Why don't we emit radio waves

In summary, at our temperature we mainly emit infrared radiation, and although we do emit radio waves, they are much fainter than the infrared we emit. The reason we see each other in visible light is because we see the light reflected off of each other, not because we see the light emitted, and this is in the visible range because that is where the sun's emission peaks. Humans can be imaged in the 8-12 um band, but we are opaque to millimeter waves and become transparent at some point. Kirchoff's law does not apply to our emission of infrared, as it is simply a result of our body temperature and not a special property of biological systems. Antennas can send out radio waves because they
  • #1
LogicalAcid
137
0
If our temperature is already above the necessary temperature to emit radio waves? At our temperature we emit mainly infrared right?
 
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  • #2
We do emit radio. It's just much, much fainter than the infrared we emit. Similarly, the sun emits much more infrared per square meter than we do, even though it peaks in the visible.
 
  • #3
At our temperature, we mainly emit infrared radiation correct?

Then why do we see each other in visible light? Here's my hypothesis:
Left to ourselves, meaning no light present (at night) we are not seen because we don't have enough energy in us to emit visible light, we emit infrared at the most. That is why even if there is no light, we can still see if we have infrared goggles.
 
  • #4
cjl said:
We do emit radio. It's just much, much fainter than the infrared we emit. Similarly, the sun emits much more infrared per square meter than we do, even though it peaks in the visible.

Then we are basically antennas? Why can't we be used as antennas then?
 
  • #5
LogicalAcid said:
Then we are basically antennas? Why can't we be used as antennas then?
Lemme rephrase that, why do antennas have the ability to send out radio waves, if we emit radio waves as well?
 
  • #6
To suggest that biological systems, emitting IR, must ALSO emit lower frequencies is false.
There is no natural requirement for a biological system emitting a specific wavelength to be required to emit all the other sub-wavelengths down to zero.
 
  • #7
pallidin said:
To suggest that biological systems, emitting IR, must ALSO emit lower frequencies is false.
There is no natural requirement for a biological system emitting a specific wavelength to be required to emit all the other sub-wavelengths down to zero.

Took it right outta my mouth, why is this?
 
  • #8


That's reasonably accurate.

The reason we see each other in visible light is because we see the light reflected off of each other, not because we see the light emitted. The reason this is in the visible range is because that's where the sun's emission peaks.
 
  • #9
LogicalAcid said:
If our temperature is already above the necessary temperature to emit radio waves? At our temperature we emit mainly infrared right?

How do you know we don't?

Humans can be clearly imaged using the 8-12 um (LWIR) band, which corresponds closely to the peak in thermal emission.

I know that humans are opaque to millimeter waves (new airport full body scanners), and o we emit in the millimeter wave as well. But at some point we become transparent, and so by Kirchoff's law we won't emit in that waveband.
 
  • #10


cjl said:
That's reasonably accurate.

The reason we see each other in visible light is because we see the light reflected off of each other, not because we see the light emitted. The reason this is in the visible range is because that's where the sun's emission peaks.

Great, I have some questions I would like to ask you instead of starting a new thread, would you mind?
 
  • #11
Andy Resnick said:
How do you know we don't?

Humans can be clearly imaged using the 8-12 um (LWIR) band, which corresponds closely to the peak in thermal emission.

I know that humans are opaque to millimeter waves (new airport full body scanners), and o we emit in the millimeter wave as well. But at some point we become transparent, and so by Kirchoff's law we won't emit in that waveband.

Kirchoff's law BRB
 
  • #12
LogicalAcid said:
Took it right outta my mouth, why is this?

As opposed to phonon's(sound waves), photons do not have interactive, potentially harmonic properties.
 
  • #13
LogicalAcid said:
Kirchoff's law BRB

I don't understand?
 
  • #14
Andy Resnick said:
I don't understand?

I went to research it.
 
