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.

Qi
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.

WiPower
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.

A4WP
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.

412 Comments

  1. Tomi Engdahl says:

    Powering the Wireless Warehouse
    Sept. 7, 2023
    Robots now travel through vast arrays of racks several stories high to pick your e-commerce orders. Here’s how fulfillment centers are keeping them powered.
    https://www.electronicdesign.com/markets/automation/article/21273248/wibotic-powering-the-wireless-warehouse?utm_source=EG+ED+Analog+%26+Power+Source&utm_medium=email&utm_campaign=CPS230907058&o_eid=7211D2691390C9R&rdx.identpull=omeda|7211D2691390C9R&oly_enc_id=7211D2691390C9R

    Reply
  2. Tomi Engdahl says:

    Langaton Qi-lataus päivittyy 2-versioon
    https://etn.fi/index.php/13-news/15445-langaton-qi-lataus-paeivittyy-2-versioon

    Langattoman lataamisen Qi-standardia on paranneltu 2-versiolla, jossa latausalustaan lisätään puhelinta tai muuta laitetta paremmin paikallaan pitävät magneetit. Uusi tekniikka on tulossa markkinoille vielä loppuvuoden aikana julkaistavissa premium-tason älypuhelimissa.

    Wireless Power Consortiumin uusi Qi2-standardi tuo merkittäviä etuja auto- ja kuluttajasovelluksissa, kuten ohjaamon langattomassa latauksessa, älypuhelimissa ja EarPods-koteloissa, kannettavissa kaiuttimissa ja terveydenhuollon laitteissa paremman tehokkuuden ja turvallisuuden ansiosta.

    Infineon on nyt ensimmäisenä puolijohdevalmistajana esitellyt referenssialustan, joka tukee Qi2 MPP -profiilia (Magnetic Power Profile). Alusta on erittäin pitkälle integroitu, halkaisijaltaan alle 43 millimetrin kokoinen, ja se pohjaa Infineonin WLC1 -ohjaimeen.

    Infineonin Qi2-alusta lataa 15 watin teholla. Kortti on taaksepäin yhteensopiva BPP-perustehoprofiilin kanssa, joten vastaanottimet, joissa ei ole MPP-tukea, voivat ladata langattomasti 5 watin teholla.

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  3. Tomi Engdahl says:

    Aalto-yliopiston langaton lataus herättää kansainvälistä huomiota
    https://etn.fi/index.php/13-news/15450-aalto-yliopiston-langaton-lataus-heraettaeae-kansainvaelistae-huomiota

    Nyt uutiskynnyksen on ylittänyt Aalto-yliopistossa kehitetty langaton lataustekniikka, jossa on onnistuttu pidentämään etäisyyttä, jonka yli lataus onnistuu.

    Aalto-yliopisto esitteli tekniikkaa jo elokuussa. Nyt siihen on tarttunut uusia innovaatioita esittelevä SciTechDaily-sivusto. Sen mukaan suomalaistutkijat ovat tehneet läpimurron, joka lupaa mullistaa langattoman lataamisen.

    Sivusto muistuttaa, että miten induktioon perustuva langaton tehonsiirto on hyötysuhteeltaan hyvää, mutta käytännössä vain, mikäli ladattava laite on kosketuksissa latausalustaan. Aalto-yliopistossa kehitetty tekniikka on tässä tärkeä askel eteenpäin.

    Latausalueen laajentaminen onnistuu säteilyhäviön poistamisella, Aalto-yliopiston tutkijat osoittivat. Kun lähettimen ja vastaanottimen silmukka-antennien virroilla on sama värähdystaajuus mutta vastakkainen vaihekulma, pääsemme eroon säteilyhäviöstä. Tämä parantaa latauksen tehoa.

    Aiemmin saman laboratorion tutkijat kehittivät lähietäisyydellä toimivan langattoman latausteknologian, jolla voi ladata tehokkaasti useita laitteita yhtä aikaa. Sen salaisuus on donitsinmuotoisen laitteen keskelle luotu tasainen magneettikenttä, joka lataa laitteet yhtä hyvin kaikkialla donitsin ympärillä, riippumatta laitteiden asennosta.

