Good day,  I have created a faraday cage with metal sheet of .5 mm thickness with aluminum foil wrapped outside and inside of the cage. I was happy at first to notice that the cellphone signal goes from one bar to nothing at all but the signal goes inside the cage intermittently and most of time stays at full strenght  signal. I tried changing places and found dead zones but still frequencies go inside. Wifi signal though still cannot be attenuated. I was planning to create a topological shielding with 10x sheet of 1 mm and layer them together to deplete the frequency but i cant afford to do it if i plan to stay inside longer because of temperature issues. The reason I am doing this is because of electronic harrasment. I researched that devices can be hacked through emf emissions of devices and i need to protect my devices from these attacks.  My question is,    is there by any chance that the signals inside can be cancelled consistently? Do i need to consider the thickness of metal sheet or do i need to just layer tin foils to be enough to reflect or absorb frequencies. Do i need to make earth stakes to transfer the electrons on the metal to earth to regain it's absorption and reflection? Do i need to create topological shielding to deplete the frequecy from GHz to MHz brcause i researched that cellhpone signals are on a MHz frequency?.   I found out as well that apperture/ appertures should be smaller than the wave.   I need your help thank you.
122577
Someone left their cell phone here, it was ringing like crazy.  I stuck it in a metal pot with a metal lid to shut it up, it still rang.  I later put it in a safe, it still rang, but so muffled as to not be annoying.  (Admittedly the safe has a gasket on the door--it provides fire, flood and walking out with the guests protection, it wouldn't defeat a serious burglar.)  How is the signal reaching the phone???
54888
I'm having trouble understanding why the earth is a viable fault path for electricity brought into my home. Isn't there really high resistance? I mean, it's dirt?   Also, let's say I connect the hot wire coming into my house directly to the ground wire. What is the path that the electricity takes to get back and "complete the circuit?"
115086
In my book, it is written that "An emf is induced in a loop when the number of magnetic field lines that pass through the loop is changing" (Faraday's law)  I understand that whenever there is a change in magnetic flux, there will an emf induced in a loop and this in turn will induce a current.  However, I really want to understand what exactly goes on to cause this. I just want to check if I am right:   There is a relative movement between the loop and the magnet (e.g. loop moving towards magnet) Thus, electrons in the loop are "moving" relative to the field A moving charge experiences a force perpendicular to the direction of the field As a force is exerted on the electrons, they move in a particular direction Current is induced   I do not know much calculus and studying high school physics but could someone please help me get an intuition behind Faraday's law or tell me if my way of thinking about it is right?
58057
The  is a proposed propulsion mechanism for spacecraft in which some form of microwave device provides the propulsion. The consensus from the physics community, including many voices on this site, is that the proposed device would violate conservation of momentum.   Several experiments have been conducted, by three main groups: (i) , from Satellite Propulsion Research Ltd, (ii) a research group at the Northwestern Polytechnical University in Xi'an, China, and (iii) Eagleworks Laboratories at NASA's Lyndon B. Johnson Space Center in Houston, Texas. However, few of these experiments have been performed in vacuum (and none of the vacuum tests has been published in a peer-reviewed journal), which means the effect of air currents around the device cannot be ruled out.  This device has been the subject of many questions on this site, including          and their many closed duplicates.  Many of these questions ask what the proposed explanations are, but then veer off into territory of the form "assuming it is true, how does it work?", so they have been (rightfully) closed as counterfactual physics. I feel this sort of bundling does a lot of harm to the discussion, and there is some scope to ask what exactly is being proposed as an explanation. So:     What do the proponents of EmDrive claim is the theoretical justification of the device's function?   Please limit answers exclusively to references, and indicate whether they are peer-reviewed or not. Please limit answers to serious attempts at explanations, as opposed to vague claims about the 'quantum vacuum' - or indicate if an experimental paper does not have any such theoretical explanation or reference.  To be clear, this is not the place to discuss whether the explanations are correct or not. If you have specific questions about any of these sources, ask it separately. (However, if your question starts with "assuming that this works", be prepared for it to be closed.) If you feel there are not enough resources on this thread, you can  but please do not post another question asking people to look for more references.
76507
Hi I am new to SPICE and after doing some research into the spice software, I need some help understanding which type and how to model microwave cavities in SPICE. I want to model a microwave cavity in SPICE, however I will need to use an equivalent structure, can I just use an LC circuit to do this ?. The microwave resonator I am trying to model is just the cavity used in labs.
