Jeremy A. Palmer

Pulsed laser ignition of reactive multilayer films

Nanostructured Al∕Pt multilayer films were ignited by single pulse irradiation from a Ti:sapphire femtosecond laser system. Critical ignition fluences (0.9–22J∕cm2) required to initiate a self-propagating reaction were quantified for different multilayer designs. Multilayers with smaller bilayer thickness required relatively lower fluence for ignition. Ignition threshold fluence was also found to be 1.4–3.6 times higher for Al-capped multilayers than for Pt-capped multilayers. Ablation threshold fluences were measured for Al (860±70mJ∕cm2) and Pt (540±50mJ∕cm2) and related to the observed difference in ignition fluences for Al- and Pt-capped multilayers.

Mesoscale RF relay enabled by integrated rapid manufacturing

Purpose – This paper presents a novel mesoscale RF (mRF) relay that integrates advanced high resolution stereolithography (SL) and micro wire electro discharge machining (μEDM) technologies. Methods and infrastructure for reliable batch assembly of electromechanical actuators and structural parts less than 5 mm3 in volume are described. Switches made using these techniques are expected to have greater power handling capability relative to current micro RF relay products.Design/methodology/approach – The conjecture is that the integration of SL and similar rapid additive manufacturing with other mesofabrication technologies can yield innovative miniature products with novel capabilities. A series of mRF prototypes consisting of a contact mechanism and actuator with return spring were fabricated assembled, inspected, and characterized for electromechanical performance. Characterization results led to specific conclusions regarding capabilities of the mRF product, and the integrated manufacturing technique.F...

Embedded micro-channel fabrication using line-scan stereolithography

Purpose – In an effort to directly manufacture devices with embedded complex and three‐dimensional (3D) micro‐channels on the order of microns to millimeters, issues associated with micro‐fabrication using current commercially available line‐scan stereolithography (SL) technology were investigated.Design/methodology/approach – Practical issues associated with the successful fabrication of embedded micro‐channels were divided into software part preparation, part manufacture, and post‐cleaning with emphasis on channel geometry, size, and orientation for successful micro‐fabrication. Accurate representation of intended geometries was investigated during conversion from CAD to STL and STL to machine build file, and fabricated vertical and horizontal micro‐channels were inspected. Additional build issues investigated included accurate spatial registration of the build platform, building without base support, and Z‐stage position accuracy during the build.Findings – For successful fabrication of micro‐channels ...

Advancing three-dimensional MEMS by complimentary laser micro manufacturing

This paper describes improvements that enable engineers to create three-dimensional MEMS in a variety of materials. It also provides a means for selectively adding three-dimensional, high aspect ratio features to pre-existing PMMA micro molds for subsequent LIGA processing. This complimentary method involves in situ construction of three-dimensional micro molds in a stand-alone configuration or directly adjacent to features formed by x-ray lithography. Three-dimensional micro molds are created by micro stereolithography (MSL), an additive rapid prototyping technology. Alternatively, three-dimensional features may be added by direct femtosecond laser micro machining. Parameters for optimal femtosecond laser micro machining of PMMA at 800 nanometers are presented. The technical discussion also includes strategies for enhancements in the context of material selection and post-process surface finish. This approach may lead to practical, cost-effective 3-D MEMS with the surface finish and throughput advantages of x-ray lithography. Accurate three-dimensional metal microstructures are demonstrated. Challenges remain in process planning for micro stereolithography and development of buried features following femtosecond laser micro machining.

An ultra-short pulse laser lathe for axisymmetric micromachining of explosives

Engineers have devised a novel ultra-short pulse laser lathe system for bulk micromachining of axisymmetric features in energetic material samples with three-dimensional cylindrical geometry. One hundred twenty femtosecond pulses from an 800-nm Ti:sapphire laser were utilized to machine hexanitrostilbene (HNS) rods with diameters less than 200 micrometers and greater than 5:1 aspect ratio without ignition and subsequent bulk combustion or detonation. To date, this work represents the smallest energetic material rod structures fabricated by this technology. Results indicate that surface roughness is dependent upon rotation speed and feed rate. Valuable explosive nano-particles were discovered, collected, and analyzed as a byproduct of fabrication.

