When a current is flowing through the auxiliary coil, it produces a magnetic field that changes the tuning frequency of the main coil. The main coil carries the chief responsibility for charging a device’s battery.
In the researchers’ chip, one of the coils - the main coil - is much larger than the other - the auxiliary coil. “The fact that those switches aren’t there anymore is a big advantage,” Juvekar says. Instead of a single coil attached to a bank of capacitors, the MIT researchers’ design uses a pair of coils attached to one capacitor each - no switches required. Or if it’s on the chip, it requires a specialized process that might be very expensive.” So it has to be a discrete component on the board, outside the chip. If a switch needs to block a very big voltage, then it’s very hard to put that on the chip. “They either have to block a very large voltage when they’re off, or they have to carry a very large current when they’re on, or in some cases both. “Those switches have very severe requirements,” Juvekar says. Between each pair of capacitors is a switch, and switching capacitors on and off changes the receiver’s frequency.
Battery magnet blocks wireless charging series#
A standard tuning circuit connects the coil to a series of capacitors, electronic components that can store charge. The MIT researchers’ chief innovation is a more compact and efficient circuit for tuning the frequency of the receiving coil. The device’s coil must be “tuned” to the transmission frequency in order to receive power. The rate at which the current in the charger alternates defines a frequency, much like the frequency of a radio transmission.
An alternating current - an electrical current that changes direction at a regular rate - passing through the charger’s coil produces a magnetic field, which induces a current in the device’s coil. In a wireless charging system, both the charger and the target device contain metal coils. They’re joined by Chiraag Juvekar, also an EECS graduate student at MIT, and Shubham Chandak, a graduate student in electrical engineering at Stanford University. Chandrakasan is the senior author on the conference paper, and the first author is Nachiket Desai, who was an MIT graduate student in electrical engineering and computer science (EECS) when the work was done. The researchers presented the new chip this week at the International Solid-State Circuits Conference. “We will see security functionality embedded into virtually every function and component of an IoT node.” “Security is one of the most critical issues in the ‘internet of things ,’” says Anantha Chandrakasan, the Vannevar Bush Professor of Electrical Engineering and Computer Science, referring to the popular idea that vehicles, appliances, civil-engineering structures, manufacturing equipment, and even livestock will soon have sensors that report information directly to networked servers. In the same way that the researchers’ chip can block power transfer from an unauthorized charger, it can slow the power transfer to a device nearer the charging coil, ensuring more equitable charge rates. When two devices share a single charger, if they are different distances from the charger’s electrical coil, their charging rates can vary enormously, to the extent that one device might charge fully while the other remains virtually uncharged. The same technology also solves another problem with wireless chargers. In an effort to get ahead of the problem of counterfeit wireless chargers - which could cause power surges that fry a device’s circuitry - researchers from MIT’s Microsystems Technology Laboratories have built a chip that blocks attempts to wirelessly charge a device’s battery unless the charger first provides cryptographic authentication.
Battery magnet blocks wireless charging portable#
In the last few years, portable electronics that can be recharged wirelessly have started coming to market. Around the same time, Britain’s Chartered Trading Standards Institute reported that of 400 counterfeit chargers it bought from a range of online retailers, 397 failed a basic safety test. At the end of 2016, Apple claimed that of 100 Apple-branded charging accessories it bought on Amazon, 90 were counterfeits. Counterfeit chargers for portable electronics are a major problem.
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