Finding where the shoe pinches

A new textile-integrated electronic sensor system measures foot pressure in three dimensions.
© Fraunhofer IIS

A new textile-integrated electronic sensor system measures foot pressure in three dimensions.

© Fraunhofer IIS/Johann Hauer

A textile-integrated sensor system measures foot pressure distribution and sends results to smartphone.

Diabetes patients often have reduced sensation in their feet, making them prone to wounds or painful pressure ulcers. A new pressure-monitoring stocking addresses this problem by monitoring foot pressure and warning the wearer of uncomfortable or harmful pressure spots. In contrast to previous systems, which only provide a short-term pressure reading from the sole of the foot, the special electronic stocking measures pressure distribution on the sole, heel, instep, and ankle in three dimensions.

Around 40 soft pressure sensors record the pressure inside the wearer’s shoe during walking and standing. The sensors are made from a highly flexible soft elastomer silicone film which can be easily integrated into textiles. This film consists of conductive and insulating layers assembled in a screen printing process, and acts as a capacitive pressure sensor. Pressure or strain cause deformations in the film, measurably altering the sensor’s electrical capacitance. Up to 40 of these sensors, each around 1 square centimeter in size, are attached to the stocking in line with orthopedic guidelines and connected to a flexible electronic control unit in the stocking cuff by a conductive polymer thread incorporated into the fabric.

The electronic control unit consists of an ASIC chip, a controller and a Bluetooth wireless interface. The electronics for this flexible application rely on the integration of 40 measurement channels in one ASIC. Wireless data transmission enables the measurement data to be displayed on a smartphone or tablet, alerting the patient if a change in foot posture or load distribution is needed.

The stocking has a wide range of potential applications. It is suitable for long-term monitoring of diabetes patients, gait and posture evaluation for orthopedic purposes, or even for sports and fitness activities. For instance, runners could use the stocking to monitor their running style or foot posture. The innovative measurement system was developed in cooperation with the Fraunhofer Institute for Silicate Research ISC and the University of Würzburg’s Center for Telematics, with support in the form of internal funding from the Fraunhofer-Gesellschaft.