Researchers at the Massachusetts Institute of Technology and Michigan State University have developed a means of adding a moisture sensor to both adult and infant diapers for less than 2 cents a unit — and with a wireless communication range of up to a meter.
“Diapers are used not just for babies, but for ageing populations, or patients who are bedridden and unable to take care of themselves," explains research assistant and co-author Pankhuri Sen. "It would be convenient in these cases for a caregiver to be notified that a patient, particularly in a multi-bed hospital, needs changing."
The solution for that: a passive radio-frequency identification (RFID) tag placed beneath the absorbent hydrogel in the diaper. As the hydrogel absorbs moisture, it swells and becomes mildly conductive — just enough to trigger the RFID tag to transmit a radio alert to a reader unit positioned up to a metre away.
While low-cost moisture sensors are nothing new - many diaper brands include variants that have an alert strip which changes colour when wet - the team's design is the first to include wireless transmission via radio signals; and although there are plenty of Wi-Fi, Bluetooth, and short-range radio sensors already on the market, these typically cost upwards of $40.
The project builds on earlier work modifying RFID tags to act as wireless sensors. performed by Kantareddy at the MIT's Auto-ID Lab two years ago — work which included ensuring that large quantities of sensors in a small area would not cause issues with interference or miscommunication.