Optimal Thickness Ratio Research Articles

Theoretical analysis of energy harvesting performance for clamped–clamped piezoelectric beam

The clamped---clamped beam has attracted increasing attention in the area of piezoelectric energy harvesting and transducer. In this paper, we present the theoretical models of clamped---clamped piezoelectric unimorph and bimorph beams with a quasi-static force in the middle. Based on the models, numerical studies are carried out to compare the generated charge, open-circuit voltage and generated energy of the piezoelectric beams under different condition. The simulation results demonstrate that the output performance of the beams are depended on the bonding position and electromechanical properties of the piezoelectric layer, and the length ratio, thickness ratio and the Young's modulus ratio (YMR) of the piezoelectric layer and substrate. Specifically, the unimorph and bimorph beams share the same optimal length ratio while their optimal width ratio and thickness ratio are different. The YMR imposes a great impact on the performance of the beam both in the unimorph and bimorph cases. As a generalization, the models are not only suitable for the beam with a non-uniform cross-section but also applicable for the beam with uniform cross-section. The analyses can be used to improve the performance of the clamped---clamped beam working as an energy harvester and transducer.

Interfacial delamination of double-ceramic-layer thermal barrier coating system

Thermal barrier coating system (TBCs) must withstand the most demanding high temperature conditions where state-of-the-art top coat material Y2O3–stabilized ZrO2 may undergo significant sintering and phase change. The concept of double-ceramic-layer (DCL) TBCs seems to be an effective way to meet the need for both thermal stability and transformation toughening. In this paper, a virtual crack closure technique based interface element method is introduced to study the mechanics associated with the interfacial delamination of DCL TBCs. The evolution of energy release rate of interfacial delamination is explored for DCL TBCs with various geometrical and material parameters. Analysis of fracture mechanisms of delamination reveals that considering the integrated thermal and mechanical functionalities of coatings an optimal thickness ratio of outer to inner ceramic layers exists, which can be preliminarily evaluated by running numerical calculations of fracture parameters and performing thermal life experiments over a wide range of thickness ratios of outer to inner coating layers. In addition, the influence of separation centered at the interface of two ceramic layers is also examined. It is demonstrated that the local separation between two ceramic layers makes delamination readily to form and propagate at the interface between the inner coating and the underlying layer.

Optimum structure of Whipple shield against hypervelocity impact

Hypervelocity impact of a spherical aluminum projectile onto two spaced aluminum plates (Whipple shield) was simulated to estimate an optimum structure. The Smooth Particle Hydrodynamics (SPH) code which has a unique migration scheme from a rectangular coordinate to an axisymmetic coordinate was used. The ratio of the front plate thickness to sphere diameter varied from 0.06 to 0.48. The impact velocities considered here were 6.7 km/s. This is the procedure we explored. To guarantee the early stage simulation, the shapes of debris clouds were first compared with the previous experimental pictures, indicating a good agreement. Next, the debris cloud expansion angle was predicted and it shows a maximum value of 23 degree for thickness ratio of front bumper to sphere diameter of 0.23. A critical sphere diameter causing failure of rear wall was also examined while keeping the total thickness of two plates constant. There exists an optimum thickness ratio of front bumper to rear wall, which is identified as a function of the size combination of the impacting body, front and rear plates. The debris cloud expansion-correlated-optimum thickness ratio study provides a good insight on the hypervelocity impact onto spaced target system.

OPTIMUM THICKNESS RATIO OF TWO SPACED PLATE SYSTEM AGAINST HYPERVELOCITY IMPACT

Analysis of two spaced aluminum plates against hypervelocity impact of a spherical aluminum projectile was performed to find an optimum thickness ratio of two plates. The smooth particle hydrodynamics (SPH) scheme used here is especially effective since the major features of debris clouds between two plates are successfully captured. For systematical analysis the extent of debris clouds is first correlated as a function of sphere diameter to front plate thickness ratio, with which a potential optimum front plate thickness range is identified. Then a critical sphere diameter causing failure of rear wall is examined while keeping the total thickness of two plates constant. In fact an optimum thickness ratio exists and is examined as a function of the size combination of the sphere diameter and plate thicknesses. The debris cloud expansion correlated optimum thickness ratio study provides a good insight on the hypervelocity impact onto spaced target system.

