaped with an irregular nanogap (1.5–4.0 nm)] were synthesized, and solution-based and single particle-based Raman measurements showed a strong relationship between the plasmonic structures and the SERS intensity. An understanding of DNA-mediated control for nanogap-engineered plasmonic nanostructures and studies of SERS-activity relationships using single particle-correlated measurements can provide new insights into the design of new plasmonic nanostructures and SERS-based biosensing applications.

A MEMS acceleration switch capable of tuning threshold acceleration to either higher or lower levels is designed and implemented with comb drive actuators as a mechanism of threshold tuning. A small sized switch (1.6 × 3.1 × 0.55 mm 3 ) is successfully realized by patterning silicon structures on a glass wafer. The resonant frequency of fabricated switches agrees well with a designed frequency of 1.1 kHz. The threshold acceleration at no tuning voltage is 10.25 g and it is subsequently tuned to 2.0 g and 17.25 g by applying 30 V to pushing comb and pulling comb, respectively. The rising time is measured to be 9.8 ms. Additional functionalities such as safe/armed position convertibility and single use latching switch are also described for diverse applications of the tunable acceleration switches.

In this paper, we describe the analysis of inkjet-printed silver (Ag) patterns on epoxycoated substrates according to several reliability evaluation test method guidelines for conventional printed circuit boards (PCB). To prepare patterns for the reliability analysis, various regular test patterns were created by Ag inkjet printing on flame retardant 4 (FR4) and polyimide (PI) substrates coated with epoxy for each test method. We coated the substrates with an epoxy primer layer to control the surface energy during printing of the patterns. The contact angle of the ink to the coated epoxy primer was 69˚, and its surface energy was 18.6 mJ/m². Also, the substrate temperature was set at 70℃. We were able to obtain continuous line patterns by inkjet printing with a droplet spacing of 60 ㎛. The reliability evaluation tests included the dielectric withstanding voltage, adhesive strength, thermal shock, pressure cooker, bending, uniformity of line-width and spacing, and high-frequency transmission loss tests.

This article describes a fourth-order 3-D printed combline filter with a Chebyshev response, operating at central frequency 3 GHz and having a 3% fractional bandwidth. The filter is designed using the coupling matrix theory, fabricated, and experimental results are presented. Comparison between simulations and measurements shows good agreement. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1388–1390, 2017. © 2017 Wiley Periodicals, Inc.

Detection of microwave signals in the battlefield or surveillance zone allows identifying enemy outposts, which may include radar or communications transmitters. This paper describes the techniques required to identify the frequency of unknown detected signals and the estimation of their incoming direction using unmanned aerial vehicles.

This paper introduces Radio Frequency Microelectromechanical Systems (RF MEMS) devices, including a switch, resonator, filter and antenna for applications that require reconfigurable RF components.

An Otto chip device fabricated on silicon and sealed with a quartz window has recently been demonstrated as a potential alternative for the traditional Kretschmann based configuration for the development of surface plasmon resonance - SPR - sensors. We have fabricated open Otto chip structures as well and have characterized the surface plasmon resonance - SPR - effect at a wavelength of 975.1 nm. In this paper we report on the potential of these structures to act as pressure sensors.

In this paper, nano-silver ink-jet printed transmission lines were fabricated to investigate RF performance on both flame retardant (FR-4) and polyimide (PI) as rigid and flexible substrates. The transmission lines were printed by using the ink-jet printer with velocity of 3.5 mm/s and were sintered in a convection oven with 250 °C. The RF performance of transmission lines was simulated and measured at low frequencies. The transmission loss is measured to be 0.22 dB@1 GHz and 0.32 dB@1 GHz, respectively, for the FR-4 and PI substrates, respectively. The return loss has over 16 dB for FR-4 substrate and over 12 dB for PI substrate. The RF performance of transmission line was investigated and discussed in regard to an influence by two substrates. The measured RF performance of fabricated transmission lines results in the possibility that flexible device is explored in low frequencies application.

This paper presents a comparison between fixed and reconfigurable 4-bit microwave discriminators. The fixed discriminator is implemented by using multi-band-stop filters to define bits used for frequency identification. The reconfigurable discriminator is implemented by using delay lines and two SPQT switches. Both designs operate at L and S bands, a comparison between both devices is provided, including simulated and measured responses for both designs.

A sealed Otto chip device has recently been demonstrated as a potential alternative for the traditional Kretschmann based configuration for the development of surface plasmon resonance - SPR - sensors. We have fabricated an open Otto chip structure on silicon and have characterized the SPR effect at a wavelength of 975.1 nm. In this paper we report on an open Otto chip pressure transducer.

In this paper, an Otto coupling configuration based SPR chip is designed, simulated and fabricated using a silicon-on-quartz (SoQ) bonding process. The simulation of the SPR effect is conducted using COMSOL Multiphysics simulator (Altsoft Co.) using the designed chip dimensions, the optical constants are interpolated from data available in the literature. The size of the fabricated SPR chip is $$30\; \times \;30\; \times \;1 {\text{mm}}^{3}$$30×30×1mm3. Resonance angle and reflectance are measured to be 42.19° and 0.411°, respectively, using an automated reflectometer. Discrepancy between measurement and simulation results is discussed by optical constant of the gold layer used as a thin metal film. The SoQ bonding process is a feasible approach for implementation of Otto coupling configuration based SPR chips.

In this paper, we propose a feed-through reduction technique for a micro-resonator with a push–pull configuration that is based on the analysis of electrical characteristics of a direct driving micro-resonator. We show that the feed-through capacitance is decreased by reducing the sizes of the driving and sensing electrodes, inserting bias electrodes between them, and by surrounding them with a bias electrode. Using the proposed methods, we succeeded in reducing the feed-through capacitance and improving the performance of the micro-resonator with a push–pull configuration. We propose designs for the push–pull configuration with small electrodes, small electrodes and the insertion of bias electrodes between the driving and sensing electrodes, and surrounding the electrodes with a bias electrode. The feed-through capacitance of the small electrode model is 41.9 fF, an approximately 50% decrease from the general model (90.1 fF). The feed-through capacitance of the model with inserted bias electrodes is 17.9 fF. The feed-through capacitance of the model surrounded with an inserted bias electrode is 10.9 fF. The electrical transmission according to the feed-through capacitance was measured for each model. The efficiency in the electrical transmission is increased from 7.83 dB (the general model) to 8.94 dB (the small electrodes), 9.18 dB (inserting bias electrodes model) and 9.40 dB (surrounded with bias electrode model). We experimentally verified that the feed-through capacitance is decreased by reducing the sizes of the driving and sensing electrodes, inserting bias electrodes, and surrounding the electrodes with bias electrodes. The feed-through capacitance reduction technique would be useful for sensors, such as a micro-resonator requiring high performance, and radio frequency (RF) devices operating at high frequencies.