Quick question: why does Q of spiral inductor have a peak?

[Guest]

您好，詹姆斯：

有两个不同的主题：

（1）。我就用一两种不同的矩形网格和一个三角形网格天线比较，我看到了3个型号之间的差异很小。你提到你看到差距非常大。当你说，必须有它的理由。我假设你在这样做是非常使用十四行诗的时间衔接学习好
， 你认为十四行诗的时间是非常准确的。当你说在simulaiton差别很大，在我看来
， 你必须有办法证明你可以得到以下数值的错误使用它十四行诗的时间。当然，你可以增加框的大小
， 使其越来越接近了它的现实。假设它没有打破数字，你应该得到的融合结果当您增加框的大小
， 降低单元尺寸不断。我很感兴趣
， 你对此有何评论。

（2）关于低频升，我想我肯定是正确的人对此发表评论。事实上，我被要求作出评论时
， 我课程。我可能还写它在IE3D的用户Manunal东西。我会来概括IE3D的用户手册了。我要么把它在这里或用户可以从泽兰德的网站（www.zeland.com）它。

在此之前，我就这，我要问你以下问题：

如果你不知道就某个特定问题的答案，请说“不”。如果您认为某些参数不是很重要，请说“这不是关键”。

为了您的研究（模拟和实验）：

1。什么是研究的目的是什么？
2。是（低
， 高频率的融合研究）电路设计者？
3。什么被认为是低频率？
4。是DC的低频考虑？
5。什么是融合的价值？
6。在你的学习，什么是框的大小？
7。是什么框的底板导电？
8。是什么在框顶板导？
9。什么是对框底部的钢板厚度？
10。什么是对框的顶部钢板厚度？
11。是什么在箱子侧壁导？我想这是在模拟临时选举
， 因为格林函数只能处理光电化学。它不应该在测量临时选举
， 因为这是不可能的事在现实中光电化学。
12。是什么在箱子的一侧墙壁的厚度？我想你不能提供的模拟厚度信息。在测量，您可能不会在意它。

我写了关于这个专题的东西很快。谢谢！

最好的问候，

 

[Guest]

您好剑-很高兴听到你可能愿意把这个问题提供一些努力。从您最近的职位，我还以为你的支持了。但是，记住
， 我会倾向于无法进行
， 如果你一直说，“这是准确的，它的准确！”当我们的目标是找到错误。此外，您也许记得
， 我写道
， 声称自己是专家或主管当局（你做了上述后再次）是无益的。请允许我解释。在美国
， 许多人（和欧洲也），尤其是我这一代，都提出了非常强烈的不信任的专家和权威。我的意思是很强烈的。这样，当你成为一个专家提供
， 作为对你的观点辩护的一部分，它实际上使你的情况要弱得多。如果你想一个强大的情况下，你不应该提请注意作为一个专家。你应该把你所强调的数据。

至于点＃1，当我说出现大的差异，我指出
， 两个人可以看看完全相同的数据
， 看到两个完全不同的事情，都可以完全100％正确的。这是一个非常重要的概念
， 你最好能知道的是经常发生的情况。这是我的天性寻找数据的差异是因为那里的有趣的研究可以做到的。所以
， 我在你的数据，或其他任何人的数据看，我期待的差异。三角形和矩形之间的差别在你的阴谋啮合结果很容易看到的。这点，如果我的软件，我可以与。试图找出这些差异的原因可能有很多乐趣，以及教育。但是，如果我们看看这些数据
， 并说已经很好的协议，这是故事的结尾。没有更多的事情要做！Soooo无聊！

因此
， 假如，我们不会依靠告诉对方我们的专家说，假设我们寻找的错误，而我们没有成功
， 直到我们找到一个错误数目相当高的信心，这里的答案您的问题：

1）目的？为了找到低频率的电感错误。

2）为了谁？主要是出于好奇，别人可能会觉得它很有趣
， 甚至是有益的，但我认为是次要的。如果你想要做的直接的实用的东西，你应该看看其他地方。

3）什么是低频率？

Anything where the current density is close to uniform through the volume of the metal. There are two transition frequencies for microstrip loss, as indicated in my paper on microstrip loss. High frequency is above the higher of the two. Low frequency is below the lower of the two.

