The Tesla Coil Army T-Shirt

Tesla invented his famous coil as a result of his research on wireless power transmission, which was his lifelong dream, he pursued inventing numerous brainchilds. At the time of developing the coil he focused on wirelessly supplying gas-discharge light bulbs. To achieve this he aimed at building high frequency, high voltage alternating current sources. He started trying to increase voltage from his own alternator with the use of a Ruhmkorff coil (induction coil or properly high voltage transformer). Neither of his goals were accomplished by the circuit as the voltage and frequency were too low, and furthermore the coil’s iron core overheated due to losses and melting insulation. It took him several steps to finally realise the core needs to be removed and a capacitor added to the primary winding of the coil. The first resulted in increased voltage and the second protected the coil from being destroyed by the excessive voltage and formed a resonant circuit from the primary winding. The voltage on the secondary winding was the highest when it was left open and kept in resonance with the primary winding. The circuit oscillations were spark-gap excited. That formed a resonance transformer, which was the merit of Tesla’s invention. He was granted a patent for it on the 25 April of 1891. Later, in 1914 he added an “extra” coil to further increase output voltage and form an energy transmitter. He called it a “magnifying transmitter”. The T-shirt shows a drawing of it from a patent granted on the 1st of December 1914. The coil never proved being capable of transferring power over long distances, as Tesla dreamt of. According to modern science it is not possible. However the coil contributed to the development of the first spark-gap excited radio transmitters, which soon were superseded by vacuum tube radios. Currently wireless power transmission is again under research as a result of market demand on wireless charging of various apparatus ranging from mobiles to electric vehicles. Coupled coils working in resonance at high frequencies are the most effective and are able to transfer power exceeding 11 kW reaching 90 % efficiency. The T-shirt is a part of the Breakthrough Inventions Collection created to commemorate key discoveries of science and technology. It presents a drawing from the original patent application.