ViArray standard platforms: Rad-hard structured ASICs for digital and mixed-signal applications

Sandias radiation-hardened ViArray standard platforms use via-configurable circuits to create quick-turn, low-cost structured ASICs (Application Specific Integrated Circuits). Via-configurable technology enables performance similar to standard-cell ASICs, but with low-volume costs approaching that of programmable logic devices. Due to their significantly lower development cost and shorter production times, ViArray ASICs are rapidly replacing custom ASICs in Sandias high-reliability digital and analog applications. This paper describes the Eiger ViArray platform, which is optimized for general-purpose digital applications, and the Whistler ViArray platform, which is optimized for mixed-signal instrumentation and state-of-health applications.

Microstereolithography production of integrated Hadamard mask structures

The use of modern microstreolithography (MSL) technology gives optics developers the freedom to integrate mounting and positioning structures directly into an optical mask structure. We have created Hadamard spectrometer masks with increments of 150 μm and less using the Sony SCS-6000 microstereolithography apparatus (MSLA). Due to laser over cure and other parameters, adjustments were made iteration by iteration until appropriate mask tolerances were met. A mounting structure was integrated with the mask for testing and application. At the computer aided design (CAD) model level, the mounting geometry can be adjusted to fit any specific mounting apparatus. By using the MSLA, features as small as 75 μm and larger than 300 mm can be created in the same build. Additionally, the conceptual design of an entire positioning system constructed using layer additive MSLA microfabrication is underway. This positioning system may be built as an integrated assembly, encapsulating necessary components. Optical characterization results are presented.

Dynamic response of an optomechanical system to a stationary random excitation in the time domain

Modern electro-optical instruments are typically designed with assemblies of optomechanical members that support optics such that alignment is maintained in service environments that include random vibration loads. This paper presents a nonlinear numerical analysis that calculates statistics for the peak lateral response of optics in an optomechanical sub-assembly subject to random excitation of the housing. The work is unique in that the prior art does not address peak response probability distribution for stationary random vibration in the time domain for a common lens-retainer-housing system with Coulomb damping. Analytical results are validated by using displacement response data from random vibration testing of representative prototype sub-assemblies. A comparison of predictions to experimental results yields reasonable agreement. The Type I Asymptotic form provides the cumulative distribution function for peak response probabilities. Probabilities are calculated for actual lens centration tolerances. The probability that peak response will not exceed the centration tolerance is greater than 80% for prototype configurations where the tolerance is high (on the order of 30 micrometers). Conversely, the probability is low for those where the tolerance is less than 20 micrometers. The analysis suggests a design paradigm based on the influence of lateral stiffness on the magnitude of the response.

Effectiveness of epoxy staking of fasteners in aerospace applications

Purpose – The purpose of this paper is to investigate the effectiveness of locking or staking of fasteners with epoxy material systems to prevent loss of preload in aerospace environments.Design/methodology/approach – A quantitative experimental method is adopted to evaluate epoxy material systems for staking of fastener assemblies subjected to varying dynamic and thermal loads. A statistical design of experiments is employed to probe specific design parameters.Findings – Results show that epoxy application can provide satisfactory fastener locking under a variety of service conditions. It is found that: Epon 828 epoxy provides superior fastener locking compared to 3M Scotch‐Weld Epoxy 2216; epoxy application around screw threads is more effective than application around screw head; and abrading the plate surfaces with 180 grit SiC paper is not an effective or useful surface preparation technique.Research limitations/implications – The paper is limited to two commercial epoxy material systems and does not...

Design, characterization, and control of a large aperture MOEMS Fabry-Perot tunable infrared filter

A miniature Fabry-Perot tunable infrared filter under development at the NASA Goddard Space Flight Center is fabricated using micro opto electromechanical systems (MOEMS) technology. Intended for wide-field imaging spectroscopy in space flight, it features a large 10-mm diameter aperture structure that consists of a set of opposing suspended thin films 500 nanometers in thickness, supported by annular silicon disks. Achieving the desired effective finesse in the MOEMS instrument requires maximizing the RMS flatness in the film. This paper presents surface characterization data for the suspended aperture film prior to, and following application of a multi-layer dielectric mirror. A maximum RMS flatness of 38 nanometers was measured prior to coating, leading to an estimate of the maximum effective finesse of 14. Results show evidence of initial deformation of the silicon support structure due to internal stress in the substrate and thin film layers. Film stress gradients in the dielectric coating on either side of the aperture add convexity and other localized deflections. The design of a tuning system based upon electrostatic positioning with feedback control is presented.