4) Yes, DC is low frequency. However, DC is a different problem as the ground plane and any sidewalls have no effect on magneto static inductance. Would be interesting to get a result there. If you can do that, please share it with us.

5) What is the converged value? An example is in the pdf I attached previously.

6) Box size? Given in the pdf I attached previously. You should be able to download SonnetLite and look at the two layer file. All the info is in there, too.

7-12) All box boundaries in this case are infinitely thick and perfect conductor. Top and bottom covers can be lossy and of any thickness but are not in this case. Sidewalls are always PEC as I often state.

Extra comment for 10) Yes we can not get perfect PEC walls in measurement. However, all computer modeling is abstraction from reality. Thus all EM analyses always give the wrong answer. We can never build anything exactly as we analyze it. We can only approximate it. Fortunately, in the case of PEC walls and in the case of many other things that we approximate, we can often get really really close. (I think you know this.)

You can do the multi-sheet model manually, it might be interesting to see if you can duplicate what I did in the previously attached pdf.

Just for the record, I will state my top level viewpoint on this matter, even though I have already done so many times. All the different EM tools (and their models, including both tube-like thickness and multi-sheet thickness) have their advantages and disadvantages and a good designer can benefit tremendously from intelligent use of multiple tools and models. And that includes tools from multiple vendors. I will take issue with anyone that seriously suggests anything to the contrary with regard to any of the available models or any of the available EM tools. I do not consider "puffing" (a standard term of the sales trade) to be serious.

 

[Guest]

Hi, All:

I don't know what "puffing" is. It must be something not related to a technical discussion. However, a well-known fact tells me that, when frequency is approaching DC, the current is approaching uniform in where the conductivity is the same. If there are conductors of finite conductivity and PEC inside a structure, the current will only go in the PEC and it will not go in the conductors when frequency is going to DC. Basically, the current goes in the least impedance path. When the frequency is approaching DC, the impedance of the path is changing and the current is changing too. The changing current distribution results in changing L when frequency is approaching DC.

All my twelve questions asked in my previous posting are related to the above fact. In some sense, before we get all the information about the conductivity, the size and the thickness of strips, the ground planes and/or the metallic enclosure box, we can t find a converged value of L when the frequency is approaching DC. That is the point. The uncertainly in L with frequency approaching DC may not very critical to circuit design due to the fact that the impedance is (j*omega*L) and it is what we are concerned. When omega is small, slight difference in L really doesn't have a significant effect on the impedance. More detail discussion is documented in the Appendix BB of the IE3D 11.5 User s Manual. Interested users can e-mail to me and I can send you a PDF file copy.

关心。

 

[Guest]

"Puffing" is when some one says something like, "Our product is the best!" or something like that. There is no way to prove that it is actually true, and a puffing statement can actually be false with no problem. It is still OK to say. This is very common in sales (in fact, it is expected and almost required), and, to one degree or another, everyone does it. It is accepted practice. Because it is accepted practice, that is something I will not take issue with.

If I read your post correctly, I think you are saying that the current will flow only (or mostly) in the perfect conductor of the box sidewalls and not in the resistive transmission line at very low frequency, and this leaves the inductance entering some kind of non-converging state. Will you please verify that my understanding of your viewpoint is correct?

PS The line I analyzed is actually 104 uM wide. Pdf with 100 uM changed to 104 uM is attached. No other changes.很抱歉，您还没有登录查看此附件

 

[Guest]

Hi, James:

I didn't say that current would only flow on PEC but not conductors with finite conductivity at low frequency. I only said that this is the situation when frequency is at DC. However, when frequency is going down and approaching DC, the current distribution is changing on the ground planes (and enclosure if there is any) as well as the strip. Depending upon the difference in the conductivity, the thickness, the size of the ground plane and enclosure, the current distribution will be different. To get the L at very low frequency precisely, we do need to get the information about the metallics in the whole cross-section of the transmission line. Don't you agree on it?

