藤田 孝之

We studied the effects of increasing the thickness of bimorph structures containing double layers of Pb(Zr,Ti)O-3 (PZT) thin films. Thick PZT films allow high-voltage application (e.g. in terms of coercive electric field and breakdown voltage) and large generative force, which are effective in microelectromechanical systems (MEMS) applications. Improvement of the deposition conditions and electrode structures facilitates the fabrication of the thin-film PZT/PZT bimorph structure. The PZT/PZT bimorph with a total thickness of 5.8 mu m, deposited using a radio-frequency (RF) magnetron sputtering system is much thicker than conventional bimorph structures. The characteristics of the two piezoelectric layers were similar to each other and revealed good electric and ferroelectric characteristics with a remanent polarization of 20 mu C cm(-2) and a coercive electric field of 50 kV cm(-1). PZT/PZT bimorph cantilevers were fabricated in order to evaluate their characteristics for actuator applications. The residual stress of the bimorph cantilever was reduced by an annealing process. The vibration test on the fabricated bimorph cantilevers during electrical voltage application revealed a twice as large displacement as compared with a single layer actuation, and the piezoelectric coefficient value d(31) was estimated to be -61 pm V-1, which is better than the value of conventional PZT/PZT bimorph cantilevers (-13 pm V-1). It was also shown that the influence of the temperature change is much less than that in unimorph structures with similar dimensions. The evaluated results demonstrate that the PZT/PZT bimorph structures are effective as MEMS devices.

© 2015 The Institute of Electrical Engineers. We designed and evaluated low power ASIC (Application Specific Integrated Circuits) for the human activity and health monitoring systems to reduce the total power consumption. The ASIC extracts walking and running steps and holds the maximum and minimum values from raw data of acceleration sensor. To realize ultra-low power consumption, the algorithm is designed to reduce the amount of the data calculation for pedometer. Power consumption was reduced to 15% from previous prototype system by using the designed ASIC.

© 2015 The Institute of Electrical Engineers of Japan. This paper presents an electrostatic vibration energy harvester with a bipolar-charged electret for high output power and for low electrostatic force. In conventional electrostatic energy harvesters, electrets are charged by monopolar charge (mainly by negative) with a high potential for large power harvesting. We propose a bipolar charging method in order to form an electret, which not only has negative charge but also positive charge. The electrostatic energy harvester, with a size of 13×12×1.2 mm3, was fabricated and charged by a -250-V monopolar potential and by a ±250-V bipolar potential. The maximum output power of the monopolar- and bipolar-charged harvester is 3.1 μW and 9.8 μW, respectively with an applied acceleration of 7 g at 352 Hz with a 0.9-MΩ load resistance. The output power is 9 μW at 1.4 g and the maximum effectiveness against the velocity-damped resonant-generator (VDRG) limit is 2.5%. By using the bipolar-charged electret, the high output power obtained from the high charging potential was compared to a conventional harvester charged by the monopolar method. Further, using the finite element method (FEM) analysis, we determined that the electrostatic force that prevents harvesting mass movement is significantly reduced on the bipolar-charged electret. The electrostatic forces under static conditions along the vertical and horizontal directions obtained through the FEM analysis were reduced to 15% and 20%, respectively, from those of the monopolar-charged electret.

© 2015 The Institute of Electrical Engineers of Japan. This paper presents an equivalent circuit model of an electrostatic energy harvester for a SPICE circuit simulator. The output power and impedance of the proposed model are approximated by using a simplified model of a voltage-controlled capacitor. The relationship between the capacitance and the electrode position is calculated by FEM analysis by taking the fringing effect into account; this relationship is applied to a sub-circuit model for the SPICE simulator. Further, the results of this study show that the output waveform and the optimal resistance obtained using the SPICE simulator correspond with the measurement results. In addition, the operation of a harvesting system connected with a commercially available power management IC is demonstrated.

In this paper, a design improvement of combination spring that consists of linear resonator and curved beam for nonlinear vibration energy harvesting is described. The intrinsic curved beam for snap-through buckling acts as mechanical frequency converter (MFC) that applies high frequency acceleration to the linear resonator. We newly designed the parallel curved beams to reduce the force required for snap-through and maximum stress during snap-through behavior. From FEM analyses, the force and the stress are reduced from 35.4 mN to 10 mN and from 350 MPa to 200 MPa, respectively. (C) 2015 The Authors. Published by Elsevier Ltd.

