1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electromagnetic radiation vs Capacitance and Inductance

  1. Jan 4, 2016 #1
    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. jcsd
  3. Jan 4, 2016 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    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.
     
  4. Jan 4, 2016 #3
    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.
     
  5. Jan 4, 2016 #4
    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.
     
  6. Jan 4, 2016 #5

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    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.
     
  7. Jan 4, 2016 #6
    I should also add you might want to check out some of the work of HG Schantz
     
  8. Jan 5, 2016 #7
    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%.
     
  9. Jan 5, 2016 #8

    davenn

    User Avatar
    Science Advisor
    Gold Member

    No, try microWatts or less
     
  10. Jan 5, 2016 #9

    anorlunda

    Staff: Mentor

    Citation please.
     
  11. Jan 6, 2016 #10
    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.
     
  12. Jan 6, 2016 #11
    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.
     
  13. Jan 6, 2016 #12

    davenn

    User Avatar
    Science Advisor
    Gold Member

    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
     
  14. Jan 6, 2016 #13
    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;)
     
  15. Jan 6, 2016 #14

    davenn

    User Avatar
    Science Advisor
    Gold Member

    That part is correct :smile:
    it was some of the other things .. including the antenna inductance thingy that you need to revise
     
  16. Jan 6, 2016 #15
    I hear ya, but what about the average inductance was incorrect? calculating the average inductance of a moving antenna between several different radio towers would be incredibly harder than calculating the inductance of a antenna at a fixed distance from a tower, don't you agree? If you are referring to the rates of inductance that I listed, they are arbitrary considering I have not listed a specific source or antenna configuration, but here in the U.S. radio stations need not apply for a license for anything less than 100 watts and a broadcast distance of 200 feet (https://www.fcc.gov/media/radio/low-power-radio-general-information). The FCC lists the power transmission as a minimum of 1 millivolt/meter for unlicensed broadcast (https://www.fcc.gov/media/radio/low-power-radio-general-information). So, I took this to imply that most broadcast radio stations transmit a lot more power, although I did not find a specific source for actual power transmission. The reason I mentioned using a resonator on the antenna is covered in this article (http://amasci.com/tesla/tesceive.html) and refers to magnifying power transmission by optimizing frequency shift through a resonator and AC input, (really interesting article). If you wouldn't mind filling me in on the specifics of my errors it would be appreciated. I don't mind being wrong once but, I'd rather not make the same mistake twice, know what I mean;)
     
  17. Jan 6, 2016 #16

    davenn

    User Avatar
    Science Advisor
    Gold Member

    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 :smile:


    Dave
     
  18. Jan 7, 2016 #17
    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 ;)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Electromagnetic radiation vs Capacitance and Inductance
Loading...