Otis Singleton
Wireless power transfer (WPT) is the transmission of electricity without wires, using electromagnetic fields to transfer power between two coils. This technology can be used to charge handheld devices like phones, electric toothbrushes, and electric vehicles (EVs). WPT can also be used to power medical devices such as artificial cardiac pacemakers and electric vehicles. While WPT is possible, it is most effective over short distances, and the efficiency and range of WPT systems can vary depending on the technology used.
| Characteristics | Values |
|---|---|
| Possibility | Wireless power transfer is possible and has been demonstrated in various applications. |
| Techniques | Wireless power transfer techniques include near-field and far-field methods. |
| Near-field Techniques | Power is transferred over short distances using magnetic fields and inductive coupling between coils. |
| Far-field Techniques | Power is transferred over longer distances using beams of electromagnetic radiation, such as microwaves or laser beams. |
| Applications | Wireless power transfer is used for charging mobile devices, electric vehicles, medical devices, and more. |
| Benefits | Wireless power transfer can increase mobility, convenience, and safety by eliminating the need for wires and batteries. |
| Efficiency | Efficiency varies depending on the technology used. Some systems claim efficiency over 90% for short-distance power transfer. |
| Data Transfer | While wireless power transfer is not designed for high-speed data transmission, some technologies support basic data transfer capabilities. |
| Range | The range depends on the technology used and can vary from a few millimeters to longer distances. |
| History | The basics of wireless power transfer were founded by Tesla, who envisioned global wireless charging using the Earth's magnetosphere. |
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What You'll Learn
Wireless power transfer (WPT)
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 and capacitive coupling between metal electrodes. Inductive coupling is the most common method of WPT and is used in charging devices such as smartphones, electric shavers, electric toothbrushes, visual prostheses, and implantable medical devices (cardiac pacemakers, cochlear implants).
In far-field or radiative techniques, power is transferred over long distances by electromagnetic radiation. Radiative coupling is based on electromagnetic fields and is described by Maxwell's complete equations.
The design of a WPT system requires a field approach for the transmitter and a circuit approach for the receiver. A WPT system can be schematized into two parts: the transmitter, which is connected to a power source, and the receiver, which is connected to the load. The transmitter converts the input power to an oscillating electromagnetic field, which is then picked up by the receiver coil and converted back to DC or AC electric current.
WPT is becoming ubiquitous in everyday life, with smartphones, electric toothbrushes, smartwatches, electric vehicles, and drones all incorporating wireless charging capabilities. WPT is also used in the space industry for wireless energy transmission between spacecraft and has the potential to be used for space-based solar power systems.
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Inductive coupling
Wireless power transfer (WPT) is the transmission of electrical energy without wires as a physical link. Inductive coupling is the most widely used wireless technology for WPT. It involves the use of electromagnetic fields to transfer power between two coils—a transmitter coil in the charging pad or base station and a receiver coil in the device being charged.
The transmitter coil generates a fluctuating electromagnetic field, and when the receiver coil is placed in this field, the voltage in the transmitter coil is induced across it. This results in an electrical current flowing through the receiver coil, which can then be used to charge a battery or power the device.
Resonant inductive coupling is an extension of inductive coupling that uses resonance to improve power transfer efficiency. It involves tuning the transmitter and receiver coils to the same resonant frequency, allowing for more efficient power transfer over a greater distance.
The use of inductive coupling for WPT has several advantages. It eliminates the need for wires and batteries, increasing the mobility, convenience, and safety of electronic devices. It is also useful for powering electrical devices where interconnecting wires are inconvenient, hazardous, or impossible.
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Near-field and far-field techniques
Wireless power transfer (WPT) techniques can be broadly categorized into near-field and far-field techniques.
Near-field techniques
In near-field or non-radiative techniques, power is transferred over short distances using magnetic fields and inductive coupling between coils of wire. This type of technique is commonly used for charging handheld devices like phones, electric toothbrushes, RFID tags, and electric vehicles. Near-field devices operate at lower frequencies and radiate little to none of their energy as electromagnetic radiation. The power transferred decreases rapidly with distance, making near-field techniques unsuitable for long-range power transmission.
