The Piezoelectric Effect

Monocrystaline quartz is one of a relatively rare group of materials that exhibit the “piezoelectric effect” By utilizing this phenomenon, quartz crystal resonators have been used to stabilize and control radio frequencies(RF) since the early part of the 20th century.

If a stress is applied to a piezoelectric material in a particular direction, electrical charges are created in a perpendicular orientation. Conversely if an electric charge is applied along a certain direction, it will cause a mechanical deflection of that material.

By placing a wafer of quartz between two electrodes, and applying an alternating current to them, providing certain conditions are met the crystal will vibrate in resonance with the frequency of the alternating current being applied. In this way one can precisely control the frequency of the circuit. The closer the frequency of the applied current to the natural resonance of the quartz wafer the greater will be the amplification of the current through the crystal. Therefore the quartz crystal will operate electrically in the same way as a discrete component type L.C circuit.

Quartz Resonators - Physical Properties

By culturing the growth of synthetic quartz under controlled conditions, extremely pure crystals can be produced. These pure crystals are known as monocrystaline quartz.

To produce quartz crystal resonators the cultured quartz bars are sliced into wafers. Depending upon the angle at which these slices are oriented to the original bar, determines the frequency range and characteristics of the resulting quartz crystal resonator. These orientations are documented and termed “the crystal cut”. A diagrammatic representation of the primary crystal cuts is shown in fig. 1. With respect to today's demand for quartz crystals - by far the majority is for the AT-Cut

Physical Properties
Temperature Characteristics

Fig. 2 shows some typical frequency/temperature curves for various AT-Cut angles. The variation of frequency with temperature is extremely predictable thus enabling the use of crystals elements within Temperature Compensated Crystal Oscillators (TCXO)

Temperature Characteristics Page 2