Molly Ayala
Wireless power transfer (WPT) is the transmission of electrical energy without wires as a physical link. Wireless power transmission systems consist of a transmitter device connected to a power source, which converts the power to a time-varying electromagnetic field, and one or more receiver devices that convert the power back to DC or AC electric current. Wireless power transmission can be achieved through inductive coupling, where power is transferred over short distances by magnetic fields, or through far-field or radiative techniques, where power is transferred by beams of electromagnetic radiation such as microwaves or laser beams. While the efficiency of wireless power transmission is generally low, it offers increased mobility, convenience, and safety for electronic devices. Building a wireless power transmitter typically involves creating an oscillator circuit with coils of wire or other conductive materials to generate a magnetic field and transmit power to a receiver device.
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What You'll Learn
Wireless power transfer (WPT) and wireless energy transmission (WET)
In near-field or non-radiative techniques, power is transferred over short distances by magnetic fields using inductive coupling between coils of wire, or by electric fields using capacitive coupling. Inductive coupling is the most widely used wireless technology and has been used since the 1800s. Applications include charging handheld devices like phones and electric toothbrushes, RFID tags, induction cooking, and wirelessly charging or continuous wireless power transfer in implantable medical devices like artificial cardiac pacemakers, or electric vehicles.
Far-field or radiative techniques, also called power beaming, transfer power by beams of electromagnetic radiation, like microwaves or laser beams. These techniques can transport energy over longer distances but must be aimed at the receiver. Proposed applications include solar power satellites and wireless-powered drone aircraft.
The basic principle of WPT and WET involves an electrically powered transmitter device that generates a time-varying electromagnetic field that transmits power across space to a receiver device. The receiver device then extracts power from the field and supplies it to an electrical load. The transmitter device is connected to a source of power, such as a mains power line, which converts the power to a time-varying electromagnetic field. The receiver device then converts this field back to DC or AC electric current.
The efficiency of wireless power transmission is generally low, but the benefits of having a device that can be charged wirelessly may outweigh the power consumption costs. For example, a wireless power transmitter and receiver can be built to transmit enough power to charge a 3.7V battery. The transmitter circuit draws 1A of current when powered with a 12V power supply, so the power output is 12W. The receiving coil can be placed near the transmitting coil, and when tuned for resonance with potentiometer R2, the LED on the receiver should light up to show that power is being transferred.
Recent research has focused on improving the efficiency of WPT systems using frequency reconfigurable metamaterials. These systems aim to manipulate the direction of the electromagnetic field to enhance the magnetic field and power transfer efficiency.
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Wireless power techniques: near and far field
Wireless power transfer (WPT); or wireless energy transmission (WET) is the transmission of electrical energy without wires as a physical link. Wireless power techniques mainly fall into two categories: near-field and far-field.
Near-field or non-radiative techniques
In near-field techniques, power is transferred over short distances by magnetic fields using inductive coupling between coils of wire. Inductive coupling is the most widely used wireless technology. Applications include charging handheld devices like phones and electric toothbrushes, RFID tags, induction cooking, and wirelessly charging or continuous wireless power transfer in implantable medical devices like artificial cardiac pacemakers, or electric vehicles.
The near-field range can be divided into two categories:
- Short-range: up to about one antenna diameter (Drange ≤ Dant)
- Mid-range: up to 10 times the antenna diameter (Drange ≤ 10 Dant)
Far-field or radiative techniques
Far-field techniques, also called power beaming, use beams of electromagnetic radiation, like microwaves or laser beams, to transfer power. These techniques can transport energy over longer distances but require the transmitter to be aimed at the receiver. Applications include solar power satellites and wireless-powered drone aircraft.
Far-field systems like lasers, focused microwaves, and large aperture RF links are well-suited for traversing large distances (>100 m) but exhibit relatively low (<10%) overall system efficiencies due to beam diffraction limits, atmospheric absorption, and multiple conversion losses.
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Wireless power systems: transmitter and receiver devices
Wireless power systems are made up of a transmitter device and a receiver device. The transmitter is connected to a power source, such as a mains power line, which converts the power to a time-varying electromagnetic field. This electromagnetic field is then transmitted across space to a receiver device, which extracts the power from the field and supplies it to an electrical load.
The transmitter device contains a coil of wire. When electricity flows through this coil, it generates an electromagnetic field around it. This is known as the transmitter coil. The receiver device also contains a coil of wire, which picks up the magnetic field from the transmitter when placed near it. This is known as the receiver coil. When the coils are closely aligned, electrical current flows through the receiver coil, which can then be used to charge a battery or power a device. This process is known as inductive coupling, which is the most widely used wireless power technology.
