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An electro-explosively actuated mini-flyer launcher
Sensors and Actuators A 292 (2019) 17–23
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Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna
An electro-explosively actuated mini-flyer launcher Cong Xu, Peng Zhu ∗ , Ke Wang, Xin Qin, Qiu Zhang, Zhi Yang, Ruiqi Shen School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China
a r t i c l e
i n f o
Article history: Received 1 February 2019 Received in revised form 4 March 2019 Accepted 18 March 2019 Available online 6 April 2019 Keywords: Shock loading Electric gun High-voltage switch MEMS Photonic Doppler velocimetry
a b s t r a c t It’s crucial to develop shock loading techniques in laboratory to create pressure and temperature jumps for a wide variety of studies in material science. In this paper we have developed an electro-explosively actuated mini-flyer launcher capable of ejecting a plastic mini-flyer, typically 0.6 mm in diameter, up to several km/s. When prepared with microelectromechanical system (MEMS) scale methods, it can be mass-produced and takes only four steps, lowering manufacturing cost. Particularly, it was designed and integrated with a high-power high-voltage switch together, omitting expensive vacuum switches as well as interconnections between components. Four auxiliary exploding foils were first exploded at a certain trigger voltage to determine the optimal size, and polyvinylidene fluoride (PVDF) film was used to measure shock pressure of electro-explosion to estimate whether it’s enough to destroy the dielectric layer between top and bottom electrodes. Electrical characterizations were then carried out to obtain some important parameters, such as delay time, jitter time, risetime and peak current flowing through main exploding foil, at a series of firing voltages ranging from 600 V to 1400 V, and the results revealed that peak current increases with the rise of firing voltage dramatically, high-current pulse can be obtained at lower firing voltage, and delay time and risetime are almost constant. Finally, Photon Doppler Velocimetry (PDV) and high-speed camera were utilized to record the acceleration histories of flyers at different firing voltages, and the results showed that the flyer velocity can be controlled by the adjustment of firing energy. All the efforts demonstrated that the mini-flyer launcher is feasible and attractive. © 2019 Elsevier B.V. All rights reserved.
1. Introduction With the advent of dynamic loading technology in 1940s, higher pressure can be obtained to impact interesting materials to study the dynamic response mechanisms of target materials under extreme conditions [1,2]. There are mainly two modes in generating high-pressure pulse. One is contact mode, the observed objective is in direct contact with shock waves or detonation waves intimately. The other is non-contact mode, a thin disk, also called flyer, is accelerated up to several km/s in a very short time. By the high-speed impact on the target, a shock wave is generated propagating with supersonic speed through the target. Due to higher pressure generated in the target, the latter has always been concerned in past decades [3]. Several driving sources including laser [4,5], electro-explosion plasma [6–8], explosive [9], high-intensity magnetic field [10] and compressed air [11] are often used to launch a flyer, however, electro-explosively driven flyer looks more attractive. Its basic principle is to use the rapid electro-explosion of a bowknot-liked metal
∗ Corresponding author. E-mail address: [email protected] (P. Zhu). https://doi.org/10.1016/j.sna.2019.03.027 0924-4247/© 2019 Elsevier B.V. All rights reserved.
foil, also called exploding foil, to create a rapid-expanding plasma to accelerate a dielectric flyer [12,13]. It’s clear that the flyer velocity can be controlled easily by the adjustment of the energy delivered to the exploding foil to meet the required pressure. Compared with plane-wave explosive lens and two-stage light-gas gun, electro˜ km/s) and higher explosively driven flyer has higher velocity (20 pressure (T˜ Pa). Besides, the supply and capacitor discharge unit (CDU) can be used repeatedly, only needing replacing the foil-flyer components after each shot [2]. We should be aware of the importance of high-voltage switch when operating an electro-explosively driven flyer launcher [14]. A fast turn-on, low impedance high-voltage switch can transfer more energy from capacitor into the metal foil, avoiding slow electroexplosion and energy loss [15,16]. Many kinds of high-voltage switches, such as triggered spark gap [17–19], semiconductor switches [20,21] and mercury vapor switches [22], were used in pulse power applications, however, triggered spark gap has tremendous advantages in high-temperature operation, leakage current and radiation hardness [23]. Even so, its poor electrical conductivity under lower operation voltage, mainly uncertain delay time and unstable peak current, hampers further development in the field of low voltage.
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Fig. 1. Schematic representation of the fireset circuit used to characterize mini-flyer launcher.
It is well-known that plasma is an excellent medium for electrical conduction, especially in high electric field. Inspired by exploding foil, we intended to utilize the plasma generated by exploding foil as a conductive medium. In this paper, an auxiliary exploding foil was designed as an “attacker” destroying dielectric film, and as a potential plasma medium during switching. After dielectric breakdown, the capacitor begins to discharge, and a high-current pulse flows through the dielectric film between the auxiliary exploding foil and bottom electrode. On account of good compatibility in structure, the sandwich high-voltage switch was integrated with an electro-explosively actuated flyer launcher together. The left pad of main exploding foil in mini-flyer launcher acts as the bottom electrode of the high-voltage switch, the dielectric film plays a role of flyer in mini-flyer launcher, and even the barrel in mini-flyer launcher can be utilized as a tamper to reflect plasma generated by the auxiliary exploding foil to punch the dielectric film. Using microelectromechanical system (MEMS) technology, the mini-flyer launcher can be mass-produced, which reduces manufacturing cost and improves experimental efficiency. Frequently 100 shock experiments can be done per day. Electrical characterizations were first conducted to determine optimal auxiliary foil and shock pressure, some key parameters such as delay time, jitter time, peak current and risetime were then investigated at different firing voltages varying from 600 V to 1400 V. Finally, a home-built Photonic Doppler Velocimetry (PDV) and high-speed imaging camera were adopted to validate the capability of ejecting a high-speed flyer. These results showcase the feasibility of the mini-flyer launcher.
