Experiment issues (electromagnetism)

[Tyler184]

TL;DR Summary

I’m attempting to create an experiment to induce EMF from one coil inductor into another, yet being able to relate my observations with my math I did so I could control certain variables.

Hey guys, for some context, I’m a high schooler doing an experiment as a passion project, my issue today is an aspect of my project.

Anyhow, my ultimate goal is to be able to “remodulate” radio signals by converting them from AM to pulses in a magnetic field strength. While I bet there are many ways todo that, my specific approach requires the use of two inductors relationship via EMF. However, it is important to note, I’m not going straight in and remodulating radio signals just yet, I want to test the theory behind them first. Which is where this experiment is coming from.

The experiment consists of two inductors as previously mentioned, perpendicular to each other (one horizontal and one vertical), and I power the horizontal one to create a magnetic field and then I stop powering it after giving it some time to build magnetic energy and as the current drops so does magnetic field intensity therefore the flux drops and it results in a change in flux with respect to time therefore inducing emf into the second, vertical inductor.

Subsequently, I attached two probes of a MM at the end of the vertical inductor to measure the induced voltage. What I found quite odd was immediately after I powered off the horizontal inductor and began measuring the voltage in the vertical, I measured no induced voltage yet a compass I had on standby, was pointing towards it even as I revolved it around the vertical inductor showing it had its own magnetic field, and the only way it could’ve gotten that was by being induced with an EMF which then would store it as magnetic energy. Compasses are very sensitive unlike an MM so perhaps my MM didn’t catch the induced voltage although the MM was on mV mode therefore it’s unlikely it didn’t catch it cause the emf was probably in the mV range.

One thing I would like to mention as it’s quite important to know, is that I powered the horizontal magnetic field via a short (no resistance) by wiring up some AA’s batteries in series to obtain 7-8 V. I originally had resistors but I found they significantly hindered the strength of the magnetic field, on top of the fact I’m struggling as is to get proper readings with my MM.

Anyway, I attached a picture of my setup so you can see it. The core is a drill bit with a 2000 relative permeability I presume (steel core). The horizontal magnetic field is 175 windings at an estimate, 178mm in length, with a 5mm core diameter. And the AWG of the windings is 22. The vertical inductor is 252 windings, 56mm long, and 2.5 mm core diameter. With a AWG of 30. Moreover, the vertical inductor is held by a magnet in this picture however that was just to hold it for the picture so you can see how it was positioned during the experiment.

Additionally, with the magnet seen in the picture I did a side experiment by taking off the vertical inductor and varying the distance between the magnet and vertical inductor(basically if the magnet is in one hand and the inductor is In the other, just imagine bringing my hands further and closer together). By doing it I was able to develop a magnetic field powerful enough to pick up a small screw. I presume the magnet induced an EMF by varying the magnetic field strength/field flux.

Next, while the inductor still had its magnetic energy stored I decided to use my MM to again measure any possible induced voltage but I measured nothing which confused me. I’ve gone to my teachers who say my MM works just fine and isn’t the issue.

Moreover, my math also isn’t making any sense, as I’m predicting an EMF of 30-0.3V within 5 time constants of not powering the first magnetic field(yes volts, not mV) which is obviously wrong. I feel it would be best to fix the observations first then I’ll further discuss my math as to not make this thread too long.

 

[berkeman]

Welcome to PF.

The experiment consists of two inductors as previously mentioned, perpendicular to each other (one horizontal and one vertical)

You are trying to couple energy between orthogonally oriented coils?

 

[Baluncore]

Young Michael Faraday had similar problems, a couple of hundred years ago.

You have arranged the coils in a symmetrical way, such that the magnetic fields of the two coils do not couple. The magnetic compass is a more sensitive instrument, and is in a better position to detect the field.

If you lay the coils parallel, and next to each other, in an arrangement more like a transformer, you will detect a greater output.

 

[Tyler184]

Baluncore and berkeman, yes I am trying to couple coils perpendicular to each other. It’s part of a larger scheme later on to cause the needle to spin on a pivotal point by introducing a third external magnetic field which causes the remodulated AM radio signal (now stored through changes in magnetic field intensity of the vertical inductor) to vary with space (rotate at certain angle increments thereby converting the magnetic field modulation to mechanical modulation).

