Wire­less charg­ing

Gary Mar­shall goes pan­ning in the river of ru­mour for nuggets of knowl­edge

Mac Format - - NEXT MONTH -

Wouldn’t it be great if you didn’t have to find a cable to charge your iPhone, iPad or maybe even your MacBook? Ap­ple’s work­ing on it.

Wire­less charg­ing is al­ready wide­spread – many smart­phones use it, and of course the Ap­ple Watch charges wire­lessly too – but so far Ap­ple has mainly stuck with ca­bles. There are sev­eral rea­sons for that. One is that wire­less charg­ing is cur­rently un­der­go­ing a stan­dards war, with three dif­fer­ent ones com­pet­ing against each other. But more im­por­tantly, Ap­ple wants to do things a lit­tle bit dif­fer­ently – and dif­fer­ently from how it charges the Watch, too.

The Ap­ple Watch charges via in­duc­tive charg­ing, also known as tightly cou­pled wire­less charg­ing. That works fairly well, but it re­quires spe­cific po­si­tion­ing to work. That’s why the Watch charger clunks into the same place ev­ery time; if the charger isn’t in the right place, you don’t get any power trans­fer. A slightly dif­fer­ent form of charg­ing, known as res­o­nant charg­ing or loosely cou­pled charg­ing, en­ables you to get your power with­out ac­tu­ally touch­ing the charger. That charger might live in­side your desk or in­side your walls – this year, wire­less charg­ing firm WiTric­ity de­moed res­o­nant wire­less charg­ers that were placed un­der desks and be­hind con­crete – or it might live in­side your next Mac (see our fea­ture on page 75).

The pa­tent to look at is WIPO doc­u­ment WO2011062827, “Wire­less Power Uti­liza­tion in a Lo­cal Com­put­ing En­vi­ron­ment”. It shows an iMac-shaped de­vice with a Near Field Mag­netic Res­o­nance (NFMR) power sup­ply wire­lessly charg­ing var­i­ous de­vices around it. “Typ­i­cally,” the pa­tent ap­pli­ca­tion says, “the dis­tance can be in the or­der of 1 me­ter or so”. A US pa­tent the fol­low­ing year added meat to the bones, clearly show­ing an iMac wire­lessly charg­ing an iPod, key­board and Magic Mouse – with the key­board re­broad­cast­ing power to com­pen­sate for range-killing in­ter­fer­ence. Ap­ple has clearly been think­ing about this for some time. Back in 2005 it filed a pa­tent for wire­lessly charg­ing an iPod, again by res­o­nant charg­ing.

It’s ex­cit­ing, but the Ap­ple Watch pro­vides a ma­jor clue that it’s still some way off; if res­o­nant charg­ing was ca­pa­ble of meet­ing Ap­ple’s stan­dards, it would be in the Watch al­ready.

Res­o­nant charg­ing, also known as loosely cou­pled charg­ing, en­ables you to get wire­less power with­out need­ing your de­vice to touch a charger.

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