Spectrally Tuned Ultrasonic Transducer Array Designs for Inspection of Difficult Materials

Supervisor: Professor Anthony Gachagan

The vision for this PhD programme is to enhance poor SNR inherent in conventional ultrasonic inspection of many 'new' exotic materials developed for higher temperature application in the next generation power plants.

The key issue with these materials is their high acoustic attenuation due to scattering as a consequence of the course granular nature of the material microstructure. This attenuation is highly frequency dependant and the resultant echo will have a lower frequency content than the originating transmitting pulse. Hence, the overall system SNR is low as there is a mismatch with the frequency response of the transducer, which effectively operates under the reciprocity theory in which the transmit and receive responses overlap.

It seems obvious that the receive part of the transducer should be tailored to match this lower spectral frequency range associated with the received echo. But this is not straight-forward to implement in a practical configuration and in general, a single piezoelectric material is used as the transmit-receive device. One approach is to extent the bandwidth of the transducer to ensure that the operating frequency of the transducer encompasses the required transmit/receive frequency range. Although, this also has practical limitations. Hence, this PhD will consider novel array transducer configurations using separate transmit-receive arrangements within a single transducer unit for inspection of difficult materials.

The PhD will cover ultrasonic array transducer design, fabrication and characterisation; electrical interface between transducer and instrumentation; and evaluation of NDE array system on range of industrial test samples.