Balun's effect on the measurement of transmission characteristics for intrabody communication channel

Effect of transformer symmetry on intrabody communication channel measurements using grounded instruments

“…The results obtained using grounding strategies 2 and 3 were equivalent. Measured IBC channel amplitude transmission characteristics in [7,11,12,14] all increase 20 dB/decade, the amplitude value at the single frequency increases with interwinding capacitance of the transformers, and it is comparable for the same RF transformers.…”

“…Consequently, the general capacitive IBC measurement setup consists of a device under test (human body), human body interface (electrodes connected in different manners), decoupling hardware, and measuring instrumentation. Galvanic decoupling is usually realized using an optical link [8] or, much more often, connecting transformers between the transmitter/receiver electrodes and the rest of the measuring equipment [4][5][6][7][9][10][11][12][13][14]. However, the influence of the transformers on the measured results has been commented in a few papers only recently [7,[11][12][13][14].…”

“…Sakai et al analyzed influence of the RF transformers on the measured capacitive IBC channel characteristics in [11,12] and found that the value of the capacitance between primary and secondary windings of the transformer (interwinding capacitance, IWC) can influence the results drastically. Interwinding capacitance of four tested baluns varied from 1.1 pF to 32.0 pF, which resulted in a 40 dB difference between the minimal and maximal amplitude of the measured capacitive IBC channel transmission characteristics.…”

“…Pereira et al in [7] developed a model of the extended IBC channel which includes a capacitive IBC channel and the test fixture (RF transformers and the transition between the coaxial cables and the other parts of the system) used in the measurements. They tested two RF transformers and measured interwinding capacitances of 27.2 pF and 8.6 pF (which were 32.0 pF and 10.9 pF in [11], respectively). The model simulation results agreed well with the measured amplitude channel characteristics in the frequency range from 1 MHz to 70 MHz, and showed that the effect of the test fixture on the channel measurement results is present even after the calibration of the measurement setup.…”

“…They focused on the galvanic coupling IBC mainly in the frequency range between 10 kHz and 1 MHz and analyzed differences when using transformers or battery powered devices, the effect of the load resistance, the use of different measurement equipment (signal generator, oscilloscope, network and spectrum analyzer), and the effects caused by different cables and connections. Three grounding strategies in a setup with a vector network analyzer (VNA) and the same balun as in [7,11] with IWC approximately 10 pF were 1) without transformers, 2) transformer at the transmitter VNA port, and 3) transformer at the transmitter and receiver VNA ports. The results obtained using grounding strategies 2 and 3 were equivalent.…”