-
#1480
by
aero
on 01 Sep, 2015 01:35
-
My intention is to simulate a real loop using phase matched dipoles or point sources, ignoring the mechanics of implementation. I think that is best because Shell can then approximate the real loop to the best of her ability. Hopefully the simulation and implementation will converge toward the same end result. But I need to go off and do that now.
aero
I don't see how multiple dipoles arranged in a circle simulates a loop, unless you're trying to implement a very high harmonic in the azimuthal direction. For TE012, there are only 2 poles around the circle.
Why is it difficult to simulate current through a piece of wire, fed by a current source?
Todd
I'm not certain that it will work but I think its worth a try. I know this code:
(define stubsideleft (list
(make source (src (make gaussian-src (frequency fmeep) (fwidth BW) ))
(component Ex)
(center (- 0 bxant) byant bzant)
(size bantsizex bantsizey antsizez)
(amplitude (exp (* 0+1i pi)))
(axis axex axey axez) )
))Specifically the line,
(amplitude (exp (* 0+1i pi))), shifts the phase of the antenna RF by pi or 180 degrees. I also know I can write a software loop in Scheme. I also know where the center of each dipole or point source is so it seems that the phase of each source should depend on the phase of and distance from the previous source around the antenna loop. Thing I'm not certain about is if the time-stepping in meep will mess with the phasing. I'm working with the assumption that it will not as meep must surly maintain proper source phasing from one time-step to the next. Without doing so, meep couldn't propagate RF waves.
Now, if anyone wants to give me the math for transforming points on the antenna loop circumference to cartesian x, y, z, I would be pleased to check it against mine. Might well save me considerable time. Or maybe meep supplies such coordinate transformation functions that I just haven't needed to look into. (It just occurred to me to look.) And just exactly how much is the phase shift from one point to the next. The arc distance divided by the wavelength? Actually, I guess it would be negative of that as phase increases with time.
-
#1481
by
aero
on 01 Sep, 2015 02:05
-
While I'm here posting, I did want to mention an idea stemming from Dr. Rodel's post about modelling copper losses as the surface integral of the square of the magnetic field at the surface. (Badly paraphrased, appopogies).
The idea is that if going to the length of actually modelling the boundary losses in this way, it would be rather simple to add a photon tunnelling model to the boundary losses. Meep could deal with that, too, assuming we could come up with an acceptable model for photon tunnelling compatible with Meep (MIT Electromagnetic Equation Propagation).
Oh, and the name kind of tells us why we can't easily simulate current in a wire. It is the Electromagnetic Equations that are propagated so to simulate a wire, it is "Write your own function" time.
-
#1482
by
Mulletron
on 01 Sep, 2015 02:32
-
-
#1483
by
deltaMass
on 01 Sep, 2015 02:52
-
If firing a magnetron into a cavity generates squeezed vacuum, I'm going to start using an oven instead. I hear that squeezed food tastes terrible.
-
#1484
by
Mulletron
on 01 Sep, 2015 02:54
-
It is the copper oxides.
-
#1485
by
zen-in
on 01 Sep, 2015 03:26
-
Indeed. But bear in mind that both the spring and the pivot counterbalance solution potentially introduce extra stiction.
I think rfmwguy is seeing stiction from someplace else other than the knife edge, maybe from his liquid conductor? I would take it out of the loop (take out the copper wires) and see what amount of stiction he is then seeing.
Personal preference I went with a rolling knife edge and haven't even been able to measure any stiction and my scales are set to .01 gram.
The balance used in Ohaus scales consists of an agate plane on the bottom with a hardened steel knife edge resting on it. Sometimes the agate will have a groove in it to hold the knife edge and keep it from wandering. When there is a groove it is well polished since any scratches or pits will erode the steel. Agate is a tough material and is harder than steel. With a large balance arm the knife edge could be a replacement blade for a jointer and the agate plane could be a quartz flat. No grease, oil or lubricant should be used on it since it will increase stiction. Guards need to be installed to keep the beam from moving enough that the knife edge leaves the agate surface. Quartz flats are usually round so as large a one as can be found would be needed. They are also available in rectangular shapes. It is an expensive way to go since I'm sure the quartz flat would not be useable as such afterwards. Here is a link to a company that makes quartz flats,
http://www.customscientific.com/flats.htm
-
#1486
by
OttO
on 01 Sep, 2015 07:35
-
Agate is a tough material and is harder than steel. With a large balance arm the knife edge could be a replacement blade for a jointer and the agate plane could be a quartz flat.
I am not sure but I heard that Iphone 6 use sapphire windows, in that case according to mohs scale it is a lot harder than quartz
-
#1487
by
Mezzenile
on 01 Sep, 2015 08:00
-
Two ideas:
1- The use of composite waveguide at the output of the magnetron could help to reduce its thermal coupling to the frustrum.
2- If composite waveguide is not available, why not to introduce a 1 or 2 mm (or even more) insulating spacer or free air séparation between the waveguide flanges of both magnetron and frustrum still to limit their thermal coupling. There would be a small RF loss and VSWR degradation but I think fully acceptable for the test.
