Graded piezocomposite for the construction of air-coupled ultrasound transducer

In some cases of ultrasound nondestructive evaluation, the use of a coupling agent can damage the object being inspected, thus requiring the use of an air-coupled ultrasound transducer. This article presents a specific configuration of a graded piezocomposite of central frequency of 820 kHz to be used for constructing a transducer capable of emitting in the air. The goal is to get a piezocomposite with a higher bandwidth when compared to a type 1-3 piezocomposite of the same electromechanical coupling factor. With a higher bandwidth the graded piezocomposite emits more energy in a wider frequency range. Both piezocomposites were constructed and used for the construction of ultrasonic transducers for emission in the air, and the following parameters were analized: displacement of the front surface of the transducers for the frequency range of 0.5 to 1 MHz, impulse response, and impedance curve.