Air coupled through transmission of aluminum and other recent results using MUTs

The air-coupled transmission of 2.3 MHz longitudinal ultrasonic waves through aluminum is reported. Microfabricated ultrasonic transducers are used to emit and receive the ultrasonic tone burst. The signal at the receiver is 30 dB above the noise floor, which implies a dynamic range of approximately 110 dB. The dynamic range is independently verified, and transmission through steel is also demonstrated. Air-coupled NDE scans of lucite plates are presented. An optimized fabrication process, based on theoretical understanding of the transducers, enables the experiments. Significant progress in the fabrication of immersion MUTs is also in evidence. An insertion loss of 4 dB is reported and transmission experiments show 100 dB of dynamic range with 100% bandwidth.