How can we cause EM waves to travel through a tiny hole in an infinite conducting plane?
("Tiny" means "much smaller than one wavelength.")

  I've always known one trivial answer to this question:

  Place a 1/2-wave dipole antenna on one side of the 
  conducting plane, run wires from this antenna through 
  the tiny hole in the plane, then place a second 1/2-wave 
  dipole on the other side of the plane and connect the 
  wires to it.  The first antenna acts as a receiver and 
  absorbs EM energy, which flows along the wires, through 
  the tiny hole, and drives the second antenna as a 
  transmitter.  The two antennas have essentially "focused" 
  the Poynting-vector flux of the incoming EM waves so that 
  it passes through the tiny hole.

  A naive description might read thus:  "we turn the radio 
  waves into 'electricity' and then back into radio waves 
  again."   This is wrong.  Since electrical energy in 
  circuits is actually composed of e-fields and b-fields 
  surrounding the circuit, the EM energy in the above 
  description never actually "changes" into "electricity",
  instead it becomes coupled to the mobile charges within
  the conductors and so gains the ability to pass through 
  a very small hole in a conductive plate.

  Note that there is no lower limit on how small the 
  hole can be in an ideal case, but of course there are 
  many practical limits in the real world case.

  Also note:  if we think in terms of photons, then
  the antennas are somehow guiding photons to flow 
  THROUGH the hole rather than being reflected from 
  the conductive plane.  With the wires installed
  in the hole, MORE photons can get through.  This seems
  silly.  However, when analyzed in terms of EM fields, it
  makes perfect sense.  The EM energy-flows surrounding
  a 2-wire waveguide don't much care if the wires are 
  spaced closely or wide, or if they pass through a tiny  
  hole in a conductive plate.  The photons which make up  
  those EM fields around the wires will happily seek out  
  the tiny hole and flow right through with no problem, 
  regardless of their frequency.


  Here's a second answer to the original question.  To allow
  EM waves to pass through the tiny hole in the infinite
  conductive plate, just place some molecules in the hole, 
  but choose molecules which are resonant at the frequency 
  of the EM waves.  Suppose the EM waves are microwaves, and
  their frequency is at the ammonia resonance (think "ammonia
  maser").   If we place some ammonia molecules in that tiny
  hole, the molecules will strongly absorb the incoming 
  radiation, then they will re-radiate it.  Part will be
  scattered backwards, but part will move forwards through
  the hole.  The presence of those ammonia molecules has 
  allowed the EM radiation to pass through the hole.

  The presence of the molecule can make a big difference.
  Suppose we make our hole somewhat larger than a single 
  ammonia molecule.  Without that molecule present, the
  amount of EM wave energy which passes through such a 
  tiny hole will be vanishingly small.  However, with the
  molecule placed into the hole, relatively enormous 
  amounts of EM power suddenly can get through.

  OK, here's a third option which doesn't involve molecules.

  Place a very small lossless loop antenna in the hole, 
  and connect it to a capacitor.  Tune the LC circuit to 
  resonate at the frequency of the incoming waves.  The 
  loop antenna will build up a very large alternating 
  current at the resonant frequency.  It will re-radiate 
  EM waves, with part of the energy scattering backwards 
  through the hole, but part being radiated out the other 
  side.  The presence of the tuned circuit in the tiny 
  hole has allowed EM waves to pass through the hole.  
  Again note that there is no theoretical limit on how 
  small the hole can be.  Obviously any PRACTICAL 
  applications will have many limits, but I'm not talking 
  about practical issues here, I'm talking "physics 
  homework questions" and "thought experiments."

  Also note that the above LC circuit acts as a macroscopic
  analogy for a molecular or an atomic oscillator.

  If the "energy sucking" controversy  is any guide, then one
  or two people will read this and say "cool", while a huge
  number of others will become enraged and launch personal
  attacks.  This message is aimed at those one or two people
  who actually ENJOY thinking.  Those who become angry and
  descend into ridicule can fight with each other this time,
  since I'm going treat their offensive behavior as it 
  deserves, and recoil in revulsion.

  "I know that most men, including those at ease with 
  problems of the greatest complexity, can seldom accept 
  even the simplest and most obvious truth if it be such 
  as would oblige them to admit the falsity of conclusions 
  which they have delighted in explaining to colleagues, 
  which they have proudly taught to others, and which they 
  have woven, thread by thread, into the fabric of their 
  lives."    -Tolstoy

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William J. Beaty                            SCIENCE HOBBYIST website
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Seattle, WA  425-222-5066    unusual phenomena, tesla coils, weird sci

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