Environmental-powered artificial muscle for energy harvesting

Abstract

Artificial muscles based on rotational motion have been developed, and it produces large-work, large-power and stroke with tensile, bending, and torsional actuation in response to external stimuli such as electrical, electrothermal, and eletrochemical. In this field, I approached artificial muscles from two perspectives to utilize them as energy harvesting. The first is to develop self-powered artificial muscles in the external environment, and the kinetic energy of the artificial muscles was converted into electrical energy using electromagnetic induction. There are two main types of self-powered artificial muscles. One type is that torsional and tensile artificial muscle be driven by temperature gradient and fluctuation produced by natural convection. It was fabricated to produce reversible, fast and large torsional stroke using commercially available shape memory polyurethane, nylon, and sewing thread. A coiled 27-μm-diameter nylon muscle fiber can be driven by 64oC fluctuations of air temperature to spin a magnetic rotor to a peak torsional rotation speed of 70,200 rpm for over 300,000 heating-cooling cycles without performance degradation. The other type is hygromorph tensile artificial muscle driven by relative humidity variation. It was fabricated using carbon nanotube yarn infiltrated with poly diallyldimethylammonium chloride. This muscle shows tensile actuation of 78%, work capacity of 2.1 J/kg over 50 times that of human muscle of the same wight, and high-mechancial energy density (1.8 MJ/m3). Using the nylon artificial muscle of this artificial muscle, I present an energy harvester. Both of embodiments of this idea are explored. The one is that torsional actuation of an artificial muscle produces direct-drive rotation of an attached magnet positioned within a purpose-built, three-phase electricity generator. Another is that tensile actuation of an artificial muscle lifts a commercial magnet in the wire coil. About 43% of generated torsional energy was converted to electrical energy using a miniature 3-phase generator, which powered three light emitting diodes during fiber untwist and subsequent retwist. The second is to generate electrical energy from mechanical energy to reverse the artificial muscle, which converts electrochemical energy into mechanical energy. This harvester was made by twisting insertion into carbon nanotube sheet and it is based on inverse mechanism of twisted carbon nanotube yarn muscle driven by electrochemical power. I have two main types of twistron mechanical energy harvesters as (1) torsional mechanical energy harvesters based on CNT yarns that are twisted, but not coiled, which I name “twisted twistron harvesters” and (2) tensile mechanical energy harvesters that are fully coiled by twist insertion, which I name “coiled twistron harvesters”. I call these devices twistron harvesters (using “tron” from the Greek suffix, meaning device), because I have discovered that these electrochemical harvesters operate by using mechanically inserted twist to increase yarn density, and thereby decrease yarn capacitance. The harvesters can convert tensile or torsional oscillation directly into electrical energy, and produce 250 W/kg and 62 J/kg. The improved methods for useful energy harvesting could not only produce an important novel source of electrical or mechanical energy, but also a means to self-powered sensors and actuator for the “Internet of Things”.