A domain decomposition method is widely utilized for analyzing large-scale electromagnetic problems. The method decomposes the target model into small independent subdomains. An electromagnetic analysis has inherently suffers from late convergence analyzed with iterative algorithms such as Krylov subspace algorithms. The DDM remedies this issue by decomposing the total system into subdomain problems and gathering the local results as an interface problem to adjust to achieve the total solution. In this paper we report the convergence properties of the domain decomposition method while modifying the size of local domain and the region shape on several mesh sizes. As experimental results show, the convergence speed depends on the number of interface problem variables and the selection of the local region shapes. In addition to that the convergence property differs according to the target frequencies. In general it is demonstrated that the convergence speed can be accelerated with large cubic subdomain shape. We propose the subdomain selection strategies based on the analysis of the condition numbers of the governing equation.

This study introduces a pattern-matching method to enhance the efficiency and accuracy of physical verification of cell libraries. The pattern-matching method swiftly compares layouts of all I/O units within a specific area, identifying significantly different I/O units. Utilizing random sampling or full permutation can improve the efficiency of verification of I/O cell libraries. All permutations within an 11-unit I/O unit library can produce 39,916,800 I/O units (11!), far exceeding the capacity of current IC layout software. However, the proposed algorithm generates the layout file within 1 second and significantly reduces the DRC verification time from infinite duration to 63 seconds executing 415 DRC rules. This approach effectively improves the potential to detect layer density errors in I/O libraries.While conventional processes detect layer density and DRC issues only when adjacent I/O cells are placed due to layout size and machine constraints, in this work, the proposed algorithm selectively generates multiple distinct combinations of I/O cells for verification, crucial for improving the accuracy of physical design.

This study discusses the behavior of resonant tunneling diode (RTD) oscillators when a transmission line (TL) stub is added. The TL stub acts as a delayed feedback unit, resulting in unstable and complex oscillation behavior. Circuit simulation showed that the circuits generate various waveforms, including chaos, by changing the stub length. Experimental demonstration of the simulation results was performed using circuits fabricated with hybrid integration techniques using an InGaAs/AlAs RTD. These complex signals have potential for various applications in the THz frequency range. On the other hand, this finding is significant for the design of THz oscillators using an RTD, since even a small metal pattern can cause such a feedback effect in the THz frequency range. In particular, interconnect wiring patterns can cause this effect because reflection due to impedance mismatch is unavoidable.

Promising proposals of a material, deposition process, and storage device have been demonstrated for neuromorphic systems. The material is Ga-Sn-O (GTO), amorphous metal-oxide semiconductor, and does not contain rare metals such as In. The deposition process is a mist chemical-vapor-deposition (CVD) method, atmospheric pressure process. Therefore, the material and fabrication costs can be simultaneously saved, and three-dimensional stacked structures will be possible. The storage device is an analog memristor, a kind of memristors, but has continuous conductance, and analog computing will be possible owing to continuous weights of synapse elements in neural networks. These structures and computing are the same as those in living brains. We have succeeded in attaining an analog memristive characteristic by optimizing the Ga:Sn composition rate, namely, completing an analog memristor. The analog memristor of the GTO thin film by the mist CVD method can be expected to be a key component for neuromorphic systems.

We describe a tunable liquid crystal lens based on Fresnel optics that enables variable focus of virtual images displayed by a head-worn VR or AR device. This lens has been fabricated using ultra-thin, light bioplastic film instead of glass, uniquely enhancing visual comfort whilst reducing weight and thickness compared to glass-based approaches.

To improve throughput in security inspection procedures, a millimeter-wave (mmW) imaging system with a high-throughput operation with reasonable resolution compared to conventional mmW imaging systems is developed. Investigates the distinctive attributes of mmW, including its safe penetration through clothing, the study demonstrates the generation of detailed two-dimensional reconstructions of objects. Through the strategic use of a lens, signal amplitudes and phases are effectively captured, yielding reconstruction images from the signal reflected from the target. Experimental validations further affirm the effectiveness of mmW imaging with a dielectric lens, showcasing successful reconstructions of targets positioned at the lens's front focal plane. Notably, the approach exhibits proficiency in discerning objects obscured behind non-metallic materials such as paper and cloth. These findings highlight the potential of utilizing Fourier transform analysis and a dielectric lens in mmW imaging, presenting a promising approach for security applications, particularly in the detection of concealed objects.

The Origin of the low turn-on voltage in the blue organic light-emitting diode using upconversion is discussed. We have discovered the properties of the intermediate state at the donor/acceptor interface such as the energy levels and the molecular interactions are key in determining the device performance.

