Tesla’s Inventions

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Tesla’s Thermo-magnetic Motor

When iron magnets are heated they lose their magnetic strength. Tesla devised a small motor with one fixed magnet and a second moving magnet attached to a flywheel and a pivot arm that pushed against a spring. At room temperature, the attraction between the two magnets was enough to compress the spring and pull the moving magnet into the flame of a Bunsen burner. This would heat up the magnet. It would lose strength. The spring would then push the magnet back, turning the flywheel. With the magnet now out of the flame, it cooled down. Its magnetic strength was restored and the cycle began all over again. <Back>

 

Tesla’s Pyromagnetic Generator

Tesla took a large horseshoe magnet. Across its poles ran a number of hollow iron tubes which were magnetized and had coils of wire wrapped around them. Under the centre of the tubes was a firebox. Above there was a boiler. The coal fire in the firebox heated the iron tubes until they reached about 600°C (1,112°F) and glowed a dull red. As the tubes heated up, they would lose their magnetism and the collapsing magnetic field would induce an electric current in the coils. Then a valve was opened and steam, at 100°C (212°F), would circulate though the tubes, cooling them. As the magnetism in the tubes was restored, electric current would again be induced in the coils. <Back>

 

Inside an Induction Motor

An electrical motor works through the interaction of two sets of magnets – one stationary, the stator, and one able to move freely, the rotor. For practical motors, electromagnets are used as they don’t weaken over time. Permanent magnets do. So both the stator and rotor are essentially coils of wire around metal cores. However, even electromagnets have no reason to set the rotor spinning. But magnetic attraction will draw a north pole on the rotor towards a south pole on the stator. To keep the motor turning, the polarity of the electromagnets has to keep on switching. In early DC motors this was done by a split ring commutator supplying current to the rotor. Tesla’s genius was that he realized that you did not have to send electricity to the electromagnets on the rotor at all. If you supplied alternating current to the coils on the stator, the magnetic field created would induce an electric current in the coils of the rotor. The magnetic field produced would oppose that on the stator and the motor would turn.

Essentially, a dynamo or generator is a motor worked in reverse. With a motor you supply electricity and get a mechanical turning force. In a dynamo you supply the mechanical turning force and get electricity. Add in the transformer and Tesla had created a complete system of generating, transmitting and utilizing power. <Back>

 

The Legendary Tesla Coil

Tesla had used coils and capacitors when experimenting with rotating magnetic fields for his motors. He continually refined the components, particularly the special transformer, or coil, at the heart of the circuit, taking out his first patent for a device to run a new and more efficient lighting system in 1891. The basic circuit connected a power supply to a large capacitor, the coil or inductor and the electrodes of an adjustable spark-gap. As the capacitor charges up, the voltage lags behind. In an inductor, voltage is felt immediately while current is held back as it has to work against the magnetic field its own passage causes.

If the size of the coil and condenser are selected to have exactly opposite timing – with voltage peaking in the capacitor just as it reaches a minimum in the coil – current and voltage can be made to chase each other back and forth. This oscillation is initiated by the spark gap. When the voltage in a capacitor builds up, it reaches a level when the air in the gap, which acts as an insulator, breaks down due to ionization and lets current flow.

In a Tesla Coil the inductor is the primary coil of a transformer. When the circuit sparks, all the energy stored over several microseconds is discharged in a powerful impulse, producing a high voltage in the secondary coil. Once the energy has been discharged, the voltage across the spark gap falls and the air becomes an insulator again, until the voltage in the capacitor builds up to the required level again. This whole process can repeat itself many thousands of times per second.

In a Tesla Coil, secondary winding is designed to react quickly to a sudden energy spike. These electrical impulses propagate along the winding as waves. The length of the coil is calculated so that, when the wave crests reach the end and are reflected back, they meet and reinforce the waves behind them, so it appears that the voltage peaks are standing still. If the high-voltage end of the secondary coil is attached to an aerial, it becomes a powerful radio transmitter. In the early decades of radio, most practicable radio transmitters used Tesla Coils. Tesla himself used larger or smaller versions of his invention to investigate fluorescence, X-rays, radio, wireless power and even the electromagnetic nature of the earth and its atmosphere. <Back>

 

Developing Electric Lighting

The inventors of early electric lighting knew two ways to produce illumination – either by creating a spark, or arc, between electrodes or by running a current through a wire or fibre, heating it up until it glowed. Arc lamps are very bright and were used in searchlights, floodlights, lighthouses and movie projectors. They were not suitable for domestic use. But heated filaments also have their drawbacks. Most materials don’t behave well when heated near their melting points. They oxidize, unless surrounded by vacuum or inert gas, or break apart through internal stress. Joseph Swan (1828 – 1914) in 1878 and Thomas Edison the following year independently developed the carbon-filament bulb. This was superseded by the more efficient tungsten-filament bulb in 1908.

