How Can We Harvest Energy from Human Movement?

By Surbhi JainReviewed by Susha Cheriyedath, M.Sc.May 24 2022

In an article recently published in the journal ACS Applied Energy Materials, researchers discussed the harvesting and application of human kinetic energy.

Study: Overview of Human Kinetic Energy Harvesting and Application. Image Credit: Kotin/Shutterstock.com

Background

Many different types of sensors are used in wearable electronic gadgets, usually contained in a wearable device that is powered by a lithium battery. Future distributed sensing in the human body and clothing, on the other hand, will necessitate distributed micro-nano-energy. 

Human motion can continuously generate energy that can be gathered to power wearable devices and dispersed sensors. In a recent study, different areas of the human body correspond to diverse power generation systems, and different applications correspond to different uses of generated electricity.

About the Study

In this study, the authors discussed the piezoelectric, electromagnetic, and triboelectric energy harvesting technologies from human motions, such as limb swing, joint rotation, force application, organ motion, and fold stretching. The benefits and drawbacks of many newly suggested human energy harvesters were also compared and examined. Potential applications of active sensing and wearable electronic devices powered by human body kinetic energy harvesting were also discussed.

The researchers offered the concept of a human energy and information exchange hub based on energy harvesting as a future perspective. This review summarized human kinetic energy harvesting technology as well as proposed power generation methods and structures.

The team described force application, joint rotation, folding and stretching, limb swing, and organ motion as five types of human body motion energy.

Observations

The energy harvester could create 4.5 mW when walking at a speed of 7 km/h. The self-powered wireless sensor network (WSN) operating duration was 2.0 ± 0.1 s. Four hundred and eighty-two measurements could be extracted from the sensor at intervals of 10 ms, and all data could be transferred to the base station at a 4 m distance.

The miniature freestanding kinetic impact-based hybridized nanogenerator (MFKI HNG) was used in the wireless temperature sensor, which could run continuously for more than 70 seconds after only 6 seconds of excitation. Under 75% strain, the polyethylene oxide/waterborne polyurethane/phytic acid (PWP) composite material was systematically tuned, and the corresponding single electrode device could give a power density of 2.3 Wm².

Under the support of a magnetic spring, the cylindrical magnet array resonated at a low frequency. A 4.3 mW power output was achieved from 0.5g acceleration at 5.5 Hz, which corresponded to a 4.1 mm amplitude. A harvester weighing only 307 grams could create 1.60 mW of power. The energy harvester could deliver an average power of 8.8 mW with a 5 Hz excitation vibration and a load resistance of 104.7 Ω.

The electromagnetic approach was the most advantageous for harvesting energy from joint bending and rotation. Because output power was proportional to the speed of the cutting magnetic induction line, a speed-up structure was essential in the energy harvester design. The piezoelectric approach was the most convenient for harvesting energy from the inertial limb swing because inertial impact energy was easier to harvest from the piezoelectric resonator device.

Flexible triboelectric or piezoelectric technologies were more adaptable for more flexible finger pushing. The generated electrical energy could be employed as a signal in an active sensor if it was proportional to the human motion and state. 

Combining stiffness with the flexibility to achieve hybrid power generation may be a future trend in human kinetic energy harvesting. Wearable devices' active sensing and power supply accomplish their unique functions. The small-signal resolution, vast linear range, high reliability, adaptability, and biocompatibility are key requirements for active sensing. The power supply devices for the generation of power are designed to increase power density and manage power efficiently.

Conclusions

In conclusion, this study elucidated that the power created by a triboelectric material could only be used as an active sensing signal due to the limited area of the human body, and the self-powering of another module of the node of the sensor still depends on the electromagnetic and piezoelectric rigid power generating structure.

The authors mentioned that if the energy efficiency of electromagnetic wave wireless transmission is low, a cable connection is still a viable option. With the advancement of flexible skin, electronics and clothing can be adorned with wires and other 5G electrical connectors, allowing information and energy to be sent throughout the human body. They also believe that the expansion of application scenarios and diversification of sensing functions could be future development trends.

The team proposed that sensor data might be collected by power generation and energy storage nodes, which could then be fused and streamlined using intelligent algorithms. 

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