The pros and cons of a perforated mesh:PROS:* reduces weight (very important for aerospace applications and for EM Drive testing)* reduces wind resistance effects (very important for large satellite dishes and for EM Drive testing to prevent gas effect that has plagued microwave pressure experiments since Maxwell's times, and as demonstrated on the first successful experiment to accurately measure microwave pressure, by Dr. Cullen in his Ph.D. thesis)* visibility of what is happening inside the microwave cavity*it prevents a microwave sealed cavity from becoming a pressure vessel as moist air inside it heats up and therefore pressure increases as PV=nRT (important for EM Drive experiments where an exhaust jet may be produced)* it diminishes buoyancy effects (important for EM Drive experiments) See deltaMass's's post for more comprehensive discussion http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403300#msg1403300* it prevents liquids like water (rain, snow, etc.) to collect inside (hat tip Shell)CONS:* perforation has to be significantly smaller than the microwave wavelength. See X-Ray's post for more discussion: http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403303#msg1403303* perforation reduces stiffness, and therefore perforated mesh is more subject to distortion* durability (the reduced stiffness of perforated plates means that eventually they will get distorted by handling stresses, this is the main reason why waveguides are not made of perforated meshes, as waveguides usually weigh little and durability concerns vastly exceed the benefits of weight saving for a waveguide)* conductivity between wires and possibly anistropy of a wire mesh, impedance in perforated plates. See zen-in's post: http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403296#msg1403296 * spurious noise and other issues from some energy leakage. See ElizabethGreene's post http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403288#msg1403288the following COULD BE A CON OR A PRO depending on input power going into heat and time length of operation:* CON: perforation means less thermally conductive metal to act as a heat sink, on the other hand the PRO: open perforation acts as a means to get convective heat transfer through the holes, so the con of reduced heat sink has to be compared with the benefits of convective heat transfer. It basically depends on the thickness (thermal diffusivity is most effective in the thickness direction than in lateral directions). A thick non-perforated plate should be better than a thin perforated plate since thermal diffusivity through a metal is much, much faster than thermal convection, therefore the benefits of a thick plate will outweigh the benefits of a perforated thin sheet until enough heat is absorbed in the thick plate at which point thermal convection benefits of the perforated plate may outweigh the benefits of a thick non-perforated plate (depends on the speed of convection).In outer space (vacuum) there is no thermal convection whatsoever, (hat-tip aero for reminding us of that) therefore the thermal sink advantage of a non-perforated plate are even more significant and have to be balanced against the weight savings for payload weight reduction from a perforated plate.
I have a question for the theorists. Isn't it our objective to pack as much energy into the cavity as we can just to see the real world physical effect?So lets imagine a cavity made of "Unobtainium" that will not melt or deform under any circumstance. And let it have an infinite Q for good measure. At what energy level do "Known" things start to happen within that cavity? Doesn't it start to create electrons and perhaps other particles? At what energy does it start to create gravitons, or will the electron creation drain energy to the point that the graviton creation energy levels can't be reached? Higgs particles if you prefer.
Quote from: aero on 07/11/2015 09:52 pmI have a question for the theorists. Isn't it our objective to pack as much energy into the cavity as we can just to see the real world physical effect?So lets imagine a cavity made of "Unobtainium" that will not melt or deform under any circumstance. And let it have an infinite Q for good measure. At what energy level do "Known" things start to happen within that cavity? Doesn't it start to create electrons and perhaps other particles? At what energy does it start to create gravitons, or will the electron creation drain energy to the point that the graviton creation energy levels can't be reached? Higgs particles if you prefer.You're alluding to something called the Schwinger limit, which refers to an E-field so intense that virtual pair production actualises from the vacuum (it is thought - nobody has seen this I think). That critical field value is about 1018 V/m
Quote from: deltaMass on 07/11/2015 10:18 pmQuote from: aero on 07/11/2015 09:52 pmI have a question for the theorists. Isn't it our objective to pack as much energy into the cavity as we can just to see the real world physical effect?So lets imagine a cavity made of "Unobtainium" that will not melt or deform under any circumstance. And let it have an infinite Q for good measure. At what energy level do "Known" things start to happen within that cavity? Doesn't it start to create electrons and perhaps other particles? At what energy does it start to create gravitons, or will the electron creation drain energy to the point that the graviton creation energy levels can't be reached? Higgs particles if you prefer.You're alluding to something called the Schwinger limit, which refers to an E-field so intense that virtual pair production actualises from the vacuum (it is thought - nobody has seen this I think). That critical field value is about 1018 V/mThat is because everyone blindly excepts the standard equations for quantum mechanics which is foolish IMHO.
