Takayuki Fujita

The incidence of falls in hospital facilities is high and can lead to a decrease in patients' quality of life and an increase in medical expenses. Therefore, the development of a system that can predict getting-up from a bed is necessary. This study proposes a get-up detecting sensor using 6-axis inertial sensor. This system can detect getting-up from a bed in real-time using machine learning with Edge AI. To evaluate the basic performance of the proposed system, a protocol was applied for four subjects, and data were collected. Alert accuracy rate and false alert rate were used as evaluation metrics, and a model was built using data from three of the subjects and evaluated with the remaining subject, which was repeated for all four subjects. For high-risk bed-leaving behavior, medium-risk pre-bed-leaving behavior, and low-risk get-up behavior, the alert accuracy rate (i.e., Recall) was 89.4%, 97.5%, and 86.3%, respectively, and the false alert rate (1-Precision) was 6.3%, 10.2%, and 0.0%, respectively. This confirmed the possibility of predicting rising behavior with high accuracy. Furthermore, as a proof of concept, a real-time get-up detection system was developed, and its practicality was demonstrated. Future challenges include reevaluating feature extraction and evaluating the performance of the proposed system with a diverse range of subjects of different ages, genders, and health statuses.

This paper reports on the improvement of the output power of piezoelectric energy harvesters (PEHs). A tapered thickness structure of a cantilever beam for uniform stress, tungsten proof mass, thick piezoelectric film, and series connection of the piezoelectric films are utilized for PEHs to increase the output power. The three-dimensional (3D) etching process of Si enables the formation of tapered thickness beam structure, which increases not only the output power, but the beam strength. The 3D shape allows to increase the weight of the proof mass, contributing to increase the output voltage and power. Furthermore, output voltage is enhanced by using series-connection of PZT cells to improve the circuit efficiency. The open-circuit output voltage and optimum power with resistance load of the fabricated harvesting device revealed 14.4 V0-P and 92 μW at an acceleration of 9.8 m/s2. The output power was improved by 8.9 times higher than that of the conventional model.

This paper reports thickness controls for cantilever beams of the piezoelectric energy harvester (PEH). The uniform stress structure for increasing output power and fillet structures for stress concentration relief of cantilever beams were fabricated by thickness controls using the micro-loading effect, resulting in a 46% increase in power generation and a nearly two-fold increase in fracture strength compared to typical cantilever beams.

© Published under licence by IOP Publishing Ltd. Multilayered piezoelectric MEMS energy harvesters based on sputtering depositions are designed and fabricated. To obtain high endurance and output power, the unimorph cantilever structure with totally 10 μm-thick multilayered PZT thin films and 80 μm-thick Si elastic layer is designed. In addition, the cantilever is designed to undergo a uniform stress on the PZT. The output power and voltage was 90 μW and 1.0 Vrms under the input acceleration of approximately 1.2 G (=11.76 m/s2) and optimum load resistance.

© 2019 IEEE. In this study, we aimed to develop a smart-cloth for workout. A flexible elastic electrode by using silicone rubber with special carbon black material, KETJENBLACK, was fabricated and tested. The flexible conductive electrode having an expansion ability of 100% or more was successfully fabricated. The compound of special carbon black, KETJENBLACK, can offer flexible electrodes and be suitable for wearable devices.

© 2019 IEEE. The ship navigation in a bay and harbor is one of the difficult situation for the congested sea area, and a coastal radio operator (port coordinator) usual supports a safe navigation by giving useful navigational information. The navigators make decision to avoid collision, and recognize the navigational situations from their information. In the other word, they manage the safe harbor traffic to control by giving the useful information. We think that their mental and physical workload shows the current and near future harbor traffic condition, and to monitor their workloads leads safe harbor control. In this study, we aim the development of monitoring system for port coordinators as the system of systems toward safe harbor traffic, and we measure ECG, body accelerations, and etc. The measured data read the mental and physical workload for the real situations of the harbor traffic. The results show the heart rate variability (R-R interval) and body accelerations read their mental and physical workload, and that displayed performance is well in the real time.