Due to the limited lifespan of Micro-Electro-Mechanical Systems (MEMS), their components need to be replaced regularly. For intelligent devices such as electronic noses, updating an intelligent gas sensor system requires establishing a new classifier model for the newly inserted gas sensor probes because of the poor consistency between the signals collected by the new and original systems. The traditional method involves retraining the new model by collecting adequate data of the gas sensor array under strict laboratory conditions, which is time-consuming and resource-intensive. To simplify and expedite this process, a federated learning method called FedGSSU is proposed for gas sensor system updating. Two datasets were used to verify the effectiveness of the proposed framework. The experimental results show that FedGSSU can effectively utilize the original classifier model to obtain a new classifier model while only replacing the gas sensor array. The consistency between the new gas sensor system and the original one reaches up to 90.17%, and the test accuracy is increased by 4 percentage points compared to the traditional method. While replacing sensors with FedGSSU will reduce recognition accuracy slightly, it is more acceptable in scenarios where high accuracy is not required than re-calibrating sensors and re-training the classifier.

This paper presents a scatterer information estimation method for both E- and H-polarizations based on a time-domain saddle-point technique (TD-SPT). The method utilizes numerical data of the response waveforms of the reflected geometric optical ray (RGO) series, which constitute the backward transient scattering field components when a line source and an observation point are at the same location. A scatterer selected in the paper is a two-dimensional (2-D) coated cylinder. The three types of scatterer information are the relative permittivity of a coating medium layer and its thickness, and the outer radius of a coated cylinder. Specifically, the scatterer information estimation formulas are derived by applying the TD-SPT represented in RGO series to the amplitude intensity ratios (AIRs) of adjacent RGO components. By focusing on the analytical results that the AIRs are independent of polarization, we analytically clarify that all the estimation formulas derived here denote polarization independence. The estimates are obtained by substituting numerical data of the peaks of the response waveforms of the RGO components and their arrival times, as well as numerical parameters of a pulse source, into the estimation formulas and performing iterative calculations. We derive approximations to the estimation errors that are useful in quantitatively evaluating the errors of the estimates. The effectiveness of the scatterer information estimation method is substantiated by comparing the estimates with the set values. The polarization independence of the estimation formulas is validated numerically by contrasting the estimates for E- and H-polarizations. The estimation errors are discussed using the approximations to the errors of the estimates when a line source and an observation point are at the same location. Thereafter, the discrepancies that arise between the estimation errors when a line source and an observation point are at different locations are discussed. The methods to control the estimation accuracy and the computational time are also discussed.

This paper proposes two VLSI implementation approaches for periods estimation hardware of periodic signals. Digital signal processing is one of the important technologies, and to estimate periods of signals are widely used in many areas such as IoT, predictive maintenance, anomaly detection, health monitoring, and so on. This paper focuses on accumulation for real-time serial-to-parallel converter (ARS) which is a simple parameter estimation method for periodic signals. ARS is simple algorithm to estimate periods of periodic signals without complex instructions such as multiplier and division. However, this algorithm is implemented only on software, suitable hardware implementation methods are not clear. Therefore, this paper proposes two VLSI implementation methods called ARS-DFF and ARS-MEM. ARS-DFF is simple and fast implementation method, but hardware scale is large. ARS-MEM reduces hardware scale by introducing an SRAM macro cell. This paper also designs both approaches using System Verilog and evaluates VLSI implementation. According to our evaluation results, both proposed methods can reduce the power consumption to less than 1/1000 compared to the implementation on a microprocessor.

A dual-band decoupling strategy via artificial transmission line (TL) for closely spaced two-element multiple-input multiple-output (MIMO) antenna is proposed, which consists of two composite right-/left-handed TLs for dual-band phase shifting and a cross-shaped TL for suscep tance elimination to counteract the real and imaginary part of the mutual coupling coefficient S₂₁ at dual frequency bands, respectively. The decou pling principle and detailed design process of the dual-band decoupling scheme are presented. To validate the dual-band decoupling technique, a closely spaced dual-band MIMO antenna for 5G (sub-6G frequency band) utilization is designed, fabricated, and tested. The experimental results agree well with the simulation ones. A dual-band of 3.40 GHz-3.59 GHz and 4.79 GHz-4.99 GHz (S₁₁&S₂₂ < -10 dB, S₁₂&S₂₁ < -20 dB) has been achieved, and the mutual coupling coefficient S₂₁ is significantly reduced 21 dB and 16.1 dB at 3.5 GHz and 4.9 GHz, respectively. In addition, the proposed dual-band decoupling scheme is antenna independent, and it is very suitable for other tightly coupled dual-band MIMO antennas.

A double step attenuation measurement technique using a non-isolating gauge block attenuator (GBA) has been proposed for accurate measurements of radio frequency and microwave high attenuation. For fixed attenuator as a device under test (DUT), a medium value (≦60 dB) attenuator is used as the GBA which connected directly between the test ports, then high attenuation of the DUT is measured in two setups as follows. 1) Thru and GBA with normal power level and 2) GBA and DUT with higher power level. This approach removes the need to isolate the GBA, therefore, accurate measurements of high attenuation can be obtained simply over a broad frequency range. For variable or step attenuator as a DUT, one of the attenuation sections of the DUT is applied as the GBA. Detailed analyses and those verification measurements are carried out both for fixed attenuator, as well as for variable attenuator and show good agreement.

