Anti-Wi-Fi paint

[tortoise]

Anti-Wi-Fi paint

The paint isn't just of interest to those concerned about wireless leaking out of the building. Movie theaters have long been interested in finding a legal way to keep cell phones silent during screenings. Electronic jammers that actively block wireless signals are illegal, but passive materials that prevent wireless signals from getting through are not. Since the wireless-blocking paint can also block the lower-frequency signals that cell phones use, addled mobile junkies would have no outlet for reaching the outside world.

[metronid]

The pharmacy that I work in has a metal shield in the ceiling as an anti theft measure.
It also seems to kill most cell phones.

Stealth bombers have a radar type paint or coating.
Maybe the movie theatres should contact the pentagon.

What if someone in the theatre needs to call 911.

The problem is rude people with cell phones.
Perhaps there should be fines listed and enforced for companies that state no cell phone useage allowed.
It would be a great revenue provider if added to red light cameras and it can be stated the purpose is not revenue but public safety.

[Bustin]

What if someone in the theatre needs to call 911.

I personally think they should step out into the lobby !

But seriously, in our sue-crazy society , the liability involved in blocking cell phone signals will be a big hurtle for those who would create cell-free zones. And yes, a little common courtesy would be the easiest way to curb the annoying situations with cell phones in theatres and restaurants .... but people are short on that , these days.

[metronid]

Ignorant?
I have a line of people at the counter for prescriptions.
I go from behind the counter and try to help with customers either dropping off or picking up medicine for the flu or
whatever ailment that they are experiencing.

The first words out of my mouth is how may I hep you.
Cell phone stuck to a customers ear and all I receive is a look like I am interupting their life.
The response is can you not see I am talking.
I reply sorry and the customer continuing talkingans staring .

The customer next in line has a young baby and the child is sick and crying.
I ask how my I help you and she replies politely and pleasantly .

The cell phone customer now says they were first.
I reply sorry but it is our policy to wait on people in pain and young children.

The cell phone customer than starts screaming that he has been treated poorly.
I said he but it could have been a she.
I take the customer request and it is for a refill on a drug that has no refill andis from an outof state doctor and a mail order pharmacy that is three years ol
I do not know what constitutes an emergency but an acne medication. 3
years old is debatable.

[metronid]

Sorry iPhone went dead
In any case I rush the acne medication through.
I call the other pharmacy and finally get through after ten minutes or so.
I then call the doctor who refuses to ok the drug because the patient has not been senn for over 2 years.
The cell phone patient is notified and shows so with a nasty comment.


About 3 days later I get a customer complaint through our central office.
It says we ignored a customer in line and denied giving a critical medicine that was needed.
It goes on to say we waited on a patient ahead of him that hadno emergency
while his an emergency.

Customer service rewards the complaint with a 25 dollar gift card and I have to call and apologize.

The cell phone customer is called and informs me that he is not mad but likes to have his way when making a purchase.I agree and apologize as is required.

It is not the cell phone that is rude.
It is just a tool for rude people.
The above situation did not occur but similar and more extreme
situations have.
Hippa prevents me from giving any real data.


s

[happyphysicsman]

They have actually been able to block any sort of low-energy electro-magnetic radiation (cell phone, wifi, etc) for years. It's called a Faraday cage (named after Faraday's law which is the underlying physics principle that predicts this behavior). All it is is a wire mesh that lays within the exterior walls of the building you wish to block the signal within.

At one point I was able to explain the physics behind it, but that is not my field of expertise so I won't attempt. This is also the reason why metronid loses signal in his pharmacy: At thick metal plate is really just a VERY fine wire mesh.

They actually have encased most upscale concert halls and performing venues within Faraday cages to block out the undesirable low-energy, electro-magnetic radiation signals that we use frequently to send data.

Bustin is right though about this sue-happy America. Only places that can get away with are able to do it. It would be much more permissible in court to have no cell service in a place like Carnegie Hall, then just your local movie theater. I don't believe a Faraday Cage in a movie theater would stand in court.

Just my two cents on the topic from a physicist perspective.

[metronid]

I can remember old TV Sets and other electronic equipment that used a metal case for shielding .
It shielded against spurious emissions and also from stray signals entering into the rf sections.
Grounding of the cage also improves the signal blockage.

