Papers by Keyword: Piezoelectricity

Abstract: This study investigates the piezoelectric properties of a composite comprising polar hydroxyapatite (HA) and BaTiO₃ using an analytical model. The analysis covers the piezoelectric coefficients d₃₃ ​and d₃₁, and the specific acoustic impedance. The findings reveal that HA exhibits an unconventional d₃₃​ behavior, while the composite demonstrates a decrease in d₃₁​ and an increase in d₃₃​, with minimal BaTiO₃ content achieving d₃₃​ values similar to those of human bone (< 1 pC/N). Additionally, the d₃₁ coefficient of HA showed an unconventional behavior, highlighting its potential usage in the transverse direction. The impedance also increases from 23.5 MRayls to 31.5 MRayls, which improves acoustic wave transmission for medical imaging and therapeutic devices. These results highlight the composite's promise for bone regeneration, implantable ultrasound transducers, and energy harvesting applications.

Abstract: Electrospun piezoelectric nanofibrous membrane developed from Polyvinylidene fluoride (PVDF) embedded with thermoplastic polyurethane (TPU) composites found to have superior stretchability and piezoactivity. The piezoresponse behavior of different in-situ bended PVDF/TPU, up to 15wt.% of TPU, is examined using various blending ratios of PVDF and TPU. It has been shown that adding TPU with PVDF at certain specific concentration increased the nanofiber's piezo-efficiency.The generated nanomembranes are annealead at different temperatures up to 100°C. An extensive analysis of the effects of annealing is conducted on these nanomats, and it is thought to be a crucial post-treatment method for improving the piezoresponse of the manufactured nanomats. Nanofibers annealed at 100°C showed best effective response compared to all other samples and this revealed the effectiveness of annealing treatment in the enhancement of piezoactivity. The best effective composition of PVDF with 15 wt% TPU after an annealing treatment of 100°C generated a maximum voltage of 3.2 V under the effect of an applied force of 3 N, where unannealed sample of the same PVDF-TPU composition generated only a voltage of 2.2 V. This annealed piezo nanogenerator (PNG), can be considered an optimum option for electromechanical energy harvesting applications that require flexibility and self-power.

Abstract: In this work, electrospun membrane with excellent optical transparency has been developed and the study focuses on the optical and electromechanical properties of the membrane. Highly transparent PVDF based membrane fabricated by electrospinning exhibited appreciable piezoelectric property. Thus the study mainly focus on the multifunctional behaviour of these nanomembrane in the field of transparent sensors and energy harvesting systems. The transmittance of the fabricated membrane is measured using spectrophotometer and beta sheets content associated with the piezo activity of the membrane is measured using the Fourier Transform Infrared spectra. The surface characterization of the electrospun membrane were performed using Scanning Electron Microscope (SEM). The piezo response range of these membrane were tested using impulse loading and force voltage-based measurements. The utilization of these transparent optical membranes in the field of micro and nanoenergy harvesting systems based on piezoelectric transduction mechanism is focused.

Abstract: In the present work, a smart structure is being investigated, where a functionally graded carbon nanotube-reinforced composite (FG-CNTRC) plate is equipped with piezoelectric actuators to provide vibration control. Due to their high mechanical properties coupled with lightweight, FG-CNTRCs are mainly used in the aerospace industry and in advanced engineering applications. The CNTs have a linear and non-linear distribution along the thickness of the plate and are distributed according to five configurations, namely: UD, FG-X, FG-O, FG-A and FG-V. The first order shear deformation (FOSD) theory is considered in the formulation of a 9-node quadratic finite element with 5 degrees-of-freedom per node, and an additional degree of freedom is provided for the piezoelectric layer. The model developed in this study assesses the free vibration behavior and controls the nanocomposite plate deflection through the electromechanical coupling factor piezoelectric. In addition, it investigates: (i) the effect of the plate configuration, (ii) the CNT volume fraction, (iii) the CNT destruction patterns, (iv) the linear and nonlinear distribution of CNTs, (v) the number of CNTRC ply, (vi) the boundary conditions and (vii) the dimensions with different locations of actuators. The results obtained show the first natural frequencies for all configurations, which are considered to be in good agreement with those available in the literature and illustrate that the effective stiffness of the nanocomposite plates can be improved further when the reinforcement is dispersed according to the FG-X pattern. In addition, for the case of the deflection control analysis, results indicate that the distributed piezoelectric layers (actuators) attenuate the deflection of the CNTRC to the desired tolerance. It is noted that patches with partial coverage compared to the case of total coverage of piezoelectric layers require more electrical power to reach the same level of attenuation. The developed numerical model is intended to be used in a variety of potential advanced engineering applications.

