Maxwell's displacement current-based wireless power transmission and driving portable, wearable electronic device schematic

Energy is the foundation of today's social development and an important symbol of human life quality. From the first use of electricity, electricity is always efficiently, safely, and accurately transmitted through metal wires/cables. As a leading technology for fossil fuels, nuclear power and hydroelectric power generation, electromagnetic induction power generation technology relies on the flow of free electrons driven by Lorentz force in metal wires. In order to meet the energy requirements of mobile electronic products, Internet of Things, and sensor networks, it is very important to realize the wireless transmission of electrical energy, especially in the fields of implantable medical devices, security, and radio frequency identification. At present, wireless power transmission technology is usually based on induction coils and/or antennas. Compared with wireless communication technology, wireless charging technology is very important in enhancing the adaptability and mobility of wireless devices and systems. Although there are three types of wireless charging technology modes, electromagnetic induction, magnetic resonance, and radio waves, these technologies are still quite complex and inefficient.

In 1861, the British scientist Maxwell proposed Maxwell's equations, the first major equation in physics, and introduced the concept of displacement current in the equations. Maxwell's displacement current is different from the conventionally observed free electron-conducting current, but due to the time-varying electric field plus the minute movement of the atom's bound charge over time and the dielectric polarization in the material. The first item of displacement currents unified the electric and magnetic fields, and predicted the existence of electromagnetic waves, which laid the physical foundation for wireless communications. The second item of displacement current was found to be the fundamental theoretical basis and source of nanogenerators, with important potential applications in wireless power supply. The theoretical origins of nanogenerators are fundamentally different from traditional electromagnetic generators. Electromagnetic generators use a changing magnetic field to generate currents. They use the Lorentz force-driven mechanism of resistive free electron conduction, while nanogenerators use surface polarization charges. The resulting polarization field changes to generate electricity, using a capacitive displacement current mechanism. Nano-generators are another major application of Maxwell's displacement current following electromagnetic wave theory and technology in energy and sensing, and will affect the future development of the Internet of Things, sensor networks, blue energy and big data and other technical fields.

Recently, Wang Zhonglin, academician of the Chinese Academy of Sciences, chief scientist of the Beijing Institute of Nano Energy and Systems, Chinese Academy of Sciences, Cao Xia, professor of Beijing University of Science and Technology, Beijing University of Science and Technology, and Wang Ning, professor of Beijing University of Science and Technology, carried out a Maxwell-based displacement current. Driven wireless power transmission research. The research team has long been engaged in the research of micro-nano energy and nano-generators. Thanks to the accumulation of research work and combined with the phenomenon of frictional electrification observed in life, the idea of ​​applying Maxwell's displacement current to wireless power transmission was proposed for the first time. The contact sliding rotary generator with a grid structure and the flexible wearable generator are further designed. The external mechanical driving/stimulation causes the polarization charge distribution and the spatial electric displacement field to periodically change with time, thereby generating a displacement current. These generators wirelessly collect the mechanical energy in the surrounding environment by the principle of displacement current, and can continuously power various portable and wearable electronic devices. This wireless power transmission technology provides a more efficient method for energy transmission at low frequencies (<5 Hz). Related research results were published on Advanced Materials.

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