[happyphysicsman]

I can remember old TV Sets and other electronic equipment that used a metal case for shielding .
It shielded against spurious emissions and also from stray signals entering into the rf sections.
Grounding of the cage also improves the signal blockage.

Perfect example of a Faraday cage at work

HPM

[happyphysicsman]

In fact in some newer home, the manufacturer is giving the home owners the option of building the home with environmentally-friendly metal studs in the wall instead of wood. When the home is finished, the owner complains about the loss of cell phone signal within the home and blames the lack of wifi strength throughout the house on the "cheap" wireless router they are using. In all actuality, the metal studs are creating a Faraday cage that is contain the wifi signal to the room with the router and keeping the cell signals from enter the home.

So, moral of the story: if you are building a new home, don't build it with metal studs.

HPM

[metronid]

An interesting faraday cage is a microwave oven.
Kind of like a faraday cage in reverse.

It is a cage that keeps the field from exiting.
The size of the holes in the grid are smaller than the microwave wavelength.
The openings are larger than the wavelength of visible light so you can see in.

A total faraday cage that is solid will still allow very low frequency magnetic fields or constant consistent ones
such as the earth's to be measured inside.

There are steps beyond the faraday cage.
A cage that is sorrounded by a magnetic field with windindings supplied by a current source can be made
to block even the earth's magnetic field.

Getting back to the paint.
Radio waves including microwave waves and light waves and all electomagnetic waves have certain charactersistics
These are seen when enetering various substrates.
Reflection Refraction Diffusion and some more.
The substrate itself will give a different results with different materials.
A red lens will only pass red light is a sort of example.
A mirror will reflect light.
ETc etc etc.

Heavily pigmented paint with metal or other reflecting material will cause the radio wave to reflect back
and not pass through.
Certain materials within the paint will act like little inductors and oscillate.
The oscillations will re radiate the signal sometimes and other times will emit a wavelength that is different
than the original.
Phosflourescence is kind of an example of the above.

The paint used in stealth bombers uses many of these qualities to foil the rdar signal.
The major fooling is in the use of reflectors that place the reflection at an angle that does the return to the source.
I am sure the military has many many tricks up its sleeves.

I have WIFIbut I still love direc connection better.

[happyphysicsman]

Like I said, optics is not my field of expertise in the vast field of physics. metronid, I am impressed the that a pharmD is so versed in the field of optics: bravo. I couldn't figure out how the metal substrates in the paint could act like a Faraday cage, and knew there was some other underlying principle at work here, but could not remember what it was. You have just beautifully reminded me, and I thank you.

HPM

[metronid]

Before even getting into pharmacy school Inorganic and Organic and 6 credits of physics plus calculus are required.
Pharnmacy school requires advanced chemistry that is quite a bit more than hydrogen bonding to oxygen etc.
It involves teaching the concept of Nuclear Magnetic Resonance and much more.
Every atom and bond type will resonate with particular peaks and bands and this can be pseudo equated to
how radio waves act and affect materials.
The only difference between an AM station at 600KhZ and a microwvae at 10 GHZ and visible light is the
frequency basically.
A mirror for visible light is comparable to a refelector used in beam antennas in many aspects.
When dealing with wifi I think about 30 cm and visible which in the nm range the only main difference is wavelength.
Electomagnetic waves also have a perpendicular electric field if memory serves me correctly.

In any case the guys in the military know how to use people that are really geeky to come up with some incredible
ideas.
The cuurent stealth technology revolves around deflecting the radar at atangle that does not go to the source and
paints that absorb the radiation.
They also have technology that I believe that is far beyond above concept which is a whole other discussion.

[happyphysicsman]

The only difference between an AM station at 600KhZ and a microwvae at 10 GHZ and visible light is the
frequency basically.
A mirror for visible light is comparable to a refelector used in beam antennas in many aspects.
When dealing with wifi I think about 30 cm and visible which in the nm range the only main difference is wavelength.
Electomagnetic waves also have a perpendicular electric field if memory serves me correctly.

...

The cuurent stealth technology revolves around deflecting the radar at atangle that does not go to the source and
paints that absorb the radiation.

