Mechanical Systems Technology Research Articles

Revolutionizing wireless communication: A review perspective on design and optimization of RF MEMS switches

Micro Electro Mechanical System (MEMS) technology revolutionized electronics by enabling miniaturization and integration of components like sensors, actuators, & switches. MEMS switches offer advantages over conventional switches, with Radio Frequency (RF) MEMS switches gaining attention in wireless communication systems. Designing and optimizing RF MEMS switches necessitate a profound comprehension of their electromagnetic and mechanical behavior, achieved using simulation and optimization techniques. This review provides an overview of different optimization techniques, including Finite Difference Time Domain (FDTD), Finite Element Method (FEM), Method of moments (MoM), Taguchi method, Response Surface Method (RSM), Artificial Neural Network (ANN) model and Evolutionary Algorithm (EA) based model, with the ANN and EA model being the most efficient due to its capability to handle complex designs and provide accurate predictions. This review aims to provide insights into the current state-of-the-art in RF MEMS switch design and optimization, stimulating further research to address existing challenges and limitations.

Design, development, fabrication and evaluation of the dynamics of a graphene based underwater acoustic vector sensor: A simulation and experimental study

In the last decade, the usage of underwater vector sensor has gained a lot of importance in the detection of low frequency underwater acoustic signals, as the noise level radiated by the submarine has been drastically reduced. Acoustic sensor based on Micro Electro Mechanical Systems (MEMS) technology is the recent advancement in the area of underwater acoustic vector sensors. We are reporting the design, fabrication, preliminary characterization and evaluation of the dynamics of a two-dimensional underwater acoustic vector sensor by simulation and experimental study. The vector sensor is realized using Reduced Graphene Oxide (rGO) as sensing element and Kapton as flexible substrate, to yield better sensitivity compared to the conventional acoustic vector sensor. Design of vector sensor is inspired by the biological sensing system of fish. The application of piezoresistive transduction principle and MEMS technology helps in miniaturisation and low frequency acoustic signal detection. The fabrication process is made simple, scalable and cost minimum by using the method of drop casting for the deposition of rGO on flexible substrate kapton, thereby eliminating the requirement of clean room. COMSOL Multiphysics 5.5 version is used to simulate acoustic vector sensors using polysilicon and rGO on substrates, silicon and flexible kapton respectively. The simulation results indicate that the sensitivity of rGO based acoustic vector sensor is −149.47 dB which is better in comparison with the sensitivity of −173.37 dB of conventional polysilicon vector sensor. By simulation, the natural frequency of the sensor is found to be 46.62 Hz, which closely matches with the theoretical value 41.06 Hz of the device as per the design criteria and hence, it could detect the low frequency acoustic signals. The displacement sensitivity of the fabricated sensor is found to be 0.0264 V/mm and 0.0276 V/mm for applied displacements in axial and radial directions respectively. The device is tested for its performance parameters i.e., sensitivity and directivity, by performing an acoustic test in the presence of an elastic medium, water. This test results infer that, the device is able to detect and give smooth output response for the acoustic signals in the low frequency range. The Y and X-channel receiving sensitivity exhibited by the sensor is found to be −128.04 dB to −134.93 dB and −130.61 dB to −136.78 dB respectively. Directivity pattern of the sensor is found to be in the shape of 8 with symmetry. As the device is a vector sensor, in addition to the scalar pressure measurement, it should be able to provide additional incentives such as acoustic particle displacement and acoustic particle velocity at any point in the acoustic field. In this paper, an experimental setup is made to generate deep and intermediate water waves, thereby attempting to simulate ocean conditions in the laboratory. Subsequently the numerical evaluation of the wave kinematics, i.e., fluid particle displacement and fluid particle velocity are performed by applying Airy's theory. An effort is also made to analyse the wave kinematics for various water depths, varying from Surface Water Level (SWL) till the sea bed. In this study, wave kinematics are analysed numerically by using experimental data and also by modelling Fluid-Structure Interactions in COMSOL Multiphysics environment. Our results show that the fluid flow of velocity 0.31 m/s results in fluid particle velocity of 0.125 m/s at time 0.215 s (around f = 5 Hz) by both the methods and fluid particle displacement is found to be 19.66 μm. The experimental test setup and videos are made publicly available1: 1https://sites.google.com/view/smithapaib/downloads

