LARGE APERTURE HYDROPHONE FOR MEASUREMENT OR CHARACTERISATION OF ACOUSTIC FIELDS

摘要

A device, a large aperture hydrophone and its construction for measurement, prediction and characterisation of propagating acoustic fields is disclosed. The device is uniformly sensitive over its aperture and integrates the acoustic field in a plane. If the aperture of the device is large enough to intercept the entire extent of the acoustic field it effectively provides the integral of the acoustic field over an infinite two-dimensional spatial plane commensurate with the plane of the aperture. A contact electrode coupling is proposed to simultaneously tauten the piezoelectric membrane that bounds the entire active area. One-dimensional Fourier Transform of the output of the large aperture hydrophone provides direct values of the Directivity Spectrum along a line in a direction orthogonal to the plane of the Large Aperture Hydrophone aperture. As such it provides a direct measurement of the Directivity Spectrum in k-space (after Fourier Transformation) along the normal to the plane of the hydrophone. A complete measurement of the Directivity Spectrum can be achieved by angulation of the large aperture hydrophone over azimuthal and polar angles. Inverse three- dimensional Fourier Transformation of the Directivity Spectrum allows quantitative calculation of the acoustic pressure field in space and time. Propagation of the field to other measurement locations is calculated by application of a phase factor in k-space. The angulation data set comprises a complete characterisation of the field. The Directivity, determination of the acoustic axis, centre frequency of the pulse, power density at the focal spot and total acoustic power of the field are easily defined and calculated from the formalism. All the regulatory parameters for medical ultrasound acoustic fields can be calculated from a single set of angulation measures performed at any convenient location in the field. The large aperture hydrophone device can also be used to provide diffraction free measurement of the acoustic properties of materials.