© 2018 IEEE. This paper describes the resonant type magnetic sensor completely compatible to the micro electromechanical systems (MEMS) batch fabrication process of SiGe. The resonant vibration of the sensor is excited by the Lorentz force that is proportional to the driving current and applied magnetic field. Since the sensitivity of the sensor reaches the order of geomagnetic field, the magnetic sensor can be incorporated into inertial measurement unit (IMU), which is fabricated with accelerometer and gyroscope. In addition, low deposition temperature of SiGe is advantageous to realize the monolithic integration of IMU combo sensors onto CMOS circuit. For inspection, the test device was fabricated with Si-SOI.

© 2018 IEEE. We have been developing a wearable device to observe the state of the human body and its circumstance. In previous studies, an ASIC (application specific integrated circuit) that provides heart rate from ECG (electrocardiogram) signal without the aid of a MPU(micro processing unit) processing was successfully developed. As a result, we drastically reduced the power consumption of the system to 2% compared with our previous system. In this study, a test model that integrates the ASIC and all other circuits including a low power MPU is constructed by using a FPGA to verify the operation of the complete system. The system operation of the test model mounted on the actual human body is confirmed on the PC based user interface software.

In this study, we aimed to develop a smart-cloth for workout. A flexible elastic electrode by using silicone rubber with special carbon black material, KETJENBLACK, was fabricated and tested. The flexible conductive electrode having an expansion ability of 100% or more was successfully fabricated. The compound of special carbon black, KETJENBLACK, can offer flexible electrodes and be suitable for wearable devices.

The ship navigation in a bay and harbor is one of the difficult situation for the congested sea area, and a coastal radio operator (port coordinator) usual supports a safe navigation by giving useful navigational information. The navigators make decision to avoid collision, and recognize the navigational situations from their information. In the other word, they manage the safe harbor traffic to control by giving the useful information. We think that their mental and physical workload shows the current and near future harbor traffic condition, and to monitor their workloads leads safe harbor control. In this study, we aim the development of monitoring system for port coordinators as the system of systems toward safe harbor traffic, and we measure ECG, body accelerations, and etc. The measured data read the mental and physical workload for the real situations of the harbor traffic. The results show the heart rate variability (R-R interval) and body accelerations read their mental and physical workload, and that displayed performance is well in the real time.

© 2017 IEEE. The evaluation of simulator-based exercise in maritime society depends on specialists who have enough on-board experience like a master and/or a professor of maritime university. That is just subjective evaluation, and the reviewed data is performance of the operated vessel such as own ship course, speed, rudder angle, and their behavior on order, action, and so on. We propose that their inside response (mental workload) is also important data to evaluate their simulator-based exercise using physiological index; moreover, we have found the heart rate variability, facial (nasal) temperature, and saliva are efficient to read their mental workload. However, the evaluation was not real time yet, it is just off-line analysis. The real time data is available that the instructor gives trainee the useful advisements on the spot during the exercise. In this paper, we propose a monitoring system as an evaluation support system for simulator-based exercise using heart rate variability, and we confirm its possibility.

© 2018 The Institute of Electrical Engineers of Japan. Blood pressure changes every second and cannot be continuously monitored by conventional cuff method. In order to solve this problem, we proposed a blood pressure estimation system by pulse transit time (PTT) method. The system includes two devices; a master device which monitors ECG for starting time of the pulse wave, and a slave device for monitoring the propagated pulse wave at the wrist. Both devices have some sensors, such as an accelerometer and barometer, for monitoring the condition of the body and wrist. The detected condition will be used for compensation of the PTT data. As a result, estimation of the blood pressure by PTT is accurate enough comparing to sphygmomanometer for home use. In addition, the relation between barometric pressure and PTT by hand position was measured and used for establishing the correction equations.

© 2018 Elsevier B.V. This study aims to report the design of high-performance piezoelectric MEMS energy harvesters using a full batch MEMS-fabrication process with a Si proof mass and multilayered Pb(Zr,Ti)O3 (PZT) thin films without bonding of a proof mass and/or bulk piezoelectric ceramics. These devices contain sputtered multilayered PZT thin films with internal metal electrodes as a thick energy-conversion layer. The thickening of the piezoelectric layer by multilayer sputter deposition technique enabled the batch fabrication of high-performance piezoelectric MEMS harvesters. These fabricated device with the footprint of 10 × 10 mm2 was found to provide a high output power of 53.7 μW per gravitational acceleration. These results are expected to be useful for the future development of alternatives to batteries for autonomous sensor systems.

