Augmented reality case study

Background
Challenge
Solution
Results

Wearable technology is a growing field where the implementation spans from defense to commercial and industrial applications. The compact and lightweight aspects of augmented reality devices can create challenges and thermal design needs. The following is based on a customer who required thermal displacement designs on their wearable electronic device.

The wearable device involved an array of printed circuit boards (PCBs) which were initially sealed into a plastic housing. Thermal testing revealed high temperature issues on the internal components and the exterior surfaces that touch the body. Original designs had a small heat sink for the CPU but its effectiveness in solving thermal issues was unclear.

The challenges of creating a safe and comfortable exterior temperature, facilitating signals to the antennas and keeping the inside devices cool were presented to the Eaton team. Within a stipulated time, we were to predict and improve the thermal performance of the glasses in a natural convection environment with plastic casing material over the antenna area.

Eaton created a computational fluid dynamics (CFD) model of the existing device and fine-tuned the model parameters to match thermal testing data that was provided. The top aluminum spreader was modified to enhance radiative and convective heat transfer by increasing its effective surface area. Next, the conductive heat transfer throughout the device was optimized to reduce temperature gradients between the hot spots and exterior surfaces. Strategically placed graphite sheets were added to spread the heat while insulating material was used to isolate heat from surfaces that will be in contact with the skin of the user.

To improve the aesthetics of the device, the aluminum spreader was mounted to the PCB using bosses in numerous locations. The PCB itself was used as a part of the thermal system which enhanced performance. Additionally, the gap between aluminum spreader and critical devices on the PCB were filled using thermal interface material.

The baseline simulation results closely met the prototypes thermal test data. The top aluminum spreader was effective in removing heat from the systems. There was significant improvement to the aesthetics and usability by introducing other conductive and insulating materials such as pourable thermal interface material, graphite, foam and the PCB itself.

Heat spreaders

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