Crystal growth of Cu(In,Ga)Se2 film by RTP annealing of the stacked elemental layers formed by E-beam evaporation

Cu(In,Ga)Se2 (CIGS) thin films were successfully prepared by the application of a rapid thermal process to the stacked elemental layers (SEL), which were deposited by electron-beam (E-beam) evaporation method in the sequence of Cu/In/Ga/…/Cu/In/Ga. For the crystal growth of the CIGS absorber layer, an Se layer was deposited on top of the SEL precursors, and RTP annealing was carried out by a 2-step process at 200°C for 5min and at 550°C for 3min. The stoichiometry of the CIGS film with Cu/(In+Ga) and Ga/(In+Ga) atomic ratios of 0.90 and 0.26, respectively, was obtained with the optimum thickness ratio of the Cu/In and Ga precursor layers. In grown CIGS film, the suppression of Se loss during the annealing is very important. A subsidiary quartz box was used for sustaining maintaining the Se vapors during the selenization process in order to prevent Se loss. The experimental results show that the method is effective for preventing Se loss without the use of toxic H2Se gas or any other Se sources. The obtained CIGS film was homogeneous, and the surface morphology was dense with quite a large grain size of about 2μm.

Thickness-ratio-dependent dielectric properties of Bi1.5Zn1.0Nb1.5O7/Ba0.5Sr0.5TiO3 bilayered thin films

Abstract Bi1.5Zn1.0Nb1.5O7 (BZN)/Ba0.5Sr0.5TiO3 (BST) thin films were prepared on Pt/Ti-coated sapphire substrates by radio frequency magnetron sputtering. The specific relationship between the dielectric properties and the thickness ratio of the BZN thickness to the BST thickness was investigated. The presence of BZN films effectively reduced the dielectric loss of the thin films. The thickness-ratio-dependent dielectric constant and dielectric loss behaviors were in good accordance with the simulation results based on the series connection theory. The optimum thickness ratio was determined to be around 0.5, exhibiting a maximum commutation quality factor of about 16,000. The built-in electric field at the region near the BZN–BST interface may be responsible for the asymmetric characteristic of the electric-field-dependent dielectric properties of the BZN/BST thin films.

On the Thickness Ratio in the Quasigeostrophic Two-Layer Model of Baroclinic Instability

Abstract It is shown that the classical quasigeostrophic two-layer model of baroclinic instability possesses an optimal ratio of layer thicknesses that maximizes the growth rate, given the basic-state shear (thermal wind), beta, and the mean Rossby radius. This ratio is interpreted as the vertical structure of the most unstable mode. For positive shear and beta, the optimal thickness of the lower layer approaches the midheight of the model in the limit of strong criticality (shear/beta) but it is proportional to criticality in the opposite limit. For a set of parameters typical of the earth’s midlatitudes, the growth rate maximizes at a lower-layer thickness substantially less than the midheight and at a correspondingly larger zonal wavenumber. It is demonstrated that a turbulent baroclinic jet whose statistical steady state is marginally critical when run with equal layer thicknesses can remain highly supercritical when run with a nearly optimal thickness ratio.

Characterization of periodic multilayer mirrors optimized for single attosecond pulse reflection

Periodic Mo/Si multilayer mirrors with high peak reflectivity and broad reflection band for reflecting single attosecond pulse are designed, by optimizing the thickness ratio between the absorber layer and the bilayer. The reflective characteristics of periodic Mo/Si multilayer mirrors with different thickness ratio are analyzed and compared both in frequency domain and in time domain, for picking out optimized thickness ratio to achieve high-efficiency attosecond pulse reflection. According to our simulation, periodic quarter-wavelength Mo/Si multilayer mirrors with different layers all show better pulse reflection capability for incident Gaussian pulses than multilayers with other thickness ratio. When studying the spectral and the temporal responses of periodic multilayer mirrors, the transfer-matrix method and fast Fourier transform have been used in our simulation.

