Quote from: rfmwguy on 12/09/2015 12:17 pmQuote from: glennfish on 12/09/2015 10:36 amA draft data store is available for critique, review, testing.http://www.rfdriven.comCurrently, there's no content, just a draft structure. The database has two views:1. A web directory view (so archive.org can grab the content) which is read only2. A user DB view (where folks can add content or search for contentNothing is frozen so now would be a good time to suggest changes, variations, etc.Ultimately I'll migrate the user DB view to something a bit more robust, but for archive.org, we have to use a directory structure of some kind, else it won't be found.If anyone wants to start adding content, PM me, and I'll set up an account for you. Please be specific where you want write permissions. Write includes delete so don't ask for everything. Ultimately delete will mean "archive" but not today.The default DB view login is Guest and the password is GuestLooking good Glenn, let me know via PM when you're ready to get my data, I'll try and input it. Or, if you prefer, ask me the questions and I'll give you everything I know...which varies from day to day...64K of memory should do the trick. Well, I'm not sure if this is an idea that people are going to support.I've got exactly one contributor request, although 26 folks have taken a look, without comment.Interesting spread of interest (map below).Thoughts?

Quote from: glennfish on 12/09/2015 10:36 amA draft data store is available for critique, review, testing.http://www.rfdriven.comCurrently, there's no content, just a draft structure. The database has two views:1. A web directory view (so archive.org can grab the content) which is read only2. A user DB view (where folks can add content or search for contentNothing is frozen so now would be a good time to suggest changes, variations, etc.Ultimately I'll migrate the user DB view to something a bit more robust, but for archive.org, we have to use a directory structure of some kind, else it won't be found.If anyone wants to start adding content, PM me, and I'll set up an account for you. Please be specific where you want write permissions. Write includes delete so don't ask for everything. Ultimately delete will mean "archive" but not today.The default DB view login is Guest and the password is GuestLooking good Glenn, let me know via PM when you're ready to get my data, I'll try and input it. Or, if you prefer, ask me the questions and I'll give you everything I know...which varies from day to day...64K of memory should do the trick.

A draft data store is available for critique, review, testing.http://www.rfdriven.comCurrently, there's no content, just a draft structure. The database has two views:1. A web directory view (so archive.org can grab the content) which is read only2. A user DB view (where folks can add content or search for contentNothing is frozen so now would be a good time to suggest changes, variations, etc.Ultimately I'll migrate the user DB view to something a bit more robust, but for archive.org, we have to use a directory structure of some kind, else it won't be found.If anyone wants to start adding content, PM me, and I'll set up an account for you. Please be specific where you want write permissions. Write includes delete so don't ask for everything. Ultimately delete will mean "archive" but not today.The default DB view login is Guest and the password is Guest

Quote from: aero on 12/10/2015 04:30 amQuote from: Rodal on 12/10/2015 01:32 amBy 235, he probably thinks that I am heavy, very heavy, that I weigh 235 lbs ~~~~~~~~~~~~~Quote from: aero on 12/10/2015 12:10 amQuote from: Rodal on 12/09/2015 11:22 pmQuote from: aero on 12/09/2015 09:22 pmDr. Rodal,I'm still missing something in the terminology.I want to model SeeShells Quartz rod in her CE3 cavity but it is fruitless if I don't get it right.I have from Shell, here http://www.technicalglass.com/technical_properties.htmlthat disapation factor < 1E-4, which equals tan delta, and the constant = 3.75 so I calculate the imaginary part of relative permittivity as 3.75E-4 . Now I get shakey. I think I haveepsilon = 3.25 +i3.25E-4 and now the terminology changes and I get more confused.You wrote CONDUCTIVITY = omega * epsilon"and the meep units wiki gives meep electrical conductivity = sigma_d = e_r *e_o * c/a . I know e_o, c and a, but if e_r is the real part = the constant, where is epsilon"?It seems self evident to me that epsilon" must factor into sigma_d somehow.Or is it so simple as sigma_d = transformation factor * epsilon" and I misinterpreted above?If you define the following values for the constitutive properties of fused quartz:(real value of) relative electric permittivity = ε_{r} = 3.75tan δ (electric) = 0.0001then, it follows that:relative complex permittivity = ε_{r}*(1 - i* tan δ_{e}) = ε_{r}*(1 - i* 0.0001) relative complex permittivity = 3.75(1 - i* 0.0001) = 3.75 - i * 0.0001*3.75 = 3.75 - i * 0.000375 COMMENTS:1) I don't understand why you wrote 3.25 instead of 3.75 in your expression (epsilon = 3.25 +i3.25E-4)2) The sign of the imaginary part should be negative, because a negative imaginary part results in power loss. A positive sign (as in your expression) would result in power production, which violates the 2nd law of thermodynamics (dielectric materials entail power loss, not power production). (As pointed out in http://forum.nasaspaceflight.com/index.php?topic=38577.msg1453316#msg1453316)3) I don't understand your discussion of electric conductivity in this context or the questions that follow. Quartz is a dielectric material, not a metal conductor. Please try to re-word your question on conductivity to explain the intended context or purpose (are you talking about the conductivity of copper ? )First, 3.25 was a nervous slip. You make me nervous Second, in the meep code,(material (make medium (epsilon epsilon_r) (D-conductivity CU-D-conduct)))the parameter : CU-D-conduct should be less than zero, that is, negative..Third, I think that I was still confused, but the light dawned. Is this the correct expression?sigma-d = epsilon" * e_r *e_o * c/a . so that conductivity = Omega * sigma_d.I'll code that up (using the negative sign), print it out and re-post here for validation.No, it is not true that conductivity = Omega * sigma_dHere it is step by step (I'm using a positive conductivity, you can add the negative sign):We know that the conductivity in SI units is σ=ω ε“ σ=ω ε“ =2 π f ε“ = 2 π f (ε“/ε') ε' = 2 π f tan δ_{e} ε' = 2 π f tan δ_{e} (ε'/ ε_{o}) ε_{o} = 2 π f tan δ_{e} ε_{r} ε_{o}Then (from , the conversion between the (dimensionless) Meep conductivity]http://ab-initio.mit.edu/wiki/index.php/Conductivity_in_Meep#Conductivity_and_complex_.CE.B5 ), the conversion between the (dimensionless) Meep conductivity σ_{D} and the conductivity σ (in SI units) is:σ_{D} = (a/c) σ /( ε_{r} ε_{o}) = 2 π f (a/c) tan δ_{e} where a= length scale (I think that aero chose a = 0.3 meters)c = speed of light in vacuum (299792458 meters / second)f = frequency (in Hertz = 1 / second)where you can interpret σ_{D} is the dimensionless Meep conductivityf (a/c) is the dimensionless frequency (notice that a/c has units of time)tan δ_{e} is the dimensionless expression corresponding to the dimensional imaginary permittivity ε“I think I've got it now, but I'm having a hard time reconciling this reference:http://meepunits.wikia.com/wiki/Meep_unit_transformation_Wikiwith this reference: http://ab-initio.mit.edu/wiki/index.php/Conductivity_in_Meep#Conductivity_and_complex_.CE.B5 ), the conversion between the (dimensionless) Meep conductivity They seem to be the inverse of one another.I chose to follow your example and calculated sigma_d = Q_D_conduct = -1.670715037160664e-12I did read the previous reference on Fused Quartz more closely and noticed that the data was at 1 MHz, so found another reference which gave data at 100MHz and 3GHz. This reference gave tan δe 0.0002 @ 100 MHz, 0.00006 @ 3 GHz so I've coded 0.00006 as the loss tangent at 3 GHz.1) the two references for conversion of Meep conductivity pointed above agree with each other, if one overlooks the subscript "D" (the meaning of the subscript is different in the two references). Rather than looking at the subscript, start from the concept that the Meep conductivity is dimensionless.2) you don't point out the reference you found for fused quartz data so it is impossible to comment on its veracity, but on principle I don't agree with choosing properties based on which Internet reference you find based solely on frequency (unless your reference is from a peer-reviewed reference showing the actual measurement vs frequency). There are different qualities of materials, dependent not only on their material make up but also on their manufacturing method. Shell may have selected her source for properties based on the supplier of her quartz. It would be a mistake to ignore that if the data is from her supplier. RF Cafe data is notoriously unreliable (as previously discussed in these threads). Microwaves 101 (http://www.microwaves101.com/encyclopedias/quartz) has data that is pretty close to the one given by Shell.

