Ferroelectric generators (FEGs) produce high energy electrical pulses for a short duration of time. This process is initiated by a high amplitude shock wave that depolarizes a ferroelectric (FE) material in microseconds. A niobium doped lead zirconate titanate composition (2/95/5 PZT) that undergoes a hydrostatic stress induced phase transformation from a FE to an antiferroelectric phase has been the material of choice for this application. Recent research has led to potential alternative materials. These include lead-based perovskite relaxor single crystal FE materials with larger remanent polarization that could increase the output electrical energy, and lead free materials that have increased remanent polarization and can address the environmental concerns associated with the use of lead-based compounds. A review of energy conversion and the properties of 2/95/5 PZT that led to its adoption provide a framework for research on alternative materials. This perspective article reviews the material properties and geometric effects that contribute to FEG performance and discusses where future materials research efforts might lead to the most significant advances of this technology.

A phenomenological model of two Co adatoms on a Cu(100) substrate was developed using a multiscale approach with “Magneto-displacement” effects taken into account. The phenomenological model used parameters obtained from density functional theory (DFT) calculations. The coupled Landau-Lifshitz equation and Newton’s equation of motion governing magnetic and mechanical degrees of freedom provide the foundation of the model. The model led to several key results. A mechanism for ferromagnetic (FM) to antiferromagnetic (AFM) transition induced by displacement of the adatoms was demonstrated. Mechanical tunability of magnetic resonant frequencies was shown. Displacement-assisted in-plane (IP) to out-of-plane (OOP) switching was demonstrated. Mechanical displacement reduces the external field needed to induce an antiferromagnetic IP to ferromagnetic OOP transition from 64T to 3T.

The use of the dielectrophoresis (DEP) process during the fabrication of particulate-based multifunctional polymer composites (MPCs) enhances their effective properties. The reconfiguration of particle alignment through DEP improves connectivity and, consequently, the electromechanical response of these materials. In this study, the motion of a spherical conductive particle subjected to a non-uniform electric is used to isolate electrostatic effects from dielectrophoresis effects. The role of frequency in charge accumulation, redistribution dynamics, and particle motion is analyzed under varying experimental conditions. To estimate the influence of direct charge exchange, conductive particle movement is compared between different cases with and without insulating conformal coating covering the electrodes. Dominant electrostatic effects are found at low frequencies while dominant dielectrophoresis effect increase as the frequency increases.

Ferroelectric elements of high-power electrical generators, utilizing the ability of ferroelectric materials to produce electric charge under mechanical stress, are subjected to either high-pressure shock or moderate-pressure impact loading. The results are reported herein on experimental investigations of a different mode for the generation of a high electric charge density, one that utilizes pre-compressed ferroelectric ceramics. Hard PZT 52/48 (Navy Type I/PZT-4) ferroelectric ceramic specimens were subjected to static uniaxial compressive stress parallel to polarization. At the moment of operation, the output terminals of the specimens were connected to an external circuit, and the applied stress was quickly removed, resulting in the generation of electric charge. The results indicate that this new method for harvesting electric charge from pre-compressed ferroelectrics produced a surface charge density of 7.4 μC/cm2 upon release of 71 MPa compressive stress, significantly higher than that calculated using the linear piezoelectric charge coefficient d33. Under pre-compressive stresses exceeding 3 MPa, d33 exhibits a nonlinear increase. Higher order terms were introduced into the electro-mechanically coupled constitutive law to model the observed behavior. No degradation of piezoelectric properties or mechanical failure of the ferroelectric specimens was detected over the full range of stress investigated, 0.4–71 MPa. Multi–element ferroelectric modules had no significant electric charge losses after 168 h of 35.4 MPa compression. Therefore, pre-compressed ferroelectrics are capable of producing large electric charges during millisecond time intervals and can be used as high-power energy storage devices.

