Biomedical Engineering Reference
In-Depth Information
2.8
2.7
2.6
2.5
2.4
2.3
2.2
2.1
2
1.9
1.8
50
60
70
80
90
100
110
Frequency (GHz)
FIGURE 2.4
Real part of relative permittivity of dioxane.
such, is extremely useful as a calibration dielectric to check if a procedure is
correct, in particular when changing the frequency from one waveguide band
to the next one. These measurements complete results published earlier up to
20 GHz [8]. They show that the dielectric constant of dioxane is equal to 2.25
over the whole microwave range and part of the millimeter waves, up to
110 GHz.
The two solid curves in Figure 2.5 show the real and imaginary parts of the
relative permittivity of methanol (CH
3
OH), respectively, from 8.2 to 110 GHz.
(Results in the frequency band 12-18 GHz are missing.) The two dashed
curves result from Debye's equation. A discrepancy between Debye's law and
the measurements is visible in the high-frequency range, above 20 GHz. These
results complete results published earlier up to 20 GHz [26].
Figure 2.6 presents (solid curves) the real and imaginary parts of the
complex permittivity of beef blood from 50 to 110 GHz. The blood was refrig-
erated and regularly stirred. When starting the measurements, the blood tem-
perature was 13°C. After preparation and during measurements, it reached an
estimated value of 20°C. These new measurements follow well Debye's law,
based on earlier published results at microwave frequencies, up to 20 GHz
(dashed curves in Fig. 2.4), despite a possible temperature effect [30].
The measurement configuration is completely closed, which provides very
accurate results. Open structures may however be necessary. For instance, the
complex permittivity of live and dead neurological cell cultures has been
measured on a setup made of open microstrip transmission lines, from 20 to
40 GHz [31]. One advantage of this configuration is that it is open. Hence, the
biological medium can be submitted to microwave exposure and the meas-
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