Wireless Power Transfer: Fundamentals, Technologies, and Applications - An Electrical Engineering Book Selection
Wireless Power Transfer: What Is It and How Does It Work?
Wireless power transfer (WPT) is a technology that allows transmission of electrical energy through an air gap to a load without any interconnecting wires. The removal of ports and cables makes products less obtrusive and makes the recharging or powering of devices more convenient.
Wireless power transfer | Electrical Engineering Books
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Wireless power transfer has many applications in various fields, such as consumer electronics, medical devices, electric vehicles, unmanned aerial vehicles, wireless sensor networks, space exploration, and more.
In this article, we will explore the history, principles, benefits, challenges, and future of wireless power transfer, as well as some electrical engineering books that cover this topic in depth.
The History of Wireless Power Transfer
Nikola Tesla and His Experiments
The concept of wireless power transfer dates back to the late 19th century, when Nikola Tesla, a visionary inventor and engineer, experimented with transmitting electricity through the air using electromagnetic waves. He built a large coil called the Tesla coil, which could generate high-voltage alternating currents and sparks. He also constructed a wireless power station called Wardenclyffe Tower in New York, which he hoped to use for global communication and wireless power transmission. However, due to financial difficulties and lack of support from investors, Tesla's project was never completed and his tower was demolished in 1917.
Modern Developments and Applications
After Tesla's experiments, wireless power transfer remained a scientific curiosity for decades, until the advent of modern electronics and communication technologies in the 20th century. In the 1960s, researchers at Raytheon demonstrated the feasibility of transmitting microwave power over long distances using parabolic antennas. This led to the development of solar power satellites, which are proposed to collect solar energy in space and beam it to Earth via microwaves.
In the 1980s, researchers at MIT developed a method of wireless power transfer based on magnetic resonance, which uses resonant coils to create a strong magnetic field that can induce currents in nearby devices. This technique can achieve high efficiency and low interference over short distances. It is widely used for charging handheld devices like phones and electric toothbrushes, as well as implantable medical devices like artificial cardiac pacemakers.
In recent years, wireless power transfer has gained popularity and attention due to the increasing demand for wireless charging solutions for electric vehicles, unmanned aerial vehicles, wireless sensor networks, and other applications. Several standards and organizations have been established to promote the development and adoption of wireless power transfer technologies, such as the Wireless Power Consortium (WPC), the AirFuel Alliance, and the IEEE.
The Principles of Wireless Power Transfer
Near-Field and Far-Field Techniques
Wireless power transfer technologies can be classified into two categories, depending on the distance over which they can transfer power efficiently: near-field and far-field.
Near-field techniques use electric or magnetic fields that decay rapidly with distance to transfer power over short ranges, typically less than a wavelength. They are suitable for applications that require close proximity and alignment between the transmitter and the receiver, such as wireless charging pads, RFID tags, induction cookers, and contactless smart cards.
Far-field techniques use electromagnetic waves that propagate over long distances to transfer power over large areas, typically more than a wavelength. They are suitable for applications that require remote and directional power delivery, such as solar power satellites, wireless powered drone aircraft, and wireless power beaming.
Inductive and Capacitive Coupling
Inductive coupling and capacitive coupling are two common near-field techniques that use magnetic fields and electric fields, respectively, to transfer power between coils of wire or metal electrodes.
Inductive coupling uses two coils of wire, one in the transmitter and one in the receiver, that are tuned to the same frequency. When an alternating current flows through the transmitter coil, it creates a magnetic field that induces a voltage in the receiver coil, which can be used to power a load. The efficiency of inductive coupling depends on the coupling coefficient, which measures how well the magnetic flux is linked between the coils. The coupling coefficient is affected by factors such as the distance, orientation, size, shape, and number of turns of the coils.
Capacitive coupling uses two pairs of metal electrodes, one in the transmitter and one in the receiver, that are connected by a dielectric medium such as air or plastic. When an alternating voltage is applied to the transmitter electrodes, it creates an electric field that induces a charge on the receiver electrodes, which can be used to power a load. The efficiency of capacitive coupling depends on the capacitance, which measures how much charge can be stored between the electrodes. The capacitance is affected by factors such as the distance, area, shape, and material of the electrodes and the dielectric medium. [^1]
Magnetic Resonance and Microwave Beaming
Magnetic resonance and microwave beaming are two advanced techniques that use magnetic fields and electromagnetic waves, respectively, to transfer power over longer distances than conventional near-field techniques. [^1]
Magnetic resonance uses two resonant coils of wire, one in the transmitter and one in the receiver, that are tuned to the same frequency. When an alternating current flows through the transmitter coil, it creates a magnetic field that resonates with the receiver coil, which can be used to power a load. The efficiency of magnetic resonance depends on the quality factor, which measures how well the coils maintain their energy at a given frequency. The quality factor is affected by factors such as the resistance, inductance, capacitance, and losses of the coils. Magnetic resonance can achieve high efficiency and low interference over short to medium distances (up to several meters), even when there are obstacles or misalignments between the coils. [^1]
Microwave beaming uses a microwave generator and a parabolic antenna in the transmitter to convert electrical energy into microwave radiation, which is directed toward a rectenna (a combination of a rectifier and an antenna) in the receiver that converts microwave radiation back into electrical energy. The efficiency of microwave beaming depends on the conversion efficiency of the microwave generator and rectenna, as well as the beam divergence and atmospheric attenuation of the microwave radiation. Microwave beaming can achieve high power delivery over long distances (up to several kilometers), but it requires precise aiming and tracking of the transmitter and receiver antennas, as well as safety measures to prevent exposure to harmful microwave radiation. [^1]
The Benefits and Challenges of Wireless Power Transfer
Advantages of Wireless Power Transfer
Wireless power transfer offers several advantages over wired power transfer, such as: [^1]
Convenience: Wireless power transfer eliminates the need for cables and plugs, making it easier to charge or power devices without worrying about compatibility or availability of power outlets.
