Publications

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Journal Articles

(In Progress) Models and Simulations for Electrohydrodynamic Processes

Pre-Print, 2024

Electrospinning has been modeled using a Langrangian as well as an Eularian approach. Depending on which model is employed, various features of the electrospinning process may be analytically or numerically studied, e.g., when analyzing fiber diameter as a function of jet instability and whipping. Numerically, Reneker et al. proposed a discrete model, which divides the jet into \(N\) elements, each possessing an individual mass \((m_i)\) and charge \((q_i)\). In this system, each mass is interconnected by viscoelastic filaments, which can be generalized by a spring-mass-damper system. Here, a positively charged element, \(m_i\), among \(N-1\) adjacent charges, is injected from a positively charged nozzle into an external electric field. In this scenario, the \(i^{th}\) mass will be accelerated by the external electric field, \(E_i\), at each point. For a three- dimensional system, calculating the electric field, \(E_i\), at each position can be computationally intensive, especially in consideration of the architecture of each electrode. However, there are numerical methods, e.g., boundary element methods…

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Controlled deposition of electrospun nanofibers by electrohydrodynamic deflection

Journal of Applied Physics, 2019

Electrospinning is a technique often used for the production of nanofibers composed of various polymers and ceramics. For enhanced material performance, it is desirable to obtain nanofibrous structures with a pre-determined microscopic fiber orientation and macroscopic geometry. However, it is challenging to control or predict the final deposition structure of an electrospun nanofiber due to the inherent instabilities induced along the polymer jet during the electrospinning process. Historically, mitigating these instabilities has been attempted electrically, magnetically, and mechanically with limited levels of success. Here, a new technique to electrically control the trajectory of an electrospun jet by electrohydrodynamic deflection is introduced. This protocol is achieved using a set of linearly actuated intermediary electrodes and a rapidly oscillating electric potential, driven by home-built AC amplifiers and a switching algorithm to control the amplitude, frequency, duty cycle, and the relative phase of the external electric field…

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Development of pseudorandom binary arrays for calibration of surface profile metrology tools

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2009

Optical metrology tools, especially for short wavelengths (extreme ultraviolet and x-ray), must cover a wide range of spatial frequencies from the very low, which affects figure, to the important mid-spatial frequencies and the high spatial frequency range, which produces undesirable scattering. A major difficulty in using surface profilometers arises due to the unknown point-spread function (PSF) of the instruments [G. D. Boreman, Modulation Transfer Function in Optical and Electro-Optical Systems (SPIE, Bellingham, WA, 2001)] that is responsible for distortion of the measured surface profile…

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Conference Papers

Development of an Automated Pressure Sensitive Thermesthesiometer and Its Application in Characterizing the Thermal Response of Human Tissue with Respect to Warm Surfaces

Proceedings of the AHFE International Conference on Human Factors and Systems Interaction: Advances in Human Factors and Systems Interaction, July 17− 21, 2017, Los Angeles, California, United States, 2017

An advanced thermesthesiometer has been developed to measure the heat flux, touch-force, and internal temperature profile of a simulated body part coming into contact with a warm surface. A suitably chosen material with properties resembling those of human tissue is used for bare skin simulation and is thermally regulated using a programmable logic controller (PLC). An automated driving mechanism provides variable touch-occurrences and pressures over specially engineered test-surfaces with varying effusivities and surface roughness…

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Binary pseudo-random gratings and arrays for calibration of the modulation transfer function of surface profilometers: recent developments

Proceedings of SPIE: Advances in X-Ray/EUV Optics and Components IV, SPIE OPTICAL ENGINEERING + APPLICATIONS, August 2-6, 2009, San Diego, California, United States, 2009

The major problem of measurement of a power spectral density (PSD) distribution of the surface heights with surface profilometers arises due to the unknown Modulation Transfer Function (MTF) of the instruments. The MTF tends to distort the PSD at higher spatial frequencies. It has been suggested [Proc. SPIE 7077-7, (2007), Opt. Eng. 47 (7), 073602-1-5 (2008)] that the instrumental MTF of a surface profiler can be precisely measured using standard test surfaces based on binary pseudo-random (BPR) patterns. In the cited work, a one dimensional (1D) realization of the suggested method based on use of BPR gratings has been demonstrated. Here, we present recent achievements made in fabricating and using two-dimensional (2D) BPR arrays that allow for a direct 2D calibration of the instrumental MTF. The 2D BPRAs were used as standard test surfaces for 2D MTF calibration of the MicromapTM-570 interferometric microscope with all available objectives…

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Development of pseudo-random binary gratings and arrays for calibration of surface profile metrology tools

The 53rd international conference on electron, ion, photon beam technology and nanofabrication, May 26-29, 2009, Marco Island, FL, United States, 2009

In previous work the instrumental MTF of a surface profiler was precisely measured using reference test surfaces based on binary pseudo-random (BPR) gratings. Here, we present results of fabricating and using twodimensional (2D) BPR arrays that allow for a direct 2D calibration of the instrumental MTF. BPR sequences are widely used in engineering and communication applications such as Global Position System, and wireless communication protocol. The ideal BPR pattern has a flat “white noise” response over the entire range of spatial frequencies of interest. The BPR array used here is based on the Uniformly Redundant Array prescription2 initially used for x-ray and gamma ray astronomy applications. The URAs superior imaging capability originates from the fact that its cyclical autocorrelation function very closely approximates a delta function, which produces a flat Power Spectrum Density (PSD)…

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Patents

Methods and systems for electrospinning

World Intellectual Property Organization (WIPO), 2019

Methods and systems for electrospinning are provided. In a method of electrospinning, a solidifiable fluid is dispensed from a nozzle and biased at a first DC voltage. A fiber stream is drawn from the fluid using a collector biased to a second DC voltage. The fiber stream may be moved orthogonal to a direct stream path using a plurality of inter-electrodes biased to one or more midstream voltages (which may vary over time). The fiber stream is collected on the collector…

Patent Number: WO2019014686A1, Application Number: PCT/US2018/042354
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