For the continuous and long term healthcare monitoring of human, low power ASICs (Application Specific Integrated Circuits) are designed. The ECG (Electrocardiogram) signal is acquired and amplified by the ECG head amplifier. The analog ECG signal is converted into digital one by using the ADC (Analog to Digital Converter). The digital ASIC converts the raw ECG signal into heart rate. The characteristics extraction can reduce the total power consumption of the system. To realize low power consumption of the ASIC, an algorithm based on fuzzy logic, which is very simple and light processing, is employed. The novel system with these circuits cuts down 80 % power consumption compared with the conventional prototype system.

We developed MEMS bi-stable spring for vibration energy harvester (VEH), which consists of intrinsically curved shape spring and gravitational acceleration. By applying the gravitational acceleration, the curved beam is offset to the gravity direction. It will make more symmetrical bi-stable motion and the symmetry is improved from 3.3 to 65.4%. We proposed that the combination between curved beam and gravity acceleration for decreasing snap-through acceleration. From the analytical result, we investigate the combination can effective to use for decreasing of snap-through force. We also fabricated the prototype device by using MEMS fabrication process. The frequency response for horizontal direction and the acceleration response for vertical direction are measured. The acceleration response shows that the gravitational acceleration improves the symmetry of snap-through force.

In this study, we report an improvement of output power from an electret type vibration energy harvester. Typical crossing-area change harvester has a stripe-shaped electret and counter electrode for making the capacitance change. In order to improve space efficiency, the counter electrodes are divided and arraignment with the same pitch of the electret. We investigate that adjoining the counter electrodes, the fringing effect is decreased and the capacitance change between the electrodes is larger than the conventional design from FEM analysis. The output power of 2.5 mu W and 5.3 mu W are obtained in each kind of counter electrode with the applied acceleration of 3 G at 350 Hz, which is about 2 or 4 times as high as our previous work.

The narrowing air-gap between coil and magnet of electromagnetic energy harvester is one of the most important parameter to improve the generated power. Because of the sputtering 15 mu m thickness NdFeB/Ta multilayer film with high temperature annealing, the large curvature distortion is occurred on Si substrate. In this paper we demonstrate a compensation method for residual stress on the sputtered NdFeB magnetic film on Si wafer. By using both-side sputtering method, we reduced the residual stress, which reduces the reliability of MEMS fabrication and performance of harvesters, from 144 MPa to 9.4 MPa. The electromagnetic type energy harvester with narrow gap of 20 mu m was successfully fabricated and evaluated.

© 2015 The Institute of Electrical Engineers of Japan. This paper presents an electrostatic vibration energy harvester with a conventional monopolar-charged and a novel bipolar-charged electret. The maximum output power of the -200 V monopolar-charged and ±100 V bipolar-charged harvester were 1.1 μW and 0.9 μW, respectively with a vibration amplitude of 350 μmppat 323 Hz with a 0.8 MΩ load resistance. The bipolar-charged harvester generates higher output power than the monopolar-charged harvester with an applied acceleration from 0 g to 0.7 g, because electrostatic force of the monopolar-chaged electret along the vibration direction prevents harvesting mass movement compared to the bipolar-charged electret. Further, we analyzed a SPICE model with electrostatic force and confirmed that the characteristics were according to the experiment results.

The objective of this paper is to evaluate pilots' body and physiological performance during their works using a large model sensor (tri-axial accelerometer and atmospheric pressure sensor) and a heart rate monitor toward safe harbors. The dis/embarkation experiment is carried out for the real pilotage. The results show that the largest acceleration 1.5-2.0 G appears during transfer from a pilot ladder to a pilot boat, and the sensor read their behavior at the ladder. The atmospheric pressure detected a height change. The heart rate read his mental workload for the decision-making for ship handling.

This paper presents an evaluation of an electrostatic vibration energy harvester with the bipolar charged electret. The energy harvester with the size of 13 x 12 x 1.2 mm(3) was fabricated. The output power of the bipolar charged with +/- 250 V harvester was 9 mu W when the acceleration was 1.4 g at 352 Hz with 0.9 M Omega load resistance. The effectiveness against the velocity-damped resonant-generator (VDRG) limit was 2.5%. The electrostatic forces of the actual device with DC bias, which simulates charged electret with monopolar and bipolar were experimentally and numerically verified. We estimated the electrostatic force by measuring the vibration amplitude versus applied acceleration of the electret mass. As a result, we investigated the bipolar charged device can reduce the effect of electrostatic force as low as no bias condition. The numerical model of the energy harvester considering the electrostatic force by FEM static analysis was also established. The comparison between the numerical model and the measurement results showed a similar inclination.

