Dear Abhishek,

being no expert on air purifying, I can only apply "common sense" to this method.

First of all, if the reported lab results are real and not based on some kind of artefact then it's a good accomplishment and should be pursued further, no matter whether we can explain it rigorously or not at present.

Second, the basic principle is certainly true: If radiation is reflected by particles then the conservation of momentum calls for an acceleration of the particles, roughly in the direction of propagation of the incident radiation.

Having said that, several questions come to mind:

- Today, we have a large amount of artificial radiation nearly everywhere on earth. Why should the superposition of yet another weak radiation field make any difference?

- Does the purifying effect depend mainly on unidirectional radiation? If so, it might work in an anechoic chamber in the laboratory but in real indoor environments there are reflections from walls, ceilings, and so on.

- The only hard facts about the device which are revealed on the web site are: The radiation is pulsed, and is located somewhere in the 2.2 to 3.5 GHz range. No diagrams of the radiation in time and/or frequency domain, no photos or drawings of the antenna or the driving circuit, only photos of the whole device as a "black" box with a "Do not open" warning attached to it. Why? Any potential competitor is free to buy a device and to re-engineer it. So, one is reminded of the little sealed boxes which were offered in the eighties and early nineties and were allegedly able to protect the computer user from the radiation of her/his (cathode ray tube) monitor; the boxes contained just a piece of metal or in the deluxe version a semiprecious stone, and were certainly harmless and effectless.

Apart from the question of the working mechanism, another issue is the use of the frequeny band mentioned above. From 2.4 to 2.5 GHz, there is a narrow ISM (industrial, scientific, medical) band in which arbitrary short range radiation is tolerated. If these air purifiers did have an excellent effect and really had to use the 2.2 to 3.5 GHz band, it would take a long time and countless international meetings to relocate all communication services from this band to other frequencies, and thus to create a broad ISM band. Until this is accomplished, I would expect that in most countries users of these air purifiers would run into serious legal trouble.

Dear Joerg Fricke ,

Thanks for your time and effort to answer my question.

Do you have anything to cite your statement -

" If radiation is reflected by particles then the conservation of momentum calls for an acceleration of the particles, roughly in the direction of propagation of the incident radiation. "

Because how can we prove that particulate matter, typically of size

Dear Abhisk,

welcome,

Adding to what has been said by the respected colleague Joerg, the microwave frequency radiation can cause rotation of the molecules and vibration. I think the rotation here is the effective motion. The molecules in particle in the atmosphere do not need to be accelerated they have already their thermal velocity because of their thermal energy which is appreciable. They move in random way and they only need to be directed to the deposition surface.

For the effect of the microwave frequencies on the molecules please see the link: http://hyperphysics.phy-astr.gsu.edu/hbase/mod3.html

So, the radiation directs the molecules to the deposition surface.

This my interpretation to the observed effect.

Dear Abhishek Bagathi ,

the statement itself is certainly true because of the initial "if". ;-)

According to the following paper, the main radius of water droplets in clouds and fog is in the range of 3 to 6 microns (p. 20 of the pdf document), and the attenuation at a wavelength of 10 cm is quite weak but not zero (p. 23). It certainly depends on the material of the particles; probably materials other than water provide a still weaker attenuation.

http://www.dtic.mil/dtic/tr/fulltext/u2/a011642.pdf

So, pondering this information, it seems that with a radiation source in private accomodations ("Pure Skies 3000", assuming radius of the home < 25 m and a density of particles similar to the density of water drops in fog, neglecting reflection by walls etc.) less than 10-6 of the radiation interacts with any particles floating in the air inside the rooms.

On the whole, not a promising approach; if the advertized results are not fakes, it would be interesting to detect the real mechanism.

The momentum of the radiation p= h/lambda where h is the Plank constant and lambda is the wavelength. As the wavelength decreases the momentum of the photon increases and becomes effective in moving the particles with which is colliding. However i think that energy contained in the waves are much more effective in such frequencies than their momentum.

Best wishes

May I utter my doubts?

• 20 resp. 30 W radiated power (setting the power intake given for the output) is little compared to the omnipresent radiation in these frequency bands.
• Especially the 2.45 Mhz is known to excite H2O molecules (which might contribute to the admitted reduction in "efficacy" at higher humidity levels). Considering the other polluants: I have no idea where their respective resonance frequencies might be.
• An omnidirectional antenna would 'push' the particles away from the antenna. Installing multiple units (as advertised) would result in this effect being reduced/nullified due to interference.
• A reduction in CO2 is not reasonable considering the stability of this molecule. Might well be it cannot be detected by NDIR sensors when absorbed by water/humidity.

Summarizing: I'm not convinced that these devices can achieve what is claimed. Although I have too little information to speculate about systematic measurement errors.

