Wireless power for charging mobile devices

Wireless power has become a hot topic as wireless charging of mobile devices is get getting some popularity. Wireless charging isn’t something new; the technology exists since 1981 and Nikola Tesla has made first wireless power experiments over 100 years ago. Wireless charging for Qi technology is becoming the industry standard on smartphones (pushed by Wireless Power Consortium) as Nokia, HTC and some other companies use that. There is a competing AW4P wireless charging standard pushed by Samsung ja Qualcomm. And there is more standards coming. Power Matters Alliance is heavily pushing their own wireless charging standard. It seems there is going to be fight on wireless charging in near future. It seems that right now we’re in the midst of a battle between two standards for wireless charging – Qi from the Wireless Power Consortium and Power 2.0 from the Power Matters Alliance. It seems that a common Wireless Power Standard Years Off as Battle Heats Up.

As obviously useful as wireless charging is, it suffers from a Tower of Babel problem with incompatible standards and competing interests keeping it from truly going mainstream. Wireless charging continues to be a niche category until there’s a common standard. Heavyweights are backing the idea of wireless charging capabilities embedded in phones, and public charging stations are beginning to pop up. Differing standards, however, still make for a rocky adoption. Realistically there probably isn’t room for two or more standards, which do essentially the same to end user but are incompatible, so expect some technologies to disappear in the near future. Charging portable devices without needing to carry a power adapter sounds handy when we can agree on one standard. “Wireless charging continues to be a niche category until there’s a common standard,” said Daniel Hays, a consultant with PricewaterhouseCoopers. “The hassle factor is still high.”

Qi seems to be at the moment standard that gets most attention. The news that Nokia to join Qi party with wireless-charging Lumia 920 have given lots of publicity to it. Even if the Lumia isn’t a big seller, the publicity and visibility it will provide for Qi should be enough to make everyone forget there was ever an alternative, if indeed there ever was. Also some HTC phones and Nexus 4 phone use this standard. Toyota launches the world’s first wireless charging of mobile phones in the car. Toyota’s car will get wireless mobile phone charger using Qi standard.

Qi has been here for some years. Qi has been around for a while, gaining the name and logo back in 2009. The Qi standard came out of water filtration units, which needed wireless power, and has been widely endorsed but devices are still quite rare. Under the Qi specification, “low power” for inductive transfer means a draw of 0 to 5 W, and that’s where mobile device charging solutions most probably go. The system used inductive coupling between two planar coils to transfer power from the power transmitter to the power receiver. The distance between the two coils is typically 5 mm, but can be expanded to 40mm.

The Qi system uses a digital control loop where the power receiver communicates with the power transmitter and requests more or less power via backscatter modulation. Besides low-power specification up to 5 watts, there is also a medium-power specification will deliver up to 120 watts. The frequency used for Qi chargers is located between about 110 and 205 kHz for the low power Qi chargers up to 5 watts and 80-300 kHz for the medium power Qi chargers.

Method: inductive coupling between two planar coils
Frequency: 110-205 kHz (80-300 KHz)
Communication: backscatter modulation

WiPower was a technology start-up company that used the principles of inductive coupling to develop a near-field wireless energy transfer system. Qualcomm bought WiPower in 2010 and started quietly negotiating with manufacturers to get the technology embedded in their kit. Qualcomm argues that the additional range of WiPower (which can charge devices up to 45mm away) allows new possibilities. WiPower system is based on modified coreless inductive technology and dynamically adjusts power supplied by the transmitter to power demanded by the receiver without the need for control systems or communication. WiPower chargers are claimed to operate at about 60-75 percent efficiency.

Method: inductive coupling
Communication: no need for specific communication

Samsung and Qualcomm’s Alliance for Wireless Power (A4WP) promises more flexibility in wireless charging. Instead of induction, this standard will use loosely-coupled (LC) wireless power transfer (a series resonance-tuned pair of magnetically-coupled coils) to transmit power. This construction allows that the transmitter and receiver don’t have to be in direct contact, which gives more flexibility to industrial designers. This designs will support simultaneous charging of multiple devices with different power requirements. A4WP specification takes advantage of Bluetooth 4.0. The biggest downside in this design is that currently there are no products with this technology are yet on the market.

