Micromachined ultrasonic Doppler velocity sensor using nickel on glass transducers

•A micromachined ultrasonic transducer chip operates in air at 180 kHz.•A nickel on glass micromachining process results in low stray capacitance.•Beampattern testing demonstrates a narrow half angle −3 dB beamwidth of 6°.•A 20 cm × 20 cm planar target is detected at a range of 1.5 m.•Target velocity is measured with a resolution of 6 cm/s at 63 samples per second.

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).