Dear Joerg Fricke ,

Thanks for your two cents! But I'm actually looking for the references for radiowaves accelerating particulate matter. I think I can establish that smaller particles scatter EM waves but the vice versa is what I want to prove!

Please let me know what you think!

Thanking you,

Abhishek.

Dear Abdelhalim abdelnaby Zekry ,

Thanks for the answer. Even I got the similar vibes regarding the observed phenomena but as I said earlier, I'm looking for something regarding the question in literature but I couldn't find much. Any references regarding the transfer of energy form waves to particles to prove the observed effect would be really helpful!

thanks,

Abhishek

Abhishek

I think you have missed Joerg's point. IF small particles scatter EM waves THEN EM waves will deflect small particles. This is the result of conservation of momentum, and of EM waves carrying momentum. Each small particle that scatters EM waves will behave like a small solar sail, and be accelerated when the EM wave is scattered. It won't be much. You can calculate how much using the power density in the wave to get a momentum per square metre and then working out how many particles per cubic metre might scatter. If you assume scatter back in the opposite direction this give the maximum impulse for each scattering. I think you will find it is much less than the thermal energy of the molecules, and so is unlikely to have any effect.

Dear Abhishek (and all other contributors to this discussion),

For particles that do not possess any net electrical charge (pure dielectrics), the only way to obtain net translational motion when immersed in an electromagnetic field is via the dielectrophoretic force. There are plenty of references for this effect - please feel free to Google. For the dielectrophoretic force to manifest itself, the applied electric field must be spatially non-uniform so that opposing ends of the dipole within the particle experience slightly different forces. The magnitude of the dielectrophoretic force is proportional to the gradient of the squared modulus of the electric field and to the dielectric contrast between the particle and its surrounding medium. For particles in air, the contrast in dielectric constant is a positive number, so the direction in which the dielectrophoretic force is experienced will be governed by the sign of the gradient term. In this case, the force will be directed towards the region of highest field intensity - which will be towards the antenna. For a time-varying applied field, there will still be a net force towards the antenna since we are dealing with the gradient of the squared modulus of the field. It's possible that the inventors of the technology in question are using pulsed EM radiation as a means to raise the magnitude of the electric field (during the pulse) without consuming large amounts of power that would otherwise be consumed if continuous sinusoidal excitation was used.

Whether the particles are charged or not, if the applied field is oscillating sinusoidally during the pulse duration, there will only be a net translational motion of the particle's centre of mass if the field is non-uniform. The oscillating electric dipole that arises on application of the sinusoidal applied field simply creates the observed scattered field via re-radiation (accelerated charges radiate EM waves) but this alone would not create motion of the particle towards or away from anything. When the field is oscillating in time, a spatially non-uniform field distribution is required to get net particle translation.

Dear Ray Simpkin ,

thanks for your insight. As we can see that the product pure skies is generating Radio waves which means that the particles are exposed to uniform electric fields which means there must be no acceleration in particles affected by the radiation.

Maybe we need to look at the radiation here as travelling electric fields yet uniform and if we do that, how can we prove that the particles are accelerated?

Dear Malcolm White ,

I see that the simplest explanation for the phenomena is the conservation of momentum but i'm intrigued by the point that how do we prove it?

If we go by conservation of momentum, we'll miss the mass of photons to proceed further. Otherwise we can look at the conservation of Energy, well it's tough to calculate the initial energy of particulate matter don't you think?

Is there a way that you could think of to prove the phenomena?

Abhishek

Photons do not have mass at all but they have momentum, so you can proceed further.

As Abdelhalim wrote "The momentum of the radiation p= h/lambda where h is the Plank constant and lambda is the wavelength." This is the momentum of each photon. The energy of each photon is h*lambda. This is all you need to relate the mean power density to the mean momentum tranfer.

See https://courses.lumenlearning.com/physics/chapter/29-4-photon-momentum/

I think my two comments are not well examined. In my first comment i pointed out the rotation of the already randomly moving molecules by the microwave such that they will be directed to the deposition surface and this is driven by the energy of the waves rather their momentum because of the momentum of such waves are very very small to drive the particles.

I wrote in my second note that: The momentum of the radiation p= h/lambda where h is the Plank constant and lambda is the wavelength. As the wavelength decreases the momentum of the photon increases and becomes effective in moving the particles with which is colliding. However i think that energy contained in the waves are much more effective in such frequencies than their momentum.

Only very short waves can have appreciable momentum.

