IEEE 802.15.6 channel
modeling subcommittee
has approved measurements for frequency range
13.550 to 13.571 MHz
and the surprising result is that human body
exhibits almost similar path loss as that of free space for a narrow
band of 21 kHz. According to these measurements, signal amplitude
reduction through the regions of hand, wrist, torso (front to back),
thigh, ankle, left to right ear is 3.3 %, 2.8 %, 3.4 %, 1.9 %, 2.8 %
and 2.0 % respectively [1].
It has also been specicified
that human body can be used as a communication channel from 5 to 50 MHz
without need of any modulation. It has been shown that for a
transmission distance of 150 cm from the fingertips of one to the
fingertips of the other hand with receiver load impedance of 10 M-ohm
and electrode sizes of 2x2 cm2 the amplitude and phase
mean value of response is as follows at different frequencies [1].
|
|
5 MHz |
10 MHz |
20 MHz |
30 MHz |
40 Mhz |
50 Mhz |
|
Amplitude (dB)
|
-47.2 dB |
-48 dB |
-48.65 dB |
-50.7 dB |
-52 dB |
-54.8 dB |
|
Phase (degrees)
|
-29.2 º |
-47.4 º |
-87.7 º |
-117.6 º |
-150 º |
- 172.7 º |
The channel also exhibits
Gaussian noise with zero mean and 2.55×10-5
variance.
References
[1] K.-Y. Yazdandoost and
K. Sayrafian, “Channel model for body area
network (BAN),”
15-08-0033-04-0006-draft-of-channel-model-for-
body-area-network.doc
https://mentor.ieee.org/802.15/file/08/15-08-0780-09-0006-tg6-channel-model.pdf
How is the phase measured? The total phase shift at the edge frequency?
SvaraRaderaIs it due to the 50-MHz travelling through 1.50 m body and thus experiences a phase shift in the measurements, or is the RC bandwidth of the body?
(Assuming 200000 km/s and 50 MHz would give you a wavelength of 4 m, i.e., 2 m for half a cycle, -180 degrees).
Unfortunately, there is not much information given in the document about the exact method of phase measurements except the following relationship.
SvaraRaderaChange of phase = (Phase of output voltage at receiver – Phase of input voltage at transmitter) in degree.