921 research outputs found

    Influence of microphone housing on the directional response of piezoelectric mems microphones inspired by Ormia ochracea

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    The influence of custom microphone housings on the acoustic directionality and frequency response of a multiband bio-inspired MEMS microphone is presented. The 3.2 mm by 1.7 mm piezoelectric MEMS microphone, fabricated by a cost-effective multi-user process, has four frequency bands of operation below 10 kHz, with a desired first-order directionality for all four bands. 7ร—7ร—2.5 mm3 3-D-printed bespoke housings with varying acoustic access to the backside of the microphone membrane are investigated through simulation and experiment with respect to their influence on the directionality and frequency response to sound stimulus. Results show a clear link between directionality and acoustic access to the back cavity of the microphone. Furthermore, there was a change in direction of the first-order directionality with reduced height in this back cavity acoustic access. The required configuration for creating an identical directionality for all four frequency bands is investigated along with the influence of reducing the symmetry of the acoustic back cavity access. This paper highlights the overall requirement of considering housing geometries and their influence on acoustic behavior for bio-inspired directional microphones

    A low frequency dual-band operational microphone mimicking the hearing property of Ormia ochracea

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    This paper introduces a directional MEMS microphone designed for hearing aid applications appropriate to low frequency hearing impairment, inspired by the hearing mechanism of a fly, the female Ormia ochracea. It uses both piezoelectric and capacitive sensing schemes. In order to obtain a high sensitivity at low frequency bands, the presented microphone is designed to have two resonance frequencies below the threshold of low frequency hearing loss at approximately 2 kHz. One is around 500 Hz and the other is slightly above 2 kHz. The novel dual sensing mechanism allows for optimization of the microphone sensitivity at both frequencies, with a maximum open-circuit (excluding pre-amplification) acoustic response captured via differential piezoelectric sensing at approximately โ€“ 46 dB (V) ref. 94 dB (SPL) at the resonance frequencies. The corresponding minimum detectable sound pressure level is just below -12 dB. The comb finger capacitive sensing was employed due to a lower electrical response generated from a ground referenced single-ended output by the piezoelectric sensing at the first resonance frequency compared to the second resonance frequency. The capacitive sensing mechanism, connected to a charge amplifier, generates a -28.4 dB (V) ref. 94 dB (SPL) acoustic response when the device is excited at either of the two resonance frequencies. Due to the asymmetric geometry and the 400 ยตm thick substrate, the device is predicted to perform as a bi-directional microphone below 3 kHz, which is shown by the measured directional polar patterns

    Design and Fabrication of a Novel MEMS Silicon Microphone

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    Design And Fabrication of Condenser Microphone Using Wafer Transfer And Micro-electroplating Technique

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    A novel fabrication process, which uses wafer transfer and micro-electroplating technique, has been proposed and tested. In this paper, the effects of the diaphragm thickness and stress, the air-gap thickness, and the area ratio of acoustic holes to backplate on the sensitivity of the condenser microphone have been demonstrated since the performance of the microphone depends on these parameters. The microphone diaphragm has been designed with a diameter and thickness of 1.9 mm and 0.6 ฮผ\mum, respectively, an air-gap thickness of 10 ฮผ\mum, and a 24% area ratio of acoustic holes to backplate. To obtain a lower initial stress, the material used for the diaphragm is polyimide. The measured sensitivities of the microphone at the bias voltages of 24 V and 12 V are -45.3 and -50.2 dB/Pa (at 1 kHz), respectively. The fabricated microphone shows a flat frequency response extending to 20 kHz.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838