In this study, we report an equivalent circuit model of an electrostatic energy harvester for a SPICE circuit simulator. In order to simulate a harvesting system, the output power of the device is calculated in the simulator. The capacitance between the electrodes is obtained by FEM analysis by taking the fringing effect into account and the result is applied to a sub-circuit model for the simulator. Mechanical vibrations are converted into electricity by an equivalent circuit model of a mass-spring structure and an electrostatic energy harvester. The simulated output power and output waveform correspond with the measurement results of our electrostatic energy harvester. We also simulate the operation of a harvesting system connected with a power management IC.

This article introduces a MEMS batch fabrication process of micro magnet array with bipolar magnetic pole for an electromagnetic vibration energy harvester. In order to obtain the large electromotive force from large magnetic flux density change, we established the fine patterned alternating magnetized bipolar magnetic structure. The batch fabrication process of bipolar magnet array is composed of two wafers processing with S-pole and N-pole magnetization and bonding process. By the prototype fabrication of bipolar magnet with the 200 mu m SN-interval, we showed the usability of the batch fabrication process of the bipolar magnet array. In addition, we estimated the generated power of energy harvester with a bipolar magnet array. Compared to a harvester with monopolar magnet array, we showed the good result for bipolar one.

This paper shows a design optimization of MEMS (Microelectromechanical Systems) electromagnetic energy harvester by using finite element method (FEM) analysis to obtain a maximum generated power. The electromagnetic energy harvester consists of the sputtered NdFeB magnet film on a high-aspect-ratio corrugated Si structure and a counter Au serpentine coil. The each dimension of the device is optimally designed by using FEM simulation. After the prototyping with MEMS fabrication process, the measurement results of the power generation are 2.65 mV of the induced electromotive force and 7.60 nW of the output power with optimum load resistance of 231 Omega at the vibration condition of 100 Hz, 294 mu m(p-p).

This paper demonstrates successful deposition and etching of Pb[Zr,Ti]O3 (PZT) thin films on pre-etched Si substrate with pits having depths of several hundred micrometers. Conventionally, for fabrication of microelectromechanical systems, PZT films are deposited onto a flat substrate because of inherent difficulties associated with stable deposition and processing. We successfully established the fabrication of PZT thin films and electrodes on non-flat and pre-etched substrate by using sputtering deposition and projection exposure techniques. The evaluation results reveal that the PZT thin film deposited onto the pre-etched substrate has good ferroelectric characteristics, including piezoelectric d33 constant of 80 pm/V. © 2014 The Institute of Electrical Engineers of Japan.

In this study, the improvement of energy harvesting from wideband vibration with random change by using a combination of linear and nonlinear spring system is investigated. The system consists of curved beam spring for non-linear buckling, which supports the linear mass-spring resonator. Applying shock acceleration generates a snap through action to the buckling spring. From the FEM analysis, we showed that the snap through acceleration from the buckling action has no relationship with the applied shock amplitude and duration. We use this uniform acceleration as an impulse shock source for the linear resonator. It is easy to obtain the maximum shock response from the uniform snap through acceleration by using a shock response spectrum (SRS) analysis method. At first we investigated the relationship between the snap-through behaviour and an initial curved deflection. Then a time response result for non-linear springs with snap through and minimum force that makes a buckling behaviour were obtained by FEM analysis. By obtaining the optimum SRS frequency for linear resonator, we decided its resonant frequency with the MATLAB simulator.

We designed and evaluated ASICs (Application Specific Integrated Circuits) for the human activity monitoring systems to reduce the total power consumption. The ASIC extracts the heart rate from measured ECG (Electrocardiogram) raw signal. To realize the ASIC with ultra-low power consumption, we used novel algorithm based on fuzzy logic which is very simple and light processing. The fabricated ASIC shows sufficient function and low power as low as 2 μW.85% of the power consumption for MPU (Micro-Processing Unit) processing was cut by using the heart rate extraction ASIC. © 2014 The Institute of Electrical Engineers of Japan.

