Microwave-induced Temperature Research Articles

Microwave-induced temperature, corticosterone, and thyrotropin interrelationships.

To delineate acute endocrine responses to microwave energy absorption, 142 unanesthetized male Long-Evans rats acclimated to experimental procedures were subjected to far-field 2.45-GHz microwave exposure for 1 h at 1-70 mW/cm/sup 2/, 4 h at 0.1-40 mw/cm/sup 2/, or sham exposure. Controls were sham exposed in a sham-exposure chamber beginning at 030 h and killed at 1230, 1330, 1530, and 1930 h. Microwave-exposed rats were equilibrated in an anechoic chamber for 3 h prior to the start of exposure. Microwave exposure was initiated at 1130 h. Exposed rats were killed at 1230 and 1530 h. Colonic temperature (T/sub col/) was measured and serum obtained for thyrotropin (TSH) and corticosterone (CS) determination immediately after exposure. Inverse relations of TSH to power density (PD) or R/sub col/ were noted in the microwave-exposed rats while CS increased with PD or T/sub col/. Similar relations of TSH and CS to T/sub col/ were also noted among ''shams.'' The increase of T/sub col/ by microwave exposure was dependent on PD but independent of an exposure duration greater than 1 h. The serum CS level increasd with PD but the effect decreased with duration of exposure. ''Low intensity'' 4-h microwave exposure inhibited normal circadian elevation ofmore » adrenocortical function in rats if the exposure was coincident with diurnal CS elevation.Inhibition of TSH became more pronounced with duration of exposure. Differences in the endocrine-body temperature relationships between sham- and microwave-exposed rats were also noted. It was concluded that endocrine control was dissociated from body temperature in the microwave-exposed rats. The endocrine control in microwave-exposed rats is different from shams.« less

Microwave-induced hazardous nonlinear thermoelastic vibrations of the ocular lens in the human eye

When a high intensity microwave energy irradiates the human eye, lens opacification and cataractogenic effects often result, due to the absorption of the incident energy and consequent conversion into heat. Besides these effects, it is presently indicated that the temperature rise due to the absorbed energy may also induce thermoelastic stresses in the ocular media and causes nonlinear elastic vibrations of the lens. The resulting mechanical effect arising from compression and tension stress would evoke hazardous physiochemical processes through micromassaging of the tissue surfaces. A theoretical evaluation of the microwave-induced temperature distribution in the eye and consequent thermoelastic stress-strain and vibration parameters, is presented. The resulting hazardous effects are quantified in terms of damage function and thermal shock resistance coefficient.

Contractile deactivation by rapid, microwave-induced temperature jumps

Contractile deactivation by rapid, microwave-induced temperature jumps

Effect of surface cooling and blood flow on the microwave heating of tissue.

The one-dimensional heat transport equation has been solved for a semi-infinite plane of tissue irradiated by microwave radiation, to determine the effects of thermal convection due to blood flow and transfer of heat from the tissue surface into space on the steady-state temperature distribution in the tissue. For microwaves in the 1 to 10-GHz range, the effective heating depth is 1 to 2 cm, and can be much deeper than the penetration depth of the radiation in the tissue. The position of the maximum tissue temperature can be varied by a centimeter or so by cooling the surface. The results suggest that microwave irradiation of simulated biomaterials is not likely to provide accurate estimates of the actual microwave-induced temperature distribution in tissue.