Pulser For Piezoelectrics Transducers Used In Non-Destructive Testing
In order to get, at the ultrasonic receiver input, a clear echo pulse, it is very important to apply on the transducer a short high amplitude pulse (hundreds of volts). The pulse frequency is low enough to allow the reception and processing of the informations received from the analysed material between two adjacent pulses, but high enough to ensure an integral control of the material. The piezoceramic disc chattering amplitude is maximum if the pulse frequency spectrum is centered on a frequency fc equal to the piezoceramic disc frequency. Ideally, the excitation pulse falling edge must be 10% to 30% lower than λ/4, where λ is the wavelength corresponding to the piezoelectric disc central frequency. The dimensions of the sonic field surface crossed by the controlled piece, the incidence angle of the ultrasonic beam on the piece- environment interface are essential elements ensuring the efficienty of the ultrasonic inspection method. In the paper a high bandwidth pulse generator for ultrasonic transducer excitation is presented. The generated signal frequency may vary between 2MHz and 17MHz, the pulses falling edge is lower than 10ns, their amplitude is U=300V (a slew rate of 30V/ns); VMOS transistors and bipolar transistors are used as switching devices.
Index Terms- Non-Destructive Testing, pulser,ultrasounds