Development of textile sensors to measure anthropometric and pressure information on children's feet
Bobux is a manufacturer of children’s shoes and approached Auckland University of Technology (AUT) to help solve the pain points that their customers and clinicians have through implement new technology within their products. The aim of this research is to embed knitted smart textile sensors in their children’s shoes to sense the growth and development of a child’s feet – specifically foot length and weight distribution. The eventual product is envisaged as an Internet of Things (IoT) device connected to a mobile phone application receiving data meaningful to the parent, clinician, and designers.
In this research, a knitted textile sensor system to measure foot length based on capacitive sensing was developed. Two prototype configurations were evaluated on 14 children, who each inserted their feet for ten seconds inside the instrumented shoes. Capacitance readings were related to the proximity of their toes to the sensor and validated against foot length and shoe size. A linear regression model was developed on capacitance readings and foot length. This regression model was found to be statistically significant (p-value = 0.01, Standard error = 0.08). Results of this study indicated that knitted textile sensors can be implemented inside shoes to measure foot length.
Furthermore, this research developed a low cost, built-in shoe plantar pressure measurement system. This is useful for podiatrists and designers, as they are interested how pressure distribution changes from infants to toddlers. The capacitive sensors were laminated using copper tape sheet on plastic backing with adhesive, elastomer layers, and combination of conductive and non-conductive fabrics. Constructed sensors were characterised using compression tests with repeated loads. Results showed that the sensors exhibited rate-independent hysteresis in estimation of pressure, for which a calibration model was developed. The system can mimic, at lower fidelity, more expensive plantar pressure measurement systems.
This research found that it is feasible to produce low-cost shoe-embedded capacitive sensors that can provide information about the development of children’s feet.