Quote from: Rodal on 12/10/2015 01:32 amBy 235, he probably thinks that I am heavy, very heavy, that I weigh 235 lbs ~~~~~~~~~~~~~Quote from: aero on 12/10/2015 12:10 amQuote from: Rodal on 12/09/2015 11:22 pmQuote from: aero on 12/09/2015 09:22 pmDr. Rodal,I'm still missing something in the terminology.I want to model SeeShells Quartz rod in her CE3 cavity but it is fruitless if I don't get it right.I have from Shell, here http://www.technicalglass.com/technical_properties.htmlthat disapation factor < 1E-4, which equals tan delta, and the constant = 3.75 so I calculate the imaginary part of relative permittivity as 3.75E-4 . Now I get shakey. I think I haveepsilon = 3.25 +i3.25E-4 and now the terminology changes and I get more confused.You wrote CONDUCTIVITY = omega * epsilon"and the meep units wiki gives meep electrical conductivity = sigma_d = e_r *e_o * c/a . I know e_o, c and a, but if e_r is the real part = the constant, where is epsilon"?It seems self evident to me that epsilon" must factor into sigma_d somehow.Or is it so simple as sigma_d = transformation factor * epsilon" and I misinterpreted above?If you define the following values for the constitutive properties of fused quartz:(real value of) relative electric permittivity = ε_{r} = 3.75tan δ (electric) = 0.0001then, it follows that:relative complex permittivity = ε_{r}*(1 - i* tan δ_{e}) = ε_{r}*(1 - i* 0.0001) relative complex permittivity = 3.75(1 - i* 0.0001) = 3.75 - i * 0.0001*3.75 = 3.75 - i * 0.000375 COMMENTS:1) I don't understand why you wrote 3.25 instead of 3.75 in your expression (epsilon = 3.25 +i3.25E-4)2) The sign of the imaginary part should be negative, because a negative imaginary part results in power loss. A positive sign (as in your expression) would result in power production, which violates the 2nd law of thermodynamics (dielectric materials entail power loss, not power production). (As pointed out in http://forum.nasaspaceflight.com/index.php?topic=38577.msg1453316#msg1453316)3) I don't understand your discussion of electric conductivity in this context or the questions that follow. Quartz is a dielectric material, not a metal conductor. Please try to re-word your question on conductivity to explain the intended context or purpose (are you talking about the conductivity of copper ? )First, 3.25 was a nervous slip. You make me nervous Second, in the meep code,(material (make medium (epsilon epsilon_r) (D-conductivity CU-D-conduct)))the parameter : CU-D-conduct should be less than zero, that is, negative..Third, I think that I was still confused, but the light dawned. Is this the correct expression?sigma-d = epsilon" * e_r *e_o * c/a . so that conductivity = Omega * sigma_d.I'll code that up (using the negative sign), print it out and re-post here for validation.No, it is not true that conductivity = Omega * sigma_dHere it is step by step (I'm using a positive conductivity, you can add the negative sign):We know that the conductivity in SI units is σ=ω ε“ σ=ω ε“ =2 π f ε“ = 2 π f (ε“/ε') ε' = 2 π f tan δ_{e} ε' = 2 π f tan δ_{e} (ε'/ ε_{o}) ε_{o} = 2 π f tan δ_{e} ε_{r} ε_{o}Then (from , the conversion between the (dimensionless) Meep conductivity]http://ab-initio.mit.edu/wiki/index.php/Conductivity_in_Meep#Conductivity_and_complex_.CE.B5 ), the conversion between the (dimensionless) Meep conductivity σ_{D} and the conductivity σ (in SI units) is:σ_{D} = (a/c) σ /( ε_{r} ε_{o}) = 2 π f (a/c) tan δ_{e} where a= length scale (I think that aero chose a = 0.3 meters)c = speed of light in vacuum (299792458 meters / second)f = frequency (in Hertz = 1 / second)where you can interpret σ_{D} is the dimensionless Meep conductivityf (a/c) is the dimensionless frequency (notice that a/c has units of time)tan δ_{e} is the dimensionless expression corresponding to the dimensional imaginary permittivity ε“I think I've got it now, but I'm having a hard time reconciling this reference:http://meepunits.wikia.com/wiki/Meep_unit_transformation_Wikiwith this reference: http://ab-initio.mit.edu/wiki/index.php/Conductivity_in_Meep#Conductivity_and_complex_.CE.B5 ), the conversion between the (dimensionless) Meep conductivity They seem to be the inverse of one another.I chose to follow your example and calculated sigma_d = Q_D_conduct = -1.670715037160664e-12I did read the previous reference on Fused Quartz more closely and noticed that the data was at 1 MHz, so found another reference which gave data at 100MHz and 3GHz. This reference gave tan δe 0.0002 @ 100 MHz, 0.00006 @ 3 GHz so I've coded 0.00006 as the loss tangent at 3 GHz.

