For consumer mobile products, it is not unreasonable to expect to get one day's worth of charge from the product. For the low-power magnetic system, this can be accomplished with two NiMH, 40 mAh batteries. In reasonable quantities, such a battery pack currently costs about $0.45. For the high-power RF system, which draws 50 to 150 mA, this would require a 400 to 1200 mAh lithium battery. These battery packs cost in the $5 to $11 range and require safety monitoring circuitry. The RF battery is 2.73 cm3. The batteries for the magnetic system take up 1.54 cm3. Consequently, the RF power packs up the ante in all directions: cost, size and weight. The MI pack offers a 45% volume savings. This becomes significant in wearable mobile devices such as a headset.

Current estimates of an OEM's total cost for a magnetic induction headset product is around $22 for two nodes, while the RF solution is between $48 - $54, or about 2.5 times higher. Using a conservative retail multiple of four, this puts the products on the shelf at $88 for the magnetic headset and $199-plus for the RF solution.

One of the biggest problems plaguing RF solutions is the effect the environment has on the signal. Any time someone walks around using an RF product (cordless or cell phone for instance), the call clarity changes with location. These ‘drop-outs’ can be attributed to antenna pattern nulls, scattering effects or one of several fading problems. RF solutions do not radiate in concentric circles like a magnetic system; instead, they favor a particular direction or pattern. While these patterns can be optimized, they are also subject to nulls.

The magnetic induction system is constant power at a given distance to the transmitter and is not generally affected by environment. For instance, if the magnetic induction system is used for a headset and worn on the body, there are no interference concerns.

Security is always an issue in any wireless system. The security issue becomes more acute as the power and distance increase. In a system in which the signal only goes a couple of meters, an eavesdropper would need to be standing within 2 meters to listen to the conversation. With an RF system that propagates 10, 100, or more meters, much more opportunity exists to eavesdrop. None-the-less, the same type of security and encryption can be implemented in a magnetic system if necessary.

Finally, one factor with pros and cons is the industry backing. A consortium has the power and money to market and hype a technology until it is a household name. Bluetooth has mastered this approach. Bluetooth's hype has had a significant effect on other competitive technologies. Unfortunately, this has the effect of pushing lesser-known technologies into the shadows so they are often overlooked or dismissed. To that end, creating a large consortium or special interest group (SIG) seems like the best way to promote technology.

However, consortiums have downsides. First, hundreds or thousands of companies, each with its own agenda, are working toward a common specification. This creates a specification with tremendous overhead for companies wanting a simple solution. This overhead increases complexity, cost, size and development time.

It also tips a hand to competitors. In many cases, to get something into the specification that benefits a company's products, the company can lose some competitive advantage. Any innovative idea may need to be disclosed either at the specification or qualification stage, allowing competitors to copy it.

While the magnetic technology has clear advantages over RF in terms of cost, power consumption, interference and security, it only works in the close proximity. Magnetic solutions are about 1/3 the cost of the RF solution and require about 10 to 30 times less power. They are also less prone to interference and eavesdropping. However, it will not drive a wireless LAN or other 100-meter applications.

By the end of this year, several RF and magnetic induction solutions will be available for wireless voice and data networks within the 100-meter space. These include Bluetooth, HomeRF, “Wi-Fi”, and MI technology. Each is poised to dominate a niche in the market. Bluetooth will enable less cost-sensitive, high-data-rate electronic devices. HomeRF will capture the in-home and small office/home office (SOHO) market. Wi-Fi, or 802.11, will enable high-speed LANs. MI is poised to be the backbone for close-proximity, low-power, low-cost, wireless devices.

About the author

Chris Bunszel is the Marketing Manager for Aura Communications. He can be reached at 978.988.0088, ext. 114 or chrisb@auracomm.com. The company's Web site address is www.auracomm.com. Physical address is 187 Ballardvale St., Wilmington, MA 01887

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