Wireless power transfer is of three main types, based on distances
One of the most common and known methods of transferring energy wirelessly is through MAGNETIC INDUCTION. Used for near-the-field transmission of power, this method is based on the factor that when the current flows through one wire, the ends of the other wire experience a voltage.
Examples of such a method are electric tooth brushes, electric razors, transformers, induction cooktops and so on.
WHY: Companies choose this type of wireless transfer mostly because this method relies on a comparatively low-frequency oscillating power that can be transferred between different fields. This transfer is done between coils that are non-resonant but are closely coupled. This method is also much simpler and is rapidly developing. As the components size is small and cheaper than other technology it is widely used in electronic devices like phone , watch etc.
EFFICIENCY: This method works at medium to high power levels with good efficiency if orientation between the sender and receiver is aligned. Companies are trying to overcome this issue by pacing multiple sender and receivers in the device to cover various orientation. Apple recently filed a patent on their power mats placing 16 coils to cover various orientation of the receiver.
GADGETS: wireless charging for low-power applications like mobile phones and similar devices are based on this method.
Magnetic Resonance is another common type of short-range wireless power transfer. This includes a process where the magnetic resonance frequency levels of both transmission and receptor coils are matched before generating the current in the transmitter coil.
WHY: While many companies support and use this method, it is still a less chosen option in small electronic devices because it needs additional components compared to magnetic induction hence it increases the size as well as the cost. This method is based hugely upon a high-frequency oscillating magnetic field that can transfer the energy between two coils with same frequencies. This technology is used in larger electronic devices like laptop , desktop etc .
GADGETS: Uses in larger electronic devices like laptop , tablet etc.
Also, Radio Frequencies are also used to transfer power over short distances. Here, radio waves are artificially generated by transmitters and transferred to receivers, which then convert these waves into electrical energy for devices.
WHY: Companies prefer this method mainly because radio frequencies can easily penetrate through different objects and travel for longer distances.
EFFICIENCY: It is quite an efficient method since it does not require a direct transmission route.
GADGETS: Cordless phones, cell phones, broadcast stations, satellite communication systems, Wi-Fi, Bluetooth modules, TV remote controls, etc. all have a working principle based on Radio frequencies.
Wireless power transfer for mid-range distances, generally use the principle of Magnetic Resonance. These are used in systems for laptops, mobile phones, tablets, implanted medical devices, vacuums, portable charging devices, etc. Here, both the receiver and transmitter circuit consists of a coil which is connected to a capacitor. Both the circuits are then tuned to have the same frequencies. Once that is done, current is passed with an increased coupling and a greater transfer of power.
WHY: Companies use this method for mid-range power transfers because the energy that is transmitted is at an increased distance and no energy is lost during transfer.
EFFICIENCY: This is quite an efficient method because a substantial amount of power can be transferred with a lower rate of energy loss.
GADGETS: Biomedical implants, smartcards are some of the latest examples of gadgets that use this technology.
Although it is still in its experimental stages, studies have shown that only 18% of energy is transferred, with a loss of 82% of energy, when power is transmitted over a distance of 50 meters. Therefore, if 1800 watts is transmitted at a distance of 50 meters, only 340 watts will be harvested at the receptor.
Regardless, one of the major methods of this type is the Microwave Power Transmission.
Developed by William C. Brown, this idea suggests the conversion of AC (alternating current) power to RF (radio frequency) power during
transmission and then re-converting it to AC power when it reaches the receptor. It consists of the transmitter and the receiver. The power
source generates microwave power in the transmitter, which is controlled by electronic circuits. This source is protected from the reflected
power by the waveguide circulator. There is a tuner here which controls the resistance that rises between the source and transmitting
antenna, which then discharges the power through the free space towards the receiver. The receiver then receives the transferred power
and converts it into DC (direct current) power.
Still in experimental stage , efficiency needs to improve for any commercial usage.
Another method for high range wireless power transfer is the Laser Power Transmission. This uses laser beams to transfer the power in the
form of light energy. This energy is then converted to electrical energy when it reaches the receiver. The power sources in this method are
sun, or electricity generators or any focused lights of high intensity. A set of optics determine the shape and size of the beam. This
transmitted laser beam is then received by photo-voltaic cells, after which it is converted into electrical signals. Generally, this method uses
cables made of optical fibres for the transmission of energy.
Examples include laser powered drones and aircrafts.
WHY: Companies use this method because lasers provide a reasonable and rational, high energy density beams which are almost non divergent, thereby allowing the use of an antenna of a much smaller diameter.
EFFICIENCY: More useful and efficient for applications of small distance, but could also be used for longer distances if high distance beams are used.
GADGETS: This method has already been successfully used in models and prototypes created by companies like LaserMotive, which developed the prototype for a space elevator that was supplied by a laser beam which could lift up to 50 kg of weight.
Additionally, there was a model plane in 2003, that was designed with a laser beam that was centred on its panel of photovoltaic cells. This model plane was powered by an infrared laser beam at NASA Marshall, and it made its first flight of an aircraft based on this technology.