VERY HIGH FREQUENCY (VHF) SPARSE LINEAR ARRAYS

The objective of the project is to develop a high frequency (50 MHz), high resolution (100 fm) 2mm by 2mm linear phased array for intravascular, endoluminal, ophthalmological and dermatological imaging. Present research and commercial systems all use single element mechanical scanning which can only produce focused image over a limited depth at very low frame rate. Thus, they are susceptible to motion artifacts. A solution would be the development of linear sequenced or phased arrays. Linear phased arrays allow not only beam steering but also dynamic focusing. The problem with phased arrays however is that they are more difficult to design and fabricate due to their smaller aperture. The problems that have to be overcome in the development of very high frequency linear phased arrays are more severe than linear arrays. The element size is even smaller and the electrical impedance larger because many more elements have to be squeezed into a very small aperture. Moreover, acoustic isolation between elements becomes more difficult to achieve. To solve these problems, a sparse array approach was proposed. A novel element reduction strategy, in that a separate transmit and receive array is designed using different element spacing for each array, will be used so that the spacings between the elements are increased without degrading the beam pattern. An increase in spacing is extremely crucial in VHF linear phased array since to avoid grating lobes, the pitch has to be less than /2 which is less than 16 fm at 50 MHz and is difficult to achieve with the current dicing technology. Using the sparse array approach, an initial design indicates that the pitch can be increased to 45 fm. Selecting an element width of 20 fm, the aspect ratio and directivity requirements can be met with a kerf (spacing between elements) width of 20 fm which is still manageable with the dicing saw (K & S 782) that the Resource has. FEA of the design will be performed and fabricated arrays will be tested at Cleveland Clinic. [unreadable]