Help with radio waves and electromagnetic fields

Click For Summary

Discussion Overview

The discussion revolves around the use of radio waves and electromagnetic fields in a product designed to turn on an LED. Participants explore the relationship between radio waves, electromagnetic fields, and Hall Effect sensors, questioning the validity of using such sensors for detecting radio waves.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions whether a Hall Effect sensor can be used to turn on an LED via radio waves, suggesting that radio waves are a form of electromagnetic fields.
  • Another participant argues that a normal Hall Effect sensor is unlikely to detect radio frequency (RF) fields unless in close proximity and may not have the necessary frequency range.
  • Some participants clarify that radio waves are indeed a form of electromagnetic radiation, while others express confusion over the definitions of electromagnetic fields and electromagnetic radiation.
  • A participant explains the distinction between near field and far field in relation to electromagnetic fields, noting that near field energy dissipates when the power source is off, while far field energy continues to propagate.
  • There is a discussion about the operational characteristics of Hall Effect sensors, with some participants asserting that they measure magnetic fields rather than electromagnetic fields, and questioning their effectiveness for RF signals.
  • One participant highlights the complexity of electromagnetic field interactions around antennas and the challenges in mathematically expressing these interactions.
  • Another participant emphasizes that standard Hall probes measure static magnetic fields and may not effectively measure oscillating fields associated with electromagnetic waves.

Areas of Agreement / Disagreement

Participants express differing views on the definitions and applicability of electromagnetic fields and radiation, as well as the effectiveness of Hall Effect sensors for detecting RF signals. The discussion remains unresolved, with multiple competing perspectives presented.

Contextual Notes

Participants note limitations in understanding the definitions of electromagnetic fields and radiation, as well as the operational constraints of Hall Effect sensors in relation to RF frequencies.

Moe123
Messages
14
Reaction score
0
I need help explaining that this assumption is not correct or correct:
A product uses Radio waves to turn on a LED. Radio waves can be a form of electromagnetic fields therefore, a Hall Effect sensor could be used in this device to turn on that LED.
 
Physics news on Phys.org
Very unlikely a normal Hall sensor could detect (unless very close) or even have the frequency range to detect most RF fields from consumer devices.
 
Are Radio Waves a form of electromagnetic field?
 
Yes, a radio-wave is an electromagnetic field.
 
I am confused with the definitions of electromagnetic fields and electromagnetic radiation
Are these 2 forms the same thing or different? Is radio waves an electromagnetic field or is it electromagnetic radiation?
I read that electromagnetic radiation consists of electric and magnetic fields, yet it goes on to state that not all configurations of electric and magnetic fields are describes as radiation...like the Earth's magnetic field.
Therein lies the question of what physicists define a 'field' to be?
 
It's not completely black and white. With a component like a tuned coil in a radio circuit to amplify RF signals it's designed to operate in the near field region zone of space where the EM fields around it store energy but are mainly reactive, out of phase and don't dissipate energy into space. The antenna on the radio is designed to interface from the near field reactive region to the far field resistive/dispersive in phase region where we consider those EM fields as radiation.

A simple example of EM field zones. Where one ends and the other begins is far more complicated.
http://www.antetec.com/uploads/userup/0911/1F1392040T.jpg
 
Last edited by a moderator:
Moe123 said:
A product uses Radio waves to turn on a LED. Radio waves can be a form of electromagnetic fields therefore, a Hall Effect sensor could be used in this device to turn on that LED.

Hall sensors respond to reasonably close and strong magnetic fields, not EM fields

Dave
 
Thanks for the input but I am still not clear on the difference between electromagnetic radiation and electromagnetic fieldIt seems from textbooks definition that radio waves are a type of electromagnetic radiation. From your definition, my inference is that a EMF is a separate component:” RF signal operates in the near field region where EMF around it “

Would not the antenna on the radio respond not to the position but rather to the wavelengths’ frequency?

I also read that electromagnetic waves are formed when an electric field couples with a magnetic field. Magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave. Therefore, lies my confusions since is this statement is correct, how can your statement that radio waves are an electromagnetic field be correct? Then, my man Maxwell makes this statement: “This velocity is so nearly that of light, that it seems we have strong reasons to conclude that light itself (including radiant heat, and other radiations if any) is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws”

I need help understanding why a radio wave is considered an electromagnetic field!

Thanks in advance!
 
Electromagnetic radiation are electromagnetic fields (the electric and magnetic field are a part of a single more complete object, an electromagnetic field) that are considered detached from the source. If you have an antenna the near EM field energy will stop when the power source is off but the EM field energy we consider radiation (far field) will continue to propagate into space. Near the antenna there is a complex interaction of fields coupling back to the antenna that can greatly modify the pattern of radiation into space and It's tricky to express exactly mathematically but for a simple dipole antenna it's fairly simple.

 
Last edited:
  • #10
Wow, thank you for this info!
But, you Nsaspook, said that a hall effect sensor,(only if it is very close), be used in this gadget that uses RF signals
The definition of the hall effect sensor that I have is the following: "A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications. In its simplest form, the sensor operates as an analog transducer, directly returning a voltage.:"
Could this sensor be used then per your definition of electromagnetic field?
Thank you!
 
  • #11
Moe123 said:
Wow, thank you for this info!
But, you Nsaspook, said that a hall effect sensor,(only if it is very close), be used in this gadget that uses RF signals
The definition of the hall effect sensor that I have is the following: "A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications. In its simplest form, the sensor operates as an analog transducer, directly returning a voltage.:"
Could this sensor be used then per your definition of electromagnetic field?
Thank you!

This thread is a jumble of confusion. Is it on EM wave/fields/radiation, or is it on Hall effect/probe?

Have you looked up the concept of a Hall probe? The standard Hall probe, as davenn has stated, measures the magnetic field strength. In fact, it is effective for a STATIC magnetic field strength! And EM wave, by definition, will have an oscillating electric and magnetic field. Unless you have a very "low frequency" EM wave, or a very fast-response probe, I don't think using a standard Hall probe will measure anything in this case. So using the Hall effect is ineffective.

Zz.
 
  • #12
Moe123 said:
Wow, thank you for this info!
But, you Nsaspook, said that a hall effect sensor,(only if it is very close), be used in this gadget that uses RF signals

You forgot this part "or even have the frequency range to detect most RF fields from consumer devices"
Hall sensors are used to measure changing magnetic fields. The cheap ones I use have a bandwidth of DC to 250kHz with a di/dt of up to 70A/usec.
https://s3.amazonaws.com/amploc/PDFs/HANDBOOK+web.pdf

250kHz is likely not in the RF range you need.
 
Last edited:
  • #13
Thank you!
 

Similar threads

Undergrad How Do Time-Varying Currents in Conductors Generate EM Fields and Waves?
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Radio waves interaction with other electromagnetic waves
  • · Replies 8 ·
Replies
8
Views
3K
Graduate Voltage and current waves in a transmission line
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad What is the cause of electrical disturbances?
  • · Replies 24 ·
Replies
24
Views
2K
Graduate The every day use of the magnetic part in EM radiation
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad Help understanding Maxwell's Equations please
  • · Replies 11 ·
Replies
11
Views
3K
Undergrad How do submarines communicate with radio waves?
  • · Replies 36 ·
2
Replies
36
Views
7K
Undergrad Can Electromagnetic Fields Exist Independently of Charges?
  • · Replies 21 ·
Replies
21
Views
3K
Undergrad When was it proven that light is an electromagnetic wave?
  • · Replies 2 ·
Replies
2
Views
2K
Graduate How can we deduce the kink effect in the electric field?
  • · Replies 5 ·
Replies
5
Views
2K