A new method to decrease grating sidelobes level in medical acoustic arrays

The design of a medical acoustic array for a given echographic system is often a compromise between the lateral resolution and the grating sidelobe level. For a fixed number of active channels, the only way to decrease the grating sidelobe level is to decrease the array pitch. This can be done by working with an acoustical pitch smaller than the electrical pitch, which is possible by using an electrical passive interpolation circuit between the electrical channels and the transducers. This method takes advantage of the fact that in echographic systems the sampling of the array is generally limited by the maximum number of electronic channels and not by the minimum technically achievable pitch on the transducer. The theoretical analysis and design of such arrays are described. This technique was used to construct a 3.75-MHz curved array. The result is a 10-dB improvement of the sidelobe level