DESAIN DAN PENGEMBANGAN MESIN MICRO-PRESS PEMBENTUK KOMPONEN MIKRO

The increasing application of micro electro mechanical systems technology on daily life devices increases the need for micro components. Furthermore, it must be supported by reliable fabrication technology to produce micro-sized products. One of these technologies is micro-sheet metal forming, which is a forming technology from sheet metal with 10-300µm thickness. The development of this technology requires a special press machine that is used in the scope of micro-scale work, named micro-press. Micro-press is still rare due to it was used for individual experiment purposes. Thus, it is necessary to develop the micro-press to support research and manufacturing of micro-part. In this study, the design of a micro-press is intended to accommodate the miniaturization problems and to be easy in fabrication and re-fabrication. Then, the micro-press will contribute to fulfill the micro-parts need. By using the VDI 2222 design method, the design of a 5kN micro-press machine with a servo motor drive is obtained, and validation of construction strength was carried out with the help of the appropriate CAE software. The results of the design validation show that the construction of the micro-press machine is quite strong. The selected component has a strength specification that is greater than required, and the maximum stress that occurs in the frame, which is 80.096 N/mm2, is still very lower than the allowable stress on the SPHC material. The magnitude of the resultant displacement shows a fairly small value, i.e. 0.178 mm.

Improvement of imaging performance of silicon micropore X-ray optics by ultra long-term annealing.

We have been developing a light-weight X-ray telescope using micro electro mechanical systems technologies for future space missions. Micropores of 20 µm width are formed in a 4-inch Si wafer with deep reactive ion etching, and their sidewalls are used as X-ray reflection mirrors. The flatness of the sidewall is an important factor to determine the imaging performance, angular resolution. It is known that hydrogen annealing is effective to smooth a Si surface. We tested 150 hour annealing to achieve the ultimately smooth sidewalls. After 50 hour, 100 hour, and 150 hour annealing, the angular resolution improved 10.3, 4.0, and 2.6 arcmin in full width at half maximum (FWHM) and 17.0, 14.5, and 10.8 arcmin in half-power width (HPW). In spite of this improvement, the edge shapes of the sidewall were rounded. Therefore, both edges of the sidewall were ground and polished, and then the angular resolution was improved further to 3.2 arcmin (FWHM) and 5.4 arcmin (HPW).

Internal Characterization-Based Prognostics for Micro-Direct-Methanol Fuel Cells under Dynamic Operating Conditions.

Micro-direct-methanol fuel cells (DMFCs) use micro-electro mechanical system (MEMS) technology, which offers high energy density, portable use, quick replenishment, and free fuel reforming and purification. However, the DMFC is limited by a short effective service life due to the membrane electrode’s deterioration in electrochemical reactions. This paper presents a health status assessment and remaining useful life (RUL) prediction approach for DMFC under dynamic operating conditions. Rather than making external observations, an internal characterization is used to describe the degradation indicator and to overcome intrusive influences in operation. Then, a Markov-process-based usage behavior prediction mechanism is proposed to account for the randomness of real-world operation. The experimental results show that the proposed degradation indicator alleviates the reduction in DMFC output power degradation behavior caused by the user loading profile. Compared with the predictions of RUL using traditional external observation, the proposed approach achieved superior prognostic performance in both accuracy and precision.

