Oudin coil

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Oudin coil used for medical 'electrotherapy', 1907.

An Oudin coil, also called an Oudin oscillator or Oudin resonator, is a disruptive discharge coil wired as a transformer designed to produce high voltage arcs and discharges, similar to a Tesla coil. It was invented by French physician Paul Marie Oudin and physicist Jacques d'Arsonval in 1882 (Due to a patent dispute a US patent was not granted until 1889). The device is a high frequency current generator which uses the principles of resonant electrical circuits. It produces an antinode of high potential. The high-voltage, self-regenerative resonant transformer has the bottom ends of the primary and secondary coils connected together and to ground. Oudin coils generate high voltages at high frequency, but produce lower currents than other disruptive discharge coils (such as the later version of the Tesla coil). The Oudin coil is modified for greater safety.

The primary coil contains seven turns of wire arranged into a large inductor which has about 0.01mH inductance. It is connected to a capacitor back via a spark gap. The capacitor bank has capacitance 0.03uF and is rated to a peak voltage of 20kV. The capacitor is charged directly from a 12kV transformer capable of delivering up to 50mA of current. When the potential across the capacitor reaches around 10kV the spark gap breaks down and the capacitor discharges violently through the inductor followed by a rapid ring down of the LC circuit formed between the capacitor and primary coil through the ionized spark gap.

The frequency of the current produced is 184 kHz defined by the self-resonant frequency of the secondary coil (which matches the resonant frequency of the primary oscillations for maximum effective Q of the coupled system). The corona streamers are at peak potentials of around a million volts. As well as high frequency discharge (which is best demonstrated in the absence of any room light) there is a disruptive transient discharge caused by the 100 Hz spark exciter at the base of the coil. This discharge is extremely powerful and should not be drawn off except by using a wand that is well fixed to the bottom of the secondary coil. The high frequency corona can be taken by the hand without discomfort although it is best to draw off the corona using a firmly held metal rod.

When over-riding the spark excited Tesla action and incorporating a high frequency signal generator, the impedance matching is of crucial importance. The Q of the secondary may be several hundred and so the on-resonance primary voltage need only be a few tens of volts to achieve several hundreds of thousands of volts at the top electrode of the Tesla coil secondary. Many hundreds of thousands of volts can be achieved with a few hundred volts on resonance in the primary which must then have a Q of hundreds to keep the power demands of the primary high frequency supply to a reasonable value, say a few hundred Watts. In a practical design it would be advisable to produce a 300v 184kHz 1kW signal source, which although not a trivial project, is the key to coupling enough power to the secondary. The impedance of the primary on resonance must be at least 100 ohms. This is achievable using a good 1kV polypropylene capacitor and good connections throughout the primary resonant circuit. Provided that the primary circuit is exactly on resonance with the Tesla coil secondary's self resonance with whatever choice of electrode is preferred, then the potential at the top electrode of the Tesla secondary will be kQ times 300v. For example, to obtain a mega volt of 184kHz energy at the top of the Tesla secondary, it is required to have kQ = 3000. If the turns ratio can be assumed to contribute a factor of only 10, then the Q of the secondary needs to be at least 300 which the supplied polythene secondary certainly satisfies.

Tools such as the Oudin Coil have been used since the end of the 19th century as tests on tissue coagulation. As first tests on animals, the results were promising that the radio frequencies could destroy cancer cells without damaging nearby tissue. Arsene D’Arsonval (French physicist and physiologist 1851-1940) would be the first to test this theory. Paul Marie Oudin (1851-1923) would later join two D’Arsonval solenoids (one smaller than the other) and named this machine “resonator.” Thus, the Oudin coil was made and used for the destruction of specific tissues in the body with minimal damage to surrounding cells.

From the Oudin coil, also known as the Oudin resonator, there was also a current that generated from it due to the high frequency. This current, known as the Oudin current, has been widely used for medical uses or attempts for medical uses. According to Anup Patel, Robert H. Quint, and Gerhard J. Fuchs, that same current was “used by many urologists for applications to bladder tumors and the prostate but ultimately fell by the wayside because it was unreliable.” They also point out that in “1909 Samuel-Jean Pozzi and E. Doyen in Paris reported using d'Arsonval currents to destroy a variety of surface cancers with high frequency high tension sparks from Oudin's resonator.” Earlier they mentioned “Doumer, also in France, had treated a variety of prosthetic ailments in multiple sessions using special prostatic electrodes connected with the Oudin resonator and the d'Arsonval solenoid.”[1] Patel also discusses the event in which Edwin Beer was able to finally treat a tumor on a bladder with a Oudin current from a high frequency resonator in 1910.

According to Eberhart, he gives a “summary of vacuum tube effects, from an oudin resonator or tesla secondary.” As he puts, in his words:

"1. Increase blood-supply to a given area.. (Hyperemia.) 2. Increase oxidization and local nutrition. 3. Increase intake of oxygen. 5. Increase output of carbon dioxide. 6. Increase secretions. 7. Increase elimination of waste products. 8. Liberate ozone, with the resultant benefit of more or less of this ozone being inhaled by the patient, and also probably carried directly into the tissues. 9. Increase bodily heat, without a corresponding rise in temperature. 10. Locally germicidal. 11. Mild and medium sparks stimulate or soothe according to length and character of application. 12. Strong sparks are caustic. 13. Sparks to spine increase arterial tension. 14. Promote absorption of plastic exudates or adhesions”[2]

It is generally thought that the currents produced in the vacuum tube are not enough to burn skin. Where technically this is correct, it will not create a burn similar to one from an X-ray, it can still cause first degree burns. After a period of constant exposure, especially with your hands, you'll feel like you grabbed a hot pan out of the oven with no gloves on, only not as intense. Getting around this while operating is simple. As Eberhart says, " High frequency currents seem to have no cumulative effect in so far as burning is concerned, and treatment may be repeated frequently without any apparent danger; thus, three seven-minute treatments may be given in one day with intervals of three to six hours between, without any serious consequence when one twenty-minute treatment may be disastrous. "[3]

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  2. ^ Eberhart, Noble. Eberhart’s Manual of High Frequency Currents.— Mcmillinmedia.com, 1911. 20 Nov. 2014.
  3. ^ Eberhart, Noble. Eberhart’s Manual of High Frequency Currents.— Mcmillinmedia.com, 1911. 20 Nov. 2014.