© Published under licence by IOP Publishing Ltd. Piezoelectric MEMS energy harvesters based on multilayer (ML) Pb(Zr,Ti)O3 (PZT) thin films with interdigitated electrodes (IDE) as their internal and top electrodes are proposed and designed. Thick PZT thin films with good piezoelectric characteristics can be deposited by using multilayer deposition technique. Furthermore, IDE is adopted to the harvester design in order to take advantage of the longitudinal piezoelectric effect, which typically has twice piezoelectric constant as large as transverse effect. The energy harvesters with two electrode configurations, parallel plate electrodes (PPE) and IDE, are designed and estimate these output power. According to the result of finite element analysis, the output power per gravitational acceleration is about 124 μW for the PPE configuration. On the other hand, the output power per gravitational acceleration for the IDE configuration is about three times as large as that for PPE. Moreover, the influence of IDE patterns and the number of PZT layers were investigated. The larger number of layers results in the larger output power.

© Published under licence by IOP Publishing Ltd. In this study, we report the design and fabrication results of an optimized curved beam structure for low frequency, under one-hundred Hz, and non-linear operation of MEMS (Micro-Electromechanical Systems) vibration energy harvester. The optimization procedure for shape and dimension of the curved beam were established combining a FEM and a numerical analysis. Simulated curved beam with bi-stable motion was evaluated for wide bandwidth operation of a vibration energy harvester and preliminary fabrication process was confirmed.

© 2018 Wiley Periodicals, Inc. In this study, we have fabricated membranes which are composed of two- and four-layer Pb(Zr,Ti)O3 thin films with internal electrodes by using sputtering depositions. Electrical and driving characteristics as ultrasonic transducers of these membranes are evaluated. By increasing number of layers, the static displacement is reduced. However, for the multilayered membrane, the dynamic displacement became large because of the large mechanical Q factor in resonant vibration. The emitted sound pressure level and characteristics of the ultrasonic transducer are estimated.

This paper describes the resonant type magnetic sensor completely compatible to the micro electromechanical systems (MEMS) batch fabrication process of SiGe. The resonant vibration of the sensor is excited by the Lorentz force that is proportional to the driving current and applied magnetic field. Since the sensitivity of the sensor reaches the order of geomagnetic field, the magnetic sensor can be incorporated into inertial measurement unit (IMU), which is fabricated with accelerometer and gyroscope. In addition, low deposition temperature of SiGe is advantageous to realize the monolithic integration of IMU combo sensors onto CMOS circuit. For inspection, the test device was fabricated with Si-SOL

We have been developing a wearable device to observe the state of the human body and its circumstance. In previous studies, an ASIC (application specific integrated circuit) that provides heart rate from ECG (electrocardiogram) signal without the aid of a MPU(micro processing unit) processing was successfully developed. As a result, we drastically reduced the power consumption of the system to 2% compared with our previous system. In this study, a test model that integrates the ASIC and all other circuits including a low power MPU is constructed by using a FPGA to verify the operation of the complete system. The system operation of the test model mounted on the actual human body is confirmed on the PC based user interface software.

In the maritime society, the training of a ship handling is carried out by a ship bridge simulator. The education using the simulator is popular worldwide because we are able to educate the same scenario, and repeat it for a lot of students until they can understand well. Moreover, we can make a scenario for the dangerous conditions and situations that we have never tried on the real vessel. The evaluation of simulator training is subjectively; it is professional subjective evaluation that comes from their experiences. In this paper, we propose a real time evaluation support system using a physiological index as the one of system of simulator systems. The system evaluates mental workload on the real time, and the system supports instructors to monitor student's mental workload during their training. The instructors understand not only their performance but also their mental workload to evaluate the training.

© 2017 IEEE. We have been developing a monitoring system to measure human information from human body. In the previous study, we developed a digital integrated circuit that enables acquisition of heart rate from ECG (Electrocardiogram) instead of MPU (Micro Processing Unit). This circuit reduced the power consumption of the MPU from 97 W to 19.7 W. In this research, we redesigned an MPU specialized for the human monitoring system to aim at further lowering power consumption and verified it with a test model. The designed MPU has fewer logic elements than the commercially available MPU and consumes 383 nW power consumption when using standard cell with low power consumption. This can be 98.0% lower than the conventional MPU.

