Piezoelectric resonance method

Attempts have been made to correlate the outstanding electric properties (piezoelectricity, pyroelectricity) of PVDF with parameters obtained from wideline NMR experiments. Samples processed by different electric methods have been included in NMR experiments. Wideline NMR studies of irreversible effects induced by relatively high static electric fields have been reported by several authors. The results of wideline NMR ( H) have been used [53] in a combined investigation with a piezoelectric resonance method to find any effects of electric poling (0.78 MV/cm at 120°C) on structure and/or orientation. However, no indications of structural or orientational changes have been found. 

H. Ohigashi, Ekctroinechanical properties of poloritedpolyvinylideoe fluoride films as stud-led by the piezoelectric resonance method. J. AppL Pkys. 47949 (1976X... 

Values of the coupling factors are determined by the piezoelectric resonance method. This analyses the impedance Z of the material when it is excited by a voltage source and uses the resonant frequency, at which Z = 0, and the antiresonant frequency, at which Z is infinite, to calculate the appropriate k [32]. This method is satisfactory for ceramics, but large errors occur when it is applied directly to the polymers, because of their large mechanical losses and subsequent high damping effects. It is necessary to use equivalent-circuit models to select the parameters that produce resonance curves that are best fitted to observed ones [33]. 

The value of tand for PVDF is typically 0.1. This is 10 times greater than the value of 0.01 for ceramics (PZT 5). As discussed earlier, it is this high mechanical loss or damping that prevents measurement of the electromechanical coupling factors using the piezoelectric resonance method. 

A tubular sonicatlon device was recently reported by Borthwick et al. [93] (see Fig. 3.9). The device requires the addition of no chemical, enzyme or particles that might complicate the subsequent determination step. Furthermore, denaturatlon of target DMA or proteins for detection Is minimized as the device tolerates moderate temperature rises this allows the use of sensitive and specific Immunological detection methods on sonicated biological materials. Because the tubular device Is composed of a piezoelectric resonator made of several material layers, selection of an appropriate operating frequency Is essential to ensure proper performance (i.e. acceptable cell disruption efficiency). This device can be used for batchwise treatment of small sample volumes or In flow systems without the risk of hazardous aerosol formation inherent in probe sonloators. 

A number of technology developments can be identified that promise to advance the applications of QCM and related piezoelectric resonance techniques. These involve modifications in the QCM device, the crystal, as well as in the systems under study and their methods of analysis. Some of these approaches have already begun to be studied and implemented. The specific areas of these improvements include increasing mass sensitivity, hybrid devices and novel resonance techniques, enabling determination of the kinetics of processes, use of cells as information-rich sensing elements, and applying data mining techniques to provide accurate analyses and outputs from complex sensor inputs in future devices. We briefly discuss each of these below. 

The deflections of a microcantilever can be measured with sub-Angstrom resolution using current techniques perfected for die AFM, such as optical reflection, piezoresistive, capacitance, and piezoelectric detection methods. One great advantage of flie cantilever technique is diat five resonance response parameters (resonance fiequency, phase, anqilitude, Q-flictor, and deflection) can be simultaneously detected. 

Most piezoelectric characterization methods were developed for crystalline ceramics and had to be adapted for piezoelectric polymers. Methods based on resonance analysis and equivalent circuits that can be used to characterize semicrystalline PVDF and its copolymers are outlined in IEEE standards (66). Details for applying resonance analysis to piezoelectric polymers have recently been explored (67). Because of the lossy nature of some polymers, the IEEE standards are not adequate, and other techniques are needed to describe piezoelectric properties more accurately. 

Nestleroth et al. [15], Segal et al. [16] considered some established novel signal processing schemes to assist in adhesive bond inspection. Sinclair et al. [17] and Filimonov [18] employed acoustic resonance methods for dynamic elastic modulus measurements in adhesively bonded structures. Yost and Cantrell [19], Achenbach and Parikh [20] and Nagy et al. [21] considered a nonlinear response of bonded structures to estimate material characteristics. In Achenbach and Parikh [20], failure was preceded by nonlinear behavior of thin boundary layers at the interfaces. Billson and Hutchins [22] considered lasers and EMATS in bond investigations. It was shown that this non-contact technique was reasonable when compared to that obtained by conventional piezoelectric transducers. Ince et al. [23] also characterized bonds with laser-generated ultrasound and through-transmission measurements. 

For measuring the mechanical characteristics of the aforementioned films such as coefficients of elasticity and viscosity, one can use the piezoelectric resonators of bulk acoustic waves [23]. It should be noted that this method may be used when the... 

More recently methods have also been developed to measure the adsorbed amount on single surfaces and not onto powders. Adsorption to isolated surfaces can, for instance, be measured with a quartz crystal microbalance (QCM) [383]. The quartz crystal microbalance consists of a thin quartz crystal that is plated with electrodes on the top and bottom (Fig. 9.11). Since quartz is a piezoelectric material, the crystal can be deformed by an external voltage. By applying an AC voltage across the electrodes, the crystal can be excited to oscillate in a transverse shear mode at its resonance frequency. This resonance frequency is highly sensitive to the total oscillating mass. For an adsorption measurement, the surface is mounted on such a quartz crystal microbalance. Upon adsorption, the mass increases, which lowers the resonance frequency. This reduction of the resonance frequency is measured and the mass increase is calculated [384-387],... 

An excellent reference describing appropriate ways of measuring the piezoelectric coefficients of bulk materials is the IEEE Standard for Piezoelectricity [1], In brief, the method entails choosing a sample with a geometry such that the desired resonance mode can be excited, and there is little overlap between modes. Then, the sample is electrically excited with an alternating field, and the impedance (or admittance, etc.) is measured as a function of frequency. Extrema in the electrical responses are observed near the resonance and antiresonance frequencies. As an example, consider the length extensional mode of a vibrator. Here the elastic compliance under constant field can be measured from... 

There exist a number of readout techniques based on optical beam deflection, variation in capacitance, piezoresistance, and piezoelectricity. Piezoelectricity is more suited for a detection method based on resonance frequency than the method based on cantilever bending. The capacitive method is not suitable for liquid-based applications. The piezoresistive readout has many advantages, and it is ideally suited for handheld devices. 

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