    Survey of Sensor Technology for Aircraft Cabin Environment Sensing

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    The aircraft cabin environment is unique due to the proximity of the passengers, the need for cabin pressurization, and the low humidity. All of these aspects are complicated by the fact that the aircraft is a semi-enclosed structure. There is an increased desire to monitor the aircraft cabin environment with various sensors for comfort and safety. However, the aircraft cabin environment is composed of a large number of factors. Some of these factors can include air quality, temperature, level of pressurization, and motion of the aircraft. Therefore, many types of sensors must be used to monitor aircraft environments. A variety of technology options are often available for each sensor. Consequently, a fair number of tradeoffs need to be carefully considered when designing a sensor monitoring system for the aircraft cabin environment. For instance, a system designer may need to decide if the increased accuracy of a sensor using a particular technology is worth the increased power consumption over a similar sensor employing a more efficient, less accurate technology. In order to achieve a good solution, a designer needs to understand the tradeoffs and general operation for all of the different sensor technologies that could be used in the design. The purpose of this paper is to provide a survey of the current sensor technology. The primary focus of this paper is on sensors and technologies that cover the most common aspects of aircraft cabin environment monitoring. The first half of this paper details the basic operation of different sensor technologies. The second half covers the individual environmental conditions which need to be sensed. This will include the benefits, limitations, and applications of the different technologies available for each particular type of sensor

    Modeling and Characterization of A Pull-in Free MEMS Microphone

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    In this study, we examine the feasibility of designing a MEMS microphone employing a levitation based electrode configuration. This electrode scheme enables capacitive MEMS sensors that could work for large bias voltages without pullin failure. Our experiments and simulations indicate that it is possible to create robust sensors properly working at high DC voltages, which is not feasible for most of the conventional parallel plate electrode-based micro-scale devices. In addition, the use of larger bias voltages will improve signal-to-noise ratios in MEMS sensors because it increases the signal relative to the noise in read-out circuits. This study presents the design, fabrication, and testing of a capacitive microphone, which is made of approximately 2 m thick highly-doped polysilicon as a diaphragm. It has approximately 1 mm 2 surface area and incorporates interdigitated sensing electrodes on three of its sides. Right underneath these moving electrodes, there are fixed fingers having held at the same voltage potential as the moving electrodes and separated from them with a 2 m thick air gap. The electronic output is obtained using a charge amplifier. Measured results obtained on three different microphone chips using bias voltages up to 200 volts indicate that pull-in failure is completely avoided. The sensitivity of this initial design was measured to be 16.1 mV/Pa at 200 V bias voltage, and the bandwidth was from 100 Hz to 4.9 kHz

    3์ค‘ ์ƒ˜ํ”Œ๋ง ๋ฐฉ์‹ ๋ธํƒ€-์‹œ๊ทธ๋งˆ ADC๋ฅผ ์ด์šฉํ•œ ๋””์ง€ํ„ธ Capacitive MEMS ๋งˆ์ดํฌ๋กœํฐ