The mechanic modulation will then be converted to optic signal modulation. However, I haven’t thought too far with this due to the lackluster results I’ve been getting which I’ve been focusing on. I originally thought this experiment wasn’t going to work at all because most(basically all) coupled coils work in parallel as that’s the way the inductors magnetic fields align (shown through faradays work as you guys mentioned) but my method albeit significantly weaker, has received some results as said before thanks to the compass.

My logic was the emf would drive a current on the edge of the windings similar to how reactance works (when the stored magnetic energy drives a current in the windings opposite to that of the changing current polarity). Ultimately, I believe the main issue is the coil orientation however as of now, this current orientation seems to be the only way to obtain a rotating coil as if they were aligned, the magnetic field of the third inductor would disrupt the original inductor (as it would have to induce a emf that orients the second inductor but would hit the first in the process thereby hindering the radio signals strength as a magnetic field). Although perhaps theres a way that already exists of converting AM to mechanical modulation and then to optic signal modulation that I haven’t seen yet. Anyway, thanks for the feedback!

 

[Dale]

My logic was the emf would drive a current on the edge of the windings similar to how reactance works

And do you feel that your experimental data has supported that logic?

 

[berkeman]

It’s part of a larger scheme later on to cause the needle to spin on a pivotal point by introducing a third external magnetic field which causes the remodulated AM radio signal (now stored through changes in magnetic field intensity of the vertical inductor) to vary with space (rotate at certain angle increments thereby converting the magnetic field modulation to mechanical modulation).

You are not going to spin a mechanical indicator with AM radio (1MHz) or baseband audio (5kHz) frequencies. What are you trying to do in the end?

 

[Tyler184]

Dale; well, I’ve gotten some results from my experiment, just not much to make it anywhere near effective. However as previous said, I don’t know of any way to bypass the issue stated above of the external magnetic field inducing a emf on the first magnetic field if it were aligned with the second one.


Berkeman; my process consists of a radio signal introducing an emf which drives the current in multiple smaller vertical inductors(for this experiment I’m only using one). In the actual device I propose, the vertical inductors would be polarizers and be very light (lighter than the one I’m using for the experiment as this one’s just to measure the emf im employing). Additionally, on each end of the horizontal core would be a radio wave producer (like what garage doors employ for reference). The radio signal would go through go through the wall of polarizers and ultimately be encoded with an optical signal mimicking that of the radio.


Moreover, I understand very well they’re are critical issues with this type of remodulation, two big ones I considered is the lack of information storage (AM has complex data which a physical modulation may not be able to modulate as well). And the possible energy loss along the way, as what I propose is a complex journey from AM to optical modulation. However, I stipulate, by evaluating key points of the AM signal function by employing a certain amount of vertical inductors the same or proportional to that of the amount of key points I want to evaluate, I can recreate the signal to a decent extent through optical modulation. The best analogy of the math I can come up with is changing the limits of the h variable(not 0) in the derivative formula or better yet, the number of intervals in a Riemann sum except obviously in the opposite order (the derivative of the radio function as that relates to the change in flux).


If you would like me to go further and show the math I did (which I mentioned has flaws) to give you a better idea of what I propose I could do that too.

 

[Dale]

I’ve gotten some results from my experiment, just not much to make it anywhere near effective.

As a scientist, what do you conclude when an experiment contradicts a hypothesis?

 

[berkeman]

Berkeman; my process consists of a radio signal introducing an emf which drives the current in multiple smaller vertical inductors(for this experiment I’m only using one). In the actual device I propose, the vertical inductors would be polarizers and be very light (lighter than the one I’m using for the experiment as this one’s just to measure the emf im employing). Additionally, on each end of the horizontal core would be a radio wave producer (like what garage doors employ for reference). The radio signal would go through go through the wall of polarizers and ultimately be encoded with an optical signal mimicking that of the radio.

Sorry, this is word salad. What is your background so far in electronics, electromagnetics and signal processing? We want to help you, but that help will be different if you are a curious 10 year old kid versus a senior in high school...

