Air Coupled Through Transmission of Aluminum and other Recent Results Using MUTs

Abstmct-The air-coupled transmissionof 2.3 MHz micromachined, narrow band devices operating at longitudinal ultrasonic waves through aluminum is 2.3 MHz, These microfabricated ultrasonic transreported. Microfabricated ultrasonic transducers are used to emit and receive the ultrasonic tone ducers (MUTs) have a dynamic range of 110 dB, burst. The signal at the receiver is so dB above and are thus the Only technology capable of air couthe noise floor, which implies a dynamic range of pled through-transmission of longitudinal waves in approximateb 110 dB. The dynamic range is memetals at high frequencies different from the pendently verifled, and transmission through steel is also demonstrated. Air-coupled NDE scans of luresonance. cite plates are presented. An optimized fabrication This paper also presents results indicating that process, based on theoretical understanding of the transducers, enables the experiments. Signifleant MUTs can transmit and receive in liquids with an progress in the fabrication of immersion M U T ~ is insertion loss of 4 dB per transducer. The transducalso in evidence. An insertion loss of 4 dB is reers have a fractional bandwidth of approximately