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　　What are the foreign object detection standards for wireless charging?

　　Wireless charging technology (Wireless charging technology; Wireless charging technology) originates from wireless power transmission technology. Wireless charging, also known as induction charging and non-contact induction charging, uses near-field induction, that is, inductive coupling, to transmit energy from the power supply equipment (charger) to the electrical device. The device uses the received energy to The battery is charged and used for its own operation at the same time. Since energy is transmitted between the charger and the electrical device through inductive coupling, no wires are needed to connect the two, so both the charger and the electrical device can have no exposed conductive contacts.

　　With the rapid development of technology, major electronic manufacturers are racking their brains to launch various forward-looking technologies, hoping to attract the attention of consumers and bring a more convenient life to mankind. Wireless charging technology and products are adapted to this trend. And born.

　　Main features:

　　Wireless charging technology has become an important tool for brand manufacturers to create product differentiation. In particular, the Qi technology standard formulated by the Wireless Power Consortium (WpC) has been widely adopted by the industry. Currently, WpC is actively developing a new version of the specifications, which will add metal foreign object detection functions and increase charging power to further consolidate its mainstream position in the market.

　　A method of contactless power transmission from a base station to a mobile device, it is based on near-field magnetic induction coils. The power transferred is approximately 5W using an appropriate secondary volume size (typically approximately 40mm external). Operating frequency range: between 110-205HZ. Two methods are supported for placing a mobile device on the surface of the base station. Mobile devices that help guide users to the correct location form a layer on the surface. Through the base station, one or several fixed-position surfaces are provided. Mobile devices can be positioned freely anywhere on the surface forming a layer that can provide power to base station locations through any surface. A simple communication protocol enables the transfer of full control capabilities to mobile devices. Considerable design system flexibility for integration into a mobile installation. Very low backup power (execution), installation dependent.

　　The electromagnetic induction charging primary coil uses alternating current of a certain frequency to generate a certain current in the secondary coil through electromagnetic induction, thereby transferring energy from the transmission end to the receiving end. At present, the most common charging pad solution uses electromagnetic induction. In fact, there is not much mystery in the technical implementation of electromagnetic induction solutions. China's local BYD Company applied for a non-contact induction type as early as December 2005. The patented charger uses electromagnetic induction technology. Magnetic field resonance charging consists of an energy sending device and an energy receiving device. When the two devices are adjusted to the same frequency, or resonate at a specific frequency, they can exchange energy with each other. It is a technology currently being studied. A research team led by MIT physics professor Marin Soljacic used the technology to light up a 60-watt light bulb two meters away and named it WiTricity. The diameter of the coil used in this experiment reaches 50cm, which cannot be commercialized yet. If the coil size is to be reduced, the received power will naturally decrease. Radio wave charging is a relatively mature technology, similar to the early use of mineral radios. The main ones are It consists of a microwave transmitting device and a microwave receiving device, which can capture the radio wave energy bouncing off the wall and maintain a stable DC voltage while adjusting with the load. This method requires only a transmitter mounted on a wall plug and a mosquito receiver that can be mounted on any low voltage product.

　　Wireless charging foreign object detection standards

　　The electromagnetic induction theory used by WpC comes from Faraday's electromagnetic theory. When a coil is energized, it will generate magnetic flux, which will then induce the surrounding coils to generate current. The conversion efficiency can be as high as 70% or more.

　　electromagnetic energy conversion

　　The method of converting electricity into magnetism, and then through magnetism into electricity, is the conversion of electromagnetic energy. Wireless charging technology uses this principle to achieve the purpose of transmitting power. Chargers commonly used in daily life also use this principle. The difference is that the magnetic conductive material in the charger uses an iron core to conduct energy; while wireless charging technology only transmits energy through the air gap. Conduct magnetic flux to achieve the purpose of magnetic energy transmission.

