Mapping of Three-Dimensional Radiation Field of Ultrasonic Transducers

Piezoelectric transducers convert radio-frequency (rf) electrical signals into mechanical ultrasonic vibrations and are the key elements in all medical and industrial ultrasound. These are used for ultrasonic imaging, NDE, determination of material property and detection/sizing of flaws[l]. In all such measurements complete knowledge of the radiation source, receiver and associated electronics as well as the field inside the immersion fluid or the material can be useful in the understanding of the material properties. The standard information that is provided for these transducers by the vendors has limited value for imaging purposes. The manufacturers provide data in the form of rf reflection from a small target, such as a ball and its frequency spectra to indicate bandwidth. Advanced precision measurements with piezoelectric transducers will require temporal and spatial distribution of the radiation field in the propagation medium. For example, in the measurement of material properties using Lamb Waves or oblique angle time-of-flight[2] measurements, we measure the phase velocity which is dependent upon the angle of incidence. If the transducer element is misoriented inside the enclosed case, any measurements using the radiation field of such a transducer would require either alignment of the transducer field such that the spatial coordinates of maxima in the amplitude and minima in the phase at all the axial distances from the transducer coincide or else a priori knowledge of three-dimensional (3-D) mapping of fields from the transducer. In the latter case, any perturbation to these fields due to the material property variation can be measured precisely. In this paper, we show a method to map three-dimensional and volumetric radiation fields for piezoelectric transducers