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Home | Blogs | Standards Of Wireless Power Transfer - Part-3
Fri May 31 11:55:23 UTC 2019

Standards Of Wireless Power Transfer - Part-3



The wireless power transmission industry uses various standards, each of which tackles a different set of uses and are supported by different companies. The 3 major standards of Wireless Power Transfer are mentioned as follows:




The AirFuel Alliance was officially created on June 1st, 2015 through the merger of Alliance for Wireless Power (A4WP) and Power Matters Alliance (PMA). The merger was the result of a deal signed between the member companies to allow for interoperability between the two standards, creating a unified standard. The alliance boasts membership of over 170 companies in various spheres of technology including companies like Samsung, Qualcomm, Energous, and Sony.


AirFuel Resonant


This technology is based on Rezence, the standard developed by A4WP that uses the principle of Resonant Inductive Coupling. This ?loosely coupled? method works by creating a wireless transfer of electrical energy between two coils, tuned to resonate at the same frequency. Based on the principles of electromagnetic coupling, resonant-based chargers inject an oscillating current into a highly resonant coil to create an oscillating electromagnetic field. A second coil with the same resonant frequency receives power from the electromagnetic field and converts it back into an electrical current that can be used to power and charge devices.


The standard supports up to 50W of power at a distance of 50mm. This technology allows for power transmission through a variety of materials including wood, concrete or stone making the installation easy while maintaining efficiency. This can allow a manufacturer to mount the transmitter inside furniture or embed in the floor of a garage to charge electric cars.


AirFuel RF

This technology uses electronic waves or radio frequencies instead of magnetic fields to charge a device. An RF transmitter transmits RF waves and a receiver embedded within a device picks them up, converts them into electricity and powers the device. RF can power devices at a distance ranging from a few centimetres to a few meters. There are 2 categories of this technology: Near Field and Far Field.


Near-Field allows any 3D item ? from a mere cup holder to a box or a drawer ? to become a transmitter/charging station. It allows for full charging (from 0-100%) and greater spatial freedom ? giving users a true ?drop and charge? experience. Far Field emits electronic waves and the transmitter locates the RF receiver in a defined area. The receiving device charges as long as it is within the charging radius (which can be over 10 feet) but, due to the distance, there may be efficiency losses that increase with distance.



Dell Latitude 7285 is the world?s first wireless charger designed to declutter today?s workspace by eliminating the need of wires. incorporating WiTricity?s technology of magnetic resonance wireless charging, the device is built to transform any workspace into a clutter-free environment.


Chargi??s connected charging platform enables a mobile-app controlled wireless charging experience that gives a chance to engage with users by providing wireless charging. It uses AirFuel?s Resonant wireless charging technology, by which customers can download an app to charge their devices, enabling venues to know which customers are using the app in real-time and communicate with them directly on their device.


Order Furniture, the biggest furniture vendor in Taiwan, is bringing wireless charging into people?s homes by launching a new line of AirFuel Resonant-enabled furniture. New sofas with built-in wireless charging PTUs will make it convenient for consumers to charge their devices while they continue to work or play or relax. Based on the elegant and functional design of AirFuel Resonant, the charging source can be hidden instead of attached upon, as Resonant offers the benefit of charging through materials such as wood, concrete or stone.


PowerSphyr was at CES (Consumer Electronics Show) 2019 boasting its AirFuel and Qi enabled transmitters. This product enables users to charge first generation (inductive) and next-generation (resonant) devices together, on a single charging surface.


MaxLinear, jjPLus and Zinwell are pioneer AirFuel Resonant based 65watt solutions that transmit both power and gigabit 5G data through walls, eliminating the need for a separate Wi-Fi access point.




The WPC, established in 2008, is a collaborative standards development group. It has over 600 member companies including major players like HP Inc, Samsung, Huawei, Haier Group and Bosch. They have developed 3 standards for a variety of applications differentiated by power and use-case: Qi standard, Cordless Kitchen standard, Medium power standard.


Qi Mobile Computing Standard

Qi is an open interface standard that defines wireless power transmission using electrical induction up to 4cm. It was developed for mobile applications and currently delivers up to 15W of power with a future extension to 60W. It is the most widely used and best-known wireless power transmission standard. Over 3700 products are currently certified with the Qi standard.


Mobile charging (5-15 watts): Most wireless charging capabilities in modern smartphones is Qi certified. The Qi standard will also be extended to support laptops in the future.


Medium Power Consumption Devices: The medium power standard fills the gap between Qi and Cordless Kitchen standards. It delivers between 30 and 65W of power with future plans to scale to 200W. It is in the early stages of development and, hence, isn?t completely defined. It is to be used for mobile devices that are too powerful for the Qi standard. One growing use-case is inductively powered cordless power tools.