By 235, he probably thinks that I am heavy, very heavy, that I weigh 235 lbs ~~~~~~~~~~~~~Quote from: aero on 12/10/2015 12:10 amQuote from: Rodal on 12/09/2015 11:22 pmQuote from: aero on 12/09/2015 09:22 pmDr. Rodal,I'm still missing something in the terminology.I want to model SeeShells Quartz rod in her CE3 cavity but it is fruitless if I don't get it right.I have from Shell, here http://www.technicalglass.com/technical_properties.htmlthat disapation factor < 1E-4, which equals tan delta, and the constant = 3.75 so I calculate the imaginary part of relative permittivity as 3.75E-4 . Now I get shakey. I think I haveepsilon = 3.25 +i3.25E-4 and now the terminology changes and I get more confused.You wrote CONDUCTIVITY = omega * epsilon"and the meep units wiki gives meep electrical conductivity = sigma_d = e_r *e_o * c/a . I know e_o, c and a, but if e_r is the real part = the constant, where is epsilon"?It seems self evident to me that epsilon" must factor into sigma_d somehow.Or is it so simple as sigma_d = transformation factor * epsilon" and I misinterpreted above?If you define the following values for the constitutive properties of fused quartz:(real value of) relative electric permittivity = ε_{r} = 3.75tan δ (electric) = 0.0001then, it follows that:relative complex permittivity = ε_{r}*(1 - i* tan δ_{e}) = ε_{r}*(1 - i* 0.0001) relative complex permittivity = 3.75(1 - i* 0.0001) = 3.75 - i * 0.0001*3.75 = 3.75 - i * 0.000375 COMMENTS:1) I don't understand why you wrote 3.25 instead of 3.75 in your expression (epsilon = 3.25 +i3.25E-4)2) The sign of the imaginary part should be negative, because a negative imaginary part results in power loss. A positive sign (as in your expression) would result in power production, which violates the 2nd law of thermodynamics (dielectric materials entail power loss, not power production). (As pointed out in http://forum.nasaspaceflight.com/index.php?topic=38577.msg1453316#msg1453316)3) I don't understand your discussion of electric conductivity in this context or the questions that follow. Quartz is a dielectric material, not a metal conductor. Please try to re-word your question on conductivity to explain the intended context or purpose (are you talking about the conductivity of copper ? )First, 3.25 was a nervous slip. You make me nervous Second, in the meep code,(material (make medium (epsilon epsilon_r) (D-conductivity CU-D-conduct)))the parameter : CU-D-conduct should be less than zero, that is, negative..Third, I think that I was still confused, but the light dawned. Is this the correct expression?sigma-d = epsilon" * e_r *e_o * c/a . so that conductivity = Omega * sigma_d.I'll code that up (using the negative sign), print it out and re-post here for validation.No, it is not true that conductivity = Omega * sigma_dHere it is step by step (I'm using a positive conductivity, you can add the negative sign):We know that the conductivity in SI units is σ=ω ε“ σ=ω ε“ =2 π f ε“ = 2 π f (ε“/ε') ε' = 2 π f tan δ_{e} ε' = 2 π f tan δ_{e} (ε'/ ε_{o}) ε_{o} = 2 π f tan δ_{e} ε_{r} ε_{o}Then (from , the conversion between the (dimensionless) Meep conductivity]http://ab-initio.mit.edu/wiki/index.php/Conductivity_in_Meep#Conductivity_and_complex_.CE.B5 ), the conversion between the (dimensionless) Meep conductivity σ_{D} and the conductivity σ (in SI units) is:σ_{D} = (a/c) σ /( ε_{r} ε_{o}) = 2 π f (a/c) tan δ_{e} where a= length scale (I think that aero chose a = 0.3 meters)c = speed of light in vacuum (299792458 meters / second)f = frequency (in Hertz = 1 / second)where you can interpret σ_{D} is the dimensionless Meep conductivityf (a/c) is the dimensionless frequency (notice that a/c has units of time)tan δ_{e} is the dimensionless expression corresponding to the dimensional imaginary permittivity ε“