© 2017 IOP Publishing Ltd. For the realization of piezoelectric microelectromechanical systems (MEMS) with multiple degrees-of-freedom, lead zirconate titanate thin films were deposited and micropatterned on the sidewalls of a pre-etched substrate with a feature depth of several hundred micrometers. The piezoelectric test structures, consisting of concave geometries and cantilevers with vertical and sloped sidewalls were successfully fabricated onto a 4 inch full sized wafer. Characterization of the fundamental properties of the lead zirconate titanate thin films indicated values comparable to those deposited on flat substrates. Actuation tests demonstrated that the triangular column cantilevers can be driven both in-plane and out-of-plane. The deposition of lead zironate titanate thin films onto a vertical sidewall created bimorph cantilevers composed of piezo/non-piezo/piezo structures in the horizontal direction. The use of microfabrication techniques to deposit lead zironate titanate thin films on pre-etched substrates gives MEMS actuators with multiple degrees-of-freedom and batch process compatibility.

The evaluation of simulator-based exercise in maritime society depends on specialists who have enough on-board experience like a master and/or a professor of maritime university. That is just subjective evaluation, and the reviewed data is performance of the operated vessel such as own ship course, speed, rudder angle, and their behavior on order, action, and so on. We propose that their inside response (mental workload) is also important data to evaluate their simulator-based exercise using physiological index; moreover, we have found the heart rate variability, facial (nasal) temperature, and saliva are efficient to read their mental workload. However, the evaluation was not real time yet, it is just off-line analysis. The real time data is available that the instructor gives trainee the useful advisements on the spot during the exercise. In this paper, we propose a monitoring system as an evaluation support system for simulator-based exercise using heart rate variability, and we confirm its possibility.

© 2017 The Institute of Electrical Engineers of Japan. Novel miniaturized tactile devices, which provide a person with vibration stimulation, are proposed. The strategy is to hit the skin with a resonantly oscillating proof mass. The tactile devices consist of a Si proof mass and a beam formed by laminated thin-film PZT and polymer. The fabricated devices generated large displacement with high durability. Tactile experiments suggest that all examinees experienced vibration at displacement of 1.3 mm for a 4 mm × 4 mm device. For wearable monitoring systems of human activities, the energy consumption was estimated at 12 μW and the major energy loss was attributed to dielectric loss.

© 2017 The Institute of Electrical Engineers of Japan. We describe a magnetic gap control structure using stripe shaped magnetic thin-film. Stripe shaped magnet film can increase the magnetic repulsive force because the high aspect-ratio magnet decreases a demagnetize-field. As a result, stripe shaped magnet film generates repulsive force for magnetic gap control structure.

© 2017 The Institute of Electrical Engineers of Japan. In this study, we have fabricated membranes which are composed of 2-layers and 4-layers Pb(Zr,Ti)O3 thin films with internal electrodes by using sputtering depositions. Electrical and driving characteristics as ultrasonic transducers of these membranes are evaluated. By increasing number of layers, the static displacement is reduced. However, for the multi-layered membrane, the dynamic displacement became large because of the large mechanical Q factor in resonant vibration. The emitted sound pressure level and characteristics of the ultrasonic transducer are estimated.

We designed and evaluated ASICs (application-specific integrated circuits) for a human activity monitoring system in order to reduce total power consumption. The ASIC extracts the HR from the measured electrocardiogram (ECG) raw signal. To create an ASIC with ultra-low power consumption, we used a novel algorithm based on fuzzy logic that is very simple and requires minimal processing power. The fabricated ASIC shows sufficient functionality and a power level as low as 2 mu W. A total of 85% of the power consumption in microprocessing unit (MPU) processing was cut by using the heart rate extraction ASIC.

