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).