2

Background

Based on helpful comments and links here and also from my question on the physics stackexchange, I have learned that the quartz crystals are nature's transducers of energy, allowing electrical energy to be converted into mechanical energy (and vice-versa). Furthermore, the Piezoelectrical properties of quartz crystals used in circuitry are best utilized by slicing (or growing) the quartz crystal in precise planes in order to facilitate the electrical conductivity across the physical lattice structure perfectly (even though energy is lost in this conversion). Lastly, "twinning" describes the natural "irregularity" from the divergent growth of crystalline structures in natural quartz that causes an inherent dampening of electrical potential, and consequently, less Q or oscillations. Therefore, as I understand the subject so far, hooking up electrodes to opposite "polar" ends of a natural quartz crystal without consideration for the physical internal lattice structure is possible to achieve low frequency oscillations, but electrically inefficient and unpredictable in the amount of amplification needed to overcome the low induction potential for piezoelectric oscillations.

Question

How do I build a quartz oscillator for a large pieces of quartz crystal ranging from a gram in weight up to several grams in weight (palm-sized and larger) for maximum Q? I would like to know what circuitry, components, voltages, amperage, and current to use to achieve some range of safe oscillation frequency for vibrating a large, irregular (natural) piece of quartz. I imagine that hooking up cathode and anode leads of hot current to a large crystal could be quite dangerous to experiment around with, from risk of electric fire to even the crystal exploding. I imagine that I would use a amplifier dial-in the desired oscillations. The oscillations do not have to be regular or precise in form, but should be maximally efficient.

Here is the best video on Youtube that I could find showing a computer simulation of my basic intention at 2:20: https://www.youtube.com/watch?v=1pM6uD8nePo

Here is the best link on physics.stackexchange that I could find: https://physics.stackexchange.com/questions/187604/vibration-of-quartz-crystal

Update

I am not attempting to make my own crystal by slicing, cutting, or grinding raw quartz, although I appreciate the interest and resources provided by the community in this direction. My sister question from the physics stackexchange is about oscillating a chunk of quartz by overcoming the known piezoelectric limitations of irregularly-structured natural quartz, and my question here is about the practical implementation of safely and efficiently applying voltage to a piece of tectosilicate mineral formation for maximum Q. Based on the answers so far, it appears that placing the electrodes on the sides of the crystal (versus the polar ends) will allow for better piezoelectric coupling. Additionally, my local Radioshack does not sell circuit amplifiers (just audio amplifiers). Any direction or help on building an amplifier (or safely modifying an audio amplifier) to adjust the amplitude of raw voltage going to the crystal would be greatly appreciated (I'm not sure if this should be a separate question). In conclusion, this questions is less about circuits and more about how a layperson should get a chunk of quartz safely between two electrodes.

Community
  • 1
PAINKILLER
  • 21
  • 4

3 Answers3

5

Since it seems that you are essentially attempting to create your own crystal from very raw materials (a chunk of quartz), what would probably be most useful would be to read about the early pioneers of the electronic quartz crystal industry. One excellent source is Christopher McGahey's PhD dissertation on the history of the industry. The most useful thing in it for you will be the footnotes and bibliography which will point you to the original sources in which inventors in the late 19th and early 20th centuries described their early experiments with quartz crystals.

Also useful will be looking at patents such as US Patent 2,212,845 which was filed in 1918 and describes an early oscillator design and US Patent 1,414,370 which describes how to make a suitable crystal.

Edward
  • 2,718
  • 1
  • 18
  • 23
2

This article and video give a good overview of the process of producing a quartz crystal. In a nutshell, you can't just take a random chunk of crystal; you have to identify the direction of the crystal structure, and cut a slice at the right angle to it, before you'll be able to exploit its piezoelectric properties to good effect.

Nick Johnson
  • 7,749
  • 3
  • 28
  • 44
1

This article gives a good overview of the influence of amateur radio on the early development of the quartz crystal industry and more importantly has a wonderful selection of references to articles published by QST magazine, amateur radio magazine, on the early experimentation with quartz crystals and the inexpensive processes used to cut, grind and polish them at home.

The referenced articles are too old and might be a little hard to find online, though I managed to get link for this one:

EDIT: For more information on specific figures for the tolerances you need to be within when grinding the wafers , you should check out this article.

Graham Nye
  • 4,218
  • 1
  • 12
  • 23
Idmond
  • 85
  • 2
  • 8
  • The (otherwise very nice) article says that the faces of the crystal "must be absolutely smooth and parallel", but this is clearly not remotely feasible with the suggested method and materials. Do you know what tolerances are really required? – Oleksandr R. Jul 13 '15 at 10:03
  • This article suggests some figures for the tolerances you need to be within when grinding the wafers for different types of crystal cuts. – Idmond Jul 14 '15 at 07:11
  • I don't have a Google account. Do you have another link? – Oleksandr R. Jul 14 '15 at 11:53
  • 1
    Thanks; that's a very nice article. In case the link becomes invalid, the tolerances suggested are on the order of single microns, not nanometres, even for 7 MHz crystals, and the surface finish seems to be non-critical. It certainly does not seem to need to be an optical-grade finish. The most important thing is that the edges should be bevelled to remove any irregularities. (By the way, I think your Google link simply does not work even for those with Google accounts. You have not granted public access to your files.) – Oleksandr R. Jul 15 '15 at 08:45
  • Thanks for the heads up! Google Link is fixed and added to the above answer. – Idmond Jul 23 '15 at 14:09