98070
I'm trying to understand the concept of capacity for a wireless channel.  Some help would be appreciated.  For a AWGN channel capacity is calculated as:  $$C=B \cdot log_2(1 + S/N)\text{ bits/sec}$$  B = bandwidth.  This is what I don't understand.  Why isn't it a factor of frequency? To me considering bandwidth only makes sense in cases where the system changes frequency.   Bandwidth is the difference between an upper and lower frequency range.  Well, what if I'm using a fixed-frequency signal?  Fupper and Flower would be the same value, right?  So does that mean B=0?  So a fixed frequency signal can't carry any data?  We know that's not true, AM radio does it.  So what am I missing? According to this formula, a fixed-frequency signal would have the same performance regardless of whether it's at high or low frequency.  This makes no sense to me.  For example say my bandwidth is 1Hz at a fixed frequency of 1Hz.  Compare this with a bandwidth of 1Hz at a frequency of 2.4GHz.  It's plainly obvious that I can cram way more bits into 2.4 x 109 cycles/second than I can with just 1/sec.  But according to this formula I can't.  Please help. What about fractional differences?  Waveforms are analog in nature, so we could have a 1Hz signal and a 1.5Hz signal.  Likewise at the high frequency range.  Say 2.4GHz minus 0.5Hz.  There is an infinite amount of space between 1 and 1.5.  Could not 1Hz and 1.001Hz serve as two separate channels?  In terms of practicality I realize this would be difficult, nearly impossible to measure this difference with modern electronics, especially with noise added, but in pure theory you could have two channels.  So in that sense, shouldn't there be an infinite amount of bandwidth between two frequencies?  Or do we only count in 1Hz whole number increments?
2633
I have a cable as in the drawing. The black parts are insulators and the brown parts are copper, so there is a big copper cable and inside are two smaller copper cables. When the big copper cable is tied to ground I can use a time domain reflectometer (TDR) on the smaller cables to determine the length of the cable. What happens if the big copper cable is in use with a current running through it that is 1000 times bigger than the current running through the two smaller copper cables? Will I still be able to determine the length with a TDR? I think there shouldn't be a capacitance between the two smaller copper cables - but how am I then able to measure with it a TDR?
27474
and they are on opposite ends of the electromagnetic spectrum, then why can't light travel through walls which is right in the middle of the spectrum?    This question has already been asked . However, I am not entirely satisfied by the answer given on that page which relies on fanciful analogies and metaphors of ants, elephants etc. I am looking for a better explanation.    I think the crux of the matter, and my dilemma, relates to formula for . This is a well known formula used to explain the fact that low frequency waves have more penetration than high frequency waves.     But then how come gamma waves have such high penetration?     Are there some assumptions behind derivation of this formula which break when we consider very high frequency waves?    Or, are there some new factors that need to be taken into account as we move into the high frequency regime?     If given a radio source and a gamma source of equal intensity, then will the radio source have more penetrability than the gamma source per formula for ? If not, why not?  Thanks for all those who posted answers to this question. The answer being proposed is that light waves have the right energy to interact with atoms and electrons in the matter and thus get absorbed. This is a quantum mechanical explanation. The skin depth, on the other hand, is derived purely on basis of classical electrodynamics. So I see there are two mechanisms at work here? Does anyone agree with this? If so, the net absorption will be the sum of absorption due to skin effect + absorption due to atomic physics. Now if we take gamma rays - agreed there will be no absorption due to atomic physics but there should be absorption in accordance with skin effect. And so I come back to original problem.
97292
Is it possible to create an electromagnetic wave of near zero frequency?   An electromagnetic wave carries energy. If we can make the frequency of an EM wave vanishingly small and make it practicality DC, will it also carry energy? I don't think it is possible. Hence there should be some fundamental limit on the minimum frequency of an EM wave.   Is there any such thing?
52781
I am trying to put together the requirements for a cable and I was wondering what would be the most suitable wire size to load the DUT with 25Amps @ 9VDC. I will have few other high current lines 13Amps @ 5VDC. There will also be 2 DC lines 160V @5Amps each.  I was wondering if all of this can be bundled (or what would be the key things to keep in mind) with some other wires carrying RF signals without causing any signal integrity issues.  I plan to use shielded Coax cables (at least 20) and bundle all of it along with some other signal lines (like DIO, SPI, CAN bus, etc) in one cable. The RF signals are not going to have a frequency higher than 15MHz but I will need to sample it quite fast to detect a time difference between 2 signals in 5 nanosecond range.  Would anyone suggest:   The right wire size for this application Would there be any issue in regards to RF measurements?   The overall cable length is going to be about 15ft.
109325
When we have an uncharged conductor with a cavity and apply an external electric field, the charges rearrange to keep the electric field inside the metal zero. The driving force is the need to keep electric field inside the metallic layer, zero. Then why is the field inside the cavity also zero? I think this is because the charges would arrange in the same way as in the case of a cavity free conductor but why can't they arrange in a different way?  Why is this arrangement not possible which clearly has a field inside the cavity but not inside the metal?
