Thermal management of an interventional medical device with double layer encapsulation

Abstract

This paper presents a thermal study of a double-layer encapsulation for an interventional medical device, which operates temporarily inside the human esophagus for cardiac imaging. The surface temperature of test samples, representing the device, was assessed by experiments and numerical simulations. The test samples consisted of a heat source, a heat sink and a double-layer encapsulation consisting of a 3D printed biocompatible polymer (thickness 0.9 mm), with an electroplated Cu inner layer (0, 10, 80 or 150 µm thick). The surface temperature of test samples was measured in a tissue-mimicking thermal phantom at 37°C, with different heat source power levels. Experimental results showed that the maximum steady-state surface temperature could be reduced significantly by a 10 µm thick Cu layer (compared to no Cu layer). Increasing the Cu layer thickness further had a rather small effect, at least for low power levels. The maximum steady-state surface temperature was an exponential function of the Cu layer thickness. Test samples with a Cu electroplated polymer encapsulation and a heat source power of 0.5 W satisfied the maximum temperature limit for thermal safety (43°C) when the Cu layer was thicker than about 80 µm. Simulated surface temperatures were in good agreement with experimental values, for a model using two different thermal contact conductance coefficients (for different materials) for the sample-phantom boundary condition. The simulation model was also used to suggest alternative materials for the outer layer of an encapsulation with a metal inner layer, for reducing the surface temperature.