MIT News reports researchers have developed low-cost wetness sensors that can be embedded in diapers to sound a clarion call when baby needs a new diaper.
The target market would be not just parents who don't wish to be so attuned to their babies' bodily functions but nurses in maternity wards and, potentially, adults who need diapers but are too embarrassed to keep checking themselves.
Previous efforts have focused on strips that change colors - which forces parents or caregivers to, you know, actually check the diaper - or for more expensive WiFi or Bluetooth-enabled diapers. RFID chips - such as the ones embedded in CharlieCards - in contrast, "are low-cost and disposable, and can be printed in rolls of individual stickers, similar to barcode tags."
The design they came up with can be incorporated in the bottom layer of a typical diaper. The sensor itself resembles a bow tie, the middle of which consists of a typical RFID chip connecting the bow tie’s two triangles, each made from the hydrogel super absorbent polymer, or SAP.
Normally, SAP is an insulating material, meaning that it doesn’t conduct current. But when the hydrogel becomes wet, the researchers found that the material properties change and the hydrogel becomes conductive. The conductivity is very weak, but it’s enough to react to any radio signals in the environment, such as those emitted by an RFID reader. This interaction generates a small current that turns on the sensor’s chip, which then acts as a typical RFID tag, tweaking and sending the radio signal back to the reader with information - in this case, that the diaper is wet.
The researchers found that by adding a small amount of copper to the sensor, they could boost the sensor’s conductivity and therefore the range at which the tag can communicate to a reader, reaching more than 1 meter away.