Electrical Imperfections Research Articles

Impact of interfacial imperfections on the Reflection and Transmission phenomenon of plane waves in a Porous-Piezoelectric model

Reflection and transmission of plane waves are extensively used to conduct non-destructive testing(NDT) or non-destructive evaluation(NDE) of composites for characterizing/mapping subsurface defects and assessing the in-situ condition of structural components without reforming the original features of the composites in a non-tarnish way. These materials composed of more than one base material are the major components in the construction and modelling of air-crafts, space-crafts, military & defense applications, and nuclear industry. Thus, the present work deals with a mathematical model focused on the phenomenon of reflection and transmission of an incident plane wave at an imperfect interface between two different Porous-Piezoelectric(PP) half-spaces. According to the nature of the PP material, an incident plane wave (I-qP1 wave) results in five reflected and transmitted waves, namely reflected and transmitted quasi-longitudinal and quasi-transverse waves in the solid phase(qP1 and qSV, respectively), quasi-longitudinal wave in the fluid phase(qP2), and electro-acoustic waves in solid and fluid phases(EA1 and EA2, respectively). Due to reasons like the presence of interfacial defects owing to accumulative damages, half-spaces are generally not perfectly bonded. Mechanical and electrical interfacial defects fundamentally affect the performances of structural components that are utilized in several fields. Thus, reflection and transmission of different waves are studied for six distinct interfaces, viz. normally stiff interface, transversely stiff interface, electrical imperfection, slip interface, complete debonding, and welded interface. With the aid of secular equations and boundary conditions, a system of algebraic equations is obtained, from which the amplitude ratios are derived. Furthermore, the energy ratios of these waves are obtained, along with the interaction energy among various waves, using the energy flux relations and amplitude ratios. The conservation of total energy at the interface of the two media and some exclusive cases of this problem validate the study. For graphically illustrating the effects of these interface conditions on the reflection and transmission phenomenon, numerical data of PP BaTiO3 and PZT−7H materials are adopted. The energy ratios of various reflected and transmitted waves are plotted against the angle of incidence as well as against wave number.

On Calibration and Direction Finding with Uniform Circular Arrays

Antenna array calibration methods and narrowband direction finding (DF) techniques will be outlined and compared for a uniform circular array. DF is stated as an inverse problem, which solution requires a parametric model of the array itself. Because real arrays suffer from mechanical and electrical imperfections, analytic array models are per se not applicable. Mitigation of such disturbances by a global calibration matrix will be addressed, and methods to estimate this calibration matrix will be recapped from literature. Also, a novel method will be presented, which circumvents the problem of a changed noise statistic due to calibration. Furthermore, local calibration, where array calibration measurements are incorporated in the DF algorithm, is considered as well. Common DF algorithms will be outlined, their assumptions regarding array properties will be addressed, and required preprocessing steps such as the beam-space transformation will be presented. Also, two novel DF techniques will be proposed, based on the Capon beamformer, but with reduced computational effort and higher resolution for bearing estimation. Simulations are used to exemplary compare calibration and DF methods in conjunction with each other. Furthermore, measurements with a single and two coherent sources are considered. It turns out that global calibration enables computational efficient DF algorithms but causes biased estimates. Furthermore, resolution of two coherent sources necessitates array calibration.

The relation of between Electrical properties and Imperfection for SnO2 thin films

The relation of between Electrical properties and Imperfection for SnO2 thin films

The relation of between Electrical properties and Imperfection for SnO2 thin films

The relation of between Electrical properties and Imperfection for SnO2 thin films

Characterization of piezoelectric composites with mechanical and electrical imperfect contacts

The aim of the present work is to study the influence of the mechanical and electrical imperfections in reinforced piezoelectric composite materials with unidirectional cylindrical fibers periodically distributed in rhombic cells under mechanical and electrical imperfect contacts. The behavior of the composites is studied through two approaches: the two-scale asymptotic homogenization method and the finite element method. The asymptotic homogenization method is applied to a two-phase composite with mechanical and electrical imperfect contacts and to a three-phase composite with perfect contact in the interphase. The constituents of the composite are homogeneous piezoelectric materials with transversely isotropic properties. The local problems are formulated for the spring-capacitor and three-phase models by the asymptotic homogenization method. The solution of each plane local problem is found using potential methods of a complex variable and the properties of doubly periodic Weierstrass elliptic functions. Closed-form formulae are obtained for the effective properties of the composites with both types of imperfect contacts and different configuration of the cells. The finite element method is implemented for analysis of piezoelectric composite materials with unidirectional cylindrical fibers periodically distributed in rhombic cells under mechanical and electrical imperfect contacts. Some numerical examples are given under the presence of both imperfect contacts and different arrangement of the cells. Comparisons between the numerical results reported by asymptotic homogenization method and finite element method are provided.

