Electric Power Generation
Abstract: There is a well documented need for the small-scale generation of electrical power to power personal electronic devices. We propose here to use a unique aspect of liquid crystals, mechanically tunable dielectric properties, to generate electricity.
If a capacitor is charged, and the capacitance is then changed by pulling the charged plates apart, mechanical work is done and electrical energy is produced. (This is the basis of existing 'heel-strike generators' using isotropic dielectric elastomer capacitors.). We disclose the description of scenarios to similarly charge a capacitor, but instead of pulling the plates apart, we change the capacitance by mechanically changing the dielectric properties of the liquid crystal, and thereby produce electrical energy
In liquid crystals, there is coupling of the flow and director rotation. Flow reorients the director, and, conversely, director reorientation induces flow. The flow induced director reorientation results in a change of the capacitance of the cell. For example, if the liquid crystal molecules are oriented initially perpendicular to the film surface, shear flow will typically reorient them so that they become almost parallel to the surfaces. If the dielectric constant is larger in the initial configuration then in the final one, as is the case for materials with positive dielectric anisotropy, the capacitance of the cell will decrease with shear.
We have discussed an elementary scenario in two different liquid crystal phases (the nematic and the chiral smectic C*) to describe the underlying principles. We found for example that the generated power of 100mm thick single film of a suitable SmC* liquid crystal can produce over 1wat 100Hz, which is even better than the expected maximum power of a few cm thick heel-strike generators of isotropic dielectric elastomers. In addition of these scenarios we anticipate using a broad range of liquid crystal materials, including liquid crystal elastomers, to fully exploit the potential of this mechanism.
The variation of the dielectric constant in liquid crystals by realignment, can be achieved by shear or pressure, is at least an order of magnitude larger than that achievable by dilation of dielectric isotropic elastomers used in existing heel-strike generators. Additionally it offers new and different type of applications, which are not available for the isotropic dielectric elastomers. For example, by placing the liquid crystal in between flexible substrates, or using elastomers with compliant electrodes, the shear flow can be induced by joint movements, such as by knees, elbows or fingers. Sheets of flexible films placed in frames near engines, behind TV sets, stereos, or covered dishwashers would not only absorb and dissipate sound, but would also generate electric power that can charge batteries of small devices such as cell phones, laptop computers, etc.
Inventors: Dr. Peter Palffy-Muhoray, Dr. Antal (Tony) Jakli, and Dr. Bahman Taheri
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