Vibration-Energy-Harvesting System: Transduction Mechanisms, Frequency Tuning Techniques, and Biomechanical Applications

Abstract

Vibration-based energy-harvesting technology, as an alternative power source, represents one of the most promising solutions to the problem of battery capacity limitations in wearable and implantable electronics, in particular implantable biomedical devices. Four primary energy transduction mechanisms are reviewed, namely piezoelectric, electromagnetic, electrostatic, and triboelectric mechanisms for vibration-based energy harvesters. Through generic modeling and analyses, it is shown that various approaches can be used to tune the operation bandwidth to collect appreciable power. Recent progress in biomechanical energy harvesters is also shown by utilizing various types of motion from bodies and organs of humans and animals. To conclude, perspectives on next-generation energy-harvesting systems are given, whereby the ultimate intelligent, autonomous, and tunable energy harvesters will provide a new energy platform for electronics and wearable and implantable medical devices.

Keywords: biomechanical design; energy harvesting; transduction; tuning; vibration.

Figure 1.

a) Organization of this review: from the foundations of materials and design through transduction and the key challenge of frequency tuning to the ultimate goal of autonomous energy harvesting systems. b) Vibration energy-harvesting system: from vibration sources and transduction mechanisms with frequency tuning techniques to biomechanical applications.

Figure 2.

a) Schematic model of generic vibration-energy harvesting. Reproduced with permission.^[50] Copyright 1996, Elsevier. b) Generic power output as a function of the ratio of structure frequency to source frequency for the case where the electrical damping matches the mechanical damping of the system.

Figure 3.

Four mechanisms for vibration-based energy harvesters including: a) piezoelectric energy harvesters including two configurations of cantilever-based and membrane-based geometries, b) electromagnetic energy harvester and c) electrostatic transduction, which is represented by a parallel plate capacitor model, and d) triboelectric transduction, where opposite charges are created and collected at the surfaces of two contacting objects.

Figure 4.

Examples of piezoelectric energy harvesters. a) A bi-resonant piezoelectric EH with two cantilever beams at different resonant frequencies. Reproduced with permission.^[57] Copyright 2016, Elsevier. b) Piezoelectric energy harvesting from flow-induced vibration. Reproduced with permission.^[60] Copyright 2010, IOP Publishing. c) An arc-shaped PZT generator to harvest energy from wind speed at multiple directions. Reproduced with permission.^[63] Copyright 2015, Elsevier. d) A zigzag-beam-shape base two-dimensional concentrated-stress low-frequency piezoelectric EH. Reproduced with permission.^[65] Copyright 2015, AIP Publishing.

Figure 5.

Examples of electromagnetic energy harvesters. a) A tunable electromagnetic micro-generator utilizing applied magnetic forces. Reproduced with permission.^[72] Copyright 2010, Elsevier. b) An electromagnetic EH using four-bar magnet configuration. Reproduced with permission.^[74] Copyright 2011, IOP Publishing. c) An electromagnetic EH with a magnetic mass moving inside a frame-carrying coil. Reproduced with permission.^[78] Copyright 2015, Elsevier. d) Micro-fabricated electromagnetic EH with magnet and coil arrays suspended by silicon springs. Reproduced with permission.^[79] Copyright 2016, IEEE.

Figure 6.

Examples of electrostatic energy harvesters. a) The three most commonly used types of electrostatic energy harvesters with the relative movements of the interdigitated electrodes. Reproduced with permission.^[86] Copyright 2002, ASME. Top: in-plane overlap; middle: in-plane gap closing; bottom: out-of-plane gap closing. b) An electret-free silicon electrostatic energy harvester that was designed for batch fabrication. Reproduced with permission.^[88] Copyright 2009, IOP Publishing. c) A structure that makes use of microball bearings to target low frequency vibrations. Reproduced with permission.^[90] Copyright 2009, IOP Publishing. d) A microscopic close up of an electrostatic EH design with interdigitated comb electrodes. Reproduced with permission.^[91] Copyright 2009, IOP Publishing. e) An EH device that makes uses of a CYTOP electret film that was able to produce a broad frequency bandwidth and a high power density Reproduced with permission.^[93] Copyright 2018, Elsevier.

Figure 7.