-
#1488
by
Rodal
on 01 Sep, 2015 12:48
-
The word ``stiction'' was coined at IBM General Products Division labs in San Jose, CA around 1980 when they encountered that head slider getting stuck to the disk surface while resting at high humidities due to liquid mediated adhesion. High lateral force had to be applied to initiate sliding to overcome high static friction or sticking, hence leading to the term stiction. This is not at all the contact issue of in the knife edge contact problem in RFMWGUY's experiment. Rather, the problem is due to the well known issue of plastic deformation at the nano-scale roughness of contact, with the material nano-contact stresses exceeding the yield stress of the metals involved in contact. It is not due to liquid mediated adhesion. On the contrary, it is a dry contact problem.
Strictly speaking it is incorrect to use the term "stiction" to the contact of two knife edges as being used in RFMWGUY's experiment or to use the word stiction for the contact issues associated with a knife-edge balance. The article on stiction in Wikipedia (like many articles in Wikipedia) lacks scholarship.
A couple of peer-reviewed articles (there are literally hundreds of articles, and dozens of books on Tribology showing this known fact) clarifying the benefits of lubrication in contact problems:
http://jbyoon0901.cafe24.com/wp-content/uploads/2013/05/APL_2011_An-insulating-liquid-environment-for-reducing-adhesion-in-a-microelectromechanicalsystem.pdf?ckattempt=1http://masters.dgtu.donetsk.ua/2014/fimm/mitina/library/article11.pdf
----------
PS: Agate is not at all a tough material when compared to steel, and when using a scientific measure of toughness. Agate is a crystalline variety of silica, found in nature, in volcanic rocks and certain metamorphic rocks, as such it is technically a ceramic material. It lacks the toughness ductility like steel, agate has a lower Fracture Toughness (measured as G1c) than steel. As to "hardness", hardness is not a scientific measure, there are different ways to measure "hardness" as they mix different scientific measures together like the yield strength, and stiffness together. In the Mohs Hardness Scale Agate can have a hardness of 6 to 7 Mohs, while steels can have a Mohs hardness from 5 to 8.5.
-
#1489
by
OttO
on 01 Sep, 2015 13:54
-
In the Mohs Hardness Scale Agate can have a hardness of 6 to 7 Mohs, while steels can have a Mohs hardness from 5 to 8.5.
An easy way to guess if there is a good contact is to use a hardness test with a penetrator shaped in the same way as the one of the scale.
If for example a pin is used on a flat plate a good approximation would be to use a pyramid penetrator.
For example quartz Vickers hardness give us 480 to 1100 and Corundum 2000 to 2700. (Steel will not be higher than 1000)
After this we could use Hertz pressure with a conical penetrator to guess the deformation.
https://en.wikipedia.org/wiki/Contact_mechanics
-
#1490
by
SeeShells
on 01 Sep, 2015 14:07
-
The word ``stiction'' was coined at IBM General Products Division labs in San Jose, CA around 1980 when they encountered that head slider getting stuck to the disk surface while resting at high humidities due to liquid mediated adhesion. High lateral force had to be applied to initiate sliding to overcome high static friction or sticking, hence leading to the term stiction. This is not at all the contact issue of in the knife edge contact problem in RFMWGUY's experiment. Rather, the problem is due to the well known issue of plastic deformation at the nano-scale roughness of contact, with the material nano-contact stresses exceeding the yield stress of the metals involved in contact. It is not due to liquid mediated adhesion. On the contrary, it is a dry contact problem.
Strictly speaking it is incorrect to use the term "stiction" to the contact of two knife edges as being used in RFMWGUY's experiment or to use the word stiction for the contact issues associated with a knife-edge balance. The article on stiction in Wikipedia (like many articles in Wikipedia) lacks scholarship.
A couple of peer-reviewed articles (there are literally hundreds of articles, and dozens of books on Tribology showing this known fact) clarifying the benefits of lubrication in contact problems:
http://jbyoon0901.cafe24.com/wp-content/uploads/2013/05/APL_2011_An-insulating-liquid-environment-for-reducing-adhesion-in-a-microelectromechanicalsystem.pdf?ckattempt=1
http://masters.dgtu.donetsk.ua/2014/fimm/mitina/library/article11.pdf
----------
PS: Agate is not at all a tough material when compared to steel, and when using a scientific measure of toughness. Agate is a crystalline variety of silica, found in nature, in volcanic rocks and certain metamorphic rocks, as such it is technically a ceramic material. It lacks the toughness ductility like steel, agate has a lower Fracture Toughness (measured as G1c) than steel. As to "hardness", hardness is not a scientific measure, there are different ways to measure "hardness" as they mix different scientific measures together like the yield strength, and stiffness together. In the Mohs Hardness Scale Agate can have a hardness of 6 to 7 Mohs, while steels can have a Mohs hardness from 5 to 8.5.
Wow! was that a flash back!
Well done Dr. Rodel. Was with a company that won 5 Editor Choice Awards for PCs in the 80's. We were very aware of the issues of stiction in hard drives. Especially when parked during a platter spin down and the RR head would "park". Our suggestion to IBM was upon spinning up again that they "bump" the RR head right at spin up to overcome the two surfaces stickion. It seemed to work and only involved a change of the devices program in its eeprom.