 

[Tyler184]

Dale; well obviously I know it’s not an effective method as simple vector addition tells you this isn’t valid, however, I got some results (not much though). Furthermore, I don’t know of any other method that follows the conditions I mentioned above of aligning the magnetic fields so unfortunately this is all I’m left with.


Berkeman; my apologies let me try and reword it: My process involves sending a radio signal through an inductor to generate electromotive force (EMF) that drives current through multiple smaller vertical inductors in front of it (though I’m using only one for this experiment). The change of the current of the radio signal with respect to time is represented in the magnitude of the emf which is how the signal is transmitted. In the actual device I propose, the vertical inductors would function as polarizers and would be much lighter than the one used in the experiment, which is only used for measuring the EMF I'm applying. Additionally, at each end of the horizontal core, there would be a radio wave emitter (similar to those used in garage door systems to detect if anything is in the way). The point of this is the radio signal would pass through the many polarizers and ultimately be encoded with an optical signal that mimics the radio signal. Is this better or perhaps should I make a video or draw a diagram of what I mean in case my wording is still very confusing and ambiguous?


As for my background in electronics, I’m a junior in highschool, I self taught some vector calc (mostly curls, divergence, and gradients) and covered some of maxwells equations. Although I haven’t reviewed that stuff in a while and I’m not thorough with it, only a basic beginner so don’t hold me to that standard. Furthermore, I know differential and integral calc to the extent of calc 2 and some calc 3, but I only know basic multi variable equations that were primarily given at a calc 2 level. I’ve also built an AM radio receiver from scratch (although it was a crystal radio which is the simplest of all designs).

 

[renormalize]

In the actual device I propose, the vertical inductors would function as polarizers and would be much lighter than the one used in the experiment, which is only used for measuring the EMF I'm applying.

What exactly is being "polarized"? An electromagnetic wave? A dielectric medium? Something else?

Additionally, at each end of the horizontal core, there would be a radio wave emitter (similar to those used in garage door systems to detect if anything is in the way).

Do you really mean a "radio wave" emitter or is it actually a "light" emitter? In my experience, a garage-door-blockage detector uses an LED source to send a light-beam across the base of the door-opening, where the beam is received by a photodetector. There are no radio signals involved.

 

[Dale]

I don’t know of any other method that follows the conditions I mentioned above of aligning the magnetic fields so unfortunately this is all I’m left with.

And who set those conditions you are following? You or nature? When you have a failed result (and your result is a failed result with fairly clear reasons for the failure), then that is nature's way of telling you that you need to do something different. A successful scientist or an engineer cannot become so fixated on a specific design that you ignore clear signs that it isn't working.

You will simply not get significant coupling between inductors with perpendicular magnetic fields.

Frankly, the approach I would take would be to simply use an ordinary antenna to receive the radio signal, convert that to an ordinary electronic voltage signal, and then use that electronic signal to drive the optical device. The reason those things are ordinary is because they work.

 

[Tyler184]

Renormalize; an electromagnetic wave is being polarized. As for the garage door, I just thought of a quick example of what I propose, your right they probably use LED light beams. I haven’t thought enough or did enough research to consider whether I want to use laser technology or simply radio waves. More likely than not, I would use radio waves but again that can change.


Dale; Do you know of any modulation technique in particular employing what you say of converting RF directly to optical?

Lastly, something I forgot to say in my background although it may be irrelevant is that I have a background making a PMW circuit and briefly studying the inner workings of an electric motor which takes part in the motivators that made me come up with this idea.

 

[Dale]

Do you know of any modulation technique in particular employing what you say of converting RF directly to optical?

Sure. The general category is called amplitude intensity modulation.

https://en.m.wikipedia.org/wiki/Intensity_modulation

You are specifically looking for RF over fiber.

https://en.m.wikipedia.org/wiki/Radio_over_fiber

 

[DaveE]

the vertical inductors would function as polarizers

What? How?
I'm pretty confused about what you are trying to do, so this might not apply. But, EM waves are linear in nature and obey the principle of superposition. This means they don't really interact in free space, they simply add together at each point in space. The waves are unchanged and pass through each other. One EM wave will not polarize or modulate another. If the waves are travelling through a non-linear medium, there will be some interaction between them.