2. Experimental procedures 2.1. Structure and principle Fig. 1 is a schematic representation of the fireset used to characterize the mini-flyer launcher. One pad of the auxiliary exploding foil was connected through a field effect thyristor (FET) switch, IGBT presented here, to positive terminal of high-voltage capacitor C1 , and the other pad was connected to the negative terminal of C1 , which was also linked with cathode of high-voltage capacitor C2 . The anode of C2 was attached to right pad of the main exploding foil, namely high-voltage terminal. Before working, the two capacitors were charged up to operation voltages, respectively. Once the IGBT was triggered, C1 discharges, generating hundreds of amperes, and the auxiliary exploding foil will was exploded into a mixture of gas and plasma to damage the parylene layer. After that, C2 discharges rapidly, thousands of amperes pass through the parylene and the main exploding foil, inducing a large amount of heat to make the
main exploding foil undergo a series of phase changes from solid through liquid to gas, even plasma. Due to the constraint of barrel, a 600 m-in-diameter parylene-copper flyer is cut out at the edges of barrel. When arriving at the end of barrel, it has been accelerated up to several km/s. UA and UM in Fig. 1 are defined as the voltages across the main exploding foil and parylene film, the IA and IM are the currents flowing in the trigger circuit and main circuit, respectively. 2.2. Materials and methods Fig. 2 illustrates process flow diagrams of the mini-flyer launcher. The bottom metal layers, consisting of 100 nm thick tungsten-titanium alloy layer (the tungsten accounts for 90% in weight) and 3.6 m thick copper layer, were first deposited on 50.8 mm × 50.8 mm ceramic substrate by sputtering magnetron, and the main exploding foil (400 m × 400 m) was patterned by ultraviolet lithography, as shown in Fig. 2 (a). The tungsten was added to prevent the copper layer from being ablated during switching, and the titanium is an adhesive between ceramic substrate and the copper layer. In Fig. 2 (b), a 25 m of parylene type C with a nominal dielectric strength of 220 V/m was coated by chemical vapor deposition (CVD), which is an in-situ polymerization technology often used in electronics industry. Parylene dimmer was first vaporized at 180 ◦ and pyrolysed into monomers at 700 ◦ , then the monomers join together to form polymer film at 35 ◦ . In Fig. 2 (c), an auxiliary exploding foil and metal flyer centered on the center of the main exploding foil were prepared using same processes with the main exploding foil. The metal flyer was deposited not only to make more inflection laser be captured by optical fiber probe of PDV, but also to improve output pressure of parylene flyer. Fig. 2 (d) shows the preparation of SU-8 barrel with a thickness of 400 m and an inner diameter of 600 m, which involves a series of processes, such as spin coat, soft bake, expose, post exposure bake, and develop. It provides room for flyer acceleration mainly, and the rest plays a part of a tamper to reflect electro-explosion plasma of the auxiliary exploding foil. Finally, the mini-flyer launcher array mounted on the ceramic substrate was split into many individuals by mechanical cutting, as shown in Fig. 2 (e) and (f). 2.3. Experimental methods 2.3.1. Current and voltage measurements It is necessary to measure the current and voltage flowing through exploding foil, whether the auxiliary or the main [12]. From the two parameters, more details about phase changes can be dis-
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Fig. 2. Process flow diagrams of the mini-flyer launcher. (a) Preparation of main exploding foil. (b) Deposition of dielectric film. (c) Preparation of auxiliary exploding foil and metal flyer. (d) Development of SU-8 layer. (e) Photograph of the undiced mini-flyer launcher array. (f) Photograph of an individual mini-flyer launcher.
tinguished with the knee points of dynamic resistivity of exploding foil, and the energy coupled into exploding foil can also be calculated. Furthermore, only when the current density exceeds 108 A· cm−2 within hundreds of nanoseconds can metal foil be exploded completely [24]. Therefore, the currents were measured using CWT Mini-HF 60 model Rogowski coil with a bandwidth of 30 MHz, and the voltages were measured using high-voltage differential probe with a bandwidth of 400 MHz. All the data were recorded using a four-input LeCroy WR104Xi-A oscilloscope with a bandwidth of 1 GHz, at a sampling rate of 10 GS/s.
where U(t) is potential difference between both sides of PVDF film. Since Rb is much greater than Rm and R, Eq. (2) will be simplified as i (t) ≈
U (t) R
(3)
So the charge Q converging on the surface of the PVDF film can be calculated by
t Q (t) =
U () d R
(4)
0
2.3.2. Pressure measurement The electro-explosion pressure of the auxiliary exploding foil can be measured by polyvinylidene Fluoride (PVDF) film. Once the PVDF film is pressed, polarization will occur in the interior, and positive and negative charges will appear on its two opposite surfaces [25]. In this paper, the PVDF film was placed between two PMMA plates, so that it will not be ablated after the auxiliary exploding foil is exploded, as shown in Fig. 3. More importantly, the resulting spherical shock wave is adjusted to be a planar wave to press the whole PVDF film, instead of focusing on one point. Of course, the pressure behind the PMMA plate pb is lower than initial electroexplosion pressure p0 , however, the initial value p0 can be derived by the attenuation coefficient of PMMA ␣ as follows: pb = p0 e
−˛x
(1)
In Fig. 3, R, Rm and Rb represent parallel resistance, matched resistance and oscilloscope resistance (1˜ M), respectively. The current across the parallel resistance R is described as i (t) =
Rm + Rb + R U (t) RRb
(2)
Combined with the sensitivity coefficient of the PVDF film Kp (20 pC·N−1 ), the force F can be obtained by F (t) =
Q (t) 1 = Kp Kp
t
U () d R
(5)
0
Finally, the shock pressure is estimated by 1 F (t) pb (t) = = A Kp
t 0
U () d AR
(6)
where A is the area of the PVDF film. 2.3.3. Flyer velocity measurement Flyer velocity is an extremely vital parameter for flyer launcher [26], which determines the magnitude of output pressure. Therefore, a home-built Photonic Doppler Velocimeter (PDV) was utilized to capture flyer velocity time history. The fundamental principle of PDV is that laser frequency will be changed when a laser beam is reflected from high-speed flyer, which adheres to Doppler effect. When the reflection laser meets original laser, frequency difference will be observed and recorded using a Keysight DSOV334 A oscilloscope with a bandwidth of 33 GHz, at a sampling rate of 80 GS/s.
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Fig. 3. The test circuit used to measure shock pressure of electro-explosion of auxiliary exploding foil.
Fig. 4. The voltages and currents across four kinds of auxiliary exploding foils, including (a) 40 m × 40 m, (b) 40 m × 80 m, (c) 80 m × 80 m and (d) 120 m × 120 m, under 0.39 F/500 V.
Finally, the flyer velocity vs. time curve can be obtained by Fourier transform. 2.3.4. High-speed photography Specialised Imaging SIM X high speed camera was utilized to image the whole action process of the mini-flyer launcher, including electro-explosion of the auxiliary exploding foil and main exploding foil, as well as the moving flyer. The exposure time of each shot was 5 ns, with interframe times of 50 ns, except for the interframe time between frame 8 and frame 9 of 200 ns. Sixteen frames were acquired by the camera. 3. Results and discussions 3.1. Size effect of auxiliary exploding foil Four kinds of auxiliary exploding foils were designed, including 40 m × 40 m, 40 m × 80 m, 80 m × 80 m and 120 m × 120 m, to determine which one is more appropriate to shock the parylene film. Apparently, a greater foil will consume
more energy, bringing more burden to trigger circuit. However, a smaller foil can only form a weak electro-explosion, which is insufficient to penetrate the parylene film. The four auxiliary exploding foils mentioned above were characterized at 0.39 F/500 V, and the results were plotted in Fig. 4. In Fig. 4 (a) and (b), voltage spike is earlier than peak current in time, and the former is generally considered as ‘burst’ time, which means the exploding foil changes from liquid phase to gas phase at the time. When it comes to ‘burst’ time, the currents in Fig. 4 (a) and (b) are still climbing, which indicate that the applied energy is surplus. Besides, the current peak (260 A) in Fig. 4 (b) is lower than Fig. 4 (a) (326 A), since the resistance of the 40 m × 80 m exploding foil is twice than the 40 m × 40 m. Although the 40 m × 80 m exploding foil has a greater electro-explosion area, which is beneficial to destroy the parylene film, it needs more energy for electro-explosion. In Fig. 4 (d), ‘burst’ time is lagged behind current peak, about 124 ns, and the risetime is 465 ns, greater than 278 ns in Fig. 4 (c), which denotes the applied energy is not enough. In Fig. 4 (c), the current peak and voltage spike are almost synchronous, showing that the 80 m × 80 m auxiliary exploding foil is optimum at the firing energy [27].
