Lucas A. Shaw

Noise Squeezing Controlled Parametric Bifurcation Tracking of MIP-Coated Microbeam MEMS Sensor for TNT Explosive Gas Sensing

This paper reports real-time explosive gas sensing (DNT) in atmospheric pressure utilizing the noise squeezing effect that occurs before a bifurcation event. A noise-squeezing controller based on the statistics of phase noise is implemented using high-speed LabVIEW field programmable gated array. A high frequency TNT-molecularly imprinted fixed-fixed microbeam sensor utilizes this nontraditional sensing strategy and performs DNT sensing at various concentrations. Experiments are conducted using both noise-based and sweep-based bifurcation tracking for a direct comparison. Results demonstrate noise-based bifurcation tracking is not only capable of performing reliable frequency tracking, but also show the method is superior to the bifurcation sweep-based tracking. Over three orders of magnitude improvement in acquisition rate is achieved, and as a result, confidence and precision on bifurcation frequency estimation is significantly improved over the bifurcation sweep tracking method, enabling DNT sensing at concentrations much below sub-ppb (parts-per-billion) level.

Scanning holographic optical tweezers

The aim of this Letter is to introduce a new optical tweezers approach, called scanning holographic optical tweezers (SHOT), which drastically increases the working area (WA) of the holographic-optical tweezers (HOT) approach, while maintaining tightly focused laser traps. A 12-fold increase in the WA is demonstrated. The SHOT approach achieves its utility by combining the large WA of the scanning optical tweezers (SOT) approach with the flexibility of the HOT approach for simultaneously moving differently structured optical traps in and out of the focal plane. This Letter also demonstrates a new heuristic control algorithm for combining the functionality of the SOT and HOT approaches to efficiently allocate the available laser power among a large number of traps. The proposed approach shows promise for substantially increasing the number of particles that can be handled simultaneously, which would enable optical tweezers additive fabrication technologies to rapidly assemble microgranular materials and structures in reasonable build times.

Organizing Cells Within Non-Periodic Microarchitectured Materials That Achieve Graded Thermal Expansions

The aim of this paper is to introduce an approach for optimally organizing a variety of different unit cell designs within a large lattice such that the bulk behavior of the lattice exhibits a desired Young’s modulus with a graded change in thermal expansion over its geometry. This lattice, called a graded microarchitectured material, can be sandwiched between two other materials with different thermal expansion coefficients to accommodate their different expansions or contractions caused by changing temperature while achieving a desired uniform stiffness. First, this paper provides the theory necessary to calculate the thermal expansion and Young’s modulus of large multi-material lattices that consist of periodic (i.e., repeating) unit cells of the same design. Then it introduces the theory for calculating the graded thermal expansions of a large multimaterial lattice that consists of non-periodic unit cells of different designs. An approach is then provided for optimally designing and organizing different unit cells within a lattice such that both of its ends achieve the same thermal expansion as the two materials between which the lattice is sandwiched. A MATLAB tool is used to generate images of the undeformed and deformed lattices to verify their behavior and various examples are provided as case studies. The theory provided is also verified and validated using finite element analysis and experimentation.Copyright

Planar microparticle assembly and photopolymerized joining with holographic optical tweezers

Holographic optical tweezers are able to assemble and permanently join polystyrene microspheres into planar patterns using an acrylamide-based photopolymerization reaction. This approach holds potential as a new method for additive fabrication of multi-material microstructures.

A Shape-Controlled Compliant Microarchitectured Material

The purpose of this paper is to introduce a new kind of actively controlled microarchitecture that can alter its bulk shape through the deformation of compliant elements. This new type of microarchitecture achieves its reconfigurable shape capabilities through a new control strategy that utilizes linearity and closed-form analytical tools to rapidly calculate the optimal internal actuation effort necessary to achieve a desired bulk surface profile. The microarchitectures of this paper are best suited for high-precision applications that would benefit from materials that can be programmed to rapidly alter their surfaces/shape relatively small amounts in a controlled manner. Examples include distortion-correcting surfaces on which precision optics are mounted, airplane wings that deform to increase maneuverability and fuel efficiency, and surfaces that rapidly reconfigure to alter their texture. In this paper, the principles are provided for optimally designing 2D or 3D versions of the new kind of microarchitecture such that they exhibit desired material property directionality. The mathematical theory is provided for modeling and calculating the actuation effort necessary to drive these microarchitectures such that their lattice shape comes closest to achieving a desired profile. Case studies are provided to demonstrate this theory.Copyright