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.