Tantalum electrolytic capacitors have performance advantages of long life, high temperature stability, and high energy storage capacity and are essential micro-energy storage devices in many pieces of military mechatronic equipment, including penetration weapons. The latter are high-value ammunition used to strike strategic targets, and precision in their blast point is ensured through the use of penetration fuzes as control systems. However, the extreme dynamic impact that occurs during penetration causes a surge in the leakage current of tantalum capacitors, resulting in a loss of ignition energy, which can lead to ammunition half-burst or even sometimes misfire. To address the urgent need for a reliable design of tantalum capacitor for penetration fuzes, in this study, the maximum acceptable leakage current of a tantalum capacitor during impact is calculated, and two different types of tantalum capacitors are tested using a machete hammer. It is found that the leakage current of tantalum capacitors increases sharply under extreme impact, causing functional failure. Considering the piezoresistive effect of the tantalum capacitor dielectric and the changes in the contact area between the dielectric and the negative electrode under pressure, a force–electric simulation model at the microscale is established in COMSOL software. The simulation results align favorably with the experimental results, and it is anticipated that the leakage current of a tantalum capacitor will experience exponential growth with increasing pressure, ultimately culminating in complete failure according to this model. Finally, the morphological changes in tantalum capacitor sintered cells both without pressure and under pressure are characterized by electron microscopy. Broken particles of Ta–Ta2O5 sintered molecular clusters are observed under pressure, together with cracks in the MnO2 negative base, proving that large stresses and strains are generated at the micrometer scale.

HIGHLIGHTS

  • The failure phenomenon of a notable surge in leakage current in two commonly used tantalum capacitors under dynamic impact is investigated.

  • A mechanical–electrical model for tantalum capacitor electrodes is established at the microscale, and we the complete failure of tantalum capacitors under higher impacts is anticipated.

  • Morphological changes in tantalum capacitor sintered cells both without pressure and under pressure are characterized by electron microscopy, and it is proved that large stresses and strains are generated at the micrometer scale.

Penetration weapons are high-value ammunition used to attack strategic hard targets, such as weapon depots, missile launch sites, airport runways, and command centers. The penetration fuze is the “brain” of a penetration weapon system, precisely controlling the burst point. Tantalum electrolytic capacitors have performance advantages of long life, high temperature stability, and high energy storage capacity, and are widely used as energy storage devices in a variety of military mechatronic equipment, including penetration weapons.1–3 Much attention has been devoted to both the energy storage characteristics and energy loss of capacitors used in these and other microsystems.4–8 Especially in projectiles and missiles, tantalum electrolytic capacitors provide a very important secondary power supply for sensors, signal processing circuits, and detonation actuators of fuzes. In recent years, there has been growing interest in the application of supercapacitors in penetrating weapons, as they offer the dual capabilities of energy storage and sensing.9–11 Moreover, with the trend toward microminiaturization in fuze development, there is a growing focus on both the energy storage and failure characteristics of tantalum capacitors.12,13 The microminiaturization of fuze volume has resulted in less space being allocated for secondary energy storage components such as tantalum capacitors during the design process. Consequently, a clearer understanding of the energy loss mechanism of tantalum capacitors during the operation of initiators is necessary to provide a theoretical basis for the development of methods for their protection. Penetration projectiles and missiles are subjected to extreme dynamic impacts of up to ten thousand times the gravitational acceleration during their launch and target penetration, which posing a serious challenge to the reliability of tantalum electrolytic capacitors.14,15 Numerous studies have been dedicated to the dynamic modeling, sensor signal processing, and mechanical protection of fuzes during the penetration process.16–18 Owing to the lack of an in-depth understanding of the properties and mechanisms of impact failure of tantalum electrolytic capacitors, conventional fuze designs have had to adopt oversized buffer materials for redundant protection, which is very inefficient.19 