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Fig. 5. Electrical signal collected by PVDF film and shock pressure vs. time curve.
Table 1 Comparison of the MEMS switch and single shot switch in Ref. [15].
MEMS switch Single shot switch
Peak current (A)
Risetime (ns)
Applied energy (F/V)
1434 1236
58 100
0.15/600 0.17/800
Table 2 Electrical characterizations of the MEMS switch at firing voltages ranging from 600 V to 1400 V. Five shots were repeated at each data point.
Fig. 6. The firing data of the device obtained at 0.15 F/600 V. UA , IA , UM , IM represent the voltage and current across the auxiliary and main exploding foils, respectively.
3.2. Shock pressure resulted from electroexplosion of auxiliary exploding foil The voltage signal (blue solid line) captured by the PVDF film was plotted in Fig. 5, correspondingly, shock pressure (red solid line) was calculated by Eqs. (1)–(6). In the first stage, electrical signal goes up sharply at the beginning of electro-explosion, followed by a voltage plateau, due to thermal expansion of the auxiliary exploding foil. At this time, the shock pressure increases linearly. In the second stage, the energy deposited into the auxiliary exploding foil causes a phase change from solid state to liquid state, however, there is no contribution to the development of temperature and expansion. As a result, the current and shock pressure increase more slowly. As more energy is coupled into the exploding foil, it begins to expand rapidly again in the last stage. Finally, shock pressure peaks in 204 ns, about 55.7 MPa, which is close to the yield strength of parylene, 59 MPa. After dielectric breakdown, the highcurrent pulse flows the dielectric film between the top and bottom electrodes. 3.3. Electrical characterizations of mini-flyer launcher Fig. 6 presents electrical behavior of the mini-flyer launcher while the C1 (0.39 F) and C2 (0.15 F) were charged to 500 V and 600 V, respectively. The voltages and currents across the auxiliary and main exploding foils, named UA , IA , UM and IM , were shown in the plot. Based on the experimental data, the firing process can be
Voltage (V)
Delay time t1 (ns)
Jitter time (ns)
Risetime t2 (ns)
Ipeak (A)
600 800 1000 1200 1400
221.4 216.8 220.4 214.7 224.1
27.1 24.1 22.8 21.3 23.8
59.5 60.8 61.3 60.0 62.2
1420 1767 2124 2796 3342
divided into two parts. After the IGBT closes, the voltage UA and current IA flow through the auxiliary exploding foil, resulting in the electro-explosion of the auxiliary exploding foil, accompanied with high-temperature and high-pressure plasma. The duration time can be defined as delay time t1 , about 221.4 ns. Then, the parylene film is broke down when the shock pressure exceeds the yield strength of the parylene, the voltage applied between the top and bottom electrodes UM drops suddenly, a large current pulse IM flows through the main exploding foil and reaches up to summit in 59.5 ns (defined as risetime t2 ). Compared with traditional vacuum switch, the delay time t1 is slightly larger, and the risetime t2 is almost equal [20]. However, the high-voltage switch presented in this document can be operated under lower voltage and easy to trigger. In contrast with previous switches [15,27], the switch has many advantages in respects of peak current, risetime, trigger energy and operation voltage, as shown in Table 1. Actually, if the switch is designed individually rather than integration with the mini-flyer launcher, its peak current will be higher, owing to the resistance of the main exploding foil. Moreover, a tiny spike, about 60 A, was observed in IM before switching when the parylene film is shocked, it is probably because the electrical conductivity is greater than original electrical conductivity under shock waves [28]. A series of firing voltages ranging from 600 V to 1400 V were applied on the C2 to study the firing behavior, five shots were repeated at each data point, and the results were listed in Table 2. Jitter time is defined as the difference between the maximum and minimum values of delay time. In Table 2, it’s exciting that the peak current increases with the firing voltage sharply. When the firing voltage is 800 V, the peak current climbs up to 1767 A in 60.8 ns, and
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the calculated current density is 1.2 × 108 A/cm2 , greater than critical current density (108 A/cm2 ). Besides, it can also be seen that the delay time t1 is independent on the firing voltage UM , about 216.8 ns, which coincides with the arrival time of peak pressure (204 ns) in Fig. 5. The risetime t2 is almost a constant, meaning that the plasma resistance is usually constant and negligible. 3.4. Flyer velocity time history of switch-launcher Fig. 7 shows a series of flyer velocity-time curves achieved with the firing energy ranging from 950 V to 1250 V. The results indicate that peak velocity goes up with the increase of the firing voltage, and the arrival time of peak velocity becomes shorter and shorter, both at the 0.15 F and at the 0.22 F. However, all the curves can be divided into three steps. 1) The flyer velocity changes slowly at the beginning of flight, because of a small volume expansion before vaporization, parylene flyer is not sheared out yet, just forming a bubble. 2) As the energy injection, a rapid expansion of metal vapor and plasma leads to a sharp rise in velocity. 3) Since air impedance is gaining ascendancy, acceleration rate begins to decrease slowly till a balance between thrust and drag. Additionally, we measured the velocity of parylene flyer without 3.6 m thick copper at 0.22 F/1100 V, and a terminal flyer velocity of 4480 km/s was observed, which is twice than the parylene-copper flyer. Although the deposition of copper film can improve the shock pressure, On the other hand, this will shorten the duration time when impacting target material. Of course, shock pressure and impact duration can also be adjusted by flyer material, flyer thickness, barrel length and firing parameters to meet experimental requirements.
Fig. 7. The flyer velocity curves achieved with a series of firing voltages ranging from 950 V to 1250 V.
3.5. High-speed photography of switch-launcher Fig. 8 shows the top-down images of the electro-explosion of auxiliary exploding foil and main exploding foil at 0.15F/1200 V, while the auxiliary exploding foil is triggered at 0.39F/500 V. The first was acquired before firing, and it can be defined as t = 0. The electro-explosion of the auxiliary exploding foil is first imaged as shown in frame 2, and plasma cloud becomes bigger and bigger. In
˜ 916) ˜ is 50 ns, except for the time between Frame 8 and Frame 9, about 200 ns. Fig. 8. High speed images of a switch-launcher at 0.15F/1200 V. The time between frames (18, The exposure time is 5 ns.