In this report, an application of vibration energy harvester for MEMS wireless sensor systems was described. The MEMS vibration harvester is one the great candidate for maintenance free power source for the wireless sensor network (WSN) and system e.g. the IoT and the Trillion Sensors Universe. By introducing some researches for the human monitoring WSN and two types of vibration harvester based on an electromagnetic and an electrostatic (electret) technologies, the present situation of vibration harvesters and their goal were summarized in the article.

This paper reports an improvement of structure design of bipolar charged electret energy harvester to prevent an electrical discharge during a corona charging process on electret. We confirmed that differential output power of 33 mu W is obtained with 8.8 g at 350 Hz sinusoidal vibration from the developed device. By using a commercially available power management IC, regulated voltage of 1.8 V is properly obtained and can drive a load resistance more than 500 k Omega.

This paper proposes collision-free structure using NdFeB thin-film magnet for vibration energy harvesters. By using stripe shaped NdFeB magnet array on the Si MEMS structure, we finally obtained 3 mN of magnetic repulsive force on 8 x 8 mm(2) specimen with 40 mu m air-gap.

© 2016 The Institute of Electrical Engineers of Japan. This paper demonstrates an improvement in the generated power of a NdFeB electromagnetic vibration energy harvester by optimizing the device dimensions considering a mass-damper-spring system and the Lorentz force. The electromagnetic harvester follows a velocity-damped-resonant-generator (VDRG) model. When the electrical and mechanical attenuation coefficients are equivalent and the device is operated at a resonant state, the maximum power will be obtained. In this paper, we simulated and optimized the power generation considering a mass-damper-spring structure and the Lorentz force. From our simulation results, we determined an optimal design for 100 Hz and 3 μmp-p of sinusoidal external vibration to generate 0.42 μW of power from the device with a 10 × 10 × 0.5 mm3 active harvesting area and 50 of Q-factor. This exhibits power that is 43 times larger than the previous design.

© 2016 The Institute of Electrical Engineers of Japan. In this paper, we present a SPICE equivalent circuit model of an electrostatic vibration energy harvester. The SPICE model consists of a generation part and a mass-spring system part considering electrostatic force. The change in capacitance between electrodes with the position of the mass is analyzed by FEM analysis and is applied for the generation part. For investigating the characteristics of the actual harvester, the harvester was fabricated and charged by a -200 V monopolar potential. The maximum output power of the monopolar-charged harvester is 1.1 μW with applied vibration amplitude of 350 μmpp at 323.3 Hz with 0.8 MΩ optimum load resistance. We confirmed that the examined and analyzed results indicate high correspondence.

Multimorph structures composed of multiple thin-film piezoelectric layers and electrode layers were realized by sputtering deposition. Cantilevers with four layers of Pb(Zr,Ti)O-3 (PZT) thin film are fabricated and evaluated. The electrical and piezoelectric characteristics of each PZT layer are very similar and are comparable to those of conventional single-layer PZT thin film. The piezoelectric constant d(31) is estimated to be -38.3pm/V from the relationship between tip displacement and applied voltage under the condition of driving four all piezoelectric layers. The generative force is also estimated from the tip displacement. It is confirmed that multimorph cantilevers have larger generative force than those of conventional unimorph and bimorph cantilevers for identical driving voltage. (C) 2015 The Japan Society of Applied Physics

Vibration energy harvesters can serve as a replacement solution to batteries for powering tire pressure monitoring systems (TPMS). Autonomous wireless TPMS powered by microelectromechanical system (MEMS) electret-based vibration energy harvester have been demonstrated. The mechanical reliability of the MEMS harvester still has to be assessed in order to bring the harvester to the requirements of the consumer market. It should survive the mechanical shocks occurring in the tire environment. A testing procedure to quantify the shock resilience of harvesters is described 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, the first important aspect is to understand the failure mechanism. Failure is found to occur in the form of fracture of the device's springs. It results from impacts between the anchors of the springs when the harvester undergoes a shock. The shock resilience of the harvesters can be improved by redirecting these impacts to nonvital parts of the device. With this philosophy in mind, we design three types of shock absorbing structures and test their effect on the shock resilience of our MEMS harvesters. The solution leading to the best results consists of rigid silicon stoppers covered by a layer of Parylene. The shock resilience of the harvesters is brought above 2500 g. Results in the same range are also obtained with flexible silicon bumpers, which are simpler to manufacture.