. Biophysical science. Biophysics. 210 The Absorption of Electromagnetic and Ultrasonic Energy /I I : 3 from to 3 /ufd/cm2. Few values lie outside of the range to One low measurement of /xfd/cm2 has been obtained for a frog nerve, but other nerve measurements are in the to /xfd/cm2 range. Values for the leakage areal resistance of the cell membrane vary from 25 to 10,000 ohm-cm2 or higher. Nerve and muscle measurements have yielded both extremes. Similar considerations apply to the electrical characteristics of whole tissues. Their impedance is hard to separate in ter
. Biophysical science. Biophysics. 210 The Absorption of Electromagnetic and Ultrasonic Energy /I I : 3 from to 3 /ufd/cm2. Few values lie outside of the range to One low measurement of /xfd/cm2 has been obtained for a frog nerve, but other nerve measurements are in the to /xfd/cm2 range. Values for the leakage areal resistance of the cell membrane vary from 25 to 10,000 ohm-cm2 or higher. Nerve and muscle measurements have yielded both extremes. Similar considerations apply to the electrical characteristics of whole tissues. Their impedance is hard to separate in terms of cellular. Figure 2. The frequency dependence of the dielectric constant of muscle. Note the three regions labeled with Greek letters indicating three types of relaxation. After H. P. Schwan and G. F. Kay, "Conductivity of Living Tissues," Annals of the New York Academy of Sciences 65: 1007 (1957). parameters but may be represented as a lumped resistivity and capacity. The ratio of the capacity to that of a vacuum is the dielectric constant. A plot of effective dielectric constants against frequency has the shape shown in Figure 2. It should be borne in mind that a variety of effects contribute to this general shape. The region labeled f3 is the one related to the change from conductance around the cells to conductance through the cells. The complex shape of the curve indicates a variety of cell sizes and shapes. The region labeled y is due to molecular relaxations discussed below. The low frequency changes labeled a indicate some other type of phenomena which is not clearly understood. Similar low frequency changes in resistivity can be seen in Figure 3. Although neither can be explained clearly, it appears likely that both are due to some common mechanism. Moreover, the low frequencies at which these occur indicate that comparatively large pieces of material are involved. All molecules tend to become polarized in an electric field. In an. Please note that these
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