Broad band single crystal transducer for contrast agent harmonic imaging

A broadband single element transducer was constructed from single crystal PMN-PT and tested to determine the feasibility of using this material for simultaneous sub-harmonic and second harmonic imaging. The transducer consisted of a 1-3 PMN-PT/epoxy composite with two quarter wave matching layers and a backing. The transducer face was spherically curved to yield a 53 mm focal point. The transducer´s impulse response had a center frequency of 5.2 MHz and -6 dB bandwidth over 130%. The transmit response for tone burst excitation indicated a shift in center frequency to 6.5 MHz and a 6 dB bandwidth of 100%. Receive sensitivity was high at the lower end of the band and decreased with increasing frequency; this behavior was probably due to electrical impedance mismatch. Contrast agent testing using Sonazoid® showed that the second harmonic could be easily detected. The sub-harmonic was not detected due to the center frequency shift under tone burst excitation. Simultaneous sub, and second harmonic testing could probably be accomplished with a lower center frequency and better electrical impedance matching.