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    ํ•™์œ„๋…ผ๋ฌธ(๋ฐ•์‚ฌ) -- ์„œ์šธ๋Œ€ํ•™๊ต๋Œ€ํ•™์› : ๊ณต๊ณผ๋Œ€ํ•™ ์ „๊ธฐยท์ •๋ณด๊ณตํ•™๋ถ€, 2022. 8. ๊น€์ˆ˜ํ™˜.๋ณธ ๋…ผ๋ฌธ์—์„œ๋Š” ํŠธ๋ฆฌํ”Œ ์ƒ˜ํ”Œ๋ง ์ ๋ถ„๊ธฐ๋ฅผ ์‚ฌ์šฉํ•œ Capacitive ๋ฐฉ์‹์˜ MEMS ๋งˆ์ดํฌ๋กœํฐ์ด ์ œ์‹œ๋˜์—ˆ๋‹ค. ํŠธ๋ฆฌํ”Œ ์ƒ˜ํ”Œ๋ง์€ ๋ธํƒ€-์‹œ๊ทธ๋งˆ ๋ฐฉ์‹์˜ ์•„๋‚ ๋กœ๊ทธ-๋””์ง€ํ„ธ ๋ณ€ํ™˜๊ธฐ์˜ ์ฒซ ๋ฒˆ์งธ ์ ๋ถ„๊ธฐ์— ์‚ฌ์šฉ๋˜์—ˆ๊ณ  ํฌ๊ฒŒ ๋‘ ๊ฐ€์ง€์˜ ๋™์ž‘์œผ๋กœ ๊ตฌ๋ถ„๋œ๋‹ค. ์ฒซ ๋ฒˆ์งธ๋กœ ์ ๋ถ„๊ธฐ์˜ ์ž…๋ ฅ์—์„œ ๋ฐ˜์ฃผ๊ธฐ ์ง€์—ฐ ์ฐจ๋™ ์ž…๋ ฅ์„ ๋นผ์„œ ์‹ ํ˜ธ ํฌ๊ธฐ๋ฅผ 2๋ฐฐ๋กœ ๋งŒ๋“ค๋Š” ๋ฐฉ์‹. ๋‘ ๋ฒˆ์งธ๋กœ DAC์˜ ํ”ผ๋“œ๋ฐฑ ์ปคํŒจ์‹œํ„ฐ๋ฅผ ์ƒ˜ํ”Œ๋ง ์ปคํŒจ์‹œํ„ฐ๋กœ ์‚ฌ์šฉํ•˜์—ฌ ์ž…๋ ฅ ์ „์••์„ ์ถ”๊ฐ€๋กœ ์ฆ๊ฐ€์‹œํ‚ค๋Š” ๋ฐฉ์‹์ด๋‹ค. ์ถ”๊ฐ€์ ์œผ๋กœ ๊ธฐ์กด์—์„œ ์ƒ˜ํ”Œ๋ง ์ปคํŒจ์‹œํ„ฐ๋ฅผ ์ฆ๊ฐ€์‹œ์ผœ ์‹ ํ˜ธ์˜ ํฌ๊ธฐ๋ฅผ ์ฆํญ์‹œํ‚ค๋Š” ๋ฐฉ์‹๊ณผ ๊ฒฐํ•ฉํ•˜์—ฌ ์‹ค์ˆ˜๋ฐฐ์˜ ์ด๋“์„ ์–ป์„ ์ˆ˜ ์žˆ๋‹ค. ๋˜ํ•œ ์ถ”๊ฐ€์ ์ธ ์ปคํŒจ์‹œํ„ฐ, ํƒ€์ด๋ฐ, ์ „๋ฅ˜ ์†Œ๋ชจ ์—†์ด ๊ตฌ์กฐ ๋ณ€๊ฒฝ๋งŒ์œผ๋กœ ์ด๋ฅผ ๋‹ฌ์„ฑํ•˜์˜€๊ธฐ ๋•Œ๋ฌธ์— ๋ณ„๋‹ค๋ฅธ trade-off ์—†์ด ์‹ ํ˜ธ์˜ ํฌ๊ธฐ๋ฅผ ์ฆํญ์‹œํ‚ฌ ์ˆ˜ ์žˆ์—ˆ๋‹ค. ์ถ”๊ฐ€์ ์œผ๋กœ ํŠธ๋ฆฌํ”Œ ์ƒ˜ํ”Œ๋ง ๋ฐฉ์‹์˜ ์ ๋ถ„๊ธฐ ์‹ ํ˜ธ ์ „๋‹ฌ ํ•จ์ˆ˜ ๋ฐ ์žก์Œ ๋ถ„์„ ๋˜ํ•œ ํฌํ•จํ•˜์˜€๋‹ค. ์šฐ๋ฆฌ์˜ readout ํšŒ๋กœ๋Š” ๊ณต๊ธ‰ ์ „์••์ด 1.8V์ธ 0.18 m CMOS ๊ณต์ •์œผ๋กœ ๊ตฌํ˜„ํ•˜์˜€๊ณ  single-ended capacitive MEMS ํŠธ๋žœ์Šค๋“€์„œ๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ์ธก์ •ํ•˜์˜€๋‹ค. ์ „๋ฅ˜ ์†Œ๋ชจ๋Ÿ‰์€ 520 ฮผA ์ด๋‹ค. ๋งˆ์ดํฌ๋กœํฐ์€ A-weighted ์‹ ํ˜ธ ๋Œ€ ์žก์Œ ๋น„๋Š” 62.1 dBA, ์Œํ–ฅ ๊ณผ๋ถ€ํ•˜ ์ง€์ ์€ 115 dB SPL์„ ๋‹ฌ์„ฑํ•˜์˜€๊ณ  ์นฉ์˜ die size๋Š” 0.98ใ€–"mm" ใ€—^2 ์ด๋‹ค.A triple-sampling ฮ”ฮฃ ADC can replace the programmable-gain amplifier commonly used in the readout circuit for a digital capacitive MEMS microphone. The input voltage can then be multiplied by subtracting a further half-period delayed differential input and using the feedback capacitor of the DAC as a sampling capacitor. This triple-sampling technique results in a readout circuit with sensitivity and noise performance comparable to recent designs, but with a reduced power requirement. CMRR improvement is achieved by subtracting differential inputs and superior noise performance compare to conventional structure, as amplifier noise and DAC kT/C noise is not amplified by triple-sampling structure while the signal is increased by its gain. Triple-sampling also can be operated as a single-to-differential circuit. A MEMS microphone incorporating this readout circuit, fabricated in a 0.18ฮผm CMOS process, achieved an A-weighted