The Army continues the development of 3D printing technology to enhance the capability to produce smaller and lighter precision weaponry. Researchers and support organizations that are affiliated with the Army Aviation and Missile Research, Development, and Engineering Center (AMRDEC) are developing nano-based structures and components for advanced weaponry, aviation, and autonomous air/ground systems applications. The first key area consists of determining in-plane and out-of-plane shear properties of test articles made by 3D printing (Fused Deposition Modeling - FDM) and comparing to the conventional extrusion/forming sheet process. Test specimens are made from three polymer materials: acrylonitrile butadiene styrene (ABS), high impact poly-styrene (HIPS), and poly-lactic acid (PLA). Laboratory testing is performed according to the ASTM D3846–02 method for determining the in-plane shear strength, while the ASTM D5379 method is used for determining the out-of-plane shear properties. A description on how the 3D printing process advances the shear properties and has the potential of improving the in-plane and cross-sectional shear properties over the conventional manufacturing process is presented. The second key area demonstrates a set of materials, processes, and techniques that support the enabling of additive manufacture (AM) of RF components. Research activities are focused on developing open-source hardware/software multi-material direct digital printing, and producing 3D printed antenna, passive components, and connectors for C-band and Ku-band systems. Material studies have demonstrated a suitable material set for RF components and identified key material performance limits. Results show how more enhancement could be achieved by optimizing the variables that affect 3D printing.
A team of researchers and support organizations, affiliated with the Army Aviation and Missile Research, Development, and Engineering Center (AMRDEC), has initiated multidiscipline efforts to develop nano-based structures and components for advanced weaponry, aviation, and autonomous air/ground systems applications. The main objective of this research is to exploit unique phenomena for the development of novel technology to enhance warfighter capabilities and produce precision weaponry. The key technology areas that the authors are exploring include nano-based sensors, analysis of 3D printing constituents, and nano-based components for imaging detection. By integrating nano-based devices, structures, and materials into weaponry, the Army can revolutionize existing (and future) weaponry systems by significantly reducing the size, weight, and cost. The major research thrust areas include the development of carbon nanotube sensors to detect rocket motor off-gassing; the application of current methodologies to assess materials used for 3D printing; and the assessment of components to improve imaging seekers. The status of current activities, associated with these key areas and their implementation into AMRDEC’s research, is outlined in this paper. Section #2 outlines output data, graphs, and overall evaluations of carbon nanotube sensors placed on a 16 element chip and exposed to various environmental conditions. Section #3 summarizes the experimental results of testing various materials and resulting components that are supplementary to additive manufacturing/fused deposition modeling (FDM). Section #4 recapitulates a preliminary assessment of the optical and electromechanical components of seekers in an effort to propose components and materials that can work more effectively.
Missiles, rockets and certain types of industrial machinery are exposed extreme vibration environments, with high frequency/amplitude mechanical vibrations which may be detrimental to components that are sensitive to these high frequency mechanical vibrations, such as MEMS gyroscopes and resonators, oscillators and some micro optics. Exposure to high frequency mechanical vibrations can lead to a variety of problems, from reduced sensitivity and an increased noise floor to the outright mechanical failure of the device. One approach to mitigate such effects is to package the sensitive device on a micromachined vibration isolator tuned to the frequency range of concern. In this regard, passive micromachined silicon lowpass filter structures (spring-mass-damper) have been developed and demonstrated. However, low damping (especially if operated in near-vacuum environments) and a lack of tunability after fabrication has limited the effectiveness and general applicability of such systems. Through the integration of a electrostatic actuator, a relative velocity sensor and the passive filter structure, an active micromachined mechanical lowpass vibration isolation filter can be realized where the damping and resonant frequency can be tuned. This paper presents the development and validation of a key component of the micromachined active filter, a sensor for measuring the relative velocity between micromachined structures.
The development of a miniature angular rate sensor based on silicon-on-insulator (SOI) microfabrication technology is presented. The design, fabrication, integration, and inertial testing of a MEMS-based angular rate sensor with large dynamic range were the driving forces behind this research. The design goals of 10-deg/h bias stability while operating through 2000-deg/s roll environments are presented. The sensor design is based on a straightforward single-mask fabrication approach that utilizes deep reactive ion etching of a 100-µm-thick device layer, with a buried 2- to 3-µm oxide layer used as the sacrificial layer, in an SOI substrate. To date, the data show demonstrated bias drift performance of 60 deg/h over this fast-roll environment.