Abstract: The effect of fiber cross-section on effective elastic and piezoelectric coefficients of piezoelectric fiber reinforced composites (PFRC) is investigated through two micromechanical analyzes viz. modified strength of materials (MSM) approach and energy approach. Results are verified with that of strength of materials (SM) approach available in the literature. A constant electric field is considered in the direction transverse to the fiber direction and is assumed to be same both in the fiber and matrix phases. It is observed that MSM and strength of materials (SM) approach predictions for the effective piezoelectric coefficient of the PFRC assessing the actuating capability in the fiber direction are in excellent agreement and also when the fiber volume fraction exceeds a critical value, this effective piezoelectric coefficient becomes significantly larger than the corresponding coefficient of the piezoelectric material of the fiber as investigated by both SM and MSM approaches. However, results of energy approach differ from both MSM and SM results and effective piezoelectric constant never exceeds to that of fiber as obtained by energy approach. It has been found for the piezoelectric fibers, cross-section of fiber has insignificant effect on the effective properties as predicted by MSM and energy approaches. Nomenclature

Abstract: This research deals with ambient energy harvesting by using zinc oxide thin film. The objectives of this thesis are to prove the ZnO film as a piezoelectric material can produce electric when vibration is applied and determine its optimal voltage. The thesis describes the sol gel spin coating technique to fabricate zinc oxide thin film. Zinc acetate dehydrate, absolute ethanol and diethanolamine were used in this thesis to act as sol gel precursor. Sol gel was coated on glass slide which wrapped by aluminum foil. The thin film was formed after preheating and annealing. The thin film was characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Photoluminescence spectroscopy (PL) and Ultraviolet-visible spectroscopy (UV-Vis) as well as analyzed using vibration technique. From XRD results, the films were preferentially diffracted at around 65° which corresponding to (1 1 2) diffraction phase. From FESEM results, it was observed that when the spin speed was increased at same annealing temperature, the thickness was also decreased. When the annealing temperature was increased at same spin speed, both grain size and thickness were increased. From the PL results, there was only film with spin speed of 2000 rpm and annealing temperature of 300 °C had slightly left wavelength which was 380 nm. Annealing temperature would affect only the intensity of PL wavelength. From the results of UV-Vis, it was observed that when the spin speed was increased at same annealing temperature, the band gap was decreased. When the annealing temperature was increased at same spin speed, the band gap was decreased. Piezoelectric test had proven the ZnO film could produce electricity. The maximum voltage (20.7 mV) was produced by the ZnO film with spin speed of 2000 rpm and annealing temperature of 300 °C.