    Nyt julkaistussa tutkimuksessa tutkijat kehittivät tavan analysoida mitä tahansa langatonta virransiirtomenetelmää sekä matemaattisesti että kokeellisesti. Näin he voivat arvioida sekä lähietäisyydeltä että kauempaa tehtävän langattoman virransiirron tehokkuutta paljon aiempaa perusteellisemmin.

    Tutkimus osoitti, että virransiirtoteho säilyy jopa 80 prosentissa viisi kertaa silmukka-antennin halkaisijan pituisella välimatkalla, kun käytetään optimaalista taajuutta sadan megahertsin vaihteluvälillä. Perinteisellä menetelmällä optimaalista taajuutta ei määritetä, vaan suunnittelijat käyttävät standardin mukaista taajuutta, jolloin teho voi jäädä alle 20 prosentin.

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  4. Tomi Engdahl says:

    Transferring RF energy from transmitter to tiny magloop with green neon bulb
    https://www.youtube.com/watch?v=SGdMViEpUQw

    Short video for a Circuitsonline user as a demonstration of what is possible.
    Half wave vertical flat on the table, 2w of power, green ‘neon’ indicator bulb.
    This will also work with a LED coupled to the low impedance high current part of the loop. At first i placed the LED right over the capacitor but this was in hindsight not a smart thing to do – both the capacitance of the LED as well as the heavy load made the resonance of the loop disappear.
    The capacitor is located at the high voltage low current side, and a ‘neon’ bulb is very happy in exactly that place.
    The power received is probably in the 1-100mW range.

    Reply
  5. Tomi Engdahl says:

    https://etn.fi/index.php/13-news/15567-qi2-laturit-tulevat-jo-joulumarkkinoille

    Langattoman lataamisen Qi-standardia on paranneltu 2-versiolla, jossa latausalustaan lisätään puhelinta tai muuta laitetta paremmin paikallaan pitävät magneetit. WPC:n eli Wireless Power Consortiumin mukaan ensimmäiset laturit ovat jo sertifiointiprosessissa ja ne ehtivät markkinoille vielä loppuvuoden aiana.

    Ensimmäiset Qi v2.0 -sertifioidut tuotteet ovat tulossa esimerkiksi Applen uuden iPhone 15 -puhelimen langattomaan lataamiseen, Valmistajista Belkin, Mophie, Anker ja Aircharge ovat jo ilmoittaneet Qi2-tuotteista. Yli 100 laitetta on tällä hetkellä testeissä tai sertifiointitestijonossa, WPC kertoo.

    Reply
  6. Tomi Engdahl says:

    DARPA is making Nikola Tesla’s dream of wireless energy a reality
    DARPA is developing a global laser-beam wireless energy transfer network to provide near-uninterruptable power supply to U.S. forces worldwide.
    https://interestingengineering.com/innovation/darpa-laser-power-transfer

    Reply
  7. Tomi Engdahl says:

    DARPA Hopes to Beam Power Across 200 Kilometers Lasers could one day relay power to remote areas, or even from orbital arrays
    https://spectrum.ieee.org/power-beaming-2665745442

    Reply
  8. Tomi Engdahl says:

    https://etn.fi/index.php/13-news/16016-langaton-lataus-paeivittyy-qi2-tekniikkaan

    WPC-järjestön eli Wireless Power Consortiumin langaton Qi-latausstandardi on noussut markkinoiden selkeäksi johtajaksi. Nyt standardin 2-versio alkaa tehdä tuloaan markkinoille. Microchip auttaa laitevalmistajia PIC-ohjaimeen perustuvalla valmiilla referenssisuunnittelulla.

    Qi-standardin 2.0-versiossa latausalustaan lisätään puhelinta tai muuta laitetta paremmin paikallaan pitävät magneetit. Tämä tuo merkittäviä etuja auto- ja kuluttajasovelluksissa, kuten ohjaamon langattomassa latauksessa, älypuhelimissa ja EarPods-koteloissa, kannettavissa kaiuttimissa ja terveydenhuollon laitteissa paremman tehokkuuden ja turvallisuuden ansiosta.

    Reply

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