A High Frequency CMUT Ring Array for Small Spot Size HIFU

Abstract

The spot size of HIFU lesion depends on many parameters like size of the transducer, frequency of operation, sonication time etc. A recently developed CMUT based HIFU application for corneal keratoplasty require high localized temperature rise within a very small confined area as short as 300-500 mu m in length. To simplify the electrical connection requirements for this relatively small sized array, even and odd numbered array elements are electrically bundled and connected to two pads through which the drive signal is applied. As the array is CMUT based, the same RF signal is applied to both element groups with DC bias voltages of opposite polarity resulting in a 180. phase difference to provide Fresnel focusing capability. This also negates the necessity of a high-frequency phased array driver, and replaces it with a single RF signal source. COMSOL simulation of ring arrays in water has been used to verify the FWHM spot length for a Fresnel focusing CMUT based HIFU device, to infer that alternated phase excitation can be used. Fresnel arrays of 1mm diameter are designed, fabricated and tested for such HIFU applications.