Method: series resonance-tuned pair of magnetically-coupled coils (loosely coupled)
Frequency: 6.78 MHz
Communications: Bluetooth 4.0

The Power Matters Alliance (PMA) is working on an open standard for wireless charging. A group of companies back up this initiative (including Google, AT&T, ZTE, Starbucks, ,McDonalds, PowerKiss). PMA uses inductive charging method used in Duracell’s Powermat product. It requires the transmitter and receiver be close together, placing the mobile device on the charging pad.

This is quite new alliance but it seems to get lots of backers: over the last few months, the PMA has seen a tenfold increase in membership. One very big thing is that AT&T is seeking from its handset vendors a commitment to one standard of wireless charging.

The PMA is working to advance the widespread acceptance of the wireless power paradigm in multiple sectors. PMA is intent on leading and organizing the Power 2.0 agenda to commercial realization, while working under the umbrella of the most trusted name in standards: the IEEE. Powermat is capable of delivering 5-to-50 watts of power. Powermat allows a built-in check for alignment via light and voice signals based on RFiD Handshake feature. When you place a Powermat-enabled device on one of its mats, the two exchange a “handshake” using RFID: The mat identifies the device, determines how much power it needs and transfers energy to it. Powermat operates at 277-357 kHz frequency. Once a device is fully charged, Powermat stops the electricity from flowing. But as much momentum as the PMA has achieved, it is far from clear whether it will be that bandwagon.

Power Matters Alliance (PMA)
Method: inductive charging
Frequency: 277-357 kHz
Communication: RFID

As obviously useful as wireless charging is, it suffers from a Tower of Babel problem with incompatible standards and competing interests keeping it from truly going mainstream. There are also attempts to support several standards on one product. Samsung Galaxy SIII wireless power supports both Qualcomm’s WiPower and Wireless Power Consortium Qi. The Samsung Galaxy S4 will support both PMA and Qi standards. NXP has developed a charging station, which allows you to use both the general mobile phone charging standards (as well as one rare third standard).

The technologies I mentioned are not the only ones trying to push to the market in the near future. Apple is trying to patent wireless charging, claiming its magnetic resonance tech is new and that it can do it better than anyone else. Digitoday writes that Finnish research organization VTT is planning to combine wireless power and NFC technologies. The reasearchers believe that in the future NFC devices could be made to work as way to get power into device and send power to other device cheaply. Technology is not ready yet, because today’s NFC antenna circuits are not optimized for power transfer and there is no standard that covers this kind of use yet. NFC operates within the globally available and unlicensed radio frequency ISM band of 13.56 MHz.

Wireless Power: Convenient, But Its Shortcomings Are Somewhat Sour article tells that close-proximity inductive coupling is commonly estimated to deliver 50 to 70% efficiency. That’s considerably worse efficiency that what you get with a well designed wired charger. Intel increases consumer-product power consumption 50% blog post says that a system that is 50% efficient on top of the ac-dc conversion, and pumps RF energy all over the place is far from ideal in world where some other parties try to conserve every single watt. In a world with 15 billion chargers, energy efficiency is a big deal. Based in that is makes me a little bit hard to believe the Power Matter Alliance claims that wireless charging could save a lots of power in the future. How Wireless Charging Will Keep Toxic Waste Out of Landfills article tries to describe how wireless power could be more eco-friendly, but it is hard to believe all those claims without good data. I can believe that wireless chargers can have better energy efficiency than some old chargers supplied with consumer devices, but I given the limitations wireless charging it is very hard to believe that wireless charger could ever be more efficient than well designed wired charger. But wireless charger could be well “good enough” to be acceptable.


  1. Tomi Engdahl says:

    What’s the Difference Between Qi and Other Types of Wireless Power Transfer?

    Interoperability, adoption, use case, readiness, and safety/regulatory are the key differentiating factors among these competing technologies.

    Apple announced that its iPhones, AirPods, and other accessories will all include Qi (pronounced “chee”) wireless charging. The Qi standard is one type of wireless power transfer, and certain to be a popular one due to Apple’s adoption. However, other types of wireless power transfer, such as AirFuel Resonant, proprietary near-field magnetic coupling (NFMC), radio frequency (RF), and ultrasound offer different value propositions.

