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Resonator/oscillator circuits

The most common approach to electronically detecting wave velocity changes in a SAW sensor is to construct a delay line or resonator oscillator circuit using the device as the frequency control element. In such arrangements relative changes in oscillator frequency are proportional to relative phase velocity changes, so we have... [Pg.308]

Most NC-AFMs use a frequency modulation (FM) teclmique where the cantilever is mounted on a piezo and serves as the resonant element in an oscillator circuit [101. 102]. The frequency of the oscillator output is instantaneously modulated by variations in the force gradient acting between the cantilever tip and the sample. This teclmique typically employs oscillation amplitudes in excess of 20 mn peak to peak. Associated with this teclmique, two different imaging methods are currently in use namely, fixed excitation and fixed amplitude. [Pg.1697]

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] ... [Pg.123]

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. [Pg.127]

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. [Pg.128]

This circuit uses the resonance of an LC filter to switch an inverter, creating a square wave at the output of the inverter. The schematic is shown in Fig. 8.51. This arrangement provides better stability than the RC resonating oscillator, and has an amazingly small parts count. [Pg.244]

The inductance of adjustable coils with a ferrite core and the capacity of trim capacitors are strongly influenced by metal screwdrivers. It is important for trim capacitors and coils in oscillator circuits to be adjusted in the precise centre of the resonance area. Should this occur at the side, then oscillators sometimes fail to REACT when there is question of a change in temperature or ageing of components. Thus more situations can be mentioned in which you can benefit from the advantages of ceramic screwdrivers. [Pg.300]

Sensors using quartz crystal are very sensitive and can detect samples of the order of pg. Usually, an organic thin film is pasted on quartz surface since the crystal surface hardly absorbs any chemical species. The organic thin film provides the potential to detect various kinds of volatilities with high selectivity and sensitivity. The principle of the gas sensor is based on Eq. (1) [32]. The quartz oscillator has a specific resonance frequency with an oscillating circuit. Its frequency is decreased by the absorption of volatilities on the quartz surface due to the increase in mass. The frequency shift caused by exposure to a volatile depends on the amount adsorbed. With a 9 MHz quartz oscillator, the frequency is decreased by 400 Hz upon adsorption of 1 pg of a compound. A resonance oscillator with a higher resonance frequency can detect smaller amounts. [Pg.198]

In general, electromagnetic resonators are of common use for material characterization at microwave frequencies. In addition, a resonator represents a basic element of a multipole filter or an oscillator circuit. Any type of electromagnetic resonator is characterized by the resonant frequency /o and the unloaded quality factor Qo of the selected resonant mode and its spectrum of spurious modes. In order to measure the resonator properties or to use a resonator as part of a filter structure, the resonator needs to be equipped with one or two... [Pg.110]

The TSM resonator was originally used in vacuo to measure metal deposition rates [1]. More recently, the TSM resonator has been shown to operate in contact with liquids [2,3], enabling its use as a solution-phase microbalance. The device is typically incorporated in an oscillator circuit, where the oscillation frequency tracks the crystal resonance and indicates mass accumulation on the device surface. This microbalance capability has facilitated a number of gas- and liquid-phase sensor applications that will be discussed in Chapter 5. [Pg.39]

Because TSM oscillators have been around for over 50 years, quite a number of circuits to measure their response have been proposed, fabricated, and tested. The frequency of operation of TSM resonators (typically < 20 MHz) allows circuits to be constructed using ordinary components and printed circuit boards. Instruments and fixtures are commerciaUy available from a number of vendors (see Appendix D) that utilize fairly simple oscillator circuits incorporating the TSM resonator as the principal fiequency-control element. These systems are sold primarily for monitoring the deposition of metal films via evaporation or sputtering in a vacuum environment. The operator must typically input the density and acoustic impedance of the metal to be deposited, and the instrument then displays film thickness as deposition proceeds. These systems can also be utilized for gas-phase sensing applications, provided the TSM device is not coated with any particularly lossy materials these can cause so much damping that oscillation ceases. The systems provide information derived only from the resonant frequency there is no indication of damping except in the instance that oscillation ceases entirely. [Pg.365]

In addition to commercial systems, there are quite a number of oscillator circuits that can be built from relatively inexpensive components to perform tiie essential measurements without the functions and convenience of a packaged instrument [22-28]. Both the commercial systems and most of these home-built oscillator circuits yield just one piece of information the resonant frequency of the TSM device. While this is sufficient for mass-loading-only applications like vacuum deposition of metal films, for some electrochemical processes, and even for appropriately selected chemically sensitive films, it can fall short when changes in the mechanical properties of a surface layer or contacting medium are significant [29]. [Pg.366]

For both damped (liquid) and undamped environments, the ideal oscillator circuit should precisely track either the series or parallel resonance (see Section... [Pg.366]

Conceptually, one-port SAW oscillator circuits are very similar to those described for one-port TSM resonators, the principal difference being a significantly higher frequency of operation (100s of MHz rather than a few MHz). Just as for TSM resonators, an external circuit is required that is capable of driving the device at resonance and tracking changes in the frequency of resonance as the device impedance is perturbed. [Pg.367]


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