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    2021-10-21 17:41:20
    Wireless Charging Explained: Working and Standards


     Fundamental principle 1.Electromagnetic induction

    2.Magnetic field resonance

    3.Radio wave
     Mainstream technical standards 1. Qi
    2. Power Matters Alliance
    3. A4WP
    4. iNPOFi technology
    5. Wi-Po technology

    Ⅰ History

    In 1890, physicist and electrical engineer Nikola Tesla had already done a wireless power transmission experiment. The international system of magnetic induction is also named after him. Tesla's wireless power transmission method uses the earth as the inner conductor and the earth's ionosphere as the outer conductor. By amplifying the transmitter in a radial electromagnetic wave oscillation mode, a low-frequency resonance of about 8 Hz is established between the earth and the ionosphere, and then the surface electromagnetic waves surrounding the earth are used to transmit energy. However, due to a lack of financial resources, Tesla's bold vision has not been realized, although later generations have fully confirmed the feasibility of this scheme in theory.

    On June 7, 2007, the MIT research team published the research results on the website of the American "Science" magazine. The research team applied resonance to the transmission of electromagnetic waves and successfully "caught" the electromagnetic waves. They used copper coils as electromagnetic resonators. One coil was attached to the power transmitting side and the other was receiving power. After the transmitter sends an electromagnetic wave of a certain frequency, it spreads through the electromagnetic field to the receiver, and the electric power is transmitted wirelessly. This technology, which they called "wireless power", has been tested many times and has successfully powered a 60-watt light bulb two meters away. The farthest transmission distance of this technology can only reach 2.7 meters, but the researchers believe that the power supply can already charge the battery within this range. And only need to install a power supply, you can power the electrical appliances in the whole house.

    Mobile phone wireless charging.jpg

    Mobile phone wireless charging

    In February 2014, computer manufacturer Dell joined the A4WP camp. At that time, relevant executives of the camp said that they would upgrade the technology to support wireless charging of ultrabooks from computer manufacturers such as Dell. Most of the traditional laptops on the market have power supplies exceeding 50 watts, but Ultrabooks use Intel's low-power processors and will be the first laptops to use wireless charging. Prior to this, wireless charging technology has always been only related to "small" mobile devices such as smartphones and small tablets. However, A4WP ("Wireless Charging Alliance"), one of the three major wireless charging camps, recently announced that its technical standards have been upgraded, and the supported charging power has increased to 50 watts, which means that high-power devices such as laptops and tablets can also realize wireless charging.

    In 2020, most flagship smartphones already support wireless charging.

    Ⅱ Fundamental principle

    1.Electromagnetic induction

    The alternating current of a certain frequency in the primary coil generates a certain current in the secondary coil through electromagnetic induction, thereby transferring energy from the transmitting end to the receiving end. At present, the most common charging solution uses electromagnetic induction. In fact, the electromagnetic induction solution does not have too much mystery in terms of technical realization. China’s BYD company applied for a non-contact induction charger as early as December 2005. The patent uses electromagnetic induction technology.

    Principles of wireless charging technology.jpg

    Principles of wireless charging technology

    2.Magnetic field resonance

    It is composed of an energy transmitting 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 under study. A research team led by Marin Soljacic, professor of physics at the Institute of Technology (MIT), used this 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 size of the coil is to be reduced, the received power will naturally decrease.

    3.Radio wave

    This is a relatively mature technology, similar to the early use of mineral radios. It mainly consists of a microwave transmitting device and a microwave receiving device. It can capture the radio wave energy bounced from the wall and maintain a stable DC voltage while adjusting with the load. This method only needs a transmitter installed on the wall plug and a "mosquito-type" receiver that can be installed on any low-voltage product.

    Ⅲ Mainstream technical standards

    There are five mainstream wireless charging standards: Qi standard, Power Matters Alliance (PMA) standard, Alliance for Wireless Power (A4WP) standard, iNPOFi technology, and Wi-Po technology.

