David Soares

Models for Resonant Sensors

The quartz crystal resonator (QCR), as its acronym implies, is a resonant physical device. Many of its behaviors and properties can be understood physically by examining its resonant behavior. The basic principle of operation for a generic acoustic-wave sensor is a traveling wave combined with a confinement structure to produce a standing wave whose frequency is determined jointly by the velocity of the traveling wave and the dimensions of the confinement structure. The most basic way of resonator modeling consequently requires applying the theory of wave propagation whereby considering material properties and geometric dimensions of the resonator. As another successful way, there is an electrical equivalent circuit often used to characterize the resonance. For these reasons, a closer inspection of the phenomenon of resonance is useful.

Interface Electronic Systems for AT-Cut QCM Sensors: A comprehensive review

AT quartz crystal microbalance sensors (QCMS) are becoming into a good alternative analytical method in a great deal of applications [1 – 16], with a resolution comparable, in many cases, to chemical techniques used for detecting species and suitable for fluids physical properties characterization [17, 18], though simpler and much less expensive. However, an appropriate evaluation of this analytical method requires recognizing the different steps involved in order to be conscious of their importance and to avoid the possible error propagation if the appropriate care is not taken. The three steps involved in a QCM system are:

The quartz crystal microbalance: a tool for probing viscous/viscoelastic properties of thin films

Techniques based upon the electrical response of the quartz crystal microbalance (QCM) have been widely used in laboratories as a routine tools. In this article we present and discuss applications of the QCM (or its variant, the electrochemical quartz crystal microbalance, EQCM) to the viscoelastic characterization of films. It is pointed out that correlations between the motion of quartz crystal and contacting films and overlayers as well as the influence of the electronic circuit on the electric state of the whole system are of fundamental importance in interpreting the results.

Test cell simulating the operating conditions of water electrolysers for the evaluation of gas evolving electrocatalysts

To evaluate promising anode, cathode, and separator materials in conditions similar to those present in a full-size water electrolyser, a test cell with electrode area of 10 cm2 was constructed. In order to operate with current densities as high as 1A cm−2 a 10 A pulsed galvanostat was developed and built which features a ‘sample-hold’ circuit to measure the IR-free electrode overvoltages and direct meter readings.

Fundamentals on Piezoelectricity

The topic of the following chapter is relatively difficult and includes different areas of knowledge. The piezoelectric phenomenon is a complex one and covers concepts of electronics as well as most of the areas of classical physics such as: mechanics, elasticity and strength of materials, thermodynamics, acoustics, wave’s propagation, optics, electrostatics, fluids dynamics, circuit theory, crystallography etc. Probably, only a few disciplines of engineering and science need to be so familiar to so many fields of physics. Current bibliography on this subject is vast though dispersed in research publications, and few of the books on this topic are usually compilations of the authors’ research works. Therefore, they are not thought for didactic purposes and are difficult to understand, even for postgraduates. The objective of this chapter is to help understand the studies and research on piezoelectric sensors and transducers, and their applications. Considering the multidisciplinary nature, this tutorial’s readers can belong to very different disciplines. They can even lack the necessary basic knowledge to understand the concepts of this chapter. This is why the chapter starts providing an overview of the piezoelectric phenomenon, doing consciously initial simplifications, so that the main concepts, which will be progressively introduced, prevail over the accessories. The issues covered in this chapter must be understood without the help of additional texts, which are typically included as references and are necessary to study in depth specific topics. Finally, the quartz crystal is introduced as a microgravimetric sensor to present the reader an application of the piezoelectric phenomenon, which will be dealt with along the following chapters.

Interface Electronic Systems for AT Quartz Crystal Microbalance Sensors

AT quartz crystal microbalance sensors (QCMS) are becoming into a good alternative analytical method in a great deal of applications [1 – 4], with a resolution comparable, in many cases, to chemical techniques used for detecting species and suitable for fluids physical properties characterization [5,6], though simpler and much less expensive.

Viscoelastic Properties of Macromolecules

An acoustic wave traveling through a material deforms the material, thereby probing its mechanical properties. The classical theory of elasticity deals with the mechanical properties of elastic solids. In accordance with Hook’s law, for small deformations stress is always directly proportional to strain. Furthermore, stress is independent of the rate of strain. The classical theory of hydrodynamics deals with properties of viscous liquids. In accordance with Newton’s law, stress is always directly proportional to rate of strain but independent of the value of strain itself.