Company Sponsored Publications

This is a list of publications referencing research performed at or sponsored by HEM Technologies.

Explosively Driven Pulsed Power

DEVELOPMENT OF AN ULTRA-COMPACT EXPLOSIVELY DRIVEN
MAGNETIC FLUX COMPRESSION GENERATOR SYSTEM
Shad L. Holt, John T. Krile and David J. Hemmert, HEM Technologies
John W. Walter, James C. Dickens, Texas Tech University
Larry L. Altgilbers , U.S. Army SMDC
Allen H. Stults, U.S. Army AMRDEC

2007 IEEE Pulsed Power and Plasma Science Conference, Albuquerque, NM, June 2007 (publication Pending)

Explosively driven magnetic flux compression generators (MFCG) are effective high current, compact, disposable pulsed power supplies. The most pervasive type of MFCG used is a helical generator because it can provide very high current gain. However, several design limitations must be overcome to allow for the use of helical MFCG in ultra compact pulsed power systems. The first limitation is the initial seed current source and high current switching mechanism. The second involves the high current, low voltage output which is unsuitable for driving high impedance loads. The current system utilizes an ultra compact, seed source previously developed by HEM Technologies. An explosively driven closing switch provides both the switching action as well as a delay generator to allow for the current rise in the MFCG. The output of the MFCG is conditioned via an exploding fuse wire and spark gap pair to convert the high current output to high voltage. HEM Technologies has performed extensive modification and testing of the end-to-end system. Current and energy gain will be presented along with typical output voltages using various fusing techniques.

 

TESTING OF NEW FERROELECTRIC ELEMENTS CUSTOM ENGINEERED FOR EXPLOSIVELY DRIVEN FERROELECTRIC GENERATOR APPLICATIONS
Shad L. Holt, John T. Krile and David J. Hemmert, HEM Technologies
Wesley S. Hackenberger, Edward F. Alberta, TRS Technologies Inc.
John W. Walter, James C. Dickens, Texas Tech University
Larry L. Altgilbers , U.S. Army SMDC
Allen H. Stults, U.S. Army AMRDEC

2007 IEEE Pulsed Power and Plasma Science Conference, Albuquerque, NM, June 2007 (publication Pending)

Explosively driven ferroelectric generators (FEGs) are reliable, compact, high voltage sources that utilize high pressures to liberate charge trapped in the crystal structure of ferroelectric materials. For the active ferroelectric element most FEG designs use commercial lead zirconate-titanate (PZT) compositions designed for either precision actuators or naval sonar transducers. However, the material properties that are important in FEG applications are not the same material properties for which these materials have been designed to maximize. FEG designs utilizing these commercial materials are performance limited by high voltage breakdown, mechanical failure and low energy densities. TRS Technologies inc. has produced a new series of ferroelectric elements designed specifically for FEG applications. HEM Technologies has performed dielectric strength and shock compression experiments on these new materials to evaluate their performance in comparison to existing commercially available materials.

 

TESTING OF NEW FERROELECTRIC MATERIALS FOR EXPLOSIVELY DRIVEN FERROELECTRIC GENERATORS
S.L. Holt, D.J. Hemmert, J.T. Krile, HEM Technologies
W.S. Hackenberger, E.F. Alberta, TRS Technologies Inc.
J.W. Walter, J.C. Dickens, Texas Tech University
L.L. Altgilbers, U.S. Army, SMDC
A.H. Stults, U.S. Army, AMRDEC

Megagauss 2006, Santa Fe NM, November 2006 (publication pending)

Very compact high voltage pulse generators can be designed to compress ferroelectric materials with explosives to release charge contained in the crystal structure of the ferroelectric. Most explosively driven ferroelectric generator research has utilized commercially available ferroelectric materials, typically lead zirconate-titanate (PZT) compositions. These commercial PZT compositions are commonly used in either precision actuators or naval sonar transducers and have been engineered to maximize the remnant polarization and therefore piezoelectric effect. However, the material properties that are important in ferroelectric generator applications such as low shock-induced conductivity, high dielectric strength, and high stress induced depolarization are often negligible or detrimental to the applications for which these commercial materials are designed. Materials specifically engineered for ferroelectric generator applications are not currently commercially available, but could provide important performance enhancements for future generator designs. This paper discusses the electrical and mechanical testing of new ferroelectric materials designed by TRS Technologies specifically for ferroelectric generator applications. These new materials are tested for dielectric strength and electrical response to shock-induced depolarization by various high-explosive charges and the results are compared to commercially available PZT compositions.

