Hiroyuki Ito

Hiroyuki Ito
Tokyo Institute of Technology | TITech · Institute of Innovative Research

About

256
Publications
16,702
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2,473
Citations

Publications

Publications (256)
Article
Transistor-based chaotic oscillators are known to realize highly diverse dynamics despite having elementary circuit topologies. This work investigates, numerically and experimentally using a ring network, a recently-introduced dual-transistor circuit that generates neural-like spike trains. A multitude of non-trivial effects are observed as a funct...
Preprint
Signal flow graph (SFG) representation of small- signal responses of nonlinear microwave circuits around a large-signal operating point is developed using the X-parameters. It is shown that, unlike the SFGs for linear circuits, negative-frequency nodes need to be included explicitly. The development elucidates the circuit-operational meaning of the...
Preprint
Signal flow graph (SFG) representation of small- signal responses of nonlinear microwave circuits around a large-signal operating point is developed using the X-parameters. It is shown that, unlike the SFGs for linear circuits, negative-frequency nodes need to be included explicitly. The development elucidates the circuit-operational meaning of the...
Article
A recently-introduced autonomous electronic chaos generator which has an elementary circuit topology not intentionally derived from canonical oscillators is considered. It comprises a bipolar junction transistor, a resistor, two inductors and one capacitor. Though its notable generative potential has been remarked, its functioning principles have t...
Article
An electronic chaos generator involving cross-coupled inverter rings with lengths equal to the smallest odd prime numbers is considered, and a spatiotemporally-varying control parameter, hypothetically corresponding to a physical variable to be sensed, is introduced akin to a baseband signal. It is shown that, owing to the fine-grained structure of...
Article
Cow behavior monitoring is critical for understanding the current state of cow welfare and developing an effective planning strategy for pasture management, such as early detection of disease and estrus. One of the most powerful and cost-effective methods is a neural-network-based monitoring system that analyzes time series data from inertial senso...
Article
Full-text available
We have developed a broadband and high-precision terahertz (THz) frequency counter based on a semiconductor-superlattice harmonic mixer (SLHM). Comparison of two THz frequencies determined using two independent counters and direct measurement of frequency-stabilized THz-quantum cascade lasers by a single counter showed a measurement uncertainty of...
Article
Full-text available
Ti/Au multi-layered micro-cantilevers with complex three-dimensional structures used as micro-components in micro-electromechanical systems (MEMS) sensors were prepared by lithography and electrodeposition, and the effective Young’s modulus was evaluated by the resonance frequency method and finite element method simulation. Effects of the constrai...
Article
Abstract An injection‐locked divider oscillator that converts a 6‐GHz‐band signal into a 3‐GHz‐band signal was developed. The injection‐locked divider oscillator was specifically designed to lock on the clock transition frequency of 87Rb of 6.824 GHz to provide a laser modulation signal at 3.417 GHz for an on‐chip coherent population trapping atomi...
Article
Full-text available
Strengthening of electrodeposited Au-based materials is achieved by co-electrodeposition with TiO2 nanoparticles dispersed in a sulfide-based gold electrolyte. TiO2 content in the composite film is adjusted by concentration of the TiO2 in the gold electrolyte. Effects of the TiO2 content on surface morphology, crystalline structure and microstructu...
Article
Sample geometry effects on mechanical strengths of gold micro-cantilevers are evaluated by a micro-bending test. Six micro-cantilevers with the same length of 50 μm are prepared, and the width and the thickness are varied to examine individual effects on the yield stress. The yield stress increases from 428 to 519 MPa when the thickness decreases f...
Article
Full-text available
Emerging applications across environmental, biomedical, and structural monitoring require the measurement of physical variables over extended regions. Because addressing many sensors individually can result in impractical bandwidth and power requirements, there is a need for distributed sensing approaches wherein readouts are obtained directly at t...
Article
Full-text available
Natural and engineered networks, such as interconnected neurons, ecological and social networks, coupled oscillators, wireless terminals and power loads, are characterized by an appreciable heterogeneity in the local connectivity around each node. For instance, in both elementary structures such as stars and complex graphs having scale-free topolog...
Article
Full-text available
Hierarchical structures of 20 nm grains embedded with twins are realized in electrodeposited Au–Cu alloys. The electrodeposition method allows refinement of the average grain size to 20 nm order, and the alloying stabilizes the nanoscale grain structure. Au–Cu alloys are face-centered cubic (FCC) metals with low stacking fault energy that favors fo...
Article
This paper reports Cu-alloying effects on the structure stability of gold-based micro-cantilevers evaluated by long-term vibration test for applications as movable micro-components in MEMS devices. Au–Cu alloy micro-cantilevers are fabricated by lithography and Au–Cu alloy electrodeposition. The composition is affected by the applied current densit...
Article
The generation of chaotic signals is relevant to a multitude of applications across telecommunications, random number generation, control and the realization of distributed sensing systems; in addition, networks of coupled chaotic oscillators replicate diverse emergent phenomena occurring in considerably larger biological neural systems. However, t...
Article
This study reports mechanical property enhancement observed in micro-cantilevers composed of Au/Ti bi-layered structure evaluated by micro-bending test. A layer of gold film is electrodeposited on a cold-rolled titanium plate using a sulfite-based gold electrolyte. Specimens used in the micro-bending test are micro-cantilevers fabricated by focus i...
