MIT's wireless charging chip can verify the authentication is completed before it can be charged

For mobile devices, counterfeit chargers have always been a huge threat. At the end of 2016, Apple directly picked up these knockoffs, claiming that 90% of the so-called original chargers bought on Amazon are fake and shoddy products.

At the same time, the British Chartered Trading Standards Committee has also focused on this issue, and the problems they discovered are even more serious. Of the 400 cottage chargers purchased online, 397 are unable to pass basic safety tests.

In the past few years, mobile devices equipped with wireless charging technology have gradually grown. In order to prevent the wireless charging market from being invaded by counterfeit and inferior products, researchers at the MIT Microsystems Technology Laboratory have developed a chip that only passes the password. Verification can start wireless charging.

In addition, this technology also solves another problem of wireless charging: when two devices share a charger, if they have different distances from the coil, the charging efficiency gap will be very large, that is, when one is full, the other is also empty. .

“Security is one of the most critical issues for IoT devices,” said Anantha Chandrakasan, a professor of electrical engineering and computer science. He believes that vehicles, furniture, civil engineering structures, manufacturing equipment, and even livestock will carry chips in the future, returning directly to the Internet. data.

Last week, researchers announced the new chip at the International Solid State Circuit Symposium.

Switch disappears

In the wireless charging system, the charger and the target device both contain metal coils inside. When charging, the alternating current will generate a magnetic field through the coil of the charger, and then the energy will be transferred from the transmission section to the receiving end. However, in order to receive energy, the coil of the device must be adjusted to the appropriate transmission frequency.

So where is the innovation of MIT researchers? In fact, the focus is on the adjustment of the receiver coil frequency, MIT researchers invented a more compact and efficient circuit. A standard tuning circuit connects the coils to a series of capacitors and electronic components. Each set of capacitors has a switch between them. The switching of the capacitor changes the transmission frequency at the receiving end.

"These switches must be very good quality," Juvekar said. “They need to block high voltages when they are off, and they are subjected to high currents when they turn on, so it must be a discrete component on the circuit board to become independent of the chip. If you have to add it to the chip, It requires a relatively special manufacturing process and the result is a rise in costs."

Unlike traditional single-coil designs, MIT researchers used a capacitor with two coils, so switching parts could be eliminated. "In fact, no switch turned into a big advantage," Juvekar said.

Variable tuning frequency

In this new chip, the coil size is also different, the main coil is much larger than the auxiliary coil. Among them, the main coil responsible for charging the device is mainly, and when the current flows through the auxiliary coil, a magnetic field is generated to change the tuning frequency of the main coil.

The resistance of the auxiliary auxiliary coil circuit can be continuously changed. When the resistance is low, the magnetic field generated by the auxiliary coil is stronger and the tuning frequency of the main coil is greatly changed. At this time, the charger cannot be charged.

When the resistance of the auxiliary coil is high, the magnetic field weakens and the charging will continue, but the charging rate will be very low, so that devices farther away from the wireless charger can obtain more power.

This chip uses an authentication technology called Elliptic Curve Cryptography. This technology is a public key encryption technology. Before charging, it exchanges information with the connected charger. Only authentic chargers can answer questions about the chip. ". However, this chip does not require a built-in security key.

Elliptic curve cryptography is a very well-established technology, but MIT's R & D personnel still improved it, reducing the power consumption of the chip. In addition, they also simplify the encryption circuit and save a lot of space.

"MIT's chip can accurately and safely manage multiple charging loads," said Baher Haroun, signal path expert at KilbyLabs. "Security is the premise of wireless energy transmission. Only security can ensure its effective use. MIT's chip can not only guarantee security, but also can authenticate who is qualified to obtain wireless transmission energy."

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