We propose reconfigurable THz wave modulation using high-definition photoinduced patterns on hybrid metal-silicon metasurface. The method suppresses lateral diffusion of photogenerated carriers and enables continuous photoconductive patterns. A tunable bandpass filter is investigated.

Optically controlled RF switches with a novel non-contact device architecture that achieves high performance in the millimeterwave-to-terahertz (mmW-THz) region are proposed and investigated through simulation. The significant change in conductivity in semiconductors caused by photogenerated carriers is used to develop RF switches having very high performance. By including a thin layer of insulator between the active semiconductor material and the metal contacts, the carrier concentration can be enhanced over that of conventional devices. For a prototype demonstration, G-band coplanar waveguide-based optical switches (using Si and Ge as active materials) with different contact geometries have been modeled and simulated. The proposed switches outperform both conventional solid-state switches and phase-change material-based switches in the switch figure-of-merit, and are promising for developing a novel class of tunable and reconfigurable mmW-THz circuits for advanced sensing, imaging, and communication.

Substrate-integrated waveguides (SIWs) have recently attracted increasing attention for the development of terahertz (THz) circuits and systems. However, conventional SIWs employ fixed metallic vias to form the waveguide sidewalls, resulting in limited tunability and reconfigurability. In this paper, we report a novel approach for the realization of high-performance tunable and/or reconfigurable THz SIW structures. In this approach, photo-induced free carriers are generated in a high-resistivity silicon pillar-array structure to form well-defined, highly conductive, vertical sidewalls. The wave propagation properties of these optically-defined photo-induced SIWs (PI-SIWs) have been evaluated using full-wave electromagnetic simulations. Higher-functionality THz components, including a single-pole double-throw switch and a phase shifter were also designed and simulated. Based on these example circuits, PI-SIWs using pillar-array structures appear to be attractive candidates for the development of tunable and reconfigurable THz components for THz sensing, imaging, and communication systems.

In this paper, optically-controlled high-performance integrated RF switches have been proposed, investigated and discussed. The switching is based on the high conductivity change (5-6 orders) due to photo-induced free-carriers in semiconductors. Initial simulation for G-band CPW-based optical switches has shown that a record-high (compared to semiconductor and VO 2 switches) intrinsic FOM (figure of merit evaluated by R on C off constant) of 153 THz can be achieved using Ge (85 THz with Si). In addition, the on/off ratio can be maintained as high as 28.1 dB at 200 GHz. The proposed device has not only superior performance, but also the advantages of compact size, easy fabrication and integration, as well as high speed and reliability, making it a great candidate for enabling advanced tunable/reconfigurable circuits that are required in millimeter-wave and terahertz communications.

We report our recent progress toward the development of optically controlled tunable/reconfigurable THz circuits/components in waveguide configurations for advanced sensing and adaptive wireless communications. The development and demonstration of a modified WR-4.3 variable waveguide attenuator based on photo-excited Si with 60-dB range and 0.7-dB insertion loss will first be reviewed. Then the investigation of a WR-5.1 reconfigurable band-stop filter (BSF) prototype based on photo-induced electromagnetic band gap (PI-EBG) structures using semiconductor mesa arrays will be presented. The center frequency of the BSF can be reconfigured from 166-200 GHz with adjustable stop-band rejection and bandwidth. Finally, the development of high-performance THz integrated switches using the same optical control methodology enabling the implementation of more advanced tunable/reconfigurable THz waveguide circuits will be envisioned, investigated and discussed. Preliminary results reveal that the optically controlled RF switches show a potentially record-high figure-of-merit (evaluated by RonCoff constant) of 153 THz, allowing them to outperform both conventional solid-state-device-based (e.g., HEMTs) and emerging phase-changing-material-based (e.g., VO2) counterparts, and therefore promising to compete with MEMS switches in the mmW-THz region for a novel class of tunable/reconfigurable circuits/components.

