LIGHTWEIGHT, AFFORDABLE, AND COMMERCIALLY AVAILABLE MEMS ACCELEROMETER AS SEISMIC SENSORS: FREQUENCY RESPONSE CALIBRATION AND FIELD TEST
Fakhri Rahadian Budi, Bagus Endar B. Nurhandoko
ITB
Abstract
Seismic method has been used as a non-destructive alternative in geotechnical testing. Through this test, several geotechnical parameters can be determined, while mantaining low costs, time and environmental impact. However, seismic wave sensors that are commonly used (geophone), are usually expensive and heavy. Since 2004, there have been several research that develop and prove the capabilities of MEMS accelerometers as cheaper and lighter seismic wave sensors. This study aims to develop a seismic wave sensor based on the MEMS ADXL335 accelerometer, calibrate its frequency response, and determine the field performance of the seismic wave sensor. The frequency response calibration is done in the range of 10-100 Hz, and will be presented as a plot of sensitivity to frequency. A subwoofer was used to simulate sinusoidal movement on a tested accelerometer with a controlled frequency, and on a 10 Hz traditional geophone as a reference. Geophone’s maximum signal gives maximum velocity of the sinusoidal movement, thus by utilizing simple harmonic oscillation equation, maximum acceleration of sinusoidal movement (and later MEMS accelerometer’s sensitivity) could be acquired. High resolution oscilloscope was used on to record MEMS accelerometer and reference geophone output signal during frequency response test. Field test was done using three identical accelerometers with ±40 cm spacing, using sledgehammer to generate seismic wave and 16-bit seismograph to record detected ground vibration. Frequency response calibration shows relatively constant responses 10 – 100 range (±3 dB tolerance towards static sensitivity), proving MEMS accelerometer’s wide bandwidth and superiority in measuring low frequency vibrations. Field test shows accelerometer’s ability to smoothly integrate with a seismograph and detect surface wave in field setting.
Keywords: ADXL335, Calibration, Capacitive MEMS Accelerometer, Field test, Frequency response, Seismic sensors
Topic: Earth and Planetary Sciences