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frame 7, we can see a glimmer of light, so it can be inferred that the main exploding foil has been heated in frame 6. So, it is very likely that the parylene is being broken down and the high-voltage switch turns on in frame 5, which is in accordance with the delay time (214.7 ns) in Table 2. In frame 8, the light radiated by plasma cloud under parylene flyer can be seen, showing that the flyer has been cut off [13]. Because the copper sputtered above parylene is opaque, we can’t see the light if parylene flyer is not sheared out. As air enters the barrel, pressure and temperature of plasma cloud decrease rapidly, and the radiation light becomes dimmer and dimmer. Nevertheless, the flyer is always complete, even if it is ejected from the barrel, as can be seen in frame 16. 4. Conclusions In this study, a mini-launcher integrated with high-voltage switch is designed and prepared with MEMS technologies. Electrical characterizations are first performed on the auxiliary exploding foil to study the size effect and shock pressure. Some critical parameters, such as delay time, jitter time, peak current and risetime are then measured at a series firing voltages. Finally, flyer velocity diagnostics and high-speed photography are used to validate the capability of the mini-flyer launcher. All the results prove that the idea of this paper is feasible and favorable, which provides a simple and efficient method for shock loading experiments. References [1] C.A. Handley, B.D. Lambourn, N.J. Whitworth, H.R. James, W.J. Belfield, Understanding the shock and detonation response of high explosives at the continuum and meso scales, Appl. Phys. Rev. 5 (2018), 011303. [2] F. Jing, J. Chen, Dynamic high-pressure generation principle and related technologies, Natl. Defense Ind. Press (2006). [3] S. Ebenhöch, S. Nau, I. Häring, Validated model-based simulation tool for design optimization of exploding foil initiators, J. Def. Model Simul. 12 (2015) 189–207. [4] D.D. Dlott, Shock compression dynamics under a microscope, in: 19th APS Shock Compression of Condensed Matter Meeting, 2015. [5] W.P. Bassett, D.D. Dlott, Shock initiation of explosives: temperature spikes and growth spurts, Appl. Phys. Lett. 109 (2016), 054902. [6] P. Zhu, K. Chen, C. Xu, S. Zhao, R. Shen, Y. Ye, Development of a monolithic micro chip exploding foil initiator based on low temperature co-fired ceramic, Sens. Actuators A Phys. 276 (2018) 278–283. [7] Q. Chen, Y. Li, T. Ma, Characterization of the super-short shock pulse generated by an exploding foil initiator, Sens. Actuators A Phys. 286 (2019) 91–97. [8] T. Hu, Y. Zhao, Y. Zhao, W. Ren, Integration design of a MEMS based fuze, Sens. Actuators A Phys. 268 (2017) 193–200. [9] Q. Zeng, B. Li, M. Li, X. Wu, A miniature device for shock initiation of hexanitrostilbene by high-speed flyer, Propellants Explos. Pyrotechnol. 41 (2016) 864–869. [10] M.D. Knudson, R.W. Lemke, D.B. Hayes, C.A. Hall, C. Deeney, J.R. Asay, Near-absolute Hugoniot measurements in aluminum to 500 GPa using a magnetically accelerated flyer plate technique, J. Appl. Phys. 94 (2003) 4420–4431. [11] M. Goff, P.J. Hazell, G.J. Appleby-Thomas, D.C. Wood, C. Stennett, P. Taylor, Gas gun ramp loading of Kel-F 81 targets using a ceramic graded areal density flyer system, Int. J. Impact Eng. 80 (2015) 152–161. [12] M. Bowden, W. Neal, High fidelity studies of exploding foil initiator bridges, part 1: experimental method in: Biennial APS Conference on Shock Compression of Condensed Matter, 2015, 060020. [13] N.J. Sanchez, B.J. Jensen, W.E. Neal, A.J. Iverson, C.A. Carlson, Dynamic exploding foil initiator imaging at the advanced photon source in: 20Th Biennial APS Conference on Shock Compression of Condensed Matter, 2017, 160023. [14] Z. Zhou, G. Ding, Z. Yang, W. Lu, H. Shen, A micro-machined pulsed power switch based on kapton films, International Conference on Advanced Technology of Design & Manufacture (2012). [15] T.A. Baginski, K.A. Thomas, A robust one-shot switch for high-power pulse applications, IEEE Trans. Power Electron. 24 (2009) 253–259. [16] T.A. Baginski, R.N. Dean, E.J. Wild, Micro-machined planar triggered spark gap switch, IEEE Trans. Compon. Package Manuf. Technol. 1 (2011) 1480–1485.
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Biographies Cong Xu was born in April 1993. He studied at School of Chemical Engineering of Nanjing University of Science and Technology in 2011 and received his bachelor’s degree in 2015. He is currently working toward a ph. D. degree from Nanjing University of Science and Technology. He is dedicated to the research on shock loading, energetic material and MEMS. Peng Zhu was born in May 1978. He studied bioengineering at School of Chemical Engineering of Nanjing University of Science and Technology in 1998 and received his bachelor’s degree in 2003. He received the master’s degree from Nanjing University of Science and Technology in 2007 and PhD degree in 2014. He was a visiting scholar in Homyel State University (Belarus) from 2010 to 2011. He has served as an associate professor at the school of chemical engineering in Nanjing University of Science and Technology since 2003. His research activities are focused on micro-reactors, microfluidics and MEMS. Ke Wang was born in 1995. He received his B.S degree in School of Chemical Engineering from Nanjing University of Science and Technology of China in 2017. He is currently working toward Doctorate from Nanjing University of Science and Technology. His research includes MEMS ignition and detonation system. Xin Qin was born in 1994. He received his B.S. degree in School of Chemical Engineering from Nanjing University of Science and Technology in 2016. His current research interests include electronic safety and arming devices, and ignition and initiation technology. Qiu Zhang was born in 1993. She received her B.S. degree in School of Chemical Engineering and Environment from North University of China in 2016. She is working toward a ph. D. degree from Nanjing University of Science and Technology. Her current research interests include the ignition and initiation of exploding foil initiator. Zhi Yang was born in 1994. He received his B.S. degree in School of Chemical Engineering from Nanjing University of Science and Technology in 2016. He is currently working toward a Doctorate from Nanjing University of Science and Technology. His research activities are focused on high-speed impact and MEMS. Ruiqi Shen was born in 1963. He received the master’s and Ph.D. degrees from the Nanjing University of Science and Technology in 1986 and 1991, respectively. He was a Visiting Scholar with the Mendeleyev University of Chemical Technology, Russia, from 2001 to 2002. He has been serving as a Professor with the School of Chemical Engineering, Nanjing University of Science and Technology, since 2000. His research activities are focused on PyroMEMS, microfluidics, nano-energetic materials, laser physics, and chemistry.
