Oil-damped piezoresistive silicon accelerometers

The characteristics of a 50 g piezoresistive accelerometer are reported. Two different but complementary techniques have been combined in an attempt to achieve a usable product, standard silicon micromachining for the sensitive element and encapsulation in a stainless steel housing filled up with oil. Using oil instead of gas for the damping is more efficient, due to its large viscosity value. Distances for critical damping are one order of magnitude larger, but the sensitivity and the resonance frequency decrease by a factor of two. The major drawback of the oil is the dependence of its viscosity upon temperature. This results in a 10 dB variation of the amplitude at the resonance frequency over a 100 degrees C temperature range. This type of accelerometer might be useful for applications with a restricted temperature range or with a low frequency range.<>