High-sensitivity piezoelectret-film accelerometers

Accelerometers based on polypropylene ferroelectret films are described and characterized by frequency response measurements of their sensitivity. For these measurements the ferroelectret sensors are mounted on an electrodynamic shaker and subjected to a well defined acceleration in the frequency range from 10 Hz to 5 kHz, while the charge output of the sensors is measured. Seismic mass, base area of the seismic mass, static pressure on the film, and number of film layers are varied and the influence on the sensitivity and the resonance frequency of the accelerometers is investigated. Sensitivities of more than 20 pC-s2/m at a resonance frequency of about 1 kHz are obtained for a multilayer accelerometer with a seismic mass of about 20 g. In addition, the linearity of the sensors is found to be of good quality. Finally, model calculations assuming a spring-mass-system are discussed for single and multilayer accelerometers and the results are compared with the measurements. Good agreement of measured and calculated data is found.