Near field magnetic induction used for Sony’s wireless earphones


JST  -By Mayuko Uno

Sony Mobile Communications (SOMC) Inc has released the Xperia Ear Duo XEA20 wireless earphones.

Its right and left earphones are independent of each other. There is no manufacturer’s suggested retail price for the product, but it is sold at ¥29,880 (excluding tax) at Sony Store. For connection between the right and left earphones, SOMC employed the “NFMI (near field magnetic induction)” method.

The “NFMI” makes the transmission through human body easier. Its time lag is several milliseconds, which is smaller than that of Bluetooth. And the lag is constant, enabling to ensure stable communications. With the latest product, communications are done via a part near the back of the head and the base of the neck by using antennas located behind the ears, preventing sound from being intermitted, SOMC said.


The right earphone of the product functions as a master (base unit) and is connected to a device such as a smartphone via Bluetooth. Audio data are transmitted from the right earphone to the left earphone and played. Because the NFMI method reduces time lag, it becomes possible to reduce lip sync (the gap between video and audio) at the time of watching video, etc with a smartphone while decreasing the amount of buffering.

The NFMI also contributed to realizing a beam forming technology at the time of collecting sound with a microphone, SOMC said. The beam forming technology emphasizes only specific sound sources by separating sound sources. In the case of earphones equipped with a microphone, a directivity is added so that the microphone collects sound near the mouth of the user.

“While common products use two microphones in total, the new product uses two microphones on each of the right and left sides, four in total,” SOMC said. “Therefore, it becomes possible to increase S/N ratio (signal/noise ratio).”

The NFMI method is used for beam forming using the four microphones. Data collected by the left microphone (of the slave) are transmitted to the right earphone and processed. Because the lag of the NFMI method is constant, it is possible to store time lag information, which is necessary for beam forming, and transmit data to the right earphone,” SOMC said.

The new product is equipped with six kinds of sensors (proximity sensor, acceleration/gyro sensor, atmospheric pressure sensor, compass and microphone) to realize gesture-based operations and the “daily assistant” function, which transmits information in accordance with the state of the user.

To increase battery life while constantly driving those sensors, SOMC developed and employed “Smart Sensing Processor CXD5602,” which is a chip made by adding a sensing processing circuit to the main CPU. Even when the main CPU is in a sleep state, the sensing processing circuit is driven with a low power consumption, the company said. With those improvements, a battery life of 22 hours is realized at the time of suspending Bluetooth communications.



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