Quartz crystal oscillator

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. 

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. 

Physics Viscometer, quartz-crystal oscillator Viscosity... 

Film electrodes have been essential components of quartz microbalance studies of stoichiometry of many electrodeposition and dissolution experiments as well as polymer electrode characterization [25]. In the quartz microbalance, changes in mass are detected by measurement of changes in the resonant frequency of a quartz crystal oscillator as the mass adhering to the surface changes. The oscillation is feasible because thin-film metal electrodes (typically gold) applied to opposing faces of a piezoelectric quartz crystal serve both to induce the oscillation and to provide a site for electrochemical reaction. 

Fig. 8.10 Mode of operation of the quartz micro balance (left schematic). Right A dendrimer as guest-selective host compound (selector) for coating of the quartz crystal oscillator. Red Selector layer green various analyte components...

The Electrochemical Quartz Crystal Microbalance (EQCM) The resonant frequency of a quartz crystal oscillator is perturbed from its base value (f ) by attached overlayers. For thin, rigid films the measured change in resonant frequency (Af) with attached mass (AM) is described by the Sauerbrey equation (10) ... 

A number of techniques can be used to monitor the growth of amyloid fibrils and provide information on the kinetics of fibril assembly or disassembly. These techniques include light scattering or dye binding assays where Thioflavin T binds to the emerging fibril structure resulting in an increase in fluorescence (Krebs et al., 2005). Fourier transform infrared spectroscopy and circular dichroism can be used to monitor a change in secondary structure as the polypeptide adopts a (3-sheet-rich confirmation (Nilsson, 2004) and a quartz crystal oscillator used to follow an increase in fibril mass as a function of time (Knowles et al., 2007). 

The EQCM comprises a quartz crystal oscillator, in which one of the Au exciting electrodes is also exposed to the solution and acts as the working electrode in a conventional (here, three electrode) cell. Provided any surface film is rigidly coupled to the underlying electrode changes in inertial mass (Am) of the electrode result in crystal resonant frequency changes (A/) that are described by the Sauerbrey equation [11] ... 

Q can be increased in appropriately designed circuits this is utilized in several instruments (radios, in quartz crystal oscillators, quartz clocks, etc.) that are "tuned" to detect resonant transitions. 

Centuries ago, time was measured by the gnomon, the clepshydra, weights and gears (eventually controlled by an escapement), incense sticks, hourglasses, and then finally mechanical clocks, pendula, and self-winding watches (mechanically wound, self-winding, or by now controlled by a quartz crystal oscillator tank circuit). 

A quartz crystal thermometer sustains a capacitance if the frequency of the RLC circuit is precisely tuned to 14 or 20 MHz (depending on the exposed crystal faces). The quartz crystal will then transmit a very precise frequency, which has a temperature coefficient (typically 1 kHz per degree centigrade). If the temperature fluctuations are precisely compensated by a feedback heater circuit, then a quartz crystal oscillator is precise to about 1 part in 1.4 x 108. 

Coating the molecular sieve on one electrode of a quartz crystal oscillator is conducted to bricate a gas sensor in this study. The detection performance of the sensors with two different pore sizes of the molecular sieve is examined from their implement in the determination of methanol, ethanol and n-hexane concentration in air. From the performance test, the ruggedness, sensitivity and selectivity of the sensor are investigated. 

The metal coverage was monitored by Auger spectroscopy (AES) and with a quartz crystal oscillator. These data were calibrated by neutron activation analysis to ensure proper determination of the amount of material deposited. The change in frequency of the quartz oscillator was proportional to the film thickness. 

Fig. 20 Quartz crystal oscillator with OTA and amplitude limiting...

For designing an ALC, a precision rectifier, a comparafor, a proportional-integral (PI) confroller, and a gain-confrollable amplifier are required. The block diagram of fhe quartz crystal oscillator with ALC is depicted in Fig. 21... 

Fig. 21 Scheme of a quartz crystal oscillator with automatic level control. The gray components belong to the automatic level control [36]... 

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