Fracture analysis on a multiferroic cylindrical shell: Effects of coupled interphase imperfections

When interphases between ferromagnetic and ferroelectric layers become imperfect, the magnetic, electric, and mechanical imperfections may have inter-couplings. A coupled generalized linear spring model is proposed to formulate such inter-couplings. As an application, fracture analysis is performed on a multiferroic cylindrical shell containing an imperfect interphase. Parametric studies are made on the numerical results of the stress intensity factor to reveal the effects of the three kinds of imperfections and their inter-couplings. Three conclusions are drawn: (a) the mechanical imperfection can enhance the stress intensity factors and meanwhile weaken and even prevent the crack interaction across the interphase; (b) the magnetic/electric imperfection cannot affect the cracks independently, and only when it is coupled with the mechanical one can it reduce the stress intensity factor; and (c) the magneto-mechanical and electro-mechanical imperfection couplings are beneficial to reducing the stress intensity factor, but the magneto-electric imperfection coupling cannot affect the cracks.

Interfacial waves between two magneto-electro-elastic half-spaces with magneto-electro-mechanical imperfect interface

The propagation of shear horizontal waves between the interface of two magneto-electro-elastic materials with an magneto-electro-mechanical imperfect contact has been studied. Mechanical, electrical and magnetical imperfections are modelled by means of a spring, a capacitor and an inductor, respectively. A general expression for the dispersion relation is given in an explicit form. Some limit cases are analysed in detail. The influence of imperfect contacts is shown in some numerical results.

Static Regime Imaging of Locations of Certain 3D Electromagnetic Imperfections from a Boundary Perturbation Formula

We are concerned, in a static regime, with an imaging approach of the locations in a three-dimensional bounded domain of certain electromagnetic imperfections. This approach is related to Electrical Impedance Tomography and makes use of a new perturbation formula in the electric fields. We present two localization procedures, from a Current Projection method that deals with the single imperfection context and an inverse Fourier process that is devoted to multiple imperfections configurations. These procedures extend those that were described in our previous work, since operating for a broader class of settings. Namely, the localization is additionally performed for certain purely electric imperfections, as established from numerical simulations. Mathematics subject classification: 65N21, 65N30, 78A25.

Interfacial waves between two piezoelectric half-spaces with electro-mechanical imperfect interface

We study the propagation of shear horizontal waves between the interface of two piezoelectric materials with an electro-mechanical imperfect contact. Mechanical and electrical imperfections are modeled by means of a spring and a capacitor, respectively. The corresponding mathematical expressions for the imperfect contact are given in this article. The system of differential equations for the waves in the considered half-space is derived and the associate solutions are found. A general expression for the dispersion relation, not reported previously in the literature, is given in an explicit form, with the diverse limit cases analyzed in detail. In some of these limit cases, new expressions are also obtained, which predict the existence of interfacial waves. In the other cases, where already reported results exist, a comparison with them is done. Some physical interpretations are derived from the limit cases. The influence of mechanical and electrical imperfect contacts are shown in some numerical examples.

Propagation behaviors of thickness–twist modes in an inhomogeneous piezoelectric plate with two imperfectly bonded interfaces

The thickness–twist modes in an inhomogeneous piezoelectric plate with two imperfectly bonded interfaces are analyzed, and an exact solution is obtained according to the spring-type relation from the equations of the linear theory of piezoelectricity. The frequency shift, the displacement and the stress components are all obtained and plotted. Both theoretical analysis and numerical examples show that the effect of mechanical imperfection is more evident than that of the electrical imperfection on the thickness–twist modes. Results show that the displacement and the stress components all change obviously due to the imperfectly bonded interfaces. The relationship between the frequency shift Δ ω and the non-dimensional number γ that is related to the imperfect interfaces is linear, which can be used to provide the foundation for a new experimental procedure for measuring the level of the interface bonding.

