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FERROMAGNETIC AND FERROELECTRIC ONE-SHOT EXPLOSIVE-ELECTRIC TRANSDUCERS
Abstract
This memorandum presents the theories of operntion and the initial
experimental verification of these theories for ferromagnetic and ferroelectric
one-shot transducers which convert a portion of the energy of a high explosive to
electrical energy with suitable power, current, and voltage. The transducers are
shown to be extremely small, simple, and versatile. (auth)
... The first paper describing explosive driven FEGs was published by Nielsen [10] in 1957. Throughout the 1960s and 1970s, FEGs were intensely studied at Sandia National Laboratory and the Naval Surface Weapons Center, but research on these generators declined until it was revived in the late 1990s at Sandia [11]. ...
... The first paper describing explosive driven FMGs was published by Nielsen [10] in 1957. In the late 1990s, Texas Tech University [15] began a systematic investigation of FMGs. ...
The modern army is currently striving to make their weapon systems smaller, lighter, and cheaper and at the same time more powerful. One of the enabling technologies that permit this is Explosive Pulsed Power (EPP). Explosive Pulsed Power consists of those devices that convert the chemical energy in explosives into electrical energy. In 2004, a series of Army Small Business Innovative Research (SBIR) Programs were initiated to develop several types of very compact EPP Generators. Based on these recent efforts, we now have a better understanding of the weaknesses and strengths of these small generators. As a result, we can now build reliable generators that provide consistent output currents and voltages. In this paper, a brief introduction to these generators will be given along some of the most recent advances in our understanding of them. This paper will only report on advances made by Army and Navy researchers and that of their contractors. A description of an explosive driven high power microwave test bed built at Texas Tech will be presented. A brief description of some applications of EPP will also be presented.
... Since 1956 Neilson 1 proposed that the stored energy of poled lead zirconate titanate ceramics with a Zr:Ti ratio of 95:5 and modified with 2% niobium (subsequently referred to as PZT95/5) can be released in large pulsed current under shock compression, the PZT95/5 ceramics have been widely studied and used for pulsed power application. [2][3][4] The pulsed power energy density can be calculated through the following defined equation 5 : W s =P r 2 /2ɛ 0 ɛ r where ɛ 0 represents the vacuum dielectric constant. ...
PZT95/5 ferroelectric ceramics are widely utilized in pulsed power devices and the remanent polarization Pr of poled PZT95/5 can characterize the shock-driven energy density. However, this remanent polarization is difficult to be measured nondestructively. In this article, a series of pyroelectric tests of poled PZT95/5 ceramics were conducted near room temperature, from 25°C to 20°C. A linear relation between Pr and pyroelectric coefficient p was found, that is, Pr=1190.5(K)×p, which provides an effective way to nondestructively estimate the value of Pr of the poled PZT95/5 ceramics by measuring the pyroelectric coefficient p at room temperature. According to Devonshire's phenomenological theory, this result could be explained by a modified equation: , where ɛr represents the relative dielectric constant, C represents the Curie constant, and α (equals to 0.52 for PZT95/5 ceramics) represents a modification factor for ceramics, respectively.
... 1-3 Initial shock demagnetization studies of magnetic materials in the 1950's focused on soft ferromagnetic materials including silectron steel, deltamax, and YIG which are only weakly magnetoelastic. [4][5][6][7][8] . Subsequently a larger emphasis was placed on examining hard ferromagnets to increase power generation. ...
This paper presents the experimental measurements of a highly magnetoelastic material (Galfenol) under impact loading. A Split-Hopkinson Pressure Bar was used to generate compressive stress up to 275 MPa at strain rates of either 20/s or 33/s while measuring the stress-strain response and change in magnetic flux density due to magnetoelastic coupling. The average Young's modulus (44.85 GPa) was invariant to strain rate, with instantaneous stiffness ranging from 25 to 55 GPa. A lumped parameters model simulated the measured pickup coil voltages in response to an applied stress pulse. Fitting the model to the experimental data provided the average piezomagnetic coefficient and relative permeability as functions of field strength. The model suggests magnetoelastic coupling is primarily insensitive to strain rates as high as 33/s. Additionally, the lumped parameters model was used to investigate magnetoelastic transducers as potential pulsed power sources. Results show that Galfenol can generate large quantities of instantaneous power (80 MW/m3), comparable to explosively driven ferromagnetic pulse generators (500 MW/m3). However, this process is much more efficient and can be cyclically carried out in the linear elastic range of the material, in stark contrast with explosively driven pulsed power generators.
