Design, fabrication, and testing of a meso-scale accelerometer made of spring steel

This paper reports a novel, low-cost, moderately sensitive, meso-scale accelerometer fabricated with spring steel foil and equipped with either a Hall Effect-based proximity sensor or a capacitive sensor. Since the sensitivity of a Hall Effect sensor is low, we attach a displacement-amplifying compliant mechanism (DaCM) to the proof-mass of the accelerometer to increase the overall sensitivity without compromising on its natural frequency. The displacement of the output of the DaCM is measured using the Hall Effect sensor. The voltage-change in the sensor is calibrated for the applied acceleration. The device is fabricated using wire-cut electro-discharge machining (EDM) of EN J42/AISI 1080 spring steel resulting in an overall size of 60 mm × 60 mm × 10 mm including the Hall Effect sensor. Testing revealed that the accelerometer can detect acceleration signals as small as 14 mg. The measured sensitivity of the accelerometer is 71 mV/g. Finite element simulation of the accelerometer showed that its natural frequency is 50 Hz, which is around 40% greater than an accelerometer with similar sensitivity without a DaCM. The design of the DaCM proposed here can be miniaturized further and fabricated with silicon microfabrication processes for enhanced sensitivity and resolution. In a second embodiment of the sensor, the designs of the DaCM and the suspension were modified to make it suitable for differential capacitive sensing. This was also fabricated and tested. This sensor gives 1 mg resolution but shows nonlinear response to changing acceleration over 0-1 g range.