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Mutually Influenced Stacking and Evolution of Inorganic/Organic Crystals for Piezo-Related Applications
Published in Sam Zhang, Jyh-Ming Ting, Wan-Yu Wu, Functional Thin Films Technology, 2021
Piezoelectric effect develops electrical charges (or deformation) in response to an external stress (or electric field) (Equation 5.1 and 5.2):P=dσε=dEwhere P is polarization (pC/m2), d is a piezoelectric coefficient (pC/N or m/V), σ is an external stress (N/m2), ε is a strain, and E is an applied electric field. Commonly used piezoelectric coefficients of d33, d31, and d15, which denote longitudinal, transverse, and shear coefficients of a material, respectively [1].
Sensing Effects and Sensitive Polymers
Published in Gábor Harsányi, Polymer Films in Sensor Applications, 2017
where the subscript E indicates that the field is held constant and the subscript T that the stress is held constant. In other words, the piezoelectric coefficient is given by the rate of change of polarization with stress at a constant field or the rate of change of strain with field at constant stress. The units of d and d* will be coulombs per newton or meters per volt. It can be shown by the laws of thermodynamics that d = d*.
Pyroelectric and Piezoelectric Polymers
Published in Inamuddin, Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Polymers in Energy Conversion and Storage, 2022
Pragati Kumar, Lakshmi Unnikrishnan
This is the procedure where the crystallites (molecular dipoles) are reoriented to enhance the piezoelectricity in polymers [31]. Applying a high electric field (E) at a moderate temperature produces the permanent alignment of the molecular dipoles of the polymer along the electric field direction. The alignment of the dipole in a single direction results in polymer materials due to the generation of spontaneous polarization on the application of an electric field and the majority of the dipoles are sealed in an arrangement of similar orientation, even after the removal of the field [32].Direct contact method: A high voltage (DC or AC in the form of sinusoidal or triangular low-frequency signals) is applied across the polymer surfaces through the deposition of conductive electrodes. The electric field strength applied across the polymer surface will usually be in the range of 5 to 100 MV/m. The piezoelectric coefficient depends broadly on three factors: (i) the magnitude and duration of the electric field applied; (ii) the magnitude and extent of uniformity of the applied temperature; and (iii) the extent of impurity and uniformity of the polymer surface [33]. The electrical poling method is widely used for commercial films.Corona poling: In this method, the charging is done on one surface of the polymer either by using electrodes or without them. An extremely sharp and conducting needle is firstly kept in a high voltage (~8–20 kV). Then it is placed over a grid which is kept over the piezoelectric polymer. The polymer is kept in an inert ambient atmosphere like dry air or argon at a sufficiently lower DC voltage of 0.2–3 kV. Inert gas is ionized around the sharp tip and moved towards the polymer and charges the surface. The charging of the polymer surface is controlled by optimizing the grid position and magnitude of the voltage applied [34].The third way of enhancing the piezoelectricity of polymers is reported in the literature by the incorporation of fillers—using a variety of materials like ceramics, carbon allotropes and compounds, metal oxides, and composites of these materials—into the piezoelectric polymer matrix [35–38]. This will be discussed later in detail.
Design of an effective piezoelectric microcantilever biosensor for rapid detection of COVID-19
Published in Journal of Medical Engineering & Technology, 2021
Hannaneh Kabir, Mohsen Merati, Mohammad J. Abdekhodaie
Silicon-based materials like Silicon (Si), Silicon (Si3N4), and Silicon Oxide (SiO2) are used commonly for biosensor fabrication. Based on the previous studies, SiO2 is one of the best materials that represented higher deflection in response to a mechanical force in comparison with two others [20]. Thus, SiO2 is recommended for the flexible layer. Both ceramics and polymers that have crystalline and semi-crystalline structures demonstrate piezoelectricity. The piezoelectric coefficient is the amount of electric charge created by the application of mechanical force. Lead zirconate titanate (PZT), barium titanate (BaTiO3), and zinc oxide (ZnO) are among the piezoelectric ceramics with high piezoelectric coefficients which are 110 pC/N, 78 pC/N, and 5 pC/N, respectively. Nowadays, lead-free materials have been attracting more researches because they are friendlier to the environment when their wastes are disposed. Polymers have different properties compared to minerals [41]. Polymers can fill the depressions, while crystals and ceramics cannot. The piezoelectric strain coefficient (d31) for a polymer is less than that of a ceramic; however, its piezoelectric stress coefficient (g31) is higher. This means that polymers perform better in terms of sensor construction. Sensors and actuators made of piezoelectric polymers are more flexible because they are light and hard and can be turned into different shapes. Polymers also show a great impact on strength and durability. Having dielectric constant, elastic stiffness, low density, and high voltage sensitivity are other polymer properties [42]. Polyvinylidene fluoride (PVDF), Poly (trifluoroethylene) (PTrFE), Polyamide-11 (Nylon-11) are among the polymers with the highest piezoelectric properties with a piezoelectric coefficient of 23 pC/N, 12 pC/N, and 8 pC/N, respectively [43]. In this study, the function of PZT, BaTiO3, and PVDF that have the highest d31 among ceramics and polymers as a piezoelectric layer of the microcantilever of the biosensor has been investigated and the results are represented in the following sections. The material properties of the flexible and piezoelectric layers are shown in Table 1.