关心。

 

[Guest]

Jian -- I would like to make sure I understand your viewpoint correctly. I think you are saying:

1) In the case that I described above, DC current flows only on the perfect electric conductor (PEC). At DC, no current flows on the finite conductivity conductor. This is because the PEC has zero resistance and the finite conductivity conductor has non-zero resistance. Current flows where there is least impedance. At DC, least impedance means least resistance.

2) As we go lower and lower in frequency, the current changes from flowing on the finite conductivy metal to the PEC metal and as this happens (as we go lower in frequency) the inductance changes too.

If my understanding of your viewpoint is not correct, please provide more detail.

Also, if there is any part of the proposed problem (conductivity, PEC, geometry, etc.) that is not specified well enough to provide a convergent solution, please tell me. I will immediately provide any missing specifications. If there is any other reason we might not get a well-behaved convergent solution, please tell me.

 

[loucy]

The above convergence study is very interesting. Allow me to cut into the exchanges and raise some questions that might be relevant. 1。

for transmission line with non-perfect conductor, is there a mathematical proof that there exist a unique fundamental mode? 2。

is there a standard/universal way of computing the S-parameters from the current for a transmission line consisting of non-perfect conductor and/or lossy dielectric? 3。

for a fixed set of S-parameters, is the equivalent circuit unique? would we get a different inductance value if we follow a procedure different from the one implemented in Sonnet?

The answer to these questions will affect one's opinions on the numerical results reported in the above numerical study.

my 2 cents: 字母a.

convergence study is a good thing to do, not only for academic reason, but also for designer engineers in practical applications. 湾

the lack of error standard is a weakness of the MoM formulation itself. there has not be a proof that the MoM procedure would converge as one refines the mesh for general problem. therefore one can expect that different implementations (by different vendors or even the same vendor) could "converge" to a different value. Some problem might not lead to a convergent result at all. It can be imagined that the argument on accuracy will continue until some more fundamental problems of the MoM formulation is resolved.

 

[Guest]

Some perceptive questions Loucy. My answers for what they are worth:

1) For EM, we have the Uniquenes Theorem (see Harrington, among others) that states there is one and only one solution to a completely specified EM problem. For the problem as stated above, it is completely specified and there is only one solution. The solution involves many transmission line modes. However, all but one mode is cut-off so all the cut-off modes become what we call fringing fields. Regardless of what you come up with for inductance, or Zo, or anything else, there is only one field solution. This is one reason it is interesting to look at current distributions. They do not depend on how you specify S-params.

2) There is no universal way to get S-param from an EM solution. There is an exact way to do it in a shielded environment as described in our paper on the unification of SOC and double delay de-embedding recently published in MTT Trans. However, no matter how you get S-params, if you have a good EM analysis and a good way to get S-params, you should be able to get an answer and show some kind of convergence.

3) Given a set of S-params, there are different ways to come up with equivalent circuits, and the results will not be identical. That is why I suggested that we could all use Sonnet's way to do it. Using other ways are fine too, as long as if we compare, we all use the same way. At low frequency, all the ways should come up with answers that are very very close. That is one reason to use low frequency for a test case.

Providing my 2 cents about your 2 cents: Yes, MoM is not guarenteed to converge. That is one reason it is interesting to check convergence. The most valuable checks are to see if MoM converges to the exact answer in exactly known problems, like stripline, thick stripline, and coupled stripline. I have published these tests and I have a nice little spread sheet that has the exact solution programmed up for all but the thick stripline case. I will post it if anyone wants it. Other cases for which there are exact answers are the coupled line de-embedded to zero length. I have never seen Sonnet MoM diverge except in cases where more precision is needed or the de-embedding is experiencing one of the well understood failure mechanisms. Given sufficient numerical precision and valid de-embedding, my experience has been that it always converges.

When we don't have an exact answer it is useful to see if two different tools converge to the same answer. If not, then it becomes interesting to figure out why. That is what I was hoping was going to happen here, but I am starting to have my doubts. Gotta go!

