Molly Ayala
Wireless power transfer (WPT) is a technology that allows the transmission of electrical energy without wires as a physical link. The concept emerged from research at the Massachusetts Institute of Technology (MIT) in the early 2000s, led by Marin Soljačić, and resulted in the establishment of WiTricity, a company specializing in this technology. 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. This technology can be used to power devices where interconnecting wires are inconvenient, hazardous, or impossible, such as electric toothbrushes, smartphones, and electric vehicles.
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What You'll Learn
Wireless power transfer (WPT)
WPT techniques can be broadly categorized into near-field (or non-radiative) and far-field (or radiative) methods. Near-field techniques, such as inductive coupling, rely on magnetic fields to transfer power over short distances using inductive coupling between coils of wire. Inductive coupling is the most widely used WPT method and is commonly employed in charging handheld devices like phones, electric toothbrushes, and electric vehicles.
Far-field techniques, also known as power beaming, utilize electromagnetic radiation, such as microwaves or laser beams, to transmit power over longer distances. These methods require the transmitter to be aimed at the receiver. Potential applications of far-field WPT include solar power satellites and wireless-powered drone aircraft.
WPT is becoming increasingly prevalent in everyday life, with smartphones and other handheld devices now incorporating wireless charging capabilities. This technology not only provides convenience but also enhances safety in hazardous environments, such as underwater or healthcare settings, where wires may pose a risk.
Furthermore, WPT plays a crucial role in powering electric vehicles and remote-controlled devices, expanding its impact beyond individual devices to broader societal and environmental spheres. WPT is also used in medical technology, enabling the wireless charging of implanted devices such as pacemakers.
Overall, WPT offers unparalleled convenience, safety, and versatility in power transmission, making it an essential technology for powering a wide range of devices and systems.
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Near and far-field techniques
Wireless power transfer (WPT) is the transmission of electrical energy without wires as a physical link. Wireless power techniques mainly fall into two categories: Near and Far-field.
Near-field techniques
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 between metal plates. The near field refers to places nearby the antenna conductors, or inside any polarizable media surrounding it, where the generation and emission of electromagnetic waves can be interfered with while the field lines remain electrically attached to the antenna. The electric and magnetic fields can exist independently of each other in the near field, and one type of field can be disproportionately larger than the other, in different subregions. The near-field range is divided into two categories:
- Short-range: up to about one antenna diameter.
- Mid-range: up to 10 times the antenna diameter.
Far-field techniques
Far-field or radiative region techniques involve the transmission of power beyond about 1 wavelength (λ) of the antenna, where the electric and magnetic fields are perpendicular to each other and propagate as an electromagnetic wave. The electromagnetic field in the far-field region of an antenna is independent of the details of the near field and the nature of the antenna. The far-field range is the usual region of antenna function, and the general purpose of conventional antennas is to communicate wirelessly over long distances, well into their far fields.
Applications of WPT
WPT is used in a variety of applications, such as charging mobile devices, electric vehicles, and some medical devices. It is also used in the transportation sector for electric vehicles and transit vehicles like buses and trains. The fastest-growing use of WPT is in wireless charging pads for mobile and handheld wireless devices. WPT is also being researched for use in IoT devices, industrial machinery, and space-based solar power systems.
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Safety concerns
Wireless power transfer (WPT) is a technology that allows for the transmission of electrical energy without wires as a physical link. This technology can be used to power electrical devices where interconnecting wires are inconvenient, hazardous, or impossible.
One of the most important issues associated with WPT systems is limiting the exposure of people and other living beings to potentially harmful electromagnetic fields. High-power electromagnetic radiation can be dangerous to humans and other animals, even at low power levels. This is especially important for earthbound applications, where large total power levels are used while maintaining a low power density for human electromagnetic exposure safety. To address this concern, a large-area receiving array can be used to distribute power density over a larger area, reducing the risk of exposure to harmful levels of electromagnetic radiation.