Preface

It is our great pleasure to welcome you to the 2021 12th Asia Conference on Mechanical and Aerospace Engineering (ACMAE) on December 29-31th, 2021, which is planned to hold in Nanjing University of Science and Technology, China. However, Since the outbreak of the global covid-19 pandemic, it has been a challenge for the academic community to organize international conferences due to travel restrictions. Considering the safety of the participants. This time we have decided to take the conference with combination of online and offline. ACMAE 2021 is dedicated to issues related to the advancement of all Mechanical and Aerospace Engineering topics.Mechanical Engineering of Nanjing University of Science and Technology, as the host of ACMAE 2021 attaches great importance to international academic exchanges and joint talent training, and has established cooperative relations with Baumann Moscow State Technical University, Samara State University and etc. Series of conferences have been organized as International Conference on Mechanical and Electrical Systems and Testing Technology, International Forum on Special Equipment and Engineering Mechanics, etc.We have honor to invite Prof. K.A. Neusypin and Prof. Chen Xiong served as the chairman of the conference respectively. In recent years, ACMAE has been successfully organized online in Yokohama, Japan (2017), Singapore (2018), Bangkok, Thailand (2019), and 2020, with the support of Japan National Defense University, and Chulalongkorn University and etc. respectively. The conference aims to build an annual academic exchange platform, focusing on the scientific research and discussion in the field of aerospace in Asia, promoting the exchange and cooperation between Asian scholars, and showing the booming development of aerospace in Asia to the world.The conference invited two top international experts and three top domestic experts in the field of aerospace to deliver keynote speeches, including Professor Genxiang Xia from university of Delaware and IEEE Member. Professor Qu Ronghai, member of degree Committee, Huazhong University of Science and Technology, Professor Luling An, expert of Nanjing University of Aeronautics and Astronautics; Prof. Wu Weitao, Professor of Nanjing University of Science and Technology, member of the Committee of Physics and Aerodynamics of Chinese Society of Aerodynamics; Professor Maria Selezneva, Deputy Head of The Department of Instrument Engineering and Technology, Bauman State Technical University, Moscow, Russia. Each speaker has delivered the speech more than 30 minutes. In addition, more than 100 experts and scholars from the world's top research institutes of aerospace technology, including Samara University in Russia, as well as domestic senior research institutes of aerospace technology, including Nanjing University of Aeronautics and Astronautics, Northwestern Polytechnical University, National University of Defense Technology, Shanghai Jiao Tong University and Xiamen University, attended the conference.This conference proceeding, contains a collection of research papers, organized as chapters, presented at ACMAE 2021. This publication, containing the conference proceedings, documents and presentations made at ACMAE 2021, is the result of the creative work of their authors and of a highly selective peer-review process.We are also grateful to colleagues for committing their active participation and promoting the conference during this difficult time. In this specific time, although we are not able to meet, I believe online conferences like these would shorten the distance between people, reduce spending and inconvenience on the way. Wish to see all of you in next year conference.Conference ChairProf. Xiong ChenACMAE 2021List of titles Organizing Committees are available in this Pdf.

Diffraction gratings for spectral devices [Review

Subject of study. This review is intended to acquaint the reader with various types of diffraction gratings and technologies for fabricating them. Method. An information search on the topic, systematization, and analysis are performed. Main results. This paper briefly discusses the areas of application and classification of spectral devices and shows the variety of problems that can be solved by means of spectral devices and that impose various requirements on diffraction gratings. It lists the main characteristics of diffraction gratings used in spectral devices and specifies the stages of their improvement. It discusses classical reflective diffraction gratings—plane (profiled and laminar) and concave. It describes the principles involved in obtaining holographic diffraction gratings and their advantages over ruled ones. It devotes special attention to concave holographic gratings with aberration correction, shows how they are classified, and briefly describes methods of optimizing the parameters of gratings that operate in monochromator systems with simple rotation and flat-field spectrographs with correction of defocusing, astigmatism, and meridional coma, as well as various methods of recording gratings in nonhomocentric beams to expand their correction possibilities. Ruled analogs of holographic gratings are used in a number of cases. It is pointed out that foreign and Russian firms that batch-produce diffraction gratings of the types described here completely satisfy the requirements of the batch-producers of spectral devices. The features of using volume phase gratings in spectral devices are considered, and it is pointed out that, even though these gratings are distinguished by high efficiency, their angular and spectral selectivity have inhibited these gratings from being widely applied in spectral devices. However, there have been active studies in recent years on expanding the regions in which volume phase gratings are used: new system solutions, recording materials, and recording methods have been proposed. Trends to create diffraction elements that combine various functions (cross gratings and grisms) are pointed out. New technologies are proposed for fabricating diffraction gratings: ruled gratings—pendulum-type ruling engines, gratings that reflect with high diffraction efficiency in an expanded wavelength range—“efficiency-achromatization” or double-blaze technologies and volume phase gratings—ultrafast laser inscription and profiled diffraction gratings that operate in the x-ray region—electron-beam lithography, to miniature spectral devices—microelectronic mechanical systems technology used in electronics, composites—concepts of a composite volume phase diffraction grating recorded by integrating several elementary fields. The Conclusion evaluates the modern level and points out development trends. Practical significance. The material presented here can be useful in the development of spectral apparatus.