Unfortunately, previous research on tantalum electrolytic capacitors has focused more on phenomenological and qualitative issues than on mechanistic and quantitative investigations. On the basis of experimental testing, Li et al.20 classified the impact failure behavior of tantalum capacitors into functional failure and parameter shift failure and discussed the possible mechanisms of each type. Among these, an increase in leakage current is the main and most dangerous failure behavior of tantalum electrolytic capacitors. Li et al.21 conducted a simulation of the microscopic deformation of electrode and dielectric particles during the impact of tantalum capacitors, and their results suggested that the increase in leakage current of tantalum capacitors may be caused by transient deformation of tantalum pentoxide dielectric particles and manganese dioxide anode particles. Jia et al.22 conducted a simulation of the formation process of leakage current in tantalum capacitors. However, none of these modeling and simulation studies has been able to predict the failure behavior of tantalum electrolytic capacitors and thereby provide guidance for the design of suitable protective methods, mainly due to the fact that these studies only considered either mechanical or electrical fields alone, rather than implementing any coupling of these fields. This shortcoming at the modeling level is also intuitively clear from the differences in order of magnitude between simulation and experimental results on leakage current.23 

To address the urgent need for reliability estimates and subsequent design recommendations for tantalum electrolytic capacitors for equipment applications, this paper conducts tests on the failure behavior of tantalum electrolytic capacitors in terms of the transient increase of leakage current under different impact loads via standardized impact test equipment (Machete hammer) and analyzes the influence of this behavior on the performance of these capacitors in fuzes and other mechatronic applications. In addition, a mechanical–electrical coupled dynamic response model of tantalum electrolytic capacitors is developed that incorporates two mechanisms of leakage current formation under compressive loading, namely, the increase in contact area between microscopic particles and the increase in equivalent conductivity. The results of simulations of leakage current based on this model are found to be consistent with the experimental tests, which enables prediction of the failure behavior of tantalum electrolytic capacitors under dynamic impact. Finally, the microscopic morphological changes of tantalum electrolytic capacitors under different compressive loads are characterized by electron microscopy, and the results provide an explanation at the microscale level for the success of the proposed mechanical–electrical coupled dynamic response model.

Tantalum capacitors are typical electrolytic capacitors, with the structure is shown in Fig. 1(a). Figure 1(b) shows a cross-section of a tantalum capacitor sintered cell. The anode and cathode are connected to the external end electrode by graphite and silver coatings. The graphite serves as a buffer layer to prevent oxidation of the manganese dioxide (MnO2) cathode, and the silver coating is in contact with the cathode and collects the moving electrons during capacitive charging and discharging. The anode of the tantalum capacitor is pure tantalum metal, which is sintered at high temperature, and the outer layer of the anode is electrochemically processed to form a tantalum pentoxide (Ta2O5) dielectric film with unidirectional conductivity, as shown in Fig. 1(c). The cathode of the tantalum capacitor is an MnO2 dielectric that is prepared by high-temperature decomposition of manganese nitrate solution. Owing to the fact that MnO2 cannot completely fill the voids between the tantalum particles, there are a large number of microscopic pores inside the tantalum capacitor.

FIG. 1.

(a) Structure of tantalum capacitor. (b) Cross-section of sintered cell. (c) Microstructure of sintered cell.

FIG. 1.

(a) Structure of tantalum capacitor. (b) Cross-section of sintered cell. (c) Microstructure of sintered cell.

Close modal

In a fuze mechatronic system, tantalum capacitors are used as energy storage capacitors to provide power for the fuze circuits to perform functional operations such as unsecuring and firing. The most dangerous threat to the reliability of these essential operations is the potential leakage current of the capacitors under extreme dynamic mechanical impact. To address this issue, the leakage currents of the two commonly used tantalum capacitors whose parameters are listed in Table I were dynamically tested under different impact loads using the experimental system shown in Fig. 2.

TABLE I.

Parameters of tantalum capacitors.

No.ModelCapacitance (μF)Withstanding voltage (V)Leakage current μA)
TAJ-7343E-107-M-025 100 25 ≤25 
TAC-3528T-107-M-025 100 25 ≤25 
No.ModelCapacitance (μF)Withstanding voltage (V)Leakage current μA)
TAJ-7343E-107-M-025 100 25 ≤25 
TAC-3528T-107-M-025 100 25 ≤25 
FIG. 2.

(a) Impact test system for tantalum capacitors. (b) Fixture for Machete hammer impact test.

