Capacitive micromachined ultrasound Doppler velocity sensor using a nickel on glass process

Abstract

The design, fabrication, modeling and characterization of a small (1 cm2 transducer chip) acoustic Doppler velocity measurement system using a capacitive micromachined nickel on glass ultrasound transducer array technology is described. The acoustic measurement system operates in both transmit and receive mode. The device consists of 168 0.6 mm diameter nickel diaphragms, and operates at approximately 180 kHz. Computational predictions suggest that in transmit mode the system will deliver an 11 degree -3dB beamwidth ultrasound. Characterization of the cMUT sensor with a variety of testing procedures including acoustic testing, Laser Doppler Vibrometry (LDV), beampattern test, reflection test, and velocity testing will be shown. LDV measurements demonstrate that the membrane displacement at center point is 0.1 nm/V2 at 180 kHz. During beampattern testing, the measured response was 0.1 mVrms at the main lobe with 90 kHz drive at 20 Vpp (frequency doubling causes the acoustics to be at 180 kHz). The maximum range of the sensor is 1.7 m. Finally, a velocity sled was constructed and used to demonstrate measureable Doppler shifts at velocities from 0.2 m/s to 0.8m/s. Doppler shifts are clearly seen as the velocity changes.