Energy harvesting bracelet

A bracelet harvests energy from the wearer’s wrist movements. This energy can be converted into electricity and used to extend the battery lifetime of personal electronics or even fully power some of these devices.

An energy harvesting bracelet (EHB) based on two mutually exclusive circular motion permanent magnetic movers is demonstrated, which is able to capture energy through the natural motions of the wearer’s wrist. The EHB can transform the translational motion in any orientation except the axial into the rotational motion of the movers, which passes through four coil transducers and induces significantly large electro-motive forces across the coils. A prototype EHB is shown to produce power that can charge a capacitor with 470 μF 25 V up to more than 0.81 V during at most 132 ms from any single excitations. With the rapid increase in wearable electronics, more efforts have been focused on harvesting human motion kinetic energy for potential applications in extending the operation time of batteries and ultimately realizing the self-power of wearable electronics.

(a) Photograph of four shake excitation types. (b) Schematic of the up-shake excitation type. (c) Mechanics analysis diagram of the movers under the worst excitation condition.

(a) Photograph of the rotation excitation type. (b) Schematic of the clockwise-rotation excitation type. (c) The corresponding output waveforms. (d) The corresponding charging-discharging curve of a 470 μF 25 V capacitor.

Many different approaches have been taken for scavenging waste biomechanical energy, such as electromagnetic, piezoelectric, and triboelectric effects. The dominant approach is the electromagnetic effect which usually can provide sufficient output power.The translational motion levitating magnet is the most common structure of the electromagnetic energy harvesters (EEHs). To maximize the power output at low frequencies, the design of efficient magnet and coil configurations has been addressed. It shows that the double-repulsion configuration in the moving magnet composite provided the best dynamics (displacement and velocity) and output response (voltage). Removing the stationary magnets, the EEH with the freely movable magnet shows a non-resonant behavior and permits significant power scavenging at low frequencies based on free/impact motion. However, these structures that inevitably bring one of the main difficulties with all previously presented EEHs have been their limited degrees of freedom. They have been limited to only one orientation for proper or ideal operation. If the harvester is tilted at an angle or rotated within the ideal orientation, the harvester output can become greatly limited or eliminated.9 In order to solve this problem, a 2-dimensinal EEH based on a fully symmetric design is presented which is able to operate in any orientation in a particular plane.11 However, the levitating magnet in the 2-dimensional EEH also does translational motion except under the rotation excitation. Otherwise, the disk-type structure is not convenient to wear. Recently, there has been scientific interest in hybrid translational-to-rotational harvesting approaches, which have demonstrated high power density. The harvester outlined in this letter is a hybrid translational-rotary device that uses two mutually exclusive circular motion permanent magnetic movers to harvest human motion kinetic energy in any orientation.