Effects of Al thickness in Ti/Al/Ti/Au ohmic contact on AlGaN/GaN heterostructures are studied. Samples having Al thickness of 30, 90 and 120 nm in Ti/Al/Ti/Au have been investigated by electrical and X-ray photoelectron spectroscopy (XPS) depth profile analysis. It is found that thick Al samples show lower resistance and formation of Al-based alloy under the oxidized Al layer.

In this research, we investigated the digital/analog-operation utilizing ferroelectric nondooped HfO₂ (FeND-HfO₂) as a blocking layer (BL) in the Hf-based metal/oxide/nitride/oxide/Si (MONOS) nonvolatile memory (NVM), so called FeNOS NVM. The Al/HfN_0.5/ HfN_1.1/HfO₂/p-Si(100) FeNOS diodes realized small equivalent oxide thickness (EOT) of 4.5 nm with the density of interface states (D_it) of 5.3 × 10¹⁰ eV^-1cm^-2 which were suitable for high-speed and low-voltage operation. The flat-band voltage (V_FB) was well controlled as 80-100 mV with the input pulses of ±3 V/100 ms controlled by the partial polarization of FeND-HfO₂ BL at each 2-bit state operated by the charge injection with the input pulses of +8 V/1-100 ms.

Transcatheter renal denervation (RDN) is a treatment for resistant hypertension, which is performed by ablating the renal nerves located outside the artery using a catheter from inside the artery. Our previous studies simulated the temperature during RDN by using constant physical properties of biological tissue to validate the various catheter RDN devices. Some other studies report temperature dependence of physical properties of biological tissues. However, there are no studies that have measured the electrical properties of low water content tissues. Adipose tissue, a type of low water content tissue, is related to RDN closely. Therefore, it is important to know the temperature dependence of the electrical constants of adipose tissue. In this study, we measured the relationship between the electrical constants and the temperature of bovine adipose tissue. Next, the obtained equation of the relationship between relative permittivity of adipose tissue and temperature was introduced. In addition, the temperature dependence of the electrical constants of high water content tissues and the temperature dependence of the thermal constants of biological tissues were also introduced into the temperature analysis. After 180 seconds of heating, the temperature of the model with the temperature dependence of the physical properties was 7.25 ℃ lower than the model without the temperature dependence of the physical properties at a certain position. From the results, it can be said that the temperature dependence of physical properties will be significant when an accurate temperature analysis is required.

Renal Denervation (RDN) has been developed as a potential treatment for hypertension that is resistant to traditional antihypertensive medication. This technique involves the ablation of nerve fibers around the renal artery from inside the blood vessel, which is intended to suppress sympathetic nerve activity and result in an antihypertensive effect. Currently, clinical investigation is underway to evaluate the effectiveness of RDN in treating treatment-resistant hypertension. Although radio frequency (RF) ablation catheters are commonly used, their heating capacity is limited. Microwave catheters are being considered as another option for RDN. We aim to solve the technical challenges of applying microwave catheters to RDN. In this paper, we designed a catheter with a helix structure and a microwave (2.45 GHz) antenna. The antenna is a coaxial slot antenna, the dimensions of which were determined by optimizing the reflection coefficient through simulation. The measured catheter reflection coefficient is -23.6 dB using egg white and -32 dB in the renal artery. The prototype catheter was evaluated by in vitro experiments to validate the simulation. The procedure performed successfully with in vivo experiments involving the ablation of porcine renal arteries. The pathological evaluation confirmed that a large area of the perivascular tissue was ablated (>5 mm) in a single quadrant without significant damage to the renal artery. Our proposed device allows for control of the ablation position and produces deep nerve ablation without overheating the intima or surrounding blood, suggesting a highly capable new denervation catheter.

A reduced dark leakage current, without degrading the near-infrared responsivity, is reported for a vertical pin structure of Ge photodiodes (PDs) on n⁺-Si substrate, which usually shows a leakage current higher than PDs on p⁺-Si. The peripheral/surface leakage, the dominant leakage in PDs on n⁺-Si, is significantly suppressed by globally implanting P⁺ in the i-Si cap layer protecting the fragile surface of i-Ge epitaxial layer before locally implanting B⁺/BF₂⁺ for the top p⁺ region of the pin junction. The P⁺ implantation compensates free holes unintentionally induced due to the Fermi level pinning at the surface/interface of Ge. By preventing the hole conduction from the periphery to the top p⁺ region under a negative/reverse bias, a reduction in the leakage current of PDs on n⁺-Si is realized.

