Methods for determining focal point and delay for ultrasound arrays and multichannel electronics
Abstract: High intensity focused ultrasound is a growing technique for tissue ablation, among other uses, and given its destructive capabilities, there is a need for control of where the energy is delivered. There exist a number of methods for focusing such ultrasound arrays, but these often assume prior knowledge of the impulse response, or require extensive full-system simulations. This thesis explores schemes for calculating impulse and frequency response of simple but still nonhomogeneous media, and implements different focusing methods, the spatiotemporal inverse filter, the Gerchberg-Saxton algorithm, and gradient descent, to test them. With a 128-channel transducer operating at 5 MHz, these techniques are carried out in a simulated 2D setting on water and concrete with first a straight edge and then an oblique one between the two media. With a focus depth of 5 cm, the techniques are able to clearly outperform the uncompensated results, and were able to produce feasible foci even for offset or multiple simultaneous foci locations. Although the optimization-based method did fail to produce adequate results for parts of the test, the overall investigation was seen as a successful venture, and that extension of the techniques to more complex media and 3D settings would be needed before any practical value can be realized.
AT THIS PAGE YOU CAN DOWNLOAD THE WHOLE ESSAY. (follow the link to the next page)