Triboelectric nanogenerators. a) The first triboelectric generator and its working mechanism. Reproduced with permission.^[28] Copyright 2012, AIP Publishing. b) Four modes of the working mechanism of TENG: contact-separation mode, contact-sliding mode, single electrode mode and freestanding model. Reproduced with permission.^[26] Copyright 2014, Royal Society of Chemistry. c) The mechanism and materials of a TENG that collect typing energy from a computer keyboard. Reproduced with permission.^[100] Copyright 2016, American Chemical Society. d) A TENG that uses both contact-separation and sliding mode to scavenge vibrational energy from multi-directions. Reproduced with permission.^[98] Copyright 2013, American Chemical Society. e) The schematic (top) and picture of a wearable TENG fabric using 3D orthogonal woven technique to collect energy from human body motions. Reproduced with permission.^[99] Copyright 2017, John Wiley and Sons. f) A ball-shape TENG that can harvester energy in full space using both contact-separation and sliding mechanisms. Reproduced with permission.^[101] Copyright 2014, John Wiley and Sons. g) A platform built based on triboelectric mechanism that is both a vibrational energy harvester and a motion sensor. Reproduced with permission.^[102] Copyright 2013, John Wiley and Sons.

Figure 8.

The principle of tuning methods: a) Schematic of normalized resonance frequency as a function of change in effective mass. b) Schematic of normalized resonance frequency of cantilever geometry-based energy harvester as a function of change in normalized beam length. c) Generic vibration model for energy harvesting of (left) untuned model and (right) tunable model with an added variable stiffness contributing to the effective system stiffness. A parallel variable spring represents the additional stiffness. d) Schematic of normalized resonance frequency as a function of normalized stiffness factor.

Figure 9.

Typical tuning approaches for cantilever-based EH. a) Two-dimensional resonance frequency approach for vibration-based energy via magnetic forces. Reproduced with permission.^[138] Copyright 2016, IOP Publishing. b) SEM photograph of the fabricated tunable device, the stiffness of which is altered by induced electrostatic forces from the tuning voltage. Reproduced with permission.^[142] Copyright 2008, Elsevier. c) A nonlinear piezoelectric energy harvester intended to scavenge energy from diverse mechanical motions. Reproduced with permission.^[64] Copyright 2015, AIP Publishing.

Figure 10.

Tuning approaches for membrane-based EH. a) Simulated energy-generating performance of thin PVDF membrane with respect to variation of radius and thickness of the harvester for the case of stretching the membrane. Reproduced with permission.^[156] Copyright 2014, IOP Publishing. b) A piezoelectric membrane-based energy harvester with induced pre-stress using PZT-5A membrane. Reproduced with permission.^[157] Copyright 2014, IOP Publishing. c) A piezoelectric circular membrane array with series and parallel connections. Reproduced with permission.^[158] Copyright 2011, IEEE. d) A nonlinear SU-8 membrane-based energy harvester via the nonlinear stiffness from stretching the membrane. Reproduced with permission.^[159] Copyright 2015, IOP Publishing. e) Resonant frequency tuning of an electroactive polymer membrane via an applied bias voltage. Reproduced with permission.^[160] Copyright 2018, IOP Publishing. f) Resonant frequency tuning of a hyperelastic membrane via applied tension. Reproduced with permission.^[161] Copyright 2016, Elsevier.

Figure 11.

Biomechanical energy harvesters described clockwise from top right. Heart motion: a single wire generator to harvest energy from a rat’s heart. Reproduced with permission.^[67] Copyright 2010, John Wiley and Sons. Index finger motion: a single wire generator (SWG) attached to a human index finger to produce power output via the bending of the finger. Reproduced with permission.^[68] Copyright 2009, American Chemical Society. Lung, diaphragm motions: A PZT energy harvester evaluated in vivo on the lung and diaphragm of a bovine. Reproduced with permission.^[177] Copyright 2014, National Academy of Sciences. Knee motion: a model for a plucked PZT piezoelectric bimorph for knee-joint energy harvesting. Reproduced with permission.^[189] Copyright 2011, IOP Publishing. Foot strike: an energy harvester using a PZT dimorph to capture heel-strike energy. Reproduced with permission.^[4] Copyright 2001, IEEE. Hand-arm and head motions: a cantilever-based piezoelectric energy harvester used for converting energy from hand-arm and head motions. Reproduced with permission.^[58] Copyright 2018, Elsevier. (Walking, cochlear implant: the intended placement of a cochlear-implant energy harvester within the human skull cavity to utilize kinetic energy from walking. Reproduced with permission.^[190] Copyright 2016, Springer Nature.