114085
The electron drift speed is estimated to be very low.How could there is current almost the instant a circuit is closed??   By the discussions it is known that The information about beginning of the flow of current is transmitted through the propagation of electromagnetic waves(electric impulse)and not with the drift velocity of the electrons. But I want any one to explain how this process takes place.CURIE:)
28726
I hope many people might feel little awkward to see this question. But I feel this is important. Because in my place where I am living I can get a radio (Audio Receiver) very cheaply. I don't know till what extent they allow the audio frequency ranges. I guess they use  ICs for Frequency Demodulators, Frequency Clippers, etc. If the Frequency demodulator doesn't work properly and allows all the frequencies that comes through air then its going to be a big problem to the humans. Can somebody answer which are all the frequency ranges that are available and which causes human hazards?
103796
I was running through the datasheet of  (Low-Cost Low-Power 2.4 GHz RF Transceiver) which has a dimension of 2.40mm X 2.40mm approx. It was really amazing to find such transceivers to be fabricated in such a small area.Infact a transceiver requires a lot of R,C and even L.Resistors, Capacitors and semiconductors are easy to be imagined on an IC but an Inductor!!!  I haven't work in any VLSI industry so it would be great if someone can tell how these inductor logic is implemented on IC. Although it is said that  are alternative solution, but thanks for pointing if my knowledge is correct.
13340
I would like to update my knowledge in this area, that is really out-of-dated and stopped somewhere like ten years ago.  I asked the very same question on my physics lecture at my studies and got the answer, that although some tests and experiments were made (by French scientists?), there is no material, either natural or man-made, that would suffer direct lightning hit and therefore could be used to "capture" and store energy from lightning, for future use or processing of any kind.  Can someone tell me, how does it looks now? Has anything changed during last ten years in this area?
38628
For an object to create different EM waves, it needs to increase the temperature, so what if we or some material could be so hot, that it would emit ultraviolet light, and thanks to that be invisible for the human eye.   I have a lot of questions about this and I would like you to answer me.   At which temperature does an object emit UV light? If an object emits UV light, we wouldn't see anything or we would see some type of violet light? Is there any material that can get to that temperature without melting? Is there any powerful insulator?   Thanks for reading this, and for breaking my dream of making someone invisible, I invite you to day-dream and imagine stupid questions.
62472
Recently I had posted a seemingly innocent question on another forum. I was trying to keep a small and relatively simple circuit down to a 2 layer board and was asking about the shielding merits of a copper pour tied to analog ground, as opposed to dedicating unbroken separate plane used for ground. Though my question was only in reference to the shielding value of such a copper pour, a major controversy started on an entirely different point. In my layout I had created a virtual ground using the typical voltage divider feeding a unity gain configured OP amp, and then had run every single analog ground return to a point adjacent to the output of that virtual ground. I had also done a copper pour on the least busy layer and tied it to that same analog ground, again at that same single point. But there soon ensued a series of posts lambasting my use of such a convoluted "spider web" scheme, with many chiming in that I should just create a ground plane and just make all connections to the nearest available point of that plane ( through  via when necessary). Well doing so certainly makes for a cleaner and simpler layout visually. But having gone the "single point" route for so many years, and having mostly successful (meaning quite and stable) designs, I'm hesitant to change. Especially as some of the arguments spoke of single point grounds as something archaic, and relegated to vacuum tube circuits. What?   So anyway, just poking around, my research on the subject seemed to show two camps on this subject. One argument is that when an unbroken ground plane is available, it is always superior. The other argument says that if its a high frequency circuit a ground plane is better, but for a low frequency circuit (including audio), the single point ground method is better, mostly to avoid ground loops.  Of course I still have a dilemma, as prototype costs are constraining me to a 2 layer board if possible this time, and this means that my pseudo ground plane will, at best, be a copper pour, broken by some short traces here and there. But before adding that complexity or possible exception to the rule, I'd like to put this specific question out for general discussion: For an audio design involving OP Amps, when is a Single point" ground scheme the bast way to go, and when is just the simpler "nearest path to a ground plane" the better (or at least an adequate) choice.   By way of example, these two layered screen shots show two reasonably similar versions of the same board, which in reality is about 4" x 2.5". In the first you can see lots of long traces on both sides of the board culminating at a single pad labeled AGND. The second is nearly the same circuit, but this time the blue copper poor area is part of the analog ground net, so all those long traces have gone away in favor of the nearest path to the ground plane/ copper pour. Aside from all possible critique about other layout issues one might see, this is just an example. I'd really like to confine this discussion to the original question.   single point ground version   Nearest path to ground plane version