In Search of Nikola Tesla Page 154

TECHNICAL APPENDIX Nikola Tesla was one of those pioneers who in their original way open and trace new fields of technology. He own theories, based on experimental observations, about electrical phenomena helped him to develop his polyphase system. Later he entered the even more complicated and new field of high frequency currents. He concentrated on efficient transmission phenomena based on step-up and step-down transformers. Others developed low frequency single-phase a.c. transformers, but he went on to invent polyphase iron-copper transformer to suit his new system of polyphase currents. ee لسما First drawing of Tesla Coil presented in his 1891 lecture With the field of high frequency a.c. he was in completely new territory but quickly discovered that the iron core was a disadvantage in a transformer and so he disposed of the iron and produced the air-core transformer, known since as the Tesla coil. Usually, this transformer was a part of high frequency generator used to produce the highest voltage in the secondary Tesla discovered that the length of wire in the secondary should be about quarter of the wavelength! The operating frequency of this generator is determined mainly by the primary resonant circuit and the secondary circuit is composed of inductance and self-capacitance of the secondary coil. It is interesting that the Tesla coil secondary, without extra 154