    1. Qi

    Qi is the world's first standardization organization to promote wireless charging technology-Wireless Power Consortium (WPC) launched the "wireless charging" standard, with two major characteristics of convenience and versatility. First of all, products of different brands can be charged with Qi wireless chargers as long as they have a Qi logo. Secondly, it overcomes the technical bottleneck of wireless charging "university". In the near future, mobile phones, cameras, computers, and other products can be charged with Qi wireless chargers, providing the possibility for large-scale applications of wireless charging.

    Basic principles of wireless charging for mobile devices.jpg

    Basic principles of wireless charging for mobile devices

    The mainstream wireless charging technology in the market mainly adopts three methods, namely electromagnetic induction, radio waves, and resonance. Qi uses the most mainstream electromagnetic induction technology.

    2. Power Matters Alliance

    The Power Matters Alliance standard was initiated by Duracell Powermat, which is a joint venture between Procter & Gamble and Powermat, a wireless charging technology company, and has relatively outstanding comprehensive strength. In addition, Powermat is also one of the supporting members of the Alliance for Wireless Power (A4WP) standard.

    Three companies, AT&T, Google, and Starbucks, have joined the PMA Alliance (abbreviation of Power Matters Alliance). The PMA Alliance is committed to creating wireless power supply standards for mobile phones and electronic devices that comply with the IEEE Association standards and has a leading position in the field of wireless charging.

    3. A4WP

    A4WP is the abbreviation of Alliance for Wireless Power standard, created by the wireless charging alliance jointly created by Qualcomm, South Korea's Samsung, and the aforementioned Powermat company. The alliance also includes members such as Ever Win Industries, Gill Industries, Peiker Acustic and SK Telecom. The goal is to establish technical standards and industry dialogue mechanisms for wireless charging equipment for electronic products, including portable electronic products and electric vehicles.

    4. iNPOFi technology

    iNPOFi ("invisible power field") wireless charging is a new wireless charging technology. Its wireless charging series products adopt intelligent electric transmission wireless charging technology, which has the characteristics of no radiation, high power conversion efficiency, and weak thermal effect.

    Compared with other existing wireless charging technologies, iNPOFi intelligent non-radiation technology has no radiation, adopts electric field pulse mode, and does not produce any radiation. The test results of China Taier Laboratory show that the radiation increase value is almost zero. In terms of high efficiency, the Tyre laboratory also determined that the charging transmission efficiency of the products of this technology is as high as 90% or more, which completely changes the low efficiency of traditional wireless charging, which is up to 70%.

    It is worth mentioning that for smart device manufacturers, inpofi uses a very small chip as the core to achieve an ultra-micro design, only 1/4 of the size of a fifty cents coin, which can be easily integrated into any device. It can also be integrated into various forms of wearable devices. This is unattainable by products based on traditional electromagnetic principles.

    As a new generation of wireless charging technology standard, iNPOFi technology is efficient, green, convenient, and economical. The charging equipment adopting this technology includes two parts: a power transmitting device and a power receiving device. The size and thickness of the transmitting device are the same as those of ordinary mobile phones. The receiving device is embedded in the mobile phone protective cover, and the mobile phone is covered with the protective cover and placed on the transmitting device for charging. During the charging process, the phone does not need to be plugged in any cable. Related testing showed that electromagnetic radiation was zero during the charging process, and the power conversion efficiency reached 94.7%, which was close to wired charging. The charging device supports a low-voltage power supply and is compatible with an ordinary USB power supply.

    5. Wi-Po technology

    Wi-Po technology, a Wi-Po magnetic resonance wireless charging technology, uses a high-frequency constant amplitude alternating magnetic field generator to generate a 6.78MHz resonant magnetic field to achieve a longer transmission distance.

    The technology realizes communication control through Bluetooth 4.0, which is safe and reliable and can support one-to-many synchronous communication. It also has over-temperature, over-voltage, over-current protection, and foreign body detection functions. Because the carrier used in this technology is a space magnetic field, energy will not be emitted like electromagnetic waves, so it will not cause radiation damage to the human body.

    Wi-Po magnetic resonance wireless charging can be applied to various scenarios such as mobile phones, computers, smart wearables, smart homes, medical equipment, and electric vehicles.

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