A binarized neural network (BNN) inference accelerator is designed in which weights are stores in loadless four-transistor static random access memory (4T SRAM) cells. A time-multiplexed exclusive NOR (XNOR) multiplier with switched capacitors is proposed which prevents the loadless 4T SRAM cell from being destroyed in the operation. An accumulator with current sensing scheme is also proposed to make the multiply-accumulate operation (MAC) completely linear and read-disturb free. The BNN inference accelerator is applied to the MNIST dataset recognition problem with accuracy of 96.2% for 500 data and the throughput, the energy efficiency and the area efficiency are confirmed to be 15.50TOPS, 72.17TOPS/W and 50.13TOPS/mm², respectively, by HSPICE simulation in 32nm technology. Compared with the conventional SRAM cell based BNN inference accelerators which are scaled to 32nm technology, the synapse cell size is reduced to less than 16% (0.235μm²) and the cell efficiency (synapse array area/synapse array plus peripheral circuits) is 73.27% which is equivalent to the state-of-the-art of the SRAM cell based BNN accelerators.

The Ground-Air Frequency Domain Electromagnetic Method (GAFDEM) is a fast and effective semi-airborne electromagnetic exploration method for subsurface anomaly targets. Based on the depth-focused transmission waveform, this method can realize the high-resolution detection of underground targets at specific depths. However, due to the high inductance and resistance parameters of the transmitting load in GAFDEM exploration, the transmission current of the depth-focused waveform decays rapidly in the middle and high-frequency bands, which restricts the detection signal intensity. To solve this problem, a broadband resonant circuit and its parameter design method are proposed. According to the typical transmission frequency range and load, the parameters are designed, and the circuit model is simulated and tested. The results show that the designed broadband resonant circuit can increase the transmission active power of the depth-focused waveform by more than 490%, reduce the reactive power by more than 37%, and increase the transmission current intensity of the target frequency by 2.64 times. Moreover, this circuit has good robustness. It can achieve a good resonance effect within the error range of ±10% of capacitor. This design provides an effective way for GAFDEM to enhance the intensity of high-frequency detection signals and improve the shallow exploration effect.

In this paper, a single-layer circular polarizer for linear polarized horn antenna is proposed. The multiple reflected waves between the aperture and array provide desired phase differences between vertical and horizontal polarizations. The measured gain of the fabricated antenna is 14.4 dBic and the half power beamwidths of the vertical polarization are 28 and 24 deg. and those of the horizontal polarization are 31 and 23 degrees in the vertical and horizontal planes. The polarizer has a low impact on the gain and beamwidth of the primary horn antenna and their changes are within 1.7 dB and 10 degrees. The 3 dB fractional bandwidth of the axial ratio is measured to be 1.4 %.

Ground penetrating radar (GPR) has the advantage of non-destructively and quickly inspecting internal structures such as voids and buried pipes under roads. However, it is necessary to estimate the internal structures from the GPR images. Recently, recognition and detection methods for GPR images using deep learning have been studied. This paper examines a data augmentation method using a cutout method necessary to estimate GPR images with deep learning accurately. We find that the cutout augmentation exhibits higher detection rates for all objects used in this study than a commonly used horizontal shift augmentation.

In recent years, the declining birthrate and aging population have become serious problems in Japan. To solve these problems, we have developed a system based on edge AI. This system predicts the future heart rate during walking in real time and provides feedback to improve the quality of exercise and extend healthy life expectancy. In this paper, we predicted the heart rate in real time based on the proposed system and provided feedback. Experiments were conducted without and with the predicted heart rate, and a comparison was made to demonstrate the effectiveness of the predicted heart rate.

In Japan, research on spatial transmission Wireless Power Transfer / Transmission (WPT) for long-distance power transmission has been conducted ahead of the rest of the world; however, until 2022, there has been no category under the Radio Law, and it has been treated as an experimental station. The authors are working on Japanese institutionalization (revision of ministerial ordinances) and global standardization of this spatial transmission WPT for social implementation. This paper describes the Japanese and international institutionalization and standardization trends. In addition, as the latest trend in R&D trends, as the next step of institutionalization, the author introduces two national projects that are being worked on by industry, academia, and government for Step 2, which can be used for a wider range of applications by relaxing the scope of use and restrictions from Step 1, which has various restrictions.

The first is about the Cross-ministerial Strategic Innovation Promotion Program (SIP) Phase 2. In SIP Phase 2, we conducted R&D on “WPT system for sensor networks and mobile devices”. This R&D is research on detecting and avoiding people so that radio exposure does not exceed protection guidelines and detecting incumbent radios and avoiding harmful interference so that more power can be transmitted under coexistence conditions.

The other is “Research and Development for Expansion of Radio Resources” to be conducted by the Ministry of Internal Affairs and Communications (MIC), which is scheduled for four years from FY2022. This is also a more concrete research and development project for Step 2 institutionalization, along with the results of the SIP mentioned above.