SNR of 62.1 dBA at 94 dB SPL with 520 ฮผA current consumption, to which triple-sampling was shown to contribute 4.5 dBA.CHAPTER 1 INTRODUCTION 1 1.1 MOTIVATION 1 1.1.1 MEMS MICROPHONE TRENDS 1 1.1.2 TYPE OF MEMS MICROPHONES 4 1.1.3 PREVIOUS WORKS 7 1.2 MEMS MICROPHONE BASIC TERMS 9 1.3 THESIS ORGANIZATION 12 CHAPTER 2 SYSTEM OVERVIEW 13 2.1 SYSTEM ARCHITECTURE 13 CHAPTER 3 INTERFACE CIRCUITS AND POWER MANAGEMENT CIRCUITS 16 3.1 PSEUDO-DIFFERENTIAL SOURCE FOLLOWER 17 3.2 CHARGE PUMP 19 3.3 LOW DROPOUT REGULATOR 22 3.3.1 DESIGN CONSIDERATION OF LOW DROPOUT REGULATOR 22 3.3.2 IMPLEMENTATION OF LOW DROPOUT REGULATOR 26 CHAPTER 4 TRIPLE-SAMPLING DELTA-SIGMA ADC 31 4.1 BASIC OF DELTA-SIGMA ADC 31 4.2 IMPLEMENTATION OF TRIPLE-SAMPLING DELTA-SIGMA MODULATOR 37 4.2.1 CONVENTIONAL 1ST INTEGRATOR STRUCTURE 37 4.2.2 CROSS-SAMPLING 1ST INTEGRATOR 40 4.2.3 TRIPLE-SAMPLING 1ST INTEGRATOR 43 4.2.4 STF ANALYSIS OF TRIPLE-SAMPLING 1ST INTEGRATOR 47 4.2.5 THERMAL NOISE ANALYSIS OF TRIPLE-SAMPLING 1ST INTEGRATOR 51 4.2 CIRCUIT IMPLEMENTATION OF DELTA-SIGMA ADC 57 CHAPTER 5 MEASUREMENT RESULTS 64 5.1 MEASUREMENT ENVIRONMENT 64 5.2 MEASUREMENT RESULTS 67 5.3 PERFORMANCE SUMMARY 72 CHAPTER 6 CONCLUSION 74 BIBLIOGRAPHY 76 ํ•œ๊ธ€์ดˆ๋ก 79๋ฐ•

    Ultra-sensitive graphene membranes for microphone applications

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    Microphones exploit the motion of suspended membranes to detect sound waves. Since the microphone performance can be improved by reducing the thickness and mass of its sensing membrane, graphene-based microphones are expected to outperform state-of-the-art microelectromechanical (MEMS) microphones and allow further miniaturization of the device. Here, we present a laser vibrometry study of the acoustic response of suspended multilayer graphene membranes for microphone applications. We address performance parameters relevant for acoustic sensing, including mechanical sensitivity, limit of detection and nonlinear distortion, and discuss the trade-offs and limitations in the design of graphene microphones. We demonstrate superior mechanical sensitivities of the graphene membranes, reaching more than 2 orders of magnitude higher compliances than commercial MEMS devices, and report a limit of detection as low as 15 dBSPL, which is 10 - 15 dB lower than that featured by current MEMS microphones.Comment: 34 pages, 6 figures, 7 supplementary figure
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