The concept of the wireless energy transmission system is not new. Many students choose it as a mini-project for school or even as a hobby project. The technology was demonstrated for the first time in 1890 by Nikola Tesla. Electrodynamics induction, or resonant inductive coupling, was introduced by Tesla with a simple demonstration of lighting up three bulbs from a power source at a distance of almost 60 feet.
Wireless energy transmission system
As the name implies, a wireless energy transmission system transmits electricity without wires. This system works only up to a certain distance and consists of the following three parts:
· The transmitter is the part where the electricity meant to be transmitted is applied. To transmit power, electric energy is converted to other forms of energy. The energy can be transmitted in the form of light, by changing the magnetic field or by electromagnetic wave.
· The medium is the path through which energy is transmitted. It can either be a vacuum, air or a solid.
· The receiver is the part that receives the transmitted energy (in the form of light, changing magnetic field, or electromagnetic wave) and converts it back to electric energy used to light a bulb, for example. The start and the end product of the system is electricity, whereas the intermediary product is any other form of energy.
Types of wireless power transmission
The three main types of wireless energy transmission system are:
· Inductive coupling power transmission
· Laser power transmission
· Microwave power transmission
Inductive coupling power transmission
Inductive coupling is the most commercially used type of wireless energy transmission system. This method is being used in many daily life examples like wireless mobile charging, electric toothbrushes and remote keys for luxury cars. It is quite similar to a simple transformer which is based on the principle of mutual induction between two circuits linked by the common magnetic flux.
Electricity generated by the transmitter coil is converted into the high-frequency alternating magnetic field. This high-frequency alternating magnetic field is received by the coil of the receiver circuit where it is converted back to high-frequency alternating current and rectified by the receiver coil.
The coupling factor controls the efficiency of the inductive coupling power transmission. The efficiency of the system will be maximum at its resonant frequency, which can be calculated by the inductance and capacitance of the circuit.
The resonant frequency is given by:
In this formula, frequency is represented by F and measures in Hz, inductance is represented by L and measures in henrys, and capacitance is represented by C and measures in farads.
Laser power transmission
The start and the end product of laser power transmission is electricity whereas the intermediary product is light. Electricity is converted into a beam of light by the transmitter. This beam is sharply focused on the receiver.
Infrared lasers are primarily used in laser power transmission. Photovoltaic cells in the receiver are adjusted to respond to the frequency and wavelength of the laser beam transmitted from the transmitter. This type of transmission has an additional advantage as it can transmit energy several meters with minimum medium loss.
Microwave power transmission
Microwave power transmission, converting electricity into microwaves, is considered the most efficient type of wireless energy transmission system but its construction is quite complex.
The transmitter of the microwave power transmission system has a microwave generator and a waveguide which is used for directing the wave in a specific direction. Different types of antennas can be used for this method, including parabolic reflectors, microstrip patch or slotted waveguide devices.
By using the slotted waveguide antenna, the efficiency of the system is enhanced up to 95% as compared to other methods having efficiency ranging from 5% to 40%.
In the receiver segment, a combination of both antenna and rectifier, known as a rectenna, is used. The received microwaves are directly converted into DC by rectenna.
Construction of a wireless energy transmission system
The circuit has very few elements and is quite easy to build. There are 10 turns in the transmitter coil with a center tap. Thick wires for the coil are recommended. BD139 NPN Transistor must be used with a heat sink.
The transmitter circuit contains a capacitor having a capacitance of 4.7 nF and a coil with 10 turns just like a tank circuit having a particular resonance frequency.
The receiver coil has the same number of turns and thickness and a capacitor of equal capacitance as that of the transmitter to match the resonance frequency. A diode IN4148, or Schottky diode, is also used in the receiver circuit as a half-wave rectifier. High-frequency alternating current can be rectified efficiently with this diode. However, you can also use a normal diode (1N4007) but it has a higher forward voltage drop that may result in a slight reduction in LED brightness.
The receiver circuit has a coil with 10 turns and is 5 cm in diameter. A coil of any diameter can be used but the diameter of both transmitting and receiving coils must be the same.
For the transmitter coil, wind two coils each with 5 turns, stack them, tape them and solder the center tap. To improve the distance of energy transmission, play with coil windings, capacitors and input voltage by changing them.
The efficiency of wireless power transmission
The proposed circuit has an efficiency of almost 10% or even less. Efficiency can be calculated by the ratio of output power to input power.
Advantage of wireless power transmission
One of the biggest advantages of wireless power transmission is convenience and companies are investing a lot of money just for the sake of ease.
Why are only low power gadgets such as smartphones or toothbrushes commercialized with wireless power? The reason is a huge efficiency loss. Five to 10 times more power is needed to get things working, which is why wire-powered devices are more popular and still ruling the world.