Piezoelectric Surface Research Articles

In-House Development of Shear Horizontal Acoustic Waves Based Sensitive Sensors for Bacterial Pathogens Detection

Surface acoustic wave can be generated at the free surface of an elastic solid. Interdigital transducers (IDTs) are fabricated on the piezoelectric substrate surface that will act as electrical input and output port. When appropriate AC voltage stimulus is applied to the input transducer, surface acoustic wave will be produced. The output or receiving port will detect the incident surface acoustic wave and convert it back to a suitably filtered electrical once. For this property, surface acoustic based devices were initially developed for the telecommunication purpose such as signal filters and resonators. SAW based devices have been modified to be sensors later on from for gas detections and have been moving towards biological detections recently for its ultra-sensitivity to surface perturbation. The main component of this device is the IDTs. Recently, there are several methods to produce IDTs; Ultra-Violet (UV), deep UV lithography, Electron beam (e-beam) lithography and X-ray lithography. Although, these methods can produce very fine and accurate electrodes in term of submicron size but the costs are extremely expensive. Thus, this paper will discuss the conventional CMOS method which is much more economical to produce the applicable IDTs for the bacterial pathogens sensing purpose. Shear horizontal surface acoustic wave (SHSAW), one of the SAW based types is used in this paper as it is most suitable for the liquid based application as it has the advantage of acoustic energy is not being radiated into liquid.

Domain pinning near a single-grain boundary in tetragonal and rhombohedral lead zirconate titanate films

The interaction of grain boundaries with ferroelectric domain walls strongly influences the extrinsic contribution to piezoelectric activity in Pb(Zr,Ti)O3 (PZT), ubiquitous in modern transducers and actuators. However, the fundamental understanding of these phenomena has been limited by complex mechanisms originating from the interplay of atomic-level domain wall pinning, collective domain wall dynamics, and emergent mesoscopic behavior. This contribution utilizes engineered grain boundaries created by depositing epitaxial PZT films with various Zr:Ti ratio onto 24o SrTiO3 tilt bicrystals. The nonlinear piezoelectric response and surface domain structure across the boundary are investigated using piezoresponse force microscopy whilst cross section domain structure is studied using transmission electron microscopy. The grain boundary reduces domain wall motion over a width of 800±70 nm for PZT 45:55 and 450±30 nm for PZT 52:48. Phase field modeling provides an understanding of the elastic and electric fields associated with the grain boundary and local domain configurations. In conclusion, this study demonstrates that complex mesoscopic behaviors can be explored to complement atomic-level pictures of the material system.

Thin linearly piezoelectric junctions

Through a rigorous mathematical analysis, we present various asymptotic models for a thin piezoelectric junction between two linearly piezoelectric or elastic bodies. Depending on the relative behavior of a stiffness parameter with respect to its thickness, the joint is replaced by either a(n) (electro)mechanical constraint or a piezoelectric material surface.

The peculiarities of the Bleustein–Gulyaev wave propagation in structures containing conductive layer

As known, anomalous resisto-acoustic effect is a fundamental property for weakly inhomogeneous piezoactive waves (Bleustein-Gulyaev, Love, and some leaky waves). It consists in that the velocity of aforementioned waves first increases, achieves its maximum, and only then decreases with increasing conductance of a layer placed at the surface of piezoelectric half-space. In this paper we continue to study the peculiarities of the effect appearance and the influence of different electrical boundary conditions on its characteristics. Conditions have been found under which the said effect appears and, respectively, disappears. The magnitude of positive change in velocity with increasing layer conductance is demonstrated to be reduced up to zero as a layer with arbitrary conductance has been moved away from the piezoelectric surface. The positive change in velocity increases when an perfectly conductive screen moves away from the “piezoelectric half-space – conductive layer” structure. The obtained results are useful for a more deep understanding the physical basis of propagation of weakly inhomogeneous piezoactive acoustic waves (Bleustein-Gulyaev, Love, and some leaky waves).

Surface effects on the post-buckling of piezoelectric nanowires

Due to the large ratio of surface to volume, surface effects play an essential role in determining the physical properties of nanoscaled structures. A theoretical model is developed in this work to investigate the effect of surface on the postbuckling behavior of piezoelectric nanowires, in which the residual surface stresses, surface piezoelectricity and surface elasticity are taken into consideration. The critical buckling strain and the amplitude of the buckled nanowire are analytically obtained. It is found that the critical buckling strain ratio increase with the decrease of the thickness of piezoelectric nanowire, which demonstrates that the surface becomes prominent when the thickness of piezoelectric nanowire is at nano-scale. The theoretical estimation agrees well with the experimental data on a single crystal ZnO nanowire. This study provided the fundamental understanding of the physical behavior of piezoelectric nanowires and is promising for designing piezoelectric nanowire based stretchable nanoelectronics.

