A micromachined array of 168 nickel-on-glass capacitive ultrasound transducers was used to demonstrate a long range Doppler velocity measurement system. By using an electroplated nickel on glass process, the total capacitance of the chip was reduced to 65 pF, resulting in a high signal to noise ratio and allowing an operable range of 1.5 m. The range is limited by room reverberation level, rather than electronic noise. The sensor array operates at a 180 kHz resonant frequency to achieve a half-angle −3 dB beamwidth of 6° with a 1 cm2 die. The cMUT array was characterized using laser Doppler vibrometry (LDV), beampattern measurements, range testing, and the ability to measure the velocity of a moving plate. The sensor is capable of measuring the velocity of a moving reflector with a resolution of 6 cm/s, at an update rate of 0.016 s, and with a range of 1.5 m (3 m round trip).
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