9C-4 Novel Method for Design and Fabrication of Single Piston Transducers for Extended Depth of Field

Traditional focused transducers use multiple elements with individual delays, or a single element and lens to achieve focusing. These approaches involve significant cost, or acoustic losses respectively, and are not well suited to low-cost applications, for example disposable transducers. In contrast, zone plate transducers use the diffraction pattern formed by a variable excitation over the surface of a single element to achieve focusing. Although this results in an inexpensive focused transducer, the focusing performance degrades with broadband excitation, and contrast is limited. Additionally it is difficult to produce diffraction patterns with an extended focal zone. We have developed a successive projection algorithm to optimize the transducer pattern to overcome these limitations and meet desired focusing properties at several frequencies and ranges simultaneously. Within diffraction limits, this technique is shown to significantly outperform conventional zone plate transducers, in some cases reducing sidelobes by as much as 20 dB. Furthermore we show that the necessary transducer patterns can be produced using off-the-shelf PCB technology, and that within the limitations of our fabrication process, we are able to experimentally validate our algorithm.