Tiny device harvests energy from the tap of a finger
Tiny device harvests energy from the tap of a finger lead image
With shrinking electronics, batteries and wired chargers have become clunky and prohibitive. The constant work being done by the human body is an untapped source of energy that can be used to power personal devices from natural motions. As a step toward creating a nonobtrusive energy mechanism, Alyssa Zhou and Michel Maharbiz developed a device that harvests energy from the tapping of a finger.
As a finger moves toward the device, it modifies the electric fields along a set of capacitive electrodes in a circuit’s top metal traces. This creates a change in capacitance, which is fed into a charge-pump circuit to charge a capacitor. Once the capacitor reaches a threshold voltage, it can begin to power downstream elements, making it easily integrable onto circuits. In a sense, the device is a single touch pixel that harvests energy from the touch itself.
Zhou and Maharbiz used the device to power a simple logic circuit as a proof-of-concept demonstration. At a tapping rate of about 25 taps per minute, it delivered about three picowatts of power. Though this can be increased with increasing tapping frequency, it is limited by the responsiveness of the electrodes, and a wide range of variables, such as finger placement and the presence of sweat, all impact on operation.
“Energy harvesting can differ significantly from person to person, so understanding these margins and designing to accommodate these variations is important,” said Zhou.
Beyond making incremental improvements to the technology, the authors envision incorporating it into everyday objects to create, for example, interactive activity books and smart clothing.
“Currently, producing energy on the order of picojoules requires us to be more inventive with the application space,” Zhou said.
Source: “Charge-pumping with finger capacitance in a custom electrostatic energy harvesting ASIC,” by Alyssa Yuan Zhou and Michel Martin Maharbiz, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/5.0014008 .
