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A two-pronged approach, review and measurement, has been adopted to characterize the conductivity of tissues at frequencies below 1 MHz. The review covers data published in the last decade and earlier data not included in recent reviews. The measurements were carried out on pig tissue, in vivo, and pig body fluids in vitro. Conductivity data have been obtained for skeletal and myocardial muscle, liver, skull, fat, lung and body fluids (blood, bile, CSF and urine). A critical analysis of the data highlights their usefulness and limitations and enables suggestions to be made for measuring the electrical properties of tissues.

The complex permittivity of aqueous solutions at 20 degrees C has been measured at concentrations between 0.001 and 5 mol/L and over a frequency range 0.13-20 GHz. The results were combined with literature values to derive empirical equations to predict the dielectric behavior of sodium chloride solutions between 0 and 5 mol/L and 5 degrees C-35 degrees C.

In vitro dielectric properties of ageing porcine tissues were measured in the frequency range of 50 MHz-20 GHz, and the total combined uncertainties of the measurements were assessed. The results show statistically significant reduction with age in both permittivity and conductivity of 10 out of 15 measured tissues. At microwave frequencies, the observed variations are mainly due to the reduction in the water content of tissues as an animal ages. The results obtained were then used to calculate the SAR values in children of age 3 and 7 years when they are exposed to RF induced by walkie-talkie devices. No significant differences between the SAR values for the children of either age or for adults were observed.

Starting from a rigorous formulation for the admittance of an open ended coaxial probe, this paper identifies the simplifying assumptions that are introduced to obtain more practical solutions. The predictions of the models are compared to each other and to experimental data obtained on an independently calibrated experimental set-up. The advantages and limitations of a model are determined by the theoretical derivation and the numerical solution. The model identified as most suitable for the measurement of the dielectric properties of biological materials is used to determine the relative permittivity and conductivity of muscle and skull bone in the frequency range 1 MHz to 20 GHz.

The dielectric behavior of the aqueous solutions of three widely differing macromolecules has been investigated: myoglobin, polyvinylpyrrolidone (PVP), and human serum low-density lipoprotein (LDL). It was not possible to interpret unambiguously the dielectric properties of the PVP solution in terms of water structure. The best interpretation of the dielectric data on the myoglobin and LDL solutions was that, in both cases, the macromolecule attracts a layer of water of hydration one or two water molecules in width. For LDL, this corresponds to a hydration factor of only 0.05 g/g, whereas for myoglobin the figure is nearer 0.6 g/g. With myoglobin, part of the water of hydration exhibits its dispersion at frequencies of a few GHz, and the rest disperses at lower frequencies, perhaps as low as 10-12 MHz. The approximate constancy of the width of the hydration shell for two molecules as dissimilar in size as LDL and myoglobin confirms that the proportion of water existing as water of hydration in a biological solution depends critically on the size of the macromolecules as well as on their concentration.

The dielectric constant and conductivity of calf thymus DNA were investigated at frequencies between 0.1 MHz and 70 GHz. This work is to investigate the dielectric properties of DNA in low gigahertz region and also to study whether the dielectric behavior of the water is affected by the presence of highly charged DNA. The results of these measurements indicate the presence of two anomalous dispersions, the one between 1 MHz and 1 GHz and the second one above 1 GHZ. The dispersion at low frequencies is likely to arise from polar groups in the DNA molecule. The relaxation behavior of unbound water in DNA solution is only slightly affected by the presence of DNA at concentrations below 1%.

site is vacant, all six O(3) oxygens have shifted 0.50 A toward Ni(1) and the center of the double six ring-a striking demonstration of the ability of the aluminosilicate framework to adjust to change: in cation position. The Ni(l)-0(3) distance, 2.29 A, is an average value that includes O(3) oxygen positions for SI sites containing no nickel ions. This fact is illustrated by the O(3) thermal ellipsoids, which are elongated in the Ni-0 direction. Finding the nickel ion on both sides of the supercage six ring may be due to the presence of the residual water, O(w2), and the resultant Ni(3)-O(w2) bond formation.Although the nickel ions prefer SI sites, they are distributed among four, and possibly five, different sites, with no site completely filled. This distribution agrees with conclusions drawn by Barry and Lay.a From esr studies of manganese in mixed cation X zeo-lites, these authors found manganese(I1) distributed in a number of sites and concluded that Mn2+ does not have very strong site preference.Also, from ir studies of CO adsorbed on various cationic forms of zeolite Y, Angel1 and Schaffer4 found that Ni2+ and Go2+ ions have no overwhelming preference for site I. Although site I has the highest occupancy in nickel faujasite (66%), it is not fully occupied. I n this respect, ie., a lack of high site preference, transition metal zeolites differ from calcium in zeolite Y, which prefers site SI,24 and rare earth ions in zeolites X and Y, which prefer SI' sites.l1Vz6J6 (24) R. P. Dodge, unpublished research.The purpose of the work described in this paper was to investigate the dielectric behavior of the protein bovine serum albumin. The investigation was made to try and solve some of the problems that had arisen from measurements obtained by other workers in the radiowave and microwave frequency range. To do this, measurements were made over as wide a concentration, temperature, and pH range as possible. It was confirmed that there was a subsidiary dispersion in the frequency range 200-2000 MHz, and the possible molecular interpretation of the dispersion is discussed. It can be concluded that this dispersion is probably due to water bound to the protein. By assuming a dielectric mixture theory the variation of the amount of bound water with concentration and pH is estimated.(1) In this paper, bovine Berum albumin will be abbreviated as BSA.