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Electricity from Smart Elastic
SEP 07, 2016 16:45 PM
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Electricity from Smart Elastic

By Dr. Peter Harrop

The commercial success of energy harvesting has been almost entirely based on variants of the electric motor and the silicon solar cell. That spans from the bicycle dynamo and wind turbine to the solar roof and solar wristwatch. Nonetheless, off-grid creation of electricity where it is needed and with no emissions should be a market of more than a few billions of dollars – it could be one hundred times that.

Unfulfilled needs: huge gaps in the market

The unfulfilled strong needs span twelve magnitudes of power. There is still no commercial MEMS vibration harvester providing the necessary microwatts. The billions of people huddled over their phones frequently have them die at the most awkward time because there is no acceptable way of charging them on the move –for example from daylight or motion. Solve that and you may provide the similar power at watt level needed for Internet of Things nodes with their multiple sensors, processing and transceivers, wearable technology and the potentially ubiquitous single board computers. Moving up to wave power, there is no commercial success at kilowatts to megawatts output. It will remain a failure as long as it relies on clanking, corroding, unresponsive metalwork.

Elastomers to the rescue?

The newest form of energy harvesting is electrostatic. It is not held back by brittle materials containing nasties like the lead, bismuth, tellurium and arsenic so often seen in advanced photovoltaics, thermoelectrics and piezoelectrics. It uses little more than benign base metals and harmless, low-cost plastics, most of which are elastomers or flexible rugged polymers. Electrostatic energy harvesting involves variants on a capacitor so thin films are the norm, not heavy rotating shafts, magnets or glass. Change the dimensions of a capacitor using gratings or sectored disks as sliding electrodes or simply stretch it and you create electricity. That can be done by oscillating a charge on the dielectric to induce current or by carrying away charge using the newly invented self-priming circuits announced by the University of Bristol in the UK in 2016 or by employing an electret as dielectric because it has an inherent surface bias. Add the option of charge created on the dielectric simply by touching it with a dissimilar dielectric, a semiconductor or a metal: the familiar static electricity we call triboelectricity.

Dielectric elastomer generators demonstrate the highest power

To use the popular jargon, the choice is threefold.  The Dielectric Elastomer Generator DEG was first demonstrated at kW level in 2015 by SBM Offshore leveraging work by Edinburgh and Bristol Universities all in the UK. From 2012, Japanese researchers such as Chiba University, CST/Nihon University and Wits Inc., all in Japan, and Scola Superiore Sant’Ana in Italy did basic work on this. At the microwatt level aspiring to milliwatts, Fraunhofer IZM develops DES as small pieces of elastic sheet.

Electret energy harvesters are first to market

Secondly, the electret energy harvester was developed in only the last few years by THHINK and Sheffield University in the UK and Japanese collaborators such as the University of Tokyo culminating in the first one being commercialised by Omron in Japan 2015. Here they demonstrate up to milliwatts with a potential of watts.

Triboelectric nanogenerators show the greatest versatility

Thirdly, the tribolelectric nanogenerator TENG was invented at Georgia Tech in the USA as recently as 2012 yet about 60 institutions are now working on them showing a virtuosity unmatched by any other form of energy harvesting though nothing is yet on sale. KAIST in Korea is impressive in this respect but the most prolific output comes from Georgia Tech working with the Chinese Academy of Sciences in Beijing and others in China. For example in August 2016 they announced an elastomer TENG sheet that can be placed over a keyboard to generate electricity to power sensors. In the same month, Chinese researchers announced a sprung steel, PTFE and acrylic TENG that can power a calculator or act as a door switch sensor.

A materials play now

Here we have a self-powered sensor directly on the heart of a living pig in China, a self-powered robot camera in your body being developed by SUNY in the USA and a biodegradable elastomer TENG for implants. The University of Wisconsin Madison makes serious power from car tires and there is proof-of-concept of an elastomer blanket over the sea waves generating one megawatt. The elastomers and flexible polymer films involved include PDMS silicones, PTFE, polyimide, PVDF and functionalised PET and FEP. There are potentially rich pickings here for those developing fluoropolymers and artificial rubbers in particular. The potential for commercialization is prioritized and forecasted in the new IDTechEx report, “Triboelectric Energy Harvesting (TENG) 2017-2027”.

Structural electronics

Beyond the exciting new capabilities of elastomers there is a bigger picture here. Structural electronics is a term embracing the replacement of components-in-a-box (think clanking wave generators down to your smart watch) with smart layers or even fabric. Electrics, electronics and load-bearing and protective dumb structure merge into smart material. The air or water balloon or blanket of elastomer for DEG wave power are the structure, the physical protection and the generator in one.

Structural supercapacitors and batteries will leverage energy harvesting structure

Solid state batteries will not shrink and grow at each cycle and they will be non-flammable and capable of forming loadbearing structure incorporating an electricity-producing feature. That electricity generating TENG elastomer film over a keyboard does not go in something: it is the product and it even doubles as a supercapacitor storing the electricity it generates. Universities in Australia, the USA and UK are developing supercapacitor car bodies.     

Often the TENG dielectric doubles as a sensor so you have a self-powered sensor where you cannot distinguish between the two components since they are not components at all. All this is one of the most important megatrends of this century. Energy Independent Vehicles EIV will variously use sails, kites, airship fabric and bodywork that both generate and store electricity again with plenty of contribution from those developing elastomers.  

More information on related topics will be covered at the IDTechEx Show! on Nov. 16-17 in Santa Clara, Calif.




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