藤田 孝之

In this paper, a bipolar charging method for electrostatic vibratory energy harvester and its analysis result of electrostatic force are described. To improve the harvesting power, higher voltage charged electret with large capacitance change structures are extensively studied. However, the higher voltage also shows a higher electrostatic force, which prevents the device movement for harvesting and causes pull-in behavior. From the result of FEM analysis on bipolar charged electret, the electrostatic force for vertical and horizontal directions were reduced by 15% and 10% from negative only charged device, respectively.

This study addresses the design optimization of the electromagnetic energy harvester consisting of the sputtered NdFeB film on a high aspect ratio corrugated Si structure and Au electroplated serpentine coil. The high-aspect-ratio Si structure has advantages that the magnetic flux density change is caused by distance change between the coil and magnet film on the fine-patterned corrugated Si, and it is easier to fabricate with high yield than previous study. We also optimized design parameters such as width and depth of the trench, coil size by using FEM analysis and theoretical calculations. Assuming the mass size of 10x10 mm(2), the trench depth of the 400 mu m, the vibration amplitude of 40 mu m (p-p) and the vibration frequency of 100 Hz, the maximum output power of 12 nW and the maximum electromotive force of 4 mV are obtained for 60 mu m and 80 mu m magnet widths, respectively.

This paper reports fabrication and evaluation of reflectance type pulse oximeter with ring-shaped photodiode. The pulse oximeter can measure a blood oxygen saturation (SpO(2)). SpO(2) is used as an index of respiratory diseases. Therefore measurements of SpO(2) prevent apnea syndrome and asthma. We have developed a system for measuring SpO(2) in daily life. A small and stably measurable sensor is required for the system. Because of realization of the sensor, LEDs are located in the center of a ring-shaped photodiode. This structure collects lights from all directions for reducing noises of body motion. In a previous study, a pulse wave sensor using the ring-shaped photodiode was fabricated, and could measure the pulse wave. In this paper, the improved sensor to measure SpO(2) is shown. Photodiodes is evaluated on current-voltage characteristics.

In this study, we report the optimization of electrode design for increasing output power of the vibration electrostatic energy harvesters. The output power depends on the capacitance change and its frequency. Without consideration for fringe effect of a parallel-plate capacitance, the narrower electrode pitch L is, the larger output power. However, under actual conditions, power output is limited by fringe effect. To consider fringe effect, the optimum electrode dimension changes due to the distance between the electret and counter electrode. By using FEM analysis with fringe effect, we find the characteristic of fringe effect at parallel-plate capacitor, and then the optimum width of counter electrode fFand electrode pitch L are obtained.

This paper shows the optimization of the structure of the electromagnetic energy harvester consisting of the sputtered NdFeB film on high aspect ratio Si trench and the Au serpentine coil. The magnetic flux density change is caused by distance change between coil and magnet film on the corrugated Si. In order to maximize the harvesting energy, the optimum parameters such as width, depth of Si trench, and coil size are investigated by FEM analysis and theoretical calculation. Assuming the trench depth of 400 μm the vibration amplitude of 400 μm_<p-p> and the frequency of 100 Hz the maximum output power of 12 nW and the maximum electromotive force of 4 mV are obtained by 60 μm and 80 μm, respectively.

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 %. © 2012 TSI Press.

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 %.

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 x 86 x 27 mu m(3) to prevent the mass fixed by the friction.

This paper presents a wearable PPG (photoplethysmographic) sensor system with a PSoC microcontroller unit (Cypress Semiconductor Corp., USA). We have developed a pulse wave monitoring system on earlobe, which has a PIC microcontroller and analog circuits. However, analog sensors need some discrete parts, resulting in difficulty in reducing the system size. The PSoC microcontroller 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 mm(2) to 466 mm(2), and the number of such devices is reduced from 26 to 6.