Quote from: Blaine on 07/11/2015 10:23 pmQuote from: deltaMass on 07/11/2015 10:18 pmQuote from: aero on 07/11/2015 09:52 pmI have a question for the theorists. Isn't it our objective to pack as much energy into the cavity as we can just to see the real world physical effect?So lets imagine a cavity made of "Unobtainium" that will not melt or deform under any circumstance. And let it have an infinite Q for good measure. At what energy level do "Known" things start to happen within that cavity? Doesn't it start to create electrons and perhaps other particles? At what energy does it start to create gravitons, or will the electron creation drain energy to the point that the graviton creation energy levels can't be reached? Higgs particles if you prefer.You're alluding to something called the Schwinger limit, which refers to an E-field so intense that virtual pair production actualises from the vacuum (it is thought - nobody has seen this I think). That critical field value is about 1018 V/mThat is because everyone blindly excepts the standard equations for quantum mechanics which is foolish IMHO.Got something better?("accepts" btw)
Quote from: Rodal on 07/11/2015 09:16 pmThe pros and cons of a perforated mesh:PROS:* reduces weight (very important for aerospace applications and for EM Drive testing)* reduces wind resistance effects (very important for large satellite dishes and for EM Drive testing to prevent gas effect that has plagued microwave pressure experiments since Maxwell's times, and as demonstrated on the first successful experiment to accurately measure microwave pressure, by Dr. Cullen in his Ph.D. thesis)* visibility of what is happening inside the microwave cavity*it prevents a microwave sealed cavity from becoming a pressure vessel as moist air inside it heats up and therefore pressure increases as PV=nRT (important for EM Drive experiments where an exhaust jet may be produced)* it diminishes buoyancy effects (important for EM Drive experiments) See deltaMass's's post for more comprehensive discussion http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403300#msg1403300* it prevents liquids like water (rain, snow, etc.) to collect inside (hat tip Shell)CONS:* perforation has to be significantly smaller than the microwave wavelength. See X-Ray's post for more discussion: http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403303#msg1403303* perforation reduces stiffness, and therefore perforated mesh is more subject to distortion* durability (the reduced stiffness of perforated plates means that eventually they will get distorted by handling stresses, this is the main reason why waveguides are not made of perforated meshes, as waveguides usually weigh little and durability concerns vastly exceed the benefits of weight saving for a waveguide)* conductivity between wires and possibly anistropy of a wire mesh, impedance in perforated plates. See zen-in's post: http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403296#msg1403296 * spurious noise and other issues from some energy leakage. See ElizabethGreene's post http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403288#msg1403288the following COULD BE A CON OR A PRO depending on input power going into heat and time length of operation:* CON: perforation means less thermally conductive metal to act as a heat sink, on the other hand the PRO: open perforation acts as a means to get convective heat transfer through the holes, so the con of reduced heat sink has to be compared with the benefits of convective heat transfer. It basically depends on the thickness (thermal diffusivity is most effective in the thickness direction than in lateral directions). A thick non-perforated plate should be better than a thin perforated plate since thermal diffusivity through a metal is much, much faster than thermal convection, therefore the benefits of a thick plate will outweigh the benefits of a perforated thin sheet until enough heat is absorbed in the thick plate at which point thermal convection benefits of the perforated plate may outweigh the benefits of a thick non-perforated plate (depends on the speed of convection).In outer space (vacuum) there is no thermal convection whatsoever, (hat-tip aero for reminding us of that) therefore the thermal sink advantage of a non-perforated plate are even more significant and have to be balanced against the weight savings for payload weight reduction from a perforated plate.Another possible pro for mesh is lower power lost due to eddy currents: https://en.m.wikipedia.org/wiki/Eddy_currentThese are normally associated with AC, but are basically heat losses due to reversing mag fields. I assume Tm radiation will also experience eddy losses, so a thinner material could be an advantage...haven't proven that, but did think it has potential. Comments welcomed.
...Another possible pro for mesh is lower power lost due to eddy currents: https://en.m.wikipedia.org/wiki/Eddy_currentThese are normally associated with AC, but are basically heat losses due to reversing mag fields. I assume Tm radiation will also experience eddy losses, so a thinner material could be an advantage...haven't proven that, but did think it has potential. Comments welcomed.