A miniaturized seven-electrode conductivity and temperature integrated sensor

Marine environmental monitoring technology is the support of marine development, and its development level and innovation capability have become important criteria for measuring a country’s marine science and technology indicators. In order to meet the application demand of large-scale and high-density deployment of marine observation network, a planar open seven-electrode conductivity and platinum resistance temperature integrated sensor is developed by using Micro Electro Mechanical System(MEMS) technology, combined with semiconductor micro and nano precision processing technologies such as mask lithography and physical sputtering. The measurement principle, probe design preparation, packaging and calibration method of this conductivity temperature sensor are presented. By calibrating and fitting the measurement data of this sensor, good measurement accuracy results were obtained. The miniaturized conductivity temperature sensor has the advantages of small size, low power consumption, low cost and high accuracy of probe processing, high batch consistency, and fully meets the application requirements of marine observation network.

3-V Input, 70-V Output, Fully Integrated Hybrid Charge Pump

A novel integrated-circuit charge-pump (CP) voltage multiplier conceived for high multiplying factors is proposed. The solution exploits a mixed architecture which merges both Cockcroft-Walton and Dickson topologies, by using on-chip 12-V poly-poly capacitors and 3.3-V CMOS transistors, maximizing the output voltage at the minimum silicon size. The proposed CP has been designed to supply a fully integrated driver for miniaturized motors in Micro Electro Mechanical Systems (MEMS) technology. It is conceived to boost the power-supply voltage to values higher than those that either a Dickson (D), Fibonacci (F), Cockroft-Walton (CW) or Serial-Parallel (SP) fully integrated CPs can generate in the selected technology process. Indeed, the output voltage of the former two CPs is limited by voltage constraints of on-chip capacitors while the multiplication efficiency of the latter two is impacted by high values of on-chip stray capacitors. Specifically, the target > 70 V output voltage has to be internally generated starting from the provided minimum power-supply voltage of 3 V. Furthermore, a mathematical model is proposed to evaluate the open load output voltage and the equivalent output resistance.

Fabrication and calibration of nanostructured vanadium-doped ZnO-based micromachined sensor with superior sensitive for underwater acoustic measurement

A high-performance micromachined piezoelectric sensor based nanostructured vanadium-doped zinc oxide (ZnO) film with air-backing has been developed and characterized for underwater acoustic application. The sensing cell with a low foot-print of 2.0 mm × 2.0 mm is fabricated by Micro electro mechanical systems (MEMS) technology using a ZnO-on-silicon-on-insulator process platform. An optimal ratio of piezoelectric coefficient to the relative permittivity is obtained about 6.3 in the Zn0.98V0.02O sensing cell, improving by an order of magnitude compared with other notable piezoelectric films, plays a mainly dominant role in the enhanced piezoelectric response. Calibrations in the standard underwater instrument have demonstrated that the presented sensor could achieve an acoustic pressure sensitivity of −165 ± 2 dB (1 V μPa−1) over a bandwidth 10 Hz–10 kHz, outperforming the same kind of reported devices. The maximum non-linearity is no more than 0.3%, the sensitivity variation is no more than ±0.7 dB in the temperature range from 10 °C to 50 °C, indicating a better stability and higher reliability. The proposed sensor with a superior acoustic sensitivity gives a great application potential in underwater acoustic measurements.

Development of a 70–110 GHz silicon corrugated horn for cosmic microwave background experiment

Next generation cosmic microwave background (CMB) polarization telescope will use large arrays of receiver with nearly 100 000 transition edge sensor (TES) detectors and receiving antennas. Such large TES and antenna array is a big challenge for the fabrication of TES and antennas. A 35-layers silicon-platelet corrugated horn for 70–110 GHz is designed and fabricated based on the micro electro mechanical system (MEMS) technology. Compared with the traditional corrugated horn, the last layer of the 35-layers silicon-platelet is designed with no corrugation to increase the beam symmetry. A parametric HFSS model of the horn was established to evaluate the performance of the horn and effect of fabrication process. The measured S11 and cross-polarization of the fabricated prototype horn are both below −20 dB while the sidelobe at 70 and 90 GHz is below −20 dB. The beam symmetry of the horn is good in 70–110 GHz band. The measured gain is greater than 15 dBi. These results show that the performance of the designed horn meets the requirement of CMB experiment.

