Twistron Mechanical Energy Harvesters

Mechanical energy harvesters are needed for diverse applications, including self-powered wireless sensors, structural and human health monitoring systems, automotive technologies, and the extraction of energy from ocean waves. Until now, few harvesters have been flexible enough to be used as yarns in textiles, and the performance of such yarns has been poor. Also, conventional harvester materials that can operate without requiring high voltages are unable to harvest the energy of large mechanical deformations. The presently described harvesters can generate up to 250 W of electrical power per kilogram of yarn and require no external energy source to provide biasing. For the important frequency range between 1 Hz and 100 Hz, no other reported harvester material can provide as high a specific power output.

The presented CNT yarn mechanical energy harvesters, termed ‘twistron’ harvesters, convert torsional or tensile mechanical energy into electrical energy without an external bias voltage. Large-stroke, mechanical deformations generate energy in both air and liquid environments, including salt water. Twistron harvesters may be customized with various sizes, coatings, strains, environments, or twist directions while maintaining functionality for a diverse range of applications.

Figure 1 : Self-powered twistron strain sensor woven into a shirt and used for monitoring breathing. When periodically strained by about 10% during breathing, this four-cm-long twistron sensor generated a periodic, peak-to-peak, open-circuit voltage of 16 mV. The inset shows (at two levels of magnification) the harvester woven into a shirt and used to monitor breathing. The yarn electrodes were 4 cm long and 250 µm in diameter.

Technical Summary:

Stretching coiled yarns generated 250 watts per kilogram of peak electrical power when cycled up to 30 hertz, as well as up to 41.2 joules per kilogram of electrical energy per mechanical cycle, when normalized to harvester yarn weight. These energy harvesters were used in the ocean to harvest wave energy, combined with thermally driven artificial muscles to convert temperature fluctuations to electrical energy, sewn into textiles for use as self-powered respiration sensors, used to power a light-emitting diode and to charge a storage capacitor.

Value Proposition:

Twistrons provide a miniaturized form of mechanical energy harvesting that performs well for commercial applications due to their high power density, low maintenance, scalability, giant stroke range, and ability to operate at high power over a broad frequency range without the need for an external bias voltage.

Figure 2 : Performance comparisons with other material-based harvesters. (A and B) Peak power (A) and frequency-normalized peak power (B) versus the frequency at which this peak power was obtained for present and prior-art technologies for piezoelectric (PZ), electrostatic (ES), triboelectric (TEG1 and TEG2), and dielectric elastomer (DEG) generators.

Applications:

Internet of Things – Wireless self-powered sensors
Wearables and electronic textiles for health monitoring and aesthetic design
Environmental Power Generation – Ocean wave power generators (e.g. wave-powered offshore sensors)
Energy harvesting shock absorbers and dampeners for earthquake-proof infrastructure
Automotive - Wireless sensors for vehicles, such as monitoring electric vehicle battery health.

Key Benefits:

Smart Textiles – Yarns may be sewn into responsive fabrics and retain energy harvesting capabilities
Customizable – Harvester is tunable to the desired stroke ranges for particular applications
High Power Density - No other material-based harvesting technology provides a higher reported gravimetric peak power for frequencies up to 600 Hz
Scalable – Delivers similar gravimetric power densities from micrometer-scale harvesters in textiles to parallel devices that harvest ocean energy
Broad Operation Range - Broad frequency range over which these provide high power; works in both air and electrolyte solutions

Publication:

Kim, Shi Hyeong, et al. “Harvesting Electrical Energy from Carbon Nanotube Yarn Twist.” Science, vol. 357, no. 6353, 2017, pp. 773–778., doi:10.1126/science.aam8771.