Contents lists available at ScienceDirect
Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna
An electro-explosively actuated mini-flyer launcher Cong Xu, Peng Zhu ∗ , Ke Wang, Xin Qin, Qiu Zhang, Zhi Yang, Ruiqi Shen School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China
a r t i c l e
i n f o
Article history: Received 1 February 2019 Received in revised form 4 March 2019 Accepted 18 March 2019 Available online 6 April 2019 Keywords: Shock loading Electric gun High-voltage switch MEMS Photonic Doppler velocimetry
a b s t r a c t It’s crucial to develop shock loading techniques in laboratory to create pressure and temperature jumps for a wide variety of studies in material science. In this paper we have developed an electro-explosively actuated mini-flyer launcher capable of ejecting a plastic mini-flyer, typically 0.6 mm in diameter, up to several km/s. When prepared with microelectromechanical system (MEMS) scale methods, it can be mass-produced and takes only four steps, lowering manufacturing cost. Particularly, it was designed and integrated with a high-power high-voltage switch together, omitting expensive vacuum switches as well as interconnections between components. Four auxiliary exploding foils were first exploded at a certain trigger voltage to determine the optimal size, and polyvinylidene fluoride (PVDF) film was used to measure shock pressure of electro-explosion to estimate whether it’s enough to destroy the dielectric layer between top and bottom electrodes. Electrical characterizations were then carried out to obtain some important parameters, such as delay time, jitter time, risetime and peak current flowing through main exploding foil, at a series of firing voltages ranging from 600 V to 1400 V, and the results revealed that peak current increases with the rise of firing voltage dramatically, high-current pulse can be obtained at lower firing voltage, and delay time and risetime are almost constant. Finally, Photon Doppler Velocimetry (PDV) and high-speed camera were utilized to record the acceleration histories of flyers at different firing voltages, and the results showed that the flyer velocity can be controlled by the adjustment of firing energy. All the efforts demonstrated that the mini-flyer launcher is feasible and attractive. © 2019 Elsevier B.V. All rights reserved.
1. Introduction With the advent of dynamic loading technology in 1940s, higher pressure can be obtained to impact interesting materials to study the dynamic response mechanisms of target materials under extreme conditions [1,2]. There are mainly two modes in generating high-pressure pulse. One is contact mode, the observed objective is in direct contact with shock waves or detonation waves intimately. The other is non-contact mode, a thin disk, also called flyer, is accelerated up to several km/s in a very short time. By the high-speed impact on the target, a shock wave is generated propagating with supersonic speed through the target. Due to higher pressure generated in the target, the latter has always been concerned in past decades [3]. Several driving sources including laser [4,5], electro-explosion plasma [6–8], explosive [9], high-intensity magnetic field [10] and compressed air [11] are often used to launch a flyer, however, electro-explosively driven flyer looks more attractive. Its basic principle is to use the rapid electro-explosion of a bowknot-liked metal
∗ Corresponding author. E-mail address: [email protected] (P. Zhu). https://doi.org/10.1016/j.sna.2019.03.027 0924-4247/© 2019 Elsevier B.V. All rights reserved.
foil, also called exploding foil, to create a rapid-expanding plasma to accelerate a dielectric flyer [12,13]. It’s clear that the flyer velocity can be controlled easily by the adjustment of the energy delivered to the exploding foil to meet the required pressure. Compared with plane-wave explosive lens and two-stage light-gas gun, electro˜ km/s) and higher explosively driven flyer has higher velocity (20 pressure (T˜ Pa). Besides, the supply and capacitor discharge unit (CDU) can be used repeatedly, only needing replacing the foil-flyer components after each shot [2]. We should be aware of the importance of high-voltage switch when operating an electro-explosively driven flyer launcher [14]. A fast turn-on, low impedance high-voltage switch can transfer more energy from capacitor into the metal foil, avoiding slow electroexplosion and energy loss [15,16]. Many kinds of high-voltage switches, such as triggered spark gap [17–19], semiconductor switches [20,21] and mercury vapor switches [22], were used in pulse power applications, however, triggered spark gap has tremendous advantages in high-temperature operation, leakage current and radiation hardness [23]. Even so, its poor electrical conductivity under lower operation voltage, mainly uncertain delay time and unstable peak current, hampers further development in the field of low voltage.
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Fig. 1. Schematic representation of the fireset circuit used to characterize mini-flyer launcher.
It is well-known that plasma is an excellent medium for electrical conduction, especially in high electric field. Inspired by exploding foil, we intended to utilize the plasma generated by exploding foil as a conductive medium. In this paper, an auxiliary exploding foil was designed as an “attacker” destroying dielectric film, and as a potential plasma medium during switching. After dielectric breakdown, the capacitor begins to discharge, and a high-current pulse flows through the dielectric film between the auxiliary exploding foil and bottom electrode. On account of good compatibility in structure, the sandwich high-voltage switch was integrated with an electro-explosively actuated flyer launcher together. The left pad of main exploding foil in mini-flyer launcher acts as the bottom electrode of the high-voltage switch, the dielectric film plays a role of flyer in mini-flyer launcher, and even the barrel in mini-flyer launcher can be utilized as a tamper to reflect plasma generated by the auxiliary exploding foil to punch the dielectric film. Using microelectromechanical system (MEMS) technology, the mini-flyer launcher can be mass-produced, which reduces manufacturing cost and improves experimental efficiency. Frequently 100 shock experiments can be done per day. Electrical characterizations were first conducted to determine optimal auxiliary foil and shock pressure, some key parameters such as delay time, jitter time, peak current and risetime were then investigated at different firing voltages varying from 600 V to 1400 V. Finally, a home-built Photonic Doppler Velocimetry (PDV) and high-speed imaging camera were adopted to validate the capability of ejecting a high-speed flyer. These results showcase the feasibility of the mini-flyer launcher.
