What are you asking?  I "think" you are asking how a structure can be resonant if it is made completely of metal.  You were probably taught in circuit theory that the voltage in a conductor is constant.  If you apply this to a large metal structure, how can it be resonant.

At high frequencies we have waves, and in fact, the voltage across a conductor is no longer constant.  It varies with the wave.  This is most commonly discussed in transmission line theory.  Anyway, currents are oscillating in the conductor producing the resonance.

Hope this was helpful!

thank you sir .I want to know that  if any wioman  wear a gold jewellery (ornament) and if in atmosphere there is  wave of frequency which has wavelength comparable with size of jewellery then it will resonate and produce ill effect for that woman for example headche .  in this case what is meaning of resonance?

A rule of thumb is that a ring will resonant at a frequency whos wavelength is approximately the circumference of the ring.  You have to consider the medium to accurately estimate wavelength.  If the circumference of the ring is 4 cm, it would resonant probably somewhere just below 8 GHz if I did my math correctly.  I don't think that would give a person a headache, but at high enough power the ring will get hot.

i want to know that what is mechanism of resonance?

what is happening inside the metal at atomic level ? is there is a transistions of electron  from valance band to conduction band at that frequency (at that frequency  energy is enough to excite electron below which electron can not excite so that energy is dissipated)

Assuming the metal in the ring is a good conductor there are already plenty of electrons in the valence band for conduction.  When a wave is incident on the ring, it pushes the free electrons to create a current.  The only way for the current to go is around the ring.  Like a child on a swing, there is a natural frequency that current can oscillate around the ring.  At frequencies off the resonance, the current does not return to the same place it started and it fights the applied wave.  On resonance, the current is perfectly in sync with the wave and the wave is able to produce large current oscillations in the ring.  This is the reason for the resonance.

thank you sir

Raymond Rumpf

Your answer was clearly written and informative!

" Assuming the metal in the ring is a good conductor there are already plenty of electrons in the valence band for conduction.  When a wave is incident on the ring, it pushes the free electrons to create a current.  The only way for the current to go is around the ring.  Like a child on a swing, there is a natural frequency that current can oscillate around the ring.  At frequencies off the resonance, the current does not return to the same place it started and it fights the applied wave.  On resonance, the current is perfectly in sync with the wave and the wave is able to produce large current oscillations in the ring.  This is the reason for the resonance."