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Piezoresistive MEMS Shock Accelerometers

Piezoresistive shock accelerometers, manufactured by MEMS technology, have low power consumption while still providing +/- 200 mV full scale output at acceleration levels greater than 50 kg. The accelerometers are electrically compatible with the same type 4-wire circuit used to condition a strain gauge full bridge and since they have much greater output compared to a strain gauge, the requirement for signal amplification is greatly reduced. They afford a wider operating temperature range when compared to mechanically isolated ICP® accelerometers. Their frequency response, dependent on model, can be uniform from DC (0 Hz) to values as high as 20 kHz. To lessen the severity of response when their resonant frequency is excited, they incorporate squeeze film damping, achieving values of 0.02 to 0.06 of critical. These damping values are much higher than those found in legacy MEMS accelerometers. Since silicon is a brittle material, over range stops are also incorporated to minimize breakage of the sensing element, and then the sensing element is sealed within a hermetic package. At comparable G levels, MEMS technology enables the smallest package size to be attained for individual accelerometers.