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MIT Witricity — Not So Original After All

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From Feed Line No. 9


by Gary Peterson

For those who believe the 2006 MIT "Witricity" demonstration was the first of its kind, look at this illustration from "Tesla Apparatus and Experiments—How to Build Both Large and Small Tesla and Oudin Coils and How to Carry On Spectacular Experiments With Them," by H. Winfield Secor, Practical Electrics, November 1921.

An experiment showing the action of the A. C. transformer and which can be performed with high frequency currents is shown at Fig. 11 above.  Two coils of wire about 24" in diameter, are constructed with the number of turns indicated in the diagram.  When the primary is connected to the condenser and the spark gap, as shown, the 110 volt 16 C. P. or a 40 watt lamp connected to the secondary, will light up even when the primary and secondary coils are separated a distance of 1 foot or more, depending upon the size of the transformer or spark coil used for the exciter."

And then there is this drawing and accompanying description from the lecture "High Frequency Oscillators for Electro-therapeutic and Other Purposes," Electrical Engineer, November 17, 1898 of a similar apparatus constructed by Tesla himself.


"When it is desired to use small currents of high tension, a secondary coil is resorted to, as illustrated in Fig. 2.  I have found it from the outset convenient to make a departure from the ordinary ways of winding the coils with a considerable number of small turns.  For many reasons the physician will find it better to provide a large hoop H of not less than, say three feet in diameter and preferably more, and to wind upon it a few turns of stout cable P.  The secondary coil S is easily prepared by taking two wooden hoops h h and joining them with stiff cardboard.  One single layer of ordinary magnet wire, and not too thin at that, will be generally sufficient, the number of turns necessary for the particular use for which the coil is intended being easily ascertained by a few trials.  Two plates of large surface, forming an adjustable condenser, may be used for the purpose of synchronizing the secondary with the primary circuit, but this is generally not necessary. In this manner a cheap coil is obtained, and one which cannot be easily injured.  Additional advantages, however, will be found in the perfect regulation which is effected merely by altering the distance between the primary and secondary, for which adjustment provision should be made, and, furthermore, in the occurrence of harmonics which are more pronounced in such large coils of thick wire, situated at some distance from the primary."

MIT WiTricity—not so original after all.
Front row: Prof. Peter Fisher and Robert Moffatt;
second row: Prof. Marin Soljačić;
third row: Andre Kurs, Prof. John Joannopoulos and Aristeidis Karalis.

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