In physics we like to look at the difference between two frequency bands as not their frequency, but the energy of the electro-magnetic radiation in the two bands. E = hv, where h is Plank's constant, and nu (v) is the frequency of the light. So in other words, the big difference between 600 kHz and 10GHz is the energy of the radiation. Which is, respectively 2.381e-9 eV or 2.381 neV and 4.135 e-5 ev or .4135 ueV.

In radiation oncology (my physics field of expertise: the one that's been slammed recently by the NY Time "wonderful" reporting ability) we're dealing radiation energy on the scale of 10 MeV or 10e9 eV.

HPM

[metronid]

The energy should be looked at.

That is why cell phones burn at their frequency.
It is also why you are not getting burned with a 27mhz walkie takie as much.
A good test would be to place your finger near a pi network or matching circuit for a amplifier
at 10 meter and one at 1 meter and see the burn difference for the same output.
I know the burning feel at 10 meters and have not tried it at one meter.

I know what the ultravuiolet does .

Do you happen to know if there is an upper limit to frequency.
I do not have that knowledge.
Just a little physics .
I would suspect at that energy level aproaching infinity that every thing would tear apart into to their quantum constituents.
I think you would have to collide things at the speed of light to reach that point of energy.

[happyphysicsman]

The burning at radio-frequency has more to do with the frequency band that our bodies resonate at. For example, you already mention magnetic-resonance imaging. In MRI, there are two pieces of equipment that are involved in the imaging process: The high powered magnetic coil, and the RF modulators that are "straped" to you. The ONLY medical concern, (As MR is extremely safe as long as there is no ferromagnetic material in the magnetic field - watch out if there is) is the SAR: specific absorption rate which they keep under careful watch and is highly regulated by government and medical agencies.

That is: the RF frequency has the potential to induce a small electric current in tissue. This electric current is quickly absorbed in the body and reveals itself as radiation dose to the tissue or a burn. In MR, there have been literally less than a handful of patients who have experiences any effects from SAR overdose since the effect is extremely low.

On the other hand, technicians for cell towers or radio frequency transmitters have to pay careful attention to their SAR as they service the tower equipment since the magnitude of waves and their energy is so great they will experience burns to their skin from over exposure.

The effect with oncology radiation is completely different. Here we place patient's cancer in the direct beam of high powered radiation which delivers a dose directly to the patient's tissue. With RF, the radiation induces and small current within the tissue which subsequently delivers the dose, thereby the RF has more of an indirect effect on human tissue.

With Cell phone, the magnitude of the signal is so low, there is a negligible effect on the human tissue. The probability of any sort tissue toxicity (what we call any undesirable effect to tissue from radiation) is extremely low...EXTREMELY LOW -> practically non-existent. I don't know of any case when a human was burned from cell phone use. Around the cell towers, its a different story since within 10 meters of the tower, the intensity is so massive, one must take precautions.


ON the question of whether or not there is an upper-bound to the frequency of electromagnetic radiation. No, I don't believe so, but we have never observed anything more energetic than few GeV's.

It is important that we make the distinction between photon, the carrier particle of electromagnetic radiation which are massless, and all other particles that have mass. There is no other quantum constituent to the photon. It has no mass, and no size and is purely an elemental particle. All other atomic particles: protons, electrons (maybe), neutrons, pions and such are made out of other purely elemental particles. We have found some, and are looking for others. Metronid pointed out that you would need large enough energies to brake the binding properties, thus the building of large, overly expensive (on the order of Billions and billions of dollars), accelerators that will collide particles braking them in pieces and seeing what is produced. Sometimes, from the large amount of energy involved, chucks of that energy is converted to larger more massive particles.

The large Hadron Collider, the most powerful, technologically advanced, expensive, and largest accelerator was built primarily to produce one such massive particle called the Higgs Boson: the super particle that will prove to be the particle that will join some foundational theories into some Grand Unified theory. I really don't know much about that as that is all high energy particle physics and way outside my relm.

My expertise is in what's referred to as computational physics. I write computer programs that solve mathematically intensive physics problems that are way too complex to do on paper. My current research, as a PhD graduate student, is centered around precise, accurate, and patient specific dose calculation for a form of radiotherapy that involved the intensive procedure of implanted small (about the size of a grain of rice) radioactive sources into the tumor bed. Usually about 60-100 sources can be used. It is a very complex problem to solve, so we write computer simulations to do it for us as we simulate the physical interactions of the radiation in the patient. Much easier way to do it.

HPM