The dependence of the dielectric permittivity of ferroelectric materials on electric field magnitude impacts the performance of ferroelectric devices. In a ferroelectric generator, a shock wave travels through the ferroelectric element and depolarizes it, and surface charges are released from the element electrodes, resulting in the generation of a megawatt power level for several microseconds. The dielectric properties of the compressed and uncompressed zones of the ferroelectric element affect the generated voltage and energy. The results of previous studies indicate that the low-field dielectric permittivity of poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 (PZT 95/5) ferroelectrics in the uncompressed zone differs significantly from the high-field permittivity. Herein, the results are presented from the experimental investigation of the high-field permittivity of poled uncompressed PZT 95/5 ferroelectric ceramics and films, PZT 52/48 ferroelectric ceramics, and rhombohedral 0.27Pb(In1/2Nb1/2)O3–0.47Pb(Mg1/3Nb2/3)O3–0.26PbTiO3 (0.27PIN-PMN-0.26PT) and 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (0.68PMN-0.32PT) ferroelectric single crystals. The dependences of the permittivity on the electric field were determined using a pulsed electric field ranging from 0.1 to 10 kV/mm. The data indicate that the application of a pulsed high electric field results in a fourfold increase in the relative permittivity of PZT 95/5 ceramics and films over the small signal value (from 300 to 1200), and a threefold increase in the permittivity of single-domain [111]c cut and poled 0.27PIN-PMN-0.26PT crystals (from 700 to 2100), while a high electric field does not have a significant impact on the permittivity of PZT 52/48 ceramics or 0.27PIN-PMN-0.26PT and 0.68PMN-0.32PT crystals cut and poled in the domain engineered [001]c or [011]c direction.

The unique ability of ferroelectrics to generate high voltage under shock loading is limited by electrical breakdown within the shock-compressed ferroelectric material. Breakdown is a hybrid process of initiation and growth. The possible mechanisms of electrical breakdown in ferroelectric films and bulk ceramics subjected to high-pressure shock loading are discussed and experiments designed to elucidate which mechanisms govern breakdown. Gigapascal shock loading experiments were performed on poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 ferroelectric film specimens in the range of 32–156 μm thickness to determine the dependence of the breakdown field on thickness and on film specimens in the range of 4–16 mm length to determine the dependence of the breakdown field on the duration of shock compression. The resulting breakdown-field vs thickness and breakdown-field vs shock transit time dependencies are consistent with a hybrid electron emission initiation and Joule heating microchannel growth mechanism. Further analysis of data previously obtained on shock-compressed 0.27Pb(In1/2Nb1/2)O3–0.47Pb(Mg1/3Nb2/3)O3–0.26PbTiO3 ferrvoelectric single crystals and Pb(Zr0.65Ti0.35)O3, Pb0.99(Zr0.52Ti0.48)0.99Nb0.01O3, Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 bulk ceramics is consistent with this dual mechanism. It appears that neither chemical composition nor microstructure (single crystal vs polycrystalline) of the ferroelectric material has a significant effect on the breakdown mechanism in shocked ferroelectrics.

A modeling approach was developed that combines lumped-element and finite element methods for analysis of synthetic jet actuator (SJA) geometries that deviate significantly from an ideal Helmholtz resonator. The diaphragm was modeled using the finite element method (FEM) coupled to lumped-element equations that govern the fluid flow. The loss coefficient [Formula: see text] was estimated based on the geometry of the cavity and orifice. A pressure acoustic FEM model of the cavity and orifice was used to determine a characteristic resonance frequency to use in place of the Helmholtz resonance frequency that appeared in the lumped element equations. The results were validated using experimental data for SJAs with geometries that deviate significantly from the Helmholtz resonator idealization. The combination of replacing the Helmholtz frequency with a more accurate characteristic frequency and using a computed value for the loss coefficient was shown to provide more accurate performance predictions for low-profile SJA designs.

Relaxor ferroelectric single crystals of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) have outstanding electromechanical properties in the linear regime. When operated across a phase transition, these properties are significantly enhanced. Understanding the phase transition mechanism under electromechanical external fields is crucial for the new application of PMN–PT that takes advantage of this phase transition. In the present study, the phase transition of PMN–0.3PT single crystals subjected to a mechanical loading/unloading process and the effects of electric field on the phase transition and electromechanical responses of PMN–0.3PT single crystal under coupled mechanical-electrical loading were systematically investigated using a thermodynamics-based phase-field model. The roles the different energy terms play in the evolution of domain and phase structures were assessed. These findings have important implications for both understanding of the phase transition of relaxor ferroelectric single crystal PMN–0.3PT and applications that take advantage of phase transitions in these materials. The model results for the reversible/irreversible phase transition of PMN–0.3PT during the mechanical loading/unloading process are qualitatively consistent with experimental results.

Let T be an SMT solver with no theory solvers except for Quantifier Instantiation. Given a set of first-order clauses S saturated by Resolution (with a valid literal selection function) we show that T is complete if its Trigger function is the same as the literal selection function. So if T halts with a ground model G, then G can be extended to a model in the theory of S. In addition for a suitable ordering, if all maximal literals are selected in each clause, then T will halt on G, so it is a decision procedure for the theory S. Also, for a suitable ordering, if all clauses are Horn, or all clauses are 2SAT, then T solves the theory S in polynomial time.