We present a novel approach for realizing tunable/reconfigurable THz circuits using photo-induced substrate-integrated waveguide (PI-SIW) architectures. In this approach, fixed metallic vias in conventional SIW are replaced by photo-induced conductive plasma sidewalls. Full-wave HFSS simulation has shown an insertion loss of 4.15 dB/mm at 280 GHz with photo-induced sidewalls formed by 80 W/cm2 light intensity (550 nm wavelength) on high resistivity silicon (HRS) wafer. To further improve the PI-SIW performance, a pillar-array structure is proposed to suppress carrier diffusion while same time increasing the achievable photoconductivity. With such pillararray structures, the insertion loss at 280 GHz has been reduced to as low as 0.96 dB/mm, and a value of 0.81 dB/mm can be potentially achieved for a 300 W/cm2 light intensity.

We report the design, fabrication, and characterization of a high-performance optically controlled WR-4.3 variable attenuator. The attenuation is based on the interaction between the incident waves and photogenerated free carriers inside an E-plane micromachined silicon absorber. Tuning is realized by illuminating the silicon with different light intensities using three 808-nm infrared laser diodes. Measurement results show that an average attenuation range of 60 dB, a 0.7-dB insertion loss, and a greater than 15-dB return loss have been achieved over the entire WR-4.3 band. In addition, a 3-dB modulation bandwidth of 350 kHz has been obtained experimentally. Initial thermal stability test of the device has also been performed, with less than 0.4-dB amplitude drift and 2° drift in phase over 30-min demonstration.

Electromagnetic band gap (EBG) structures offer unique solutions for effectively manipulating electromagnetic waves over a broad range of frequencies for a wide range of applications. However, most EBG designs reported so far either require sophisticated fabrication processes or have limited tunability and reconfigurability. In this paper, we investigate the potential to implement high performance tunable and reconfigurable EBG components using a novel optical control approach. This technology allows the generation of EBG structures through spatially-resolved photogeneration of free carriers in a semiconductor, without any complex fabrication processes. As a prototype demonstration, a reconfigurable microwave frequency tunable band-stop filter (BSF) based on photo-induced uniplanar EBG structures has been investigated through simulation. In this approach, the required EBG patterns are directly illuminated onto a Ge ground plane mounted to the bottom of a Duroid substrate for tunability using a digital light processing (DLP) projector. On the basis of HFSS simulations, the bandwidth of the BSF can be tuned by modifying the EBG pattern filling factor. The center frequency of the BSF could also be tuned from 8-12 GHz by adjusting the period of the EBG structure. In addition, two limiting factors, i.e., localized heating effects and finite lateral spatial resolution (due to carrier diffusion), that may affect the circuit performance in this technology have been investigated and discussed. By using a mesa-array structured ground plane, this approach is promising for developing tunable and reconfigurable circuits such as filters from the microwave to terahertz regimes.

In this paper, we report the design and simulation of two optically controlled tunable and reconfigurable G-band (140220 GHz) waveguide devices based on electromagnetic band gap (EBG) structures. The first device based on a pre-patterned EBG structure can be reconfigured between a band-stop filter (BSF) and a transmission line. The second device based on photoinduced EBG structures using a mesa-array shows increased level of tunability and reconfigurability with a BSF center frequency tunable from 175-200 GHz. The proposed tunable and reconfigurable THz devices are promising for a wide range of applications including multiple-frequency-band THz wireless communications.

