Energy Harvesters for Wearable Electronics and Biomedical Devices

Abstract

Energy harvesters (EHs) are widely used to transform ambient energy sources into electrical energy, and have tremendous potential to power wearables electronics and biomedical devices by eliminating, or at least increasing, the battery life. Nevertheless, the use of EHs for a specific application depends on various aspects including the form of energy source, the structural configuration of the device, and the properties of materials. This paper presents a comprehensive review of the classification of EHs, notably thermoelectric generators (TEGs), triboelectric nanogenerators (TENGs), and piezoelectric generators (PEGs) that allows a wide variety of devices to be operated. The EHs are discussed in terms of their operating principles, optimization factors, state‐of‐the‐art materials, and device structure, that directly influence their operational efficiency. Besides, the breakthrough performance of each of the EHs listed above is highlighted. From the review and analysis, the maximum output power density of 9.2 mW cm−2, 50 mW cm−2, and 64.9 µW cm−2, respectively, are obtained from the TEG, TENG, and PEG, respectively. Furthermore, recent applications relevant to a specific EH and their output performance, are also enlightened. Eventually, the essential outcomes and future direction from this review are discussed and encapsulated.

Self‐powered technology based on nanogenerators for biomedical applications

“…When TEG is in a temperature gradient environment, holes and electrons spread from the hot side to the cold side, causing a potential difference due to the accumulation of the carries in the cold side. [ 94 ] Figure 1C depicts the working principle of TEGs. The efficiency of TEG is determined by the dimensionless figure of merit of thermoelectric material, which can be specified as where where σ is electrical conductivity, S is the Seebeck coefficient of the thermoelectric materials, k e represents the thermal conductivity of the electron, k lat is the lattice thermal conductivity, and T is the absolute temperature; L , e , n , and define Lorenz number, electrical charge carrier, carrier concentration, and carrier mobility, respectively.…”

Flexible Thermoelectric Generator Based on Polycrystalline SiGe Thin Films

“…The flexible TEG based on the SiGe layers produced an output power of 0.45 µW cm −2 at RT for ΔT = 30 K. These results will enable the development of environmentally friendly and highly reliable flexible TEGs to operate micro-energy devices in the IoT. The power density obtained in this study is comparable to or even better than other energy harvesting technologies such as piezoelectric materials, biofuel cells, solar energy harvesters, and RF harvesters [1][2][3][4]. However, issues remain for practical implementation, in particular ensuring a temperature gradient in the real environment.…”

“…The power density obtained in this study is comparable to or even better than other energy harvesting technologies such as piezoelectric materials, biofuel cells, solar energy harvesters, and RF harvesters [1][2][3][4]. However, issues remain for practical implementation, in particular ensuring a temperature gradient in the real environment.…”

“…Energy harvesting technologies will be essential for creating a sustainable society [1][2][3][4]. In particular, flexible thermoelectric generators (TEGs) will be a key technology for use in ubiquitous sensors and wearable devices in the Internet of Things (IoT) [5].…”

Experimentation of a Wearable Self-Powered Jacket Harvesting Body Heat for Wearable Device Applications

“…In this case, the motion of charge carriers (electrons and holes) leads to a temperature difference across the device [1]. The thermoelectric energy harvester (TEEH) demand is increasing over recent decades, especially in personal gadgets and implantable [2] wearable biomedical devices [3,4]. Immense reduction in portable device power consumption has improved battery's drainage duration in personal electronic gadgets.…”