This paper presents mechanics based tools for the design of multifunctional polymer composite materials. The class of composite discussed consist of a low permittivity matrix material (typically polymer) with ferroelectric inclusions (piezoelectric/ferroelectric particles, rods, platelets) dispersed throughout. The high permittivity of the inclusions causes the electric field to concentrate in the matrix, which makes it challenging to get the electric field into the inclusions. Elasticity (biharmonic Laplace's equation) and electrostatics (harmonic Laplace's equation), provide closed form solutions for single inclusion geometries, providing the electric field distribution in the inclusion and in the matrix. These solutions are used to validate finite element models used to address interactions between inclusions. This discussion addresses 2-D dielectric circular inclusions embedded in a linear polymer matrix. The approach is readily extended to other inclusion geometries such as ellipse, sphere, and ellipsoid (plates and rods).

This paper presents a study on the effect of electrostatic interactions between adjacent dielectric particles. Multifunctional polymer composite materials include a low permittivity matrix material, typically polymer, with dielectric (piezoelectric/ferroelectric) inclusions dispersed throughout. The high permittivity of the inclusions leads to an electric field concentration in the matrix. Interparticle electrostatic interactions arise due to the presence of charged particles in the matrix. These interactions affect the overall properties of the composite. This issue has led to an increasing interest in the electrical properties of multifunctional polymer composite materials. Based on closed-form solution for single inclusion geometries, Finite Element Method (FEM) models are validated. Additional particles of the same geometry are introduced. The electrostatic interactions between particles and the electric field distribution in the composite are studied. Different configurations of particles are presented as well as different particles sizes to assess the effect on the electric field within the particles.

Unification techniques have been proven to be useful for formal analysis of cryptographic systems. In this paper, we introduce a new unification problem called local XOR unification, motivated by formal analysis of security of modes of operation. The goal in local XOR unification is to find a substitution making two terms equivalent modulo the theory of exclusive-or, but each variable is only allowed to be mapped to a term from a given set of terms. We present two versions of the local XOR unification problem, and give algorithms to solve them, proving soundness, completeness and termination.

This work demonstrates that magnetoelectric composite heterostructures can be designed at the length scale of 10 µms that can be switched from a magnetized state to a vortex state, effectively switching the magnetization off, using electric field induced strain. This was accomplished using thin film magnetoelectric heterostructures of Fe81.4Ga18.6 on a single crystal (011) [Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32 (PMN-32PT) ferroelectric substrate. The heterostructures were tripped from a multi-domain magnetized state to a flux closure vortex state using voltage induced strain in a piezoelectric substrate. FeGa heterostructures were deposited on a Si-substrate for superconducting quantum interference device magnetometry characterization of the magnetic properties. The magnetoelectric coupling of a FeGa continuous film on PMN-32PT was characterized using a magneto optical Kerr effect magnetometer with bi-axial strain gauges, and magnetic multi-domain heterostructures were imaged using x-ray magnetic circular dichroism—photoemission electron microscopy during the transition to the vortex state. The domain structures were modelled using MuMax3, a micromagnetics code, and compared with observations. The results provide considerable insight into designing magnetoelectric heterostructures that can be switched from an ‘on’ state to an ‘off’ state using electric field induced strain.

Recently, interest has been emerging in the application of symbolic techniques to the specification and analysis of cryptosystems. These techniques, when accompanied by suitable proofs of soundness/completeness, can be used both to identify insecure cryptosystems and prove sound ones secure. But although a number of such symbolic algorithms have been developed and implemented, they remain scattered throughout the literature. In this paper, we present a tool, CryptoSolve, which provides a common basis for specification and implementation of these algorithms, CryptoSolve includes libraries that provide the term algebras used to express symbolic cryptographic systems, as well as implementations of useful algorithms, such as unification and variant generation. In its current initial iteration, it features several algorithms for the generation and analysis of cryptographic modes of operation, which allow one to use block ciphers to encrypt messages more than one block long. The goal of our work is to continue expanding the tool in order to consider additional cryptosystems and security questions, as well as extend the symbolic libraries to increase their applicability.

Compact autonomous ultrahigh power density energy storage and power generation devices that exploit the spontaneous polarization of ferroelectric materials are capable of producing hundreds of kilovolt voltages, multi-kiloampere currents, and megawatt power levels for brief interval of time. The storage life of these devices is four orders of magnitude longer than that for electrochemical batteries and electrochemical capacitors. Herein is an up to date survey of ferroelectric materials used for these high power devices. Several types of ferroelectric ceramics possess the ability to be depolarized under adiabatic compression and can be successfully used for high power applications. In addition to bulk ferroelectric ceramics, multilayer ferroelectric films are very efficient materials for high power systems. Of particular importance is the ability of relaxor ferroelectric single crystals to produce significantly higher electric charge density and energy density than ceramics, making them promising materials for high power applications. Also provided is a brief survey of recent developments of ferroelectric materials for high energy density and power density dielectric capacitors. Numerous ceramics have been developed, including antiferroelectric and relaxor antiferroelectric solid solutions, providing high energy density and efficiency simultaneously.

