Crystal oscillators

Schwing-kreis, m. oscillating circuit circuit, -kristall, m. crystal oscillator, -neigung, /. oscillating tendency. -lohr, n. swing pipe, -rohre, /. oscillatory valve. 

Fig. 5. Oscillation photograph No. 4 from zunyite. Axis of oscillation [010], crystal oscillated 45° from (100). Molybdenum K radiation filtered through zirconia.

AT-cut, 9 MHz quartz-crystal oscillators were purchased from Kyushu Dentsu, Co., Tokyo, in which Ag electrodes (0.238 cm2) had been deposited on each side of a quartz-plate (0.640 cm2). A homemade oscillator circuit was designed to drive the quartz at its resonant frequency both in air and water phases. The quartz crystal plates were usually treated with 1,1,1,3,3,3-hexamethyldisilazane to obtain a hydrophobic surface unless otherwise stated [28]. Frequencies of the QCM was followed continuously by a universal frequency counter (Iwatsu, Co., Tokyo, SC 7201 model) attached to a microcomputer system (NEC, PC 8801 model). The following equation has been obtained for the AT-cut shear mode QCM [10] ... 

A technique for such measurements is the electrochemical quartz crystal microbalance (EQCM figure 14) [71]. Here, the working electrode is part of a quartz crystal oscillator that is mounted on the wall of the electrochemical cell and exposed to the electrolyte. The resonance frequency / of the quartz crystal is proportional to mass changes Am A/ Am. With base frequencies around 10 MHz, the determination of Am in the ng range is possible. 

Figure 3.24 depicts a piezoelectric sensor consisting of two oscillator circuits a detector crystal oscillator and a reference crystal oscillator. The two are identical except for the fact that the reference oscillator is not coated with biological material and is intended to correct for temperature and humidity fluctuations, as well as other interfering effects. The two oscillator frequencies are fed to a mixer that provides the difference in frequency between the two crystals. In order to use the piezoelectric effect to detect a target dissolved substrate it should be reacted with a suitable biocatalyst immobilized on the crystal by entrapment (deposition from an acrylamide solution), cross-linking, irradiation or pre-coating. 

Avery sharp electromechanical resonance occurs at certain discrete frequencies of the voltage applied. If mass is added to the surface of the quartz crystal oscillating in resonance, this resonance frequency is diminished. This frequency shift is very reproducible and is now understood precisely for various oscillation modes of quartz. Today this phenomenon, which is easy to understand in heuristic terms, is an indispensable measuring and process control fool, with which a coating increase of less than one atomic layer can be detected. 

In period measurement a second crystal oscillator is essentially used as a reference oscillator that is not coated and usually oscillates at a much higher frequency than the monitor crystal. The reference oscillator generates small precision time intervals, with which the oscillation duration of the monitor crystal is determined. This is done by means of two pulse counters the first counts a fixed number of monitor oscillations m. The second is started simultaneously with the first and counts the oscillations of the reference crystal during m oscillations of the monitor crystal. Because the reference frequency F,. is known and stable, the time for m monitor oscillations can be determined accurately to 2/F,.. The monitor oscillation period is then... 

All unite developed up to now are based on use of an active oscillator, as shown schematically in Fig, 6.5. This circuit keeps the crystal actively in resonance so that any type of oscillation duration or frequency measurement can be carried out. In this type of circuit the oscillation is maintained as long as sufficient energy is provided by the amplifier to compensate for losses in the crystal oscillation circuit and the crystal can effect the necessary phase shift. The basic stability of the crystal oscillator is created through the sudden phase change that takes place near the series resonance point even with a small change in crystal frequency, see Fig. 6.6. 

Normally an oscillator circuit Is designed such that the crystal requires a phase shift of 0 degrees to permit work at the series resonance point. Long-and short-term frequency stability are properties of crystal oscillators because very small frequency differences are needed to maintain the phase shift necessary for the oscillation. The frequency stability Is ensured through the quartz crystal, even If there are long-term shifts In the electrical values that are caused by phase jitter due to temperature, ageing or short-term noise. If mass Is added to the crystal. Its electrical properties change. 

Automatic control of Film Deposition Rate with the crystal oscillator for preparation of alloy films. 

Longterm operation of crystal oscillators in thin film deposition J.Vac. Sci. Technol. 8, 622 (1971)... 

Physics Viscometer, quartz-crystal oscillator Viscosity... 

The same procedure is followed for all crystals. In dealing with photographs of monoclinic crystals oscillated round a or c, or triciinic crystals oscillated round any axis, care should be taken to use the appropriate origin for each reciprocal lattice level. (See Figs. 91 and 94.) As an example, the procedure for the first (hfcl) level of a triclinic crystal is illustrated in Fig. 98. 

These piezoelectric crystal oscillators are very accurate mass sensors because their resonant frequencies can be measured precisely with relatively simple electronic circuitry. For certain quartz crystals, the resonant frequency is inversely related to the crystal thickness. A crystal resonating at 5 megahertz is typically 300 micrometers thick. If material is coated or adsorbed on the crystal surface, the resonant frequency will change (decrease) in proportion to the amount of material added. The effect of adsorbed mass on the oscillator frequency varies according to the operational mode of the device. In any case, interpretation of mass via changes in frequency or amplitude assumes that the coated films are rigidly elastic and infinitesimally thin (that is, an extension of the crystal). 

CRYSTAL OSCILLATOR. This device is a precise mechanical resonator and frequency generator. The need for a stable, accurate, and... 

F ig. 20. Response characteristics of ru-tricosenuic acid coaled quad/ crystal oscillator at 22 C exposed to acetic acid. A greater change in ihc resonance frequency can he obtained if the lilm is specially sensitized to detect acetic acid... 

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