Some harsh environments, such as those encountered by aerospace vehicles and various types of industrial machinery, contain high frequency/amplitude mechanical vibrations. Unfortunately, some very useful components are sensitive to these high frequency mechanical vibrations. Examples include MEMS gyroscopes and resonators, oscillators and some micro optics. Exposure of these components to high frequency mechanical vibrations present in the operating environment can result in problems ranging from an increased noise floor to component failure. Passive micromachined silicon lowpass filter structures (spring-mass-damper) have been demonstrated in recent years. However, the performance of these filter structures is typically limited by low damping (especially if operated in near-vacuum environments) and a lack of tunability after fabrication. Active filter topologies, such as piezoelectric, electrostrictive-polymer-film and SMA have also been investigated in recent years. Electrostatic actuators, however, are utilized in many micromachined silicon devices to generate mechanical motion. They offer a number of advantages, including low power, fast response time, compatibility with silicon micromachining, capacitive position measurement and relative simplicity of fabrication. This paper presents an approach for realizing active micromachined mechanical lowpass vibration isolation filters by integrating an electrostatic actuator with the micromachined passive filter structure to realize an active mechanical lowpass filter. Although the electrostatic actuator can be used to adjust the filter resonant frequency, the primary application is for increasing the damping to an acceptable level. The physical size of these active filters is suitable for use in or as packaging for sensitive electronic and MEMS devices, such as MEMS vibratory gyroscope chips.
The ability to monitor shock level is important for missile health monitoring to predict the performance after storage and eliminate potentially damaged units. Shock sensing is also of interest for monitoring the handling conditions of fragile shipments and providing a measure of unit-level quality control not currently available. A MEMS bi-polar single axis latching shock sensor has been developed with the goal of monitoring shock events and with the potential to "wake up" other sensing circuitry after a shock event occurs. An important feature of the sensor is that power is only consumed when a shock event occurs, making it suitable for long-term remote monitoring applications. The shock sensor has been designed, fabricated and characterized. High volume, low unit cost production will be enabled through the use of standard MEMS fabrication technologies such as DRIE and SOI wafer processing.
In this paper, we propose a novel miniature MEMS based thermoacoustic cryo-cooler for thermal management of cryogenic electronic devices. The basic idea is to exploit a new way to realize a highly-reliable miniature cryo-cooler, which would allow integration of a cryogenic cooling system directly into a cryogenic electronic device. A vertical comb-drive is proposed as the means to provide an acoustic source through a driving plate to a resonant tube. By exciting a standing wave within the resonant tube, a temperature difference develops across the stack in the tube, thereby enabling heat exchange between two heat exchangers. The use of gray scale technology to fabricate tapered resonant tube provides a way to improve the efficiency of the cooling system, compared with a simple cylinder configuration. Furthermore, a tapered tube leads to extremely strong standing waves with relatively pure waveforms and reduces possible harmonics. The working principle of this device is described here. The fabrication of this device is considered, which is compatible with current MEMS fabrication technology. Finally, the theoretical analysis of key components of this cryo-cooler is presented.
Adaptive optics systems are used to maintain an optical system at its optimum performance through real time corrections of a wavefront. Deformable mirrors have traditionally been relatively large, expensive devices, suitable for systems such as large telescopes. The objective of the present work is to expand the range of systems that can employ adaptive optics by developing a small, low-cost MEMS deformable mirror. This deformable mirror uses a continuous membrane and has 61 actuators arranged in to approximate a circular pattern. Each actuator has an associated spring suspension, allowing it to push as well as pull on the membrane, producing locally convex or concave curvature. The folded springs are positioned so as to maximize the lateral stability. Maximum actuator displacement is six microns at less than 200 volts. The actuator resonant frequency, is greater than 10 kHz, allowing high-frequency updates of the mirror shape. To operate at high speed, the device must be sealed in a low-pressure environment. Each microactuator uses a vertical comb drive to achieve large travel at a reasonable voltage. The continuous membranes are made of silicon or silicon nitride. Both the actuator and membrane are fabricated with bulk micromachine process technologies. The design targets laser based communication specifications and medical imaging applications.
A scanning two-axis tilt mirror has been modeled, fabricated and tested. The tilt mirror device is fabricated from single crystal silicon using bulk micromachining technology. The mirror is octagonal and is suspended by outer torsion hinges, a gimbal, and inner torsion hinges. Response to a driving voltage is investigated, along with frequency response. Finite element modeling was performed and the results compared with experimental data, with good agreement. Using automated and semi-automated placement equipment, linear arrays of the tilt mirrors have been produced.
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