    The No. 1 value-added differentiator for Qi is interoperability. If you see the Qi logo on a product, it is Qi-certified. Qi-certified devices (e.g., phones) are guaranteed to work with Qi-certified transmitters (e.g., charge pads, enabled autos, embedded furniture). This is important in the world of consumer electronics, where users can expect to have Qi transmitters in common locations throughout their daily life: home, car, office, coffee shops, airports, hotels.

    AirFuel is another standard that offers interoperability using a different type of protocol, frequency, and process than Qi. Theoretically, AirFuel promises the same interoperability benefits as Qi (all AirFuel devices will work with all AirFuel transmitters), but the current reality is that Qi has scale via adoption that AirFuel can’t match.

    Proprietary NFMC is, by definition, “proprietary” or “non-interoperable” with other devices. Proprietary systems don’t make sense for consumer mobile devices, but make a lot of sense for non-consumer devices like medical tools/devices, commercial-grade equipment, industrial electronics, unique form-factor devices, etc.

    RF and ultrasound are each in very early stages of development. Individual companies are launching “standards” (such as Ossia’s “Cota Standard”), but the standards are unlikely to become ubiquitous without much broader support from ecosystem partners and further technology readiness.

    Qi technology is undoubtedly the leader in number of mobile devices deployed worldwide. Apple, Google, HTC, LG, Motorola, Nokia, and Samsung have launched Qi mobile phones (note: Google added Qi for Nexus 4, but dropped it from future models citing “slow charging times” that must be addressed before they include it again). Likewise, infrastructure adoption is unparalleled with Qi included in over 35 automotive models, IKEA furniture, Corian countertops, and standalone Qi transmitters of different shapes, colors, and sizes (to name only a few…).

    AirFuel adoption is limited mostly to pilot scale.

    Proprietary NFMC has surprising levels of deployment, partially owed to the fact that certain niches have been using wireless power since the 90s. For example, implanted neurostimulators, electronic toothbrushes, and industrial equipment interconnects have been leveraging magnetic-coupling technology for over two decades.

    RF has no major commercial deployment, but has been impressively displayed by a variety of technology developers, including phone-charging demos where multiple phones are charged simultaneously at distances up to 15 feet away from the source.

    AirFuel Resonant’s major promise is use case. AirFuel utilizes loosely coupled technology, which means that multiple devices can charge from a single transmit coil simultaneously; orientation and distance (up to ~50 mm) is flexible; power levels can scale reasonably above 50 W; and device charging can be invisible and more intuitive (i.e., embedding transmitters under the counter versus visibly embedding in or on the counter).

    For AirFuel to succeed, it needs adoption and scale. Superior technology and use case may win over customers in the long term, but there’s a significant uphill climb given Qi’s current market leadership.

  2. Tomi Engdahl says:

    Magnetic Connective Wireless Charging and Data Transfer

    Magnetic connective wireless charging (Magconn) is an innovative magnetic connection technology that is a simple and safe low-cost alternative to induction charging and conductive wireless charging, with all the benefits of a direct plug-in connection, even for data transmission, data acquisition and sending pulse signals or audio. The product is most versatile and its potential applications are multiple. Magconn is proving to be of major interest to product designers working on devices destined for the Internet of Things, including rugged, smart, wearable, and wireless devices.

    Magnetic connective wireless charging is the name given to the worldwide patented Magconn product technology. Although it may seem somewhat contradictory, the name Magconn is a most apt one, when one thinks about the term “wireless” in a different context. “Inductive and conductive wireless charging” have used the term “wireless”: in theory, it is correct usage of the word as the power is actually transmitted wirelessly, albeit at an extremely short range. However, the wireless device still has to be physically rested on or in a charging platform, hence eliminating the process of plugging in the device when it needs to be charged.

    Magconn is a lower cost alternative that offers so much more! There is no charging efficiency loss, no energy loss and not heat loss, as effectively it is direct contact. Direct contact means no loss in charging times. Magconn uses magnets to automatically self position and self center the device to the charger.