Ultrasonic technique for monitoring of liquid density variations.

A novel ultrasonic measurement technique for density measurements of different liquids in extreme conditions has been developed. The proposed density measurement method is based on transformation of the acoustic impedance of the measured liquid. The higher accuracy of measurements is achieved by means of the λ/4 acoustic matching layer between the load and the ultrasonic waveguide transducer. Introduction of the matching layer enhances sensitivity of the measurement system. Sometimes, the density measurements must be performed in very complex conditions: high temperature (up to 200 °C), pressure (up to 10 MPa), and high chemical activity of the medium under measurement. In this case, the special geometry metal waveguides are proposed to use in order to protect the piezoelectric transducer surface from influence of a high temperature. The experimental set-up of technique was calibrated using the reference liquids with different densities: ethyl ether, ethyl alcohol, distilled water, and different concentration (20%, 40%, and 60%) sugar-water solutions. The uncertainty of measurements is less than 1%. The proposed measurement method was verified in real conditions by monitoring the density of a melted polypropylene during manufacturing process.

Comparing the Voltage Output of Water in Drop and Flow Form Using a Piezoelectric Sensor and Hydroelectric Turbine

Due to the harmful effects of broadly used energy sources, alternative energy sources have been widely studied. One area of interest is transferring kinetic water energy in nature, as in that from water flowing or falling, into electrical output. This work address the question of whether more voltage would be created by (rain) drops hitting a piezoelectric surface or by that same volume of water flowing through a hydroelectric turbine. To test this question, we built an apparatus for the piezoelectric (drops) system and purchased a small hydroelectric turbine for the flow system. We then used the two systems to measure the amount of voltage generated by drops of water and compared the data produced by each apparatus to see which system produced the greatest amount of voltage. The results showed that, despite the change in the form of the water, the average voltage produced both by the drops hitting the piezoelectric sensor and by the flow running through the turbine was virtually the same. The drops created on average slightly more voltage than the flow (whose volume was converted to the same estimated volume of each singular drop for comparison) did. These data show that directly harnessing the kinetic energy found in falling raindrops is as viable an option for an alternative energy source as are hydroelectric turbines doing the same with the kinetic energy found in flowing water.

The surface effect on axisymmetric wave propagation in piezoelectric cylindrical shells

Based on the surface piezoelectricity theory and first-order shear deformation theory, the surface effect on the axisymmetric wave propagating in piezoelectric cylindrical shells is analyzed. The Gurtin–Murdoch theory is utilized to get the nontraditional boundary conditions and constitutive equations of the surface, in company with classical governing equations of the bulk, from which the basic formulations are obtained. Numerical results show that the surface layer has a profound effect on wave characteristics in nanostructure at a higher mode.

Size effects on electromechanical coupling fields of a bending piezoelectric nanoplate due to surface effects and flexoelectricity

Due to large surface to volume ratio and manifest strain gradients typically present in nanostructures, it is essential to incorporate both surface effects and flexoelectricity in studying the size-dependent electromechanical coupling behaviors of piezoelectric materials at the nano-scale. In the current work, a modified Kirchhoff plate model with the consideration of residual surface stress, surface elasticity, surface piezoelectricity, and flexoelectricity is developed to investigate the electroelastic responses and vibrational behaviors of a bending piezoelectric nanoplate (PNP). The governing equations and the corresponding boundary conditions accounting for both the surface effects and the flexoelectricity are derived by the variational principle. Ritz approximate solutions of the static bending and the free vibration indicate that these nano-scale features are more prominent for thinner plates with smaller thickness. The simulation results also reveal that the influence of the flexoelectricity and the surface effects upon the bending behaviors of the PNP depends on the applied electrical loading and the plate dimensions. Moreover, it is also observed that the frequency tuning of PNP-based nanoresonators by adjusting applied electrical load can be modified by both the flexoelectricity and the surface effects. The current work is expected to provide increased understanding on the theoretical basis for the design and applications of PNP-based nanodevices.

Surface effects on the energy-generating performance of piezoelectric circular nanomembrane energy harvesters under pressure loading

The influence of surface effects on the energy-generating performance of piezoelectric circular nanomembrane energy harvesters under blood pressure is studied. The effects of surface elasticity, surface piezoelectricity, residual surface stress and geometry nonlinear strain are incorporated in the present model. An approximated closed-form solution for the electrical energy of the nanomembrane is derived by using the energy method. Results show that positive surface elasticity and residual surface stress reduce the electrical energy and the surface piezoelectricity effect increases the electrical energy. The influence of surface effect on the energy-generating performance of piezoelectric circular membranes is more significant for a membrane with a small thickness and a large radius-to-thickness ratio.

