A quantitative assessment of bubble-curtain effects upon interelectrode resistance of a conductimetric cell

Adhesion of gas bubbles upon electrode surfaces of a conductimetric cell causes a reduction in the effective surface area of the electrodes and hence leads to false estimations of measured conductivities. By considering the random dispersal of bubbles on the electrode surfaces, the increase of interelectrode resistance due to bubble adhesion is determined as a function of the fractional surface area covered by the gas bubbles. An experimental study using an electrolytic tank with electrodes partially covered by spherical Styrofoam (insulating) spheres (which simulate the gas bubbles) is carried out. Computed results due to the present model and those of other existing models (based on Maxwell's and Bruggeman's formulations) are compared with the measured data.     

A Note on "Variation in the Surface-Charge Density of an Excitable Nerve Membrane Exposed to Optical Radiation"

An error depicting the dimensional inconsistency in the expression for surface density of an excitable nerve membrane obtained by Agrawal et al. in the above paper, is indicated. This error arises mainly due to the incorrect definition and evaluation of surface-charge density adopted in the paper. Further, the analysis presented completely ignores the beam-wave parameters of the optical radiation. Hence, necessary corrections to the expression for surface-charge density and modifications to the reflection coefficient at the membrane surface, by taking into account the beam-wave characteristics, are presented here.     

Noninvasive beam-wave reflectometric instrumentation for measuring complex permittivity of dielectric materials at microwave frequencies

A noncontact and nondestructive method of measuring at microwave frequencies the complex permittivity of a selected region in a dielectric slab is described. For this purpose the test dielectric sample is irradiated with a focused (gaussian) microwave beam by means of a suitable applicator. From the characteristics of the reflected beam wave measured at a reflectometric bridge arrangement, the complex permittivity of the exposed region is determined. Some theoretical and experimental results analysing the test conditions are presented. Application of this method to biological in vivo (or in vitro) measurements of dielectric properties of bones and tissues, with selective partial-body microwave irradiation, is discussed.     

Radiation characteristics of a waveguide excited dielectric sphere backed by a metallic hemisphere

The experimental results of the radiation characteristics of waveguide excited dielectric spheres backed by metallic hemispheres are reported. The test antenna consists of a dielectric loaded hemispherical horn excited by a circular waveguide. The test data have shown that such a structure produces a radiation pattern with low sidelobe levels, increased on-axis gain, and reduced 3 dB beamwidth as compared to a waveguide excited dielectric sphere of same diameter and an optimum horn having an aperture of identical cross section area. Also, it presents a low VSWR over the waveguide band.     

Radiation characteristics of waveguide-excited dielectric spheres with matched sphere-air boundary

The results of experiments on the radiation characteristics of circular-waveguide-excited dielectric spheres with matched sphere-air boundaries are reported. The test data have shown that a waveguide-excited dielectric sphere, backed by a metallic hemisphere and with simulated quarter-wavelength matching at the dielectric?air boundary through surface perturbations, produces a directive pattern with a low side-lobe level, increased on-axis gain and reduced 3 dB beam-width, as compared with a simple wavegudie-excited dielectric sphere of the same diameter and an optimum horn with an aperture of identical cross-sectional area. Also, it presents a low voltage standing-wave ratio over the waveguide band.     

Microwave Interference with the Function of an Implanted Cardiac Pacemaker

The effect of external microwave radiation on an implanted cardiac pacemaker is studied. Based on a clinical case history [1] indicating an effective blocking in a patient of the implanted pacing activity due to microwave radiation, the process by which microwave energy may cause this observed effect is analyzed. The problem is formulated in terms of thermoelastic theory in which the absorbed microwave energy of the biomedium containing the implanted pacemaker represents a volume of heat source and a resulting thermoelastic motion sets up acoustic waves; these in turn, cause microphonic oscillations in the pacemaker which correspond to the noisy high-frequency artifact recorded on the ECG tracings [11.     

Radiation characteristics of a dielectric sphere-loaded corrugated pipe

The fields radiated by a feed structure consisting of a dielectric sphere placed in front of, but displaced from, the open end of a corrugated pipe with quarter-wave teeth, carrying the HE11mode, are derived. It is shown that this feed system has near-circular far-field characteristics with increased on-axis gain. The feed also has a reduced input VSWR due to the aperture-sphere separation. Theoretical expressions are derived for the radiated far-field components, by treating the off-set sphere as a microwave lens. Experimental results obtained from a test feed confirm the theoretical calculations made.