Mobility: Wireless power transfer enables the devices to move freely while being powered or charged.
Safety: Wireless power transfer reduces the risk of electric shock, fire, corrosion, and contamination caused by exposed wires and contacts. It also eliminates the need for batteries, which can leak, explode, or pollute the environment.
Reliability: Wireless power transfer improves the durability and performance of devices by avoiding mechanical wear and tear, loose connections, and oxidation of wires and contacts.
Flexibility: Wireless power transfer enables the design of devices that are compact, lightweight, waterproof, or wearable. It also allows for dynamic and adaptive power delivery to multiple devices with different power requirements.
Disadvantages and Limitations of Wireless Power Transfer
Wireless power transfer also faces several challenges and limitations that need to be overcome or mitigated, such as: [^1]
Efficiency: Wireless power transfer suffers from high power loss due to factors such as distance, misalignment, interference, reflection, absorption, and conversion losses. The efficiency of wireless power transfer depends on the technique, frequency, distance, and load of the system.
Cost: Wireless power transfer requires additional components and circuits to generate, transmit, receive, and convert electromagnetic energy. The cost of wireless power transfer depends on the complexity, quality, and scale of the system.
Safety: Wireless power transfer can pose potential health risks to humans and animals due to exposure to electromagnetic fields or radiation. The safety of wireless power transfer depends on the intensity, frequency, duration, and distance of exposure, as well as the biological effects of electromagnetic fields or radiation.
Interference: Wireless power transfer can cause electromagnetic interference with other devices or systems that use or are sensitive to electromagnetic fields or radiation. The interference of wireless power transfer depends on the frequency, power level, modulation scheme, and shielding of the system.
Standardization: Wireless power transfer lacks universal standards and regulations that can ensure compatibility, interoperability, safety, and efficiency of different systems and devices. The standardization of wireless power transfer depends on the collaboration and coordination of various stakeholders, such as manufacturers, consumers, researchers, regulators, and policymakers.
The Future of Wireless Power Transfer
Emerging Technologies and Trends
Wireless power transfer is a rapidly evolving technology that has many opportunities for innovation and improvement. Some of the emerging technologies and trends that are expected to shape the future of wireless power transfer are: [^1]
Smart wireless power transfer: This refers to the integration of wireless power transfer with information and communication technologies (ICT), such as sensors, actuators, controllers, processors, networks, cloud computing , and artificial intelligence. Smart wireless power transfer can enable intelligent control, optimization, and adaptation of the power transmission and consumption, as well as data and energy sharing and trading among devices and systems. Smart wireless power transfer can also support various applications in smart cities, smart homes, smart grids, smart transportation, and smart healthcare.
Wireless energy router: This refers to a device that can receive, convert, store, and distribute wireless power to multiple devices or systems with different power requirements and preferences. Wireless energy router can act as a hub or a relay for wireless power transfer networks, as well as a gateway or an interface for wired power grids. Wireless energy router can also perform functions such as power management, load balancing, fault detection, and security protection. Wireless energy router can enable flexible and efficient power delivery and utilization in various scenarios.
Wireless energy internet: This refers to a network that connects multiple wireless energy routers and devices or systems that can generate, transmit, receive, store, and consume wireless power. Wireless energy internet can integrate different wireless power transfer techniques and standards, as well as different energy sources and loads. Wireless energy internet can also support data and energy exchange and trading among peers, communities, and energy markets. Wireless energy internet can enable a decentralized and distributed power system that is resilient, sustainable, and economical.
Electrical Engineering Books on Wireless Power Transfer
If you are interested in learning more about wireless power transfer and its applications, here are some electrical engineering books that cover this topic in depth: [^1]
Wireless Power Transfer: Principles and Applications by Zhen Zhang and Hongliang Pang
This book presents a detailed overview of multiple-objective wireless power transfer technologies, including the latest research developments and emerging applications. It covers the fundamental theory, intelligent control, configuration analysis, and emerging power electronics techniques of wireless power transfer. It also discusses the methodologies and approaches of various wireless charging techniques, such as contactless power for electric vehicles, in-flight charging for unmanned aerial vehicles, and underwater wireless charging. It is a comprehensive technical reference for academic researchers and industry professionals in power and energy engineering, as well as an excellent textbook for postgraduate courses in relevant areas of industrial and electronic engineering.
