藤田 孝之

This paper describes flexible and stretchable wiring for human monitoring systems by using magnetic powder conductor buried in the hollow tube of the silicone rubber substrate. The conductor powder was coated with Au sputtering and Cu plating for improving conductivity. From preliminary results of fabrication and measurements, the wiring shows resistance of few kω for over 40% stretch ratio.

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.

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.

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.

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.

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.

In this paper, we present a design approach for electrostatic energy harvester under low acceleration. In electrostatic energy harvester, the electrostatic force that prevents mass movement or causes pull-in is occurred due to the charged electret. We propose a dual-phase electrode arrangement and bipolar charged electret to reduce the electrostatic force. Utilizing dual-phase electrode arrangement or bipolar charged electret, the electrostatic energy harvester can reduce electrostatic force both vertical and horizon directions in a static condition from FEM analysis. It is found that the approached electrostatic energy harvester can generate more power than conventional structure in a low acceleration from SPICE equivalent circuit model. In addition, the air-gap can be smaller and the limited output power can be higher by reducing vertical electrostatic force.

エレクトレットを用いた静電型エナジーハーベスタは,振動マスにエレクトレットを成膜・荷電し対向電極との静電誘導で発電するデバイスである.そのため,発電電力や電力が最大になる最適負荷はマスの振動周波数や振幅によって大きく変化する.電気回路シミュレータ(SPICE)では可変容量のモデルを作成することで,時間変化に対する電極間の容量変化を表すことができる.そこで,本研究では有限要素法を用いてフリンジ効果を考慮した電極間の静電容量を解析し,その結果を等価回路モデルに利用することで,SPICEシミュレータ上でマスの動きに対するハーベスタの発電波形や最適負荷を解析した.その結果と実デバイスとの比較を行うことで,SPICEの等価回路モデルが発電量や最適負荷の見積もりに有用であることを確認した.

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.

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.

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.

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 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.

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 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.

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 shows the fabrication of the prototype of electromagnetic MEMS energy harvester and the power generation experiment al results. The electromagnetic energy harvester consists of the sputtered NdFeB magnet film on high aspect ratio corrugated Si trench and the Au serpentine coil. The each structure of the device is fabricated with the optimum geometry designed by the FEM simulation. In the result, we obtained 2.65 mV of the induced electromotive force and 7.60 nW of the output power. The experimental results agreed well with simulation results, and we confirmed the usefulness of the analytical method for the estimation of the power generation.