Thickness shear mode

Some attempts to exploit sensor dynamics for concentration prediction were carried out in the past. Davide et al. approached the problem using dynamic system theory, applying non-linear Volterra series to the modelling of Thickness Shear Mode Resonator (TSMR) sensors [4], This approach gave rise to non-linear models where the difficulty to discriminate the intrinsic sensor properties from those of the gas delivery systems limited the efficiency of the approach. 

As an example of the use of array methodology to study chemical sensor properties let us consider the thirteen molecular structures reported in Figure 5. To investigate the sensing properties of these molecules we studied the behaviour of the response of thickness shear mode resonators (TSMR) sensors, each coated with a molecular film, to different concentration of various volatile compounds (VOC). Analyte compounds were chosen in order to have different expected interaction mechanisms. 

A piezoelectric mass sensor is a device that measures the amount of material adsorbed on its surface by the effect of the adsorbed material on the propagation of acoustic waves. Piezoelectric devices work by converting electrical energy to mechanical energy. There are a number of different piezoelectric mass sensors. Thickness shear mode sensors measure the resonant frequency of a quartz crystal. Surface acoustic wave mode sensors measure the amplitude or time delay. Flexure mode devices measure the resonant frequency of a thin Si3N4 membrane. In shear horizontal acoustic plate mode sensors, the resonant frequency of a quartz crystal is measured. 

Fig. 4.3 Shear mode vibrations in a thickness-shear-mode (TSM) device. Incremental increase AX is due to increased thickness...

In this part we will describe recent achievements in the development of biosensors based on DNA/RNA aptamers. These biosensors are usually prepared by immobilization of aptamer onto a solid support by various methods using chemisorption (aptamer is modified by thiol group) or by avidin-biotin technology (aptamer is modified by biotin) or by covalent attachment of amino group-labeled aptamer to a surface of self-assembly monolayer of 11-mercaptoundecanoic acid (11-MUA). Apart from the method of aptamer immobilization, the biosensors differ in the signal generation. To date, most extensively studied were the biosensors based on optical methods (fluorescence, SPR) and acoustic sensors based mostly on thickness shear mode (TSM) method. However, recently several investigators reported electrochemical sensors based on enzyme-labeled aptamers, electrochemical indicators and impedance spectroscopy methods of detection. 

Thickness shear mode 807 Thin film e363 arrays 636 gold electrodes el06 Thiocholine 345, el69 Thiols 563... 

A quartz crystal sensor chip was bonded with a microfluidic glass chip for acoustic wave detection (see Figure 7.46). The sensor was operated in the thickness-shear mode (TSM). This has allowed rat heart muscle cell contraction to be studied based on the measurement of the resonant frequency changes [133]. 

First, the underlying principles upon which bulk acoustic wave (BAW) devices operate are described. When a voltage is applied to a piezoelectric crystal, several fundamental wave modes are obtained, namely, longitudinal, lateral and torsional, as well as various harmonics. Depending on the way in which the crystal is cut, one of these principal modes will predominate. In practice, the high-frequency thickness shear mode is often chosen since it is the most sensitive to mass changes. Figure 3.4 schematically illustrates the structure of a bulk acoustic wave device, i.e. the quartz crystal microbalance. 

Quartz crystal microbalance — The quartz crystal microbalance (QCM) or nanobalance (QCN) is a thickness-shear-mode acoustic wave mass-sensitive detector based on the effect of an attached foreign mass on the resonant frequency of an oscillating quartz crystal. The QCM responds to any interfacial mass change. The response of a QCM is also extremely sensitive to the mass (density) and viscoelastic changes at the solid-solution interface [i-vi]. 

Martin SJ, Frye GC, Ricco AJ, Senturia SD (1993) Effect of surface-roughness on the response of thickness-shear mode resonators. Anal Chem 65 2910-2922... 

Note that the source tenn is non-zero only in regions where it varies spatially. This is an important consideration in the mechanism by which acoustic waves are launched in the thickness-shear mode resonators that we consider later. 

Devices based on piezoelectric crystals, which allow transduction between electrical and acoustic energies, have been constructed in a number of conrigurations for sensor applications and materials characterization. This cluqtter examines those devices most commonly utilized for sensing a( licatisurface acoustic wave (SAW) device, the acoustic plate mode (APM) device, and the flexural plate wave (FPW) device. Each of these devices, shown schematically in Figure 3.1, uses a unique acoustic mode. 

Figure 3.1 Schematic sketches of the four types of acoustic sensors, (a) Thickness-Shear Mode (TSM) resonator (b) Surface-Acoustic-Wave (SAW) sensor, (c) Shear-Horizontal Acoustic-Plate-Mode (SH APM) sensor, and (d) Flexural-Plate-Wave (FPW) sensor.

The thickness-shear mode (TSM) resonator, widely referred to as a quartz crystal microbalance (QCM), typically consists of a thin disk of AT-cut quartz with circular electrodes patterned on both sides, as shown in Figure 3.2. Due to the piezoelectric properties and crystalline orientation of the quartz, the application of a voltage between these electrodes results in a shear deformation of the crystal. The crystal can be electrically excited in a number of resonant thickness-shear modes. 

The term quartz crystal microbalance is an unfortunate name for this device for several reasons (1) The word crystal is redundant when it follows quartz, a crystalline material (2) the devices do not invariably act exclusively as microbalances, being subject to a number of other physical perturbations as well (3) the name could also correspond to a SAW, APM, or FPW device fabricated from quartz. The term thickness-shear mode (TSM) resonator follows the convention used for the SAW, SH-APM, and FPW notations in that it describes the nature of the acoustic mode upon which the device is based. 

Figure 3.14 Cross-sectional view of a thickness-shear mode resonator with a polymer film coating the upper surface [40]. Shear displacement profiles are shown at maximum excursion. (Reprinted with permission. See Ref. 140]. > 1991 IEEE.)...

Equations 3.19 and 3.36 can be combined to find the change in (electrical) motional impedance that arises from a viscoelastic film on a thickness-shear mode resonator [40] ... 

Figure 6.1 The thickness-shear mode resonator (TSMR) the pair of electrical leads comprise a single port.

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