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Friday Fun: What is your favorite wavelength? August 2, 2013

Posted by mareserinitatis in electromagnetics, Friday Fun, physics.
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I want to know everyone’s favorite color…by their wavelength.  If you need help, here you go:


My personal favorite is right around 400 nm.  And it’s entirely for aesthetic reasons.

So what is yours and why?

(Yeah, I know…everyone is going to pick some non-optical frequency.  And yes, you have to stick to photons.  Maybe we can do sonic waves another week…)

Wordless Wednesday: Coming unglued July 31, 2013

Posted by mareserinitatis in electromagnetics, engineering, photography.
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Does this make me multilingual? July 16, 2013

Posted by mareserinitatis in computers, electromagnetics, engineering, grad school, math, physics, research.
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I began my programming education quite young and have maintained my skills over the years.  I have recently been thinking of documenting some of the various languages and software programs I’ve learned to use, so here is as good a place as any.

  • 4th grade – TI Basic
  • 8th grade – Logo
  • 10th grade – BasicA and Apple Basic (pretty close to the same thing)
  • 12th grade – Fortran and QBasic (these were at the college)

In college:

  • took a class on C and had to learn unix, too
  • learned Maple in a calc course
  • learned matlab for a research project and used it extensively in a numerical analysis course
  • learned mathcad for a physics lab course
  • learned mathematica for intro to differential equations and used that for many other classes

During my MS, I was exposed to half a dozen software packages for computational electromagnetics modeling (half of which are trademarked, so I’m not going to bother listing them).

In the past couple years at work, I’ve gotten pretty handy with Scilab.

After all of this, you would think that I have a pretty complete toolkit.  I should be able to do pretty much whatever I need with what I’ve already learned.  I find it ironic, therefore, that I am back to using Fortran (one of the first things I learned).  I also have been spending the past month trying to learn IDL (which, if you don’t mind me saying, seems like a less friendly version of matlab), so there is something new, again.  Also, I have people pestering me to learn python.

Looking at this list, I’m starting to think I’m learning things so that I can simply forget them again later.  I’m pretty sure I’ve forgotten more than I remember.

Repost: The varied and graphically-intensive world of nomograms March 3, 2013

Posted by mareserinitatis in electromagnetics, engineering, geology, geophysics, grad school.
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I spent a good chunk of time yesterday dealing with Smith charts, and I remembered in the recesses of my brain that I had once posted something about them in the old blog.  Sadly, it wasn’t as technically intensive as it could have been, but I still decided it was fun enough for a repost.  If you would like to read something with a bit more technical content, you can check out Fluxor’s post on Smith charts at EngineerBlogs.

A nomogram is an incredibly useful tool. It is a visual “solution” to an equation. Usually it is some sort of chart or plot that allows you to figure out “what you’ve got” and you can move from there to “what you need”.

Anyone who works on the analog side of electrical engineering often gets to play with Smith charts, which were of course invented by Baker*. They’re rather confusing looking things:

The usefulness in Smith charts is that they can allow you to determine things like how much more transmission line you need to get an impedance match in your device. Rather than trying to solve an equation using complex values, you can just move along the curve in a Smith chart. (Disclaimer: While I learned how to use Smith charts in my microwave engineering course, I unfortunately would need to spend some time with my buddy Pozar to remember how to do it now.) I’m also aided in my negligence by the fact that there are a lot of nifty software programs that will compute the necessary values, reducing the necessity of using a Smith chart. (Thank goodness for computers. If it weren’t for computers, I’d probably have to learn how to use a slide rule, too.)

What brought this up is that I was introduced to a nomogram used by scientists in the field of paleomagnetism. The nomograms in this case showed relationships in demagnetization of magnetic minerals. For instance, if you have a mineral that has been exposed to a temperature of 400°C for 1000 seconds in the lab, you can follow the line on the nomogram and discover that the same amount of demagnetization could be caused by sitting in a temperature of 350°C for 100 million years.

So why do I spend time mentioning this on my LJ? Could it be because knowing that there are graphical methods to approximate solutions to problems is good to know? It is good to know, but it’s not why I bring it up. The reason I felt the need to post about it is because I had an entirely different picture of nomograms when I was sitting in class:

tastee nom-o-grams


*Just kidding. It was developed by Phillip H. Smith.

Repost: Microwave Unsafe or Unsafe Microwave June 22, 2012

Posted by mareserinitatis in electromagnetics, engineering, food/cooking, science.
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(Note: this is from the old blog, back when living in Minneapolis)

There’s nothing like a nice, hot cup of English Breakfast or Earl Grey in the morning…until you reach into the microwave and burn your hand on your mug.

