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Wireless charging principle deep analysis

Edit:Shenzhen Keliway Technology.,LtdUpDate:May 16, 2018

With the continued popularity of battery-powered consumer electronic devices such as portable media players, smart phones, and tablet computers, homes are flooded with a large number of different chargers and bundled cables. The concept of charging the device wirelessly, that is, without any direct connection, has been in the works for some time now, and it is rapidly bringing people's interest to make it more flexible and useful. However, what are the different design technologies and challenges that engineers need to deal with?


Since there is no need to use cabled cable, there are many attractive places for wireless charging of consumer devices. Perhaps it should be said more clearly that the purpose of wireless charging is to provide a new way of charging the battery of the device through innovative ways other than wires or connectors.


Wireless charging methods have become very popular in many consumer devices such as electric toothbrushes. One of the most important methods is the sensing method based on Maxwell's law. That is, the magnetic field from one coil changes in another coil that is coupled to it. Generate current. Although sensing methods using magnetic fields are suitable for many small devices such as those described above, the use of this method in more modern consumer electronics devices such as tablet PCs and smart phones faces many engineering design challenges.


As the power supplied to the battery increases, the relative efficiency or flexibility requirements for placing the coupled coil also increase. The main consideration of this sensing method is how to control the electromagnetic interference (EMI) generated or "sent" energy and the signal transmitted to the 'receiving' device using the sensing magnetic field. The receiving device then converts the magnetic field energy into electrical energy and charges the battery. Wi-Fi, Bluetooth, Near Field Communication (NFC), cellular systems, and FM radio are examples of many wireless voice and data connection methods that may be subject to such electromagnetic fields.


Of course, another consideration is to make the power transfer efficiency as high as possible, even under challenging constraints such as higher power levels and wider placement errors. In the past few years, the industry has put forward many new ideas on how to implement sensing charging technology, but the progress of avoiding EMI effects is not as smooth as expected, because achieving EMI compliance requires arduous efforts.


Recent challenges in this area have been further developed thanks to the unremitting efforts of the Wireless Charging Alliance (WPC). WPC is an action plan of the Consumer Electronics (CEA) organization in the United States. Its purpose is to encourage further research and development and make wireless charging more compelling, so it is favored by the larger consumer groups.


Another well-known constraint of the sensing method is the need to accurately pair the charger and the charged device, which can be best described with an electric toothbrush example. There is a small tower on the charger substrate that rises from the substrate on which the toothbrush to be charged is placed. Using this method, two coils can be perfectly matched to ensure the transmission of magnetic energy. Any slight misalignment will completely lose power transmission capability. This method of use is obviously inconvenient when using other devices that require slightly higher power levels, such as smart phones or tablet computers. Finally, there is a problem of how to solve the problem of electric heat loss. The higher the charger power, the greater the heat loss. This is even more of a problem for highly sensitive lithium-ion batteries, and is likely to create component stress in today's highly compact consumer electronics designs.


The use of capacitor architecture is another wireless charging method that can replace magnetic field wireless charging. The principle of this method is similar to Maxwell's law of electric field. This concept has been adopted by Murata and has been widely introduced into new designs. The company's approach is to use a quasi-static electric field and transmit energy through a capacitor, which consists of two electrodes that are physically separate elements. Bringing these two components close to each other creates an array of capacitors that can be used to transmit energy