The technology of Wireless Power Transfer is emerging and fast-growing among the technology trend 2020 ~ 2030. It is the spread of electrical energy without wires as a physical connection. One transmitter device is used in a wireless power transmission system which is driven by electric power. This device generates an electromagnetic field that transmits power through space to a receiver device and removes power from the field and stores it to an electrical load. The technology of wireless power transmission may eradicate the use of wires and batteries. It would increase the movement, opportuneness, and safety of an electronic device for all customers. The wireless power transfer is very useful to power electrical devices. It is suitable where interconnecting wires are difficult and hazardous.
Groups of wireless power transfer
There are two main groups of wireless power techniques:
- Near-field or non-radiative technique:
The power is conveyed over short distances by magnetic fields using inductive coupling between coils of wire.
- Far-field or radiative technique:
The power is transferred by beams of electromagnetic radiation as similar to microwaves or laser beams in this technique. These techniques may passage energy extended distances and must be pointed at the receiver.
Block diagram of a wireless power system
The wireless power system contains a transmitter device linked to a basis of power for instance a mains power line that converts the power to a time-changing electromagnetic field, and receiver devices that obtain the power and convert it back to DC or AC electric current. By a certain type of antenna device at the transmitter, the input power is changed to an oscillating electromagnetic field. A comparable coupling device or antenna at the receiver changes the oscillating fields to an electric current. Frequency is an important parameter that controls the type of waves that determines the wavelength. Same fields and waves are used by Wireless power as wireless communication devices. Only minute quantities of power reach the receiver in wireless communication technologies. Efficiency is the most important parameter as with wireless power transfer the amount of energy received is the important entity. Due to this reason the wireless power technologies are possible to be additionally limited by distance than wireless communication technologies.
The wireless power transfer can be used to enhance wireless information transmitters or receivers. This sort of communication is recognized as (WPC) wireless powered communication. The network is known as (SWIPT) Simultaneous Wireless Information and Power Transfer when the harvested power is used to supply the power of wireless information transmitters.
Electric and magnetic fields are created by charged particles in a matter like electrons. A stationary charge creates an electric field within the space around it. A gentle current of charges creates a static magnetic flux around it. The above fields contain energy but cannot carry power because they’re static. However time-varying fields can carry power. Accelerating electric charges, like are found during an AC (AC) of electrons in a wire, create time-varying electric and magnetic fields within the space around them. These fields can exert oscillating forces on the electrons during a receiving “antenna”, causing them to maneuver back and forth. These represent AC which may be wont to power a load.
Near-field or nonradiative region: This directs the world within about 1 wavelength (λ) of the antenna. The oscillating electric and magnetic fields are distinct and power is often transferred via electric fields by capacitive coupling between metal electrodes or through magnetic fields by inductive coupling. These fields aren’t radiative, meaning the energy stays within a brief distance of the transmitter.
Far-field or radiative region: The magnetic and electrical fields are perpendicular to each other and propagate as an electromagnetic wave; examples are radio waves, microwaves, or light waves beyond about 1 wavelength (λ) of the antenna. This is a part of the energy is radiative, meaning it leaves the antenna whether or not there’s a receiver to soak up it. The portion of energy which doesn’t strike the receiving antenna is dissipated and lost to the system. The amount of power produced as electromagnetic waves by an antenna depends on the ratio of the antenna’s size Dant to the wavelength of the waves λ,  which is decided by the frequency: λ = c/f. At low frequencies f where the antenna is far smaller than the dimensions of the waves, Dant > λ = c/f.Practical beam power devices require wavelengths within the centimeter region or below, like frequencies above 1 GHz, within the microwave range, or above.
Near-field (nonradiative) techniques
The near-field mechanisms of electrical and magnetic fields are quasi-static oscillating dipole fields at a large relative distance. Since power is proportional to the square of the sector strength, the facility transferred decreases as (Drange/Dant)−6. Or 60 dB per decade. In other words, if far apart, doubling the space between the 2 antennas causes the facility received to decrease by an element of 26 = 64. Unlike during a radiative system where the utmost radiation occurs when the dipole antennas are oriented transverse to the direction of propagation, with dipole fields the utmost coupling occurs when the dipoles are oriented longitudinally.
Inductive coupling: The power is transferred between coils of wire by a magnetic field in inductive coupling.
Resonant inductive coupling: It is a form of inductive coupling in which power is transferred by magnetic fields between two resonant circuits.
Capacitive coupling: It creates the use of electric fields for the transmission of power between two electrodes forming a capacitance for the transfer of power.
Resonant capacitive coupling: It may also be used with capacitive coupling to extend the range.
Magneto dynamic coupling: With this method, power is transmitted between two rotating armatures, one in the transmitter and one in the receiver.
Far-field (radiative) techniques
These techniques have frequently multiple kilometer ranges in which the distance is abundantly better than the diameter of the device(s). Well-collimated laser light and high-directivity antennas create a beam of energy that may be made to match the figure of the receiving area.
Microwaves: In the microwave range, power transmission through radio waves may be made more directional, permitting longer-distance power beaming, with shorter wavelengths of electromagnetic radiation.
Lasers: The power may be transmitted by converting electricity into a laser beam which is received and concentrated onto photovoltaic cells in the case of electromagnetic radiation closer to the visible region of the spectrum. This method is usually said to be as power beaming as power is beamed at a receiver which may convert it to electrical energy.