2. Experimental procedures 2.1. Structure and principle Fig. 1 is a schematic representation of the fireset used to characterize the mini-flyer launcher. One pad of the auxiliary exploding foil was connected through a field effect thyristor (FET) switch, IGBT presented here, to positive terminal of high-voltage capacitor C1 , and the other pad was connected to the negative terminal of C1 , which was also linked with cathode of high-voltage capacitor C2 . The anode of C2 was attached to right pad of the main exploding foil, namely high-voltage terminal. Before working, the two capacitors were charged up to operation voltages, respectively. Once the IGBT was triggered, C1 discharges, generating hundreds of amperes, and the auxiliary exploding foil will was exploded into a mixture of gas and plasma to damage the parylene layer. After that, C2 discharges rapidly, thousands of amperes pass through the parylene and the main exploding foil, inducing a large amount of heat to make the
main exploding foil undergo a series of phase changes from solid through liquid to gas, even plasma. Due to the constraint of barrel, a 600 m-in-diameter parylene-copper flyer is cut out at the edges of barrel. When arriving at the end of barrel, it has been accelerated up to several km/s. UA and UM in Fig. 1 are defined as the voltages across the main exploding foil and parylene film, the IA and IM are the currents flowing in the trigger circuit and main circuit, respectively. 2.2. Materials and methods Fig. 2 illustrates process flow diagrams of the mini-flyer launcher. The bottom metal layers, consisting of 100 nm thick tungsten-titanium alloy layer (the tungsten accounts for 90% in weight) and 3.6 m thick copper layer, were first deposited on 50.8 mm × 50.8 mm ceramic substrate by sputtering magnetron, and the main exploding foil (400 m × 400 m) was patterned by ultraviolet lithography, as shown in Fig. 2 (a). The tungsten was added to prevent the copper layer from being ablated during switching, and the titanium is an adhesive between ceramic substrate and the copper layer. In Fig. 2 (b), a 25 m of parylene type C with a nominal dielectric strength of 220 V/m was coated by chemical vapor deposition (CVD), which is an in-situ polymerization technology often used in electronics industry. Parylene dimmer was first vaporized at 180 ◦ and pyrolysed into monomers at 700 ◦ , then the monomers join together to form polymer film at 35 ◦ . In Fig. 2 (c), an auxiliary exploding foil and metal flyer centered on the center of the main exploding foil were prepared using same processes with the main exploding foil. The metal flyer was deposited not only to make more inflection laser be captured by optical fiber probe of PDV, but also to improve output pressure of parylene flyer. Fig. 2 (d) shows the preparation of SU-8 barrel with a thickness of 400 m and an inner diameter of 600 m, which involves a series of processes, such as spin coat, soft bake, expose, post exposure bake, and develop. It provides room for flyer acceleration mainly, and the rest plays a part of a tamper to reflect electro-explosion plasma of the auxiliary exploding foil. Finally, the mini-flyer launcher array mounted on the ceramic substrate was split into many individuals by mechanical cutting, as shown in Fig. 2 (e) and (f). 2.3. Experimental methods 2.3.1. Current and voltage measurements It is necessary to measure the current and voltage flowing through exploding foil, whether the auxiliary or the main [12]. From the two parameters, more details about phase changes can be dis-
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Fig. 2. Process flow diagrams of the mini-flyer launcher. (a) Preparation of main exploding foil. (b) Deposition of dielectric film. (c) Preparation of auxiliary exploding foil and metal flyer. (d) Development of SU-8 layer. (e) Photograph of the undiced mini-flyer launcher array. (f) Photograph of an individual mini-flyer launcher.
tinguished with the knee points of dynamic resistivity of exploding foil, and the energy coupled into exploding foil can also be calculated. Furthermore, only when the current density exceeds 108 A· cm−2 within hundreds of nanoseconds can metal foil be exploded completely [24]. Therefore, the currents were measured using CWT Mini-HF 60 model Rogowski coil with a bandwidth of 30 MHz, and the voltages were measured using high-voltage differential probe with a bandwidth of 400 MHz. All the data were recorded using a four-input LeCroy WR104Xi-A oscilloscope with a bandwidth of 1 GHz, at a sampling rate of 10 GS/s.
where U(t) is potential difference between both sides of PVDF film. Since Rb is much greater than Rm and R, Eq. (2) will be simplified as i (t) ≈
U (t) R
(3)
So the charge Q converging on the surface of the PVDF film can be calculated by
t Q (t) =
U () d R
(4)
0
2.3.2. Pressure measurement The electro-explosion pressure of the auxiliary exploding foil can be measured by polyvinylidene Fluoride (PVDF) film. Once the PVDF film is pressed, polarization will occur in the interior, and positive and negative charges will appear on its two opposite surfaces [25]. In this paper, the PVDF film was placed between two PMMA plates, so that it will not be ablated after the auxiliary exploding foil is exploded, as shown in Fig. 3. More importantly, the resulting spherical shock wave is adjusted to be a planar wave to press the whole PVDF film, instead of focusing on one point. Of course, the pressure behind the PMMA plate pb is lower than initial electroexplosion pressure p0 , however, the initial value p0 can be derived by the attenuation coefficient of PMMA ␣ as follows: pb = p0 e
−˛x
(1)
In Fig. 3, R, Rm and Rb represent parallel resistance, matched resistance and oscilloscope resistance (1˜ M), respectively. The current across the parallel resistance R is described as i (t) =
Rm + Rb + R U (t) RRb
(2)
Combined with the sensitivity coefficient of the PVDF film Kp (20 pC·N−1 ), the force F can be obtained by F (t) =
Q (t) 1 = Kp Kp
t
U () d R
(5)
0
Finally, the shock pressure is estimated by 1 F (t) pb (t) = = A Kp
t 0
U () d AR
(6)
where A is the area of the PVDF film. 2.3.3. Flyer velocity measurement Flyer velocity is an extremely vital parameter for flyer launcher [26], which determines the magnitude of output pressure. Therefore, a home-built Photonic Doppler Velocimeter (PDV) was utilized to capture flyer velocity time history. The fundamental principle of PDV is that laser frequency will be changed when a laser beam is reflected from high-speed flyer, which adheres to Doppler effect. When the reflection laser meets original laser, frequency difference will be observed and recorded using a Keysight DSOV334 A oscilloscope with a bandwidth of 33 GHz, at a sampling rate of 80 GS/s.
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Fig. 3. The test circuit used to measure shock pressure of electro-explosion of auxiliary exploding foil.
Fig. 4. The voltages and currents across four kinds of auxiliary exploding foils, including (a) 40 m × 40 m, (b) 40 m × 80 m, (c) 80 m × 80 m and (d) 120 m × 120 m, under 0.39 F/500 V.
Finally, the flyer velocity vs. time curve can be obtained by Fourier transform. 2.3.4. High-speed photography Specialised Imaging SIM X high speed camera was utilized to image the whole action process of the mini-flyer launcher, including electro-explosion of the auxiliary exploding foil and main exploding foil, as well as the moving flyer. The exposure time of each shot was 5 ns, with interframe times of 50 ns, except for the interframe time between frame 8 and frame 9 of 200 ns. Sixteen frames were acquired by the camera. 3. Results and discussions 3.1. Size effect of auxiliary exploding foil Four kinds of auxiliary exploding foils were designed, including 40 m × 40 m, 40 m × 80 m, 80 m × 80 m and 120 m × 120 m, to determine which one is more appropriate to shock the parylene film. Apparently, a greater foil will consume
more energy, bringing more burden to trigger circuit. However, a smaller foil can only form a weak electro-explosion, which is insufficient to penetrate the parylene film. The four auxiliary exploding foils mentioned above were characterized at 0.39 F/500 V, and the results were plotted in Fig. 4. In Fig. 4 (a) and (b), voltage spike is earlier than peak current in time, and the former is generally considered as ‘burst’ time, which means the exploding foil changes from liquid phase to gas phase at the time. When it comes to ‘burst’ time, the currents in Fig. 4 (a) and (b) are still climbing, which indicate that the applied energy is surplus. Besides, the current peak (260 A) in Fig. 4 (b) is lower than Fig. 4 (a) (326 A), since the resistance of the 40 m × 80 m exploding foil is twice than the 40 m × 40 m. Although the 40 m × 80 m exploding foil has a greater electro-explosion area, which is beneficial to destroy the parylene film, it needs more energy for electro-explosion. In Fig. 4 (d), ‘burst’ time is lagged behind current peak, about 124 ns, and the risetime is 465 ns, greater than 278 ns in Fig. 4 (c), which denotes the applied energy is not enough. In Fig. 4 (c), the current peak and voltage spike are almost synchronous, showing that the 80 m × 80 m auxiliary exploding foil is optimum at the firing energy [27].
