Near-Field Magnetic Induction Communication (NFMIC) systems differ from other wireless communications in that most conventional wireless RF systems use an antenna to generate and transmit a propagated electromagnetic wave. In these types of systems all of the transmission energy is designed to radiate into free space. This type of transmission is referred to as "far-field."
According to Maxwell's equation for a radiating wire, the power density of far-field transmissions attenuates or rolls off at a rate proportional to the inverse of the range to the second power (1/range2) or -20dB per decade. This slow attenuation over distance allows far-field transmissions to communicate effectively over a long range. The properties that make long range communication possible are a disadvantage for short range communication systems.
FreeLinc, a U.S. technology corporation located in Utah, has developed and holds numerous patents pertaining to Near Field Magnetic Induction Communication. The system uses a short range (less than 2 meters) wireless physical layer that communicates by coupling a tight, low-power, non-propagating magnetic field between devices. The concept is for a transmitter coil in one device to modulate a magnetic field which is measured by means of a receiver coil in another device.
NFMI systems are designed to contain transmission energy within the localized magnetic field. This magnetic field energy resonates around the communication system, but does not radiate into free space. This type of transmission is referred to as "near-field." As shown in the graph below, the power density of near-field transmissions is extremely restrictive and attenuates or rolls off at a rate proportional to the inverse of the range to the sixth power (1/range6) or -60dB per decade.
In Diagram 2, the carrier frequency is 13.56MHz and has a wavelength (_) of 22 meters. The crossover point between near-field and far-field occurs at approximately _/2_. At this frequency the crossover occurs at 3.52 meters, at which point the propagating energy from the NFMI system conforms to the same propagation rules as any far-field system; rolling off at -20dB per decade. At this distance the propagated energy levels are -40dB to -60dB (10,000 to 1,000,000 times) lower than an equivalent intentional far-field system.
FreeLinc's Near-Field Magnetic Induction Communication Systems require low power thus allowing extended talk-time up to 20 continuous hours in most radio accessory applications. This NFMIC intellectual property has been integrated into secure wireless communication accessories, such as headsets and speaker microphones, for public safety, military personnel and other users of two-way radios.
Near Field Magnetic Induction Communication technology enables users of two-way radios to experience wireless mobility, wireless safety and wireless security with portable radio accessories. More information regarding Near Field Magnetic Induction Communication based products can be seen at www.freelinc.com
For further reference please see, below, US Patents Owned by FreeLinc, Orem, Utah.
|5,771,438||Jun 23, 1998||Short-Range Magnetic Communication System|
|5,912,925||Jun 15, 1999||Diversity Circuit for Magnetic Communication System|
|5,982,764||Nov 09, 1999||Time-Multiplexed Short-Range Magnetic Communications|
|6,459,882||Oct 01, 2002||Inductive Communication System and Method|
|6,819,762||Nov 16, 2004||In-the-Ear Headset|
|7,035,608||Apr 25, 2006||Methods and Apparatus for Tuning in an Inductive System|
|7,142,811||Nov 28, 2006||Wireless Communication Over a Transducer Device|
|7,149,552||Dec 12, 2006||Wireless Headset for Communications Device|
|7,215,924||May 08, 2007||Techniques for Inductive Communication Systems|
|7,254,366||Aug 07, 2007||Inductive Communication System and Method|
|7,236,741||Jun 26, 2007||Methods and Apparatus for Tuning in an Inductive system|
|RE39982 (reissue of 5,912,925)||Jan 01, 2008||Diversity Circuit for Magnetic Communication System|
|Application Number||Filing Date||Title|
|09/993,328 (reissue application of 5,982,764)||Nov 06, 2001||Time-Multiplexed Short-Range Magnetic Communications|
|11/264,169||Nov 02, 2005||Wireless Headset for Communications Device|
|11/469,751||Sep 01, 2006||Wireless Headset and Microphone Assembly for Communications Device|
|11/544,950||Oct 06, 2006||Wireless Communication Over a Transducer Device|
|Application Number||Filing Date||Title|
|10/413,434||Apr 11, 2003||Transceiver Device and Fastener|
|10/782,541||Feb 18, 2004||Methods and Apparatus to Detect Location and Orientation in an Inductive System|
|Country||Patent Number||Issue Date||Title|
|China||ZL96195357.8||Dec 01, 2004||Short-Range Magnetic Communication System|
|Singapore||51212||Mar 31, 2005||Short-Range Magnetic Communication System|
|Mexico||196825||Jun 05, 2000||Short-Range Magnetic Communication System|
|EP (Germany)||69630894.0-08||Nov 27, 2003||Short-Range Magnetic Communication System|
|EP (United Kingdom)||0872032||Nov 27, 2003||Short-Range Magnetic Communication System|