| 摘要 |
A variable capacitor comprises two conductive plates with a liquid crystal material having an anisotropic dielectric constant disposed therebetween. The conductive plates are treated with a surfactant to align the liquid crystal molecules in a predetermined direction at the interfaces between the conductive plates and the liquid crystal material. A low-frequency control voltage above a threshold voltage is applied across the conductive plates to orient the molecules of the liquid crystal material so that the molecular axis with the highest dielectric constant aligns parallel to the applied voltage. Upon removal of the control voltage, the liquid crystal molecules resume their original orientation. In this way, the dielectric constant of the variable capacitor is varied between two predetermined values, thus varying the capacitance of the variable capacitor between two discrete values proportional thereto. An alternative control provides continuous control over a range of capacitance values. Such a variable capacitor may be suitably employed in an electrodeless high intensity discharge lamp ballast for maintaining the ballast load in tune during both starting and running conditions.
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