 

CHARACTERIZATION OF EXPLOSIVELY DRIVEN FERROELECTRIC GENERATOR MATERIAL
S.L. Holt, D.J. Hemmert, J.W. Walter, HEM Technologies
J.J. Mankowski, J.C. Dickens, M. Kristiansen, Texas Tech University
L.L. Altgilbers, U.S. Army, SMDC
A.H. Stults, U.S. Army, AMRDEC

Megagauss XI, London, September 2006 (publication pending)

Explosively driven ferroelectric generators (FEGs) are reliable, compact, high voltage sources for driving ultra-compact high power devices.  When energized by an explosive shockwave, they become depolarized, acting similar to a charged high voltage capacitor.   However, due to the relatively low energy of these devices, they must be well matched to the load for maximum energy transfer.  This requires proper characterization of the material electrical output as a function of the input shockwave.  HEM Technologies and Texas Tech University characterized a ferroelectric ceramic, EDO EC-64, for different pressures to calculate its equivalent series resistance and determine its maximum output power.  The ferroelectric was then tested against a matched load for comparison. 

 

Ultra-Compact Pulsed Power

HIGH POWER DISCHARGE TESTING OF SMALL BATTERIES TO POWER AN ULTRA-COMPACT CURRENT SEED SOURCE
David J. Hemmert and John Walter, HEM Technologies

15th International Pulse Power Conference, June 2005

Abstract:
The need for inexpensive, disposable, single use, ultra-compact, pulsed power devices has increased dramatically over the past few years. This is driving the development of extremely small pulsed power devices constructed from off-the-shelf components. However, the majority of readily available electronic components are designed and characterized only for long life use such as batteries. HEM Technologies has recently evaluated several candidate batteries for an ultra-compact pulsed power application. The need was to develop a current seed source in a form factor of 150 cm3 for a compact magnetic flux compression generator (MFCG). Recent research has evaluated some batteries down to sizes N and AA. However, for the designed seed source, smaller batteries were required. Candidate batteries included sizes CR 2, 23A, down to CR2032. To evaluate the batteries, they were discharged into a resistive load of 1Ω down to 22 mΩ for 1 sec. The resulting V-I and power density results are presented.

 

COMPARISON OF ULTRA-COMPACT SEED SOURCES FOR MFCGS
John Walter and David Hemmert, HEM Technologies

15th International Pulse Power Conference, June 2005

Abstract:
The increasing need for small, expendable, pulsed power payloads is driving the development of ultra-compact pulsed power systems and components. The primary compact pulsed power device considered is the magnetic flux compression generator, due to the large stored energy density in high explosives. To maximize the total system volume available for the MFCG, an ultra-compact seed current source is required. HEM Technologies has constructed and evaluated seed current sources utilizing two different technologies: a battery-powered capacitive discharge and an explosively driven ferroelectric. These devices were constructed to fit into a volume less than 200 cubic centimeters. Details of the design tradeoffs and experimental results are presented. Comparisons between the two technologies, potential improvements and limitations to each are discussed.

 

Pulsed Power Solutions

REAL TIME FEEDBACK CONTROL SYSTEM FOR AN ELECTROMAGNETIC LAUNCHER
R. Karhi, J. Mankowski, and M. Kristiansen, Texas Tech University
D. Hemmert, S. L. Holt, HEM Technologies

Megagauss XI, Santa Fe NM, November 2006

The design and implementation of a real time feedback control system for a distributed energy, bench top, electromagnetic launcher is presented. The feedback control system provides optimum pulse shaping by real time control of solid state switches. Advantages of pulse shaping control include increased energy efficiency and control of armature exit velocity. LabVIEW 8.0 software is used to program a National Instruments CompactRIO programmable automation controller (PAC). This provides real time processing by use of the reconfigurable I/O (RIO) FPGA technology. The program controls switch timing from two analog feedback signals. A flux ruler sensor along the bore length provides one of these feedback signals and is used to calculate armature position and velocity. Real time velocity updates occur every centimeter of bore travel for the system. The other feedback signal comes from a Pearson coil which monitors the current. The program uses this data to control pulse shape and width. Collected data is used to characterize the system under test for different load conditions.

