@article{hyland_hunter_liu_veety_vashaee_2016, title={Wearable thermoelectric generators for human body heat harvesting}, volume={182}, ISSN={["1872-9118"]}, DOI={10.1016/j.apenergy.2016.08.150}, abstractNote={A thermoelectric generator (TEG) can be used to harvest electrical energy from human body heat for the purpose of powering wearable electronics. At the NSF Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST), TEGs are one of the enabling technologies being explored to advance the center’s mission of creating wearable, self-powered, health and environmental monitoring systems. As part of this effort, an exploration of the relevant parameters for maximizing the wearable TEG power output from the body heat and maintaining the body comfort is particularly important. For this purpose, the heat from the body must be directed into TEG with minimal loss, the generator must be designed for maintaining a high temperature differential across the thermoelectric material, and the generator must have a small form factor to maintain the body comfort. In order to address these requirements, an optimum TEG design was developed and experiments were conducted both on a temperature-controlled hot plate and on different body locations including the wrist, upper arm, and chest. The TEG was further fabricated into a T-shirt and the power was recorded for different human activities. Comparison of the experiments on various body locations and on the T-shirt yielded the highest to lowest power generated on the upper arm, wrist, chest and T-shirt, respectively. The prospect of powering a wearable electrocardiogram sensor by a TEG on the upper arm is discussed.}, journal={APPLIED ENERGY}, author={Hyland, Melissa and Hunter, Haywood and Liu, Jie and Veety, Elena and Vashaee, Daryoosh}, year={2016}, month={Nov}, pages={518–524} }
 @article{nicolescu_escuti_2011, title={Polarization-insensitive, stacked, liquid crystal polarization grating bandpass filters}, volume={7934}, ISSN={["0277-786X"]}, DOI={10.1117/12.875473}, abstractNote={We introduce a polarization-insensitive tunable bandpass filter design having the following unique properties: (i) high peak transmittance (~ 80 - 90%) that is independent of input polarization, (ii) non-mechanical tuning over a potentially large wavelength range (> 100 nm) with a narrow passband (< 10 nm possible), (iii) low-cost, simple, and compact (thin-film) construction with a large clear aperture suitable for many simple camera systems. This is a stacked birefringent filter approach similar to Lyot and Solc fiters but with significantly less loss due to the removal of polarizers from the system. The filter is based on a stacked configuration of polymer polarization gratings (PGs) and either fixed or tunable wave plates. PGs are a class of thin film anisotropic diffraction gratings, which exhibit unique properties including zero-order transmittance that is independent of incident polarization, and practically all diffracted light appears within the zero- and first-diffraction orders with efficiency ranging from nearly 100% to 0%. In this work we explore a variety of filter stack configurations and analyze them theoretically using Jones Calculus and Poincare Sphere reasoning. Both fixed and tunable filter configurations are presented and analyzed in terms of finesse, full width at half maximum, free spectral range, and tuning range. We then present preliminary experimental data for a three stage fixed bandpass filter.}, journal={OPTICAL COMPONENTS AND MATERIALS VIII}, author={Nicolescu, Elena and Escuti, Michael J.}, year={2011} }
 @article{nicolescu_mao_fardad_escuti_2010, title={Polarization-Insensitive Variable Optical Attenuator and Wavelength Blocker Using Liquid Crystal Polarization Gratings}, volume={28}, ISSN={["1558-2213"]}, DOI={10.1109/jlt.2010.2078487}, abstractNote={We demonstrate a variable optical attenuator (VOA) based on liquid crystal polarization gratings (LCPGs), which eliminates the need for complex polarization management found in competing LC technologies. We then configure the VOA as a multi-channel wavelength blocker resulting in a simple, compact architecture with high performance and low cost. Together with a dual fiber collimator, relay lenses, a diffraction grating, a quarter wave plate, and a mirror we achieve optical attenuation of ~50 dB with minimal polarization dependent loss (≤ 0.3 dB) and insertion loss ( ≤ 2.5 dB). The device also manifests competitive wavelength flatness (≤ 0.35 dB variation), response times ( ~ 40 ms), and temperature dependent loss (≥ 47 dB maximum attenuation up to 85°C). We describe the principle of operation, explain the fabrication process and optimization challenges, and finally present the system design and experimental results for a four-channel, 100 GHz wavelength blocker in the C-band.}, number={21}, journal={JOURNAL OF LIGHTWAVE TECHNOLOGY}, author={Nicolescu, Elena and Mao, Chongchang and Fardad, Amir and Escuti, Michael}, year={2010}, month={Nov}, pages={3121–3127} }
 @article{nicolescu_escuti_2010, title={Polarization-independent tunable optical filters using bilayer polarization gratings}, volume={49}, ISSN={["2155-3165"]}, DOI={10.1364/ao.49.003900}, abstractNote={We demonstrate a polarization-independent tunable optical filter based on switchable polarization gratings (PGs) formed using reactive and nonreactive liquid crystals (LCs). PGs are anisotropic diffraction gratings that exhibit unique properties, including a zero-order transmittance that is independent of incident polarization and that can vary from approximately 0% to approximately 100%, depending on wavelength and applied voltage. A stack of several PGs of varying thicknesses combined with an elemental angle filter yields polarization-independent bandpass tuning with minimal loss. We introduce a novel hybrid PG consisting of both reactive and nonreactive LC layers, which allows very thick gratings to be created with thin active LC layers. We demonstrate a tunable optical filter with a peak transmittance of 84% of unpolarized light, a minimum full width at half-maximum of 64 nm, and a maximum tuning range of 140 nm.}, number={20}, journal={APPLIED OPTICS}, author={Nicolescu, Elena and Escuti, Michael J.}, year={2010}, month={Jul}, pages={3900–3904} }