Wireless charging technology is developing rapidly
In 1894, Nikolai Tesla demonstrated wireless power transmission to an astonishing audience in his laboratory in New York: crossing the room to power the lights wirelessly, as if by magic.
Although his discovery has aroused great interest, in the next century, wireless power transmission is still limited to a number of small non-contact charging applications, such as car wireless chargers, such as pacemaker batteries, electric toothbrushes and razors.
In most electronic products, the volume is bulky, the mobility is poor, and the battery technology is very backward, the demand for wireless charging in the industry is not large. But with the emergence of small, powerful and always online mobile devices, wireless charging has finally created a real application demand, and the invention of Tesla has also received people's attention.
Advantages of wireless charging
The convenience of wireless charging for users is obvious, but its advantages are far more than avoiding the trouble of using cables. Because wireless charging is expected to make equipment manufacturers finally remove all external connectors, this wireless technology can make equipment cheaper, lighter and more reliable. Connector socket has many disadvantages, easy to be polluted by dirt and water, easy to cause physical damage, and occupy space, affect the aesthetics of the product, wireless charger, and increase the manufacturing cost.
It can be said that the real reason why a USB or similar connector is still reserved on the mobile phone at present is power supply, not data. Apple's controversial decision on its recently released iPhone to remove the headphone jack appears to be a warning that other common mobile device connectors will soon disappear.
Principle of wireless charging
At present, most wireless charging technologies rely on the principle of magnetic induction. Simply put, this technique places the coil on one side of the transformer in the device and the coil on the other side of the transformer in the charger. When the two coils are very close together, the charger can generate a magnetic field and induce a current in the coupled device. This is a kind of near-field non radiation technology. Its actual working distance is very short, about 1cm. Its ability to penetrate obstacles is poor, and its thickness is only a few millimeters.
More and more modern equipment uses resonant inductive coupling, which is a technology invented by Tesla a a century ago. By tuning two coils to the same frequency for resonance, the performance of ordinary magnetic induction can be improved. This technical improvement can achieve higher efficiency, can significantly increase the actual operating distance to a few centimeters, has better penetration for barrier materials, and can greatly improve the ability to charge multiple devices at the same time.
One competing solution for Tesla's wireless charging technology is capacitive coupling, which uses similar principles but is based on capacitors rather than transformers. Although the research on capacitive coupling is still going on, it seems that it has been covered by the development trend of magnetic induction technology recently. In addition, the industry also has some research and development of wireless power transmission through radio-frequency radiation, even ultrasonic and other methods.
Generally speaking, when a rechargeable device is placed in the effective range, the vehicle wireless charger, efficient and convenient charging system must be able to detect its existence, so as to avoid wasting electric energy and effectively guide power to one or more devices. In addition, chargers need to be able to detect other interfering metal objects (such as jewelry, keys and incompatible equipment) and avoid providing them with wireless power, so as to avoid heating and damage (in fact, the magnetic induction kitchen induction cooker uses relevant principles to cook food). The sensing device can achieve these goals by periodically "scanning" its vicinity at a lower power and by using multiple coils to determine the direction. In fact, the modern general wireless charging specification includes two-way data transmission, which can communicate with its client devices to achieve the best charging effect and security.
Wireless charging standard
For several years, wireless charging of mobile devices has been a battle between different competing standards, wireless chargers, but the battle seems to be coming to an end. Over the past three years, Qi standard has become an obvious leader in wireless charging of mobile devices. It is developed and promoted by Wireless Power Consortium (WPC), and its members include Samsung, Qualcomm, Texas Instruments, apple, Sony, LG, Philips, Bosch and many other important technology companies.
Last year, apple showed strong support for the standard by integrating the Qi standard into the iPhone 8 and iPhone x, a reversal of Apple's earlier unwillingness to adopt a wireless charging scheme. IKEA has also demonstrated support for the Qi standard by building wireless chargers into a range of furniture and lamps, which have been available for about three years. Automakers are also now integrating chargers into their cars.
The latest version of Qi standard is based on resonant inductor coupling technology. At present, most of the devices use the Qi low power specification, which can provide up to 5W power and is suitable for charging mobile phones, smart watches, wearable devices and other small devices. At present, the equipment used in the new generation of medium power specification of Qi can also be provided, which can achieve a power of up to 15W, with faster charging speed, and is suitable for charging larger devices such as notebook computers. The higher power standard of Qi standard is under development, which can provide 120W to 1kW power.