I’ve noticed something very irritating. Since I moved into my new place, all of my dishes get hot and some of them have cracking glaze after use in the microwave. The most irritating thing, aside from the pain, is that I’ve noticed my favorite mug is expanding and shrinking. It expands when heated and then contracts as it cools. This, unfortunately, has caused my tea basket to get physically stuck in the mug, which never happened with my old microwave (thus eliminating the notion that heating of the basket causes it to expand and get stuck).

Traditionally, this means that my dishes are not “microwave safe”. In other words, there is something in the dishes that heats up when put in the microwave. That means that you can destroy the dishes and burn yourself.

It wouldn’t be that big an issue except that all of these dishes worked fine in my other microwave back in Fargo.


This has led me to look into what might be causing the problem. Hypothetically, if something is microwave safe in one microwave, it should be that way in all microwaves.


There are lots of places that give you the basics of how a microwave works. A brief overview is that it emits electromagnetic waves which cause water molecules in food to rotate. The frequency of most commercial microwaves for the home is around 2.45 GHz, which is apparently a good frequency to get water molecules to “flip”. Flipping, rotating, shaking are all ways that molecules move, and molecular movement translates into heat. So the microwave makes all these water molecules do their jig because it excites them at just the right tempo. If you try exciting them at a different frequency or tempo, the water molecules won’t respond as well.

It’s harder to find information about how microwaves create these fields. It turns out that they generate electromagnetic waves with something called a magnetron. (An excellent and quite detailed description of how they work can be found here. According to The Art of Electronics, magnetrons fall under the category of “exotic devices”. This is probably code for “uses an electromagnetic field in a non-obvious way” or maybe “doesn’t always use silicon to do its job”. Interestingly enough, these are the same devices used to create fields for radar, including the Doppler radar that is used to look at cloud cover and precipitation. (If you’re a Wunderground nerd, like me, you spend a lot of time looking at images generated by Doppler radar.)

Again, I’ll summarize. There is a cathode (something which generates electrons) running down the middle of a cylindrical chamber. The chamber is subdivided into resonant chambers. Resonant chambers are areas where electromagnetic energy creates a standing wave. (A good though not exact analogy from sound, which is also a wave, would be an organ pipe.) The electrons formed around the cathode form into groups which spin and sweep past the resonant chamber openings. Because moving charge creates an electromagnetic wave which becomes a standing wave in the resonant chambers. This wave then creates a current in a wire or “feed”, which conducts a current to a waveguide. A waveguide is basically a replacement for a wire. It conducts an electromagnetic field when the power is too high or you could easily lose too much power through a wire. (Wires can be awfully lossy.) All it looks like is a rectangular tube, but the size of the tube is important because this will determine the frequency of the waves it can carry. (Remember, we want to have things pretty sharply focused at 2.45 GHz.) This tube leads into the microwave chamber which is tada! a Faraday cage. This is something that will contain electromagnetic energy inside of it without letting it escape as well as keep electromagnetic energy from your surroundings out. In this case, we want the energy inside. Waves which don’t hit our food will hit the side of the chamber and bounce around until it hits the food.

That metal screen is part of the Faraday cage and is keeping your brains from being baked when you’re pressing your nose to the glass going, “When will it be done?!”

Many microwaves contain things that look like fans but are actually “mixers” or “stirrers”. They cause the waves to bounce more randomly and create a more even distribution of the waves for heating. When the waves hit your food, they can only penetrate to about an inch. How far the wave goes into the food is quantified by something called a “skin depth”. Because your food isn’t a good conductor (like copper) which has pretty much no penetration depth, you will often notice that things get hot on the outside but not on the inside, like often happens to me when I reheat lasagna.

Food is also not a pure dielectric (like air or styrofoam) where the wave passes through and can’t generate a current inside. Food which is more conductive (which will likely have more water) will tend to heat up better or faster (as well as internally distribute that heat better) than food that doesn’t. Conductive food will also tend to have more water. In this case, you may be heating up a fruit-filled pie. The pie filling has a lot of water and will heat up fast, but the crust doesn’t and doesn’t seem to get as warm. You bite in, expecting the filling to be the same temp as the crust but end up getting burned instead.

People who design fast food meals ought to consult with microwave engineers on optimal heating set up. :-)

As I mentioned before, microwave safe dishes don’t contain anything that will heat up when exposed to microwaves. Dishes which aren’t microwave safe contain some molecules that will be able to rotate, twist or vibrate in some way similar to water, causing the dish to heat up.

