The study published on Friday in the journal IEEE Sensors described the smart diaper consisting of a passive radio frequency identification (RFID) tag below a layer of super absorbent polymer.

When the hydrogel is wet, the originally insulating material expands and becomes slightly conductive to trigger the RFID tag to send a radio signal to a nearby RFID reader up to one meter away, which in turn can send a notification to a smartphone or computer, according to the study.

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 one meter away.

To test the sensor's performance, the researchers placed a tag within the bottom layers of newborn-sized diapers and wrapped each diaper around a life-sized baby doll, which they filled with saltwater whose conductive properties were similar to human bodily fluids.

They placed the dolls at various distances from an RFID reader, at various orientations, such as lying flat versus sitting upright. They found that the particular sensor they designed to fit into diapers was able to activate and communicate to a reader up to one meter away when the diaper was fully wet.

The researchers said the design is the first demonstration of hydrogel as a functional antenna element for moisture sensing in diapers using RFID.

RFID tags, which don't require batteries, are relatively low-cost and disposable, and can be printed in rolls of individual stickers, similar to barcode tags. They estimated that the sensor costs less than two U.S. cents to manufacture.

Pankhuri Sen, a research assistant at MIT, envisions that the sensor could also be integrated into adult diapers, for patients who might be unaware or too embarrassed to report themselves that a change is needed.

The smart diapers could also help prevent rashes and some infections like urinary tract infections, in both aging and infant populations.