High Power Consumption Devices - Cordless Kitchen: This standard, although still developing, defines methods to transfer power up to 2200W to power smart kitchen appliances like electric cooktops, blenders and rice cookers. The draft specification is currently only available to members of WPC.


The specifications of this standard aim to provide the flexibility and convenience of a cordless kitchen with a modern design. The lack of power cords also enables users to use the kitchen space with increased efficiency and in different ways. This is because the power transmitters would be installed underneath kitchen counters and tables, with no wires in sight. Cordless appliances are also comparatively safer because they do not posit any electrical or fire hazard.



Practically, all wireless chargers for modern phones comply with the Qi standard. Phillips and Haier have showed off their latest blenders and other cooking appliances in recent years. Moreover, the critically acclaimed iPhone Xs, iPhone Xs Max and the Samsung Galaxy s10 have Qi compliant wireless charging mechanism where their coils can act as both receivers and transmitters. Due to this they are able to charge accessories and other Qi compliant phones. All Powermat compliant devices also support Qi since 2018 when Powermat joined the WPC.




The Open Dots Alliance is a non-profit organization formed by JVIS USA which developed the Open Dots specification. It is a conductive wireless power transmission technology primarily used for charging mobile devices. It is called Open because the specification and certification is open and public. It is also called Dots because products employ the standard use a distinctive pattern of contact ?dots? to transfer power.


The technology, called Surface Energy, uses a board with conductive pads on it having alternating polarities. It is also called a plug-less power strip. Once a device with ?dots? is detected, the pads in contact are powered and the charging begins. The contact can be entirely random and the board needs to contain adequate detection and rectification circuitry. These devices are considered safe because both the input and output have DC currents which are safer than AC currents.


The Open Dots specification specifies a voltage of 15-20V between the conductive pads and can provide 50W for the 15V pads and up to 160W for the 20V pads. For applications like mobile phone charging, the voltage is regulated down to 5V.


According to the inventor, Mitch Randall, the technology can support around 100 devices charging simultaneously with a large enough board and is equivalent to plugging in to a wired power outlet.


In recent years, this standard was used in 12 automobile models of five major brands namely, Ford, RAM, Dodge, Chrysler and Scion. Other members as of 2018 are Toyota, JVIS USA, Zii Energy, Incipio, and Venture.



Both WPC and AirFuel Alliance have their own specifications and merits.


AirFuel is one of the standards that offers the ability to use and exchange information using a different type of protocol, frequency, and process than Qi. Theoretically, it promises the same benefits as Qi (in a way that all AirFuel devices work with all AirFuel transmitters), but Qi has scale via adoption that AirFuel cannot match.


Technologies using Qi standards are the leader in number of mobile devices used worldwide. Apple, Google, HTC, LG, Motorola, Nokia, and Samsung have all launched Qi based mobile phones. Similarly, Qi technology is included in many vehicle models, IKEA furniture, Corian countertops, and standalone Qi transmitters of different shapes, colours, and sizes.


AirFuel adoption is limited mostly to pilot scale. Dell launched a laptop in 2017; LG launched a limited-edition phone; and a variety of infrastructure and accessories have pilot uses in hotels, sports venues, airports, and coffee shops around Asia, Europe, and the U.S.


Also, Qi has a very low frequency, while Rezence has AM and FM frequencies.


There are 3 main parts of the Qi specification:


a.     Interface definition


The primary interface guides the interaction of a power transmitter and receiver. It defines the positioning of the transmitter and receiver with respect to each other and specifies their electrical behaviour in terms of transmitter coil current and power consumption along with the voltage generated in the receiver.


The secondary interface in the Qi standard explains the interaction of the receiver-transmitter system with its environment. It defines power consumption, UI features, foreign object detection and thermal effects of inductive charging.


b.     Performance requirements


Specific performance requirements cannot be accessed by the public and are only available to the paying members of WPC. The basic requirements are that transmission efficiency needs to be over 70% at 1cm distance. The transmitter shuts off if the efficiency drops below that threshold. Efficiency is easily detected by comparing transmitted and received power via a data connection.


Qi also defines 3 levels of transmission voltage.


5 volts for USB applications

12 volts for applications inside automobiles

19 volts for laptops


c.      Compliance testing


To be Qi compliant and having the authorization to carry the Qi logo, a device needs to be tested by authorized testing labs using test procedures defined by WPC. The device then needs to be tested for compatibility with other, previously certified products.


Any changes to a device like change in the magnetic properties, firmware and communication protocols, interface materials or changes in the transmission subsystem require it to undergo recertification. Minor changes like product colour, name or changes to other unrelated subsystems do not require recertification.


Wireless Power Transfer - ( Introduction & History) Part 1

Wireless Power Transfer (Types of Wireless Power Transfer) - Part 2

Standards Of Wireless Power Transfer - Part-3

Wireless Power Transfer: Advantages and Disadvantages - Part 4

Wireless Power Transfer - ( Comparison )Part 5

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