 

Staff Publications

This listing is intended to show the qualifications of the HEM Technologies staff and not to imply any association with or sponsorship by HEM Technologies for the research described within.

Explosively Driven Pulsed Power

S. Holt, J. Dickens, J. Walter, S. Calico, "Design of Explosive-Driven Ferroelectric Pulse Generators", 15th International Pulse Power Conference, proceedings pending publication, 2005.

D. Hemmert, J. Mankowski, J. Rasty, A. Neuber, J. Dickens, M. Kristiansen, “Conductivity Measurements of Explosively Shocked Aluminum and OFHC Copper Used for Armature Material in a Magnetic Flux Compression Generator,” Proceedings of the 14th IEEE International Pulsed Power Conference, Vol. 2, pp. 1073- 1076, 2003.

D. Hemmert, J. Rasty, A. Neuber, J. Dickens, X. Le, M. Kristiansen, “Conductivity Measurements of MFCG Armature Material Under Shock and High Strain Rates Utilizing a Split-Hopkinson Pressure Bar Apparatus,” Proceedings of the 13th IEEE International Pulsed Power Conference, Vol. 1, pp. 265-268, 2001.

DC and RF Breakdown and Flashover

A. Neuber, G. Edmiston, J. Krile, H. Krompholz, J. Dickens, M. Kristiansen, “Interface Breakdown During High-Power Microwave Transmission,” IEEE Trans. on Magnetics, vol. 43, iss. 1, pp. 496-500, Jan. 2007.

J. Krile, A. Neuber, T. Gibson, and H. Krompholz, “Monte Carlo simulation of high power microwave window breakdown at atmospheric conditions,” accepted for publication by Applied Physics Letters, vol. 89, no. 20, Nov. 2006.

K. P. Morales, J. T. Krile, A. A. Neuber, and H. G. Krompholz, “Pulsed Dielectric Surface Flashover in Atmospheric Conditions,” IEEE Trans. on Dielectrics and Electrical Insulation, vol. 13, no. 4, pp. 803-809, Aug. 2006.

G. Edmiston , J. Krile, A. Neuber, J. Dickens, and H. Krompholz, “High Power Microwave Surface Flashover of a Gas-Dielectric Interface at 90 to 760 Torr,” accepted for publication the IEEE Transactions on Plasma Science, 2006.

J. Krile, A. Neuber, G. Edmiston, J. Dickens, H. Krompholz, " Surface Flashover Under RF and Unipolar Excitation at Atmospheric Conditions," to be published in Proceedings of the 27th Int. IEEE Power Modulator Conference, Washington D.C., May 14-18, 2006 (invited)

A. Neuber, J. Krile, G. Edmiston, H. Krompholz, J. Dickens, M. Kristiansen ,“Interface Breakdown During High Power Microwave Transmission,” submitted to 13th EML Symposium, May 22-25, 2006, Berlin, Germany.

J. Krile, G. Edmiston, K. Morales, A. Neuber, H. Krompholz, M. Kristiansen, “Similarities of Dielectric Surface Flashover under Atmospheric Conditions for Pulsed Unipolar and RF Excitation,” Laser Physics, vol. 16, no. 1, pp. 194-201, 2006.

A. Neuber, G. Edmiston, J. Krile, K. Morales, J. Dickens, H. Krompholz, "High Power Microwave Breakdown Limits of Dielectric/Gas Interfaces,” presented at the 2005 International COE Forum on Pulsed Power Science November 13 – 14 at Kumamoto, Japan. (invited)

A. Neuber, J. Krile, G. Edmiston, H. Krompholz, J. Dickens, "Limits of High Power Microwave Transmission due to Interface Breakdown," presented (oral) at 2005 Tri-Service VED Workshop, 12-16 September 2005

K. P. Morales, J. T. Krile, A. A. Neuber, and H. G. Krompholz, “Pulsed Dielectric Surface Flashover in Atmospheric Conditions,” submitted to IEEE Transactions on Dielectrics and Electrical Insulation, Sept. 2005.

