Koji Sonoda

Wearable Photoplethysmographic Sensor System with PSoC Microcontroller

This paper presents a wearable PPG (photoplethysmographic) sensor system with a PSoC micro controller unit (Cypress Semiconductor Corp., USA). We have developed a pulse wave monitoring system on earlobe, which has a PIC micro controller and analog circuits. However, analog sensors need some discrete parts, resulting in difficulty in reducing the system size. The PSoC micro controller includes a CPU, analog and digital blocks to configure mixed-signal circuits, and an internal oscillator in a single IC package. Therefore, PSoC allows designers to reduce the number of external discrete devices and the system size. The novel system consists of a photo interrupter, the PSoC, and the Bluetooth module, which are on PCBs (Printed Circuit Board) of 18, 13, and 10 mm in diameter, respectively. The photo interrupter detects the pulse wave due to the change in volume of blood vessels. The PSoC includes an analog filter, amplifiers, and digital circuits to calculate HR (heart rate) from the pulse wave of human body. The system was able to detect the pulse wave and transmit the HR data to a PC wirelessly. The power supply voltage is 3.3 V, and the total current consumption is about 51 mA. In comparison with the previous work, the area of discrete RCL (resistor, capacitor, and inductor) devices is reduced from 1230 mm2 to 466 mm2, and the number of such devices is reduced from 26 to 6.

Ultra Low Power ASIC for R-R Interval Extraction on Wearable Health Monitoring System

This study shows a development of an ultra low power application specific integrated circuit (ASIC) that extracts R-R intervals from electrocardiogram (ECG) data on a human monitoring system. The continuous human monitoring is substantially useful to realize a high quality of life human society especially for elderly people who live alone. However, it is difficult to realize such a system that can operate longtime without maintenances because of its battery limitation. A micro controller unit (MCU) has to be continuously operated to samples the ECG waveform, which is known as one of a power hungry device in the system. In order to reduce the power consumption of the MCU, an ultra low power ASIC for ECG feature extraction is developed for replace a role of MCU to extract the R-R intervals of ECG feature values.

Development of Electret Energy Harvester with Micro Spacer

This paper describes a development of MEMS (Micro Electromechanical Systems) -based electrostatic energy harvester for scavenging energy from ambient vibration. Generally, power output of electret harvester is increased with the narrower air-gap between an electret and an opposite electrode. However, electrostatic attraction force between the electret and the opposite electrode is also increased. Hence the gap control is crucial to avoid the pull-in. We measured the displacement of the vibrating mass moved by electrostatic force. As a result, the electric discharge between the Si grid and the base electrode (BE) is occurred when the BE was supplied over 110 V. The vibrating mass is pulled-in at 150 V if the discharge does not occur at the potential. Therefore we proposed and design the electrostatic energy harvester using the micro spacer to prevent the pull-in situation. The size of the spacer is 86 × 86 × 27 μm3 to prevent the mass fixed by the friction.

Crystal orientation dependent etching in RIE and its application

We found that an appropriate mixture of SF6, C4F8 and O2 gases in a standard Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) apparatus achieves crystal orientation dependent etching. The etched shapes after the RIE of silicon wafers with (100), (110), and (111) surface orientation are investigated by the masks with circular openings and isolated pattern. The results of the etching process show (111) terraces; i.e., the etching rate of the (111) plane is slower than that of other planes similar to the alkaline-based wet etching. The etching rate in the horizontal direction in each crystallographic orientation is examined by etching a wagon wheel pattern. We also demonstrate an application, Through-Silicon Via (TSV) holes with horn-shaped openings using this process.

Design Optimization of Electromagnetic MEMS Energy Harvester with Serpentine Coil

This paper presents a design optimization of a novel electromagnetic MEMS energy harvester by using a fine patterned NdFeB array with a serpentine shaped coil for gathering electromotive force. The serpentine coil can be easy to be fabricated in comparison with a spiral coil that fabricated in the previous work. The magnetic flux density is calculated by FEM analysis. The various line-and-space parameters of the magnet and the coil are investigated for the optimization of the output power. The electromotive force and the output power are calculated by a theoretical equation. As a result of optimization, the electromotive force of 31.3 mV and the output power of 0.722 μW are obtained when an applied vibration amplitude is ±200 um at 595 Hz with magnet line and space of 70 μm.

SPICE Modeling of Piezoelectric Energy Harvesting Device Utilizing Stress Influence

This paper presents a SPICE modeling of piezoelectric energy harvesting (PEH) device. We developed a wireless sensor system with the PEH device as an application. The PEH device is composed of a stainless cantilever, which has a piezoelectric film on the both side surface. The PEH device oscillates at resonance frequency when the tip of the cantilever is plucked. In SPICE simulator, an equation of motion of the cantilever is described to express a mass-spring-damper system by behavioral source. The stress of the piezoelectric film is computed by theoretical calculation and FEM analysis. Then, the stress, the piezoelectric coefficient d31, and the area of the film surface formulate the electrical charge. The output voltage is given by the charge varying and an inherent capacitance. The comparison between an analysis and an experiment is represented. The output power of theoretical calculation and measurement are 310 μJ and 920 μJ respectively has occurred by plucking once. We also developed a prototype system of WSN node utilizing the PEH device. The system transmits the temperature data a few times by plucking once.

Daisy-chain Shape Wearable Health Monitoring System by Using Fuzzy Logic Heart-Rate Extraction

Continuous human monitoring is substantially useful to realize a high QoL (quality of life) society. In the previous work, we fabricated a prototype system for monitoring an electrocardiograph (ECG), heart rate (HR), 3 axes human body acceleration, temperature for human body and human circumstances, simultaneously. These data are transmitted to the host PC and used for analyzing the human activities and conditions such as a heart rate variability (HRV). The HRV that calculated from HR is valuable for recognizing a mental or physical stress of human subjects. In this study, we demonstrate a fuzzy logic HR extraction algorithm on the prototype system to realize an autonomous HRV monitoring system. On-board fuzzy algorithm will reduce the communication traffic and improve an accuracy of the HR extraction. From the implementation result, the error ratio of the HR extraction is improved from 0.9 % to 0.4 %.