FIG. 2.

(a) Impact test system for tantalum capacitors. (b) Fixture for Machete hammer impact test.

Close modal

The Machete hammer is a standardized experimental device used to emulate the mechanical impact conditions of projectiles during launching and penetration, providing dynamic impact loads with pulse widths of more than 100 μs and peak accelerations of up to 30 000 times that due to gravity. The tantalum capacitor, together with a standard accelerometer (East China Institute of Optoelectronic Integrated Devices, Type 214-BM1009), was threaded onto the hammer head of the Machete hammer, ensuring that the impact loads to which it was subjected could be accurately and dynamically measured. The sensitivity of the accelerometers was 3.1 μV/g, with a maximum linear range of 70 000g. Simultaneously, the capacitor was connected to an electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd., CHI600E series) for dynamic measurement of leakage currents during impact. To enhance the credibility of the test data, ten identical devices of each type of capacitor in Table I were tested repeatedly.

The output of the piezoelectric accelerometer is a voltage. The conversion formula from this electrical quantity to a non-electrical quantity is as follows:
acc=Voutk,
(1)
where acc is the acceleration, usually expressed in units of the acceleration due to gravity (g), Vout is the voltage output of the accelerometer, and k is the sensitivity of the sensor.

The dynamic fluctuation behavior of the leakage current of a tantalum capacitor under impact loads with peak accelerations 4600g, 6300g, 8000g, 11 000g, and 15 000g were tested by switching the gears of the Machete hammer. As shown in Fig. 3, the leakage current of the capacitor shows a dramatic increase during the impact pulse that is almost synchronized in time with the impact acceleration. Further, as shown in Fig. 4(a), the peak leakage currents at these four impact loads are 1.22 mA, 1.64 mA, 2.08 mA, 2.26 mA, and 2.52 mA, all of which are far beyond the 25 μA normal leakage current in the absence of an impact load. Also, from its error bars, it can be seen that the leakage current behavior of a given type of tantalum capacitor under different impact loads has very good consistency.

FIG. 3.

Transient fluctuations of leakage current under different impact loads.

FIG. 3.

Transient fluctuations of leakage current under different impact loads.

Close modal
FIG. 4.

(a) Peak leakage currents under different impact loads. (b) Typical unsecuring and firing circuits for penetrating fuze equipment. (c) Functional failures of fuze mechatronic systems.

FIG. 4.

(a) Peak leakage currents under different impact loads. (b) Typical unsecuring and firing circuits for penetrating fuze equipment. (c) Functional failures of fuze mechatronic systems.

Close modal
To reveal the functional influence of the above leakage current increases on the fuze mechatronic system, an analysis was carried out based on the fuze detonation control circuit shown in Fig. 4(b). The tantalum capacitor was fully charged by the external lithium battery before the fuze started to work. From conservation of energy, the fuze could only detonate the ammunition normally under the condition that the total energy stored in the capacitor remained greater than the energy threshold for detonation after exclusion of the energy consumption of the discharge resistor and the energy loss of the leakage current, calculated as follows:
CUs221RL0tLU2(t)dtId2RDtdIA2RDtA,
(2)
where C is the capacitance of the tantalum capacitor, Us is its initial voltage of the capacitor, U(t) is its instantaneous voltage, RL is its discharge resistance, tL is the total working time of the fuze until the final detonation, Id is the leakage current of the tantalum capacitor, RD is the resistance of the detonator, td is the impulse time of the leakage current, IA is the minimum current required for the unsecuring and firing operation of the fuze, and tA is the time for the unsecuring and firing operation.
When there is no mechanical loading, the tantalum pentoxide electrolyte is nearly electrically insulated, which is why tantalum electrolytic capacitors have an ultra-low leakage current of less than 25 μA under normal conditions. However, under extreme mechanical loads, tantalum pentoxide electrolytes exhibit piezoresistance, i.e., the electrical conductivity of the material changes when subjected to external forces, and are no longer ideal insulators. Piezoresistive effects frequently provide the underlying mechanism for pressure sensors.24–26 In this case, electrons can pass through the tantalum pentoxide dielectric layer and continue to transfer between the particles to eventually form a leakage current from the cathode to the anode inside the capacitor. This property is described by the piezoresistive coefficient
π=ΔRRP,
(3)
where R is the initial resistance, P is the external stress, and ΔR is the change in resistance.
With this mechanism of leakage current formation driven by piezoresistive effects, the contact area between microscopic particles in the tantalum capacitor electrodes also has an important influence on the magnitude of the total leakage current, since a leakage current can only be formed on the contact interfaces of neighboring particles. Considering the porous morphology of the tantalum capacitor electrodes, the contact area is also directly influenced by their mechanical loading. As shown in Fig. 5, the contact area of the Ta2O5 and MnO2 increases with increasing pressure under an impact load, which can initially be regarded as point contact. According to Hertz contact theory, the contact radius r is calculated as follows:
r=34R01μ12E1+1μ22E2P3.
(4)
The contact area S can be calculated as
S=π34R01μ12E1+1μ22E2P3/2,
(5)
where R0 is the initial radius of the Ta2O5, μ1 and E1 are the Poisson’s ratio and elastic modulus, respectively, of Ta2O5, and μ2 and E2 are those of MnO2.
FIG. 5.