Damage mechanism and anti-penetration performance of explosively welded plates impacted by projectiles with different shapes

The damage mechanism and anti-penetration performance of explosively welded steel/aluminum plates, which was different from common target for the well surface-to-surface combination, impacted by spherical and cubical projectiles at different incident angles were studied by ballistic experiments and numerical simulation. The total thickness of the plate is 5mm. A 14.5mm slip chamber gun was used to launch the spherical steel projectile with diameter of 6mm and cubical steel projectile with side length of 4.2mm in the experiments. Penetration process was numerically simulated by dynamic finite element program LS-DYNA3D. The effects of projectile shape, kinetic energy and target thickness distribution as well as incident angle, which is 0°, 30°, 45° and 60°, respectively, on the anti-penetration performance of the plates were investigated. The results show that when the target is penetrated by the projectile, the damage mechanism of steel front plate is shearing and plugging and that of aluminum rear plate is prolonging deformation. It is easier for the spherical projectile than the cubical projectile with the same initial kinetic energy to perforate the plates. The optimized thickness ratio of steel and aluminum is about 3:1 for spherical projectile and about 3:2 for cubical projectile. The ballistic limit velocity increased with the improvement of incident angle for both spherical and cubical projectiles. The good accordance of numerical and experimental results indicates that the finite element method (FEM) and the Tie-Break model can predict the anti-penetration performance of the explosively welded plates well.

Optimization of electrode geometry and piezoelectric layer thickness of a deformable mirror

Deformable mirrors are the most commonly used wavefront correctors in adaptive optics systems. Nowadays, many applications of adaptive optics to astronomical telescopes, high power laser systems, and similar fast response optical devices require large diameter deformable mirrors with a fast response time and high actuator stroke. In order to satisfy such requirements, deformable mirrors based on piezoelectric layer composite structures have become a subject of intense scientific research during last two decades. In this paper, we present an optimization of several geometric parameters of a deformable mirror that consists of a nickel reflective layer deposited on top of a thin lead zirconate titanate (PZT) piezoelectric disk. Honeycomb structure of gold electrodes is deposited on the bottom of the PZT layer. The analysis of the optimal thickness ratio between the PZT and nickel layers is performed to get the maximum actuator stroke using the finite element method. The effect of inter-electrode distance on the actuator stroke and influence function is investigated. Applicability and manufacturing issues are discussed.

Energy Conversion Efficiency of Rainbow Shape Piezoelectric Transducer

With the aim to enhance the energy conversion efficiency of the rainbow shape piezoelectric transducer, an analysis model of energy conversion efficiency is established based on the elastic mechanics theory and piezoelectricity theory. It can be found that the energy conversion efficiency of the rainbow shape piezoelectric transducer mainly depends on its shape parameters and material properties from the analysis model. Simulation results show that there is an optimal length ratio to generate maximum energy conversion efficiency and the optimal length ratios and energy conversion efficiencies of beryllium bronze substrate transducer and steel substrate transducer are (0.65, 2.21%) and (0.65, 1.64%) respectively. The optimal thickness ratios and energy conversion efficiencies of beryllium bronze substrate transducer and steel substrate transducer are (1.16, 2.56%) and (1.49, 1.57%) respectively. With the increase of width ratio and initial curvature radius, both the energy conversion efficiencies decrease. Moreover, beryllium bronze flexible substrate transducer is superior to the steel flexible substrate transducer.

Density of States-Based Design of Metal Oxide Thin-Film Transistors for High Mobility and Superior Photostability

A novel method to design metal oxide thin-film transistor (TFT) devices with high performance and high photostability for next-generation flat-panel displays is reported. Here, we developed bilayer metal oxide TFTs, where the front channel consists of indium-zinc-oxide (IZO) and the back channel material on top of it is hafnium-indium-zinc-oxide (HIZO). Density-of-states (DOS)-based modeling and device simulation were performed in order to determine the optimum thickness ratio within the IZO/HIZO stack that results in the best balance between device performance and stability. As a result, respective values of 5 and 40 nm for the IZO and HIZO layers were determined. The TFT devices that were fabricated accordingly exhibited mobility values up to 48 cm(2)/(V s), which is much elevated compared to pure HIZO TFTs (∼13 cm(2)/(V s)) but comparable to pure IZO TFTs (∼59 cm(2)/(V s)). Also, the stability of the bilayer device (-1.18 V) was significantly enhanced compared to the pure IZO device (-9.08 V). Our methodology based on the subgap DOS model and simulation provides an effective way to enhance the device stability while retaining a relatively high mobility, which makes the corresponding devices suitable for ultradefinition, large-area, and high-frame-rate display applications.

