In this paper, we propose a piezoelectric energy harvester to scavenge the impact energy from human footsteps at low input frequencies. The device consists of an amplification mechanism and piezoelectric bimorphs. When a human foot strikes the proposed harvester, the amplification mechanism deforms the piezoelectric bimorphs in the 31-mode to produce a large mechanical strain, meaning that the output power can be generated with high efficiency. A maximum output power of 27.5 mW was generated by the proposed harvester at an input frequency of 1.5 Hz (representing fast walking), while 18.6 mW was generated at 1.0 Hz (representing slow walking). Comparison experiments also showed that the proposed harvester can produce much a higher output power than that the same harvester operating in the 33-mode under the same working conditions.
The development of wearable electronics and sensors is constrained by the limited capacity of their batteries. Therefore, energy harvesting from human motion is explored to provide a promising embedded sustainable power supply for wearable devices. Herein, the principles, development, and applications of human motion excited energy harvesters are reviewed. The energy harvesters are classified based on the human motions with distinguished characteristics: center of mass motion (COM), joint motion, foot strike, and limb swing motion. According to the motion characteristics, the principles, features, and limitations of different energy harvesters are discussed, and the power generation performances are compared. Finally, various self-powered applications enabled by embedded energy harvesters are introduced, so as to show the great potential of embedded energy harvesting systems in boosting the development of the wearables.
Scavenging energy from human motion is a potential way to meet the increasing requirement of electrical power supply for portable electronics. However, since the conventional energy harvesters may collect both positive and negative work, the users have to pay extra efforts. This work aims at developing a smart energy harvester to accurately identify and capture the negative work of human ankle motion. During normal walking, only the dorsiflexion at stance phase performs negative work. Thus, one-way clutch is employed to filter ankle plantarflexion and mechanical contact switch array is used to disconnect electrical load, avoiding capturing positive work when ankle dorsiflexion is at swing phase. With the one-way clutch and mechanical contact switch array, the energy harvester can effectively target negative work as energy scavenged without consuming electrical energy. A wearable and light prototype is built to test its power output and users’ metabolic expenditure during walking. The energy harvesting system is also modeled and analyzed. The experimental results show that the energy harvester produces an average power of 0.35 W at 4.9 km h−1 while reducing metabolic expenditure by 0.84 W, so as to achieve lower cost of harvesting compared with the previous work.
In this study, a harvesting device embedded into a suspended backpack was developed to harness part of a human's biomechanical energy and reduce dynamic force of the backpack on the carrier. The harvester utilized a spring mass damping system to translate the human body's vertical movement during walking into the rotation of a gear train, which then drives rotary generators to produce electricity. A prototype was built to examine the theoretical study, which showed that the experimental tests agreed with the simulation. Compared with previous work, the harvester in this work had a 40% higher harvesting energy efficiency.
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