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<p>[QUOTE=&quot;-jeffB, post: 3832256, member: 27832&quot;]I think you&#039;re off-base here. Yes, different materials resonate at different frequencies, but:</p><p><br /></p><p>1) The whole system is being <i>driven</i> by a <i>fixed</i>-frequency oscillator (the ultrasonic transducer. I don&#039;t think there&#039;s an easy/efficient way to convert that energy into non-harmonically-related different frequencies; it would alternate between reinforcing and interfering with those other resonant frequencies.</p><p><br /></p><p>2) Soft plastic will <i>dissipate</i> energy rather than building up a resonance (unless it&#039;s under tension like a gut guitar string; even then it&#039;ll dissipate energy, but can still build up a good vibration).</p><p><br /></p><p>3) A frame <i>firmly</i> holding a coin will form a <i>compound</i> system with its own set of resonances, but there won&#039;t be <i>friction</i> between the two. There may be antinodes where they make contact, but even if there are nodes there, the objects will move <i>together</i>. (If this weren&#039;t the case, pianos and guitars would wear through their strings quickly at the bridges.)[/QUOTE]</p><p><br /></p>

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