Acoustic transduction in air from two bulk-micromachined silicon structures
is investigated. Both contain silicon diaphragms of the order of 2 mm(2) i
n close proximity to a metallized substrate. One diaphragm is mass-loaded t
he other is not. Their resonant frequencies (70 and 360 kHz) are dominated
by squeeze film trapping of ambient air, and the 4 of each device is about
8. The lower frequency (LF) device is characterized by electrical and acous
tic measurements using a calibrated microphone. Novel diagnostic methods th
at exploit the non-linear nature of the transducer are described. The adequ
acy of calibration by reciprocity is confirmed at 70 kHz and applied to the
high frequency device. An insertion loss of 19 dB is measured, which compa
res well with reports of other silicon-based transducers. Observed losses a
re accounted for by squeeze-film damping applied to the diaphragm-substrate
gap. The ability to control the bandwidth by the squeeze film effect, the
good efficiency, and the relatively standard method of construction could m
ake such ultrasonic transducers useful in specialist applications.