Quote from: Rodal on 12/09/2015 11:22 pmQuote from: aero on 12/09/2015 09:22 pmDr. Rodal,I'm still missing something in the terminology.I want to model SeeShells Quartz rod in her CE3 cavity but it is fruitless if I don't get it right.I have from Shell, here http://www.technicalglass.com/technical_properties.htmlthat disapation factor < 1E-4, which equals tan delta, and the constant = 3.75 so I calculate the imaginary part of relative permittivity as 3.75E-4 . Now I get shakey. I think I haveepsilon = 3.25 +i3.25E-4 and now the terminology changes and I get more confused.You wrote CONDUCTIVITY = omega * epsilon"and the meep units wiki gives meep electrical conductivity = sigma_d = e_r *e_o * c/a . I know e_o, c and a, but if e_r is the real part = the constant, where is epsilon"?It seems self evident to me that epsilon" must factor into sigma_d somehow.Or is it so simple as sigma_d = transformation factor * epsilon" and I misinterpreted above?If you define the following values for the constitutive properties of fused quartz:(real value of) relative electric permittivity = ε_{r} = 3.75tan δ (electric) = 0.0001then, it follows that:relative complex permittivity = ε_{r}*(1 - i* tan δ_{e}) = ε_{r}*(1 - i* 0.0001) relative complex permittivity = 3.75(1 - i* 0.0001) = 3.75 - i * 0.0001*3.75 = 3.75 - i * 0.000375 COMMENTS:1) I don't understand why you wrote 3.25 instead of 3.75 in your expression (epsilon = 3.25 +i3.25E-4)2) The sign of the imaginary part should be negative, because a negative imaginary part results in power loss. A positive sign (as in your expression) would result in power production, which violates the 2nd law of thermodynamics (dielectric materials entail power loss, not power production). (As pointed out in http://forum.nasaspaceflight.com/index.php?topic=38577.msg1453316#msg1453316)3) I don't understand your discussion of electric conductivity in this context or the questions that follow. Quartz is a dielectric material, not a metal conductor. Please try to re-word your question on conductivity to explain the intended context or purpose (are you talking about the conductivity of copper ? )First, 3.25 was a nervous slip. You make me nervous Second, in the meep code,(material (make medium (epsilon epsilon_r) (D-conductivity CU-D-conduct)))the parameter : CU-D-conduct should be less than zero, that is, negative..Third, I think that I was still confused, but the light dawned. Is this the correct expression?sigma-d = epsilon" * e_r *e_o * c/a . so that conductivity = Omega * sigma_d.I'll code that up (using the negative sign), print it out and re-post here for validation.

Quote from: aero on 12/09/2015 09:22 pmDr. Rodal,I'm still missing something in the terminology.I want to model SeeShells Quartz rod in her CE3 cavity but it is fruitless if I don't get it right.I have from Shell, here http://www.technicalglass.com/technical_properties.htmlthat disapation factor < 1E-4, which equals tan delta, and the constant = 3.75 so I calculate the imaginary part of relative permittivity as 3.75E-4 . Now I get shakey. I think I haveepsilon = 3.25 +i3.25E-4 and now the terminology changes and I get more confused.You wrote CONDUCTIVITY = omega * epsilon"and the meep units wiki gives meep electrical conductivity = sigma_d = e_r *e_o * c/a . I know e_o, c and a, but if e_r is the real part = the constant, where is epsilon"?It seems self evident to me that epsilon" must factor into sigma_d somehow.Or is it so simple as sigma_d = transformation factor * epsilon" and I misinterpreted above?If you define the following values for the constitutive properties of fused quartz:(real value of) relative electric permittivity = ε_{r} = 3.75tan δ (electric) = 0.0001then, it follows that:relative complex permittivity = ε_{r}*(1 - i* tan δ_{e}) = ε_{r}*(1 - i* 0.0001) relative complex permittivity = 3.75(1 - i* 0.0001) = 3.75 - i * 0.0001*3.75 = 3.75 - i * 0.000375 COMMENTS:1) I don't understand why you wrote 3.25 instead of 3.75 in your expression (epsilon = 3.25 +i3.25E-4)2) The sign of the imaginary part should be negative, because a negative imaginary part results in power loss. A positive sign (as in your expression) would result in power production, which violates the 2nd law of thermodynamics (dielectric materials entail power loss, not power production). (As pointed out in http://forum.nasaspaceflight.com/index.php?topic=38577.msg1453316#msg1453316)3) I don't understand your discussion of electric conductivity in this context or the questions that follow. Quartz is a dielectric material, not a metal conductor. Please try to re-word your question on conductivity to explain the intended context or purpose (are you talking about the conductivity of copper ? )

Dr. Rodal,I'm still missing something in the terminology.I want to model SeeShells Quartz rod in her CE3 cavity but it is fruitless if I don't get it right.I have from Shell, here http://www.technicalglass.com/technical_properties.htmlthat disapation factor < 1E-4, which equals tan delta, and the constant = 3.75 so I calculate the imaginary part of relative permittivity as 3.75E-4 . Now I get shakey. I think I haveepsilon = 3.25 +i3.25E-4 and now the terminology changes and I get more confused.You wrote CONDUCTIVITY = omega * epsilon"and the meep units wiki gives meep electrical conductivity = sigma_d = e_r *e_o * c/a . I know e_o, c and a, but if e_r is the real part = the constant, where is epsilon"?It seems self evident to me that epsilon" must factor into sigma_d somehow.Or is it so simple as sigma_d = transformation factor * epsilon" and I misinterpreted above?

Often, you only care about the absorption loss in a narrow bandwidth, where you just want to set the imaginary part of ε (or μ) to some known experimental value, in the same way that you often just care about setting a dispersionless real ε that is the correct value in your bandwidth of interest.One approach to this problem would be allowing you to specify a constant (frequency-independent) imaginary part of ε, but this has the disadvantage of requiring the simulation to employ complex fields (doubling the memory and time requirements), and also tends to be numerically unstable. Instead, the approach in Meep is for you to set the conductivity σD (or σB for an imaginary part of μ), chosen so that \mathrm{Im}\, \varepsilon = \varepsilon_\infty \sigma_D / \omega is the correct value at your frequency ω of interest. (Note that, in Meep, you specify f = ω / 2π instead of ω for the frequency, however, so you need to include the factor of 2π when computing the corresponding imaginary part of ε!) Conductivities can be implemented with purely real fields, so they are not nearly as expensive as implementing a frequency-independent complex ε or μ.