High-precision optical fiber Fabry–Perot composite sensor for pressure and temperature

Simultaneous monitoring of pressure and temperature in the skull cavity, kidneys, and cardiovascular organs and sites is urgently needed during clinical consultation and minimum invasive procedures. In this paper, the pressure/temperature fiber Fabry–Perot composite sensor fabricated by the micro electro mechanical system (MEMS) technology was studied. A variable step size fast Fourier transform-Minimum Mean Square-Error (FFT-MMSE) cavity length demodulation algorithm was proposed. This improved the demodulation accuracy and the rate of the cavity length signal. The experimental results showed that the optical fiber Fabry–Perot composite sensor had good response characteristics for pressure and temperature. It could maintain good linearity in the pressure measurement range of 0∼14 kPa and the temperature measurement range of 35∼50 °C. The pressure sensitivity was 9.811 nm/kPa, the temperature sensitivity was 1.707 nm/°C, and the temperature cross-sensitivity was 27.6 Pa/°C. The sensor has the characteristics of small size, fast response speed, high sensitivity, and strong stability. So it has great application potential in the field of biological medicine.

Ultrafine Aerosol Particle Sizer Based on Piezoresistive Microcantilever Resonators with Integrated Air-Flow Channel.

To monitor airborne nano-sized particles (NPs), a single-chip differential mobility particle sizer (DMPS) based on resonant micro cantilevers in defined micro-fluidic channels (µFCs) is introduced. A size bin of the positive-charged fraction of particles herein is separated from the air stream by aligning their trajectories onto the cantilever under the action of a perpendicular electrostatic field of variable strength. We use previously described µFCs and piezoresistive micro cantilevers (PMCs) of 16 ng mass fabricated using micro electro mechanical system (MEMS) technology, which offer a limit of detection of captured particle mass of 0.26 pg and a minimum detectable particulate mass concentration in air of 0.75 µg/m3. Mobility sizing in 4 bins of a nebulized carbon aerosol NPs is demonstrated based on finite element modelling (FEM) combined with a-priori knowledge of particle charge state. Good agreement of better than 14% of mass concentration is observed in a chamber test for the novel MEMS-DMPS vs. a simultaneously operated standard fast mobility particle sizer (FMPS) as reference instrument. Refreshing of polluted cantilevers is feasible without de-mounting the sensor chip from its package by multiply purging them alternately in acetone steam and clean air.

Improved robust Kalman filter for state model errors in GNSS-PPP/MEMS-IMU double state integrated navigation

The integration of Global Navigation Satellite System (GNSS) with Inertial Navigation Systems (INS) has been actively researched and widely applied as it can provide reliable positioning information continuously. In recent years, Micro Electro Mechanical Systems (MEMS) technology achieves rapid development and Micro Electro Mechanical Systems and Inertial Measurement Unit (MEMS-IMU) has aroused wide concern due to its excellent properties in some cases. However, the observations from MEMS-IMU are easy to be influenced by motion state and location environment because of its manufacturing process. It is not easy to judge whether gross errors are in the state model or the observation model by the widely adopted robust filter based on innovation. In this contribution, we present an improved robust filter with a double state model on the basis of the chi-square distribution of the square of the Mahalanobis distance. The vehicle motion model acts as the external constraint information and can be adopted to construct robust statistic with the results from INS mechanization. And then a robust factor was determined to adjust the observation noise covariance matrix. To evaluate the performance of this method, the simulation test and the field test based on locomotive platform of Nottingham Geospatial Institute (NGI) were carried out. According to the results, in the simulation test, the position improvements are 33%, 30% in the north and east directions; in the real test, the loosely and tightly coupled was adopted and the position accuracy can be improved by about 50–60% in the horizontal direction and the improvement of the pitch and the roll accuracy was lower than the azimuth accuracy due to poor observability and experimental scene which is of the characteristics of small elevation change. Therefore, the proposed robust filter could diminish the effect of the gross error from MEMS-IMU and enhance the integrated system.

京都大学大学院工学研究科 進化型機械システム技術産学共同講座（三菱電機）

京都大学大学院工学研究科 進化型機械システム技術産学共同講座（三菱電機）

Improving Linear Projects Georeferencing to Create Digital Models Using UAV Imagery

Global Positioning System (GPS) on Unmanned Aerial Vehicles (UAV) platform relies on Micro Electro Mechanical Systems (MEMS) technology with a precision of 10 m at shooting time at UAV camera stations positions. Nonetheless, obstacles to the GPS signal at the finest flight altitude can prevent accurate camera stations positions retrieval. In this research, three different georeferencing techniques were compared with geometric precision. The first is Direct Georeferencing (DG), which mainly depends on using Navigation GPS onboard without using any Ground Control Points (GCPs). The second is Indirect Georeferencing (IG), which mainly depends on three GCPs used to assist Aero-Triangulation (AT). The third is Modified technique depends on the same three GCPs used in the second method and enhanced location of camera stations usage of the Linear Relation Model (LR Model). The study area was in the south of the Moscow Region, Russia. Threeimaging strips have been taken using the DJI PHANTOM 4 PRO UAV. The accuracy assessment was carried out using image-derived coordinates and checkpoints (CPs) residuals. This study emphasizes that the Modified methodology using enhanced camera stations positions gave better accuracy than using the drone GPS camera stations positions.