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Fig. 5. Electrical signal collected by PVDF film and shock pressure vs. time curve.
Table 1 Comparison of the MEMS switch and single shot switch in Ref. [15].
MEMS switch Single shot switch
Peak current (A)
Risetime (ns)
Applied energy (F/V)
1434 1236
58 100
0.15/600 0.17/800
Table 2 Electrical characterizations of the MEMS switch at firing voltages ranging from 600 V to 1400 V. Five shots were repeated at each data point.
Fig. 6. The firing data of the device obtained at 0.15 F/600 V. UA , IA , UM , IM represent the voltage and current across the auxiliary and main exploding foils, respectively.
3.2. Shock pressure resulted from electroexplosion of auxiliary exploding foil The voltage signal (blue solid line) captured by the PVDF film was plotted in Fig. 5, correspondingly, shock pressure (red solid line) was calculated by Eqs. (1)–(6). In the first stage, electrical signal goes up sharply at the beginning of electro-explosion, followed by a voltage plateau, due to thermal expansion of the auxiliary exploding foil. At this time, the shock pressure increases linearly. In the second stage, the energy deposited into the auxiliary exploding foil causes a phase change from solid state to liquid state, however, there is no contribution to the development of temperature and expansion. As a result, the current and shock pressure increase more slowly. As more energy is coupled into the exploding foil, it begins to expand rapidly again in the last stage. Finally, shock pressure peaks in 204 ns, about 55.7 MPa, which is close to the yield strength of parylene, 59 MPa. After dielectric breakdown, the highcurrent pulse flows the dielectric film between the top and bottom electrodes. 3.3. Electrical characterizations of mini-flyer launcher Fig. 6 presents electrical behavior of the mini-flyer launcher while the C1 (0.39 F) and C2 (0.15 F) were charged to 500 V and 600 V, respectively. The voltages and currents across the auxiliary and main exploding foils, named UA , IA , UM and IM , were shown in the plot. Based on the experimental data, the firing process can be
Voltage (V)
Delay time t1 (ns)
Jitter time (ns)
Risetime t2 (ns)
Ipeak (A)
600 800 1000 1200 1400
221.4 216.8 220.4 214.7 224.1
27.1 24.1 22.8 21.3 23.8
59.5 60.8 61.3 60.0 62.2
1420 1767 2124 2796 3342
divided into two parts. After the IGBT closes, the voltage UA and current IA flow through the auxiliary exploding foil, resulting in the electro-explosion of the auxiliary exploding foil, accompanied with high-temperature and high-pressure plasma. The duration time can be defined as delay time t1 , about 221.4 ns. Then, the parylene film is broke down when the shock pressure exceeds the yield strength of the parylene, the voltage applied between the top and bottom electrodes UM drops suddenly, a large current pulse IM flows through the main exploding foil and reaches up to summit in 59.5 ns (defined as risetime t2 ). Compared with traditional vacuum switch, the delay time t1 is slightly larger, and the risetime t2 is almost equal [20]. However, the high-voltage switch presented in this document can be operated under lower voltage and easy to trigger. In contrast with previous switches [15,27], the switch has many advantages in respects of peak current, risetime, trigger energy and operation voltage, as shown in Table 1. Actually, if the switch is designed individually rather than integration with the mini-flyer launcher, its peak current will be higher, owing to the resistance of the main exploding foil. Moreover, a tiny spike, about 60 A, was observed in IM before switching when the parylene film is shocked, it is probably because the electrical conductivity is greater than original electrical conductivity under shock waves [28]. A series of firing voltages ranging from 600 V to 1400 V were applied on the C2 to study the firing behavior, five shots were repeated at each data point, and the results were listed in Table 2. Jitter time is defined as the difference between the maximum and minimum values of delay time. In Table 2, it’s exciting that the peak current increases with the firing voltage sharply. When the firing voltage is 800 V, the peak current climbs up to 1767 A in 60.8 ns, and
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the calculated current density is 1.2 × 108 A/cm2 , greater than critical current density (108 A/cm2 ). Besides, it can also be seen that the delay time t1 is independent on the firing voltage UM , about 216.8 ns, which coincides with the arrival time of peak pressure (204 ns) in Fig. 5. The risetime t2 is almost a constant, meaning that the plasma resistance is usually constant and negligible. 3.4. Flyer velocity time history of switch-launcher Fig. 7 shows a series of flyer velocity-time curves achieved with the firing energy ranging from 950 V to 1250 V. The results indicate that peak velocity goes up with the increase of the firing voltage, and the arrival time of peak velocity becomes shorter and shorter, both at the 0.15 F and at the 0.22 F. However, all the curves can be divided into three steps. 1) The flyer velocity changes slowly at the beginning of flight, because of a small volume expansion before vaporization, parylene flyer is not sheared out yet, just forming a bubble. 2) As the energy injection, a rapid expansion of metal vapor and plasma leads to a sharp rise in velocity. 3) Since air impedance is gaining ascendancy, acceleration rate begins to decrease slowly till a balance between thrust and drag. Additionally, we measured the velocity of parylene flyer without 3.6 m thick copper at 0.22 F/1100 V, and a terminal flyer velocity of 4480 km/s was observed, which is twice than the parylene-copper flyer. Although the deposition of copper film can improve the shock pressure, On the other hand, this will shorten the duration time when impacting target material. Of course, shock pressure and impact duration can also be adjusted by flyer material, flyer thickness, barrel length and firing parameters to meet experimental requirements.
Fig. 7. The flyer velocity curves achieved with a series of firing voltages ranging from 950 V to 1250 V.
3.5. High-speed photography of switch-launcher Fig. 8 shows the top-down images of the electro-explosion of auxiliary exploding foil and main exploding foil at 0.15F/1200 V, while the auxiliary exploding foil is triggered at 0.39F/500 V. The first was acquired before firing, and it can be defined as t = 0. The electro-explosion of the auxiliary exploding foil is first imaged as shown in frame 2, and plasma cloud becomes bigger and bigger. In
˜ 916) ˜ is 50 ns, except for the time between Frame 8 and Frame 9, about 200 ns. Fig. 8. High speed images of a switch-launcher at 0.15F/1200 V. The time between frames (18, The exposure time is 5 ns.