Japan encounters an urgent issue of “Carbon Neutrality” as a member of the international world and is required to make the action plans to accomplish this issue, i.e., the zero emission of CO₂ by 2050. Our world must change the industries to adapt to the electrification based on the renewable powers. Microwave chemistry is a candidate of electrification of industries for the carbon neutrality on the conditions of usage of renewable energy power generation. This brief paper shows an example of “Microwave Pidgeon process” for smelting magnesium in which heating with burning fossil coals can be replaced with microwave energy for discussing how microwave technology should be developed for that purpose from both the academic and industrial sides.

In this work, we propose a 1T1R ReRAM CiM architecture for Hyperdimensional Computing (HDC). The number of Source Lines and Bit Lines is reduced by introducing memory cells that are connected in series, which is especially advantageous when using a 3D implementation. The results of CiM operations contain errors, but HDC is robust against them, so that even if the XNOR operation has an error of 25%, the inference accuracy remains above 90%.

This paper introduces a wireless-powered relay transceiver designed to extend 5G millimeter-wave coverage. It employs an on-chip butler matrix, enabling beam control-free operation. The prototype includes PCB array antennas and on-chip butler matrix and rectifiers manufactured using a Si CMOS 65nm process. The relay transceiver performs effectively in beam angles from -45° to 45°. In the 24 GHz wireless power transmission (WPT) mode, it generates 0.12 mW with 0dBm total input power, boasting an RF-DC conversion efficiency of 12.2 %. It also demonstrates communication performance at 28 GHz in both RX and TX modes with a 100 MHz bandwidth and 64QAM modulation.

Numerous meteorological disasters recur almost annually. One of the most effective means to observe these phenomena causing such disasters is meteorological radar. A group comprising Toshiba, the National Institute of Information and Communications Technology (NICT), and Osaka University has developed an X-band phased array radar, improving observation time from the conventional 10-minute duration to just 30 seconds by using phased array technology. The initial radar was installed at Osaka University in May 2012, and was recently replaced by a dual-polarization one. Phased array radar has demonstrated superior temporal and spatial resolution compared to conventional radars and has shown equivalent accuracy in observing variables such as rain rate. Future research is expected to illuminate the advantages and limitations of dual-polarization phased array radar networks, fostering their widespread adoption not only in Japan but also globally.

Nonradiative dielectric waveguide is a transmission medium for millimeter-wave integrated circuits, invented in Japan. This transmission line is characterized by low transmission loss and non-radiating nature in bends and discontinuities. It has been actively researched from 1980 to 2000, primarily at Tohoku University. This paper explains the fundamental characteristics, including passive and active circuits, and provides an overview of millimeter-wave systems such as gigabit-class ultra-high-speed data transmission applications and various radar applications. Furthermore, the performance in the THz frequency band, where future applications are anticipated, is also discussed.

Radiation-induced temporal errors become a significant issue for circuit reliability. We measured the pulse widths of radiation-induced single event transients (SETs) from pMOSFETs and nMOSFETs separately. Test results show that heavy-ion induced SET rates of nMOSFETs were twice as high as those of pMOSFETs and that neutron-induced SETs occurred only in nMOSFETs. It was confirmed that the SET distribution from inverter chains can be estimated using the SET distribution from pMOSFETs and nMOSFETs by considering the difference in load capacitance of the measurement circuits.

Integrating RGB and event sensors improves object detection accuracy, especially during the night, due to the high-dynamic range of event camera. However, introducing an event sensor leads to an increase in computational resources, which makes the implementation of RGB-event fusion multi-modal AI to CiM difficult. To tackle this issue, this paper proposes RGB-Event fusion Multi-modal analog Computation-in-Memory (CiM), called REM-CiM, for multi-modal edge object detection AI. In REM-CiM, two proposals about multi-modal AI algorithms and circuit implementation are co-designed. First, Memory capacity-Efficient Attentional Feature Pyramid Network (MEA-FPN), the model architecture for RGB-event fusion analog CiM, is proposed for parameter-efficient RGB-event fusion. Convolution-less bi-directional calibration (C-BDC) in MEA-FPN. extract important features of each modality with attention modules, while reducing the number of weight parameters by removing large convolutional operations from conventional BDC. Proposed MEA-FPN w/ C-BDC achieves a 76% reduction of parameters while maintaining mean Average Precision (mAP) degradation to <2.3% during both day and night, compared with Attentional FPN fusion (A-FPN), a conventional BDC-adopted FPN fusion. Second, the low-bit quantization with clipping (LQC) is proposed to reduce area/energy. Proposed REM-CiM with MEA-FPN and LQC achieves almost the same memory cells, 21% less ADC area, 24% less ADC energy and 0.7% higher mAP than conventional FPN fusion CiM without LQC.

In this work, fluctuation patterns of ReRAM current are classified automatically by proposed fluctuation pattern classifier (FPC). FPC is trained with artificially created dataset to overcome the difficulties of measured current signals, including the annotation cost and imbalanced data amount. Using FPC, fluctuation occurrence under different write conditions is analyzed for both HRS and LRS current. Based on the measurement and classification results, physical models of fluctuations are established.