Schematic of Hertz contact theory.

FIG. 5.

Schematic of Hertz contact theory.

Close modal
To provide a reliable parametric basis for the simulation of the leakage current of a tantalum capacitor under impact load, the piezoresistive properties of tantalum pentoxide dielectrics were first measured accurately by hydrostatic pressure loading experiments. The corresponding relationship between impact acceleration and pressure is as follows:
a=lwmcP,
(6)
where mc is the mass of the capacitor, a is the impact load, P is the applied pressure, and l and w are the length and width, respectively, of the capacitor.

The piezoresistive property calibration system consisted of a pressure tester (Dongguan Zhizhi Precision Instrument Co., Ltd., ZQ-990L) applying a modulatable and precise static pressure to the tantalum pentoxide sample, and an electrochemical workstation (CHI600E) applying a constant voltage of 10 V to the sample and measuring the value of the current through the sample in real time.

The results of the experimental calibration are shown in Fig. 6(a), from which it can be seen that the resistance of the tantalum pentoxide dielectric continues to decrease with increasing pressure. It is noteworthy that its piezoresistance curve has two distinct threshold pressure points, one (P1) at 5.9 kPa and the other (P2) at 44.8 kPa. When the pressure exceeds P1, the resistance of the tantalum pentoxide dielectric starts to decrease sharply, and when the pressure reaches P2, the resistance starts to decrease slowly and tends toward stability. The double-exponential fitting method is a commonly used nonlinear fitting approach, typically employed for fitting data exhibiting exponential growth or decay trends. After transforming the resistance values to conductivity, there is a distinctly nonlinear monotonic relationship between conductivity and pressure, and the double-exponential fitting method is therefore appropriate here, as shown in Fig. 6(b). The equation for double-exponential fitting is as follows:
Sc=A1exp(M1p)+A2exp(M2p),
(7)
where the conductivity Sc is in units of μS/m and the pressure in units of kPa. The results of the fitted parameters are shown in Table II. The goodness-of-fit R2 value of the piezoresistive calibration is up to 0.997 58, which indicates that this fitting function can be reliably used to simulate the leakage current of tantalum capacitors under impact load.
FIG. 6.

(a) Resistance of tantalum pentoxide samples under different pressures. (b) Conductivity of tantalum pentoxide samples under different pressures and the fitting function.

FIG. 6.

(a) Resistance of tantalum pentoxide samples under different pressures. (b) Conductivity of tantalum pentoxide samples under different pressures and the fitting function.

Close modal
TABLE II.

Parameters of the fitted equation for piezoresistive properties.

A1A2M1M2
0.7984 −0.8681 5.385 × 10−4 −54.56 × 10−4 
A1A2M1M2
0.7984 −0.8681 5.385 × 10−4 −54.56 × 10−4 

To simulate the tantalum capacitor more accurately, its microstructure was first characterized to provide a reliable reference for the finite element geometric model. The electrode structure inside the capacitor was surface-scanned by energy spectroscopy, as shown in Fig. 7(a). In particular, the yellow smoother parts are the sintered spherical particles composed of tantalum positive electrode and tantalum pentoxide dielectric, and the blue part with rough and uneven surface is the irregular bulk substrate of the MnO2 negative electrode.