Sometimes you have dishes which are “thermally conductive”…that is, they transfer heat well. While you’re heating up your food, the dish is pulling a lot of that heat away from the food and into itself, causing the dish to get hot.

However, that doesn’t seem to be my situation. My previous microwave was much a higher power and seemed to heat up the food fine without heating up the dishes. My current one seems to do nearly the opposite. And since these are the same dishes, I have to conclude that it is in fact the microwave with the issue.

My first guess is one that doesn’t seem plausible. I don’t think it has anything to do with the size/shape of the magnetron or waveguide. Those are fairly large objects that can be mass constructed well within tolerances. I could be wrong, but that’s my initial guess. This also minimizes the chance that there may be some sort of mismatch between the magnetron and the waveguide.

Looking at the remaining possibilities, I’ve come up with three.

The first is that my microwave is poorly designed in the sense that it doesn’t direct electromagnetic energy well. This may be part of the problem as it seems to heat the dishes in areas away from the food. I don’t think that this is the entire issue because, if designed poorly, the wave should just bounce around until it hits something with high water content. However, I can’t say it’s not doing this.

There are two other possibilities. It turns out that magnetron frequency can change both with the temperature and the current through the cathode. Although the cathode temperatures get pretty high, I doubt that it would be that huge a change from a prototype once it gets over the initial change.

The last option seems most likely to me: the cathode isn’t working exactly the way it’s supposed to (which can be characterized by something called a “pushing curve”). If the current from the cathode is too high or too low, this will change the way the electrons behave, which will alter the frequency of the wave being generated by the magnetron.

In doing some research on my microwave, it turns out to have a horrid reputation. They die a lot, like within a year. Unfortunately, they’re so cheap that it’s not worth it to send them in for repairs because you have to pay for shipping to and from. When microwaves die like this, a lot of times it can be due to power problems, and thus the design of the controlling electronics or the high voltage power system can come into play. (Did I mention that magnetrons require huge voltages to operate???)

It appears that perhaps this line of microwaves may not have the best electronics design, and for whatever reason, the power into the magnetron isn’t quite right. This is causing my dishes to heat and expand while not heating my food optimally.

I guess I’ll be using oven mitts to take everything out of there until it decides to kick the bucket.

When I was at the conference… March 13, 2012

Posted by mareserinitatis in electromagnetics, engineering, physics, research.
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When I was at the conference last week, I had one fellow come up and look at my poster.  He is working on a similar problem but in a different application, and he made some comment about how he definitely thought what I was doing had merit.  (After seeing his talk, it made sense because he was trying something similar.)

However, we spent about 20 minutes arguing as to what we thought was going on in one of my plots.  He kept suggesting something that I had ruled out with experiment.

Tonight I’m looking at papers on some theory related to this project, and I think I have managed to find the answer to that mysterious plot.  Sadly, I was way off in my explanation, but I have to admit that apparently I wasn’t the only one.  The fellow I was arguing with had it wrong as well.

The real answer appears to be way cooler than either of us thought.  I love physics.

Time to get out of the lab November 3, 2011

Posted by mareserinitatis in electromagnetics, engineering, humor.
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I received a card in the mail from a friend.  When I opened it, and without reading it, my eyes feel on the letters Zo.

My first thought was, “Characteristic impedance?  I didn’t know she was interested in electrical engineering, let alone transmission line theory.”

Upon closer reading, I discovered she was actually making a reference to her daughter Zoe.

I think I need to spend less time around electrical engineers.

The force is weak with this one… June 16, 2011

Posted by mareserinitatis in electromagnetics, geology, geophysics, physics, science.
Tags: electromagnetic energy,

I had an interesting question from someone today: why do we use electromagnetics to study so many things?  Why can’t we use gravity or something similar?  Specifically, they were wondering about non-invasive methods for studying the human body.

It’s easiest to start with Newton’s Law of Gravitation, which tells us how much gravitational force one object (M) exerts on another (m):

and Coulomb’s Law (which explains the force of attraction between electrical charges, Q and q):

If we want to find the ratio of gravitational force to electrical force, we end up with something like this:

Now, let’s imagine we’re just looking at the gravitational and electrical forces between two electrons from 1 m away.  We use G=6.673•10-11 m3 kg-1 s-2 (the gravitational constant), M=m=9.11•10-31 kg (the masses of the two electrons), εo=8.854•10-12 C2 kg-1 m-3 s2 (the permittivity of free space, although may be just as easy to think of it as an electrical constant), and Q=q=1.602•10-19 C (this being the charge of an electron).  Using these values, all our units will disappear, which is good because we’re looking at a ratio of two forces and shouldn’t have any units, and we end up with a value of about 2•10-43.

