Electronic Design

Magnetic Induction To Spur The Growth Of Personal-Area Networks

Several RF solutions will soon start competing for short-distance wireless voice and data communications in personal-area networks (PANs), where transmission distances span 10 to 100 m. These include Bluetooth, HomeRF, and WiFi (or 802.11). But for PANs under 3 m, these solutions can't meet user requirements. Here, magnetic-induction technology is poised to dominate. PAN applications require the lowest-cost, lowest-power, and smallest footprint for adoption by the mass market. These metrics are the main advantages of magnetic-induction communication systems.

The low power consumption of magnetic-induction technology is possible by a combination of a low carrier frequency (10 to 15 MHz), the small processing power required, design techniques, and transmitter characteristics. Each helps save power in the magnetic-induction system. For example, Aura Communications' LibertyLink magnetic-induction transceiver draws only 7 mA at 2 V for transmitting full-duplex voice or data across a 1-m link. RF solutions require 10 to 20 times this amount.

For PAN devices, especially consumer devices, price is probably the biggest concern. Recently, much ado has been made over chip price. But discussing chip price is misleading if it makes up only a fraction of the overall cost of building a system. For instance, Bluetooth has continually quoted a $5 solution.

MicroLogic Resources, an independent research firm specializing in wireless communications, estimates the cost of a two-node wireless Bluetooth link at $43.24. By comparison, a magnetic-induction link has a bill-of-materials under $20. Plus, due to its low power requirement, it uses a $0.45 Ni-MH battery pack. RF solutions use expensive ($5 to $10) lithium batteries for comparable talk time.

A recently released "ear bud" style magnetic-induction headset weighing only 13 grams includes a 12- by 27-mm (324 mm2) pc board with only 33 components. On the other hand, a recently released Bluetooth headset weighs more than twice as much, has a board of 22 by 38 mm (836 mm2), or 2.5 times the area, and has 170 components. This difference is significant for a consumer product worn on the ear.

A magnetic-induction system offers other advantages over RF. It has no nulls, no scattering effects or multipath fading, less stringent FCC limitations, improved frequency reuse schemes, built-in security, and reduced interference from other devices. RF solutions have an advantage in working distance (they may work up to 10 m or more), but PAN applications only need 3 m.

Don't forget performance. A magnetic-induction system, based on Aura's LibertyLink system, is capable of full-duplex, 64-kbit/s CVSD encoded voice and point-to-multipoint, 204.8-kbit/s data transfers. These data rates and the ability to have several slaves for each master make PAN applications like wireless headsets, PDA synchronization, game controllers, wireless desktops, and telematics affordable and consumer friendly.

Of the four available technologies for short-range wireless applications, each is poised to dominate a different market niche. Bluetooth will enable the lesser cost-sensitive, high-data-rate electronic devices. HomeRF will capture the in-home audio and small-office/home-office market. WiFi will enable enterprise-wide high-speed LANs. Magnetic-induction technology will be the backbone for close-proximity, low-power, low-cost wireless devices.

Expect the magnetic solution to run about one-fourth of RF's price, requiring about 10 to 20 times less power. It will also be much less prone to interference and eavesdropping.

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