Qualitative Analysis of MEMS Microphones 16 th ANNUAL
- Slides: 44
Qualitative Analysis of MEMS Microphones 16 th ANNUAL 2004 INTERNATIONAL MILITARY & AEROSPACE / AVIONICS COTS CONFERENCE, EXHIBITION & SEMINARS Walter C. Babel III Qamar A. Shams James F. Bockman SAIC NASA Langley Research Center
Introduction MEMS Microphones are desirable for NASA applications because they have: • Small Volume • Low Mass • Low Power • Low Voltage • Low Cost Before they can be used in mission-critical applications, they need to be thoroughly tested
B&K 4134 Microphone Overview • Very High Quality • Industry Standard • PULSE System/Software • High Voltage Required
Electret Microphone Overview • Small • Cheap • Lower Quality
MEMS Microphone Overview • Omnidirectional • 0. 5 m. A current draw • Free-plate design • Higher Temperature Acoustical Wave Floating Diaphragm Insulated Spacers Backplate
General Comparison
MEMS Capacitive Microphone Design • Is an electrostatic transducer Acoustical Wave • Capacitance change due to an external mechanical input (electrostatic transducer) • Clamped diaphragm introduces nonlinearities associated with in-built residual stress in the diaphragm • The Si. Sonic design uses a flat free-plate that is held in proximity to the back plate by electrostatic attraction. • As diaphragm is a free-plate (it has no edge moments and has no tension), it has higher fidelity than a clamped arrangement. Backplate Airgap Clamped Diaphragm Acoustical Wave Floating Diaphragm Insulated Spacers Blackplate
Si. Sonic MEMS Microphones SP 0101 NZ • 10 K Ohms Output impedance • 0. 5 m. A max. current drain SP 0102 NC • 100 Ohms Output impedance • 0. 25 m. A max. current drain SP 0103 NC • 100 Ohms Output impedance • 0. 35 m. A max. current drain • Integrated Amplifier SP 0101 NZ SP 0102 NC SP 0103 NC
Basic Structure of MEMS Microphone Diaphragm Spacers Base
SP 0101 General Outline Microphone Diaphragm Signal Power and Detection Circuit OUT Charge Pump
SP 0102 General Outline Microphone Diaphragm Signal Power and Detection Circuit OUT Charge Pump
SP 0103 General Outline Microphone Diaphragm Signal Power and Detection Circuit OUT Charge Pump 20 d. B Amplifier
Basic Functional Analysis (Clamped and Free floating diaphragm) The model of clamped and free floating movable plate capacitor is shown by: where F is the electrostatic attraction force caused by supply voltage V. The mechanical elastic force FM can be expressed as: where K is a spring constant and is assumed to be linear. FE can be calculated by differentiating the stored energy of the capacitor w. r. t. the position of the movable plate:
Frequency Response Analysis Overview • Measures output of microphones as frequency of sound source is varied • Frequency changed from 100 Hz through 50, 000 Hz • Non-linearities (power vs. Sound Intensity) of speaker system factored out
SP 0101 NC 3 / SP 0102 NC 3 / SP 0103 NC 3 Frequency Response Testing Hardware MEMS Microphone High-Pass Filter (10 Hz) nx Amplifier nx Buffer Software FFT Channel Select Hard Disk Voltmeter
Anechoic Chamber Test Setup
MEMS Microphone Comparison Amplitude (V) 100 -10000 Hz Frequency (Hz)
MEMS Microphone Comparison Amplitude (V) 100 Hz – 25 k. Hz Frequency (Hz)
MEMS Microphone Comparison Amplitude (% of 1 k. Hz Value) 100 Hz – 10 k. Hz Frequency (Hz)
MEMS Microphone Comparison Amplitude (% of 1 k. Hz Value) 100 Hz – 25 k. Hz Frequency (Hz)
MEMS Array Test Layout Anechoic Chamber MEMS Array Speaker Lab. VIEW Hardware Amplifier
MEMS Array Close-Up Numbering Convention MEMS Array Audio Source
MEMS Array Frequency Data 100 – 10000 Hz
MEMS Array Frequency Data 100 – 50000 Hz
MEMS Array Frequency Data 100 – 10000 Hz
MEMS Array Frequency Data 100 – 10000 Hz