Wireless Power Transmission for Sustainable Electronics by Naoki Shinohara
This book provides a comprehensive introduction to the theory, design, and applications of wireless power transmission for sustainable electronics. It covers the basic concepts, principles, methods , and applications of wireless power transmission for sustainable electronics. It covers the basic concepts, principles, methods, and challenges of wireless power transmission using electromagnetic waves, such as microwaves, millimeter waves, and lasers. It also discusses the applications of wireless power transmission for various devices and systems, such as wireless sensors, biomedical implants, electric vehicles, unmanned aerial vehicles, space systems, and environmental monitoring. It is a comprehensive and up-to-date reference for researchers, engineers, students, and enthusiasts who are interested in wireless power transmission and its environmental implications.
Wireless Power Transfer for Electric Vehicles by Shu Yuen (Ron) Hui and Wuhua Li
This book provides a systematic and in-depth treatment of wireless power transfer for electric vehicles. It covers the fundamentals, technologies, standards, and applications of wireless power transfer for electric vehicles. It focuses on the design and optimization of wireless charging systems for electric vehicles, including inductive power transfer, capacitive power transfer, magnetic resonance power transfer, and microwave power transfer. It also presents the latest developments and innovations in wireless charging systems for electric vehicles, such as dynamic wireless charging, bidirectional wireless charging, wireless charging with vehicle-to-grid integration, and wireless charging with renewable energy sources. It is a valuable resource for researchers, engineers, practitioners, and students who are involved in the research and development of wireless power transfer for electric vehicles.
Conclusion
Wireless power transfer is a fascinating and promising technology that can revolutionize the way we power and charge our devices. It has many advantages over wired power transfer, such as convenience, mobility, safety, reliability, and flexibility. It also has many applications in various fields, such as consumer electronics, medical devices, electric vehicles, unmanned aerial vehicles, wireless sensor networks, space exploration, and more. However, it also faces some challenges and limitations that need to be overcome or mitigated, such as efficiency , cost, safety, interference, and standardization. Wireless power transfer is also a rapidly evolving technology that has many opportunities for innovation and improvement. Some of the emerging technologies and trends that are expected to shape the future of wireless power transfer are smart wireless power transfer, wireless energy router, and wireless energy internet. Wireless power transfer is a fascinating and promising technology that can revolutionize the way we power and charge our devices. If you are interested in learning more about wireless power transfer and its applications, you can check out some of the electrical engineering books that cover this topic in depth.
FAQs
Here are some frequently asked questions about wireless power transfer:
Q: How efficient is wireless power transfer?
A: The efficiency of wireless power transfer depends on the technique, frequency, distance, and load of the system. Generally speaking, near-field techniques have higher efficiency than far-field techniques, and lower frequency techniques have higher efficiency than higher frequency techniques. The efficiency also decreases as the distance between the transmitter and receiver increases, and as the load impedance mismatch increases. The typical efficiency range of wireless power transfer systems is from 10% to 90%.
Q: How safe is wireless power transfer?
A: The safety of wireless power transfer depends on the intensity, frequency, duration, and distance of exposure to electromagnetic fields or radiation, as well as the biological effects of electromagnetic fields or radiation. Generally speaking, near-field techniques have lower safety risks than far-field techniques, and lower frequency techniques have lower safety risks than higher frequency techniques. The safety also increases as the distance between the transmitter and receiver increases, and as the shielding or filtering of electromagnetic fields or radiation increases. The typical safety standards and regulations for wireless power transfer systems are based on the specific absorption rate (SAR) or the maximum permissible exposure (MPE) limits for humans and animals.
Q: How standardized is wireless power transfer?
A: The standardization of wireless power transfer is still an ongoing process that involves various stakeholders, such as manufacturers, consumers, researchers, regulators, and policymakers. There are several standards and organizations that have been established to promote the development and adoption of wireless power transfer technologies, such as the Wireless Power Consortium (WPC), the AirFuel Alliance, and the IEEE. However, there are still many challenges and issues that need to be resolved or harmonized, such as compatibility, interoperability, efficiency, safety, and regulation.
Q: What are some applications of wireless power transfer?
A: Wireless power transfer has many applications in various fields, such as consumer electronics, medical devices , electric vehicles, unmanned aerial vehicles, wireless sensor networks, space exploration, and more. Wireless power transfer can provide convenience, mobility, safety, reliability, and flexibility for these applications. Some examples of wireless power transfer applications are:
Wireless charging pads: These are devices that use inductive or capacitive coupling to charge handheld devices like phones, tablets, laptops, and smartwatches by simply placing them on a pad or a mat. They can eliminate the need for cables and plugs and provide a universal charging solution for different devices.
Wireless charging stations: These are devices that use magnetic resonance or microwave beaming to charge elect