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DIELECTRIC PROPERTIES OF THE HUMAN BODY IN THE WAVELENGTH RANGE FROM 1 TO 10 cm*)
Recently, measurements have been made of the absorption constant \(\alpha\) and the phase constant \(\beta\) for wavelengths of 1.27 and 10.0 cm. All measurements were carried out in waveguides at a temperature of \(37.0 \pm 0.5^\circ\)C. Table I gives the mean values of several measurements. The accuracy of the measurements in the worst case is not less than \(\pm 10\%\).
Table I
| Object of investigation | \(\lambda = 1.27\) cm: \(\alpha\) (neper/cm) | \(\lambda = 1.27\) cm: \(\beta\) (radian/cm) | \(\lambda = 10.0\) cm: \(\alpha\) | \(\lambda = 10.0\) cm: \(\beta\) | Notes |
|---|---|---|---|---|---|
| Blood | 9.5 | 31.0 | 0.65 | 4.6 | Coagulated with 1/500 mg of heparin |
| Blood | 9.7 | 28.9 | — | — | Coagulated with 1/500 mg of heparin |
| Blood serum | 10.3 | 34.7 | 0.84 | 5.3 | Centrifuged sample |
| Blood serum | 6.4 | 23.2 | 0.81 | 4.1 | Centrifuged sample |
| Skin | 6.3 | 25.4 | 0.65 | 4.5 | Breast |
| Skin | — | — | 0.73 | 4.6 | Breast |
| Skin | 1.95 | 9.2 | 0.21 | 1.45 | Breast |
| Fat | 1.0 | 8.6 | 0.20 | 1.70 | Sections cut at different depths from the surface |
| Fat | 1.5 | 8.7 | — | — | Sections cut at different depths from the surface |
| Fat | 0.9 | 11.9 | — | — | Sections cut at different depths from the surface |
| Fat | 0.95 | 11.7 | — | — | Sections cut at different depths from the surface |
| Bones | 1.2 | 12.9 | — | — | |
| Bones | 1.45 | 12.5 | — | — | |
| Breast carcinoma | 8.1 | 28.6 | 0.73 | 4.8 | Histological examination confirmed Scirrus carcinoma in all samples |
| Breast carcinoma | 6.9 | 25.2 | 0.60 | 5.0 | Histological examination confirmed Scirrus carcinoma in all samples |
) T. S. England, Nature 166*, 480 (1950).
With the aid of this table, the real \((\varepsilon')\) and imaginary \((\varepsilon'')\) parts of the dielectric permittivity were calculated. The relative (with respect to air) values are given in Table II, which also includes data obtained earlier for the wavelength \(3.18\ \text{cm}\).
Table II
| Object | \(\varepsilon'\), \(10.0\ \text{cm}\) | \(\varepsilon'\), \(3.18\ \text{cm}\) | \(\varepsilon'\), \(1.27\ \text{cm}\) | \(\varepsilon''\), \(10.0\ \text{cm}\) | \(\varepsilon''\), \(3.18\ \text{cm}\) | \(\varepsilon''\), \(1.27\ \text{cm}\) |
|---|---|---|---|---|---|---|
| Blood | 53 | 45 | 32 | 15 | 23 | 20 |
| Blood serum | 70 | 57.5 | 45.5 | 22.5 | 24 | 29 |
| Skin | 43.5 | 35.5 | 23 | 16.5 | 16 | 13 |
| Fat | 6.5 | 4.5 | 3.4 | 1.6 | 0.95 | 1.1 |
| Bones | — | 7.6 | 6.3 | — | 1.45 | 1.1 |
As can be seen, the dielectric properties of most objects are close to those of water; fat and bones are relatively transparent to radiation. The increase in the absorption coefficient (at \(10\ \text{cm}\)) in comparison with water is probably explained by additional ionic conductivity. At shorter wavelengths, ionic conductivity has no effect, as follows both from theory and from experiment.
A. K.