A compact and high flow-rate piezoelectric micropump with a folded vibrator

This paper presents the design, fabrication, dynamic analysis, and experimental results of an efficient resonantly-driven piezoelectric micropump. The micropump consists of a folded vibrator, two polydimethylsiloxane (PDMS) check valves and compressible spaces. A newly developed folded vibrator with piezoelectric sheets serves as the resonantly-driven actuator. The vibrator provides uniform strain distribution in piezoelectric sheets surfaces to improve their utilizing efficiency. The PDMS check valves used in this design increase pump’s working stability and largely reduce the leakage rate. In addition, the performance of the micropump is significantly improved by two compressible spaces near the check valves. Experimental results on a prototype with dimensions of 20 mm × 20 mm × 28 mm demonstrate that the maximum flow rate of 118 ml min−1 and maximum back pressure of 22.5 kPa are obtained when the micropump is driven by a sinusoidal voltage of 120 Vpp at 361 Hz. A stable minimum flow rate of 160 μl min−1 can be obtained with driving voltage of 4 Vpp. The maximum power consumption of the micropump is approximately 62 mW for 118 ml min−1 at zero backpressure.

Piezoelectric effects and electromechanical theories at the nanoscale.

Considerable effort has been made to study the piezoelectric effect on the nanoscale, which serves as a physical basis for a wide range of smart nanodevices and nanoelectronics. This paper reviews recent progress in the research on the piezoelectric properties and electromechanical effects of piezoelectric nanomaterials (PNs). The review begins with an introduction to existing PNs which exhibit a diverse range of atomic structures and configurations. The nanoscale measurement of their effective piezoelectric coefficients (EPCs) is summarised with an emphasis on the major factors determining the piezoelectric properties of PNs. The paper concludes with a review of the electromechanical theories that are able to capture the small-scale effects on PNs, which include the surface piezoelectricity, flexoelectricity and Eringen's nonlocal theory. In contrast to the classical theories, two types of EPCs are defined, which were found to be size-dependent and loading condition-selective.

Collective lipid bilayer dynamics excited by surface acoustic waves.

We use standing surface acoustic waves to induce coherent phonons in model lipid multilayers deposited on a piezoelectric surface. Probing the structure by phase-controlled stroboscopic x-ray pulses we find that the internal lipid bilayer electron density profile oscillates in response to the externally driven motion of the lipid film. The structural response to the well-controlled motion is a strong indication that bilayer structure and membrane fluctuations are intrinsically coupled, even though these structural changes are averaged out in equilibrium and time integrating measurements. Here the effects are revealed by a timing scheme with temporal resolution on the picosecond scale in combination with the sub-nm spatial resolution, enabled by high brilliance synchrotron x-ray reflectivity.

Dynamics of a piezoelectric beam subjected to water droplet impact with water layer formed on the surface

Rain impact energy harvesting using piezoelectric energy harvester has gained much attention recently. However, previous works have only considered the effect of single water droplet. In the case of raindrop, water would accumulate on the surface of the energy harvester and form a shallow water layer. This article models the dynamics of a piezoelectric beam, served as a raindrop energy harvester, subjected to water droplet impact with water layer formed on the surface. The impact of water droplet on the tip of the energy harvester is modelled as an impulsive force, and the water layer on the surface of the energy harvester is modelled as an added mass to the energy harvester. An attempt to model the force generated by the water ripple as a distributed load on the piezoelectric beam is presented. Numerical studies have been conducted based upon the proposed mathematical model verified by experimental results. The results showed that the presence of the water layer affects the output voltage and the dominant frequency of the energy harvester. It reveals that the effect of water (or rain) accumulation on the piezoelectric surface should be considered in deriving an optimal operating condition of such energy harvester.

Inhomogeneous wave reflection in a rotating piezoelectric body

The purpose of this paper is to address the wave reflection over the rotating piezoelectric boundary surface in the framework of inhomogeneous wave theory which can introduce an additional reflected surface wave over the boundary surface to solve the problem of discrepancy between independent wave modes and boundary equations. A set of homogeneous equations in displacements and electric potential is derived within the rotatory coordinate system in the presence of the Coriolis and centrifugal acceleration presenting noticeable influence upon the wave propagation and reflection. Other than the transverse wave, the performed plane example shows that there is a critical point of when angular velocity equals the wave frequency for the quasi-longitudinal wave. The results also reveal that the angular velocity is accompanied by the modification of reflected waves especially in the case of reflected surface mode as well as the reflection angles, the amplitudes, and energy ratio coefficients.