Far-field techniques
Far-field or radiative techniques, also known as power beaming, involve transferring power over longer distances using beams of electromagnetic radiation, such as microwaves or laser beams. These techniques require the transmitter to be aimed at the receiver. Applications for far-field techniques include solar power satellites and wireless-powered drone aircraft. Far-field techniques have the advantage of being able to transfer power over greater distances, but they often suffer from low efficiency due to the omnidirectional nature of the antennas used.
Comparison
While near-field techniques are widely used for commercial applications due to their convenience and ability to charge devices wirelessly over short distances, far-field techniques offer the potential for long-range power transmission, which is useful for certain specialized applications. However, far-field techniques face challenges due to low efficiency and the need for line-of-sight between the transmitter and receiver.
Advancements
There have been advancements in both near-field and far-field WPT systems. For example, resonant inductive coupling can increase the coupling between antennas, allowing for more efficient transmission at greater distances in the near field. In the far field, techniques like field intensity shaping aim to improve efficiency by delivering and confining energy within the spatial location of the receiving device.
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Power beaming
The technology can use either microwaves or lasers to transmit power. Microwaves have a more established track record due to the lower cost of equipment, while lasers offer the advantage of narrow beam concentration, enabling smaller transmission and receiver installations. In 2019, a laser beam successfully transmitted 400 watts over a distance of 325 meters, and a power-beaming system developed by PowerLight Technologies conveyed hundreds of watts during a demonstration at the Port of Seattle in the same year.
While power beaming offers many benefits, there are also challenges to making the technology reliable, effective, secure, and wide-ranging.
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Safety considerations
Wireless power transfer (WPT) is the transmission of electrical energy without wires as a physical link. It is designed to increase the mobility, convenience, and safety of an electronic device for all users.
- Temperature Monitoring and Foreign Object Detection: WPT systems often include temperature monitoring and foreign object detection to prevent overheating or damage, reducing the risk of electrical accidents or fires.
- Waterproofing and Durability: Some WPT technologies, like inductive charging, are waterproof and durable, making them suitable for outdoor and rugged environments. This reduces the risk of electric shock.
- Flexibility: WPT can work through various materials, such as wood, plastic, and glass, allowing for flexibility in the design and placement of charging pads.
- Aesthetics: WPT charging pads can be seamlessly integrated into furniture, vehicles, and consumer electronics, enhancing aesthetics and reducing cord clutter.
- Mobility and Portability: WPT is particularly useful for mobile and handheld devices, such as smartphones and wearables, as it eliminates the need for physical connectors or wires.
- Human Safety: WPT systems aim to limit the exposure of people and other living beings to potentially harmful electromagnetic fields. For earthbound applications, a large-area 10 km diameter receiving array allows for a human-safe power density of 1 mW/cm^2, which is comparable to the power level in modern electric power plants.
- Frequency and Power Levels: The method of WPT and the electromagnetic frequency used may limit the amount of power that can be safely transferred. Higher frequencies, such as 6.78 MHz, are recommended for consumer device wireless power transfer as they have minimal impact on other licensed bands and reduce eddy current losses in nearby metal objects.
- Regulations: Well-designed WPT products are required to meet local RF exposure regulations to ensure safety.
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Frequently asked questions
Yes, wireless power transfer (WPT) is possible and is based on technologies using time-varying electric, magnetic, or electromagnetic fields.
Wireless power transfer works by using electromagnetic fields to transfer electrical energy from a power source to an electrical device without the need for physical connectors or wires. The most common approach is inductive coupling, which uses electromagnetic fields to transfer power between two coils – a transmitter coil in the charging pad and a receiver coil in the device being charged.
Wireless power transfer can eliminate the use of wires and batteries, increasing the mobility, convenience, and safety of an electronic device. It is useful for powering electrical devices where interconnecting wires are inconvenient, hazardous, or impossible.
Wireless power transfer is commonly used for charging mobile devices such as smartphones and electric toothbrushes. It is also used for electric vehicles (EVs) and some medical devices such as cardiac pacemakers and cochlear implants. There is ongoing research to extend wireless power transfer capabilities to other applications, such as IoT devices and solar power satellites.