In this article, we described concepts for improving the shock reliability of MEMS electrostatic vibration energy harvesters. The harvester is based on silicon mass spring system supporting an electret. We determined experimentally that the primary cause of failure of the harvester under shock excitation is impact between the anchors of the springs. The impact creates chipping damages on the anchors which induces breakage of the springs. The springs are vital for proper functioning of the harvester, so that when they are broken, the device losses all its functionalities. Avoiding impact between moving parts of the harvester is difficultly feasible. However, avoiding impact on vital parts of the device is easily feasible with the use of shock absorbing bumpers. The concept of rigid bumpers is first investigated. While this approach improves the survival chances of the springs under a shock excitation, chipping damages are observed on the rigid bumpers. The residue from the chipping damages may hinder the functionality of the harvester. To limit the chances of chipping damages on the bumpers, flexible in place from rigid bumpers are investigated. By using Hertz contact model approach, it is shown that flexible bumpers allow reducing the risk of chipping damages by a factor five. (C) 2014 Published by Elsevier Ltd.

Current commercial wireless tire pressure monitoring systems (TPMS) require a battery as electrical power source. The battery limits the lifetime of the TPMS. This limit can be circumvented by replacing the battery by a vibration energy harvester. Autonomous wireless TPMS powered by MEMS electret based vibration energy harvester have been demonstrated. A remaining technical challenge to attain the grade of commercial product with these autonomous TPMS is the mechanical reliability of the MEMS harvester. It should survive the harsh conditions imposed by the tire environment, particularly in terms of mechanical shocks. As shown in this article, our first generation of harvesters has a shock resilience of 400 g, which is far from being sufficient for the targeted application. In order to improve this aspect, several types of shock absorbing structures are investigated. With the best proposed solution, the shock resilience of the harvesters is brought above 2500 g.

This paper presents a wearable PPG (photoplethysmographic) sensor system with a PSoC microcontroller unit. The PSoC includes a CPU, analog and digital blocks to configure mixed-signal circuits, and an internal oscillator in a single IC package. The PSoC allows designers to reduce the number of external discrete devices and the system size. The novel PPG sensor system consists of a photo interrupter, the PSoC, and the Bluetooth module, which are on PCBs (Printed Circuit Boards) 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 also includes an analog filter, amplifiers, and digital circuits to calculate HR (heart rate) from the pulse wave of human body. The system could detect the pulse wave and transmit the HR data to a host PC wirelessly. The supply voltage is 3.3 V, and the total current consumption is about 51 mA. In comparison with our previous work, the area of discrete RCL (resistor, capacitor, and inductor) devices was reduced from 1230 mm2 to 466 mm2, the number of those devices was reduced from 26 pieces to 6 pcs, and the weight of the system was reduced from 13 g to 7 g. We also investigated a pulse voltage driving method for the LED of the photo interrupter to reduce the current consumption of the LED. And we describe an energy harvester for autonomous power source for the monitoring system. © 2013 Copyright TSI® Press.

A microfabrication process for poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) based flexible piezoelectric devices is proposed using heat controlled spin coating and reactive ion etching (RIE) techniques. Dry etching of P(VDF-TrFE) in CF4+O-2 plasma is found to be more effective than that using SF6+O-2 or Ar+O-2 feed gas with the same radiofrequency power and pressure conditions. A maximum etching rate of 400 nm/min is obtained using the CF4+O-2 plasma with an oxygen concentration of 60% at an antenna power of 200 W and a platen power of 20 W. The oxygen atoms and fluorine atoms are found to be responsible for the chemical etching process. Microstructuring of P(VDF-TrFE) with a feature size of 10 mu m is achieved and the patterned films show a high remanent polarization of 63.6 mC/m(2).

This paper introduces the basics of energy harvesters and demonstrates two specific vibratory-type energy harvesters developed at the University of Hyogo. The fabrication and evaluation results of the vibratory-type energy harvesters, which employ electrostatic and electromagnetic mechanisms, are described. The aim of developing these devices is to realize a power source for an autonomous human monitoring system. The results of harvesting from actual human activities obtained using a data logger are also described. Moreover, challenges in the power management of electronic circuitry used for energy harvesting are briefly discussed.

