Talk-Polywell.org

There will always be some form of currency, and people will always be selfish greedy assholes.

Forest > trees

I never read these Fuzzy books.

Is it something alike the Moties books (The Mote in God's Eye)?

Short synopsis: Jack Holloway, independent sunstone miner/jack of all trades meets a native bipedal creature the size of a child (~2ft tall). The planet they are on is privately owned by the company doing most of the mining, but only has ownership because the Colonial Authority classed the planet as having no native sentient species. Spoiler: That classification is wrong, and the books deal with the discovery, fallout and what various people/groups do in response.

To add, it has some interesting legal drama, since the big decision is whether killing a fuzzy is murder or not is the clinch point on whether they're sentient.

Like many authors writing at the time, you also find some fun stuff in the technology--The only four handwaviums I know of are the hyperdrive, "contra-gravity," collapsium, and a complete mass-energy converter. They use nuclear power for almost everything, even flashlights usually have a nuclear battery of some sort in them. Fun stuff.

Tom Ligon wrote:No snide comments from me on this project. I applaud amateur science, and this one smells a little like some other work I've heard of. Specifically, electromagnetic effects getting past a Faraday cage, especially repulsive effects. I've seen a small scale, ultra-low-force demonstration of it.

During his national service, working on radar, my dad placed an old transistor radio with a ferrite rod aerial inside a Faraday cage and it kept playing just fine...

alexjrgreen wrote:During his national service, working on radar, my dad placed an old transistor radio with a ferrite rod aerial inside a Faraday cage and it kept playing just fine...

Must have been a poor Faraday cage at the frequency in question, or maybe a nearby flamethrower station.

A Faraday cages ability to block a electrical signal/ current is indeed relative. Even a crude cage can stop DC current / signals. But as the signal increases in frequency, it can penetrate a Faraday cage if the openings between wires is not small enough. A demonstration by an instructor at MIT demonstrates this- an excellent video electronic course in my opinion. He climbed into a Faraday cage with a radio. With it tuned to an AM station the signal was blocked, but an FM station with a higher frequency signal penetrated well.

https://video.search.yahoo.com/yhs/sear ... mp=yhs-001


Dan Tibbets

The Faraday cage will block anything where the holes are smaller than half the frequency, correct?

I think it's the full wavelength but they're fuzzy and look at orders of magnitude rather than factors. Microwave ovens have about 2mm wide holes, but the wave is 122mm long. So people leave in a healthy margin.

As a rule of thumb, the power transmission through a small hole in a conducting sheet will scale like (diameter/wavelength) to the sixth power. So if you make the hole diameter one tenth of a wavelength , the power that goes through will be about one part in a million
So the rule of thumb you need to be about one magnitude lower in size for the shield to be effective. So if you want to block a 1 cm wavelength the whole the no larger than 1/10 of a centimeter. No shield is 100% effective but you can easily get the point were it is negligible in effect.

ow .I think I just made my head hurt

So, if the hole is half the wavelength, thats (1/2)^6 = 0.015625 or 1.5% getting through. Still pretty effective at blocking the signal.

In relation to the original topic of the thread, I guess this means his Faraday cage either has large holes in the mesh (which didn't seem to be the case as it appeared to be screen door screen from the pictures) or the wavelength of the signal causing the deviation is pretty short. All assuming his Faraday cage actually is one.

The most common point of failure in faraday cages is the opening to gain access to the interior. For some reason people tend to inadequately shield their openings. Also as he's actually generating some electromagnetic effects there is a possibility that there may be some grounding requirements to help eliminate transient effects. Is not necessary to ground a faraday cage for it to operate but there are some circumstances where it would be required. Without actually physically seeing his set up I cannot comment further but one would assume he is already taken all the necessary precautions

I went back and looked at the faraday cage in the beginning picture and it is NOT a good design or sound construction.

The rule of thumb I recall for a Faraday cage is avoid any holes not smaller than half a wavelength in circumference, and even that's big if you need really good isolation. A hole or slot 1 wavelength in circumference will transmit RF energy easily, evidenced by the use of such structures as antennas. Circumference of the holes seems to matter more than area. And yes, it would be very easy to get a very large slot around the edge of the door if the design is poor.

If you look a the picture you can see one spot where there is a fairly large hole(near the white lead) and were the black wires enter is not shielded properly.
The wiring also looks like it was not the type for noise reduction.

hanelyp wrote:Circumference of the holes seems to matter more than area.

That depends upon if you have a linear polarization and whether that is polarized to the opening like a slit, or if you have a circular polarization, which can fit through smaller area but requires a larger width hole. GPS signals for instance are all right hand circular, so need close to round holes to fit through--they don't like slits. Radar signals from a linear source are easy to pick up in a slot or slotted waveguide array, which is as you say, more concerned with circumference than area, but waveguides stipulate specific frequencies within the guide, so it is even more complicated than circumference.

No, I don't normally know this stuff but I spent all yesterday studying radar antennae geometry because of an IP I want to pursue.