Time-frequency localisation of defects using broadband pulsed arrays

The spatial periodicity of an array of emitters with an alternating polarity structure is utilised to generate a wavefront with a range of interesting properties. This wavefront is generated by simultaneously exciting the elements with a pulse with carefully selected broadband characteristics. The creation of these waves leads to a broadband interference effect that causes the wavefront to cover a large range of solid angles. More interestingly, however, is the continuous variation of the frequency of the wavefront as a function of angle. Whilst this pulsed array system demonstrates many interesting phenomena, it can also be applied to practical scenarios within the field of non-destructive testing. As the generated wavefront propagates through the sample, it will be scattered by discontinuities that may be present in the sample. This scattered wave will have a unique time of flight and frequency, and this information can be used to locate the position of defects. Due to the frequency variation of the wavefront, the angular position of the defect can be calculated from the frequency of the scattered wave. The radial position of the scatterer can be estimated using the time of flight of the wave. This approach has some advantages over the phased array techniques, which are currently utilised within the field of ultrasonic inspection. Whilst phased array techniques are versatile and can control the generated ultrasonic beam, they require complicated electronics and beam-forming algorithms to achieve this. This requirement is avoided with the pulsed array, as all of the array elements are activated simultaneously. Also, as the time-frequency characteristics of the scattered wave maps directly to the polar co-ordinates, only a single measurement is needed to locate a defect. This is in contrast to other ultrasonic methods that only utilise the time of flight information of the scattered wave, and hence multiple measurements are needed to localise a defect.