Inductive Power Transfer

Inductive Power Transfer Technology [IPT] - allows the transfer of electrical power without physical contact. A magnetic field links energy directly to where it is required. IPT is immune to dirt, dust, water, ice and chemicals.

Wireless Energy Transfer

Wireless energy transfer or wireless power transmission is the process that takes place in any system where electrical energy is transmitted from a power source to an electrical load, without interconnecting wires.

Wireless transmission is employed where instantaneous or continuous energy transfer is needed, but interconnecting wires are inconvenient, hazardous, or impossible.

This type of energy transfer is distinct from wireless transmission of information [radio]. In radio, the percentage of the power that is received is only important if it becomes too low to successfully recover the signal. With wireless energy transfer, the efficiency of the transfer is more critical.

Development Of IPT

Electromagnetic induction is not a new technology. Inductive power technology resulted from combining two core capabilities:

1. Electromagnet - invented in 1825 by William Sturgeon invented the electromagnet - a conducting wire wrapped around an iron core.
2. Induction - a changing magnetic field can induce an electrical current in an adjacent wire — was discovered by Michael Faraday in 1831.

By combining these two discoveries, Nicholas Joseph Callan first demonstrated the transmission and reception of electrical energy without wires in 1836.

Callan’s induction coil consisted of two insulated coils [primary and secondary windings] both placed around a common iron core. A battery intermittently connected to the primary would ‘induce’ a voltage in the longer secondary causing a spark to jump across its free terminals.

In an induction coil or electrical transformer, which can have either an iron core or an air core, the transmission of energy takes place by simple electromagnetic coupling through a process known as mutual induction.

Using this method it is possible to transmit and receive energy over a considerable distance. To draw significant power by induction, the two inductors must be placed fairly close together.

If resonant coupling is used, where inductors are tuned to a mutual frequency, significant power may be transmitted over a range of many meters.

As wireless technologies were further developed during the early 1900s, different wireless transmission methods were further investigated with the the goal to generate an effect locally and detect it at a distance. Efforts were also made to power more significant loads than the high-resistance sensitive devices that were being used to simply detect the received energy.

Except for RFID tags, wireless power transmission beyond room-sized or community-sized distances has not been widely implemented. This has largely been due to the assumption that any system for broadcasting energy to power electrical devices will have negative health implications.

Whilst focused beams of microwave radiation are a definite health risks, however, resonant coupling wavelengths are far lower, making it no more dangerous than being exposed to radio waves.

Components

The main components required for inductive power transmission are:

The size of the components is dictated by:

1. distance from transmitter to receiver
2. the wavelength of the radiation
3. the laws of physics - specifically the Rayleigh Criterion or Diffraction limit. These laws dictate that any beam will spread (microwave or laser) and become weaker and more diffuse over greater distance. The larger the transmitter antenna or laser aperture, the tighter the beam and the less it will spread as a function of distance (and vice versa). Smaller antennas also suffer from excessive losses due to sidelobes.

Power & Efficiency

Power levels are calculated by combining the above parameters, with the gains and losses due to the antenna characteristics and the transparency of the medium through which the radiation passes. That process is known as calculating a Link Budget.

The efficiency of wireless power is the ratio between power that reaches the receiver and the power supplied to the transmitter.

Wirelessly transmitted energy is dispersed as the energy radiates into the environment or is lost as heat at the transmitter or receiver.

Wired transmission loses far less power as wires are good conductors and help to confine and guide the energy to where it is needed.

Generally, wireless energy transfer works best at short range; although long distances are possible if the transmitters and receivers are physically large, or the energy is able to be formed into a tight beam, such as with lasers or large microwave dishes. The ultimate angle subtended by a beam is limited by diffraction.

When phased arrays are used for wireless transmission, the phased array normally needs to be contiguous due to a phenomenon called the thinned array curse; gaps in the array act as a diffraction grating and causes side bands that lose energy.

Benefits of IPT

Advantages of iPT include:

Longevity - with virtually no components prone to wear and tear, the longevity of the system is greatly increased. There is no friction in the system, hence no limit to the acceleration possible. With no galvanic contact, there is no corrosion.

Safety - unlike combustion power-sources that have the risk of sparks from static electricity or friction, IPT provides power to environments previously considered too difficult or previously accepted as a hazard.

Low Maintenance - there are no batteries to be replaced.

Continuity Of Service - because the power source is constant and uninterrupted.

Unobtrusive - no components protrude above ground, meaning no obstruction to forklifts or feet.

IPT Applications

There are a number of current applications for IPT, categorized by the distance the power induction.

Short Distance IPT Applications

• The electric toothbrush battery charger
• The induction cooker stovetop
• Surgical Implants - Transcutaneous energy transfer (TET) systems in artificial hearts like AbioCor and other surgically implanted devices.
• Consumer Electronics - devices using induction to charge portable consumer electronics such as cell phones.

Medium Distance IPT Applications

A new company, Powercast introduced wireless power transfer technology using RF energy at the 2007 Consumer Electronics Show, winning best Emerging Technology.

The Powercast system is applicable for a number of devices with low power requirements. This could include LEDs, computer peripherals, wireless sensors, and medical implants. Currently, it achieves a maximum output of 6 volts for a little over one meter.

A different low-power wireless power technology has been proposed by Landis

Long Distance IPT Applications

Power transmission via radio waves can be made more directional, allowing longer distance power beaming, with shorter wavelengths of electromagnetic radiation, typically in the microwave range.

A practical wireless energy transmission system using this principle, may use a high-power ultraviolet beam to form a vertical ionized channel in the air directly above the transmitter-receiver stations. This concept is used in virtual lightning rods, the electrolaser electroshock weapons and has been proposed for disabling vehicles.

SmartStuds

Smartstuds® are rapidly being installed in Europe, Asia and the United States for tunnels, bridges, roads, walkways and pedestrian crossings.

Wireless Display Lighting

Inductive Power Transfer technology is also well suited for use in wireless display lighting.

UV and Fluorescent tubes: UV or conventional fluorescent tubes may be driven from an IPT source. High strike voltages are not a problem and the tube current can be precisely controlled. The tubes are some 30% more efficient at 25 kHz than they are at 50/60 Hz and for a given light output they last longer. The brightness may be controlled by modulating the IPT signal with far better control than is possible at 50/60 Hz.

Neon and Argon Signs: Neon and Argon signs require very high strike voltages of several kV. These are easy to generate with IPT systems so the tubes are easy to light and will operate in wet and dirty environments without difficulty. They may be switched on/off at speed to give a controlled brightness using low cost transistor switches. This option is not possible at 50/60 Hz.

Very large displays: Very large displays for instant replays at sports functions and the like may be made completely wireless using IPT power supplies. The information to be displayed is coupled to the displays by radio signals. The power to drive display modules is coupled by IPT. The modules can be made completely waterproof with an IP65 rating – they can be operated continuously in a tropical downpour. The whole display has no connectors, no sockets, and no exposed wires. Modules can also be made self-addressing so that they may be placed anywhere in the display and automatically display the appropriate part of the picture with colour and brightness matching across the whole display.

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