Make oscillator, that can generate an electromagnetic field in the near field

Thread Starter

Matteo2

Joined Feb 8, 2024
1
Good evening aac, I'm new to the forum and I would like your support regarding the construction of a simple circuit. I would like to build an oscillator that can generate an electromagnetic field in the near field. I read many previous answers but I didn't find anything, my circuit therefore involves a 12 V battery, connected to a solenoid (temporary choice), with a high frequency to be able to reduce the overall dimensions. I need it as teaching, I hope you can help me guys, thanks
 

KeithWalker

Joined Jul 10, 2017
3,096
Your description is rather vague. What , exactly, are you proposing that your device will do? There are many solutions to producing an alternating magnetic field. How powerful should it be? How should it radiate its energy - focused, planar, spherical or other? Please include any other details that may help us to make meaningful suggestions.
 

Wendy

Joined Mar 24, 2008
23,427
High power oscillators are fairly easy to make, we need to know the end use for it to be of any help. Or in other words what Keith said.
 

MisterBill2

Joined Jan 23, 2018
18,538
You want an oscillator to generate a magnetic field with an unstated magnitude and an unknown frequency.
So let us know the frequency and how strong a magnetic field and there will be several designs to choose from. AND a bit about the intended application will help a lot.
 

Wendy

Joined Mar 24, 2008
23,427
OK, in a bit read that as in a day or so I will provide a schematic of an oscillator that can drive very low impedance coil, I will probably news 400 Hertz because that is the nearest real AC frequency in use (aircraft). It is also low enough in frequency you might be able to use it OK in magnetic coupling.

If we could make this coil resonant with a known capacitance it would be helpful. I will draw it in there do you have a way of measuring an inductance or frequency? Many newer DVM's come with a built in frequency counter.

How deep is your electronics knowledge?
 

Papabravo

Joined Feb 24, 2006
21,225
You should be mindful of the fact that the FCC might take a dim view of you experiments. If they do contact you for any reason, my advice would be to cooperate fully and disclose whatever they ask for. Federal judges are know for imposing harsh penalties on willful violations of the law, and they tend to go easier on unintnetional violators who cooperate in their investigations.

Alternatively you could get yourself an amateur radio license and experiment to you hearts content in full knowledge of the law and compliance with the same.

What exactly is your risk tolerance profile?
 
Last edited:

MisterBill2

Joined Jan 23, 2018
18,538
These two posts relate to the same questions that I posed, which were about power level and frequency. I doubt the FCC would have any issues with a 300 HZ power oscillator, as I have not even heard of issues with the foolish experiments of wireless charging of electric cars.
Consider that a ten kilowatt radiator coupling to a pickup coil with 90% efficiency is still radiating a whole thousand watts elsewhere. The know that with less power than that, Ham radio operators can communicate all over the world. My point being that energy fields do not suddenly diminish with convenient border lines.
 

KeithWalker

Joined Jul 10, 2017
3,096
Am I missing some posts on this issue? The only information I have to work with is in post #1. He doesn't mention aircraft, frequencies or wireless charging.
 

Wendy

Joined Mar 24, 2008
23,427
Let's not go off topic, I was the one who mentioned 400 Hertz. I was aiming for a frequency that is both easy to control and low enough you are not going to be transmitting any objectionable radio frequencies.
 

Wendy

Joined Mar 24, 2008
23,427
If the coil is too small it will blow the 555. But it is the bare bones basic if you wanna delve deeper into this concept I will be forced to design for a small coil again if you can set up a resonance things would go much better:

Basic 555 oscillator.png
frequency for the 555 oscillator is determined by the formula f=.7/RC .or 1.0KHz in this case (I hold one of my stock drawings and modified it. If I was truly designing this from scratch this is not how I would do it again I will probably post that later once we get more information from the thread starter.
 

Wendy

Joined Mar 24, 2008
23,427
What is the strength of the magnetic field that is produced from the square wave into an inductor?
Is that question to me? at this point it is theoretical until the TS gives us more info, funny thing is I've been thinking of running similar experiments.
 

MisterBill2

Joined Jan 23, 2018
18,538
What is the strength of the magnetic field that is produced from the square wave into an inductor?
It would be a challenge to "feed a square wave into an inductor", because of the nature of inductance tends to delay current change as the applied voltage increases.
A sort of approximation can be seen in a class "C" RF power amplifier, which is a very non-linear device. Of course, in that case the inductor is paired with a capacitor and the result is a sine-wave is developed at the resonant frequency.
AND THEN, given that the magnetic field is produced by the current, not the applied voltage it would take a massive applied voltage to sort of produce a square wave current and magnetic field. THAT might not even be possible in theory, much less in fact. Consider that V= L x dI/dT, and for a square wave the dI/dT goes toward infinity (which is a very large number)
 

Papabravo

Joined Feb 24, 2006
21,225
Is that question to me? at this point it is theoretical until the TS gives us more info, funny thing is I've been thinking of running similar experiments.
Yes, I was wondering if you had done any calculations to give the TS if he ever comes back. If you were to say 50 mT and the TS wants 500 mT then you would have to go back to the drawing board.
 