Abstract: To date, flexible, sensitive and biocompatible pressure sensors for fluctuation signals in human body have been mainly demonstrated for detecting body and muscle motion, pulse rate, heart rate and arterial blood pressure. However, because of the lack of sufficient sensitivity and flexibility, pulse signals with relatively low intensity cannot be identified and captured, such as signals derived from microcirculation in human body. As confirmed and validated by researchers, once PVDF and its copolymer based nanocomposite sensing material are applied in piezoelectric sensors, its sensitivity and piezoelectricity are highly relevant. Therefore, as one of the most effective methods to improve the permittivity and piezoelectricity of PVDF and its copolymer based nanocomposite, the effect of increasing the content of β-phase crystal was investigated in this work. In this project, the sensor possessing a novel sensing layer with the nanofiller was investigated and fabricated. The proposed sensor was designed in a simple but efficient sandwich structure. The sensing layer of the proposed sensor was made of polyvinylidene fluoride (PVDF) and polyvinylidenefluoride-trifluoroethylene (PVDF-TrFE) based nanocomposite with Zinc Oxide (ZnO) nanostructure acting as a filler portion which was fabricated by the method of Chemical Bath Deposition (CBD). The fabricated nanocomposite sensing layers were characterized. The microstructures and morphologies of pristine PVDF (P), PVDF-TrFE (PT), PVDF/ZnO (P/Z) and PVDF-TrFE/ZnO (PT/Z) with different concentration were characterized by Scanning Electron Microscope (SEM). The degree of crystallinity for P, PT, P/Z and PT/Z was obtained by X-ray Diffraction meter (XRD). In conclusion, PT exhibited better performance in both morphology and crystallinity as a sensing membrane material. More β‐phase in PT was obtained than that in P. ZnO, as a semiconductor filler, would have substantial influence on enhancing the dielectric constant by acting as a nucleating agent and forming a nanostructure with large aspect ratio.

Abstract: Piezoelectric composite materials with a polymer matrix are important for underwater acoustic and biomedical imaging applications. The dependence of electromechanical properties of piezoelectric composite on constituent material characteristics and shape of piezoelectric inclusions is a central problem that provides the opportunity to tailor the performance of piezoelectric composites according to design needs. A numerical model has been developed to investigate the electromechanical properties of 1-3 piezoelectric composites with a passive and active polymer matrix. Maxwell Homogenization method is employed to homogenize the solution domain. It is demonstrated that the use of PVDF as an active polymer matrix has a significant influence on piezoelectric charge coefficient d₃₁, hydrostatic coefficient d_h, voltage coefficient g_h, and hydrophone figure of merit g_hd_h when compared to the passive Araldite-D polymer matrix. Overall, a 5 to 30% volume fraction of PZT-7A fiber inclusions in an active polymer matrix is the optimum ratio that has a significant effect on piezoelectric properties. The accuracy and effectiveness of homogenized material constants were verified by comparing the derived composite properties with experimental work published elsewhere. These results provide much needed intuitiveness in the development of piezoelectric polymer composite with better performance for transducer applications.

Abstract: ABO₃ perovskite ceramics due to their chemical nature and size difference of the cations A (where A is a divalent metal) and B (where B is a tetravalent metal) have non-centro-symmetric polymorphs and display significant piezoelectric properties. One path to improve piezoelectric properties is through alloying these materials. In order to assess the feasibility of this, we have investigated the structure, elastic and piezoelectric properties of prototypical cubic and tetragonal phases of ABO₃ bulk ceramic oxides and their alloys: {A_xA`<sub>(1-x)</sub>}BO<sub>3</sub> and A{B<sub>x</sub>B`_(1-x)}O₃ by density functional theory based first-principle calculations. Using 2x2x2 super cells as models in our calculations, we have covered the full alloying range by varying concentration, x, in steps of 12.5%. We have created models using Ba, Sr, Pb, for A and A`, and Ti, Zr for B and B` both in cubic and tetragonal super cells. Here, we will report the structural and piezoelectric properties of tetragonal phases of ABO₃ bulk ceramic oxides and their alloys.

Abstract: Amongst current aircraft research topics, morphing wing is of great interest for improving the aerodynamic performance. A morphing wing prototype has been designed for wind tunnel experiments. The rear part of the wing - corresponding to the retracted flap - is actuated via a hybrid actuation system using both low frequency camber control and a high frequency vibrating trailing edge. The camber is modified via surface embedded shape memory alloys. The trailing edge vibrates thanks to piezoelectric macro-fiber composites. The actuated camber, amplitude and frequency ranges are characterized. To accurately control the camber, six independent shape memory alloy wires are controlled through nested closed-loops. A significant reduction in power consumption is possible via this control strategy. The effects on flow via morphing have been measured during wind tunnel experiments. This low scale mock-up aims to demonstrate the hybrid morphing concept, according to actuator capabilities point of view as well as aerodynamic performance.