Monolithic fabrication of lead zirconate titanate [Pb(Zr,Ti)O-3 or PZT] based thin film resonant devices such as microcantilevers, Lamb wave and bulk acoustic wave resonators are demonstrated. High-performance PZT thin films with a thickness of 2.6 mu m are prepared on a silicon on insulator wafer by a sputtering deposition process. A highly selective reactive ion etching process is employed for micro-patterning of PZT, platinum electrodes, and SiO2 insulation layer. Self-actuation of the PZT microcantilevers is demonstrated and the frequency response is characterized using a laser Doppler vibrometer. The frequency response of the Lamb wave resonator is evaluated by measuring its transmission characteristic using a network analyzer. For a Lamb wave resonator with a length of 240 mu m and an interdigital period of 80 mu m, the 1st order and 2nd resonance frequencies are 15.3 and 41.8 MHz, respectively.

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. © 2013 IEEE.

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.

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. © 2013 IEEE.

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. © 2013 IEEE.

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.

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.

In this paper, we address the fabrication and characterization of bimorph structures with relatively thick double-layered Pb(Zr,Ti)O-3 (PZT) thin films. The PZT/PZT layers are deposited by RF magnetron sputtering. Hysteresis loops of polarization and electrical field for the top and bottom PZT thin films revealed good ferroelectric characteristics with remanent polarization at approximately 20 mu C/cm(2) and a coersive electric field of about 100 kV/cm. The vibration tests of fabricated bimorph cantilevers during electrical voltage application revealed a twofold displacement compared with single layer driving, and the piezoelectric coefficient value d(31) is estimated to be 13 pm/V. The residual stress difference between the top and bottom layers after the annealing process is calculated to be -0.32 MPa. For a further thickening of the bimorph structure, 6-mu m-thick PZT/PZT is also sputtered. The thicker bimorph has a smaller residual stress difference, -30 MPa, between the two layers prepared without the annealing process. The evaluated results demonstrate that the PZT/PZT bimorph structures are applicable to micro-electromechanical systems (MEMS) devices. (C) 2012 The Japan Society of Applied Physics

This study presents a wafer-level batch fabrication technique of NdFeB film for MEMS (Micro Electromechanical Systems) based electromagnetic type energy harvester. By using 20 mu m thickness NdFeB sputtered magnetic film on a trench-etched Si microstructure, fine patterned magnet structures for energy harvester had been realized. However the size of the sputtered sample was limited to the slightly small size. In this study, we improve the sputtering equipment to apply the NdFeB film process on a four-inch Si wafer. The film characteristics, estimation of the compatibility with the MEMS process and also energy harvesting result are presented. (C) 2012 Elsevier Ltd....Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o.

Electro-magnetically actuated Vibratory Beam Actuator (VBA) with high resolution and stability has been reported. The VBA senses acceleration from the frequency changes of the beams supporting a proof-mass. In this paper, piezoelectric PZT (Pb[Zr, Ti]O-3) thin films are employed to actuate the beam and to sense the vibration frequency for miniaturizing the VBA. Well-established fabrication processes including dry-etching PZT are applied to the VBA fabrications. For the acceleration sensing by using VBA, a self-oscillation system, which includes phase-lock-loop (PLL) to maintain resonant oscillations of the beams is constructed. Gravity sensing test, i.e. inclining the sensor, demonstrates a good linearity between applied acceleration and sensing signal. The VBA, promising as a next generation accelerometer, is miniaturized to the area of 4 mm(2). (C) 2012 Elsevier Ltd .... Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o.

In this paper, fabrication method of acceleration sensor with low parasitic capacitance is descried. By using Silicon on Honeycomb Insulator (SOHI) wafer as a base material instead of Silicon on insulator (SOI) wafer, parasitic capacitance has reduced to 20%. The sensitivity of the acceleration sensor measured from differential capacitance change revealed 1.5 fF/G. The linear relationship between gravity acceleration and detection capacitance is measured by using commercial C/V converting circuit. By combining the SOHI acceleration sensor and specially designed C/V converting circuit with ultra-low power consumption, the sensitivity of the acceleration sensor can be expected to increase in 22 times than that for SOI wafer. The C/V converter circuit with ultra low power consumption of 1.13-mu W will realize long term and continuous monitoring of human activities by assembled with capacitive-type sensors based on SOHI wafer.