J. Krile, A. Neuber, J. Dickens, H. Krompholz, “DC and Pulsed Dielectric Surface Flashover at Atmospheric Pressure,” IEEE Trans. on Plasma Sci., vol. 33, no. 4, pp. 1149-1154, August 2005.

K. Morales, J. Krile, A. Neuber, H. Krompholz, “Pulsed Dielectric Surface Flashover at Atmospheric Conditions,” to be published in Proceedings of the 15th Int. IEEE Pulsed Power Conference, Monterey, CA, June 13-17, 2005

J. Krile, A. Neuber, J. Dickens, H. Krompholz, G. Edmiston, “Similarities of Dielectric Surface Flashover at Atmospheric Conditions for Pulsed Unipolar and RF Excitation,” to be published in Proceedings of the 15th Int. IEEE Pulsed Power Conference, Monterey, CA, June 13-17, 2005

G. Edmiston, A. Neuber, H. Krompholz, J. Dickens, J. Krile, "High Power Microwave Surface Flashover of a Gas-Dielectric Interface at 90 to 760 Torr," to be published in Proceedings of the 15th Int. IEEE Pulsed Power Conference, Monterey, CA, June 13-17, 2005

J. Krile, A. Neuber, J. Dickens, H. Krompholz, “Imaging of Dielectric Surface Flashover in Atmospheric Conditions,” IEEE Trans. on Plasma Sci. Special Issue on Imaging, vol. 33, no. 2, pp. 270-271, April 2005.

J. Krile, A. Neuber, H. Krompholz, J. Dickens, "Unipolar Surface Flashover," presented at the 46th Annual Meeting of the Division of Plasma Physics November 15-19, 2004, Savannah, GA, Meeting ID: DPP04APS

J. Krile, A. Neuber, J. Dickens, H. Krompholz, “DC Flashover of a Dielectric Surface in Atmospheric Conditions,” IEEE Trans. on Plasma Sci., vol. 32, no. 5, pp. 1828-1834, Oct. 2004.

J. T. Krile, A. A. Neuber, H. G. Krompholz, and J. C. Dickens, „DC and Pulsed Dielectric Surface Flashover at Atmsopheric Pressure,“ 2004 Power Modulator Conference, San Francisco, CA, 2004.

D. Hemmert, K. Shiraki, T. Yokoyama, S. Katsuki, H. Bluhm, and H. Akiyama, “Optical Diagnostics of Shock Waves Generated by a pulsed Streamer Discharge in Water,” Proceedings of the 14th IEEE International Pulsed Power Conference, Vol. 1, pp. 232- 235, 2003.

J. Krile, A. Neuber, J. Dickens, and H. Krompholz, “Flashover Across a Dielectric Surface at Atmospheric Pressure,” Joint Fall Meeting of the Texas Sections of the APS and AAPT and Zone 13 Society of Physics Students, Lubbock, TX, Oct 2003.

J. Krile, A. Neuber, J. Dickens, and H. Krompholz, “Physics Of Dielectric Surface Flashover At Atmospheric Pressure,” Proceedings of the 14th IEEE Int. Pulsed Power Conference, Dallas, TX, June 15-18, 2003.

R. Jorgenson, L. Warne, A. Neuber, J. Krile, J. Dicken, and H. Krompholz, “Effect of Dielectric Photoemission on Surface Breakdown: An LDRD Report,” Sandia Report SAND2000-3044, June 2003.

D. Hemmert, A. Neuber and J. Dickens, “Microwave Breakdown Studies of He-N2 Mixtures in a Pillbox Cavity from 760 to 3040 Torr,” International Power Modulator Conference, pp. 232-235, 2002.

D. Hemmert, A. Neuber, H. Krompholz, J. Mankowski, and D. Saeks, "Field enhanced microwave breakdown in gas for a plasma limiter", The 29th IEEE International Conference on Plasma Science, pp. 322, 2002.

J. J. Mankowski, D. Hemmert, A. Neuber, H. Krompholz, “Field Enhanced Microwave Breakdown in Gas for a Plasma Limiter,” IEEE Transactions on Plasma Science, Vol. 30, pp. 102-103, 2002.