Article
Long-term structure stability of micro-cantilevers employing the Ti/Au layered design is evaluated by vibration test to demonstrate the advantage toward design of MEMS micro-components. Length of the micro-cantilevers is ranged from 200 to 1000 μm, and the width is at 20 μm. Two types of the Ti/Au layered design are evaluated in this study. One is...
Article
We describe microgravity generation and the resolution evaluation results of a sub-1-mG microelectromechanical system (MEMS) accelerometer (1 G = 9.8 m/s²). To realize input acceleration below 1 mG, we show the principle of generating microgravity acceleration by adjusting the tilt angle. The change in acceleration induced by a tilting board is qua...
Article
We developed a microwave oscillator and a micro electromechanical systems-based rubidium cell for the miniaturization of atomic clocks. A thin-film bulk acoustic resonator (FBAR) having a resonant frequency of the fundamental mode in the 3.5 GHz band was employed instead of a crystal resonator. It delivers a clock transition frequency of Rb atoms o...
Article
DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) is a future Japanese space gravitational-wave antenna. The most important objective of DECIGO, among various sciences to be aimed at, is to detect gravitational waves coming from the inflation of the universe. DECIGO consists of four clusters of spacecraft, and each cluster consists...
Article
A high-resolution capacitive-sensor interface for sub-1mG MEMS accelerometers is presented herein. A time-domain capacitive-sensor interface based on a relaxation oscillator with noise reduction is proposed to achieve a high resolution. A prototype interface is fabricated using a 0.18-µm CMOS process. The prototype is linked with a sub-1mG MEMS acc...
Article
Full-text available
DECIGO (DECi-hertz Interferometer Gravitational wave Observatory) is the planned Japanese space gravitational wave antenna, aiming to detect gravitational waves from astrophysically and cosmologically significant sources mainly between 0.1 Hz and 10 Hz and thus to open a new window for gravitational wave astronomy and for the universe. DECIGO will...
Article
This letter proposes an ultralow-power 5.96-GHz phase-locked loop (PLL) with a current-reuse VCO under low supply voltage of 0.5 V. While the current-reuse VCO can achieve lower power consumption, it has the drawback of amplitude-imbalance of differential outputs due to its asymmetric structure. Proposed amplitude regulation technique utilizes only...
Article
This paper proposes a cascaded fractional-N phase-locked loop (PLL) based on a high-frequency piezoelectric resonator (PZR). Sub-ppb-order frequency resolution is achieved by a channel adjustment technique. Besides its small form factor, a high-Q PZR at gigahertz frequencies realizes a very low phase-noise synthesizer for RF applications. However,...
Article
We demonstrate a terahertz (THz) frequency reference transfer with high accuracy and stability. Phase information of the THz frequency standard is coherently duplicated onto an optical carrier as an intermediary for exploiting low-loss optical-fiber technology. The transferred information on the optical carrier is retrieved into the THz domain with...
Conference Paper
NICT atomic fountains CsF1 and CsF2 and their frequency reference based on a cryogenic sapphire oscillator (CSO) are being upgraded with aiming at operations at the low 10 −16 level. The CSO was upgraded from “dewar-type” to “cryocooler-type” and a long-term continuous operation became available without routine liquid helium transfer. A rapid adiab...
Conference Paper
NICT has commenced development of an accurate and stable frequency standard for THz frequency band. We succeeded in phase-locking a single-mode 3THz quantum cascade laser (THz-QCL) to a THz reference. Using the phase-locked THz-QCL and a hot electron bolometer mixer, a THz wave generated by photomixing was evaluated. The result showed that the phas...
Conference Paper
NICT carried out the first calibration of the GPS link between Koganei and Kobe by using GPS, TWSTFT and Clock Transport (CT). We presented the result of the calibration in EFTF 2015. The differential correction of GPS link by GPS, TWSTFT and CT were 102.5, 102.1 and 104.9 ns respectively. The CT result showed a discrepancy of 2 ns. By applying the...
Article
This study introduces a 5.8 GHz RF-powered transceiver that includes a transmitter using an IF-based quadrature backscattering (IFQB) technique. The IFQB transmitter can produce a quadrature modulated signal without active RF circuits, such as PLL, local generation, and local distribution circuits. Thus, the IFQB technique can significantly reduce...
Article
This paper presents a low-power RF-CMOS-transceiver IC-module with small antennas on a printed circuit board (PCB). Active mixer-first architecture is employed on a receiver for achieving both acceptable sensitivity and lower power. We also show strategies for lowering power consumption of the transmitter and the phase locked loop (PLL): a high-gai...
Conference Paper
National Institute of Information and Communications Technology (NICT) in Japan has responsibilities to generate and to maintain Japan Standard Time (JST), and to disseminate the JST throughout the country. For these purposes, NICT is operating multiple sets of Cesium frequency standard systems and Hydrogen maser systems to generate stable and reli...
Article
In this paper, we present a voltage-controlled oscillator (VCO), which achieves highly linear frequency tuning under a low supply voltage of 0.5 V. To obtain the linear frequency tuning of a VCO, the high linearity of the threshold voltage of a varactor versus its back-gate voltage is utilized. This enables the linear capacitance tuning of the vara...
Article
In this study, we present an RF energy harvesting power management unit (PMU) for battery-less wireless sensor devices (WSDs). The proposed PMU realizes a duty-cycled operation that is divided into the energy charging time and discharging time. The proposed PMU detects two types of timing, thus, the appropriate timing for the activation can be reco...