FIG. 7.

Finite element geometric modeling of tantalum capacitor. (a) SEM image. (b) Elevation view of geometric model.

FIG. 7.

Finite element geometric modeling of tantalum capacitor. (a) SEM image. (b) Elevation view of geometric model.

Close modal

Therefore, a geometrical combination of a rectangle and a sphere as shown in Fig. 7(b) was established in COMSOL software as the basic unit for tantalum capacitor simulation. A shell of specific thickness, representing the tantalum pentoxide dielectric, was set on the surface of the spherical structure of the tantalum positive electrode. The mechanical–electrical coupled physical field setup was performed in COMSOL based on Eqs. (4)(7). The specific parameters of the finite element modeling are shown in Table III.

TABLE III.

Parameters of finite element model.

MaterialSize (μm)Elastic modulus E (GPa)Density ρ (kg/m3)Conductivity G (S/m)Relative permittivity ɛr
Ta 3 (radius) 185 17.2 × 103 8 × 106 
Ta2O5 5 (radius) 140 7.9 × 103 S(p10 
MnO2 7 × 7 × 2 25 5.1 × 103 1 × 10−8 
MaterialSize (μm)Elastic modulus E (GPa)Density ρ (kg/m3)Conductivity G (S/m)Relative permittivity ɛr
Ta 3 (radius) 185 17.2 × 103 8 × 106 
Ta2O5 5 (radius) 140 7.9 × 103 S(p10 
MnO2 7 × 7 × 2 25 5.1 × 103 1 × 10−8 

In the mechanical field simulation, 0–3 MPa pressure was applied to the capacitive unit, and as the applied pressure was increased, the portion of Ta2O5 in contact with MnO2 experienced significant deformation, and the contact area between the two is shown in Fig. 8(a). Since the Young’s modulus of tantalum metal is much larger than those of tantalum pentoxide and manganese dioxide, the deformation at the tantalum metal/tantalum pentoxide interface is only negligible on the sub-nanometer scale, which is not discussed in this paper. Figures 8(b) and 8(c) show the stress distribution and deformation when 2.5 MPa was applied to the cell. It can be seen that when the cell is under pressure, the stress distribution is mainly concentrated in the region of contact between Ta2O5 and MnO2, and the deformation and contact area of Ta2O5 and MnO2 reach 120 MPa and 0.12 μm, respectively, which will have an impact on the scale of the current.

FIG. 8.

(a) Contact area of the contact interface between tantalum pentoxide and manganese dioxide. (b) Capacitance cell stress distribution at 2.5 MPa. (c) Deformation of capacitance cell at 2.5 MPa.

FIG. 8.

(a) Contact area of the contact interface between tantalum pentoxide and manganese dioxide. (b) Capacitance cell stress distribution at 2.5 MPa. (c) Deformation of capacitance cell at 2.5 MPa.

Close modal

In addition to the contact area, piezoresistive effects also contribute greatly to the size of the current. Therefore, the influence of Ta2O5 conductivity and contact area was also considered in the electric field simulation. The space charge density distribution of the sintered cell at 0.5 MPa pressure and 2.5 MPa pressure is shown in Fig. 9. It can be clearly seen that the space charge density increases when the pressure inside the electrode is larger, with a maximum of 1.2 × 103 C/m3 at 0.5 MPa and a maximum of 3.1 × 103 C/m3 at 2.5 MPa.

FIG. 9.

Space charge density distributions of basic unit at (a) 0.5 MPa and (b) 2.5 MPa.

FIG. 9.

Space charge density distributions of basic unit at (a) 0.5 MPa and (b) 2.5 MPa.

Close modal

The current density modulus is the average of the internal current density of the electrode, and the surface current is the surface integral of the current density passing through the Ta2O5 and MnO2 contact surface, and these quantities provide a characterization of the total leakage current of a tantalum capacitor, including the joint contribution of the piezoresistive effect and the increase in contact area.