  3. Tomi Engdahl says:

    EV Charging Moves Forward with Collaborations

    More firms are partnering to innovate at the pace of the fast-evolving automotive market, as shown by WiTricity’s use of TI semiconductor components in its new automotive wireless charger solution.

    As a result of the rapid growth rate in the electric vehicle (EV) market, wireless charging solutions are quickly emerging. Many semiconductor companies, technology developers, and carmakers are working on new wireless charging automotive solutions. Sometimes they join forces to do so, as is the case for WiTricity and Texas Instruments.

    WiTricity’s DRIVE 11 wireless charging technology can optimize energy transfer between the source and vehicle in a wide range of real-world operating conditions including parking misalignment, differing vehicle ground clearance, and varying battery voltage conditions. The DRIVE 11 features Texas Instruments’ C2000 real-time control microcontroller.

    “New automotive technologies, such as wireless charging, are entering the market at a rapid pace,”

    WiTricity is working with major automakers and Tier 1 suppliers to make wireless EV charging a commercial reality. The DRIVE 11 evaluation system is an end-to-end reference design for “ON and OFF” wireless charging for pure electric and hybrid vehicles. With up to 11kW of power and up to 94% efficiency, the system is suited for applications based on the SAE TIR J2954 standard, which is an industry guideline that establishes wireless power transfer between infrastructure, vehicle suppliers, and OEMs for plug-in electric and electric vehicles (PH/EVs). Licensing agreements have been announced with Toyota, Delphi, TDK, IHI, Shindengen, Daihen, and BRUSA.

  4. Tomi Engdahl says:

    Andrew Tarantola / Engadget:
    San Jose-based Energous, which is developing wireless charging tech that works from three feet away, says the FCC has approved its product, set for debut at CES — Charging your mobile device wirelessly is certainly less of a hassle than plugging it in, but still requires the device …

    FCC approves first wireless ‘power-at-a-distance’ charging system
    The WattUp Mid Field transmitter refills batteries from 3 feet away.

    Charging your mobile device wirelessly is certainly less of a hassle than plugging it in, but still requires the device be in physical contact with its station to actually work. That’s about to change now that the Federal Communications Commission has approved the first wireless charger that works from up to three feet away.

    The transmitter converts electricity into radio frequencies, then beams the energy to nearby devices outfitted with a corresponding receiver. This differs from the resonant induction method that the Pi wireless charging system relies upon and offers a greater range than the Belkin and Mophie chargers that require physical contact with the device.

    The WattUp can charge multiple devices simultaneously and should work on any number of devices

    the company does plan to show off the new technology at CES 2018

  5. Tomi Engdahl says:

    In the car, you can charge your cellphone wirelessly

    Now that Apple’s iPhone also supports wireless downloading, technology begins to attract more car makers. At Las Vegas CES, On Semiconductor develops a solution for mobile phone charging safely in a car.

    Together with ConveniantPower Systems, ON Semi has developed a solution around its VCV6500 power management circuitry. The solution uses different coils to support multiple devices and deliver up to 15 watts of charging power.

    Companies make the most of the new detection technology for foreign objects so that the charging field can be implemented relatively large without the connection to the wrong devices.

    According to Sem, in addition to safety, it is important to carry out a wireless download where the device is simply “dropped” on the platform for charging. The VCV6500 power management circuit operates on a 5 volt input voltage and can be used to produce both wireless Qi and PMA standards.

    Source: http://www.etn.fi/index.php/13-news/7370-autossa-voi-pian-ladata-kannykan-langattomasti

  6. Tomi Engdahl says:

    Wireless charging: advanced technology delivers real benefits

    Power needs to catch up with data and become wireless to truly empower the latest generation of mobile devices. In this technical article, Infineon reviews the design challenges and standards that drive this new sector before looking at technologies that make this vital step possible.

    As with many emerging technologies, multiple incompatible standards develop which stifle progress until a universal solution emerges. Wireless charging has two industry alliances and two standards. The Wireless Power Consortium (WPC) supports the Qi inductive standard that supports tightly coupled charging. Qi has become the mainstream standard, covering over 80% of all wireless charging receivers. The Power Matters Alliance (PMA) and the Alliance for Wireless Power (A4WP) were formed as separate organizations. PMA focused on tightly coupled inductive solutions whereas A4WP worked on loosely coupled resonant technology. PMA and A4WP merged and rebranded as the AirFuel Alliance (AFA).