Low-Cost MEMS-Based NARX Model for GPS-Denied Areas

Autonomous vehicle navigation has witnessed a huge revolutionary revision regarding development in Micro-Electro Mechanical System (MEMS) technology. Most recently, Strapdown Inertial Navigation System (SDINS) has successfully been integrated with Global Positioning System (GPS). However, different grades of MEMS inertial sensors are available and choosing the convenient grade is quite important. Noises in inertial sensor are mostly treated through de-noising the additive errors to improve the precision of SDINS output. Unfortunately, integration in SDINS mechanization causes a growing in SDINS error output which considered the main challenge in integrating MEMS inertial sensors with GPS. This paper aims to promote the long-term performance of the MEMS-SDINS/GPS integrated system. A new integrated structure is proposed to model the nonlinearities that exist in SDINS dynamics in addition to the error uncertainty in the inertial sensors’ measurements. A robust Nonlinear AutoRegressive models with eXogenous inputs (NARX) based algorithm are designed for data fusion in the proposed GPS/INS integrated system. Validation for the proposed integrated system has been carried out using different field tests data in order to assess the accuracy of the system during GPS denied environment. The results obtained demonstrate that the proposed NARX model is applicative and satisfactory which shows a desired prediction performance.

Design and optimization of MEMS piezoelectric energy harvester for low frequency applications

Piezoelectric vibrational energy harvester (PVEH) suits best for harvesting vibrational energy from the environment due to the simplicity in design, operation, and compatibility with the micro electro mechanical system (MEMS) technology. In this work, the effect of geometrical parameters on the performance of an Aluminium Nitride (AlN) based MEMS PVEH is analyzed in detail and optimized for lower resonant frequency and higher output power. Electromechanical modeling and validation are carried out for an energy harvester with various proof mass shapes. The optimized PVEH is having a trapezoidal beam and a triangular-shaped proof mass. The effect of the amount of proof mass coverage on the performance parameters is also analyzed. The least resonant frequency is found for the design in which the proof mass coverage is 57 % of the overall length of the harvester and the power peaks when the proof mass coverage becomes 80 %. The proposed structure generated output power of 0.24 $$\mu$$ W at a resonant frequency of 158.8 Hz when an input acceleration of 0.5 g is applied. Then an array using the proposed structure is simulated and compared to an array of conventional rectangular energy harvesters and it is found that array using the proposed structure provides 1.79 times higher power at a lower resonant frequency than the conventional array.

A Preliminary Prototype High-Speed Feedback Control of an Artificial Cochlear Sensory Epithelium Mimicking Function of Outer Hair Cells.

A novel feedback control technique for the local oscillation amplitude in an artificial cochlear sensory epithelium that mimics the functions of the outer hair cells in the cochlea is successfully developed and can be implemented with a control time on the order of hundreds of milliseconds. The prototype artificial cochlear sensory epithelium was improved from that developed in our previous study to enable the instantaneous determination of the local resonance position based on the electrical output from a bimorph piezoelectric membrane. The device contains local patterned electrodes deposited with micro electro mechanical system (MEMS) technology that is used to detect the electrical output and oscillate the device by applying local electrical stimuli. The main feature of the present feedback control system is the principle that the resonance position is recognized by simultaneously measuring the local electrical outputs of all of the electrodes and comparing their magnitudes, which drastically reduces the feedback control time. In this way, it takes 0.8 s to control the local oscillation of the device, representing the speed of control with the order of one hundred times relative to that in the previous study using the mechanical automatic stage to scan the oscillation amplitude at each electrode. Furthermore, the intrinsic difficulties in the experiment such as the electrical measurement against the electromagnetic noise, adhesion of materials, and fatigue failure mechanism of the oscillation system are also shown and discussed in detail based on the many scientific aspects. The basic knowledge of the MEMS fabrication and the experimental measurement would provide useful suggestions for future research. The proposed preliminary prototype high-speed feedback control can aid in the future development of fully implantable cochlear implants with a wider dynamic range.