Just a very quick note as it's a crazy day here for a Sat. Perforated on .040 http://www.sequoia-brass-copper.com/alloy-101-ofe-ofhc-copper-sheet.html Which will be a Oxygen Free High Conductivity Copper and it's the same stuff used in waveguides. But I'm putting holes in it!!!Have a great Saturday. I'll be back on later.Shell
Quote from: rfmwguy on 07/11/2015 10:16 pm...Another possible pro for mesh is lower power lost due to eddy currents: https://en.m.wikipedia.org/wiki/Eddy_currentThese are normally associated with AC, but are basically heat losses due to reversing mag fields. I assume Tm radiation will also experience eddy losses, so a thinner material could be an advantage...haven't proven that, but did think it has potential. Comments welcomed.Comment: At 2.45 GHz, for copper, the skin depth is only 1.322 micrometers, or 52.04 microinches. Let's say that you use a 0.09 mm thin copper mesh, then the skin thickness is still 1/68 th of that thickness (1.47 %) .If one uses .040 http://www.sequoia-brass-copper.com/alloy-101-ofe-ofhc-copper-sheet.html instead, the skin thickness is 1/769 th of that thickness (0.13 %)
Quote from: rfmwguy on 07/12/2015 12:06 amQuote from: Rodal on 07/11/2015 11:16 pmQuote from: rfmwguy on 07/11/2015 10:16 pm...Another possible pro for mesh is lower power lost due to eddy currents: https://en.m.wikipedia.org/wiki/Eddy_currentThese are normally associated with AC, but are basically heat losses due to reversing mag fields. I assume Tm radiation will also experience eddy losses, so a thinner material could be an advantage...haven't proven that, but did think it has potential. Comments welcomed.Comment: At 2.45 GHz, for copper, the skin depth is only 1.322 micrometers, or 52.04 microinches. Let's say that you use a 0.09 mm thin copper mesh, then the skin thickness is still 1/68 th of that thickness (1.47 %) .If one uses .040 http://www.sequoia-brass-copper.com/alloy-101-ofe-ofhc-copper-sheet.html instead, the skin thickness is 1/769 th of that thickness (0.13 %)Would less surface area in mesh translate into less overall loss?Great point, yes roughly proportional to the area.
Quote from: Rodal on 07/11/2015 11:16 pmQuote from: rfmwguy on 07/11/2015 10:16 pm...Another possible pro for mesh is lower power lost due to eddy currents: https://en.m.wikipedia.org/wiki/Eddy_currentThese are normally associated with AC, but are basically heat losses due to reversing mag fields. I assume Tm radiation will also experience eddy losses, so a thinner material could be an advantage...haven't proven that, but did think it has potential. Comments welcomed.Comment: At 2.45 GHz, for copper, the skin depth is only 1.322 micrometers, or 52.04 microinches. Let's say that you use a 0.09 mm thin copper mesh, then the skin thickness is still 1/68 th of that thickness (1.47 %) .If one uses .040 http://www.sequoia-brass-copper.com/alloy-101-ofe-ofhc-copper-sheet.html instead, the skin thickness is 1/769 th of that thickness (0.13 %)Would less surface area in mesh translate into less overall loss?
...Whew...this was one of the reasons I chose to go this route, doc.
On sealed and closed cavities vs. open cavities, both in air and containing air.The sealed cavity will exhibit a buoyancy effect because increased temperature will cause the enclosed air to exert wall pressure and cause slight ballooning of the cavity walls. For example, a sealed thin aluminium soft drink can when heated a few tens of degrees will exhibit on order 50 ug-w of buoyancy.The open cavity will lose heated air in order to maintain constant pressure with the outside. Thus its weight will decrease because a volume of heated air weighs less than that same volume of colder air.Both effects cause an apparent loss in weight. It's to be expected that an open cavity will produce a bigger weight loss than a sealed cavity, because of the high stiffness of the sealed cavity.This weight loss can readily be factored out by eithera) measuring thrust in the horizontal direction, orb) differencing the measured weights with thrust-downward resp. thrust-upward
The capacitor-coil assembly is wired as a tank circuit and mounted in a common acrylic housing filled with a Phase Change Material (PCM), for limited thermal control of the assembly.
For the current case of long runs with a small lattice and modest resolution, memory should not be an issue. And run time might not be an issue for some. It is for me because I am required (by the wife) to turn my computer off at night. With 32 complete cycles requiring just less than 1 hour run time, 100 cycles should complete in less that 3 hours but 1000 cycles would exceed my allotted run window of about 14 hours maximum. A 30 hour computer run is not that bad in a laboratory environment. It's just to much for me to do at home. If I can learn how to start meep from saved data, that may be an easy solution. But if it is decided that 10,000 cycles are needed, well, that's not so easy.