"A Pocket Sized Monitor of Dangerous Microwave Power Levels"
A miniature battery-operated microwave power monitor is described which operates across the threshold range of biologically dangerous power levels with approximately frequency-independent characteristics up to about 100GHz. CMOS circuitry causes an alarm signal to occur, or enables one to integrate the total microwave energy received over a given period on the basis of a thermal change of resistance in a thin Ge film due to microwave absorption.
Biological Effects by Microwaves
Domestic and industrial applications of microwaves are everyday extended implying protection conditions and safety standards which require a better knowledge of biological effects associated with microwave radiations. Interactions of microwaves with living systems are reviewed on the basis of levels of organization which may be molecular, unicellular and pluricellular. Among a large number of publications, those giving correlated experimental observations at low or medium power density or associated to frequency dependent effects are particularly examined. Results are still insufficient for establishing permissible exposure levels lower than that derived from thermal biological effects. These thermal effects are now being studied as the induction of hyperthermia in living tissues, for instance, as an adjunct to the cancer treatment.
Absorption of Microwaves by Microorganisms
RECENTLY S. J. W. and Dodds reported that 136 GHz microwaves interfere with the growth of Escherichia coli cells1. Here we report further investigations of the absorption of 65 to 75 GHz microwaves by cells of E. coli BR as well as isolated protein, RNA and DNA, and its effect on some metabolic processes. Our equipment has been described1,2. Cells were grown for 24 h at 37° C in nutrient broth (NB) and either (a) washed twice in 0.85 per cent NaCl and deposited as a pellet by centrifugation or (b) resuspended after washing to a cell concentration of 1 × 106 cells/ml. in 0.5 per cent glucose + 0.5 per cent casamino-acids + 50 µg/ml. thymine in 0.1 M phosphate buffer, pH 6.9 (GCT). To examine the effect of microwaves on cell growth, 0.5 ml. aliquots of cells suspended in GCT were placed in vials 1.5 cm in diameter. Some vials were put on top of microwave horns and others incubated at the same temperature (25° C) out of the radiation field. At various times the vials were removed and the number of cells/ml. determined by dilution and plating on nutrient agar. The effect of microwave absorption on metabolic processes was investigated by resuspending the washed cells to a concentration of 1 × 108 cells/ml. in 1.0 per cent glucose in 0.1 M phosphate buffer, pH 6.9. Aliquots of 0.2 ml. of this suspension were placed in the vials and after positioning on the microwave apparatus 0.3 ml. of a solution was added, which contained 0.8 µCi/ml. of one of the following: thymine-2-14C, uracil-2-14C or algal 14C protein hydrolysateplus two of the following: unlabelled thymine, 50 µg/ml.; uracil, 100 µg/ml.; or casamino-acids, 500 µg/ml. After various times the cells from each vial were deposited onto a Millipore filter and washed with 100 ml. of 1 N HCl; the filter was dried and radioactivity counted. The microwave absorption spectra of the cells, H2O, protein, RNA and DNA were obtained by making films of the material on a thin mica window. The films were dried at 80 per cent relative humidity and covered with a second thin piece of mica. The difference between the microwave absorption of a blank and the film gave the absorption spectrum of the film of cells or biological material.