One of the downside with current smart wearables is that most need to be recharged quite often, every day, week or month, and we’re still a long way of 10 year battery life offered by typical watches. I’m hopefully that eventually many devices won’t need to be recharged at all as we’ll have made improvements both in terms of power efficiency and energy harvesting using solar, body heat, vibrations and other techniques.
Takakuni Douseki, professor at the Department of Electronic and Computer Engineering of Ritsumeikan University, has been working on micro energy harvesting, and his latest “wireless involuntary urination sensor system” notifies the user when it’s time change the diapers without the need of any battery, instead using energy generated by urine and stored in a capacitor in order to transmit the data wirelessly.
The prototype is using a modified baby diaper with a 320x5mm activated carbon piece, and a 1.8mm aluminum electrode placed between the absorbent and a waterproof sheet. The amount of electricity generated increases with the amount of urine, with the current peaking at the time of “release” as shown in the chart below.
All that electricity is stored in a capacitor, and when the amount of urine reaches a threshold level (80 cm3), the system transmits an ID signal over a wireless connection up to 5 meters. The system may be commercialized later for example to care of patients suffering from incontinence. The research paper about urine energy harvesting and self-powered diaper can be found on IEEE website.
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