In today's fast-paced and well-connected world, consumer electronics are evolving rapidly. As a result, the amount of discarded electronic devices is becoming a major health and environmental concern. The rapid expansion of flexible electronics has the potential to transform consumer electronic devices from rigid phones and tablets to robust wearable devices. This means increased use of plastics in consumer electronics and the potential to generate more persistent plastic waste for the environment. Hence, today, the need for flexible biodegradable electronics is at the forefront of minimizing the mounting pile of global electronic waste. A "bioadvantaged" approach to develop a biodegradable, flexible, and application-adaptable electronic components based on crop components and graphene is reported. More specifically, by combining zein, a corn-derived protein, and aleuritic acid, a major monomer of tomato cuticles and sheellac, along with graphene, biocomposite conductors having low electrical resistance (approximate to 10 omega sq(-1)) with exceptional mechanical and fatigue resilience are fabricated. Further, a number of high-performance electronic applications, such as THz electromagnetic shielding, flexible GHz antenna construction, and flexible solar cell electrode, are demonstrated. Excellent performance results are measured from each application comparable to conventional nondegrading counterparts, thus paving the way for the concept of "plant-e-tronics" towards sustainability.

In this work, we present a novel approach to the implementation of optically controlled reconfigurable terahertz (THz) waveguide filters based on photo-induced electromagnetic band gap (PI-EBG) structures using semiconductor mesa arrays. In this approach, EBG structures are dynamically generated through spatially-resolved photogeneration of free carriers in semiconductor mesa structures; the use of mesa arrays improves the spatial resolution, leading to more refined PI-EBG patterns and improved circuit operation at THz frequencies. A band-stop filter prototype in the WR-5.1 band (140-220 GHz) was designed, simulated, and analyzed in detail. Simulations show that the stop-band rejection and bandwidth of the proposed device can be adjusted by changing the filling factor of the photo-patterns illuminated onto the mesa array. The center frequency of the stop-band can also be tuned from 166 to 200 GHz by changing the period of the PI-EBG patterns. The proposed reconfigurable THz waveguide filters based on PI-EBG are promising for a wide range of applications in advanced THz sensing, imaging, and communications.

Specific Absorption Rate (SAR) is a measure of the electromagnetic exposure of portable devices imposed by regulatory agencies. In this paper, we model peak spatial-average SAR of multiple-antenna portable devices using a simple mixed quadratic function of the transmitted vector signal. The model takes into account the movement of location on peak SAR as the transmitted signal varies in amplitude and relative phase between antennas, and can be applied to any number of antennas. Examples with two and four antennas are presented.

Tunable and reconfigurable terahertz (THz) devices such as modulators/variable attenuators, tunable filters, coded apertures, phase shifters and high-level switches (e.g., DPDT) that are required for advanced imaging and adaptive wireless communication applications are challenging to realize. We report a promising approach to develop the above THz devices based on spatially-resolved optical modulation (SROM) using photo-induced (PI) free carriers in semiconductors. The fundamental mechanism for this approach will first be introduced followed by prototype demonstrations for reconfigurable coded-aperture imaging masks, beam steering/forming antennas and waveguide-based tunable attenuators. The potential to develop more advanced tunable/reconfigurable THz devices (e.g., tunable delay lines, SPDT, DPDT switches) using optically-controlled waveguide architectures such as PI electromagnetic band gap (EBG) structures and dynamically-reconfigurable PI substrate-integrated waveguides (SIWs) will also be discussed on the basis of performance-improved SROM using the so-called mesa-array technique.

Double-perovskite Ba2YMoO6 ceramics were prepared via the solid-state reaction route. Their dielectric properties were investigated as a function of temperature (100°C≤T≤800°C) and frequency (300Hz≤f≤5MHz). In the temperature below 600°C, two thermally activated dielectric relaxations can be well identified. The low-temperature relaxation was ascribed to be a dipolar relaxation caused by oxygen vacancy diffusion, and the high-temperature relaxation is found to be a Maxwell–Wagner relaxation due to surface-layer effect.

Device models to support circuit design efforts using monolithically-integrated enhancement- and depletion-mode high-speed InAlN/AlN/GaN HEMTs are reported. Physically- motivated modifications to the conventional empirical compact models have been included to enhance model accuracy over bias and temperature. The models have been extracted from DC through 110 GHz at baseplate temperatures from 25 °C through 100 °C; good agreement is obtained between measurement results and the extracted model.