  • #15
pallidin said:
To suggest that biological systems, emitting IR, must ALSO emit lower frequencies is false.
There is no natural requirement for a biological system emitting a specific wavelength to be required to emit all the other sub-wavelengths down to zero.

We emit infrared because we aren't at absolute zero, not due to any unusual property of biological systems. The radiation our bodies emit more or less follows a black body spectrum, and we do indeed emit at lower frequencies, all the way down to zero. Your statements suggest the IR emissions are special, when it is really the gaps and other variations due to our deviations from black body emitters that are special. Your statement applies to bioluminescence, but not to body heat.


LogicalAcid said:
Lemme rephrase that, why do antennas have the ability to send out radio waves, if we emit radio waves as well?

The question doesn't make sense. Why would the fact that we emit radio waves make you think antennas can't?

But anyway, note that there's two types of emission here. You and an antenna both emit thermal radiation in a range of frequencies including the radio band but peaking in the infrared spectrum. Heat an unpowered antenna up to body temperature in the sun, and its emission spectrum will be quite similar. These emissions are very weak, though. An object at human body temperature won't be emitting particularly large amounts of power, and most of that will be in the infrared range.

Radio transmitters do not produce radio waves by thermal emission. They do it far more directly, by literally pushing the electrons in the antenna back and forth at the frequency desired. Accelerating charges radiate, and by doing this you can emit very large amounts of power in a very narrow portion of the spectrum.
 
  • #16
LogicalAcid said:
Then we are basically antennas? Why can't we be used as antennas then?

Because it could trigger painful sparks every now and then so no, thank you.
 
  • #17
We should be emitting radio waves too , or at least i think so. It's just we emit much more infrared and infrared has a lot more energy than radio waves, infrared dominates.
 
  • #18


To be totally fair, most night-vision goggles are based around photomultipliers. They also have some IR sensitivity, but that is mainly so that they can use an IR light source to "illuminate" an area without being seen. But that's an engineering point. You are more or less correct about the underlying emission phenomenon.
 
  • #19
You are conflating two concepts here:

An antenna is something that transmits and receives COHERENT radio transmissions. This is done by applying electromotive force of the appropriate phase and frequency, blah blah blah.

Thermionic emission is what the human body does, with respect to radio waves. Just the heat of the body causes some ultra-long-wave IR (AKA RF) waves to come off. They are not, in any way, coherent. Similarly, the body is not a coherent absorber. The energy we absorb from RF waves is just dissipated as heat, not conducted down our length to a detector. A lot of the art of antenna design is optimizing it for sensitivity to what we are interested in.
 
  • #20
(Moderator note -- 2 similar threads merged)
 

1. Why don't humans emit radio waves?

Humans do actually emit radio waves, but at very low levels. Our bodies contain charged particles that move in a magnetic field, which creates a weak electromagnetic field. However, these radio waves are much lower in frequency and power compared to the radio waves we use for communication.

2. How come we can't see radio waves?

Our eyes are only sensitive to a small range of electromagnetic radiation known as visible light. Radio waves have a much lower frequency and longer wavelength, making them invisible to the human eye. We need specialized equipment, such as antennas and receivers, to detect and interpret radio waves.

3. Can animals emit radio waves?

Yes, some animals can emit radio waves. For example, dolphins use echolocation, which involves emitting and receiving high-frequency sound waves, including radio waves. Certain species of birds also emit and receive radio waves as part of their communication and navigation systems.

4. Why do we use radio waves for communication?

Radio waves are used for communication because they can travel long distances and penetrate through obstacles like buildings and trees. They are also easy to produce and manipulate, making them ideal for transmitting information over long distances without the need for physical wires or cables.

5. Are radio waves harmful to humans?

Radio waves are non-ionizing radiation, meaning they do not have enough energy to break apart atoms and damage DNA. As a result, they are generally considered safe for humans in the low levels we are exposed to in everyday life. However, excessive exposure to high-powered radio waves, such as those from radar or microwave ovens, can cause tissue damage and potential health risks.

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