As the pressure increases from 0.1 MPa to 3 MPa, the current density modulus increases from 0.87 A/m2 to 24.6 A/m2, and the leakage current increases from 0.33 mA to 9.4 mA, as shown in Fig. 10(a). To investigate the influence of the piezoresistive effect and the contact area on the current density modulus, the conductivity of Ta2O5 was set to the initial value without impact, while the contact area changed with pressure. Thus, the contribution of the contact area, as well as the piezoresistive effect on the current density modulus, could be obtained. When the pressure is less than 0.25 MPa, the contribution of the contact area to the current density modulus is dominant (>50%), which is because the change in contact area will occur at low pressure. When the pressure is greater than 0.25 MPa, with increasing conductivity, the contribution of the conductivity to the current density modulus gradually increases and becomes dominant, reaching 91.94% at 3 MPa, because the conductivity changes significantly after the pressure exceeds the threshold of 0.25 MPa, as shown in Fig. 10(b).

FIG. 10.

(a) Current density modulus and leakage current. (b) Contribution of contact area and conductivity to current density modulus. (c) Leakage current simulation results and experimental values for tantalum capacitor.

FIG. 10.

(a) Current density modulus and leakage current. (b) Contribution of contact area and conductivity to current density modulus. (c) Leakage current simulation results and experimental values for tantalum capacitor.

Close modal

The 0–3 MPa pressures to which the tantalum capacitor was subjected correspond to an impact acceleration range of 0–31 200g according to Eq. (6). When the impact acceleration is less than 16 000g, the leakage current value from the impact simulation is basically in agreement with to the experimental value, indicating the validity of the simulation. This simulation considered the piezoresistive effect of Ta2O5 and calibrated its conductivity, as well as simulating the contact area between Ta2O5 and MnO2 during the impact, both of which have been neglected in previous studies, making the present simulation results more accurate, as shown in Fig. 10(c). Within the experimental testing range of 4000g–15 000g, the simulated values closely align with the actual values in magnitude. The computed R2 value for this model is 0.6680, indicating a relatively strong fit to experimental values and suggesting its applicability in predicting leakage current values under higher impact accelerations.

Further, leakage current values greater than 16 000g–30 000g are predicted by this model. Clearly, when the impact load increases from 16 000g to 30 000g, the value of the leakage current increases exponentially with the impact load from 3.48 mA to 9.37 mA, which exceeds the safety threshold of a tantalum capacitor by a factor of six.

Most previous studies have concentrated on microscopic analyses of tantalum capacitor failures under standard conditions, neglecting to address their behavior under extreme impact.27,28 To better understand the mechanism of leakage current drift of tantalum capacitors, the internal electrode of a tantalum capacitor was imaged by a scanning electron microscope (SEM). An adaptive fixture for applying pressure was designed to observe the microscopic state of the sintered cell both in the absence of pressure and under pressure. Figure 11 shows the results of this microscopic characterization of a sintered electrode under pressure. The changes in the same region of the sintered cell inside the tantalum capacitor before and after pressure are shown in Figs. 11(a) and 11(b). It can be seen that the Ta positive electrode and Ta2O5 dielectric sintered particles in this region are closely bonded before pressure is applied, and the MnO2 negative electrode substrate remains relatively intact without any obvious debris. After being subjected to pressure, the MnO2 negative electrode substrate has a large crack, with obvious debris, and the distribution of sintered particles between the Ta positive electrode and the Ta2O5 dielectric has become more scattered. As can be seen from Figs. 11(c) and 11(d), after the sintered cell has been subjected to pressure, there are obvious cracks and debris in the MnO2 negative electrode base. Figures 11(e) and 11(f) show that the Ta positive electrode inside the tantalum capacitor and the sintered particles of Ta2O5 dielectric have obvious crushing cracks. Within the scale of 10–20 μm, an obvious misalignment between Ta and Ta2O5 sintered material and MnO2 can be observed after application of pressure, which proves that large stresses and strains have been generated in the electrode at a molecular level, which is consistent with the conclusions of the simulation.

FIG. 11.

