Wireless power transfer or wireless power transmission (WPT) is the transmission of electrical energy from source of power (sender) to destination (receiver) or electrical device without using any wires or cords. It is extremely useful in cases where the use of wires becomes risky or inconvenient, and where the delivery of energy needs to be continuous. In such cases, power is transmitted through magnetic induction, magnetic resonance, radio frequency, lasers, microwaves, etc
It is not a new concept. Rather, it has been present for a long time and has been in application for satellite communications, Radio Frequency Identification tags, etc. Although these applications transfer power in smaller amounts, within Microwatts to Milliwatts, wireless power transfer is also being used in industries and other high-power applications. Fundamentally, the method of wireless power transfer uses the basic concept of Faraday?s law of induction, which states that a changing magnetic field causes an alternating current (AC). This method consists of the use of two coils: a transmitter or primary coil, and a receiver or secondary coil. Both of these coils act like inductors, or transformers without any cores, basically making them two air coils which are inductively coupled.
Wireless power transfer is a general term for technologies that transmit energy using electromagnetic fields. These technologies are systems that consist of a transmitter or primary device which is connected to a source of power, and the receiver device, which receives the power and converts it into currents. The system of wireless power transfer reduces the existing transmission cables, towers and substations of high-tension power between the generating stations and the end-consumers. This system was also made to essentially lower the costs of distribution and transmissions, thereby reducing the end cost of electrical energy for the consumers. Wireless power transfer was established so that power could be transmitted to places where wired transfers of energy was not possible.
In 1865, when Maxwell published his Theory of Electromagnetism, he stated that electromagnetic waves move at the speed of light, and then concluded that light itself was one such wave like that. In the 1890s, Nikola Tesla also experimented in the field of wireless power and energy transfers and transmitted power by inductive and capacitive coupling, using radio frequency-based transformers, which are now famously known as Tesla Coils. These coils measured 16 meters in diameter and were known to transmit high voltage currents without any wires. These were also patented and were used for generating high frequency alternating currents. He was one of the first pioneers of this technology.
In 1904, Nikola Tesla designed and constructed the Wardenclyffe Tower, which was used mainly for the wireless transfer of electrical power. Nikola Tesla?s system was one of the very first systems which could transmit electricity without wires. He used a radio frequency resonant transformer of the famous Tesla coils between 1891 and 1898 to transmit electrical energy. This could produce high voltages as well as high frequency alternating currents. This way, he could also transfer power and energy over short distances without any wire connections. 1893, Tesla also demonstrated the illumination of around 200 vacuum bulbs by means of a resonant circuit without using wires for power transmission at the World Columbian Exposition in Chicago. The receiver worked on the same principle like that of radio receivers where the device was supposed to be in the transmitter. In the 1900s, when Nikola Tesla started working on the Wardenclyffe Tower, he demonstrated a prototype of small-scale wireless power transfer for a ?World Wireless System? that could broadcast information as well as power around the world. Tesla?s ideas and experiments failed a lot of times, he still stated that the experiments were successful, although he had no proof that these experiments were ever able to transmit power beyond the short-range distances.
Later, in 1995, Professor Grant Covic and Professor John Boys of the University of Auckland developed systems which could transfer large amounts of energy and power across small air gaps. Then, in 2011, in order to develop and improve the resonator performances, Fei Zhang made due use of strongly coupled electromagnetic resonator technologies to transmit energy over a longer field distance. Currently, in recent years, wireless power transfer has spread its uses around the world in many areas. The biggest example of this is the production of power by placing different satellites with different solar arrangements in Earth?s orbit, and then transmitting this power in the form of microwaves back to the earth. Not only that, with an advancement in technology, wireless power transfer has also helped in the development of fuel-free-electric vehicles, robots, electronic appliances, mobile phones etc.
There have been several tried and tested applications of wireless power transfer. Such a type of transfer could eliminate the need for traditional charging systems. Instead of using a power cord or USB to plug in a laptop, computer or mobile phone, wireless power could be used and implemented in places in a way that these devices could get a continuous charge, that too wirelessly. This could also make such devices safer since power cords can cause shocks and fires, as well as reduce the cost of power chargers for customers. Applications have also been tried on higher level of devices, like vehicles that run on electric power as opposed to gas or fuel. If more people start driving such electric vehicles, there will be a need for more mobile WPT systems, which will increase the practicality of such vehicles. Wireless power transfers could also present possible solutions to save renewable energy using satellites that could collect sunlight and sending this energy back in the form of Microwave power transfer. Along with the potentials and benefits, Wireless Power transfer also has limitations that need to be considered.
1) The capital cost for practically implementing Wireless power transfer can be extremely high for long distance transfer.
2) Microwaves can interfere with ore sent communicating systems and disrupt them
3) If proper change linkages are not done, power supply cannot take place.
4) When compared to traditional charging methods, wireless power transfer is less efficient.
5) Magnetic induction needs perfect alignment of power source (sender) and receiver.
Power transfer by Magnetic Induction Mostly found in standard traditional transformers, Inductive Power Transfer Principle greatly influences the working of wireless power transfer. But it is also different from that of traditional transformers. The two coils in a transformer are closely located to each other and contain ferrite materials to increase coupling, whereas the coils in inductive chargers have an air gap between them. The magnetic induction, commonly known as inductive power transmission system, uses the inductive coupling between two circuits as a mode of power transfer. It has two transformers- the primary transformer, which is contained within the element of power source, and the secondary transformer, which is contained within the item wherein the batteries will be charged. The two coupled circuits have an increased magnetic field because they are in the form of coils. A current then passes through the transmitter coil thereby generating a magnetic field. This is then connected to the secondary coil, and when there is a change in the primary/transmitter current, the secondary or the receiver coil is also induced with a power voltage.
Example: The most common and simplest example of this principle is the working of a transformer that is coupled loosely. The inductively coupled coils here work on the law of magnetic or electromagnetic induction. Examples of this are the inductive battery chargers of electric toothbrushes or mobile phones or even induction cookers.
The Principle of Magnetic Resonance in the working of wireless power transfer has proved to be efficient in overcoming the issue of a drop in the efficient transfer of power due to the distance between the primary and the secondary coils. The power here, is transferred by matching the magnetic resonance frequency of both the transmitter and the receptor. In this method, a capacitor is inserted in both the power transmitter as well as the power receptor sides, to form a LC resonance circuit, which includes an inductor and a capacitor. The power is then transferred after matching the frequency levels on both sides. This method is different in a way that even when the coupling coefficient is low, you catic n obtain a high transmission efficiency. WiTricity is one such organisation that helps to enable wireless power transfer over distance, especially focusing on wireless charging systems for electric vehicles. Example: Magnetic resonance uses tuned coils or wire and lumped element resonators to transmit energy. The most common examples of this principle are portable charging devices, chargers used for electric vehicles, RFID tags or smart cards.
The Radio Frequency (RF) Wireless Power Transfer is a working principle which uses electronic waves or radio frequencies as opposed to magnetic fields. Like the previous methods, this method also uses a transmitter and a receptor. The RF transmitter transfers the radio frequency waves and the receiver which is placed within a device picks the waves up, converts these waves into electricity and thereby powers the electronic device.
Example: Radio frequencies can be used to operate a wide variety of low-power devices. GPS tags, medical sensors, e-book readers, tablets, headsets, etc. are some of the most common devices that work on the principle of RF wireless power transfers.