Optimum wall thickness ratio based on the minimization of entropy generation in a viscous flow between parallel plates

The influence of the geometrical and physical parameters on entropy generation for a viscous flow between infinite parallel walls of finite thickness is studied by solving the momentum and energy conservation equations. The conjugate heat transfer problem in the fluid and solid walls is solved analytically using thermal boundary conditions of the third kind at the outer surfaces of the walls and continuity of temperature and heat flux across the fluid–wall interfaces. Analytic solutions for the velocity and temperature fields in the fluid and walls are used to calculate the local and global entropy generation rate. Conditions under which this quantity is minimized are determined for certain suitable combination of geometrical and physical parameters of the system. Special attention has been given to the effect of the wall thickness on the entropy generation rate. It is found that the global entropy generation reaches a minimum for specific values of the wall thickness ratio, when the other parameters are fixed.

Nonlinearity analysis of piezoelectric micromachined ultrasonic transducers based on couple stress theory

This paper studies the static deformation behavior of a piezoelectric micromachined ultrasonic transducer (PMUT) actuated by a strong external electric field. The transducer membrane consists of a piezoelectric layer, a passive layer and two electrode layers. The nonlinearities of the piezoelectric layer caused by electrostriction under a strong electric field are analyzed. Because the thickness of the transducer membrane is on the microscale, the size dependence of the deformation behavior is evaluated using the couple stress theory. The results show that the optimal ratio of the top electrode diameter and the membrane diameter is around 0.674. It is also found that this optimal value does not depend on any other parameters if the thicknesses of the two electrodes are negligible compared with those of the piezoelectric and passive layers. In addition, the nonlinearities of the piezoelectric layer will become stronger along with the increase of the electric field, which means that softening of the membrane stiffness occurs when a strong external electric field is applied. Meanwhile, the optimal thickness ratio for the passive layer and the piezoelectric layer is not equal to 1.0 which is usually adopted by previous researchers. Because there exists size dependence of membrane deformation, the optimal value of this thickness ratio needs to be greater than 1.0 on the microscale.

Development of piezohydraulic actuator driven by piezomembrane pump

A piezohydraulic actuator (piezopump-driven cylinder system) has the advantage over the conventional contact/non-contact piezoelectric motors in terms of achieving large thrust, high velocity, and long traveling distance. In this study, a serial-connection 5-chamber piezomembrane pump (SCCPP) was introduced and used for replacing piezostack pumps so as to decrease cost of piezohydraulic actuators. The border-upon piezomembranes work in anti-phase, a SCCPP is equivalent to several single-chamber pumps running in series. The theoretical study suggests that the performance of a SCCPP-driven actuator depends mainly on the efficiency of check valves, structural parameters of piezomembrane/pump chamber/cylinder, the number of pump chambers, and liquid bulk modulus. A piezomembrane has an optimal thickness ratio (metal to piezoelectric) for the actuator to achieve maximal power. A SCCPP-driven actuator was fabricated and tested under three/four/five chambers running. The testing results show that the thrust, velocity, power, and even optimal frequency of the piezohydraulic actuator all increase linearly with number of working chambers and driving voltage. At 180 V and 280 Hz, the achieved thrust, velocity, power, and step length from the actuator under five piezomembranes running are 75 N, 9.8 mm/s, 184.5 mW, and 35.2 µm, respectively, which are about 2.1/2.7/5.7/2.7 times than those of three piezomembranes running.

Optimization and Dynamic Modeling of Galfenol Unimorphs

Design and modeling of a bi-laminate, Galfenol-driven composite beam is presented in which the elasticity of the adhesive layer is considered. The optimal thickness ratio necessary to maximize the tip deflection is found by minimization of the internal energy of the beam. Model simulations show that use of a substrate material with high modulus leads to larger tip deflections. Stainless steel was therefore utilized as substrate in the experiments. In order to reduce eddy currents, a laminated silicon steel frame was employed to magnetize the beam. A dynamic model is proposed by coupling the structural dynamics of the beam and adhesive layer with the magnetostriction generated by the Galfenol layer. The latter is described with a linear piezomagnetic law with uniform magnetic field distribution along the length of the beam. Galerkin discretization combined with Newmark numerical integration are employed to approximate the dynamic response of the beam. The model is shown to describe both the transient and steady-state response of the composite beam tip displacement under harmonic excitation between 10 and 320 Hz. The RMS error between model and data range between 1.44% at 10 Hz and 6.34% at 320 Hz, when the same set of model parameters (optimized at quasistatic frequency) is utilized.