This paper describes a programmable differential bandgap reference (PD-BGR) for ultra-low-power IoT (Internet-of-Things) edge node devices. The PD-BGR consists of a current generator (CG) and differential voltage generator (DVG). The CG is based on a bandgap reference (BGR) and generates an operating current and a voltage, while the DVG generates another voltage from the current. A differential voltage reference can be obtained by taking the voltage difference from the voltages. The PD-BGR can produce a programmable differential output voltage by changing the multipliers of MOSFETs in a differential pair and resistance with digital codes. Simulation results showed that the proposed PD-BGR can generate 25- to 200-mV reference voltages with a 25-mV step within a ±0.7% temperature inaccuracy in a temperature range from -20 to 100°C. A Monte Carlo simulation showed that the coefficient of the variation in the reference was within 1.1%. Measurement results demonstrated that our prototype chips can generate stable programmable differential output voltages, almost the same results as those of the simulation. The average power consumption was only 88.4 nW, with a voltage error of -4/+3 mV with 5 samples.

Extremely low-voltage charge pump (ELV-CP) and its dedicated multi-stage driver (MS-DRV) for sub-60-mV thermoelectric energy harvesting are proposed. The proposed MS-DRV utilizes the output voltages of each ELV-CP to efficiently boost the control clock signals. The boosted clock signals are used as switching signals for each ELV-CP and MS-DRV to turn switch transistors on and off. Moreover, reset transistors are added to the MS-DRV to ensure an adequate non-overlapping period between switching signals. Measurement results demonstrated that the proposed MS-DRV can generate boosted clock signals of 350 mV from input voltage of 60 mV. The ELV-CP can boost the input voltage of 100 mV with 10.7% peak efficiency. The proposed ELV-CP and MS-DRV can boost the low input voltage of 56 mV.

This paper introduces a computer-aided low-power design method for tapered buffers that address given load capacitances, output transition times, and source impedances. Cross-voltage-domain tapered buffers involving a low-voltage domain in the frontier stages and a high-voltage domain in the posterior stages are further discussed which breaks the trade-off between the energy dissipation and the driving capability in conventional designs. As an essential circuit block, a dedicated analytical model for the level-shifter is proposed. The energy-optimized tapered buffer design is verified for different source and load conditions in a 180-nm CMOS process. The single-V_DD buffer model achieves an average inaccuracy of 8.65% on the transition loss compared with Spice simulation results. Cross-voltage tapered buffers can be optimized to further remarkably reduce the energy consumption. The study finds wide applications in energy-efficient switching-mode analog applications.

There has been a growing interest in the application of radar technology to the monitoring of humans and animals and their positions, motions, activities, and vital signs. Radar can be used, for example, to remotely measure vital signs such as respiration and heartbeat without contact. Radar-based human sensing is expected to be adopted in a variety of fields, such as medicine, healthcare, and entertainment, but what can be realized by radar-based animal sensing? This paper reviews the latest research trends in the noncontact sensing of animals using radar systems. We also present examples of our past radar experiments for the respiratory measurement of monkeys and the heartbeat measurement of chimpanzees. The trends in this field are reviewed in terms of the target animal species, type of vital sign, and radar type and selection of frequencies.

GaN solid state power amplifiers (SSPA) for wireless power transfer and microwave heating have been reviewed. For wireless power transfer, 9W output power with 79% power added efficiency at 5.8GHz has been achieved. For microwave heating, 450W output power with 70% drain efficiency at 2.45GHz has been achieved. Microwave power concentration and uniform microwave heating by phase control of multiple SSPAs are demonstrated.

This paper presents a comprehensive design approach to load-independent radio frequency (RF) power amplifiers. We project the zero-voltage-switching (ZVS) and zero-voltage-derivative-switching (ZVDS) load impedances onto a Smith chart, and find that their loci exhibit geodesic arcs. We exploit a two-port reactive network to convert the geodesic locus into another geodesic. This is named geodesic-to-geodesic (G2G) impedance conversion, and the power amplifier that employs G2G conversion is called class-G2G amplifier. We comprehensively explore the possible circuit topologies, and find that there are twenty G2G networks to create class-G2G amplifiers. We also find out that the class-G2G amplifier behaves like a transformer or a gyrator converting from dc to RF. The G2G design theory is verified via a circuit simulation. We also verified the theory through an experiment employing a prototype 100W amplifier at 6.78 MHz. We conclude that the presented design approach is quite comprehensive and useful for the future development of high-efficiency RF power amplifiers.