Propagation of thickness-twist waves in an inhomogeneous piezoelectric plate with an imperfectly bonded interface

The propagation of thickness-twist waves in an inhomogeneous piezoelectric plate with an imperfectly bonded interface is investigated. Based on the spring-type relation, the imperfectly bonded interface is dealt with, and the exact solution is obtained from the equations of the linear theory of piezoelectricity. The amplitude ratio between the incident wave and the reflected wave, the displacement component and the stress component are all obtained and plotted. Both theoretical analysis and numerical examples show that the effect of the mechanical imperfection on the wave propagation is more evident than that of the electrical imperfection. When the incident wave frequency and the mechanical imperfect parameter meet some particular relation, no reflected waves can appear in the piezoelectric plate. The results are of fundamental importance to the design of resonators and other devices when imperfect joints are considered.

Photonic Instantaneous Frequency Measurement System Using Complementary Modulation

A novel photonic instantaneous frequency measurement system based on complementary modulation is proposed and experimentally demonstrated. A dual-electrode dual-output Mach-Zehnder modulator is used to simultaneously achieve electrooptical modulation and complementary modulation sideband (MS) filtering. By suppressing the optical carrier at one of the modulator outputs, complementary MS filtering is mapped into two complementary average optical powers from which the RF frequency is derived. The obtained frequency measurement is independent of both optical and RF powers, and is also robust to electrical circuitry imperfections.

Effect of an imperfect interface on the SH wave propagating in a cylindrical piezoelectric sensor

Under harsh in situ conditions, the interface in piezoelectric sensors may be damaged mechanically and/or electrically. The damaged interface would in turn affect the electromechanical behaviors of the sensors. The purpose of the present work is to study the effect of the imperfect interface on SH wave propagating in a cylindrical piezoelectric sensor. The dispersion relations of SH wave are derived analytically and the phase velocity are obtained numerically. Parametric studies on the phase velocity indicate that the mechanical imperfection may reduce the phase velocity under certain circumstances; however, the electrical imperfection has no obvious effect on the phase velocity in any cases; with the thickness of the piezoelectric layer increasing, the phase velocity may increase, decrease or keep unchanged, depending on the combination of the values of the wave number and the mechanical imperfection parameter.

Rotating Cell for in Situ Raman Spectroelectrochemical Studies of Photosensitive Redox Systems

A recently developed rotating spectroelectrochemical cell for in situ Raman spectroscopic studies of photoreactive compounds without marked decomposition of the sample is presented. Photochemically and thermally sensitive redox systems are difficult to be studied under stationary conditions by in situ spectroelectrochemistry using laser excitation as in Raman spectroscopy. A rotating spectroelectrochemical cell can circumvent these difficulties. It can be used for any type of a planar electrode and for all electrode materials in contact with aqueous or nonaqueous solutions as well as with ionic liquids. The innovative technical solution consists of the precession movement of the spectroelectrochemical cell using an eccentric drive. This precession movement allows a fixed electrical connection to be applied for interfacing the electrochemical cell to a potentiostat. Hence, any electrical imperfections and noise, which would be produced by sliding contacts, are removed. A further advantage of the rotating cell is a dramatic decrease of the thermal load of the electrochemical system. The size of the spectroelectrochemical cell is variable and dependent on the thickness of the cuvettes used ranging up to approximately 10 mm. The larger measuring area causes a higher sensitivity in the spectroscopic studies. The as constructed spectroelectrochemical cell is easy to handle. The performance of the cell is demonstrated for ordered fullerene C(60) layers and the spectroelectrochemical behavior of nanostructured fullerenes. Here the charge transfer at highly ordered fullerene C(60) films was studied by in situ Raman spectroelectrochemistry under appropriate laser power and accumulation time without marked photodecomposition of the sample.