MEMS Microphone Resonance Problem As can be seen from the last slide, testing showed evidence of sharp discrepancies between the B+K standard and the MEMS microphones tested Although many of the discrepancies can be attributed to differences in holder types and not the microphones themselves the data seemed to indicate mechanical resonances in the MEMS diaphragm
MEMS Microphone Resonance Data
MEMS Microphone Resonance Data Normalized to 1000 Hz
MEMS Microphone Resonance Reduction Filter
MEMS Microphone Resonance Reduction Filter
Directionality Testing Overview Linear Testing • Used to determine location of sound source ? ? Rotational Testing • Used to determine “omnidirectionality” of microphone
Linear Array Directionality Testing Linear Testing • Eight equidistant MEMS microphones • Lab. VIEW acquires data • Weighted average determines sound location in x-axis
Rotational Directionality Testing Anechoic Chamber Computer Lab. VIEW Hardware Speaker Microphone Stepper Motor 50 x Amplifier Stepper Motor Control Board 12 V/1 A Power Supply
Rotational Directionality Testing Rotational Testing • MEMS microphones tested against electret • Rotated through 360 degrees in 3. 6 degree steps • “Omnidirectionality” dependent on package style • For similar packages, electret and MEMS are similar Note: Circle has radius of 1. 5 volts
Background Noise Measurement of MEMS Microphones (MEMS Microphone isolated from ambient sounds and vibration) • Acoustic isolation is achieved by means of high vacuum. • Microphone remains close to room temperature and pressure • Attainable levels of isolation (e. g. , -155 d. B at 40 Hz) enable noise measurements at frequencies as low as 2 Hz. )
Background Noise Measurement in Acoustic Isolation Vessel B&K ½” Mic (B&K 4134) PC Monitor Scan Frequency
Environmental Testing Overview No Change Humidity Testing • Preliminary environmental tests • Lab. VIEW acquires data • No functional change for large humidity range
Radiation Testing Overview Co-60 Cobalt-60 gamma source 50 x Amplifier V Radiation Testing • Preliminary radiation exposure tests (Co-60) • Capacitive elements = radiation detectors • No functional change for 4000 kpm (DC offset, noise) o’scope
Current MEMS Microphone Work
Current MEMS Microphone Work
Current MEMS Microphone Work
Current MEMS Microphone Work
Conclusions MEMS Microphones are adequate for many distributed or disposable systems External circuitry is currently required to minimize effects of resonance of MEMS units Savings in space, weight, and cost make them useful for certain NASA applications, but cannot be considered a “replacement technology” at this time.
- Directional properties of microphones
- Nintendo mems
- Mems stiction
- Mems magnetic actuator
- Hagen poiseuille law
- Sugar mems
- Mems gyroscope
- Sensata technologies wikipedia
- Mems accelerometer
- Mems inertial navigation system
- Mems cantilever beam
- Mems
- Is mems a female
- Mems
- Mems mirror
- Mems
- Mems
- Mems micromirror
- Max en mems
- Mems speaker
- Mems clean room
- Mems
- Memsag
- Annual cash flow analysis
- Annual worth method
- Annual worth example
- Annual cash flow analysis
- Rumus present worth
- Future worth analysis adalah
- What is capital recovery factor
- Annual worth analysis
- Holistic qualitative or quantitative
- Ualitative
- Qualitative vs quantitative
- Power bi for qualitative data
- Acrolein test
- Molisch test positive result
- Principles of qualitative data analysis
- Qualitative analysis of organic functional groups
- Multiple regression analysis with qualitative information
- General chemistry with qualitative analysis
- Quantitative vs qualitative data collection
- Qualitative analysis skills
- Semi quantitative analysis definition
- Qualitative text analysis