Thermal Management and Concurrent System Design of a Wearable Multicomputer

Abstract

This paper describes the concurrent system design and thermal management of the Navigator2 which is used as a computerized maintenance manual for aircraft inspection with speech recognition capabilities. The Navigator2 is a wearable computer that includes a novel dual architecture, spread spectrum radio, and variable gain amplifier (VGA) head-mounted display. The semi-custom electronic design includes two electronic boards-a custom designed system board and a 486-based processor board. The system board captures glue logic functions and provides support for two PCMCIA slots, a power management microcontroller, memory backup batteries, and a power supply. The thermal design of the Navigator2 develops concurrently with the overall design in a series of stages. A framework of concurrent thermal engineering consisting of three basic stages is used to maintain interdisciplinary interaction while satisfying thermal design goals. In the first stage of the thermal design, a cooling arrangement that meets the needs of other disciplines is proposed, and an enhanced-conduction thermal design with aluminum heat spreaders and active power-saving is explored. In the second stage, the thermal contact between heat spreaders and electronic components is optimized, and physical experimentation is performed with liquid heat sinks and conductive elastomers as thermal contact interfaces. In the third stage, numerical simulations are performed to ascertain the effectiveness of the thermal design, giving the thermal designer flexibility to change critical parameters and perform sensitivity analyses. A simplified computational model is used to investigate the performance of thermal interface devices and the effect of the heat spreader design on the maximum electronic component temperatures. Although the simplified model proves adequate for thermal design purposes, a detailed geometrically-accurate computational model assesses the adequacy of the exposed heat spreader surface area and predicts temperature distributions with better agreement to the experimental measurements on the Navigator2