    Currently, there are three topologies for wireless charging, offering different advantages. Single-coil inductive is the simplest and most prevalent solution. Supported by Qi and AirFuel, this employs a single transmitter coil and requires exact and close positioning of the device and the transmitter, which precludes charging through surfaces. This approach can only charge a single device.

    Multi-coil enables intelligent systems that detect the coil closest to the device and direct the power accordingly. The broader charging field allows you more freedom in placing the device to be charged.

    AFA supports a resonant approach that relies on resonance between the transmitter and receiver to transfer energy far more efficiently. This approach charges multiple devices from a single coil and allows for a greater distance (up to 50mm) between the transmitter and receiver. This flexibility in positioning of the device gives a ‘drop and go’ experience with efficiencies up to 80%.

    The resonant approach permits higher power ratings, allowing laptops or power tools to be charged wirelessly.

    There are two primary topologies used for resonant (AirFuel) applications, Class D and Class E. Class D offers an almost flat efficiency curve over a wide load range and is therefore suited to general-purpose wireless charging stations, such as those found in public places where a wide variety of devices could be charged. Class D is suitable for a wide range of power levels.

  7. Tomi Engdahl says:

    USB Type-C Power Delivery and Wireless Charging Now Available in One IC

    They’ve arrived. ROHM’s dual-mode devices enable simultaneous charging, automatically switching charging operation without the need for an MCU.

    While wireless charging continues to gain traction, a growing number of portable devices also are adopting the USB Type-C Power Delivery (USBPD) standard, which allows for charging up to 100 W (20 V/5 A). To deliver the wide power-supply range required by USBPD, a boost function must be added to a system to charge two-cell (approx. 8.4 V) batteries from conventional 5-V chargers. And if you want to enable the two different charging methods at the same time, it requires mounting charge ICs along with peripheral components as well as an MCU to control charge switching—all of which presents a barrier to introduction.

    However, ROHM shows it can be done in a simpler manner. The company developed dual-input charging ICs supporting both USBPD and 5-V inputs in a single package that’s compatible with wireless as well as USBPD charging technologies. Support also is provided for USB Battery Charging Specification Revision 1.2 (USB BC 1.2), the key standard for establishing the proper way to charge a battery from a USB port (up to 7.5 W [5 V/1.5 A]). This facilitates configuration of dual-mode systems capable of simultaneous charging via USBPD or from an ac adapter.

    The BD99954GW/MUV (Fig. 1) generates a charging voltage from 2.56 to 19.2 V for one to four cells (in series) through boost-buck control.

  8. Tomi Engdahl says:

    At CES 2018 Powercast, Energous to Demo Wireless Charging at a Distance

    On Dec. 26th Powercast Corporation said that it will unveil at CES (booth #40268) an FCC- (Part 15) and ISED-approved (Innovation, Science, and Economic Development, Canada) three-watt PowerSpot transmitter which can deliver over-the-air charging to multiple electronic devices from a few inches to 80 ft. away, and that charging mats or direct line of sight are not needed.

    Up until this point wireless charging has been very short range, based on either Qi or Powermat standards

    The Powercast PowerSpot transmitter, on the other hand, sends RF energy on the 915-MHz ISM band over the air to a receiver chip embedded in a device, which converts it to DC to recharge its batteries or directly power the device. This remote charging technology behaves like Wi-Fi, where enabled devices automatically charge when within range of a power transmitter.

    Charging rates will vary with distance, type, and power consumption of a device.

    he PowerSpot transmitter uses Direct Sequence Spread Spectrum (DSSS) modulation for power and Amplitude Shift Keying (ASK) modulation for data, and includes an integrated 6-dBi directional antenna with a 70-deg. beam pattern.

