Ritsumeikan University prototyped a "wireless involuntary urination sensor system," which notifies the user of the timing of replacing a paper diaper via wireless communication without using a battery.
The university expects that it will be used at nursing facilities that care patients of urinary incontinence. It demonstrated the system for mass media.
The system carries out wireless communication by using electricity generated by using urine. The amount of urine stored in the diaper is estimated from the interval of signal reception, and the user is notified of the optimal timing of replacing a diaper.
The system does not require a battery for wireless communication, and the paper diaper incorporating electrodes is disposable. The electronic circuit part (for wireless communication, etc) called "sensor" is expected to be repeatedly used.
The system was developed by Takakuni Douseki, who researches micro energy harvesting, etc as a professor at the Department of Electronic and Computer Engineering, Ritsumeikan University. For the demonstration, a commercially-available paper diaper for infants was modified. It contains (1) activated carbon that is 320mm in length and 5mm in width and (2) an aluminum electrode whose width is 1.8mm between absorbent and a waterproof sheet.
The current of electricity generated by the system increases as the amount of input urine increases. Also, at the time of pouring in urine, the current rapidly increases.
"I believe that the difference in current is caused by urine soaking into the fine pores of the activated carbon, realizing a high sensitivity," Douseki said.
Electricity generated from urine is stored in a capacitor in the sensor. When the amount of urine reaches a certain level, the system transmits wireless signals. The number of involuntary urinations and the amount of urine can be estimated because (1) the interval of signal reception shortens in accordance with the amount of input urine and (2) the interval shortens especially at the time of pouring in urine.