Microscopic characterization of tantalum capacitor sintered cell in a pressure experiment. (a) Morphology of a given region before application of pressure. (b) Morphology of the same region after application of pressure; (c) Fragmentation of the MnO2 negative base. (d) Magnified view of the region in (c) outlined by the dashed box. (e) Disintegration of Ta positive and Ta2O5 dielectric sintered particles. (f) Magnified view of the region in (e) outlined by the dashed box.

FIG. 11.

Microscopic characterization of tantalum capacitor sintered cell in a pressure experiment. (a) Morphology of a given region before application of pressure. (b) Morphology of the same region after application of pressure; (c) Fragmentation of the MnO2 negative base. (d) Magnified view of the region in (c) outlined by the dashed box. (e) Disintegration of Ta positive and Ta2O5 dielectric sintered particles. (f) Magnified view of the region in (e) outlined by the dashed box.

Close modal

To provide a basis for reliability design of tantalum capacitors, commonly utilized as micro-energy storage devices in penetration fuzes, we have characterized and modeled the surge of leakage current in such capacitors under extreme dynamic impact. Further, by establishing a mechanical–electrical model, we have studied the changes of leakage current, and we have performed a numerical simulation to verify the experimental results.

In summary, the following conclusions can be drawn from the experimental and simulation results:

  1. The maximum leakage current that the two commonly used type of tantalum capacitors can endure typically is calculated as 1.32 mA. Two models of tantalum capacitors underwent impact testing with a Machete hammer at impacts of 4600g, 6300g, 8000g, and 15 000g, and it was found that the leakage current for both models exceeded the safety threshold when subjected to impacts greater than 6300g.

  2. A simulation model for the leakage current of tantalum capacitors under shock has been established, incorporating a micro-scale geometric model of the capacitor electrodes, and this has been used as the basis for a COMSOL simulation. The model takes the contact area between Ta2O5 and MnO2 and the piezoresistive effect of Ta2O5 dielectric into account when the capacitor is subjected to pressure. As anticipated, the leakage current of a tantalum capacitor undergoes exponential escalation as the impact increases, reaching 9.37 mA at an impact force of 30 000g. This current exceeds the safety threshold by a factor of six, and we therefore posit that under more substantial impact loads, tantalum capacitors will inevitably undergo total failure.

  3. A micrometer-scale characterization has revealed changes in the internal electrodes of tantalum capacitors before and after shock. Microstructural alterations induced by pressure in tantalum capacitors have been characterized by SEM. At a scale of 10–20 μm, dislocation and deformation of the dielectric and negative electrode become apparent upon the imposition of pressure, which provides conclusive evidence of substantial stress and strain generation at the micrometer scale.

By analyzing the relationship between impact acceleration and leakage current, and by calculating the failure threshold of tantalum capacitors using the simulation model, we have provided a theoretical foundation for the reliability design of tantalum capacitors for application in penetration fuzes.

This research was funded by the National Natural Science Foundation of China (Grant No. 52007084).

The authors have no conflicts to disclose.

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

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Xiangyu Han received his bachelor’s degree from Nanjing University of Science and Technology, Nanjing, China, in 2022. He is pursuing a master’s degree in mechatronic engineering at Nanjing University of Science and Technology. His current research focuses on the penetration dynamics and failure of energy storage devices.

Da Yu received his Ph.D. degree in engineering from Nanjing University of Science and Technology in 2022. He is currently a postdoctoral fellow in the School of Mechanical Engineering, Nanjing University of Science and Technology. His research interest include the transfer of dynamics in penetrating projectile-fuze multibody system, dynamics simulation of penetrating projectile-fuzes, and failure analysis of transient impact devices.

Cheng Chen received his bachelor’s degree from the PLA Artillery Academy and his master’s degree from the Army Artillery Air Defense Academy. He has been engaged in the project management and quality supervision of information, electronics, software, and control products for more than ten years.

Keren Dai received his B.E. and Ph.D. degrees from Tsinghua University, Beijing, China, in 2014 and 2018, respectively. He is currently an associate professor in the School of Mechanical Engineering, Nanjing University of Science and Technology. His research interest include system modeling and simulation, signal processing, power management systems, and micropower devices.