This paper reports a fabrication process of pulse wave sensor and detection result of pulse wave using the ring-shaped sensor, which has ring-shaped photodiode. An LED is located at the center of a photodiode. This structure achieved noninvasive detection of the pulse wave and does not have the directivity. Therefore, the ring-shaped sensor is expected to reduce noises of body motion (motion artifacts). We evaluated the characteristics of the photodiode and detected the pulse wave using the fabricated sensor. As a result, the ring-shaped sensor can detect the pulse wave. Furthermore, detection of the pulse wave can be applied to measure the pulse wave velocity (PWV).

The efficiency of transportation system depends on many factors, such as traffic congestion, vehicle accidents and road conditions. To improve the reliability, productivity and safety of the system, many researchers propose to use a wireless sensor network (WSN) as a solution. A WSN usually consists of many tiny sensor nodes for sensing, data processing and communication. In this study, we present the development of a small-sized, low-power and lightweight wireless sensor node. It is equipped with a 3-axes accelerometer, an altimeter sensor, humidity sensor, temperature sensor, 315 MHz RF transceiver module and a typical coin-sized lithium battery (3.0 V, 220 mAh). The entire sensor node fits within a 28 x 20 x 8 mm(3) volume and is only 7 grams (not including the antenna). An 8-bit MCU is included in the RF transceiver module to control sensor node operation. It collects and transmits sensors data in real time to the RF repeater with bit rate 24 kbps. During continuous operation, the sensor node consumes less than 3 mA current. Thus for a 220 mAh battery, the wireless sensor node can continue operating for more than 75 hours.

Surface MEMS (microelectromechanical systems), which is fabricated by the microprocessing techniques based on thin film deposition and processing, are incorporated into consumer electronics and automobiles. The structures of the surface MEMS having thin shape with small aspect ratio are difficult to drive to the lateral direction. The conventional electrostatic actuators have comb electrodes, resulting in a complex structure. This research addresses on the actuators available to move in a lateral direction by using thin-film Pb(Zr,i)O-3. Test cantilevers with two segmented top electrodes on the piezoelectric film are fabricated and the driving characteristics are evaluated. Applications of electrical voltages with reversed phases to the segmented top electrodes at the resonant frequency with lateral oscillation mode moved the cantilever with large displacement of 7 mu m. A non-linear effect in the frequency response was also observed for the large applied voltages.

Continuous monitoring of human physical and mental conditions are heavily required solving issues to realize a high quality of life society. The human condition data especially; heartbeat, ECG (electrocardiogram), respiration and blood pressure are very important vital signs to prevent a human sudden disease, such as a heart attack. In this study, we fabricated a novel sensor to monitor the heartbeat and respiration, which is made on a flexible thin film of P(VDF/TrFE) as a sensing material and PDMS (poly dimethyl siloxane) as a substrate material. The PDVF (poly vinylidene fluoride) that is thin, flexible and piezoelectric material can be used for the flexible force sensor. The fabrication steps and some experimental results for human monitoring system are described.

To realize extremely low-power consuming sensor systems, a SOHI (Silicon on Honeycomb Insulator) wafer, which has ultra-small parasitic capacitance, is proposed and an accelerometer is fabricated to demonstrate use of the technique. In case of using a low-power-consumption switched capacitor measurement circuit, parasitic capacitance decreases sensor sensitivity dramatically. The concept of the SOHI wafer is a special SOI (Silicon on Insulator) wafer with the buried SiO2 layer replaced with a honeycomb-shaped SiO2 thick layer (20 mu m thick) to reduce the parasitic capacitance. In this paper, two types of SOHI wafer, which could reduce the parasitic capacitance to about 21% and 2% of typical SOI wafers, respectively are proposed. On a trial production, the structure of a prototype three-dimensional accelerometer is fabricated. By demonstrating the application of sensor fabrication, the SOHI wafer is shown as a useable material as the base substrate. Also, the ability to realize the accelerometer with low parasitic capacitance by using the SOHI wafer is demonstrated.

The size of conventional Geiger counters is large because the detector (GM tubes: Geiger muller tubes) is fabricated by mechanical processing. In this paper, an MEMS (micro electro mechanical systems) GM tube using a wafer level packaging is proposed. The MEMS-GM tube with glass/Si/glass stacked structure was fabricated by using anodic bonding and polymer bonding. With the supplied voltage of 2.6 kV to the MEMS-GM tube, pulse waves were observed when a radioactive material approached to the fabricated device.

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.

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.