 

[Tyler184]

Dale; so I’ve been taking a while(basically the whole day) to respond as I’ve been reviewing the resources you’ve provided and going back to the drawing board as you had suggested. I know the existence of pulse code modulation however the medium of optical fiber I didn’t know. I’ve thought of a new way to redesign my experiment and please correct me if this is wrong. I’m sure my explanation isn’t enough so view the diagram as needed for your reference.

Now to explain the diagrams: Instead of making the vertical polarizers perpendicular to the horizontal magnetic field, this magnetized needle (basically a compass needle) with a polarizer imbedded in the middle of it is in the same direction as the horizontal magnetic field. The needle is held up by a hollow rod that also holds up two other inductors, one behind and one in front of the magnetized needle.


The inductor I labeled as “varying inductor” is where the rf signal will go and it will reproduce the varying magnetic field as described. In the experiment I would use this in, I wouldn’t send rf signals but let a magnetic field decay to represent a changing magnetic field strength. Anyhow, this magnetic field will attempt to align the magnetized needle with its magnetic field. In this experiment I need to have the needle have a neutral position, to differentiate and classify different magnetic field strengths which is where the second inductor labeled the “neutral inductor” comes into play.


Basically, my logic is, since I plan to modulate the signals based on em wave polarity, I need the needle to turn in order to rotate the polarizer imbedded in its center, however, what I noticed was that it would not rotate as an inductor began slowly losing its strength once unpowered. This was due to its sensitivity making it impossible to know when the magnetic field strength is at its max or min. Therefore the neutral inductor induces an opposite magnetic field to that of the varying inductor, not necessarily to cancel it out but to apply constant force in the opposite direction to cause the needle to rotate in the tug of war between the two inductors.

The laser or LED beam would go through the changing polarizer and into an optic fiber which comes back to me so I can observe the polarization of the laser with the naked eye.

Again, this might be wrong and unknowingly to me might be silly as I might’ve overlooked common flaws with it, but a different approach is better than forcing an inefficient existing one as you had mentioned.


Ultimately an issue I hadn’t previously mentioned that comes with modulating polarity is the many refractions that occur especially in the optical fiber that can disrupt and change the polarity (which is the main reason polarity hasn’t been modulated). However, after this experiment described above, by describing the em waves as photons rather than waves, I suggest we could use a photo multiplier to significantly increase the sheer number of photons which will then be polarized thereby increasing the insurance in case some photons are refracted. I’m not sure if this would actually work however it’s a theory beyond the experiment.


DaveE; if I understand you right, then you think I want to have em waves modulate each other in a way where em waves interact with free space. However I plan to use a physical polarizer (as described above) to modulate the signal.

 

[Dale]

That is good. It is an important skill to go back to the drawing board in response to test results.

 

[Tyler184]

Dale, Is the concept good?

 

[Dale]

Dale, Is the concept good?

I have no idea what you are trying to accomplish, so I cannot judge if the concept is good or not. It seems like maybe you are trying to get a needle to point in the direction of the magnetic field of a radio wave. But I am not sure.

 

[Tyler184]

That is what I am trying to accomplish.

 

[Fred Wright]

For what it's worth, you can modulate a solid state laser by making its power source voltage proportional to the modulating signal voltage. No coils or weirdness involved.

 

[Dale]

It seems like maybe you are trying to get a needle to point in the direction of the magnetic field of a radio wave.

That is what I am trying to accomplish.

So, the problem with that isn't the device, it is the thing you are trying to accomplish. A fairly low radio frequency is 500 kHz. The direction of the magnetic field can change that fast. To point a needle with 1 cm radius in the direction of the magnetic field would require that the tip of the needle could go about 31 km/s. This works out to something like 90 times the speed of sound.

If you polarize the incoming wave, then the magnetic field will change direction about once every microsecond. So, you would have to be able to flip the direction of the needle in a microsecond. That will be similarly tough. I think it would be difficult to even build a needle that could withstand those forces, let alone a mechanism to deliver them.