The brittle fracture may occur in the application of piezoelectric ceramics, but the traditional research is still limited to the static fracture of the materials. Based on the improved Hopkinson pressure bar loading system and high-speed photography technology, the experimental study on the fracture behavior of piezoelectric ceramics under impact loading was carried out. The dynamic mechanical and electrical response of lead zirconate titanate (PZT) and the possible electric breakdown phenomenon were analyzed. The experimental results show that the output voltage is stable and the maximum output voltage is 889 V when the impact load does not cause the material to fracture. When the material breaks, its macroscopic output voltage fluctuates due to electric breakdown. Combined with the finite element simulation of the impact fracture process, the distribution characteristics of the stress field and electric field near the crack during the fracture process were analyzed. The results show that the sliding between grains formed the crack cavity parallel to the electric field during the impact process. Furthermore, based on the theory of dielectric breakdown, the possibility of electric breakdown in the initial defect and the elliptical cavity formed by the impact is analyzed.
In order to reveal influence of external capacitance on the voltage input and input energy provided by the PZT-5H piezoelectric ceramic composite structure under high-speed impact loading, experiments have been performed by using one-stage light gas gun loading system combining with a power supplier circuit and power output testing system, which the aspect ratio of 1:1 column projectile impact monolithic and multi-piece piezoelectric ceramic composite structure at the near impact velocity and different storage capacity. The experimental results show that the more larger storage capacitance is, the smaller the piezoelectric ceramic output voltage is. However, the smaller of the capacitor voltage is, the smaller the value of energy storage is; with the energy storage capacitance increasing, the piezoelectric capacitance ratio and the energy conversion rate of piezoelectric ceramics decreases; In addition, the storage energy capacitor increases with the increasing of the piezoelectric ceramic layers; the relationships of storage energy capacitor and piezoelectric ceramic capacitor has a great influence on the input voltage and storage energy for storage energy capacitor. © 2018, Editorial Board of Journal of Northwestern Polytechnical University. All right reserved.
Previous studies examining the response of magnetoelastic materials to shock waves have predominantly focused on applications involving pulsed power generation, with limited attention given to the actual wave propagation characteristics. This study provides detailed magnetic and mechanical measurements of magnetoelastic shock wave propagation and dispersion. Laser generated rarefacted shock waves exceeding 3 GPa with rise times of 10 ns were introduced to samples of the magnetoelastic material Galfenol. The resulting mechanical measurements reveal the evolution of the shock into a compressive acoustic front with lateral release waves. Importantly, the wave continues to disperse even after it has decayed into an acoustic wave, due in large part to magnetoelastic coupling. The magnetic data reveal predominantly shear wave mediated magnetoelastic coupling, and were also used to noninvasively measure the wave speed. The external magnetic field controlled a 30% increase in wave propagation speed, attributed to a 70% increase in average stiffness. Finally, magnetic signals propagating along the sample over 20faster than the mechanical wave were measured, indicating these materials can act as passive antennas that transmit information in response to mechanical stimuli.
As ferroelectric ceramics possess a special feature of high spontaneous polarization Ps, a poled ferroelectric ceramic material can be used for the generation of high energy electric pulses by means of an induced phase transition method to convert the ferroelectric phase to an antiferroelectric one, thus releasing its stored energy. Depending on the load impedance of the external matching network, the output energy can be made to reach a value close to Ps 2/2 εr,ε0. If this method is used for the generation of a high voltage or a high current pulse, the inherent insulation problem of ceramics due to the presence of a large quantity of pores and defects, the non-uniformity of the material, the low resistivity, as well as the carrier injection during the depoling process tends to limit and affect the performance of the system. We present some new experimental results to demonstrate the importance of the insulation problem and discuss the possible factors that would limit the output energy of the system
A device technique is discussed, which permits the electroacoustic generation of electrical or of acoustic megahertz pulses or pulse sequences with kilowatt powers. The devices consist of groups of piezoelectrically active elements, separated by acoustic delay lines. A sudden change in applied pressure or electric field generates electrical or acoustic wave trains; they may be programmed to contain information. This paper presents a first order design theory for such piezoelectric pulse train and code generators, with emphasis on arrangements producing electrical output from electrical input. The output depends on the load, and on the geometric arrangement; the latter controls the superposition of responses from the elements. The optimum impedance for a noninductive load is found, and the energy conversion efficiency for this case is estimated; it increases with the number of active elements. Selected experimental devices are described; typically they contain from 4 to 16 piezoelectric elements of 0.01 to 0.1 cm thickness and 5 cm2 cross section, generate pulse frequencies from 1 to 10 MHz, pulse trains from 3 to 10 cycles, and code signals of 20 μs duration. Performance limitations are introduced by bonding technology, geometric tolerances, electric breakdown, and circuit inductance. Copyright © 1967 by The Institute of Electrical and Electronics Engineers, Inc.
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