In the previous section, instead of actually measuring using scientific equipment the “boiling wave” that arrives to the ear cochlea and makes us hear microwaves as clicks (something that would require using a hydrophone inside the brain tissue) we presented a model that calculates this.
We assumed that it is enough to calculate the wave generated in the head and not in the rest of the body. Is this valid? Another group of scientists say that this would suffice if you have a source of electromagnetic radiation close to your head, like a mobile. If this is not the case, but instead radiation comes from a distance, then you need to consider the whole body.
We will present the following study:
Yitzhak NM, Ruppin R, Hareuveny R.
Bioelectromagnetics. 2014 Oct;35(7):491-6. doi: 10.1002/bem.21869. Epub 2014 Aug 6.
So as mentioned previously, first you have to calculate how much of the energy carried by the electromagnetic wave will be absorbed by the human body. You will calculate the Specific Absorption Rate (SAR).
Then you will find the temperature rise induced by the energy absorption. Afterwards, you will calculate how much pressure is induced in the tissue by this temperature rise. In order to do that you need to know the elastic properties of the tissues (such as the coefficient of linear expansion and other elastic parameters).
Engineers could measure chunks of tissue e.g. epithelial tissue/skin and determine those values. In the absence of measurements, approximate values for soft and hard tissues could be used based on different materials. For instance as mentioned “For the Lamé elastic parameters of the soft tissues, the values λ=2.1 GPa and μ=22.3 kPa will be employed [Margulies and Meaney, 1998]. These are pressure values; temperature rise will cause pressure in the tissue.
But how do you put all the tissues together or how do you know where is where in the body order to model it?
Similarly to what was mentioned previously, you go the REMCOM site and you get a whole body mesh, which the company has created using MRI data from the Hershey Medical Center of the Penn State University.
Here is again the relevant link:
One of the REMCOM models used by the scientists is that of “male body, with height of 1.875 m, resolution of 5*5*5mm3 and 39 different tissue types”. As mentioned in the study, “the meshes of these models were converted directly from the data generated by the Visible Human Project sponsored by the U.S. National Library of Medicine.”
Following this approach, the scientists used an power density of 1mW/cm2 for modelling the incidence of electromagnetic radiation of different frequencies (note: they also took into account incidence from the front side or the backside, and polarization either vertical or horizontal).
As they increased the frequency they noted that the human body absorbed differently in different frequencies. In particular, it must be mentioned that for vertical polarization only, there was one peak of absorption at 60MHz and for both there was a peak at 200MHz and 750MHz. The frequencies where maximal absorption of electromagnetic radiation by the body occurs are termed resonance frequencies. As the authors suggest, modelling of the head only without taking into account how much the body absorbs cannot lead to accurate results.
The calculated using the model the acoustic pressure in the cochlea after determination of the generated pressures and thermoelastic waves as shown in the following figure. Their conditions are: 915MHz pulse of 70μs width.
2/2 FranceInfo105.5MHz,SFR 900MHz |70µs pulse of 915 MHz on a human?Acoustic pressure 500-1000µPa #MicrowaveAuditory
Note that in the case of the microwave auditory effect we have a pressure wave and we therefore need to be searching about mechanosensitive targets which are molecules responding to stress by conformational change e.g. actin, adhesion molecules, extracellular matrix proteins. Upon conformational change or unfolding they can expose domains that can be bound by other proteins and initiate signaling cascades or they can change their binding affinities or they can become stable or unstable and influence related pathways.
The synapse is very rich for instance in actin and other mechanosensitive molecules. It has also been mentioned that tension can increase vesicle density at the synapse.
Other mechanisms including the soliton model of action potentials are mentioned at this page https://www.tylerlab.com/neuromechanobiology/ at the last figure.