Design modeling of CMUT´s for medical imaging

The fact that CMUT transducers have not yet made it into commercial products indicates that so far the transducers does not meet the needs of the imaging community. This may be due to low sensitivity for the available arrays, a quality that is improving. But it may also be linked to other problems. One is to maintain high and uniform electromagnetic coupling in the arrays. This is shortly discussed. Another possible reason is linked to neighbor coupling between CMUT´s through the fluid, which leads to resonances. Their dependence on the viscosity in the fluid outside the array is discussed, and how they may be damped by use of lossy uniform layers on top of the CMUT´s. It is also shown how the effects of these resonances may be reduced by use of low impedance amplifiers. Receive amplifiers may be made that does not degrade the signal to noise ratio of the array in reception, even with a large impedance mismatch between CMUT element and amplifier. For many applications medical imaging will soon require full two dimensional (2D) focusing. This requires a high number of independent transducer elements, on the order of several thousands. In turn one then must have at least some focusing electronics close to the CMUT elements. A solution to this problem which assumes that the electronics is integrated between the CMUT arrays and the ultimate backing of the structure is discussed. The discussion assumes that the structure may be considered to be uniform in the transverse direction. Simulations indicate that with improving technologies for bonding of silicon wafers this may be a viable technology.