Light has electric and magnetic components. Until now, scientists thought the effects of the magnetic field were so weak that they could be ignored. What Rand and his colleagues found is that at the right intensity, when light is traveling through a material that does not conduct electricity, the light field can generate magnetic effects that are 100 million times stronger than previously expected. Under these circumstances, the magnetic effects develop strength equivalent to a strong electric effect. from the article
Although quartz is not conductive (meaning it doesn't carry electricity like most metals such as copper), it has certain electrical properties that make it very useful for certain electronics. In particular, it is piezoelectric. "Piezoelectricity" is a word derived from the Greek word "piez" or "piezein", meaning "to press"; Piezoelectric materials are non-conductive materials which generate electricity when you subject them to pressure, and vice-versa: They undergo physical deformation when you run electricity through them. If you compressed a pice of quartz using a pair of pliers or a vise, it would generate a very small electrical charge, and if you connected a piece of quartz to either end of a battery, the crystal would bend or warp slightly. These effects are too small to be visible to the human eye; You won't actually see the crystal bending or shaking, and you won't notice sparks coming from it, but there will be very tiny effects, and these can be detected and used by electronic circuits.
Quartz resonators consist of a piece of piezoelectric material precisely dimensioned
and orientated with respect to the crystallographic axes. This wafer has one or more
pairs of conductive electrodes, formed by vacuum evaporation. When an electric field is
applied between the electrodes the piezoelectric effect excites the wafer into mechanical
vibration. Many different substances have been investigated as possible resonators, but
for many years quartz has been the preferred medium for satisfying the needs for
precise frequency generation. Compared to other resonators e.g. LC circuits, mechanical
resonators, ceramic resonators and single crystal materials, the quartz resonator has
proved to be superior by having a unique combination of properties. The material
properties of quartz crystal are both extremely stable and highly repeatable. The
acoustic loss or internal fraction of quartz is particularly low, which results in a quartz
resonator having an extremely high Q-factor. The intrinsic Q of quartz is 107 at 1 MHz.
Mounted resonators typically have Q factors ranging from tens of thousands to several
hundred thousands, orders of magnitude better than the best LC circuits. The second key
property is its frequency stability with respect to temperature variations....
and orientated with respect to the crystallographic axes. This wafer has one or more
pairs of conductive electrodes, formed by vacuum evaporation. When an electric field is
applied between the electrodes the piezoelectric effect excites the wafer into mechanical
vibration. Many different substances have been investigated as possible resonators, but
for many years quartz has been the preferred medium for satisfying the needs for
precise frequency generation. Compared to other resonators e.g. LC circuits, mechanical
resonators, ceramic resonators and single crystal materials, the quartz resonator has
proved to be superior by having a unique combination of properties. The material
properties of quartz crystal are both extremely stable and highly repeatable. The
acoustic loss or internal fraction of quartz is particularly low, which results in a quartz
resonator having an extremely high Q-factor. The intrinsic Q of quartz is 107 at 1 MHz.
Mounted resonators typically have Q factors ranging from tens of thousands to several
hundred thousands, orders of magnitude better than the best LC circuits. The second key
property is its frequency stability with respect to temperature variations....
...Modes of vibration, cuts and
frequency ranges
The AT-cut resonator uses the thickness shear mode of vibration (fig.3). A standing
wave is set up in the crystal blank by the reflection at both major surfaces of traverse
waves travelling in the thickness direction. The major mechanical displacement is in the
plane of the crystal at right angles to the direction of wave propagation. At resonance
an odd number of half wave lengths are contained in the thickness plane of the crystal
blank. Therefore the thickness is the primary frequency determining dimension.
frequency ranges
The AT-cut resonator uses the thickness shear mode of vibration (fig.3). A standing
wave is set up in the crystal blank by the reflection at both major surfaces of traverse
waves travelling in the thickness direction. The major mechanical displacement is in the
plane of the crystal at right angles to the direction of wave propagation. At resonance
an odd number of half wave lengths are contained in the thickness plane of the crystal
blank. Therefore the thickness is the primary frequency determining dimension.
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