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Background

I have recently started doing a lot of research on the piezoelectric effect with the hopes of gaining a better understanding of the topic. When I can I like to do experiments on top of reading because it helps cement the knowledge I learned more effectively. The main topic I am looking into right now is quartz crystals. I have researched the molecular structure of quartz and what causes the piezoelectric effect but I am having a hard time finding out how the shape effects the frequency. I have mostly found resources on what makes small perfectly made factory quartz crystals oscillate but I have not been able to find any information on the processes of natural quartz.

The main thing I hope to gain from your knowledge is the understanding of how natural quartz crystals behave when a force or voltage is applied to them. I have a collection of quartz crystals ranging in sizes but I cant complete any successful tests with them on a larger scale.

Questions

Question 1- What effect would a force have on a cluster of natural quartz crystals? I ask this because the molecular structure would be intertwined so I wonder how it would be polarized when a force is applied and what kind of oscillation would be caused. Also how much would the efficiency drop by when compared to a perfect set of quartz crystals?

Question 2- When I have a single quartz crystal that is not uniform how can I determine its internal lattice structure to best predict its poles for any possible experiments I may conduct? I have been unable to read any voltage being created when a force is applied to any of my non uniformed crystals.

Question 3- I know that irregular quartz crystals with deformations will be less efficient but is it even possible to apply a force and read a return voltage with conventional tools and if so how would this best be done with that larger set of crystals.

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Even well-ordered single crystals have many resonance modes at different frequencies. A natural cluster of quartz crystals might have a confusing jumble. Like doing resonance analysis of a model doing a catwalk strut.

Bragg x-ray diffraction was (is?) used to probe lattice structure to find alignment of crystal planes. X-ray tools can also be used to probe stress applied to crystals.

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  • \$\begingroup\$ Very interesting! I did not know that but is there a way to apply a force and read a return voltage using more conventional tools? Is a single large quartz crystal too jumbled to be able to attach probes and read a voltage after applying a force? I ask this because I have not been able to get a successful reading which I think is because of the way a mangled quartz crystal structure is poled. What would be your advice for resolving this issue or is it even possible because I dont see why larger quartz crystals wont oscillate when a force is applied even if its just a jumbled mess. \$\endgroup\$ – CyClone Aug 8 at 18:24
  • \$\begingroup\$ A jumbled mess may well oscillate mechanically (am thinking of a "ringing" crystal goblet). But applying electrode probes to exploit crystal's piezo properties may not give you much joy. Electronic crystal resonators try to limit resonant modes to one, and align crystal planes with carefully-ground surfaces that have electrodes pressed or plated on. Spurious mechanical resonances are always present, but suppressed by design. \$\endgroup\$ – glen_geek Aug 9 at 0:51
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During WW 2, the USA used submarines to bring Brazilian quartz into US hands.

The "natural quartz" was crucial, but the quartz was ground and etched into very thin regions.

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regarding thicknesses, etc, I've heard the central part of a standard crystal, etched very thin, and plated on both sides of the thin region with silver, with the thicker edges clamped in a holder, is the mechanical approach.

And why would natural quartz be crushed and re-melted and then a mono-crystal slowly drawn from the melt? Because fewer inclusions, and thus cleaner energy storage and higher quality_factor and narrower resonant peaks will result.

I'm not sure "more reliable oscillation" is what results with a MELT/REGROW.

I've seen circuits that can make a Q=200 (poor quality ceramic resonators) oscillate.

However, purer crystals and the use of Low_Thermal_Noise (Boltzmann, Johnson, Nyquist noise) circuitry and PI_filter interfaces and careful Power_supply filtering and careful Gound layout and shielding, can produce oscillations with close-in-phase-wander.

Such very clean close_in waveforms allow Synthetic Aperature Radar success, and allow communication receivers to handle information even in the presence of strong adjacent_channel jamming.

Thus the spacecraft mapping Venus, or the military satellites using radar to look thru clouds and track ships on oceans, or mapping the Brazilian Jungle using side_looking Radar in the 1960s (Motorola built those), need purer crystals and attendant circuits.

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  • \$\begingroup\$ Yea I watched some old videos where they would grind them up and use high pressure and heat to melt and grow their own quartz crystals to perform a task more reliably than cutting natural ones. The issue I am having is I want to know why that is necessary besides from the obvious which is a more prefect uniform crystal would oscillate more reliably. My question is what effect does a force have on a natural quartz crystal (not altered) and how would one go about reading this. Also is there some sort of way to determine what the output frequency would be based on the size of a perfect crystal. \$\endgroup\$ – CyClone Aug 8 at 18:07
  • \$\begingroup\$ Very interesting! Do you know of any sources that describes the effect a force has on a larger set of non uniformed quartz crystals / cluster of quartz crystals? My goal is to not get a specific result its more or less just to be able to test them. I will get more in depth with this topic and try and make a more "exact" crystal but for now I am keeping it basic and working my way towards it. The only issue is I have found it harder to find resources on what happens to larger crystals when a force is applied. \$\endgroup\$ – CyClone Aug 9 at 2:30

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