ABSTRACT Aiming at developing miniaturized ultrasonic image sensors with high spatial resolution, this paper proposes multi-layered ultrasonic transducers employing air-gap structure. Theoretical analysis suggests that if the device is optimally designed, its performance is little affected by the layer supporting the air-gap structure, and that low-loss, wide-bandwidth transducers having practical mechanical strength could be developed. The transducer consisting of polymer/Pyrex-glass/ZnO/Pyrex-glass layers was fabricated, and a conversion loss of 11.6 dB and -3 dB relative bandwidth of 7.8% were obtained. The transducer was also applied to nondestructive testing, and its basic performance was shown.
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