Thickness effects on magnetoelectric coupling for Metglas/PZT/Metglas laminates

Thickness effects on the ME coefficient αME and electromechanical resonance frequency of Metglas/PZT/Metglas tri-layered laminates are investigated. The thickness of the magnetic plate is changed by assembling different numbers of the Metglas thin sheets (30 μm for each layer) while the PZT plate is maintained at constant thickness (0.5 mm). At 1 kHz of the applied alternating magnetic field, only one peak presents in the ME coefficient (αME) versus static magnetic field (HS) curve. As the thickness ratio n increases, the peak value of μME first increases and reaches a maximum at approximately n = 0.519, and then decreases afterward. The peak position (Hoptim) moves steadily toward a higher value as n increases. It is suggested that the relaxation factor k of the magnetic phase is reduced as n increases, causing the decrease of the piezomagnetic coefficient d11,m and the increase of Hoptim. By employing the micromechanics model and considering the degradation of d11,m with n, an optimized thickness ratio of 0.5 is predicted, which is in agreement with the experimental observations. The resonance frequency of the laminate increases with n, which is consistent with the calculation using a straightforward mixture law.

Performance of a constant-stress piezoelectric generator for battery-less remote control/switch

This paper introduced a novel constant-stress piezoelectr ic cantilever generator (CSPCG) for human-powered battery- less remote controls (switches). The CSPCG consists of a piezoelectric monomorph cantilever and a deflection-limiting device (DLD). The DLD was designed to be a circular arc to shape the bended cantilever and yield constant strain through length. Considering the energy converting ability and reliability, the DLD's radius was figured out as a function of working stre ss and thickness of the piezoelectric plate and substrate plat e. Contrasted with a deflection-free piezoelectric cantile ver generator (DFPCG), the energy performance of the CSPCG was evaluated. Research results show that the two generators share the same optimal thickness ratio for them to achieve the maximal electric energy output. When the same stress and end-deflect ion were provided, the electric-energy generation of the CSPCG is above 4 and 1.5 times that of the DFPCG, respectively. While, the stress and end-deflection of the CSPCG is only 0.49 and 0.7 7 times that of the DFCPG when equal electric energy is generated. This suggests that a CSPCG with a DLD can enhance energy-generating capability and reliability, or decrease end-displacement of piezoelectric cantilever. A CSPCG was fabricated and used to power a low-power remote-control circuit at one-push excitation.

A Study of Load Capacity of Finite Slider Bearings with Slip Surfaces and Stokesian Couple Stress Fluids

A mathematical model for the hydrodynamic lubrication of finite slider bearings with velocity slip and couple stress lubricants is presented. A numerical solution for the mathematical model using finite element scheme is obtained using four node linearly interpolated quadrilateral elements. Stiffness integrals obtained from the weak form of the governing equations were solved using Gauss Quadrature to obtain a finite number of stiffness matrices. The global system of equations was obtained for the bearing and solved using Gauss Seidel iterative scheme. The converged pressure solution was used to obtain the load capacity of the bearing. Numerical experiments reveal the existence of an optimum velocity slip for which maximum benefit is obtained for the slider bearing in terms of bearing load. Increase in the slip parameter beyond this optimum value was shown not to augment the bearing load. Computations put forth also affirm that the bearing load is augmented with increase in couple stress parameter. An optimal film thickness ratio was also obtained for which load capacity is maximized with or without the application of slip to the bearing surfaces.

Structural Design of Symmetric Laminated Ceramic Nozzle and Study on it’s Erosion Behavior

Al2O3+(W,Ti)C/Al2O3+TiC symmetric laminated ceramic materials and nozzles were produced by hot pressing in order to reduce the tensile stress at the entry and the exit region of nozzles and improve their erosion wear resistance.The test results show that both hardness and toughness of laminated ceramic materials are improved than the simple materials.Under same erosion conditions,the laminated ceramic nozzles have superior erosion wear resistance to that of the common ceramic nozzle;the experimental value of optimal layer thickness ratio is 2.In addition,the residual thermal stress generated in the preparation of laminated ceramic materials is analyzed by finite element method(FEM).Relationship between stress distribution and layer thickness ratio is obtained.It is suggested that the residual thermal stress lead to grain refining mechanical properties strengthening,and improve the erosion wear resistance of laminated ceramic nozzles improving.The theoretical value of optimal layer thickness ratio is 2,the experimental results are consistent with the theoretical prediction.