Recent announcement about development of a plastic wireless power transmission sheet got me interested in this subject (See Plastic Sheet For Wireless Transmission). As it turns out, people have been interested in wireless power transmission since the early 1800’s, when following Faraday’s discovery of electromagnetic induction, Nicholas Joseph Callan developed an induction coil device, which demonstrated that electrical energy could be transmitted and received without wires (See Wikipedia article on Wireless Energy Transfer). Early successes in transmitting power wirelessly over short distances led to transmission of energy over long distances using electromagnetic radiation such as radio waves and microwaves. In the late 1800’s, “Wizard of the West” and “Master of Lightning” NikolaTesla mesmerized people by his remarkable inventions using high frequency alternating current.
At this stage, I could not resist taking a break and lazily scanning the pictures and stories in my copy of the book by 
Margaret Cheney and Robert Uth (Metrobooks, 2001), “TESLA: Master of Lightning”. What a delightful experience! I also remembered a movie I saw a while back – The Prestige, showing an interesting twist on Tesla’s “magnifying transmitter”, which could magically make a living man disappear in the midst of massive flashes of lightning. Science, Magic and Fantasy – sometimes, the boundaries merge!
Anyway, I digress…
The main purpose of this post is to briefly describe how the 4-layer plastic sheet developed by the University of Tokyo researchers works. I am not an electrical engineer, therefore I don’t claim to understand its circuitry in great detail. However, in simple terms, there are two major parts of this device (See original paper for details):
- Contact-less position sensing sheet (2 layers)
- Power transmission sheet (2 layers)
In the contact-less position sheet, the first layer contains an organic FET (Field Effect Transistor) active matrix and the second layer contains a position-sensing coil array of copper wires looped around in a circular pattern. A 91% change in output voltage of the FET is seen when the distance between the receiver coil (part of the electronic device such as a Light Emitting Diode, LED) and the position sensing coil is reduced to 1 mm. In this way, the exact location of the receiver coil is detected.
In the power transmission sheet, the first layer contains a MEMS switching matrix and second layer contains an array of copper wires looped around in a circular pattern for power transmission. When a voltage is applied to the MEMS switch, its resistance drops allowing passage of alternating current to the transmission coils. Power is now transmitted with high efficiency to the nearby receiving coil through electromagnetic coupling. And there you go – you can now light up your Christmas tree!!
I welcome your comments if you can provide more details on how this system works. Get as technical as you want!
As promised in my previous post, I will now dig deeper into the Thin film organic FET’s. Hang in there….
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