Would it be sufficient to record the data and play it back at a lower speed later? Or alternatively would it be sufficient to detect much lower frequencies (eg 10s of Hz to low 100s of Hz)

 

[Tyler184]

Fred; well yea I could do that, I did some research in that, here’s a link of a video I found about it: Link. However that’s not my goal of this experiment, my goal is to test my proposed type of modulation (polarity modulation). It is quite weird but I want to ensure it’s not wrong.

Dale; you’re right, that is a critical issue in modulation I hadn’t thought of. Perhaps my mechanism could slow it down and play at a slower speed as you mentioned by using bytes in the same way pulse width modulation does: by assessing certain voltages with certain 0’s and 1’s but with my modulation technique it would be with specific angles. Although for this experiment it’s just testing to see if the needle would spin properly and I observe laser pulses on one end of the optic fiber

 

[renormalize]

However that’s not my goal of this experiment, my goal is to test my proposed type of modulation (polarity modulation).

In addition to the more common modulations AM (amplitude), FM (frequency) and PM (phase), there exists a fair amount of literature on PoM (polarization modulation). From what I gather though, mechanical methods like you are proposing are not practical. Instead, devices like electro-optical modulators and metasurfaces (2D metamaterials) are used to rapidly switch polarizations. For example, here's the abstract of recent paper on PoM as applied to wireless (https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202103379):

Polarization Modulation for Wireless Communications Based on Metasurfaces
Abstract:
"As an alternative to conventional wireless communication techniques that use amplitude, frequency, and phase modulations, polarization modulation (PoM) provides an additional degree of freedom for the modulation of carrier waves and allows the realization of simple transceiver designs. PoM also enhances physical-layer security in wireless communication systems owing to its vector-attribute and direction-dependence features. In this study, a prototype of PoM wireless communications based on a digital coding metasurface that can dynamically control the polarization of electromagnetic waves in a certain frequency band is demonstrated. The binary digital signals can be encoded on the optical rotation states of the circularly polarized beams through the real-time control of the bias voltages applied on the metasurface and successfully decoded at the receiving end. Because the metasurface is separated from the emitting antenna, the design can simplify the setup for multichannel communications and provide more flexibility by setting the emitting antennas at different operating frequencies at any time."

 

[berkeman]

However that’s not my goal of this experiment, my goal is to test my proposed type of modulation (polarity modulation). It is quite weird but I want to ensure it’s not wrong.

It's very good that you are thinking creatively and doing the math and doing experiments to test out your creative ideas. In this case, though, there are reasons that polarization angle modulation would be a poor choice for many communication channels.

Can you think of some reasons why RF (or optical) polarization modulation would have serious limitations in real channels? Each form of modulation has advantages and disadvantages, especially with respect to communication channel characteristics. For example, RF FM has some advantages over AM in many real-world channels, which is why FM radio music quality is usually superior to AM radio music quality. Can you think of (or find with a Google search) what problems RF AM might have in the real world communication channel between the transmission (Tx) tower and your receive (Rx) antenna on your car?

 

[Tyler184]

renormalize; unfortunately I don’t have access to the whole research article to read their work so I could only read the abstract. However, I do agree with you that the use of metasurfaces is likely more efficient than my mechanical method. Perhaps I might involve metasurfaces in a second experiment and research them more. However, I feel it’s too complicated for a start. For a start I would like to create my proposed experiment and see the results as it’s much more simple than using meta surfaces to calculate certain angles. Do you guys agree?

Berkeman; your right that this form of modulation has its flaws in efficiency for communication with respect to other forms such as AM or FM. However, it can have its advantages, one such one I forsee although I might be wrong is its rigid properties of polarity allow the information to be stored that can’t be attenuated with distance (it would still lose strength as it’s still an em wave but its information isn’t stored in its strength so its signal isn’t hindered) unlike other forms of modulation. However, it could lose pieces of information through refractions however a photo multiplier would provide the insurance to lose some pieces of information.

 

[Dale]

Why don't you make two antennas, enclose each in a polarizing filter of opposite polarity, and acquire/produce two signals, one for each polarization?

 

[Tyler184]

Dale; I mean I guess that polarizes rf signals but what does it accomplish? Cause I want to begin experimenting with polarity modulation but just polarizing rf signals doesn’t mean I’m modulating any signals. I feel like what I proposed, as long as it’s not completely wrong which from what I’m getting at it’s not, is a good first experiment.