Nanoindentaiton testing has revealed pop-in events in load–displacement curves of relaxor single crystal PMN-0.3PT ferroelectric materials that occur when the indentation depth is small (e.g., dozens of nanometers). Although there has been speculation of an occurrence of phase transition, there is a relative lack of investigation on the domain evolution associated with the phase transition when the pop-in events appear. In the present study, nanoindentation of this material was systematically modeled using phase-field simulations, which capture the domain and phase evolution of a PMN-0.3PT ferroelectric single crystal. The results, qualitatively similar to the experimental results, revealed details of the contribution of phase transformations to pop-in events. The influence of indenter shape, size, and external electric field on the pop-in event was also examined. This work provides a computational evaluation of the effects of the phase transition mechanism in ferroelectric materials under nanoindentation and gives insight into local mechanical loading effects on these electromechanically coupled crystals.

This article focuses on computational studies evaluating the influence of crystallinity, residual stresses, and out-of-plane (OOP) deterministic switching on Terfenol-D nano/microstructures. The computational models use both coupled and uncoupled Landau–Liftshitz–Gilbert equations with elastodynamics to study strain-induced magnetization reorientation. A Voronoi tessellation approach models the crystal distribution in the microstructures subjected to residual stresses with good agreement to experimental data including large changes in coercivity values, i.e., from 100 to 3000 Oe. Parametric studies show how the coercivity is manipulated with residual stresses, including a magnetoelastically induced perpendicular-magnetic-anisotropy (PMA), important for memory applications. Additional parametric studies focus on epitaxially deposited micro-disks, revealing that residual stresses can create magnetoelastically dominant easy axes along the ⟨110⟩ directions, which are energetically favorable relative to the intrinsic ⟨111⟩ magnetocrystalline easy axes. Modification of the global easy axis is used to design a strain-mediated multiferroic composite consisting of a 20 nm epitaxially deposited Terfenol-D memory bit with PMA grown on a PZT substrate. The multiferroic disk achieves OOP deterministic clocking with an applied voltage.

Rewriting modulo equations has been researched for several decades but due to the lack of suitable orderings, there are some limitations to rewriting modulo permutation equations. Given a finite set of permutation equations E, we present a new RPO-based ordering modulo E using (permutation) group actions and their associated orbits. It is an E-compatible reduction ordering on terms with the subterm property and is E-total on ground terms. We also present a completion and ground completion method for rewriting modulo a finite set of permutation equations E using our ordering modulo E. We show that our ground completion modulo E always admits a finite ground convergent (modulo E) rewrite system, which allows us to obtain the decidability of the word problem of ground theories modulo E. 2012 ACM Subject Classification Theory of computation → Equational logic and rewriting

Automated methods can be used to generate cryptosystems by combining the primitives in an arbitrary fashion, to weed out insecure cryptosystems, and to prove the security of those that survive. In this paper, we study several algorithmic problems arising from the verification of automatically synthesized cryptosystems built from block ciphers, in a theory that includes ACUN . One of these is static equivalence to an algorithm that produces a sequence of random terms. The other is invertibility, the problem of determining whether, given an automatically synthesized cryptosystem, built from block ciphers, and the ability to compute inverses, is it always possible to compute the original plaintext from the ciphertext? We show that static equivalence to random in this theory is undecidable in general. In addition, we identify a reasonable special case for which there is a decidable condition implying security, along with an algorithm for verifying it. For invertibility, we identify a reasonable class of cryptosystems for which invertibility is equivalent to a simple syntactic condition that can be easily verified.

Authenticated encryption schemes are ways of encrypting messages which simultaneously assure the secrecy and authenticity of data. Designing authenticated encryption schemes can be error-prone. In this paper, we consider the authenticity of authenticated encryption schemes . We introduce the notion of symbolic authenticity, and present two inference systems for verifying symbolic authenticity. The first inference system works for authenticated encryption schemes for messages of fixed length. It is sound, complete and terminating. The second one works for authenticated encryption schemes for messages of arbitrary length. It is sound, terminating, and complete under some condition. These inference systems can be used to automatically synthesize authenticated encryption schemes.