Inductive switching of cholesteric liquid crystal display device
View Patent ↗A system including a cholesteric liquid crystal (ChLC) display device and an erasing device. The display device (e.g., a writing tablet, liquid crystal paper) is inductively coupled to the erasing device for inductively erasing an image on the display device. Also featured is a ChLC display device that can be inductively erased.
1. A system comprising: a writing tablet including a cholesteric liquid crystal layer on which applied pressure changes reflectance of the liquid crystal and forms an image, an erasing device, wherein said writing tablet is inductively coupled to said erasing device, and said erasing device provides voltage pulses that induce voltage pulses that erase the image on said writing tablet, wherein said erasing device includes a primary coil electrically connected in parallel with a first capacitor and attached to a waveform generator, and wherein said writing tablet includes a secondary coil.
2. The system of claim 1 , comprising associated electronics, wherein said associated electronics includes a second capacitor, said second capacitor being in parallel with said secondary coil.
3. The system of claim 2 wherein said first capacitor and said primary coil form a first resonant circuit, and said second capacitor and said secondary coil form a second resonant circuit, and wherein a resonant frequency of the first resonant circuit and a resonant frequency of the second resonant circuit are substantially equal to a frequency of said voltage pulses provided by said waveform generator.
4. The system of claim 2 wherein said writing tablet comprises display electrically conductive layers disposed on either side of said cholesteric liquid crystal layer, substrates that sandwich said cholesteric liquid crystal layer and said display electrically conductive layers between said substrates, and electrical conductors that interconnect said secondary coil and said associated electronics with said display electrically conductive layers, wherein said voltage pulses are applied from said primary coil to said secondary coil.
5. The system of claim 4 wherein said secondary coil includes a printed conductive film on one of said substrates.
6. The system of claim 1 wherein said erasing device does not physically contact said writing tablet during said inductive coupling.
7. The system of claim 1 wherein said induced voltage pulses are AC voltage pulses that have an amplitude and frequency that result in said erasing of said writing tablet such that a reflective said image on said writing tablet is changed to an essentially transparent focal conic texture.
8. The system of claim 1 wherein said voltage pulses and said induced voltage pulses are AC voltage pulses.