    The company expects that up to 30 devices left in the zone on a countertop or desktop overnight can charge by morning, sharing the transmitter’s three-watt (EIRP) power output

    Powercast’s Lifetime Power Energy Harvesting Development Kit for Battery Recharging is a demonstration and development platform for recharging batteries wirelessly from RF energy. It is designed to be used with an app and is configured for out-of-the-box operation. The battery recharging boards utilize the P1110B Powerharvester Receiver, which converts RF energy into DC power. Either the PowerSpot transmitter or TX91501-3W transmitter is the source of RF energy, with both operating at 915 MHz. Other RF energy sources operating from 850-950 MHz can also be used as power sources (UHF RFID readers, for example).

    Powercast will begin production of its standalone PowerSpot charger now that it is FCC-approved, and is also offering a PowerSpot subassembly to consumer goods manufacturers who want to integrate it into their own products (think lamps, appliances, set-top boxes, gaming systems, computer monitors, furniture or vehicle dashboards).

  9. Tomi Engdahl says:

    At CES 2018 Powercast, Energous to Demo Wireless Charging at a Distance

    on December 26th, Energous Corp., the developer of WattUp charging technology, announced that it had received “Industry-First FCC Certification for Over-The-Air, Power-At-A-Distance Wireless Charging.” The FCC determined that the WattUp RF beam forming based wire-free at-a-distance charging is safe and meets the current regulatory health and safety guidelines established by the FDA (and enforced by the FCC).

    The WattUp Mid Field transmitter sends focused, RF-based power to devices at a distance.

    The company claims it is the first FCC certification for power-at-a-distance wireless charging under Part 18 of the FCC’s rules; Part 18 rules permit higher-power operations than are permitted under the Part 15 rules that were used to approve Powercast’s at a distance charging devices.

    WattUp Mid Field and Far Field Transmitters sense and communicate to authorized receiver devices via Bluetooth Low Energy (BLE), only sending power when needed and requested by those devices. WattUp is software-controlled, determining which devices receive power, when, and in what priority.

    WattUp uses the 5.850 GHz-5.875 GHz band for the transmission of power. This is just outside of the 5.8 GHz Wi-Fi band. Other technical specifications of the WattUp charging solution include:

    A GaN-based 5-10 W RF receiver IC
    A GaN-based 10-15 W RF power amplifier (PA)
    An RF-based charging solution allowing for full 2D / planar movement
    Support for 90-deg. charging angles (sideways charging)
    Accommodation of metal and other foreign objects
    PA integration into the overall system leading to a lowered BOM cost

  10. Tomi Engdahl says:

    Wireless charging. It doesn’t really do what it says on the tin

    As far as consumers and their smart phone go, wireless charging sounds a great idea. And if it was a reality it would be. Let’s face it, relative to much of our technology-driven lives, wireless is the way to go.

    As well as that, wireless charging capability can add costs to the design of a phone which have to be passed onto the consumer, and that is not a good thing in such a cost competitive market.

    Convenience wise I really don’t see the point. You have to plug your charging pad into an electrical socket and then place you phone precisely on the charging pad. So in effect you have replaced one charging wire with another.

    Ok so wireless charging you phone in your car is a good thing.

    Wireless charging happens in two ways; conductive which links conductive material in a charging pad to integral conductive material in the phone, and inductive which uses a charging station which has an induction coil in it.

    Inductive charging is a complex business and not necessarily very efficient or fast. It employs two electromagnetic coils to create a magnetic field between two devices

    Back in the 1860s radio waves were first considered for power transportation by James Maxwell and twenty years after that Heinrich Hertz showed evidence of radio waves using his sparkgap radio transmitter. At the same time engineer and physicist Nicola Tesla was convinced wireless power transfer was feasible. He built a giant coil connected to a high tower with a metre diameter ball on it and then proceeded to push close to 300kw of power into the thing. Unfortunately the experiment failed due to the power scattering in multi-directions.

    Coming back to the modern day and the inaccurately titled, wireless charging concept, there are plenty of electronics developments that are moving the idea forward.

    AURIX and XMC microcontroller families provide design-flexible chipsets for wireless charging apps and reference designs for both inductive and resonant wireless charging solutions for in-car, at home or in public places.

    The controller supports today’s 15W charging standards

    The XMC based 2.5W low-power solution supports both one-to-one and multi-device charging on a single transmitter by using small high-frequency coils which can be implemented in a variety of form factors.


Leave a Comment

Your email address will not be published. Required fields are marked *