Capacitive micromachined ultrasound Doppler velocity sensor

An acoustic Doppler velocity measurement system using microelectromechanical systems (MEMS) capacitive micromachined ultrasound transducer (cMUT) array technology is introduced. This low power acoustic velocity measurement system operates in both transmit and receive modes. The device consists of 64 0.6 mm diameter polysilicon and gold diaphragms, and operates at approximately 180 kHz with a quality factor of 30. Computational predictions suggest that in transmit mode the system will deliver a sound pressure level (SPL) of approximately 66 dB SPL at 1 m from the source with an 11 deg, −3 dB beamwidth when driven with a 12 V excitation. In receive mode, the predicted sensitivity is 2.2 mV/Pa at the preamplifier output. Based on experimentally determined electronic noise densities of approximately 4×10−16 V2/Hz, resolution may be as good as 0 dB SPL in a 5 Hz band. This suggests that with good reflection, a range of approximately 8 m (4 m out and 4 m back) is achievable. Velocity resolution is expected to be on the order of 1 cm/s with a 5 m/s maximum measurable velocity. At this point, all predictions are computational. Fabrication will be complete in the next month and experimental characterization of system performance will be presented at the meeting.