Wearable RFID

The miniaturization of sensors and wireless  systems is generating  explosive  growth in applications  based on  wearable electronic  devices. At the Auto-ID Lab at the University  of Adelaide, in Australia, we are  working with the Queen Elizabeth Hospital  and the Hospital Research Foundation to develop  wearable sensor-equipped passive RFID  tags for use in health-care applications, such  as monitoring the daily activities of the elderly  in hospitals and at home.

 

Part of our research  is aimed at developing lightweight, low-profile,  low-cost  antennas.  It is a considerable challenge to develop antennas  that can be integrated with passive tag  circuitry capable of delivering the power required  to run the tag logic and sensory circuits,  such as accelerometers.

 

In particular, the  antennas need to be concealable, flexible and  designed for comfort, especially during the  wearer’s sleep. It’s also essential that the electrical  connections remain intact when the tags  are worn around the clock.  Another challenge is that most antennas are  easily detuned when located on or near a  human body, resulting in reduced read range.  Thus, the effects of human tissue, such as skin  and fat, in close proximity to the antenna must  be included in design considerations. 

 

To address these problems, we are taking advantage  of recent developments in conductive  fabrics. Instead of using metal foil to construct  an antenna, we use fabrics made from silver  thread and conductive plastics. Generally,  eliminating the effects of the human body on  antenna performance requires the use of large  metal sheets between the body and the antenna  (ground plane). Such designs are not desirable  for a wearable tag, so we use conductive fabrics  to produce a barrier and achieve good performance.  This produces a flexible antenna and a  garment that can be easily laundered.

 

With the cost concern in  mind, we are exploring designs that includes snap-on tags that can be sterilized  and reused. Another is to embroider antennas  into fabric to create more flexible structures  that can be easily integrated into clothing.