Resonant frequency of a human body

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Discussion Overview

The discussion revolves around the resonant frequency of a human body, particularly focusing on the differences observed when the body is grounded versus ungrounded. Participants explore various aspects of resonance, including potential driving frequencies and the implications of grounding on resonant behavior. The conversation touches on both acoustic and electromagnetic resonance, as well as theoretical calculations related to human height.

Discussion Character

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

Main Points Raised

  • Some participants inquire about the specific driving frequency that causes the human body to resonate and request details about the context of the original question.
  • One participant shares an anecdote about experiments with insects, suggesting that the resonant frequency of the human body may not change whether it is grounded or not, although this is contested.
  • Another participant proposes that the discussion may pertain to electromagnetic (EM) resonance rather than acoustic resonance, indicating a distinction between the two types.
  • A participant mentions a formula for calculating resonant frequency based on height, noting that the frequency appears to be lower when the person is grounded.
  • Some participants reference literature on mechanical vibration effects on humans, although they acknowledge that this may not directly relate to the original question.
  • One participant provides a specific resonant frequency value (80MHz) based on average human height and discusses its implications for radio frequency dosimetry.
  • Another participant introduces the concept of standing waves and nodes, suggesting that grounding may affect the resonant characteristics of the body.

Areas of Agreement / Disagreement

Participants express differing views on whether the resonant frequency of the human body changes when grounded. Some argue that it remains constant, while others suggest it may decrease. The discussion includes multiple competing perspectives without a clear consensus.

Contextual Notes

Participants reference various assumptions and conditions, such as the influence of grounding on resonant behavior and the specific context of resonance (acoustic vs. electromagnetic). There are unresolved questions regarding the driving frequencies and the applicability of the discussed formulas.

Who May Find This Useful

This discussion may be of interest to individuals studying bioelectromagnetics, acoustics, or those exploring the effects of resonance in biological systems.

shpresa
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Does anyone know why the resonant frequency of a grounded human is smaller when ungrounded?
 
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shpresa, Welcome to Physics Forums!

Will you please give more information? What is the driving frequency causing the human body to resonate? Can you give some example of your experiment? What is the source of your question?

I once consulted on a project to kill insects some engineers were working on. Their idea was to bombard flies with high power acoustic frequencies that would cause their bodies to resonate so strongly they would literally explode. Our experiments showed it did not matter if the flies were in flight or resting on a leafy surface. Their little bodies exploded when irradiated with our sound beam in either case. We may infer from this experiment that the resonant frequency of the human body remains the same, whether grounded or not.

Cheers,
Bobbywhy
 
Bobbywhy said:
shpresa, Welcome to Physics Forums!

Will you please give more information? What is the driving frequency causing the human body to resonate? Can you give some example of your experiment? What is the source of your question?

I once consulted on a project to kill insects some engineers were working on. Their idea was to bombard flies with high power acoustic frequencies that would cause their bodies to resonate so strongly they would literally explode. Our experiments showed it did not matter if the flies were in flight or resting on a leafy surface. Their little bodies exploded when irradiated with our sound beam in either case. We may infer from this experiment that the resonant frequency of the human body remains the same, whether grounded or not.

Cheers,
Bobbywhy

Maybe he's talking of EM resonance? That'll be different from acoustic right?
 
Well there is no experiment. This was a question my professor asked me.
All I know is that one can find the resonant frequency of a body based on its height using the following formula:

f=114/h (MHz)
where f is the resonant frequency, h is the height of the person in meters. Now this resonant frequency has a higher value when the person is not standing with his feet on the ground, that means the resonant frequency is smaller when the person is grounded or standing with his feet on the ground.
Sorry for my English, hope you could understand my question.
 
Yes I guess its about EM resonance since we learned this from Bioelectromagnetics course...
 
Bobbywhy said:
Our experiments showed it did not matter if the flies were in flight or resting on a leafy surface. Their little bodies exploded when irradiated with our sound beam in either case. We may infer from this experiment that the resonant frequency of the human body remains the same, whether grounded or not.

Not necessarily. If you had been trying to break their legs by resonance rather than explode their body, it would have made a huge difference if they were standing on something (i.e. the body mass supported by 6 springs), or in flight.

FWIW there is a huge literature on the effect of mechanical vibration on humans - but we know know that's not what the OP was asking about.
 
shpresa said:
Yes I guess its about EM resonance since we learned this from Bioelectromagnetics course...

You are not sure? Seems odd.

Anyway, EM resonance of the human body is important in the field of radio frequency dosimetry.

According to my handbook, the average man is 1.75 meters tall, and has a resonant frequency of 80MHz. This is close to, but not exactly the same as, what your formula predicts.

This 80MHz peak causes the average absorption (watts per kg) for a given incident power density to be 10 times higher than at 1MHz or 200MHz.

Why would resonant freq be smaller for grounded human?
Here is a clue, see if you can figure it out:

The 80MHz resonance from dosimetry handbook (and your formula) are based roughly on the human body resonating as a dipole.

What kind of resonator are you if you ground your feet?
 
Last edited:
the_emi_guy said:
You are not sure? Seems odd.

According to my handbook, the average man is 1.75 meters tall, and has a resonant frequency of 80MHz. This is close to, but not exactly the same as, what your formula predicts.

Interesting. That ought to be VHF transmissions, right?
 
Ah, you mean grounded in the sense "standing on the ground". Consider a standing wave along the length of a human body. If you are standing on the ground, and your shoes are sufficiently damping, then your feet are a node. If you are hovering in the air, then your feet don't need to be a node.

Compare a blowing a pipe with one end covered versus an open pipe.
 

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