Implanted Antenna Improves In-Body Communications

In short-range Biotelemetry applications, antennas are implanted inside the body to forge communication links between medical sensors and exterior instruments. Ultra Wideband (UWB) signal transmission from an in-body implanted antenna to on-body or outside-body devices for biomedical applications has been considered by Ali Khaleghi from Rikshospitalet University Hospital (Oslo, Norway) and Ilangko Balasingham from Norway's University of Science and Technology. The researchers computed the received energy density of the UWB signal in terms of the distance from the body surface of a human anatomy model at the frequency range of 1 to 6 GHz. An implanted UWB elliptic-disc dipole antenna was designed and optimized for use in the chest of the model. The human-body model was analyzed using numerical electromagnetic (EM) code.

The researchers were able to derive path-loss factors of the UWB channel for different distances from the body surface and different implantedantenna depths. The results showed that energy coupling from the nonradiative near field of the body-implanted antenna is dominant for the signal transmission. If near-field components are exploited, the communication link quality can be improved in the range of 14.5 to 18 dB for implant depths of 35 and 55 mm, respectively. At those depths, the calculated energy losses because of the body tissues are a respective 15 and 9.4 dB.

To improve communication link quality, the researchers advise using the implanted antenna's nonradiative near-field region to design and place the receiving antenna as close to the body surface as possible. See "Improving In-Body Ultra Wideband Communication Using Near-Field Coupling of the Implanted Antenna," Microwave And Optical_ Technology Letters, March 2009, p. 585.

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