However, there is another problem with incandescent lamps. In a domestic 60-watt light bulb, for example, no more than a few per cent of the energy radiated is visible. Most is lost as heat. But in 1859, Alexandre-Edmond Becquerel (1820 – 91) discovered that certain substances fluoresced when a current was passed through a Geissler tube – that is, a partially evacuated glass cylinder.

Tesla developed this into the phosphorescent lamp – phosphorescent substances are slower to emit light than fluorescent ones and continue to glow for some time after the power is switched off. He began by powering conventional filament or arc lamps with high-frequency currents. This caused the diffuse gases inside to glow and made certain solid materials give off light. The bulbs remained cold because most of the electrical energy passed through them turned into light, rather than heat. Consequently, they were much more efficient. But although he used these experiments to illustrate his celebrated lectures, he seldom patented them.

Having developed apparatus that produced higher frequencies and voltages than were available to anyone else, by 1890, he was able to light phosphorescent tubes without connecting wires. The energy was transmitted to them at radio frequencies. At higher energies, Tesla’s tubes gave off X-rays. <Back>

 

Tuning-In to Early Radio

Radio communication uses electromagnetic waves in the range of frequencies lying between around one hertz, or one cycle per second and a few giga-hertz, or a thousand million cycles per second. The wavelength of electromagnetic radiation is the distance from one crest to the next. In an ordinary AM broadcast signal, say about 1,000 kHz on the AM dial, wave crests are spaced at about 969 ft (295 m) apart. The number of crests going by in one second is called the frequency. In all waves, the frequency multiplied by the wavelength equals the velocity. The velocity of radio waves is the speed of light.

The height of a wave is called its amplitude. In radio waves that is given in volts. For waves of the same voltage or amplitude, the more of them that arrive per second the higher the energy, so higher frequency gives more power. A single burst of high-frequency gamma rays is extremely dangerous, while the lower frequencies of radio disperse more easily and pack less of a punch.

Radio communication requires a transmitter that produces a signal powerful enough to be detected some distance away, while at the same time incorporating useful information in that signal. The receiver must be able to pick up that signal and extract the information. Once scientists had understood the nature of electromagnetic waves and detected them, the race was on to produce frequencies and voltages high enough to make wireless transmission. With what he called the ‘magnifier coil’ – now known as the Tesla Coil – Tesla had found a way to produce both.

It quickly became clear to Tesla that, once radio transmission had become practicable, the airwaves would be full of signals. What was needed was a way to develop circuits that worked on pre-selected frequencies so that the desired signal could be picked out from among a background of static and unrelated radio traffic. Tesla perfected tuning which lies at the heart of all communication systems today. <Back>

 

The Remote Control Boat

Tesla’s tub-like craft was powered by large batteries on board. Radio signals activated switches, which controlled the boat’s propeller, rudder and running lights. But even registering the arrival of a radio signal pulse taxed the rudimentary technology of 1898. Tesla had to invent a new kind of coherer or a radio-activated switch to achieve this. The coherer was a canister with a little metal oxide powder in it. The powder orients itself in the presence of an electromagnetic field, such as radio waves, and becomes conductive. In Tesla’s coherer, the canister flips over after the signal has passed, restoring the powder to a random, non-conductive state.

Each signal advanced a disc one step, making a new set of contacts. So if the contacts had previously given the combination ‘right rudder/propeller forward full/light off’, the next step might combine ‘rudder center/propeller stop/lights on’. The connected circuits operated levers, gears, springs and motors, then flipped the coherer over so it was ready to receive the next instruction. Tesla assumed that this system could be used on radio-guided torpedoes. But it was too far ahead of its time. The US Navy did finance some trials in 1916, but the money went to one of Tesla’s competitors as his patent had expired. Nevertheless, as the 20th century progressed, more and more uses were found for remote control. <Back>

 

Ozone Therapy

It had long been thought that ozone had healing properties and Tesla patented an ozone-generating machine in 1896, forming the Tesla Ozone Company in 1900. His portable ‘ozonizers’ were used to disinfect rooms as ozone kills germs. He is also thought to have ozonated olive oil. He gave one of his machines to his long-serving secretary George Scherff for his wife who was ill at the time. ‘I believe that it will do you and Mrs Scherff a lot of good,’ he wrote, ‘unless you have no electricity supply circuit in your house, in which case, it will be necessary to move into other quarters.’ <Back>