Mobile Medical Monitoring

Thermally conductive polymer improves armband sensor device

The SenseWear Armband monitoring device, made by BodyMedia Inc., Pittsburgh, PA, uses a combination of sensors that continually gather data about movement, heat flow, skin temperature, ambient temperature and galvanic response, transmitting it wirelessly. The device has already been awarded the Gold medal in the Medical & Clinical products category in this year’s Industrial Design Excellence Awards (IDEA), sponsored by the Industrial Design Society of America and BusinessWeek magazine.

A thermally conductive liquid crystal polymer developed by Cool Polymers, Warwick, RI, was used to injection mold a part the size of a watch battery that acts as a heat pipe to conduct body heat to a heat sensor on the patient’s arm. The data thus collected by this and other sensors, are then transmitted via a wireless connection to a PC or remote server. Design engineers wished to replace traditional diecast aluminum as the heat conductor because they wanted to improve the dimensional accuracy of production parts and reduce weight. According to Mikhail Sagal, engineering manager at Cool Polymers, “our major design challenge was to mold a very small part with thermally conductive plastic that would still maintain the appropriate features for sensors and electronics.”

Prior to parts production, a prototype was tested against an identical part made from aluminum to ensure it would meet the heat transfer and engineering specifications of the customer. The LCP selected provides the required thermal conductivity of 50 W/mK while allowing the design freedom associated with injection molding. Other thermally conductive plastics are available in a variety of base resins and range in thermal conductivity from 2 W/mK (similar to glass) up to 100 W/mK (similar to cast aluminum).

The armband is designed for clinicians and researchers who need to collect continuous and accurate physiological and lifestyle data, anytime and anywhere. This eliminates the need for expensive and cumbersome lab equipment, subjective paper journals, or low-accuracy pedometers and accelerometers. As an added advantage the armband can be enhanced for 2-way communication that enables it to receive customized sensor protocols and user configurations, act as a platform to collect data from other third-party devices, and upload data without removing the armband from the body.

—SG