The behavior for complex fields was changed for Meep 0.10. Also, in Meep 0.9 there was a bug: when you specified χ(3) in the interface, you were actually specifying \chi^{(3)}/\varepsilon_\infty^4. This was fixed in Meep 0.10.

Quote from: rfmwguy on 12/10/2015 12:26 pmFrom horn antenna on wikipedia:"The horn shape that gives minimum reflected power is an exponential taper. Exponential horns are used in special applications that require minimum signal loss, such as satellite antennas and radio telescopes. However conical and pyramidal horns are most widely used, because they have straight sides and are easier to design and fabricate."While they call it exponential, I've always heard logrithmic. So, I'm all stoked up about the baritone when it arrives. Note: my wife is already wondering about me, the arrival of the baritone will convince her to summon the white coats https://en.m.wikipedia.org/wiki/Horn_antennaIt depends on what variables you chose to define the problem. Suppose that you have only two variables, x and y, related by:x = y^2this square function formula (which is well-behaved: there is only one value of x for a given value of y) can also be written in terms of its mathematical inverse:y = Sqrt[ x]but the formulation in terms of the inverse, the square root, introduces a number of complexities (there are two possible values of y for a given value of x, and for negative values of x, y becomes imaginary). It is better to solve the problem in terms of x = y^2. Similarly the problem can be posed in terms of the exponential or its inverse, the logarithmic function. The preferred formulation is in terms of the exponential which has nicer properties, including the beautiful fact that the derivative of the exponential function is the same function: the exponential. Ditto for its integral.

From horn antenna on wikipedia:"The horn shape that gives minimum reflected power is an exponential taper. Exponential horns are used in special applications that require minimum signal loss, such as satellite antennas and radio telescopes. However conical and pyramidal horns are most widely used, because they have straight sides and are easier to design and fabricate."While they call it exponential, I've always heard logrithmic. So, I'm all stoked up about the baritone when it arrives. Note: my wife is already wondering about me, the arrival of the baritone will convince her to summon the white coats https://en.m.wikipedia.org/wiki/Horn_antenna

Quote from: SteveD on 12/10/2015 03:55 amQuote from: Rodal on 12/08/2015 08:18 pmAcoustic ==> speed of soundElectromagnetic ==> speed of lightAcoustic fundamental natural frequencies are millions of times less than the fundamental natural frequencies in electromagnetic cavities. Wavelengths are correspondingly vastly different. Mode shapes are different tooWhile all of this is true, if the thing looks like a horn, I'd think at least a cursory check of the acoustical literature might be in order to see if it points to mathematical function describing the shape that rfmwguy experimentally arrived at. The questions, as I see it, are 1. why does the proposed optimal frustum shape look like this, 2. what formula produces the shape and 3. does that formula suggest further optimization. At the very least, a search of acoustical literature might turn up some elegant math to describe the shape.Ok, if it's so simply prove it. What is the function for the optimal shape (highest Q) of an asymmetrical resonance cavity?"

Quote from: Rodal on 12/08/2015 08:18 pmAcoustic ==> speed of soundElectromagnetic ==> speed of lightAcoustic fundamental natural frequencies are millions of times less than the fundamental natural frequencies in electromagnetic cavities. Wavelengths are correspondingly vastly different. Mode shapes are different tooWhile all of this is true, if the thing looks like a horn, I'd think at least a cursory check of the acoustical literature might be in order to see if it points to mathematical function describing the shape that rfmwguy experimentally arrived at. The questions, as I see it, are 1. why does the proposed optimal frustum shape look like this, 2. what formula produces the shape and 3. does that formula suggest further optimization. At the very least, a search of acoustical literature might turn up some elegant math to describe the shape.

Acoustic ==> speed of soundElectromagnetic ==> speed of lightAcoustic fundamental natural frequencies are millions of times less than the fundamental natural frequencies in electromagnetic cavities. Wavelengths are correspondingly vastly different. Mode shapes are different too

Quote from: Emmett Brown on 12/10/2015 01:22 amQuote from: RFPlumber on 12/09/2015 06:48 pm1. You have thrust but it is small for your test bench to measure. How did you make the aluminum frustum? I mean it is hard to solder aluminum... so how is it held together? One possibility is that your frustum has a very low Q and hence a very low thrust level...You can see the seam of the cone in this pic. It's pretty tight, but it hasn't been soldered yet. (There's a few inches of overlap where those clips at the back are). I've done some brazing on this (the maggie mount plate) already. Yes, it's not the easiest, but if you can get it clamped properly, it's not too bad.I was still debating on when to make it permanent - whether I was going to just run simulations, or bite the bullet and get the miniVNA to tune it.Don't know where your budget is but two options on the VNA.http://www.ebay.com/itm/138M-4-4G-SMA-signal-source-generator-simple-spectrum-analyzer-Tracking-source-/111493176997?hash=item19f582dea5I have this one, ~$70-100 bucks, the software I have is buggy (I think it was corrupted) and I had a very hard time getting them to responding to my emails for new software. The reports are basically favorable, but mention the software issue and make sure you get it with your order. The second one is around $600 miniVNA tiny http://miniradiosolutions.com/54-2/Software is clean and the device works well. rfmwguy, TheTraveler and I have bought this model.ShellPS: Nice work and a thought on coupling the parts together.

Quote from: RFPlumber on 12/09/2015 06:48 pm1. You have thrust but it is small for your test bench to measure. How did you make the aluminum frustum? I mean it is hard to solder aluminum... so how is it held together? One possibility is that your frustum has a very low Q and hence a very low thrust level...You can see the seam of the cone in this pic. It's pretty tight, but it hasn't been soldered yet. (There's a few inches of overlap where those clips at the back are). I've done some brazing on this (the maggie mount plate) already. Yes, it's not the easiest, but if you can get it clamped properly, it's not too bad.I was still debating on when to make it permanent - whether I was going to just run simulations, or bite the bullet and get the miniVNA to tune it.

1. You have thrust but it is small for your test bench to measure. How did you make the aluminum frustum? I mean it is hard to solder aluminum... so how is it held together? One possibility is that your frustum has a very low Q and hence a very low thrust level...