This study introduces a novel single-diode rectenna, enhancing the rf-dc conversion efficiency using harmonic control of the antenna impedance. We employ source-pull simulations encompassing the fundamental frequency and the harmonics to achieve a highly efficient rectenna. The results of the source-pull simulations delineate the sourceimpedance ranges required for enhanced efficiency at each harmonic. Based on the source-pull simulation results, we designed two inverted-F antenna with input impedances within and without these identified source impedance ranges. Experimental results show that the proposed rectenna has a maximum rf-dc conversion efficiency of 75.9% at the fundamental frequency of 920 MHz, an input power of 10.8 dBm, and a load resistance of 1 kΩ, which is higher than that of the comparative rectenna without harmonic control of the antenna impedance. This study demonstrates that the proposed rectenna achieves high efficiency through the direct connection of the antenna and the single diode, along with harmonic control of the antenna impedance.

We propose microwave heating via electromagnetic coupling using zeroth-order resonators (ZORs) to extend the uniform heating area. ZORs can generate resonant modes with a wavenumber of 0, which corresponds to an infinite guide wavelength. Under this condition, uniform heating is expected because the resulting standing waves would not have nodes or antinodes. In the design proposed in this paper, two ZORs fabricated on dielectric substrates are arranged to face each other for electromagnetic coupling, and a sample placed between the resonators is heated. A single ZOR was investigated using a 3D electromagnetic simulator, and the resonant frequency and electric field distribution of the simulated ZOR were confirmed to be in good agreement with those of the fabricated ZOR. Simulations of two ZORs facing each other were then conducted to evaluate the performance of the proposed system as a heating apparatus. It was found that a resonator spacing of 25mm is suitable for uniform heating. Heating simulations of SiC and Al₂O₃ sheets were performed with the obtained structure. The heating uniformity was evaluated by the width L_50% over which the power loss distribution exceeds half the maximum value. This evaluation index was equal to 0.397λ₀ for SiC and 0.409λ₀ for Al₂O₃, both of which exceed λ₀/4, the distance between a neighboring node and antinode of a standing wave, where λ₀ is the free-space wavelength. Therefore, the proposed heating apparatus is effective for uniform microwave heating. Because of the different electrical parameters of the heated materials, SiC can be easily heated, whereas Al₂O₃ heats little. Finally, heating experiments were performed on each of these materials. Good uniformity in temperature was obtained for both SiC and Al₂O₃ sheets.

The load-independent zero-voltage switching class-E inverter has garnered considerable interest as an essential component in wireless power transfer systems. This inverter achieves high efficiency across a broad spectrum of load conditions by incorporating a load adjustment circuit (LAC) subsequent to the resonant filter. Nevertheless, the presence of the LAC influences the output impedance of the inverter, thereby inducing a divergence between the targeted and observed output power, even in ideal lossless simulations. Consequently, iterative adjustments to component values are required via an LC element implementation. We introduce a novel design methodology that incorporates an external quality factor on the side of the resonant filter, inclusive of the LAC. Thus, the optimized circuit achieves the intended output power without necessitating alterations in component values.

This paper proposes a novel configuration for a wideband single-carrier transmitter using a sub-terahertz frequency. For wideband single-carrier transmission over a bandwidth of several gigahertz, the frequency response non-flatness derived from transmitter components in an operating band seriously deteriorates the transmission quality due to inter-symbol interference. A promising approach to address this problem is equalizing the frequency response non-flatness at the transmitter. The proposed novel configuration has a feedback route for calculating the inverse frequency response and multiplying it with a transmission signal spectrum in the frequency domain. Moreover, we verify that employing the proposed transmitter configuration simplifies the receiver configuration by lowering the calculation complexity to minimize the inter-symbol interference to meet the signal-to-interference-and-noise ratio requirements. To confirm the feasibility of the proposed configuration, the transmission quality obtained using the proposed configuration is measured and evaluated. Experimental results confirm that the proposed configuration improves the error vector magnitude value to over 5 dB for a 10 Gbaud transmission and the transmission data rate of 25 Gbps.

Considering the non-convexity of hybrid precoding and the hardware constraints of practical systems, a hybrid precoding architecture, which combines limited-resolution overlapped phase shifter networks with lens array, is investigated. The analogy part is a beam selection network composed of overlapped low-resolution phase shifter networks. In particular, in the proposed hybrid precoding algorithm, the analog precoding improves array gain by utilizing the quantization beam alignment method, whereas the digital precoding schemes multiplexing gain by adopting a Wiener Filter precoding scheme with a minimum mean square error criterion. Finally, in the sparse scattering millimeter-wave channel for the uniform linear array, the proposed method is compared with the existing scheme by computer simulation by using the ideal channel state information and the non-ideal channel state information. It is concluded that the proposed scheme performs better in low signal-to-noise regions and can achieve a good compromise between system performance and hardware complexity.