Surface effects on the scattering of compressional waves by a piezoelectric nano-cylinder

Based on the surface piezoelectricity model, surface effects on the scattering behaviors of plane compressional waves by an embedded piezoelectric cylinder with nanoscale radius are investigated. The existence of surface stresses and surface electric displacements exerting on the boundary conditions is taken into account through generalized Young-Laplace equations, and the potential function method is employed to derive the analytical expressions of wave fields and electric potential. For two typical incident frequencies, the influence of surface properties on the distribution of electroelastic fields around the cylinder is discussed in detail. In comparison with the results obtained from the classical continuum theories, it is found that the surface effects play a prominent role on the dynamic stress and electric field concentrations, especially under a high-frequency excitation.

Piezoelectric surface acoustical phonon amplification in graphene on a GaAs substrate

We study the interaction of Dirac Fermions in monolayer graphene on a GaAs substrate in an applied electric field by the combined action of the extrinsic potential of piezoelectric surface acoustical phonons of GaAs (piezoelectric acoustical (PA)) and of the intrinsic deformation potential of acoustical phonons in graphene (deformation acoustical (DA)). We find that provided the dc field exceeds a threshold value, emission of piezoelectric (PA) and deformation (DA) acoustical phonons can be obtained in a wide frequency range up to terahertz at low and high temperatures. We found that the phonon amplification rate RPA,DA scales with TBGS−1 (S=PA,DA), TBGS being the Block−Gru¨neisen temperature. In the high-T Block−Gru¨neisen regime, extrinsic PA phonon scattering is suppressed by intrinsic DA phonon scattering, where the ratio RPA/RDA scales with ≈1/n, n being the carrier concentration. We found that only for carrier concentration n≤1010cm−2, RPA/RDA>1. In the low-T Block−Gru¨neisen regime, and for n=1010cm−2, the ratio RPA/RDA scales with TBGDA/TBGPA≈7.5 and RPA/RDA>1. In this regime, PA phonon dominates the electron scattering and RPA/RDA<1 otherwise. This study is relevant to the exploration of the acoustic properties of graphene and to the application of graphene as an acoustical phonon amplifier and a frequency-tunable acoustical phonon device.

Electron energy and temperature relaxation in graphene on a piezoelectric substrate

We study the energy and temperature relaxation of electrons in graphene on a piezoelectric substrate. Scattering from the combined potential of extrinsic piezoelectric surface acoustical (PA) phonons of the substrate and intrinsic deformation acoustical (DA) phonons of graphene is considered in a (non-)degenerate gas of Dirac fermions. It is shown that in the regime of low energies or temperatures the PA phonons dominate the relaxation and change qualitatively its character. This prediction is relevant for quantum metrology and electronic applications using graphene devices and suggests a new experimental setup for probing electron-phonon coupling in graphene.

Surface Effects on the Electrostatic Potential Generated in a Bent Gallium Nitride Nanowire

The aim of this paper is to conduct the first study of the surface effects on the voltage output of bent gallium nitride (GaN) nanowires (NWs), which are promising for nanogenerators. To reach this goal, a 3-D composite beam model was developed and the corresponding theoretical framework was established for the structural responses of piezoelectric NWs. In this study molecular dynamics simulations (MDS) were first carried out to determine the exact material properties for several small NW samples. The MDS-derived size-dependence of parameters provide fitting points for the 3-D composite beam with a core-shell geometry. With the aid of the finite element techniques the equivalent material properties obtained from above fitting procedure enable the use of the core-shell model for larger structures where MDS were not feasible. The obtained results showed that the influence of the surface layer greatly modifies the potential distribution on the cross section and raises the voltage output of bent GaN NWs by up to 120%. In particular, the contribution from the surface piezoelectricity to the surface effect is found to be predominant over that of the surface elasticity and surface stresses.

Novel piezoelectric effect and surface plasmon resonance-based elements for MEMS applications.

This paper covers research on novel thin films with periodical microstructure—optical elements, exhibiting a combination of piezoelectric and surface plasmon resonance effects. The research results showed that incorporation of Ag nanoparticles in novel piezoelectric—plasmonic elements shift a dominating peak in the visible light spectrum. This optical window is essential in the design of optical elements for sensing systems. Novel optical elements can be tunable under defined bias and change its main grating parameters (depth and width) influencing the response of diffraction efficiencies. These elements allow opening new avenues in the design of more sensitive and multifunctional microdevices.