Quote from: SteveD on 12/10/2015 04:48 pmQuote from: SteveD on 12/10/2015 03:55 amQuote from: Rodal on 12/08/2015 08:18 pmAcoustic ==> speed of soundElectromagnetic ==> speed of lightAcoustic fundamental natural frequencies are millions of times less than the fundamental natural frequencies in electromagnetic cavities. Wavelengths are correspondingly vastly different. Mode shapes are different tooWhile all of this is true, if the thing looks like a horn, I'd think at least a cursory check of the acoustical literature might be in order to see if it points to mathematical function describing the shape that rfmwguy experimentally arrived at. The questions, as I see it, are 1. why does the proposed optimal frustum shape look like this, 2. what formula produces the shape and 3. does that formula suggest further optimization. At the very least, a search of acoustical literature might turn up some elegant math to describe the shape.Ok, if it's so simply prove it. What is the function for the optimal shape (highest Q) of an asymmetrical resonance cavity?"Don't be silly, there is no such function, this question cannot be answered in principle. Any cavity with perfect reflection has the highest Q, the modes of resonance will affect Q, all of which are in principle "correct," and moreover, a cavity like a trombone is not meant to maximize a quantity like Q, it is meant to maximize the harmonic over/undertones of acoustic vibration given a certain frequency. It has nothing to do with Energy efficiency, although power in vs power out is of some relevancy to a trombone's ability to hold a note correctly. Note though that there is no solution to "the optimal trombone shape;" it's a question that requires more information.To answer your question I think you would have to specify a mode, frequency, and the properties of your reflector-- change any of these variables and the "highest Q" configuration may change, and for any given set of those variables, there is probably an infinite number of "optimal shapes," many of which would be simpler than others.

Quote from: Rodal on 12/10/2015 12:54 pmQuote from: rfmwguy on 12/10/2015 12:26 pmFrom horn antenna on wikipedia:"The horn shape that gives minimum reflected power is an exponential taper. Exponential horns are used in special applications that require minimum signal loss, such as satellite antennas and radio telescopes. However conical and pyramidal horns are most widely used, because they have straight sides and are easier to design and fabricate."While they call it exponential, I've always heard logrithmic. So, I'm all stoked up about the baritone when it arrives. Note: my wife is already wondering about me, the arrival of the baritone will convince her to summon the white coats https://en.m.wikipedia.org/wiki/Horn_antennaIt depends on what variables you chose to define the problem. Suppose that you have only two variables, x and y, related by:x = y^2this square function formula (which is well-behaved: there is only one value of x for a given value of y) can also be written in terms of its mathematical inverse:y = Sqrt[ x]but the formulation in terms of the inverse, the square root, introduces a number of complexities (there are two possible values of y for a given value of x, and for negative values of x, y becomes imaginary). It is better to solve the problem in terms of x = y^2. Similarly the problem can be posed in terms of the exponential or its inverse, the logarithmic function. The preferred formulation is in terms of the exponential which has nicer properties, including the beautiful fact that the derivative of the exponential function is the same function: the exponential. Ditto for its integral.Aha! Believe it or not, I follow you Doc and it makes sense.Now, if Meep could calculate an exponential frustum with resonance of 2.45 GHz given only one fixed value: large diameter 11 inches (279.4 mm). Length and small diameter would be defined by ideal Return Loss resonance of +30dB or so at 2.45 GHzMy apologies in advance if Meepers just put their fists through their monitors

small_rad = 1big_rad = 5.5length = 5step = .1constant = 10^(log10(big_rad/small_rad)/length)z = 0while z <= length : current_radius = (constant^z)*small_rad make_cylinder(radius = current_radius, height = step, center = (0,0,z)) z = z + step

Now, if Meep could calculate an exponential frustum...

Don't know where your budget is but two options on the VNA.http://www.ebay.com/itm/138M-4-4G-SMA-signal-source-generator-simple-spectrum-analyzer-Tracking-source-/111493176997?hash=item19f582dea5I have this one, ~$70-100 bucks, the software I have is buggy (I think it was corrupted) and I had a very hard time getting them to responding to my emails for new software. The reports are basically favorable, but mention the software issue and make sure you get it with your order. The second one is around $600 miniVNA tiny http://miniradiosolutions.com/54-2/Software is clean and the device works well. rfmwguy, TheTraveler and I have bought this model.

Quote from: rfmwguy on 12/10/2015 03:51 pmNow, if Meep could calculate an exponential frustum...The easy way to define shapes in meep is to build it out of the primitives sphere, cylinder, cone, block, and ellipsoid. Anything other than that will require manual construction of the shape. Unless it proves really necessary, lmbfan's suggestion to approximate it with a series of primitives should work, though I think using the 'cone' primitive would give a better approximation of the horn shape.Given the equation for the shape, we can have it calculate the indiviual cones. Meep is controlled through a general purpose programming language (Scheme) so many things are possible. What the documentation calls the "ctl file" is actually a Scheme source file.

...last_radius = small_radiuswhile z <= length : current_radius = (constant^z)*small_rad make_truncated_cone(radius1 = last_radius, radius2 = current_radius, height = step, center = (0,0,z)) last_radius = current_radius z = z + step