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frame 7, we can see a glimmer of light, so it can be inferred that the main exploding foil has been heated in frame 6. So, it is very likely that the parylene is being broken down and the high-voltage switch turns on in frame 5, which is in accordance with the delay time (214.7 ns) in Table 2. In frame 8, the light radiated by plasma cloud under parylene flyer can be seen, showing that the flyer has been cut off [13]. Because the copper sputtered above parylene is opaque, we can’t see the light if parylene flyer is not sheared out. As air enters the barrel, pressure and temperature of plasma cloud decrease rapidly, and the radiation light becomes dimmer and dimmer. Nevertheless, the flyer is always complete, even if it is ejected from the barrel, as can be seen in frame 16. 4. Conclusions In this study, a mini-launcher integrated with high-voltage switch is designed and prepared with MEMS technologies. Electrical characterizations are first performed on the auxiliary exploding foil to study the size effect and shock pressure. Some critical parameters, such as delay time, jitter time, peak current and risetime are then measured at a series firing voltages. Finally, flyer velocity diagnostics and high-speed photography are used to validate the capability of the mini-flyer launcher. All the results prove that the idea of this paper is feasible and favorable, which provides a simple and efficient method for shock loading experiments. References [1] C.A. Handley, B.D. Lambourn, N.J. Whitworth, H.R. James, W.J. Belfield, Understanding the shock and detonation response of high explosives at the continuum and meso scales, Appl. Phys. Rev. 5 (2018), 011303. [2] F. Jing, J. Chen, Dynamic high-pressure generation principle and related technologies, Natl. Defense Ind. Press (2006). [3] S. Ebenhöch, S. Nau, I. Häring, Validated model-based simulation tool for design optimization of exploding foil initiators, J. Def. Model Simul. 12 (2015) 189–207. [4] D.D. Dlott, Shock compression dynamics under a microscope, in: 19th APS Shock Compression of Condensed Matter Meeting, 2015. [5] W.P. Bassett, D.D. Dlott, Shock initiation of explosives: temperature spikes and growth spurts, Appl. Phys. Lett. 109 (2016), 054902. [6] P. Zhu, K. Chen, C. Xu, S. Zhao, R. Shen, Y. Ye, Development of a monolithic micro chip exploding foil initiator based on low temperature co-fired ceramic, Sens. Actuators A Phys. 276 (2018) 278–283. [7] Q. Chen, Y. Li, T. Ma, Characterization of the super-short shock pulse generated by an exploding foil initiator, Sens. Actuators A Phys. 286 (2019) 91–97. [8] T. Hu, Y. Zhao, Y. Zhao, W. Ren, Integration design of a MEMS based fuze, Sens. Actuators A Phys. 268 (2017) 193–200. [9] Q. Zeng, B. Li, M. Li, X. Wu, A miniature device for shock initiation of hexanitrostilbene by high-speed flyer, Propellants Explos. Pyrotechnol. 41 (2016) 864–869. [10] M.D. Knudson, R.W. Lemke, D.B. Hayes, C.A. Hall, C. Deeney, J.R. Asay, Near-absolute Hugoniot measurements in aluminum to 500 GPa using a magnetically accelerated flyer plate technique, J. Appl. Phys. 94 (2003) 4420–4431. [11] M. Goff, P.J. Hazell, G.J. Appleby-Thomas, D.C. Wood, C. Stennett, P. Taylor, Gas gun ramp loading of Kel-F 81 targets using a ceramic graded areal density flyer system, Int. J. Impact Eng. 80 (2015) 152–161. [12] M. Bowden, W. Neal, High fidelity studies of exploding foil initiator bridges, part 1: experimental method in: Biennial APS Conference on Shock Compression of Condensed Matter, 2015, 060020. [13] N.J. Sanchez, B.J. Jensen, W.E. Neal, A.J. Iverson, C.A. Carlson, Dynamic exploding foil initiator imaging at the advanced photon source in: 20Th Biennial APS Conference on Shock Compression of Condensed Matter, 2017, 160023. [14] Z. Zhou, G. Ding, Z. Yang, W. Lu, H. Shen, A micro-machined pulsed power switch based on kapton films, International Conference on Advanced Technology of Design & Manufacture (2012). [15] T.A. Baginski, K.A. Thomas, A robust one-shot switch for high-power pulse applications, IEEE Trans. Power Electron. 24 (2009) 253–259. [16] T.A. Baginski, R.N. Dean, E.J. Wild, Micro-machined planar triggered spark gap switch, IEEE Trans. Compon. Package Manuf. Technol. 1 (2011) 1480–1485.
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Biographies Cong Xu was born in April 1993. He studied at School of Chemical Engineering of Nanjing University of Science and Technology in 2011 and received his bachelor’s degree in 2015. He is currently working toward a ph. D. degree from Nanjing University of Science and Technology. He is dedicated to the research on shock loading, energetic material and MEMS. Peng Zhu was born in May 1978. He studied bioengineering at School of Chemical Engineering of Nanjing University of Science and Technology in 1998 and received his bachelor’s degree in 2003. He received the master’s degree from Nanjing University of Science and Technology in 2007 and PhD degree in 2014. He was a visiting scholar in Homyel State University (Belarus) from 2010 to 2011. He has served as an associate professor at the school of chemical engineering in Nanjing University of Science and Technology since 2003. His research activities are focused on micro-reactors, microfluidics and MEMS. Ke Wang was born in 1995. He received his B.S degree in School of Chemical Engineering from Nanjing University of Science and Technology of China in 2017. He is currently working toward Doctorate from Nanjing University of Science and Technology. His research includes MEMS ignition and detonation system. Xin Qin was born in 1994. He received his B.S. degree in School of Chemical Engineering from Nanjing University of Science and Technology in 2016. His current research interests include electronic safety and arming devices, and ignition and initiation technology. Qiu Zhang was born in 1993. She received her B.S. degree in School of Chemical Engineering and Environment from North University of China in 2016. She is working toward a ph. D. degree from Nanjing University of Science and Technology. Her current research interests include the ignition and initiation of exploding foil initiator. Zhi Yang was born in 1994. He received his B.S. degree in School of Chemical Engineering from Nanjing University of Science and Technology in 2016. He is currently working toward a Doctorate from Nanjing University of Science and Technology. His research activities are focused on high-speed impact and MEMS. Ruiqi Shen was born in 1963. He received the master’s and Ph.D. degrees from the Nanjing University of Science and Technology in 1986 and 1991, respectively. He was a Visiting Scholar with the Mendeleyev University of Chemical Technology, Russia, from 2001 to 2002. He has been serving as a Professor with the School of Chemical Engineering, Nanjing University of Science and Technology, since 2000. His research activities are focused on PyroMEMS, microfluidics, nano-energetic materials, laser physics, and chemistry.