Cooling of Transducer array used for Ultrasound radiation Force

Abstract

This thesis proposed a way to cool an ultrasound transducer. The cooling method is to have a an area on the casing of the transducer that has a high thermal conductivity, and a high emissivity. This layer is meant to passively transfer heat from the casing to the surroundings. This area on the casing is connected to the transducer stack through a copper layer that is separated for the stack by thermal paste. This cooling method was simulated using a two step method. The first step was to determine the amount of heat transferred from the highly conductive area on the casing to the surrounding, assuming constant surface temperature. The second step was to simulate the heat transfer from the transducer stack to the casing assuming evenly distributed constant heat generation in the transducer stack.

The conductive casing that was simulated was a prism surrounding the sides of the transducer stack, but not the top and bottom. This prism was off height 4cm. It was found that the casing material should have as high conductivity and emissivity as possible in order to increase heat transfer. The thickness of thermal paste was found to have a large impact on the heat transfer from the transducer stack to the conductive casing. Thisnecessitates care when applying thermal paste to make sure it has the desired thickness.

The warmest area of the transducer would based on the simulations be close to the backing. In order to increase heat transfer out of the transducer, it was therefore proposed to add a thermal conductive layer just above the backing off the transducer. This method was shown in simulations to be effective in increasing heat transfer. With this added thermal conductive layer the transducer would stabilize around $56C^o$ for a heat generation of 8.3W evenly distributed throughout the transducer.