The interaction of the different processes of life and electromagnetic fields has always intrigued scientists and researchers since when it was found in the early 18th century .
Since then the scientists have worked with different frequency ranges of which the most important ones are the microwave frequency. One definition given by Nanda  is that microwaves are the radiation waves in the electromagnetic spectrum that have a frequency between 300 MHz to 300 GHz or in other words wavelength of 1 mm to 1 m. An important property of this radiation is that it is nonionizing and because of its nature it can be easily absorbed at the molecular level and produces obvious changes in its vibration energy .
Significance of Study
Biological transformation because of exposure to low strength microwave or materials showing resonant response to microwave frequencies are of special interest to areas of uses of radiations and in better understanding of our general biology . Due to the intriguing outcome of the growth of yeast due to exposure to low-intensity microwave radiations as founded by Devyatkov,  and theoretical reasons by Frohlich in 1980 , which predicted the causes of such biological response with respect to frequencies and intensity.
Biological Significance of Microwaves
Grundler  studied the growth of yeast photometrically at about 41’8 GHz frequencies. At certain frequencies, the growth rate remained constant but at other frequencies, a variation in growth rate was recorded, an increase of 12 percent growth rate in the normalized growth rate was recorded and at other a reduction of 29 percent. A unique discovery was the finding of multiple and at short interval resonant frequencies between 41.64 GHz and 41.79 GHz, each of them having a bandwidth of about 10Mhz. But before we could come to establish any conclusions or findings it was necessary to investigate these results in better conditions . The extremely frequency-dependent response of yeast growth rate with microwave radiations makes more sense if we link it with the cell cycle of yeast. The frequency of the radiation which is the same as the frequency of the cell cycle results in its coherent excitation. The kind of outcome due to resonance on the growth rate obtained is very similar to the response we expect from the stimulus changes periodically with time on the amplitude of a periodic oscillator.
It was believed previously that not all frequency waveforms are significant in biology but the studies by researchers like Frey and Browers showed that because of their biological significance the use of microwaves needs to be controlled. The microwaves have thermal effects that can impact when the living beings have exposure for a long term them . Many organisms that are living have dielectric properties and have been tested do not observe clear resonance phenomenon.
One of the experiments was conducted by Grundler who showed that the yeast cells show a resonant growth when they are radiated with micro and millimeter waves. Their study was based on the findings of Devyatkov to some extent who suggested that 42 GHz should be used as in their experiment it showed up to 4% exponential rate which corresponded to the density of flux. A fine structure of frequency was there of 8MHz. They used the method of photometry which has some inherent disadvantages as well and gave the results only in the stirred suspension to 106 millimeter radiation . Grundler and his colleagues needed to develop a method to study single-cell kinetics and growth due to microwave exposure. This meant direct irradiation and as compared to the controls because of the radiation double peaks as well as asymmetries were induced in the normal cell cycles that the yeasts cells usually have. The changes along with the time distribution in the division of cell cycles showed that there might be sub groups present of the cells. The irradiation displaced the one peak value while the other one was closer to the control value in the double peaked distributions. The observed effect was that microwaves stabilized to about ±1MHz (of 42 GHz being used) produce sub cultures or groups of cells even in an area of small single layer of about 0.2mm2. This showed the resonance dependence similar to the ones that were there in the 8MHz resonance in the photometry method. When the frequency of 42GHz was double to be 84GHz the radiation effects were again significant and appeared in the second cycle of cell division. The temperature in this experiment was set to be lower at about 25 degree centigrade which had an elongated effect on the cell cycle and extended the time to 5 hours. Thus the studies overall showed that influence of the microwave irradiation is restricted o the G1 phase of the cell cycle in yeast .
Initially the study was conducted using photometric measurement but the method has some limitations whereas the experiment requires a measurement of frequencies very sharp and precise as the stabilization and measurement of frequency requires for it. Also it was important to lock the phase, this was done in the study using backward-wave tube. The spectrum as a result was obtained having a width that ranged to 1 MHz at frequency 42 GHz. The next step was to couple it with microwave which was done through a Teflon structure that had a surface area of 10 cm2. Since the photometry method was being used the cell suspension also made use of a Laser interferometric thermometry. This was for accurate measurement of the change in temperature and could show temperature even in the suspension of 40 mW of power and 0.02°C temperature. In the experiment varying amounts of power were absorbed in the suspension of about 6 mW to 34 mW. The two options to measure this power use was first determining the change in temperature which ranged to 0 5°C caused by the microwave irradiation which has a heating effect. The second measure for finding out the power change was to find out the difference in the wave powers that were running backward and forward. The expected effect of the temperature on the growth rate in the absence of radiation has been found to be ranging between 31 to 34TC. There was expected a relative increase or change of about 2.7 percent. To measure the increasing concentration of the cell because of the growth effect Light scattering method was employed that made use of 2 double-beam photometers. Later the photometer was also used for the control without having a microwave coupling. The method was repeated and used for about 82 tests and was carefully fed into the computer system for accurate graphing and calculations.
Powerful frequency dependence is demonstrated in this fine-tuning study again. In addition, a line width of approximately 10 MHz exhibits a behavior similar to resonance . It may be noted that no correlation is found between the absorbed microwave power and the observed effects, between the range of 6 mW to 34 mW. And the negative effects are specially measured at high intensities and positive intensities are measured at low intensities. But the results that were calculated in this study could not be exactly compared with one another due to the absolute frequency uncertainty of + 20 MHz. However, in general terms, the aforementioned effects may be reproduced with the usage of a setup that has been improved in various aspects. Within the frequency range of 41,770 MHz to 41,795 MHz, by far the most remarkable effects have been observed . And then a further reassurance set of thirty runs was performed in order to testify and confirm the reproductively of the effects and to define the framework of resonance. The results of this experimentation were demonstrated in the study. Despite the relative broad scatter at the minima the presence of a resonating structure of nearly 10 MHz is reconfirmed. The broad scatter indicates the impact of a biological or physical parameter , which was unknown until now. While summarizing, it was reaffirmed that changes occur in the growth rate of yeast due to the low intensity of microwave irradiation. Exhibiting a strong resonant behavior, these effects have nothing to do with the microwave power used and are dependent upon the frequency . These effects are hard to be explained in simple thermal response terms. In order to carry on this investigation, the further dependent biological parameters and the irradiation antenna’s geometry should both be altered so as to get a stronger signal of the effect of the biological or physical parameters along with a clearer understanding of the biological reactions produced as a result.
The studies on the effect of microwave irradiation show that the influence is because of their heating effect. On the other hand, some studies have revealed that their effect can also be non-thermal. This was also one of the aspects treated in the experiment of Grundler  in the form of energy that is responsible for even changes in the cell cycle and internal molecular level changes. The research can have a significant impact on microwave therapy which is for renewing and regeneration of cells . The implications also include the alleviation of the impact that X-rays might have on the growth of the cells. This is possible at both the organism cellular level . After the experiments on the yeast, the study in the field of biotechnology has revealed that the phenomenon can be used as microwaves have effect at all biological levels in animals, microorganisms and even in human beings. Not just this, even in the biogenetics field the mechanism can be used to produce certain genetic changes .
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