 

[DaveE]

OK, I'm still a bit confused about much of this, but you seem to now have a laser to either modulate or measure? If so, spend a bit of time reading about these real world devices that would be used for this. But be forewarned, it's not easy and not cheap. The people I worked with in industry that designed this sort of thing ALL had PhDs in physics. There are other E-O modulator types for AM, these are the the common ones for polarization rotation, you can buy some of these off the shelf (Thor Labs, for example).
- Pockels cell
- Kerr effect
- Faraday effect
Note that in each case the device will most often have a special material (crystal) to mediate or amplify the effect (LiNbO₃ is a common choice).

While it's great that you are so interested in these experiments, often the best way to succeed in the lab is to first learn the fundamentals and research what others have done before. What you are trying to do is hard enough, even if you don't have to invent it first. Recognize going in that it is unlikely that you are trying something that will work well that someone in industry or academia hasn't tried and published before (Bell Labs comes to mind). It is quicker and easier to read about their work than do it yourself.

PS: You'll also want to know about polarization preserving optical fibers. The cheap stuff won't do.

 

[Dale]

I mean I guess that polarizes rf signals but what does it accomplish? Cause I want to begin experimenting with polarity modulation but just polarizing rf signals doesn’t mean I’m modulating any signals.

Well, you haven’t described your modulation scheme in sufficient detail for me to suggest more. But with access to the two polarization channels you should be able to shift and mix the signal to achieve whatever scheme you have in mind.

That said, I am not an expert on this topic. I work in MRI, and while phase is important polarization is not. Since our RF magnetic fields are all in the near field I am not even sure polarization is meaningful.

 

[Tyler184]

DaveE; I don’t have a laser as of now but I plan to buy one soon for this. I completely agree this is a complex field, I for one, don’t know much in the grand scheme of physics let alone specific niche fields such as optics. I reviewed the three optic phenomenons you linked, and to be quite frank, Pockels effect and Kerrs effect seem to be more complicated than the Faraday effect. Mostly because the math wasn’t linked so I was going purely based off visuals alone and it seemed like it involved a lot of complex geometry which obviously is beyond my scope. Fardays law seems aswell, however the concept makes a bit more sense as it’s more similar to my own experiment. So correct me if I’m correct in my interpretation; the faraday effect is when a linearly polarized light (that is interpreted as a superposition of opposite polarized circular light for our purposes) goes through a transparent medium that has its own magnetic field somehow although I don’t understand how, but it does and the magnetic field of the transparent medium interacts with the em wave such that on the other side there’s a polarity change labeled β; and depending on the specific circular polarity you were observing(left or right), it appeared to move clockwise or counterclockwise.


Regardless if I interpreted it right or not, I feel it’s best for me todo a first experiment getting used to optics then studying theory and improving my experiment from there rather than deeply studying theory and then attempting to make a complex design without prior experience. I’ve done what your describing with my AM radio and it was a complete disaster as I studied a lot of theory without ever having practical experience and making a simple crystal radio proved to be challenging. That’s why for this one I want to try some of the practical stuff people have already done then I study the theory in as much depth as I can understand. From there I will improve the original experiment. Also, for this experiment could I use this optic fiber and this thin film as a polarizer: fiber optic, polarizer. This article says thin film polarizers can polarize lasers which is where I got it from: Link. For future reference I want to try and add photo multipliers to eliminate the need for expensive polarity preserving optic fiber, as, my logic is the sheer numbers of photons could outweigh the ones that are refracted although then again, that might not work.

Dale; good point, if you want I could make a video explaining things? What you offered is a pretty decent idea but I feel with the trajectory this is going (deeper into optics), the idea of simply producing only horizontally or only vertically polarized light without modulating it to carry a specific information could be a bit sidetracked although correct me if I’m wrong as regardless of your background, you still have much more experience and knowledge in this field then me I’m sure.

 

[Dale]

simply producing only horizontally or only vertically polarized light without modulating it to carry a specific information

To be clear, I am not suggesting that you should stop where I did and only do that. I am suggesting you could start there. Then you can modulate/demodulate at that point using whatever polarization modulation scheme you have in mind.