　　Energy curve and operating frequency

　　According to the specification defined by WpC, the operating frequency is defined in the range of 110k~205kHz, and its series resonant frequency is defined as 100kHz. Judging from the power versus frequency curve, the closer the operating point is to 100kHz, the greater the energy obtained by the receiving end. High, the farther away from 100kHz, the lower the energy obtained by the receiving end, so that different energy requirements can be adjusted. Another way to adjust is to use a fixed 140kHz method. By adjusting the working cycle of the frequency, you can also adjust the energy. The lower the working cycle, the lower the energy obtained. The higher the working cycle, the higher the energy obtained. .

　　transmission distance

　　The distance that electromagnetic fields can be transmitted increases with the higher the operating frequency. According to the WpC standard, this operating frequency belongs to the low-frequency operating band, so the distance between the transmitting coil and the receiving coil is not long. The WpC standard defines the distance that can be operated normally as within 5 millimeters (mm). The farther the distance, the worse the overall conversion efficiency will be.

　　signaling

　　In addition to the energy that needs to be transferred, packetizing messages is one of the main focuses. The receiving end will pass the required energy information back to the transmitting end. The transmitter needs to decode the received energy and adjust it according to the energy required by the receiver. This signal is transmitted through the electromagnetic field. The original operating frequency (110k? 205kHz) is used as the carrier frequency. The packet message is carried in the electromagnetic field of energy transmission. The signal is composed of a series of codes; the frequency of the signal About 2k? 4kHz is about fifty times the frequency of the carrier. This way, the transmission energy can be used while also transmitting the message back. There is no need to use other components to transmit the message. But using 2k? The frequency of the 4kHz signal has an embarrassing disadvantage - it belongs to the frequency band that can be heard by the human ear, so when the system is working, if you listen very close, there will be very subtle sounds. Because WpC has been defined in this way, this sound is currently unavoidable and can only be made as quiet as possible.

　　Efficiency and charging time

　　The efficiency defined by WPC is the percentage divided by the power input of the DC power supply to the transmitter as the denominator and the output power of the receiver as the numerator. This refers to the efficiency of energy conversion. The current efficiency is mainly limited by the matching of coils and capacitors, and secondarily by the selection of electronic components. The current efficiency is about 70%. Calculated based on the output energy of 3 watts (W), the input power required at the transmitter is 4.3 watts. 1.3 watts of it is converted into other energy, mainly heat energy. What the average user is more likely to notice is the charging time. The power of each battery will be expressed in ampere hours (Ah). For example, 2,000 milliamp hours (mAh) means that 2 amps can be discharged for 1 hour; or 2 amps can be charged for 1 hour (theoretical value). The greater the charging current, the shorter the time it takes for the battery to be fully charged. Currently, due to limitations of most receivers, they can only output about 600 mA, so the charging time will be lengthened.

　　Comply with FOD/medium power application requirements WpC accelerates standard formulation work

　　WpC just made a move in early 2013, which was to convert the Qi version from 1.0 to 1.1. One of the major changes is the addition of Foreign Object Detect (FOD) function.

　　In fact, under normal circumstances, if a metal foreign object is placed on the transmitting end, it will not generate heat; the situation where it will generate heat is when a metal foreign object is placed on the transmitting end and the receiving end is stacked up. Because the electromagnetic field will generate eddy currents on the metal foreign objects, heating the metal foreign objects will cause the shell to melt and cause danger. Therefore, WpC defines version 1.1, which limits the temperature of metal foreign objects to below 60°C, which means that the launch system must try to prevent the temperature of foreign objects from exceeding 60°C.

　　According to estimates from international market research agencies, the compound annual growth rate of the output value of wireless charging technology in the next four years will be as high as 73%. The support attitude of major international brand mobile phone manufacturers and telecom operators towards wireless charging technology is one of the keys to the speed of market promotion; Certification specifications and safety regulations are obstacles that the industry must overcome urgently. WPC's product compatibility specifications for medium and high power are about to be released. By then, the application landscape will extend from smartphones to tablets and laptops and other mobile devices with higher charging wattage. It is expected that wireless charging will generate related products in the next few years. Applications and designs will bloom everywhere, opening a new page of technological convenience for human life.

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