I'm looking for the the best rolling surface. It may not be a point like in a watch's jeweled movement, but I needed to distributing the heavy contact weight of the frustum and counter balance. That's why I did the the ^ angle with a hardened steel angle iron. It provides a curved contact with a light graphite filling (simple pencil lead) on the microscopic imperfections on the radius. Rolling over surface are 2 side by side graphite composite tubes. Even at .01g I can detect no surface contact generated resistance to movement. I'm not sure what the coefficient of friction is but, it is below what I can detect.
The problem with 2 knife edges which are heat treated. Heat treating forms crystalline structures in the steel on the edge. While they are hard they are also brittle and will tend to fracture along the crystalline boundaries. That tendency to fracture at the contact points is the reason for this patent.
http://www.google.com/patents/US3413044If I was going to be able to detect any friction in the setup I would have gone to this pivot system. I still may, I don't want to see any lateral movement in the beam while oscillating.
Shell
-
#1491
by
Rodal
on 01 Sep, 2015 14:21
-
...Wow! was that a flash back!...
It's fascinating how the lives of different people in this thread are intertwined in disparate fields, and we are all here discussing experiments and analysis of a seemingly impossible space propulsion
-
#1492
by
Star One
on 01 Sep, 2015 14:37
-
Agate is a tough material and is harder than steel. With a large balance arm the knife edge could be a replacement blade for a jointer and the agate plane could be a quartz flat.
I am not sure but I heard that Iphone 6 use sapphire windows, in that case according to mohs scale it is a lot harder than quartz
The iPhone 6 doesn't use such a screen.
-
#1493
by
RERT
on 01 Sep, 2015 15:16
-
Folks - sorry to go AWOL after volunteering to do something, but my father has been visiting for some days. He's 81 - he doesn't need much looking after, but he does spend his days wandering through my house and garden pointing out chores which need doing, and organizing me to do them straight away...
I said I would do fourier analysis on the beam movements of rfmwguy's first experiment if someone would post the time-series, which was very soon done.
Of course, I omitted to mention that I would need the magnetron on/off audio signal to make much progress. With that I can match up the magnetron signal to the filtered beam signal and see what it tells us.
The rough analysis so far doesn't say much beyond what can be seen by eye in the plots posted,
R.
-
#1494
by
OttO
on 01 Sep, 2015 15:36
-
The iPhone 6 doesn't use such a screen.
Are you sure? I search a bit and found this:
Sapphire windows are used in Apple Touch ID of the iPhone 5s, iPhone 6, and iPad mini 3and the display of the Apple Watch. Also, sapphire covers are used for the rear camera in every iPhone 5 or newer.https://en.wikipedia.org/wiki/Sapphire
-
#1495
by
SeeShells
on 01 Sep, 2015 16:03
-
-
#1496
by
birchoff
on 01 Sep, 2015 16:04
-
-
#1497
by
rfmwguy
on 01 Sep, 2015 16:10
-
NSF-1701 New Video - Static test of assembly today without electrodes in galinstan, which adds dampening and drag. When the galinstan was removed, there were wild movements of laser spot, as I noted when I first designed the test stand. Therefore I re-attached Doc's oil dampener, which greatly reduced vertical meanderings. The oil dampener addition and galinstan removal provided a laser spot displacement on the target of approximately the same amount. IOW, galinstan and no oil dampener and 500 mg weight added approximately equal no galinstan and oil dampener and 200 mg weight added. So, the drag/viscosity of galinstan is equal to about 300 mg...far more than I imagined.
Here's the video for detailed analysis:
-
#1498
by
aero
on 01 Sep, 2015 16:11
-
Found this article in the opinion pages of the New York edition. (Times) This may not be a good scientific source but the author nails it IMO.
But the failure to replicate is not a cause for alarm; in fact, it is a normal part of how science works.
Suppose you have two well-designed, carefully run studies, A and B, that investigate the same phenomenon. They perform what appear to be identical experiments, and yet they reach opposite conclusions. Study A produces the predicted phenomenon, whereas Study B does not. We have a failure to replicate.
Does this mean that the phenomenon in question is necessarily illusory? Absolutely not. If the studies were well designed and executed, it is more likely that the phenomenon from Study A is true only under certain conditions. The scientist’s job now is to figure out what those conditions are, in order to form new and better hypotheses to test.
http://www.nytimes.com/2015/09/01/opinion/psychology-is-not-in-crisis.html?partner=EXCITE&ei=5043&_r=0Moderator: If this violates copyrights please remove the post.
-
#1499
by
deltaMass
on 01 Sep, 2015 16:21
-
This Gordian knot is cut by running a truly stand-alone system on self-contained battery power. Especially considering the tiny forces purported to be involved. Even with stand-alone operation, there are six thermal effects to be dealt with and stiction too. But if you insist:
1. What is the maximum current flowing through the Galinstan wires? If the wires can be made thinner, that would go partway to reducing surface tension.
2. The best place for the Galinstan is right by the pivot. That minimises the lever arm of spurious torques.