There are a few different methods for wireless power transfer, but one of the most common approaches is resonant inductive coupling. In this method, the efficiency is increased by using resonant circuits. This can achieve high efficiencies at greater distances than non-resonant inductive coupling. However, there can be energy loss as radio waves propagate between the transmitter and receiver coils, reducing overall efficiency.
Another method of wireless power transfer is capacitive coupling, also known as electric coupling. This method uses electric fields for the transmission of power between two electrodes (an anode and cathode) forming a capacitance for the transfer of power. The transmitter and receiver electrodes form a capacitor, with the intervening space as the dielectric.
Wireless power systems offer several benefits over traditional wired power systems. They can eliminate the use of wires and batteries, increasing the mobility, convenience, and safety of electronic devices. They are also useful in powering electrical devices where interconnecting wires are inconvenient, hazardous, or not possible. Additionally, wireless power systems can reduce the environmental impact of battery disposal, as they can be used to power small devices such as clocks, radios, and remote controls.
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Wireless powered communication (WPC) and wireless powered receivers (WPCN)
Wireless power transfer (WPT) is the transmission of electrical energy without wires, using electromagnetic fields. This technology can increase the mobility, convenience, and safety of electronic devices. Wireless power transfer techniques fall into two categories: near and far field. In near-field or non-radiative techniques, power is transferred over short distances by magnetic fields using inductive coupling between coils of wire. In far-field or radiative techniques, power is transferred by beams of electromagnetic radiation, such as microwaves or laser beams, and must be aimed at the receiver.
Wireless powered communication (WPC) and wireless-powered communication networks (WPCN) are two of the three typical operating modes to harvest and transfer power over a wireless network, along with simultaneous wireless information and power transfer (SWIPT). In WPC, wireless devices use harvested radio frequency (RF) energy to transmit or decode information to and from other devices. This can extend the life of wireless networks and enable features like self-sustainability and low cost. WPCN involves transferring energy in the downlink and information in the uplink.
The basic components of a wireless power transmitter include an NPN transistor, magnet wire or insulated wire, and a resistor to protect the transistor from burning out. The incoming power is converted to a high-frequency oscillating signal, which is sent to a wire coil, generating a magnetic field. The power receiver has another wire coil, which picks up the magnetic field from the transmitter when placed near it and converts it to an electric current. This simple circuit can power a light bulb without any wires at a distance of almost one inch.
While the efficiency of wireless power transmission is low, it can be useful for charging devices wirelessly and powering electrical devices where interconnecting wires are inconvenient or hazardous. Wireless power transfer has been used to power aircraft and may be used to power wireless information transmitters or receivers. Recent developments include the first mid-field radio frequency (RF) transmitter certified by the FCC in 2017 and a license granted in 2021 for an over-the-air (OTA) wireless charging system combining near-field and far-field methods.
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Wireless power transmission applications
Wireless power transmission has a variety of applications that are useful in our daily lives. The technology can be used to charge devices wirelessly, eliminating the need for charging cables and increasing user convenience. This is particularly beneficial for handheld devices such as phones and electric toothbrushes, where interconnecting wires can be inconvenient or hazardous.
In the medical field, wireless power transmission is used for implantable medical devices like artificial cardiac pacemakers, allowing for transcutaneous recharging without wires passing through the skin. This technology can also be applied to electric vehicles, powering them wirelessly and reducing the need for frequent charging stops.
Wireless power transmission can also be used in industrial settings, such as powering automated guided vehicles in factories. Additionally, it has applications in wireless information transmission, known as Wireless Powered Communication (WPC). This includes powering wireless information transmitters or receivers, enabling Simultaneous Wireless Information and Power Transfer (SWIPT) and Wireless Powered Communication Networks (WPCN).
The technology can further be applied in situations where wires are not possible, such as powering a light bulb without any wires, demonstrating its versatility and potential for creative projects.
While the efficiency of wireless power transmission is still being improved, its applications are diverse and offer increased convenience, mobility, and safety for users.
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Frequently asked questions
The purpose is to transmit electrical power from a source to a device without physical connections.
The components required include a flyback transformer, a power NPN transistor, a resistor, and a coil of wire.
First, take the copper wire and bend it into a large loop. Solder the red wire from the flyback transformer to the copper antenna. Mound the circuit, transformer, and antenna on a surface. Solder a long wire to the ground of the transformer and attach it to a grounded conductor.
A wireless electricity transmitter uses electromagnetic fields to transfer electrical energy to a device without physical connectors or wires. The transmitter coil creates an electromagnetic field that induces a flow of electrical current in the receiver coil, charging the device's battery.
Wireless power transfer is commonly used for charging mobile devices such as smartphones and electric toothbrushes, as well as electric vehicles and medical devices.
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