How Are You Influencing Medical Devices Related to Military?

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By Nelson Gernert

 

The challenge of thermal management for military-related medical devices, the need for extraordinary reliability (to deal with field conditions like sand or salt water), and portability, coupled with increasing demands for devices with "field-replaceable" components make up a set of needs rarely encountered in commercial medical applications.

Our thermal engineers generally rely on passive heat transfer devices, such as heat pipes, to meet these challenges. Heat pipes, without moving parts to fail (a key consideration for ensuring reliability), can be used as stand-alone heat exchangers or form the basis for heat pipe heat sink and other combinations. The straightforward design of heat pipes makes them relatively easy to fabricate and miniaturize, and continual advances in wicking structure technology allow reliable operation in any orientation.

We also make use of advanced materials, such as annealed pyrolytic graphite (APG), to develop thermal components that are smaller, lighter, and more efficient than traditional heat sinks using aluminum or copper. APG can also be encapsulated for applications such as surgical instruments, where it is critical to avoid contact between APG and human tissue.

The area where heat pipe technology most impacts military medical devices is diagnostic imaging, including electronics-rich technologies, such as magnetic resonance imaging (MRI), computerized tomography (CAT scan), ultrasound, and radiography (X-ray). A heat pipe’s time-to-failure performance in the millions of hours makes it ideal for these applications.

The advantages of heat pipes for military medical technology are being reflected in some newly issued specifications. A recent specification for a CAT scan cooling system, issued by a DARPA contractor, involved design for a condenser fin, duct, and forced air supply along with a set of heat pipes. The project may also require the use of a variable-conductance heat pipe using fluid whose vapor pressure responds to tiny variations in temperature. We expect to see more military specifications involving passive heat transfer devices for medical devices, because they provide excellent reliability with relatively low size and weight.

 

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