Quote from: SeeShells on 12/10/2015 12:45 pmDon't know where your budget is but two options on the VNA.http://www.ebay.com/itm/138M-4-4G-SMA-signal-source-generator-simple-spectrum-analyzer-Tracking-source-/111493176997?hash=item19f582dea5I have this one, ~$70-100 bucks, the software I have is buggy (I think it was corrupted) and I had a very hard time getting them to responding to my emails for new software. The reports are basically favorable, but mention the software issue and make sure you get it with your order. The second one is around $600 miniVNA tiny http://miniradiosolutions.com/54-2/Software is clean and the device works well. rfmwguy, TheTraveler and I have bought this model.Just a minor correction: the $70 device above is not a VNA, it is not even a scalar NA, it is actually a spectrum analyzer (I own this device, this is what I call a NWT-70-like spectrum analyzer). There is apparently a way to use it as poor-man's scalar NA by utilizing a source of flat wide-band noise (they sell the module), but IMHO this is a really perverted way. The corresponding scalar NA is nwt-4000 http://www.ebay.com/itm/NWT4000-138M-4-4G-sweep-simple-spectrum-analyzer-generator-Case-/181745836241?hash=item2a50e560d1:g:MmoAAOSwstxVVV0t, and it will already set you back $245. I own this one too. The reason I say "corresponding" is that these are all clones of the original projects by a German guy BG7TBL http://www.dl4jal.eu (The page is in German, but the credit is still due). He also wrote the software ("WinNWT") which is what will be enclosed with those ebay shipments from China. The software is half-English and half-German, and it has been written to support all kinds of devices by BG7TBL, so a large part of it is not even applicable to the particular functionality provided by each of these 2 devices. At the end of the day it does work though, so the $245 price tag is likely the lowest one can get a scalar NA for.If I knew about miniVNA back then I would likely order one instead of these, but, also, not everyone needs a vector NA. A scalar one is just fine for finding resonance frequencies.I wish I could advise you on what mode to tune the cavity for, but as I keep repeating, my understanding is that nobody really knows the answer.

Quote from: Rodal on 12/10/2015 11:57 amQuote from: aero on 12/10/2015 04:30 amQuote from: Rodal on 12/10/2015 01:32 amBy 235, he probably thinks that I am heavy, very heavy, that I weigh 235 lbs ~~~~~~~~~~~~~Quote from: aero on 12/10/2015 12:10 amQuote from: Rodal on 12/09/2015 11:22 pmQuote from: aero on 12/09/2015 09:22 pmDr. Rodal,I'm still missing something in the terminology.I want to model SeeShells Quartz rod in her CE3 cavity but it is fruitless if I don't get it right.I have from Shell, here http://www.technicalglass.com/technical_properties.htmlthat disapation factor < 1E-4, which equals tan delta, and the constant = 3.75 so I calculate the imaginary part of relative permittivity as 3.75E-4 . Now I get shakey. I think I haveepsilon = 3.25 +i3.25E-4 and now the terminology changes and I get more confused.You wrote CONDUCTIVITY = omega * epsilon"and the meep units wiki gives meep electrical conductivity = sigma_d = e_r *e_o * c/a . I know e_o, c and a, but if e_r is the real part = the constant, where is epsilon"?It seems self evident to me that epsilon" must factor into sigma_d somehow.Or is it so simple as sigma_d = transformation factor * epsilon" and I misinterpreted above?If you define the following values for the constitutive properties of fused quartz:(real value of) relative electric permittivity = ε_{r} = 3.75tan δ (electric) = 0.0001then, it follows that:relative complex permittivity = ε_{r}*(1 - i* tan δ_{e}) = ε_{r}*(1 - i* 0.0001) relative complex permittivity = 3.75(1 - i* 0.0001) = 3.75 - i * 0.0001*3.75 = 3.75 - i * 0.000375 COMMENTS:1) I don't understand why you wrote 3.25 instead of 3.75 in your expression (epsilon = 3.25 +i3.25E-4)2) The sign of the imaginary part should be negative, because a negative imaginary part results in power loss. A positive sign (as in your expression) would result in power production, which violates the 2nd law of thermodynamics (dielectric materials entail power loss, not power production). (As pointed out in http://forum.nasaspaceflight.com/index.php?topic=38577.msg1453316#msg1453316)3) I don't understand your discussion of electric conductivity in this context or the questions that follow. Quartz is a dielectric material, not a metal conductor. Please try to re-word your question on conductivity to explain the intended context or purpose (are you talking about the conductivity of copper ? )First, 3.25 was a nervous slip. You make me nervous Second, in the meep code,(material (make medium (epsilon epsilon_r) (D-conductivity CU-D-conduct)))the parameter : CU-D-conduct should be less than zero, that is, negative..Third, I think that I was still confused, but the light dawned. Is this the correct expression?sigma-d = epsilon" * e_r *e_o * c/a . so that conductivity = Omega * sigma_d.I'll code that up (using the negative sign), print it out and re-post here for validation.No, it is not true that conductivity = Omega * sigma_dHere it is step by step (I'm using a positive conductivity, you can add the negative sign):We know that the conductivity in SI units is σ=ω ε“ σ=ω ε“ =2 π f ε“ = 2 π f (ε“/ε') ε' = 2 π f tan δ_{e} ε' = 2 π f tan δ_{e} (ε'/ ε_{o}) ε_{o} = 2 π f tan δ_{e} ε_{r} ε_{o}Then (from , the conversion between the (dimensionless) Meep conductivity]http://ab-initio.mit.edu/wiki/index.php/Conductivity_in_Meep#Conductivity_and_complex_.CE.B5 ), the conversion between the (dimensionless) Meep conductivity σ_{D} and the conductivity σ (in SI units) is:σ_{D} = (a/c) σ /( ε_{r} ε_{o}) = 2 π f (a/c) tan δ_{e} where a= length scale (I think that aero chose a = 0.3 meters)c = speed of light in vacuum (299792458 meters / second)f = frequency (in Hertz = 1 / second)where you can interpret σ_{D} is the dimensionless Meep conductivityf (a/c) is the dimensionless frequency (notice that a/c has units of time)tan δ_{e} is the dimensionless expression corresponding to the dimensional imaginary permittivity ε“I think I've got it now, but I'm having a hard time reconciling this reference:http://meepunits.wikia.com/wiki/Meep_unit_transformation_Wikiwith this reference: http://ab-initio.mit.edu/wiki/index.php/Conductivity_in_Meep#Conductivity_and_complex_.CE.B5 ), the conversion between the (dimensionless) Meep conductivity They seem to be the inverse of one another.I chose to follow your example and calculated sigma_d = Q_D_conduct = -1.670715037160664e-12I did read the previous reference on Fused Quartz more closely and noticed that the data was at 1 MHz, so found another reference which gave data at 100MHz and 3GHz. This reference gave tan δe 0.0002 @ 100 MHz, 0.00006 @ 3 GHz so I've coded 0.00006 as the loss tangent at 3 GHz.1) the two references for conversion of Meep conductivity pointed above agree with each other, if one overlooks the subscript "D" (the meaning of the subscript is different in the two references). Rather than looking at the subscript, start from the concept that the Meep conductivity is dimensionless.2) you don't point out the reference you found for fused quartz data so it is impossible to comment on its veracity, but on principle I don't agree with choosing properties based on which Internet reference you find based solely on frequency (unless your reference is from a peer-reviewed reference showing the actual measurement vs frequency). There are different qualities of materials, dependent not only on their material make up but also on their manufacturing method. Shell may have selected her source for properties based on the supplier of her quartz. It would be a mistake to ignore that if the data is from her supplier. RF Cafe data is notoriously unreliable (as previously discussed in these threads). Microwaves 101 (http://www.microwaves101.com/encyclopedias/quartz) has data that is pretty close to the one given by Shell. Let's check some numbers, (always a good hygienic thing to do prior to implementing any model), in SI units:σ= 2 π f tan δ_{e} ε_{r} ε_{o}fortan δ_{e} = 0.0001 (fused quartz as per Shell's supplier reference)ε_{r} = 3.75 (fused quartz as per Shell's supplier reference)f = 2.4 E+09 (the same frequency, in Hertz, you used previously)ε_{o} = 8.854187817 E-12 (permittivity of free space vacuum)henceσ= 2 π 2.4 E+09 0.0001 3.75 8.854187817 E-12 = 5.006925 E-05Which is a small number (about the conductivity of drinking water [at very low frequencies, not at microwave frequencies]), as one would require for a dielectric However, this number (5.006925 E-05) is much larger than the published value for conductivity of fused quartz [at very low frequencies](see for example https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity)σ=1.30 E−18which is actually 13 orders of magnitude smaller.The reason suggested (in http://ab-initio.mit.edu/wiki/index.php/Conductivity_in_Meep#Conductivity_and_complex_.CE.B5 ) for using a fictitious conductivity σ=ω ε“ instead of the imaginary part of the dielectric permittivity ε“ to model the dielectric in Meep is in order to save computer time and for numerical stability since the analysis in terms of complex numbers is much more time consuming and much less numerically stable (a big problem for a Finite Difference formulation ! ).QuoteOften, you only care about the absorption loss in a narrow bandwidth, where you just want to set the imaginary part of ε (or μ) to some known experimental value, in the same way that you often just care about setting a dispersionless real ε that is the correct value in your bandwidth of interest.One approach to this problem would be allowing you to specify a constant (frequency-independent) imaginary part of ε, but this has the disadvantage of requiring the simulation to employ complex fields (doubling the memory and time requirements), and also tends to be numerically unstable. Instead, the approach in Meep is for you to set the conductivity σD (or σB for an imaginary part of μ), chosen so that \mathrm{Im}\, \varepsilon = \varepsilon_\infty \sigma_D / \omega is the correct value at your frequency ω of interest. (Note that, in Meep, you specify f = ω / 2π instead of ω for the frequency, however, so you need to include the factor of 2π when computing the corresponding imaginary part of ε!) Conductivities can be implemented with purely real fields, so they are not nearly as expensive as implementing a frequency-independent complex ε or μ. If working on this, I would check both formulations (the analysis in terms of the fictitious conductivity and the analysis in terms of complex numbers, using the imaginary permittivity) for a small problem with known solution, that can be readily solved by Meep with the complex formulation to double check that the analysis in terms of fictitious conductivity is indeed a good model for the dielectric.What does your Meep-expert friend (Dr. Dominic if I recall his name correctly) have to say on this matter ?You can never take these numerical codes on faith. The reference points to an important bug for calculations using the complex field formulation, in one of the Meep versions, for example.QuoteThe behavior for complex fields was changed for Meep 0.10. Also, in Meep 0.9 there was a bug: when you specified χ(3) in the interface, you were actually specifying \chi^{(3)}/\varepsilon_\infty^4. This was fixed in Meep 0.10.

