# Electromagnetic radiation vs Capacitance and Inductance

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1. Jan 4, 2016

### marciokoko

Im trying to compare, visually in my head, the difference between transmitting data vs something like radio or microwaves vs how inductance and capacitance.

I understand that the way the wave is modulated for example, AM or FM, can be interpreted as 0s or 1s.

Im trying to compare this to "transmitting power" via inductance or capacitance. Where in inductances for example, a magnetic field created by an electric current, is "converted" to an electric current on the other "side".

In the "data transmission" case, energy transmitted from a source, through a medium, is actually energy being transferred from the source atoms to atoms in the medium, until the energy reaches the destination atoms.
In the "wireless power transmission" case, energy from the source is ???, recycled through a circuit, but in doing so, it creates a disturbance called a magnetic field which has the "same" effect on the other "side". But a magnetic field is in essence a transfer of energy between subatomic particles?

But actually electricity is derived from magnetism? Because "electricity" defined as a form of energy resulting from the existence of charged particles. So in "wireless power transmission", movement from those particles is causing the energy to be "received" on the other side.

Yet "wpt" is so "short distance" compared to "data transmission".

2. Jan 4, 2016

### Simon Bridge

Data does not exist - the electricity does.
Consider: we set up a system to send information by throwing stones - I throw all kinds of stones at you and when they hit you they sting a little to a lot depending on how big the stone is. You rank how much each hit stings onj a scale of 1-10, and anything 5 or below we count as 0, and anything 6 or above we count as 1 ... so I can send a string of 1's and 0's with the stones.

The data (the string of 1's and 0's) is completely imaginary: it is the result of our senses - it does not exist outside of our sensorum.
What exists is the stones hitting you: they hurt.

The reslationship between transmitting data electromagnetically and the power transmittion by inductors etc you are talking about is exactly the same.
The inductors inducing currents in each other is the "stones hitting you" part. The pattern of the currents representing 1's and 0's is the data part.

Note: electricity and magnetism are both manifestations of the same thing. Electrical and magnetic phenomena are unified through Maxwell's equations ... it is convenient in different cases to use different approximations.

3. Jan 4, 2016

### marciokoko

Yes I understand the data part is just the interpretation of the physical phenomenon.

But wireless power transmission case Is so short distance. Why? In electromagnetic radiation, the source produces a high energy wave (disturbance) which radiates from source to destination. But in inductance, the source produces a magnetic disturbance which radiates from source to destination. Unfortunately the magnetic radiation is not that powerful or rather efficient at radiating and thus transforming back into electricity.

4. Jan 4, 2016

### indio007

Wireless power transmission uses near field not far field "radiation". Near field effects fall off exponentially from the surface of the emitter. Technically, the E field and B field are decoupled. All kinds of strange things happen in the near field.

5. Jan 4, 2016

### Simon Bridge

This is not correct - power can be wirelessly transmitted arbitrary distances. See the work of Nicolai Tesla.
But if we are only interested in what happens at close distances we don't bother with the maths for long distance. However - long and short range effects still follow the same laws.

This is also not correct - both methods produce electric and magnetic "disturbances" together (you cannot have one without the other). Solenoid to solenoid transmission works in exactly the same way as radio transmission.

There is nothing intrinsically more or less efficient about transmission with or without a solenoid - it's all moving charges back and forth in a wire.

The shape of the wire affects the shape of the resulting electromagnetic field and the type of oscillations the charges undergo affect the shape of the disturbances.
The maths that describes these effects is usually very complicated so we use approximations - the approximations give the appearance that things are different.
Sometimes we are only interested in short range effects - like in a power supply transformer: the components are engineered to make sure that short range effects are dominant and we concentrate on short-range approximations in the maths. However, we still need to shield transformers so the longer range effects don't mess stuff up.

6. Jan 4, 2016

### indio007

I should also add you might want to check out some of the work of HG Schantz

7. Jan 5, 2016

### DocWonder

radiowaves induce power in your antenna also, it is just so small that it has to be amplified to be of any use. A typical car antenna receives anywhere from 20-50 miliwatts in good reception areas. In fact there are currently phone cases for the iphone 6s that use ambient radiowaves to recharge the battery. It does this by using an antenna to direct the radiowaves to coils which induce the charge to the battery just like sitting the phone on a wireless charger. the result was an average increase of battery life by 33%.

8. Jan 5, 2016

### davenn

No, try microWatts or less

9. Jan 5, 2016

### Staff: Mentor

10. Jan 6, 2016

### DocWonder

http://www.pcmag.com/article2/0,2817,2483713,00.asp, that is for cell phone case sorry I did not post sooner I have odd work hours. As for the correction on miliwatts to microwatts, lets be honest there is no true way to measure the average inductance of a car antenna as a car is in motion and radio wave reception depletes exponentially from the source. If you parked at 30-35 degrees from a radio station tower with the appropriate resonator hooked to your antenna you could pick up a watt or two, but if you were driving in a valley between two large mountains and dense fog you might not get but a few heavily distorted picowatts.

11. Jan 6, 2016

### DocWonder

I am sorry about not posting a citation for the rudimentary explanation of inductance variations on car antennas, but that would take several citations and involve the fundamentals of radio transmissions, current radio station technology, resonators, em interference, and well a couple others I probably forgot to mention. Before somebody starts picking my last post apart I was referring to fm stations, so we don't get carried away with am, satellite, and ambiant solar radiation.

12. Jan 6, 2016

### davenn

you seem to have many mis-understandings and really need to read up on some basic RF propagation, EM field power levels and how they are calculated, and antennas, including your weird theory about avg inductance readings of a car antenna

Dave

13. Jan 6, 2016

### DocWonder

I guess so, I was under the impression that the farther from a source and the more obstruction the lower the reception. I was simply pointing out that as distance changes from the source the power received would change as well, but if you would please point out what I said that was incorrect so I can change that in the future that would be greatly appreciated;)

14. Jan 6, 2016

### davenn

That part is correct
it was some of the other things .. including the antenna inductance thingy that you need to revise

15. Jan 6, 2016

### DocWonder

16. Jan 6, 2016

### davenn

if the antenna doesn't change length, then nor does any inductance it has. Inductance is measured in H ( Henries) rarely do we see inductors
as big as 1 Henry most are in the uH or mH range
I suspect you are either not sure the meaning of inductance, or you are mixing up inductance with some other word ??

I have realised what you are getting at .... I want to see if you discover what it is and come to the correct term to use

Dave

17. Jan 7, 2016

### DocWonder

bingo I got it, I was using the incorrect word. I meant transmitted and received. I used inductance believing it to mean induced ( like when situations are induced by actions) where inductance is a term used in electronics to explain "a change in electromotive force by generating a change in the current flowing" (www.merriam-webster.com, 2016). Thanks for the clarification, I am a psychologist so some terminology gets jumbled for me. Physics has always been a hobby for me though, thanks for the pointer ;)