Ultrahigh performance air-coupled transducer based on polyimide aerogel matching layer

Air-coupled piezoelectric ultrasonic transducers suffer from severe acoustic impedance mismatch between piezoelectric resonators and air, rendering them nearly ineffective without matching layers. Commercially available matching layer (∼ 1.1 MRayl) would only allow 5 % of acoustic energy being transmitted from piezoelectric resonator into air, greatly restricted the applications of air-coupled transducers. We made a parylene C coated polyimide aerogel, which has an extremely low acoustic impedance (0.034 MRayl), low attenuation and high mechanical strength. When using this new material as the matching layer, more than 90 % energy can be transmitted from pure piezoelectric ceramic into air. For 1-3 piezoelectric composites, the transducer made of the new matching material produced 537 % enhancement compared with that of a transducer made of commercial matching layer. This giant advance in air-coupled transducers due to the new matching layer brought in many application potentials of airborne ultrasound technology, including non-destructive evaluations of devices that could not be merged into liquid, distance ranging and object detections in self-driven cars and unmanned aerial vehicles.