This paper presents a theoretical analysis and experimental confirmation of a tunable ring resonator that can independently change its resonant frequency and bandwidth. The tunable ring resonator comprises a ring resonator, three tunable capacitors, and switches. The resonant frequency changes according to the capacitance of tunable capacitors, and the bandwidth varies by changing the state of the switches. The unique feature of the resonator is that the resonant frequency remains steady when the bandwidth is changed. The fundamental characteristics are shown based on linear circuit simulation and electromagnetic simulation results. The resonator is fabricated using GaAs FET single-pole single-throw switches. The fabricated resonator changes the resonant frequency from 1.5 GHz to 2.0 GHz and the fractional bandwidth from 5% to 30%.

This paper looks into the underlying RF energy harvesting issues at low input ambient power levels below 0 dBm where efficiency degradation is severe. The proposed design aims to improve the rectenna sensitivity, efficiency, and output DC power. In the same manner, we are using a straightforward and compact size rectenna design. The receiving antenna is a coplanar waveguide (CPW) slot monopole antenna with harmonic suppression property and a peak measured gain of 3 dBi. Also, an improved antenna radiation characteristics, e.g radiation pattern and gain covering the desired operating band (ISM 2.45 GHz), is observed. The rectifier is a voltage doubler circuit based on microstrip (MS) structure. Two architectures of rectenna were carefully designed, fabricated and tested. The first layout; antenna, and rectifier were fabricated separately and then connected using a connector. The peak efficiency (40% at -5 dBm) achieved is lower than expected. To improve the efficiency, a high compactness and simple integration between antenna and rectifier are achieved by using a smooth CPW-MS transition. This design shows improved conversion efficiency measurement results which typically agree with the simulation results. The measured peak conversion efficiency is 72% at RF power level of -7 dBm and a load resistance of 2 kΩ.

The aim of this research is to support real-time drawingin talking by using multimodal user interface technologies. In this situation, if talking and drawing are considered as commands by mistake during presentation, it will disturb users' natural talking and drawing. To prevent this problem, we introduce two modes of a command mode and a free mode, and explore smooth mode switching techniques that does not interfere with users' natural talking and drawing. We evaluate four techniques. Among them, a technique that specifies the command mode after actions using a pen gesture was the most effective. In this technique, users could quickly draw diagrams, and specifying mode switching didn't interfere with users' natural talk.

This paper reports a 24GHz ISM band radar module for pedestrian detection in crosswalks. The radar module is composed of an RF transceiver board, a baseband board, and a microcontroller unit board. The radar signal is a sawtooth frequency-modulated continuous-wave signal with a center frequency of 24.15GHz, a bandwidth of 200MHz, a chirp length of 80µs, and a pulse repetition interval of 320µs. The radar module can detect a pedestrian on a crosswalk with a width of 4m and a length of 14m. The radar outputs the range, angle, and speed of the detected pedestrians every 50ms by radar signal processing and consumes 7.57W from 12V power supply. The size of the radar module is 110×70mm².

This paper presents an ultra-low-power class-AB bulk-driven operational transconductance amplifier operating in the subthreshold region. Employing the partial positive feedback in current mirrors, the effective transconductance and output voltage swing are enhanced considerably without additional power consumption and layout area. Both traditional and proposed OTAs are designed and simulated for a 180 nm CMOS process. They dissipate an ultra low power of 192 nW. The proposed OTA features not only a DC gain enhancement of 14 dB but also a slew rate improvement of 200%. In addition, the improved gain leads to a 5.3 times wider unity-gain bandwidth than that of the traditional OTA.

Break arcs are generated in a 48VDC resistive circuit. Circuit current I₀ when electrical contacts are closed is changed from 50A to 300A. The break arcs are observed by a high-speed camera with appropriate settings of exposure from horizontal direction. Length of the break arcs L is measured from images of the break arcs. Time evolutions of the length L and gap voltage V_g are investigated. The following results are obtained. By appropriate settings of the high-speed camera, the time evolution of the length L is obtained from just after ignition to before arc extinction. Tendency of increase of the length L is similar to that of increase of the voltage V_g for each current I₀.