Best wishes

Dear all, here comes just a raw idea:

a) According to the web site, the link in your first answer points to, Abdelhalim, (and according to your further contributions) it is most likely that part of the field energy transferred to the molecules is stored as rotation.

b) According to your point of view, Ray, the basic mechanism could be some kind of dielectrophoresis. This can take place even in an AC field provided the molecules can change their dipole orientation fast enough.

c) According to the manufacturer, the antenna is some kind of coil (unfortunately, we know neither form nor size).

As a starting point, let us assume a simple circular coil, and neglect for the moment any effects caused by phase differences (traveling waves) of the current in the coil. Then the electric field lines form coaxial closed loops. I understand that in dielectrophoresis the molecules move tangentially to the E field, along with or against the field gradient. But in the case at hand, the field gradient is directed perpendicular to the E field.

If we would further assume that the magnetic spin of the rotating molecular dipoles can change its direction fast enough to follow the direction of the B field of the antenna, we might arrive at the conclusion that this is a case of magnetophoresis, driving the molecules toward the antenna.

(To remain at peace with the conservation of momentum, we have to assume that the fields of the molecules excert an attracting force on the antenna.)

If possible at all, I think that this effect would take place mainly in the near field of the antenna, while the molecules further away approach the antenna just by diffusion, due to the developing gradient of concentration.

I share U Dreher's scepticism. The main reason for doing momentum and energy calculations is to see (and learn) just how insignificant the contribution from this source is, and put this into consideration when assessing how likely this is to be a real effect.

Dear All,

thanks for the responses. Here's another idea for which I need some validation. checkout this paper : https://www.kwasan.kyoto-u.ac.jp/~isobe/tmp/dust/1-s2.0-0019103582900410-main.pdf

where they discuss dust particle dynamics under solar radiation pressure .As per @Malcolm White's answer, conservation of energy is the key principle there. Can we use this analogy to prove or establish something in this situation?

Please throw your two cents!

It is good to be cautious about what can't happen. It is difficult to predict all the details - sometimes the maths follows observations. Your paper on dust in space reminds me that I seem to remember reading (before they were found) that the establishment were certain that there couldn't be ripples in Saturn's rings. Now they have fun explaining them!

Several other contributors also suggested you looked at the energy.

Dear Ray Simpkin ,

Are you suggesting that the re-radiation due to the particles oscillations because of microwaves is creating a non-uniform field and causing the dielectrophoretic forces? because microwaves are just a uniform travelling electric and magnetic fields and can't create dielectrophoretic forces. This is how I understood and please tell me if I'm wrong.

Sincerely,

Abhishek.

Dear All,

check out this interesting paper from the Journal of PIER :

http://www.jpier.org/PIERB/pierb76/07.17040602.pdf

These guys used Generalized Multi-particle Mie Theory to calculate scattering parameters of small particles and accurately obtained the direction of motion caused by exerted Lorentz force on particles in terms of discrete dipole approximation. Basically, A bulk model based on Effective medium theory is designed to analyze the scattering parameters of particles much smaller than incident wavelength.

I'm currently planning to use this approach for my purpose and extend the same to Rayleigh scattering and see what's going on! My bet is on Radiation Pressure has something to do with the movement of dust particles and I'm not sure about the dielectrophoretic forces as I couldn't find any promising references.

Thanks for all the help and for pointing me towards the right direction. I'll keep you updated and let me know what you guys think of this approach as well!

Peace,

Abhishek.

Hi Abhishek,

Regarding non-uniform electric fields: the radiation from the illuminating antenna will not be uniform in its spatial distribution since its a diverging wave probably close to a spherical wave in form. For a far-field radiation pattern, the magnitude of the radiated electric field (not the power) decays as 1/r which constitutes a non-uniform field. The effect is small as far the dielectrophoretic force on a small dipole is concerned, but it's not zero. The re-radiation due to dipole oscillations that I referred to is the physical mechanism by which all EM scattering occurs regardless of the nature of the field excitation. The original work on the dielectrophoretic force was pioneered by Herbert Pohl back in the 1950's. I've attached his 1957 paper. There's plenty of stuff in the literature that cites his work.

Perhaps you might be interested to look at

https://docplayer.net/41362613-Dust-particle-removal-by-electrostatic-and-dielectrophoretic-forces-with-applications-to-nasa-exploration-missions.html

Nikolay Pavlov thanks for the interest. but from the given paper, it is evident that dielectrophoretic forces affect the dust particles movement. My question was can the dielectrophoretic forces or some sort force be generated from the waves in microwave/radio frequency that can move the dust particles. I hope I'm clear.

Dielecrophoretic forces are proportional to gradient of averaged square of the electric field. It is usually very weak force still.

So I guess in rather intense and sharply changing electric field you may see some force, perhaps you may consider standing waves produced by magnetrons like in microwave oven.

Nikolay Pavlov Thanks for the insight. I'll try to do the calculations and let you know.