Wendy

Joined Mar 24, 2008
23,427
The first step is the design of the coil, is it an air wound or a solenoid? Can the TS tell us it's inductance?
 

MisterBill2

Joined Jan 23, 2018
18,538
The first step is the design of the coil, is it an air wound or a solenoid? Can the TS tell us it's inductance?
I would suggest that a very early step in the design of a coil is to know the frequency range and the power level it is intended to operate at. Toroid coils are known to be fairly self-shielding and so will not produce much external magnetic field.
Without knowing the desired frequency there is no way to guess the inductance.
So until the original poster answers the questions there is no reason to make random guesses.
 

Ya’akov

Joined Jan 27, 2019
9,169
Good evening aac, I'm new to the forum…
Buon giorno, Matteo. Welcome to AAC.

I assume your lingua madre is Italiano—but your English is far better than my Italian. As you are probably already aware, English is the language of AAC, and we certainly appreciate you using it. But, please don‘t hesitate to use machine translation if you aren’t already. (e.g.: https://translate.google.com) Sometimes the result of a person speaking in their native language and translating it is better than they can do in the second language.

But to be clear, so far your English hasn’t really been a problem.

…I would like your support regarding the construction of a simple circuit.
If you spend more time here (and we hope you will, and pass on your knowledge to others) you will come to recognize this phrase is often the introduction to a long, complicated thread about a circuit that turns out not to be so simple. What appears to be “simple” to the neophyte is, to the eye of the expert, not simple at all.

As you can see from the posts by folks who would like to help, they are struggling with the details that you didn’t provide in your post. It may well be that you don’t really have these details yet—and this is where the hidden complexity lies.

So, to help you, we need to know more than you‘ve said. As it stands there are so many directions we can go from the starting point you‘ve provided that any attempt at an answer is like throwing dice, then flipping some coins, then guessing—in other words, someone might guess at some things and get near your problem, but such an answer is going to be far from optimal even if it is close enough to bend, file, and wrestle into a “working“ solution.

I would like to build an oscillator that can generate an electromagnetic field in the near field.

I need it as a teaching…
So, start with a description of the problem this is going to solve. What will this oscillator do when it is working? You say ”a teaching”, does this mean as a tool to teach others or as a way to teach yourself?

What will the EMF in the near field be doing? Why?

I think you get the idea, and this is a very important part since if you try to simplify your problem when you don’t know how to solve it, you won’t know what you are omitting that is important. If you did, you wouldn’t be asking.

I read many previous answers but I didn't find anything, my circuit therefore involves a 12 V battery, connected to a solenoid (temporary choice), with a high frequency to be able to reduce the overall dimensions.
These things fall into the category of constraints and they may—or may not—be real ones.

Why do you need to use a 12V battery? If it wasn’t a good idea could you use a different power source? Why have you chosen to connect it to a solenoid, and by solenoid to you mean a device designed to be an electromagnetic actuator or are you just using the word “solenoid” to mean “coil”?

While solenoid is absolutely a correct term for a coil, in an English conversation about practical circuits and not EE or physics, we will use the terms coil or inductor for a device that is primarily desired for its lumped inductance and reserve solenoid for a device that is primarily desired for its magnetic field (to operate an actuator, converting the EM force to mechanical force).

I hope you can help me guys, thanks
I am certain that there are many people here who can help as long as you can provide the information to make that possible. The large number of responses expressing confusion about what you want might be daunting, but don’t sweat it, just explain what you will be doing with this, and what the real constraints are, and things will get on track.

Buono fortuna, I hope you will find AAC a good place to hang out, learn, and teach what you‘ve learned.
 

MisterBill2

Joined Jan 23, 2018
18,538
OK, now we have some more information, which is that the supply should be a 12 volt battery, and that the creation is for teaching purposes. Why an oscillator will allow a smaller coil is not clear to me.
A "small coil" of perhaps 20 turns of perhaps #24 wire, about 5 cm in diameter, will produce a magnetic field that will deflect a magnetic compass when it is powered by a single 1.5 volt "AA" cell. It is not so very impressive but it demonstrates the effect quite well.. The same coil powered by a larger cell can deflect a small magnet suspended from a non-magnetic material frame can demonstrate the effect to a larger group, without any oscillator to distract the focus of attention.
 
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