Energy Harvesting and Storage with Soft and Stretchable Materials

Abstract

Soft robotics can interact with humans safely. 3) Devices built from stretchable materials have a greater mechanical degree of freedom. This allows electronics, displays, and sensors to be integrated into places that would be difficult or impossible with rigid devices and enables new types of human-computer interfaces. It also allows robotics to have enhanced levels of dexterity and complexity in movement (consider the octopus as an inspiring example). 4) Devices that can be deformed elastically can be engineered to have new or emerging properties, such as antennas that change frequency with elongation, [21] intelligent materials that can perform unconventional forms of logic, [22,23] or composites that change thermal conductivity, [24] electrical conductivity, [25] or dielectric properties with deformation. [26][27][28] Most robotic and electronic devices require electricity to function, as shown on the left side of Figure 1A. Electricity can power sensors, enable computation, drive locomotion, and transmit information. Although most devices use electricity from an outlet, such "tethered" devices create notable limitations. In addition to limiting the degree of freedom of robotic materials, plug-in devices must be within a chords-length of a functioning outlet, thereby confining the range of use of such devices. Although battery operated devices can operate for some time without being plugged-in, the need to do so periodically is at best a nuisance that limits the operating time of a device. At worst, it can lead to issues such as lack of compliance with wearable devices (that is, the device is taken off for charging and never put back on) or disruptions in operation (a particular problem for health care devices or remotely deployed devices). Thus, there is a compelling interest in harvesting energy from the ambient to create tetherless devices or even devices that need less charging. Figure 1A (right side) provides examples of applications that may benefit from harvesting, such as internetof-things (IOT) devices, soft robots, wearables, implantables, and deployables (that is, devices sent to remote locations that do not have electrical outlets). Energy Harvesting CategoriesStrategies to harness energy typically convert waste or otherwise unused energy from the ambient into electricity. Although This review highlights various modes of converting ambient sources of energy into electricity using soft and stretchable materials. These mechanical properties are useful for emerging classes of stretchable electronics, e-skins, bio-integrated wearables, and soft robotics. The ability to harness energy from the environment allows these types of devices to be tetherless, thereby leading to a greater range of motion (in the case of robotics), better compliance (in the case of wearables and e-skins), and increased application space (in the case of electronics). A variety of energy sources are available including mechanical (vibrations, human motion, wind/fluid motion), electromagnetic (radio frequency (RF), solar), and ther...

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