Which radiation between infrared and microwave is more penetrating?

[Cosma]

For a few weeks I have been undergoing transcranial photobiomodulation (tPBM) sessions using a helmet, and I discovered that it uses near-infrared radiation, and I was very surprised, because the theory should state that instead it is the microwaves that are more penetrating into the skull, so why do they use infrared? And which of the two, infrared and microwave, is more penetrating?

 

[berkeman]

Welcome to PF.

Instead of just "penetration", it's more important that whatever is penetrating interacts with the brain tissue in a desirable way to provide the therapeutic benefit. See this article for example:

https://pmc.ncbi.nlm.nih.gov/articles/PMC10840571/

Transcranial photobiomodulation (tPBM), a non-invasive and non-thermal brain stimulation therapy, was proposed over 50 years ago. Numerous related devices are also available in the market. tPBM was known as low-level laser (light) therapy at the early stage, but more and more researchers prefer tPBM in recent years because it is more indicative of its scientific principle.15

tPBM refers to applying low irradiance (0.01 to 10  W/cm2) red to near-infrared (NIR) (600 to 1300 nm) light16,17 through the skull directly to brain tissue to achieve neuroprotection, behavioral improvement, and so on. One of the most recognized molecular mechanisms of tPBM is that cytochrome c oxidase (CCO) may dissociate inhibitory nitric oxide (NO) after absorbing photons, thereby enhancing mitochondrial activity and promoting ATP biosynthesis.18 Because brain disorders are closely related to mitochondrial activity, tPBM may have beneficial effects on various brain diseases.19

During the past two decades, a tremendous number of pre-clinical experiments with animals and clinical trials with humans have demonstrated beneficial effects. Clinical trials with humans include, in particular, the treatment of ischemic stroke,20–24 Alzheimer’s disease (AD),25–28 Parkinson’s disease (PD),29–34 traumatic brain injury (TBI),35–40 depression,41–44 aging,45–50 etc.

In these studies, the parameters of the light used are extremely sophisticated and deserve to be deliberated. For wavelength, researchers prefer using 808 nm-light [Figs. 1(a) and 1(b)], which has a strong absorption peak of CCO with an excellent penetration depth.142 Furthermore, there also exist extensive studies that have applied other wavelengths (e.g., 610, 1070, 1267 nm) of light for brain disease treatment for specific biological targets including but not limited to mitochondrial stimulation.51,74,75,143

 

[Baluncore]

... , so why do they use infrared?

IR can be accurately directed towards a particular target area. Rapid absorption of the IR energy, prevents escape of IR into other areas.

Microwaves have longer wavelengths, so would be more difficult to focus on a target. Microwaves also penetrate deeper into the body and the surrounding workspace, leading to EMI and thermal safety problems.

 

[Cosma]

Welcome to PF.

Instead of just "penetration", it's more important that whatever is penetrating interacts with the brain tissue in a desirable way to provide the therapeutic benefit. See this article for example:

https://pmc.ncbi.nlm.nih.gov/articles/PMC10840571/

ok thanks for the reply, I remember this article and in fact it specifies that certain wavelengths together with particular transmission parameters increase the depth. But could microwaves have the same depth, due to the lower frequency?

 

[Cosma]

IR can be accurately directed towards a particular target area. Rapid absorption of the IR energy, prevents escape of IR into other areas.

Microwaves have longer wavelengths, so would be more difficult to focus on a target. Microwaves also penetrate deeper into the body and the surrounding workspace, leading to EMI and thermal safety problems.

thanks for your answer, I ask you the same question I asked Mr. Berkerman, and therefore, is it true that microwaves are more penetrating than infrared in areas such as the skin or skull (bone) due to the longer wavelength? ?

 

[berkeman]

But could microwaves have the same depth

What therapeutic mechanism do you expect from these penetrating microwaves? What clinical trials have used microwaves?

BTW, have you done much reading yet on transcranial magnetic stimulation (TMS)?

 

[Baluncore]

... therefore, is it true that microwaves are more penetrating than infrared in areas such as the skin or skull (bone) due to the longer wavelength? ?

You are missing the point, good penetration of radiation, that comes out on the other side, is a liability. It is also a problem when the whole upper body, including the eyeballs, is heated by microwaves.

Yes, penetration is a function of wavelength, but not for the reasons you might expect. Because the tissue is a dielectric, not a good conductor, skin effect is not the factor that determines penetration.

The thickness of the skull is less than the wavelength of microwaves, but it is more than the wavelength of IR. For that reason, IR will be scattered and absorbed by the fine structure of the head, while microwaves will pass through without being scattered by the fine structure.

 

[Cosma]

What therapeutic mechanism do you expect from these penetrating microwaves? What clinical trials have used microwaves?

BTW, have you done much reading yet on transcranial magnetic stimulation (TMS)?

I had written the question out of main curiosity, given that it is an established fact that lower frequencies are more penetrating, that's all. no I don't know any other type of microwave stimulation, it was just curiosity

 

[Cosma]

You are missing the point, good penetration of radiation, that comes out on the other side, is a liability. It is also a problem when the whole upper body, including the eyeballs, is heated by microwaves.

Yes, penetration is a function of wavelength, but not for the reasons you might expect. Because the tissue is a dielectric, not a good conductor, skin effect is not the factor that determines penetration.

The thickness of the skull is less than the wavelength of microwaves, but it is more than the wavelength of IR. For that reason, IR will be scattered and absorbed by the fine structure of the head, while microwaves will pass through without being scattered by the fine structure.

ok yes I understand, so the radiance levels are also kept low to avoid excessive heating in the eyes for example, ok thanks for the clarification

 

[Cosma]

@berkeman @Baluncore I would like to ask you a little question, perhaps a little too banal. but the neurons (which usually respond to different frequencies) but if excited by an electrical signal lasting a few picoseconds or femtoseconds, what happens, is it polarized and therefore excited, or is the signal too short and is not perceived?

 

[Baluncore]

... if excited by an electrical signal lasting a few picoseconds or femtoseconds, what happens, ...

Neurons are chemistry. The delivery of a single short pulse of energy, that is not repeated, will probably not be sensed by the nervous system, it will be lost in the thermal noise. However, that will depend on the total energy involved, how many photons, of what wavelength, and how those photons are converted into an electrical signal, which presumably would be by, the ionisation of some specific neurotransmitter chemical bond.

 

[Cosma]

Neurons are chemistry. The delivery of a single short pulse of energy, that is not repeated, will probably not be sensed by the nervous system, it will be lost in the thermal noise. However, that will depend on the total energy involved, how many photons, of what wavelength, and how those photons are converted into an electrical signal, which presumably would be by, the ionisation of some specific neurotransmitter chemical bond.

ok I understand thanks baluncore