What this means is that the gravitational force is 43 orders of magnitude smaller than the electrical force…or you could put a decimal point with 42 zeros and then a 1 behind it, and that’s how much smaller the force is.  When it’s already difficult to measure current values that contain many, many electrons (as compared to the two electrons we examined), it’s going to be impossible to find something that exerts a force that is 43 orders of magnitude smaller than what we can already pick up.

You can pick up small changes in gravitational forces when talking about large geophysical features – like ore deposits and mountain ranges.  In fact, they use this principle a lot in exploration geophysics, where they use gravimeters to look for mineral resources.  Our bodies are less sensitive than that, though, and can only pick up gravity when we are talking about changes in the size of planets or moons.  However, we are sensitive to changes in acceleration, so you can feel changes in gravitational pull when riding on an elevator, but that is because the change is both fast and of a reasonable size.

Anyway, the huge difference is why we are permeated (ba dum ching!) by devices that detect and use changes in electromagnetic radiation but not in gravitational energy.

The Widget Revealed May 18, 2011

Posted by mareserinitatis in electromagnetics, engineering, research, work.
Tags: rfid,

Yesterday, NDSU filed the provisional patent on my widget.  This means I am provisionally an inventor, according to the USPTO.  I think that no one can ever again question my engineer cred.

Okay, not really.  What it really means is that I can talk about it now without worrying anyone else will take the idea.  However, I also have a paper in the works (which, once I finish fighting with LaTeX, will be submitted shortly), so I won’t bore you with the details.

The widget, if you’re curious, is an UHF RFID tag that works on metal, using the metal surface for its antenna, and it’s about 2 mm thick.  (Commercial tags for metal are about 2-3 times this thick, minimum.)  The goal we’re working toward is, of course, a flexible, paper-thin antenna that will work on metal.  I actually think that’s doable, but I can’t say for sure how long it’ll take.  (And I’d be wrong if I guessed, anyway.)

So that’s the gist of it.  Details will be in the paper…whenever and where ever I manage to get it published.

Sterred, not shaken March 15, 2011

Posted by mareserinitatis in electromagnetics, engineering, grad school, physics, science.
Tags: fields, , radians, spheres, steradian, stiridian

A couple years ago, I was taking a class, and the professor put up a slide talking about stiridians.

What the heck is that, I thought?

It turned out that it was a misspelling.  Apparently one of the references my prof chose happened to use that misspelling, and he had merely copied it.  After class, I tried to politely let him know his error.

So what the heck is a steradian, anyway? And how would I know such an obscure word?

In order to understand what a steradian is, we should step back and look at it’s one dimensional analog, the radian.  (Because I’m using an analog, I believe that qualifies me as an analog engineer!)  If you’ve had trig, you’re familiar with the radian: it’s an angle in a circle that creates an arclength equal to the radius of a circle.  For those of you who prefer Babylonian Units, one radian is approximately 57.3°.  Graphically, it looks like this:

When you work with antennas, you generally have to work in three dimensions (unless you get lucky and have an axis of symmetry).  The reason we need three dimensions is because we’re working with both electric and magnetic fields, both of which are vector quantities and change within a sphere.  As an example, this shows the fields for a dipole antenna:

The electric field direction is in blue and the magnetic in red.

It turns out that when we’re describing these patterns, it’s useful to think of the surface of a sphere.  We need to describe where the field is strong or weak over that sphere.  Unfortunately, using a two dimensional measure of angle is inadequate for a field.

This is where the steradian comes in.  If we want to describe an area of strong field, we can describe it’s span in steradians.  This is a measurement of ‘unit solid angle’ – although it’s easier to think of in terms of the area of a sphere.

A steradian is the area equal to the square of the radius of the sphere.  That’s it! There are 4π steradians on the surface of a sphere (similar to the 2π radians in a circle). And you can imagine that this is what it looks like:

Also, like a radian, the steradian is a unitless measure, but you can annotate it using sr (much like some people indicate radians with rad).

As I mentioned, I used this in antennas, and I actually wrote an explanation in my MS thesis.  So, obscure as it may be, I had actually spent a bit of time dealing with the topic. And now that you all know about it, I sure hope that professor corrected his notes lest one of you sees it.


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