the expression becomes
S(t) RloadAloop Lloop dBnorm (t)
Vout (t) = -
Loop oop +Rload dt
RloadAloop (_)n+l( Lloop d(")Bnorm(t) (3-109)
Lloop Rloop +Rload dt(")
Moreover, Equation 3-109 can be further simplified to
S- RloadAloop dBnorm(t)
Rloop +Rload dt
RloadAloop o op n d")Bnorm (t)3-110
Rloop +Rload R0oop +Rload dt(")
The first term in Equation 3-110 is identical to Equation 3-90; the time-domain
output of the loop antenna obtained by taking the inverse Fourier transform of Equation
3-89, assuming co < oo. The second term is the manifestation of the upper frequency
response limit in the time domain. The second term will become zero if L1oop = 0,
which corresponds to coo = .
3.3.2.2 Loop antenna implementation
Now that the output of the loop antenna has been characterized in the time and
frequency domains, the implementation of the MSE magnetic field and magnetic field
time-derivative antennas can be discussed.
Both the magnetic field and the magnetic field time-derivative measurements
utilize square loops of 50 Q coaxial cable as shown in Figure 3-23. The coaxial cable
is placed in 4 inch PVC pipe to help keep a rigid shape. The inner conductor of the
cable is the actual wire comprising the loop antenna. The outer shield is necessary
to keep current from being induced on the inner conductor by an external electric
field. The outer shield of the cable can be thought of another loop of wire placed at
almost exactly the same spatial location as the inner conductor. Therefore, identical
voltages will be induced on the inner conductor and the shield of the coaxial cable.
As discussed in the previous section, the voltage output of a wire-loop antenna is