Abstract
Background: Wireless body area network (WBAN) including bio-sensor network is expected to be a new communication system in ubiquitous society including medicine or point of care from the view point of easy connection of equipment．In this case, reduction of risk of information leak to a third party through special propagation is necessary. Human body communication (HBC) through the human body is a good solution for this problem. On the other hand, radio frequency (RF) communication should be carried out with a small power from the viewpoint of minimal invasion. Thus, high efficiency signal injection into human body is necessary. This paper provides the RF signal injection method with automatic impedance matching circuit operated by the use of Peripheral Interface Controller (PIC©)) for this purpose.
Methods: Automatic impedance matching circuit is assembled according to the design concept. In our proposed method, with the measurement results of magnitude of forward wave and reflected wave, voltage standing wave ratio (VSWR) is calculated. On the basis of VSWR values, according to the predetermined control flow of automatic impedance matching, controller operates so as to cancel out the imaginary component of human body impedance at the injection point. Results: Experimental results show that injection circuit with automatic impedance matching operated effectively in an actual environment so as to cancel out the imaginary component of human body impedance. Conclusion: The proposed method provides good RF signal injection in WBAN. Effectiveness of the proposed method is shown by the laboratory test measurement. The proposed method can cover the wide range of human body impedance. Moreover, the proposed method has potential for application in time varying human body impedance due to body movement.Keywords: Wireless BAN, human body communication, sensor network, point of care communications, PIC, impedance matching.
Graphical Abstract
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