On August 4, 2011, the US Patent & Trademark Office published a patent application from Apple that reveals two specific concepts of an "Inductive Charging System" for use with iOS devices. The first concept involves an oddly designed charging tower. Apple envisions a user wrapping their earphone cables around this charging tower and placing a new conductive metal mesh earphone on the media device to begin the charging process. The second system, which seems to be a little more practical, involves an acoustic charging mechanism which wouldn't require a charging tower. Instead of creating separate inductive chargers for various media players and tablets as others have done, Apple is trying to create a single inductive charger that would fit the needs of multiple devices.
The Problem with Current Inductive Charging Techniques
Inductive charging techniques, which operate without requiring direct conductive connections, have been developed for certain applications, such as electric toothbrushes, where the proximity to water makes a conductive connection impractical. An electric toothbrush could be recharged using a relatively small inductive receiving coil because it is typically placed in a charging stand for a long period of time (many hours) and is only used for a short period of time (about two minutes).
However, to inductively charge other types of electronic devices, such as portable media players or cell phones, at an acceptable rate, a significantly larger receiving coil is required. Providing this larger receiving coil involves either incorporating the larger receiving coil into the portable electronic device, which increases the size of the portable electronic device, or alternatively incorporating the larger receiving coil into a bulky attachment to the portable electronic device.
Apple's Inductive Charging Solution
Apple's invention relates to a technique for inductively charging an electronic device which involves winding an audio cable for the electronic device around a charging mechanism multiple times so that one or more conductors in the audio cable form an inductive receiving coil. Next, a magnetic field is created through the charging mechanism to induce a current in the inductive receiving coil. Finally, the induced current in the inductive receiving coil is used to charge a rechargeable battery for the electronic device.
In some embodiments, after winding the audio cable around the charging mechanism, the technique further involves electrically coupling a first contact, which is coupled to the one or more conductors in the audio cable, to a second contact associated with the electronic device to complete a circuit between the inductive receiving coil and the electronic device.
In some embodiments, the first contact is located on a first earphone (e.g., an earbud) which is attached to the audio cable. In a further variation, the first contact is conductive metal mesh screen that also protects a driver for the first earphone.
In some embodiments, the second contact is located on a second earphone which is also attached to the audio cable. In a further variation, electrically coupling the first and second contacts involves electrically coupling the first and second contacts through an intervening conductor, wherein the intervening conductor is located in a housing which is configured to hold the first and second earphones.
In some embodiments, the one or more conductors within the audio cable include multiple conductors which are coupled in series to form a single receiving coil having more windings than an audio cable with only a single conductor. In some embodiments, the audio cable comprises: a headphone cable; an earphone cable; or a microphone cable.
Apple's Inductive Charging Tower & Technique
Apple's inductive charging technique involves wrapping an iOS device's audio cable (which becomes a "receiving" coil) around a charging tower 102 as shown in patent FIG. 1. In this patent figure we see that the charging tower is coupled to a charger base 112, which receives power through a power cord 114. One contact for the receiving coil is on the body of media player 108, and other contact 110 is located on one of the earphones.
In an alternative embodiment, instead of completing the inductive receiving coil by coupling a contact on one earphone to an associated contact located on media player, the inductive receiving coil is completed by coupling together two contacts located on the earphones. In this case, each earphone has a contact which is coupled to a different set of conductors in the audio cable, and the act of coupling the contacts together completes the inductive receiving coil.
The Charging Tower
Apple's patent FIG. 2 illustrates the structure of the charging tower. Note that the charging tower is coupled to a charger base which supports the charging tower and contains a transformer 202 and a transmitting coil 206. During operation, the transformer receives power through a power cord which is coupled to a wall socket. The transformer converts the voltage of the A/C power received from the wall socket and uses the resulting voltage to drive transmitting coil.
The transmitting coil is wrapped around a ferromagnetic core 204 which runs the length of charging tower. A time-varying current flowing through transmitting coil creates a varying magnetic flux in the ferromagnetic core which creates a time-varying magnetic field through a receiving coil that is wrapped around the charging tower. This time-varying magnetic field induces a time-varying current in the receiving coil. Next, the time-varying current in the receiving coil is used to charge the associated electronic device.
Note that using the ferromagnetic core improves the magnetic flux and hence improves the charging efficiency. However, the magnetic flux could also propagate through air, which means that the system could also work without a ferromagnetic core.
Conductive Metal Mesh Earphone Screens
Apple's patent FIG. 4 illustrates how an earphone 404 could include a conductive metal mesh screen 410 which also functions as an electrical contact. Note that this metal mesh screens also protects the driver for the earphone. Also note that this type of electrical contact is different from the electrical contact 110 illustrated in FIG. 1, which is located on the housing of an earphone, and is separate from the screen which protects the earphone driver.
This type of electrical contact (through the earphone mesh) could also be used to receive current for a conventional non-inductive charging system. This eliminates the need to provide a separate interface to receive the charging current in a conventional charging system.
In one variation, this conductive metal mesh screen includes a number of separate conductive regions which function as independent contacts. In this way, the metal mesh screen could provide multiple contacts instead of a single contact. These separate conductive regions could be created by fabricating the mesh using alternating regions of conductive metal wires and non-conductive plastic wires.
Apple's Alternative Acoustic Charger System
Apple's patent FIG. 7 illustrates an alternative charging system that uses an acoustic output to charge a portable media player in accordance with the disclosed embodiments. In the acoustic charging system illustrated in FIG. 7, an earphone is fitted into a recess in an acoustic charger 702. This recess could be lined with a rubber gasket to achieve a tighter fit. Next, a speaker 704 within the acoustic charger produces an acoustic signal which causes a corresponding speaker in earphone to vibrate. These vibrations cause a transducer within speaker 706 to effectively operate "in reverse" to generate a current in earphone conductors 708. This current could be used to charge the battery of the attached portable electronic device. Note that the vibrations could be generated in a non-audible frequency range (less than 20 Hz or greater than 20K Hz) to prevent users from hearing the acoustic charging signal.
Apple's patent application20110188677 was originally filed in Q1 2010 by inventors Fletcher Rothkopf, Anna-Katrina Shedletsky and Stephen Lynch.
Also see our reports "Future Apple Hardware to Harness the Power of Magnetic Induction, " and "Apple Wins Patents for Inductive Charging Docks...," which presents some very interesting and simple designs. Today's second inductive charging system involving acoustic output seems to have some smarts to as did other previous designs as we noted above. Admittedly Apple's first design as presented here today is surely an odd one. Try to imagine charging multiple mobile devices at one time with intermingled and tangled cables. That's simply not going to fly. In fact it's a little humorous just thinking about it. Yet to be fair to Apple's invention, we did point out that "the magnetic flux could also propagate through air, which means that the system could also work without a ferromagnetic core." Translation: No tower required.
For now, let's hope that there's a clean and simple inductive charging system solution on the way like their outlined acoustic charger or the wireless version of the charger as we noted above. I think that everyone just wants a simple to use wireless charger. The simpler the better.
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