High Sensitive Detection of Volatile Organic Compounds Using Tin Oxide Semiconductor Sensors with Hot-Wire-Type Structures

Introduction Detection of VOCs (volatile organic compounds) has been required because it is detrimental to human health. In particular, in working environment with organic solvents, the need for VOC detectors has grown to reduce the damage to workers. For this purpose, we have developed SnO2 semiconductor sensors with hot-wire-type structures.The hot-wire-type semiconductor sensor can detect ppm concentration gas with a simple structure suitable for mass-production, resulting in practical use in various applications [1]. In this work, we have achieved high sensitivity and selectivity for VOCs by optimizing SnO2 loaded with several metal oxides. Moreover, the newly developed VOC sensor has excellent durability against the poisonous siloxane, leading to commercial products thanks to these advantageous characteristics.To improve convenience for portable use of VOC detectors, we have developed VOC sensors fabricated by micro electro mechanical systems (MEMS) technology to save power consumption [2]. The power consumption of the MEMS VOC sensor was greatly reduced in comparison with conventional hot-wire-type sensors, without sacrificing high sensitivity to VOCs. The low power consumption of the MEMS sensor makes it possible to extend the battery life, which would lead to further spread use of the VOC detectors. Experimental Figure 1 shows the structure of a hot wire semiconductor sensor, which consists of a platinum wire coil and a sintered SnO2 bead. A solution containing several metals was dropped and immersed in the sintered SnO2. Thereafter, metal oxides were supported on SnO2 by current heating to fabricate a hot-wire semiconductor VOC sensor. The coil served as both a heater and electrodes for the semiconductor bead; the total resistance of the sensor (Rs) was approximated by a parallel electric circuit consisting of the coil resistance and the semiconductor one (Fig.2). For the evaluation of the characteristics, the sensor output voltage (V s) was obtained by incorporating the sensor into a bridge circuit and applying a voltage. The operating temperature of the VOC sensor was controlled to be approximately 450 ℃. The sample gas sensitivity was calculated as difference between V s in mixture of air and sample gas (V s gas) and V s in clean air (V s air).Figure 3 shows a cross-sectional schematic of the MEMS VOC sensor. In the MEMS sensor, a Pt micro-heater/electrodes, patterned by using photolithography, was constructed on about 100 μm square insulating membrane cross-linked to the Si substrate. A sensitive layer of SnO2 with thickness of a few tens µm was deposited on the Pt micro-heater by thick film technology. After sintering the SnO2 thick film on the platinum pattern, several metal oxides were added. Results and Conclusions Figure 4 shows the typical gas sensitivity characteristics of the fabricated hot-wire-type semiconductor sensor to various VOCs. The sensor showed high sensitivity for vapors such as acetone, ethyl acetate, and toluene in a concentration range that affects human health. On the other hand, the sensor showed low sensitivity to interfering gases such as methane and hydrogen. These results demonstrate that the sensors have sufficient selectivity for practical use. Optimization of loaded metal oxides successfully controlled oxidation activity of SnO2 optimally, resulting in improved VOC sensitivity and further reduced interfering gas sensitivity. Furthermore, the sensor showed significantly better durability against toxic siloxane gas than the conventional one, resulting in long-life use in real field. The improved durability against siloxane poisoning is attributable to the controlled oxidation activity of SnO2 by loaded metal oxides. The developed sensor is useful for monitoring VOC as a practical detector that can measure in real time.Next, we investigated the MEMS VOC sensors. Quick thermal response owing to the miniaturized structure enabled us to achieve working temperatures (~500 °C) of the sensor only in 30 milliseconds. Thus, we could operate the MEMS sensor in a pulsed voltage mode, in which averaged power consumption was less than 1 mW. We confirmed that the MEMS sensors, even with the pulsed voltage operation, reproduced high sensitivity to VOCs obtained in the conventional sensor. In addition, the MEMS sensor exhibited long term stability for more than two years. The MEMS VOC sensor would contribute to the improvement of working environment with the spread use of VOC detectors.In conclusion, we have successfully developed hot-wire-type semiconductor VOC sensors ready for commercial use. We have also developed VOC sensors fabricated by MEMS technology to save power consumption.