What is Electromagnetic Fields

时间：03-25 整理：3721RD 点击：

Hello ,
What the use of Electromagnetic Fields in electronics?

There are magnetic fields, if that's what you mean. A close sister to electricity and electronics.

It is easy to confuse magnetic with electromagnetic. Normally we speak of electromagnetic waves: light, infrared, radio broadcast, x-ray, cosmic background radiation, etc. Photons are the form of the transmission. We don't usually think of it in terms of electromagnetic fields.

Question too vague, answer too broad.

Almost everything in electronic engineering deals with a greater or lesser depth in some concept of electromagnetic fields. The most you pursue in terms of performance, the most accurate ( and complex ) is the model you will infer about that.

This is so simple.This is the combination of electric and magnetic field.

let you assume one conductor.you passed the electrical supply through this conductor and outside of this conductor some magnetic field will be created.this is called EMF.

how antenna receive these wave?

As the electric field vector passes over a given point of the antenna, a corresponding voltage is induced. That is how, in simple terms, an antenna receives the electromagnetic waves.

You can see it as the electic losses in a capacitor, the energy that wasn't recieved in the second part of the cap nor reflected to the first

There are a couple of phenomens and its related formulas with which applyed to different contourn conditions we call these knowledge areas by different names (Antennas, Microwaves, Laser, EMI, etc...), but all of them essencially follows the same basic rules, more specificly the 4 equations from Maxwell Laws. For your question in particular, the physics behind the induction of an electromagnetic wave into an helicoidal antenna, for example, is the Faraday's law, which is nothing than a particular case of the above equations.

As the electric field vector passes over a given point of the antenna, a corresponding voltage is induced. That is how, in simple terms, an antenna receives the electromagnetic waves.

What is the range of voltage generated in antennas?
can we increase it how?
how to see that generated voltage?

You are asking conceptual questions for what need to have some kind of engineering awareness/feeling on this matter. In addition, the whole question itself remains vague, considering that the answer is geometry/bandwidth dependent.

[EDIT] Correct terminology : (Electro)magnetic field

Anyway, seems like now you're somehow able to answer yourself the original question you posed:

the power radiated should not decrease just like a voice of someone talking but the losses in the air (that are frequency dependant) will attenuate the signal till stop being heard. Obstacles will attenuate the power radiated too as walls do to your voice.

The power applied to the antenna is like your voice, the higher you scream the farer the range will be.

That simply depends on the strength of the electric field at that point (in the first approximation)- the antenna actually disturbs the electric field to some extend.

For a simple radio, the AC voltage produced at the antenna can be of the order of microvolts (/meter; to be accurate). Satellites beam only a few watts of power (they live on solar power and storage cells) and that is picked up by your dish antenna.

Can we check voltage induced by digital multi meters?

You should first read and study about digital multimeters and what they can (and cannot) do, their scope and limitations and other specifications.

I've been trying to get a grasp on this terminology most of my life. There's a lot to absorb. My mind has been slow to draw connections between various realms of the phenomena.

Example, Radio and TV broadcasts send out electromagnetic waves. And so does an led send electromagnetic waves down a glass fiber. However these applications are so different that I found it easy to imagine a broadcast antenna as a big electromagnet, supplied by AC at high frequencies. I thought my radio detects magnetic flux lines emanating from the antenna. However this is not the case, it appears. Instead the antenna sends out photons. I've read there is 'near field' and 'far field', so perhaps that has something to do with it.

As for the led, I read that it sends out light photons. These travel down the glass fiber, reflecting off the walls.

Radio waves do not travel down a glass fiber. Light waves do not emanate from an antenna. Yet both are electromagnetic waves. To my understanding, both are photons. It adds up to many differences and similarities. I realize I need to try to get a better better grasp on it all, as time goes by.

In the interests of scientific understanding, it is important to devise terminology which is specific to the phenomenon it describes, and yet also takes into account the fact that other phenomena are related. We are (or at least I am) prone to 'mental disconnects'.

Yes, radio, TV and light are all electromagnetic waves. The confusion comes when you think in terms of photons.

Waves will spread out in all directions but it is difficult to think of photon going into all direction at the same time.

True that radio waves do not travel down an optical fiber but they do travel down inside a hollow copper tube (waveguides) happily just like the former. The difference is simply due to their difference in wavelengths.

Electromagnetic waves have both (electric and magnetic) components and it is possible to detect both. Changing electric field is equivalent to a magnetic field and a changing magnetic field is equivalent to an electric field.

The low noise antenna fitted onto the dish receiver can detect both horizontal polarization, vertical polarization and also circular polarization (a new beast). Most satellite transmissions are these days circularly polarized and they effectively avoid the ghosts (me too scared by the ghosts).

I believe it is the engineers who have introduced too many different terms and added the confusion. I still have the problems with the vector potential (in electromagnetic theory).