Quote from: zen-in on 12/10/2015 04:12 amI'm not going to take sides on this and I am not going to send an email to Chris. Everyone should just settle down and get back on track before Chris gets so annoyed at the whole lot of us that he shuts down the thread for good. Let's see some experimental results and focus on what we know and what we can do to get to the bottom of this em-drive phenomena. Enough with the distractions.I have been on this EM Drive thread since thread number one. Some people presently contributing to these threads were not present at that time and may be unfamiliar with its history, and how these threads are such a headache for the NSF moderators and for NSF administration.Thread number had to be closed, completely shut down by NSF administration for several days because of exchanges that also resulted in banning of individuals. At that time it was unknown whether the EM Drive would continue to exist.This kind of stuff happens on the EM Drive thread much more often than in the conventional threads about NASA and Space X.Multiple people have been banned and are sorely missed.If the audience wants these threads to continue it is a question of self moderation and not arguing with moderators on their established guidelines, in order to make the moderator and NSF administration's job easier - or at least more similar to their regular monitoring of other threads-.

I'm not going to take sides on this and I am not going to send an email to Chris. Everyone should just settle down and get back on track before Chris gets so annoyed at the whole lot of us that he shuts down the thread for good. Let's see some experimental results and focus on what we know and what we can do to get to the bottom of this em-drive phenomena. Enough with the distractions.

Quote from: RFPlumber on 12/10/2015 06:31 pmJust a minor correction: the $70 device above is not a VNA, it is not even a scalar NA, it is actually a spectrum analyzer...RFPlumer, Thanks!!! I'll pull this software down to see if I can get it running as a second check. I knew it wasn't the best when I bought it but I got it before I had any funding and was using personal funds.Shell

Just a minor correction: the $70 device above is not a VNA, it is not even a scalar NA, it is actually a spectrum analyzer...