H. Krompholz, L. L. Hatfield, M. Kristiansen, D. Hemmert, B. Short, J. Mankowski, M. D. J. Brown, L. L. Altgilbers, "Gas breakdown in the sub-nanosecond regime with voltages below 15 kV", IEEE Transactions on Plasma Science, Vol. 30, pp: 1916- 1921, 2002.

D. Hemmert, A. Neuber, H. Krompholz, L. L. Hatfield, and M. Kristiansen, “Dielectric/Gas Interface Breakdown Caused by High Power Microwaves,” presented at the 3rd Annual Directed Energy Symposium, Albuquerque, NM, October 2000.

D. Hemmert, A. Neuber, J. Dickens, H. Krompholz, L. L. Hatfield, and M. Kristiansen, “Dielectric/Gas Interface Breakdown Caused by High Power Microwaves,” 13th International Conference on High Power Particle Beams, Nagaoka, Japan, June 2000.

David Hemmert, Andreas A. Neuber, James C. Dickens, Hermann Krompholz, Lynn L. Hatfield, and Magne Kristiansen, “High Power Microwave Window Breakdown Under Vacuum and Atmospheric Conditions,” Proceedings of SPIE -- Volume 4031 Intense Microwave Pulses VII, pp. 90-98, July 2000.

D. Hemmert, A. A. Neuber, J. Dickens, H. Krompholz, L. L. Hatfield, M. Kristiansen, “Microwave Magnetic Field Effects on High Power Microwave Window Breakdown,” IEEE Transactions on Plasma Science, Vol. 28, pp. 472-477, 2000.

A. Neuber, D. Hemmert, H. Krompholz, L. L. Hatfield, M. Kristiansen, "Pressure dependence of high power microwave solid dielectric/gas interface breakdown", IEEE 27th International Conference on Plasma Science, pp. 124, 2000.

D. Hemmert, A. Neuber, J. Dickens, H. Krompholz, L. L. Hatfield, and M. Kristiansen, "Influence of the microwave magnetic field on high power microwave window breakdown" IEEE International Conference on Plasma Science, pp. 229, 1999.

A. Neuber, D. Hemmert, H. Krompholz, L. Hatfield, and M. Kristiansen, "Initiation of high power microwave dielectric interface breakdown", Journal of Applied Physics, Volume 86, Issue 3, pp. 1724-1728, 1999.

A. Neuber, D. Hemmert, J. Dickens, H. Krompholz, L. L. Hatfield, and M. Kristiansen, “Imaging of High-Power Microwave-Induced Surface Flashover,” IEEE Transactions on Plasma Science, Vol. 27 pp. 138-139, 1999.

A. Neuber, P. Ferguson, K. Hendricks, D. Hemmert, H. Krompholz, L. L. Hatfield, M. Kristiansen, "Characterization of the power handling capability of an S-band double disc gas cooled microwave window", IEEE International Conference on Plasma Science, pp. 253, 1999.

A. Neuber, J. Dickens, D. Hemmert, H. Krompholz, L. L. Hatfield, and M. Kristiansen, “Window Breakdown Caused by High Power Microwaves,” IEEE Transactions on Plasma Science, Vol. 26, p.296-303, 1998.

A. Neuber, J. Dickens, D. Hemmert, H. Krompholz, L. L. Hatfield, M. Kristiansen, "Breakdown of dielectric/vacuum interfaces caused by high power microwaves", IEEE 25th International Conference on Plasma Science, pp. 205, 1998.

D. Hemmert, A. Neuber, J. Dickens, H. Krompholz, L. L. Hatfield, and M. Kristiansen, “Window and Cavity Breakdown Caused by High-Power Microwaves,” Proceedings of the 11th IEEE International Pulsed Power Conference, Vol. 1, pp. 135-140, 1997.

Pulsed Power Switching

C. James, J. C. Dickens, S. Holt, "Evaluation of Switch Jitter on a High Pressure Coaxial Spark Gap", 2007 IEEE Pulsed Power and Plasma Science Conference, June 17-22, 2007, Albuquerque, NM.

 

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