Acoustical evaluation of a prototype sector-vortex phased-array applicator.

A prototype sector-vortex phased-array applicator for ultrasound hyperthermia was constructed and acoustically evaluated. The array transducer consists of special lead-titanate ceramic elements of 16 sectors and two tracks attached on a element is driven by a complementary pair of power MOSFETs at 750 kHz. An annular focal field approximated by the Mth order Bessel function is theoretically predicted to be formed when the array elements are driven with a phase distribution that rotates M (</=8) times per rotation along a track. A 3-D acoustic field measurement system was constructed using a multichannel membrane hydrophone, and fields from the prototype transducer were measured at various drive modes in water. The measured multidimensional field patterns agree well with theoretical predictions at each mode. Focal acoustic power from the transducer was also measured at various drive modes by deflection of a plate located in the focal region. It is demonstrated that the applicator is capable of producing focal acoustic power at the level required for hyperthermia.