Another safety consideration is the potential for tissue heating due to electromagnetic fields. This is a concern for implantable medical devices, such as pacemakers, where wireless power transfer is used for transcutaneous recharging. To minimize the risk of tissue heating, it is important to optimize the power efficiency of the wireless link, reducing the amount of heat generated in the tissue.
WPT systems are also designed with temperature monitoring and foreign object detection to prevent overheating or damage, reducing the risk of electrical accidents or fires. Additionally, some wireless charging technologies, like inductive charging, use waterproof and durable materials, making them suitable for outdoor and rugged applications.
Furthermore, wireless power transfer using lasers for consumer applications must comply with laser safety requirements standardized under IEC 60825. Without proper safety mechanisms, even low-power laser beams can cause blindness in humans and other animals. The first wireless power system using lasers for consumers, Wi-Charge, complied with safety regulations and was approved by the US Food and Drug Administration (FDA).
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History
The history of wireless power transmission dates back to the 19th century, with many developments of theories and experiments exploring the transmission of electrical energy without wires. In 1826, André-Marie Ampère discovered the connection between current and magnets, and Michael Faraday described the electromotive force in a conductor loop by his law of induction in 1831.
During the late 19th century, Nikola Tesla played a significant role in wireless power transmission. He patented the Tesla Coil in 1890, which generated high-frequency alternating currents. Tesla conducted large-scale experiments on wireless power transmission in Colorado Springs in 1899, demonstrating the feasibility of this technology. He powered a field of fluorescent lamps located twenty-five miles from their power source without using wires.
In 1901, Tesla began constructing the Wardenclyffe Tower, designed to transmit wireless power and communication. However, the project faced financial challenges and was never completed. Despite this setback, Tesla continued to work on wireless transmission theories until his death in 1943.
In the early 20th century, William C. Brown made significant contributions to wireless power transmission. In the 1960s, he achieved the first long-distance wireless power transmission and invented the rectenna, which efficiently converted microwaves to DC power.
More recently, in 2005, an MIT team led by Marin Soljacic invented a practical method of wireless energy transmission for household use. This led to the founding of WiTricity Corp. in 2007 to commercialize wireless electricity technology.
The development of wireless power transmission technology has come a long way since its early beginnings, and it continues to evolve and find new applications in the modern world.
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Applications
Wireless power transmission has a wide range of applications, from charging handheld devices to powering vehicles and even some medical devices.
One of the most common applications of wireless power transfer technology is charging handheld devices such as smartphones, electric toothbrushes, and shavers. This technology uses inductive coupling, where power is transferred over short distances by magnetic fields, to charge devices wirelessly. This method is also used in induction cooking and electric vehicles.
Wireless power transfer is also used in medical devices, such as implantable cardiac pacemakers and high-power neuroprosthetic devices like visual prostheses. The technology allows for the transcutaneous recharging of biomedical prosthetic devices, avoiding the need for wires to pass through the skin.
In the transportation sector, wireless power transfer is being explored as a method for charging electric vehicles (EVs) and even trains. Wireless power transfer systems, such as resonant inductive coupling, offer more efficient power transfer over greater distances, making them suitable for powering vehicles.
Additionally, wireless power transfer has applications in industrial settings, such as powering automated guided vehicles used in factories. Laser-based power beaming is also being explored for powering drones, autonomous ground vehicles, and transmitting power from renewable energy sources like solar and wind farms to a central grid.
While wireless power transfer is primarily used for low-power applications, ongoing research and development efforts aim to extend its capabilities to power IoT devices, industrial machinery, and space-based solar power systems.
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Frequently asked questions
Wireless power transfer (WPT) is the transmission of electrical energy without wires as a physical link. It uses electromagnetic fields to transfer electrical energy from a power source to an electrical device.
Wireless power transmission systems use an electrically powered transmitter device to generate 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.
Wireless power transfer can increase the mobility, convenience, and safety of an electronic device. It eliminates the need for interconnecting wires and batteries, improving design aesthetics and enabling waterproofing.
Wireless power transfer is commonly used for charging mobile devices, electric vehicles, and some medical devices. It is also used in automated guided vehicles in factories and for powering transit vehicles like buses and trains.
