Thickness-Shear Mode TSM Resonator

This is the correct name for most popular mass sensors, although they are better known as Quartz Crystal Microbalances (QCMs). A piezoelectric crystal vibrating in its resonance mode is a harmonic oscillator. For microgravimetric applications, it is necessary to develop quantitative relationships between the relative shift of the resonant frequency and the added mass. In the following derivation, the added mass is treated as added thickness of the oscillator, which makes the derivation more intuitively accessible. 

The change of resonance frequency, caused by the infinitesimally small change of the crystal thickness dt, is then obtained by differentiating (4.3). 

the relative increase of crystal thickness (shown in Fig. 4.3) lowers the resonant frequency. Equation (4.5) can be written in terms of the total mass M deposited per unit area and its finite change AM as 

Substitution for crystal thickness t from (4.3) yields the relative change of the resonant frequency. 

Constants v, p, and F are the material properties of the crystal. Because the density of the deposited film, pf, is known, the QCM becomes a thickness monitor. (In fact, monitoring of thickness of thin films during their deposition was the original application of QCM.) 

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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( licatithickness-shear mode (TSM) resonator, the surface 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. 

In this review, we discuss the development and appUcation to electrochemical problems of a bulk acoustic wave device, the thickness shear mode (TSM) resonator, whose operation (in the simplest case of a... 

If the wave propagates through the substrate, the wave is called a bulk wave. The most commonly used BAW devices are the thickness shear mode (TSM) resonator and the shear-horizontal acoustic plate mode (SH-APM) sensor. The TSM, also widely referred to as a quartz crystal microbalance (QCM), is the best-known and simplest... 

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]. 

Generally, the cut angle of quartz crystal determines the mode of induced mechanical vibration of resonator. Resonators based on the AT-cut quartz crystal with an angle of 35.25° to the optical z-axis would operate in a thickness shear mode (TSM) (Fig. 1.1) [4]. Clearly, the shear wave is a transverse wave, that is, it oscillates in the horizontal direction (jc-axis) but propagates in the vertical direction (y-axis). When acoustic waves propagate through a one-dimensional medium, the wave function (ij/) can be described by [11] ... 

Nanofiber films are used as a sensing interface for thickness shear mode (TSM) piezoelectric sensors. TSM sensors coated with nanofiber films made of poly-lactic acid-co-glycolic acid (PLAGA) polymers were studied under various ambient conditions and were reported to possess better sensitivities than their thin film counterparts [2]. For TSM resonators, the resolution varies linearly with the surface area of the sensing interface. Hence, polymer nanofiber would be an ideal material for this purpose. 

Figure 1 Wave propagation modes of piezoeiectric resonators. Ciosed arrows indicate particie dispiacement, open arrows direction of wave propagation. TSM, thickness shear mode FPW, fiexurai piate wave SAW, surface acousfic wave SH-APM, shear horizonfai acousfic piafe mode. (Reprinted with permission from Angewandfe Chemie infernafionai Edition (2000) 39 4004-4032 2003 Wiiey-VCH.)...

Fig. 13.1 Ditferent types of acoustic devices that can be used for sensing application FBAR film bulk acoustic resonators, TSM thickness shear mode, SMR solidly mounted resonators. Other designations are in the text...

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