In this paper, a precise design method of high-order bandpass filters (BPFs) with complicated coupling topologies is proposed, and is demonstrated through the design of an 11-pole BPF using TM₀₁₀ mode dielectric resonators (DRs). A novel Z-shaped coupling structure is proposed which avoids the mixed use of TM₀₁₀ and TM_01δ modes and enables the tuning and assembling of the filter much easier. The coupling topology of the BPF includes three cascade triplets (CTs) of DRs, and both the capacitive and inductive couplings in the CTs are designed independently tunable, which produce consequently three controllable transmission zeros on both sides of the passband of filter. A procedure of mapping the coupling matrix of BPF to its physical dimensions is developed, and an iterative optimization of these physical dimensions is implemented to achieve best performance. The design of the 11-pole BPF is shown highly precise by the excellent agreement between the electromagnetic simulated response of the filter and the desired target specifications.

Recent years have seen a general resurgence of interest in analog signal processing and computing architectures. In addition, extensive theoretical and experimental literature on chaos and analog chaotic oscillators exists. One peculiarity of these circuits is the ability to generate, despite their structural simplicity, complex spatiotemporal patterns when several of them are brought towards synchronization via coupling mechanisms. While by no means a systematic survey, this paper provides a personal perspective on this area. After briefly covering design aspects and the synchronization phenomena that can arise, a selection of results exemplifying potential applications is presented, including in robot control, distributed sensing, reservoir computing, and data augmentation. Despite their interesting properties, the industrial applications of these circuits remain largely to be realized, seemingly due to a variety of technical and organizational factors including a paucity of design and optimization techniques. Some reflections are given regarding this situation, the potential relevance to discontinuous innovation in analog circuit design of chaotic oscillators taken both individually and as synchronized networks, and the factors holding back the transition to higher levels of technology readiness.

In this paper, we delve into wireless communications in the 300 GHz band, focusing in particular on the continuous bandwidth of 44 GHz from 252 GHz to 296 GHz, positioning it as a pivotal element in the trajectory toward 6G communications. While terahertz communications have traditionally been praised for the high speeds they can achieve using their wide bandwidth, it will also be shown that they have the potential to achieve high efficiency and support numerous simultaneous connectivity. To this end, new performance metrics, EIRP_λ and EINF_λ, are introduced as important benchmarks for transmitter and receiver performance, and their consistency is discussed. We then show that, assuming conventional bandwidth and communication capacity, the communication distance is independent of carrier frequency. Located between radio waves and light in the electromagnetic spectrum, terahertz waves promise to usher in a new era of wireless communications characterized not only by high-speed communication, but also by convenience and efficiency. Improvements in antenna gain, beam focusing, and precise beam steering are essential to its realization. As these technologies advance, the paradigm of wireless communications is expected to be transformed. The synergistic effects of antenna gain enhancement, beam focusing, and steering will not only push high-speed communications to unprecedented levels, but also lay the foundation for a wireless communications landscape defined by unparalleled convenience and efficiency. This paper will discuss a future in which terahertz communications will reshape the contours of wireless communications as the realization of such technological breakthroughs draws near.

We develop new 3D full vectorial finite element bidirectional beam propagation method (3DFV-BiBPM) in order to handle the nonradiative dielectric waveguide (NRD guide) components that have arbitrary cross sectional profiles. The BiBPM is one of the transfer-matrix-based methods where only transverse cross sections have to be discretized using the finite difference or the finite element scheme, and it can treat backward and multiple reflections as opposed to the standard BPM. An NRD guide with air-gap and a filter with a sapphire resonator are numerically analyze considering dielectric losses to investigate the validity of our approach.

In this paper, we propose the transient analysis technique to analyze the multilayered dispersive media by using a combination of fast inversion Laplace transform (FILT) and the continued fraction expanded methods. Numerical results are given by the reflection response, inside-time response waveforms, and electric field distributions of the reflection component. Further, we verify the calculation accuracy of FILT method for the two types using a convergence test.

Numerical dispersion property is investigated for the finite-difference time-domain (FDTD) method based on the iterated Crank-Nicolson (ICN) scheme. The numerical dispersion relation is newly derived from the amplification matrix and its property is discussed with attention to the eigenvalue of the matrix. It is shown that the ICN-FDTD method is conditionally stable but slightly dissipative.

This paper introduces a computational approach for transient analysis of extensive scattering problems. This novel method is based on the combination of physical optics (PO) and the fast inverse Laplace transform (FILT). PO is a technique for analyzing electromagnetic scattering from large-scale objects. We modify PO for application in the complex frequency domain, where the scattered fields are evaluated. The complex frequency function is efficiently transformed into the time domain using FILT. The effectiveness of this combination is demonstrated through large-scale analysis and transient response for a short pulse incidence. The accuracy is investigated and validated by comparison with reference solutions.

We report on a method for reconstructing the spectrum of incident light from a single image captured by a snapshot multispectral camera. The camera has a dielectric multilayer multispectral filter array (MSFA) integrated onto a CMOS image sensor. Sparse estimation algorithm was applied to reconstruct the spectrum. Using Gaussian functions with various bandwidths and central wavelengths as the bases matrix, the algorithm has been shown to be highly accurate for estimating the spectra of both narrowband monochromatic and broadband fluorescent light emitting diodes (LEDs), regardless of the wavelength band.