A piezoelectric medium containing a cylindrical inhomogeneity: Role of electric capacitors and mechanical imperfections

Often, during fabrication processes of fiber–matrix composites, the pertinent interface may be made imperfectly bonded either deliberately or undesirably. The effect of electric capacitors and mechanical imperfections on the electro-mechanical fields associated with an anisotropic piezoelectric matrix containing a cylindrical inhomogeneity made of a different anisotropic piezoelectric material is of interest. In fact the interface imperfection condition presented in this paper is quite general, in the sense that any combination of mechanical and electrical imperfections may exist. The interface electrical imperfection is mimicked by the electric capacitors. The capacity of the capacitors is a measure of the electrical imperfection. The notion of complete electric barrier realizes when the capacity is equal to zero. For finite values of capacity, different electrical imperfections are modeled. When the capacity is infinitely large, perfect electrical interface reveals.

Effect of Spontaneous Polarization Screening on Dielectric Response of Ferroelectric Polydomain Films

A theoretical study on the effect of spontaneous polarization screening on the dielectric response of ferroelectric films with 180° domains going through the film thickness (through-domains) is presented. It has been shown by several researchers that the dielectric response of ferroelectrics is always deteriorated (e.g. due to electric field, mechanical stress, or lattice imperfections) in the thin electrode-adjacent passive regions. As a result, these regions behave as a low dielectric material reducing the total dielectric response of the ferroelectric capacitor. This “depolarizing” effect can be modeled by a low-dielectric layer between the ferroelectric and the electrode. The strong electric field in the dielectric layer can induce free charge injection from the electrode to the ferroelectric-dielectric layer interface. We study how these free charges affect the dielectric response of the ferroelectric capacitor with through-domains. We found that their presence strongly influences the domain wall contribution to permittivity of the ferroelectric. This effect is controlled to a great extent by the domain wall thickness.

Base station antenna systems with built-in processing for the reduction of the effects of hardware imperfections

The effects of many mechanical and electrical manufacturing imperfections of antenna arrays can be minimized with an internal pattern database. Such deficiencies are the non-idealities of amplitude and phase characteristics of sub-arrays and active modules. The idea of the suggested method is to store measured pattern characteristics into the antenna's internal memory at delivery and later, during operation, to use this data to support, for example, a beam forming algorithm, or just to create a static optimum. Thus, the antenna "knows" its behaviour. This method is both more cost-effective than a fine tuning of the hardware items on the production line, and often, the only choice, if relatively inaccurate sheet metal antennas are considered; but naturally, requires some active RF hardware. Our tests demonstrate S-band patterns within 2 dB or 3/spl deg/ of the theoretical ones if an EPROM database at 1/spl deg/ intervals is used. The improvement of the depth of wanted minima can exceed 12 dB.

Correlation of the Physical Location of Crystal Defects with Electrical Imperfections in GaAs p-n Junctions

A thermal-mapping technique is presented which, when applied to a p-n junction, can locate hot spots that are only slightly warmer than surrounding regions. Among the Zn-diffused GaAs devices to which this method has been applied, these hot spots have always been found to be associated with an irregularity (usually a microplasma) in the I-V characteristic. Furthermore, etching has revealed a crystal imperfection coinciding with each hot spot. Selective etching at these sites causes the removal of the imperfect region and a corresponding significant improvement in the diode reverse characteristic, though less than 4% of the total diode area has been removed.

The prehistory of solid-state physics

Prehistory implies the selection of a date when history begins. In solid-state physics this is very recent, dating, perhaps, from Debye's specific-heat theory of 1913, but most of all from the famous diffraction experiment of Friedrich, Knipping, and Von Laue in March 1912. It was this tool of perfection which laid the ground for imperfection to become of interest to physicists. The growth of solid-state physics marks, I think, a basic change in the attitude of physicists toward matter. Virtually all the development of mechanics, marvellous though it was, was based on a treatment of matter that was essentially structureless and whose measured elastic constants and densities gave the constants to put into equations that became ever more elaborate. When physicists at last paid attention to the structure of real crystals, they soon became aware of imperfections, both theoretically and experimentally, and the great flourishing of solid-state physics in the last three decades has been mostly based on the elucidation of the role of mechanical, ionic, and electrical imperfections in a crystal, accompanied, of course, by a continued development of understanding of bonding and dynamics of the ideal lattice.