## 3 IBC Time Domain Responses Based on Corrected Transfer Function
The _THD\({}_{4}\)_ deviation from the ideal case is around (55-58)%, which indicates signal transmitted via baseband technique in IBC is not suitable (pulse-shape - spike-shape). For passband experiments, two input square waves (one at 500 Hz, the other at 50 kHz) are modulated to the same carrier of 500 kHz. The 500 kHz carrier is chosen because it is located at around the center of low attenuation frequency band as shown in Figure 4. The general block diagram of passband experiment set-up is again shown in Figure 5(a), which consists of a vector signal generator (Agilent, N5182A MXG Vector Signal Generator), a differential probe and a signal analyzer (Agilent, N9020A MXA Signal Analyzer). The corresponding flow chart is displayed in Figure 5(c). During the experiment, the input square wave (500 Hz or 50 kHz) with 50% duty-cycle, peak to peak amplitude of 1 V, was modulated to high frequency band using BPSK with 500 kHz carrier by vector signal generator. The modulated signal was then applied to the cleansed human skin by the electrodes. The received signal was detected via differential probe and the demodulation was performed by the digital vector signal analysis software (Agilent, 89601A) on signal analyzer. During the demodulation  
Figure 6: Input and Output of baseband IBC transmission for 500 Hz square wave: (**a**) S = 6 cm; (**b**) S = 11 cm. process, the center frequency was set to 500 kHz, and the symbol rate was set to the original frequency of the square wave. However, the equipment software can only perform demodulation [32] on the limited bandwidth corresponding to the symbol rate. And the limited bandwidth contains only four non-zero harmonics of the square wave in our experiments. Therefore, in order to make fair comparison, we considered the similar situation in the calculation process by actually limiting the demodulation bandwidth of containing up to the first 4 non-zero harmonics, as indicated to Equation (11). Both calculation and measurement results of demodulation signals in passband transmission are shown in Figure 7.  
As seen in Figure 7, the time-domain signal outputs basically retain the shape of input square pulses (compared with the sum of 1 st four harmonics). As expected, there are always amplitude differences between the calculated and measured results. The amplitude deductions of the measured output signal  
Figure 7: Input and Output (after demodulation) in passband IBC transmission for square wave: (**a**) 500 Hz square wave at S = 6 cm. (**b**) 500 Hz square wave at S = 11 cm. (**c**) 50 kHz square wave at S = 6 cm (**d**) 50 kHz square wave at S = 11 cm. for an extra 5-cm distance are around 46% and 55% for 500 Hz and 50 kHz, respectively. In the calculated result, the amplitude deduction is around 57% for 500 Hz and 50 kHz input. The differences between calculated and measured results mainly come from the dynamic physiological process of human body. The amplitudes of the calculated output waveforms are about 19.4 mV for both 500 Hz and 50 kHz input square waves at S = 6 cm; while the amplitudes of the calculated output waveforms are around 4.8 mV for S = 11 cm. The reason is that both input square waves were carried on the same the carrier frequency at 500 kHz, and the bandwidths of the two waves are within the relatively flat low-attenuation frequency band; hence they suffer the similar attenuation for a fixed separation S. The output pulses shown in Figure 7(a,b) have the _THD\({}_{4}\)_ around 41.9% in calculation and around 42.3% in measurement. Comparing with those values (upper ninety %) in baseband IBC transmissions, passband IBC transmission obtains lower distortion and has a much better communication performance. In Figure 7(c,d), the _THD\({}_{4}\)_ in measurement is around 42.4% and 41.7% at S = 6 cm and 11 cm, respectively. All passband _THD\({}_{4}\)_ are close to ideal square wave case, indicating rather low distortion for passband transmissions.