Design and process of force-electric fusion for electromagnetic driven Si based MEMS S&A

In order to meet the technical requirements for precise control of the arming time in high-dynamic environments and ammunition safety, this article proposes a silicon-based MEMS safety system force-electric fusion design scheme for small-caliber ammunition platforms. Modeling and computational analysis are conducted on the sensitive units in S&A. A mechanical equilibrium model is established to study the centrifugal overload and electromagnetic forces, followed by verification through dynamic simulation. The design aimed to achieve the safety and arming control of the MEMS security system using a plate-type electromagnetic driving scheme. A low driving energy electromagnetic coil model is designed, and the driving capability of the electromagnetic coil is analyzed. It is found that under the condition of a distance of 0.1mm and 8V, a driving force of 270mN could be achieved. Considering the complex operating conditions during the arming process, a low damping model is developed for the arming degree of the MEMS arming device. After the design is completed, the S&A and electromagnetic coils are processed and prepared using deep silicon etching and microcasting techniques. Finally, threshold verification is conducted for the recoil and centrifugal arming mechanisms of the S&A. The designed S&A ultimately achieved a size of less than or equal to ∅20mm.


Introduction
The Safety and Arming Device (S&A) is a core component of fuze, which utilizes a movable explosion-proof mechanism to achieve energy transmission and isolation.MEMS S&A devices can be classified according to the driving principles, including environmental force-driven, electrothermal-driven, electromagnetic-driven, pyrotechnic-driven, and other forms of driving [1].The main issue with environmental force-driven devices is their relatively large overall size and their reliance on typical ballistic environments.They perform poorly in environments where mechanical factors are less obvious [2,3].Electrothermal-driven devices face the challenge of high energy requirements.Due to the low coefficient of thermal expansion of silicon, the entire system requires the introduction of displacement amplification mechanisms such as micro-levers or micro-springs, which increases the complexity of the overall structure [4,5].The main problem with pyrotechnic-driven devices lies in safety concerns and the high demand for device airtightness [6].Other driving forms, such as piezoelectric-driven devices, require a significant amount of driving energy, making system integration challenging [7,8].Considering factors such as simplicity of motion, reliability, and low driving energy requirements, electromagnetic-driven devices offer a relatively simple, reliable, and adaptable solution.They are suitable for weak environmental force conditions and can be combined with advanced silicon-based manufacturing techniques [9].Electromagnetic-driven MEMS safety and arming devices generate a magnetic field through the magnetic effect of the current, which drives the explosion-proof slider to disengage the safety mechanism[10~12].This article proposes a silicon-based MEMS safety system force-electric fusion design scheme for small-caliber ammunition platforms.

Models and Methods
In order to address the issues of poor assembly process and inaccurate control of the arming time of the traditional UV-LIGA fabricated MEMS safety systems, this article proposes a silicon-based MEMS safety system force-electric fusion design scheme for small-caliber ammunition platforms as shown in Figure 1.
Figure 1.Design of MEMS S&A The working principle of the S&A system is as follows: When the ammunition is launched: Firstly, the MEMS spring located at the rear end of the explosion-proof slider senses the launch overload and fractures, completing the confinement of the explosion-proof slider by the rear frame of the MEMS safety system.Secondly, to meet the requirements of the muzzle safety distance, after the ammunition is fired, the arming device supplies driving current to the MEMS electromagnetic coil, generating an induced electromagnetic field.At this time, the induced electromagnetic force of the coil and the centrifugal force of the ammunition form a combined force in the opposite direction at the threshold determination mechanism, which is smaller than the fracture strength of the threshold determination mechanism.Once the muzzle safety distance requirement is satisfied, the electromagnetic force resets, and the explosion-proof slider undergoes displacement under the action of centrifugal force until the explosion-proof slider reaches the locking mechanism.This enables the proper transmission sequence for the MEMS detonator.
Modeling and computational analysis are conducted on the sensitive units in S&A as shown in Figure 2.  The design aimed to achieve the safety and arming control of the MEMS security system using a plate-type electromagnetic driving scheme.A low driving energy electromagnetic coil model is designed as shown in Figure 4, and the driving capability of the electromagnetic coil is analyzed as shown in Figure 5.This allowed for autonomous intelligent control of the MEMS arming device to remotely disarm at the appropriate timing.It is found that under the condition of a distance of 0.1mm and 8V, a driving force of 270mN could be achieved.Considering the complex operating conditions during the arming process, a low damping model is developed for the arming degree of the MEMS arming device.This allowed for autonomous intelligent control of the MEMS arming device to remotely disarm at the appropriate timing.

Fabrication and Test
After the design is completed, the S&A and electromagnetic coils are processed and prepared using deep silicon etching and microcasting techniques, as shown in Figure 6.

Figure 2 .
Figure 2. Parameterized design of sensitive units in security systems A mechanical equilibrium model is established to study the centrifugal overload and electromagnetic forces, followed by verification through dynamic simulation as shown in Figure 3.

Figure 3
Figure 3 Display Dynamics Simulation of S&AThe design aimed to achieve the safety and arming control of the MEMS security system using a plate-type electromagnetic driving scheme.A low driving energy electromagnetic coil model is designed as shown in Figure4, and the driving capability of the electromagnetic coil is analyzed as shown in Figure5.This allowed for autonomous intelligent control of the MEMS arming device to remotely disarm at the appropriate timing.

Figure 4 .Figure 5 .
Figure 4. Structure of electromagnetic coils.(a) Schematic diagram of the overall electromagnetic coil; (b) composition module

Figure 6 .
Figure 6.EMS S&A deep silicon etching process.(a) Deep silicon etching process; (b) Preparationof physical obiects; (c) The photomicrographs of the silicon trench.Finally, threshold verification is conducted for the recoil and centrifugal arming mechanisms of the S&A.The designed S&A ultimately achieved a size of less than or equal to ∅20mm.Building upon the previous research, it improved the intelligence, safety, and adaptability of the equipment, resulting in higher functionality integration.The MEMS spring designed in this article for sensing emission overload can resist emission overload below 30100g and achieve centrifugal safety release at 20000rpm.

Figure 7 .
Figure 7. Experiments of recoil release and centrifugal release.(a) Experimental system for recoil release; (b) Experimental system for centrifugal release; (c) Result of threshold verification Building upon the previous research, the design of this article improved the intelligence, safety, and adaptability of the equipment, resulting in higher functionality integration.