 

[Guest]

I have given Jian a few days to confirm that I understood his viewpoint correctly, but a reply has not been forthcoming. I am guessing he has realized his blunder and I will proceed on that assumption.

We are all human and we all make blunders (myself most certainly included), so, as far as I am concerned, there is and should be no shame there. These things happen, that's all there is to it. Best thing to do is to realize it happened, deal with it, then get on with life.

First, yes, it is true, if you have a perfect electric conductor (PEC) connected in parallel with a lossy conductor at low frequency (and DC), all the current flows in the PEC and that will change the inductance. However, for the problem presented, the current flows down the transmission line, and then the PEC sidewalls of the containing box act as ground current return back to the source (ie, port). Thus, the lossy conductor is connected in series with the PEC box sidewalls. The complete current flow forms a loop, an ideal and very stable situation for calculating inductance.

The reason I am making this post is because it seems there is an awful lot of "folklore" that is starting to accumulate about RF design. Some of the folklore is correct, but most of it is just plain wrong. I do not want the incorrect low frequency inductance scenario proposed in prior posts to become part of that folklore.

To set the record straight, for the geometry I described, the low frequency inductance (ie, when current is uniform in the metal of the lossy line) is constant right down to and including DC. All current that flows out on the line from port 1 returns on the PEC sidewalls. It is does not suddenly switch from the lossy line to the PEC sidewalls. It has to flow on both, going down one and coming back on the other.

If people will take the time to think just a little bit, bad ideas will be immediately rejected. All you have to do is imagine building the transmission line and connecting a 1.5V DC battery to it. You will immediately realize how the low frequency current flows.

I shall point out one blunder I made in this thread. I suggested that this problem (low frequency inductance) was of limited practical importance. On this matter I was completely wrong. Note the following article that I spotted while browsing the most recent issue of MTT Trans (I at least glance at every article in every issue of the MTT Trans. when it comes). It seems this problem is of critical importance and has been the subject of extensive research in the VLSI field:

Capture High-Frequency Partial Inductance More Accurately by Gauss Quadrature Integration With Skin-Effect Model
Du, Y.; Dai, W.
Page(s): 1287- 1294

It would still be nice to see inductance, or even resistance, results from any other EM tools for the 200 uM long line at 10 MHz, but I have a feeling that that will not, and perhaps can not, happen.

 

[Guest]

Hy, all

I would like to add my 2 cent to this very interersting thread.

Apart from the wrong assumption on the low freq behaviour of currents in lossy metals PEC I think Jean is correct when he states that the tube model can be complete in that there is no need to take into account for the volume currents. In fact, at least in principle, the well known equivaence principle states that the volume fields (and currents) that are inside the metal can be removed provided that a proper set of electric and magnetic equivalent currents is placed on the metal boundary. These two quantity are related by a sort of "surface impedence" and I think that the Jean dissertation on the diffraction angle proves that, when the imaginary part of Er is much grater then its real part the surface impedence can be computed using the plane wave model.

To be more precise I think that to justify this computation of the surface impedence it is also necessary to assume that the metal thikness is quite higher than the skin depth. In fact, even considering the planar model, it is clear that when the two faces of the metal layer are close, there is a coupling between the related currents which is not taken into account by the "scalar" surface impedance. In the planar case one could easely refine the model to include also this coupling effect but I can not see an easy way to generalize this model to an arbitrary geometry. In the general case one should compute a sort of generalized impedence matrix which relates the tangent E to the electrical current impressed on the metal boundary. In principle the computation of this matrix can be done using a volume solver which meshes the metal volume (FEM, FDTD ..) or also using a MoM solver like IE3D. May be that IE3D has done something to address this problem but the lack af details and the fact that Jean speaks only of the normal diffraction to justify his method let me think that this is not the case.

These considerations let me to think that the IE3D tube model can be appropriate (and probably also very efficient) to deal with a thick metal at a high frequency but probably it is not appropriate for the test case proposed by Rautio. In fact at DC the skin depth is infinite and the simple surface impedence model is not applicable.

Of course the last word is left to a the facts (ieto the comparison of the results of a simulation with a measurement or better with an analytical data).