A PAN receiver essentially measures the modulation of the electric field
in the vicinity of the body. As the electric field lines are
necessarily perpendicular to the surface of the body (a conductor),
the best geometries place one electrode close to the body and the
other the maximal reasonable distance away from the body perpendicular
to the bodies surface.
The essential tradeoff for signal strength lies in the relative
coupling of the ground electrode to the ground, and to the body. When
the electrodes are directly between the body and ground, as in the
receiver in configuration <#326#>A<#326#> in Figure #pangeom#327>, the ground
electrode is better coupled to the body than it is to the ground. In
geometries such as those in configuration <#328#>B<#328#>, however, the
coupling of the ground electrode to ground (#tex2html_wrap_inline1344#) gets weaker and
weaker as it is moved up the body, while the ground electrode to body
coupling (#tex2html_wrap_inline1346#) stays nearly the same.
#figure331#
Figure 6-1: Simplified View of PAN
#table338#
Table 6.1: Simulation results at various receiver heights
In the simplified version of PAN shown in Figure #pansimple#352>, the
relationship between changes in height of the receiver and the values
of #tex2html_wrap_inline1354# and #tex2html_wrap_inline1356#, the above mentioned capacitances, and #tex2html_wrap_inline1358#,
the coefficient corresponding to the number of millivolts at the
receiver per volt at the transmitter, are fundamental to understanding
the geometry constraints of PAN.
The results of a full simulation with various receiver heights appear
in Table #tableheights#355>. The simulation was done with a 170cm
high, 40cm radius cylinder approximating a person. The transmit
electrodes were beneath the person and the receive were beside them at
various heights.
#figure356#
Figure 6-2: Signal Strength vs. Receiver Height
As seen in Figure #graphsig#363>, receiver voltage changes linearly
with height. The curving of the line at the beginning and end of
graph are due to edge effects near the persons feet and head.
A foot to foot configuration is far better, with a value of #tex2html_wrap_inline1360# on
the order of #tex2html_wrap_inline1362#.