Xerox Engineering Research Fellows
2020 Research Opportunities
The Institute of Optics
Research Project: Myopia Development: Role of Optical Quality of the Eye
Myopia is one of the leading causes of visual impairment worldwide and is linked to severe eye diseases such as maculopathy, retinal detachment and glaucoma. The overall prevalence of myopia has increased substantially in recent years. With higher levels of myopia becoming a significant public health concern, it is of crucial importance to find effective treatments to slow myopic progression in children. Among many potential causes of myopia development such as genetics, visual environment, accommodative ability, research focus in this project is on understanding how the optics of the eye across the visual field influences myopia progression and control. The project provides a research opportunity to learn the human eye and visual optics by using advanced ocular imaging technology, adaptive optics vision simulator, and customized lens design using optical ray tracing.
Research Project #1: Fabrication and Testing of Pumpless Indirect Evaporative Air Conditioners Using our Superwicking Metal Heat Exchanger
Evaporative cooling is well known for centuries, where a stream of air passing through a wet surface cools through the liquid-vapor phase transition as water evaporates. Compared to traditional vapor-compression air-conditioners (ACs), evaporative cooling uses much less energy and has a lesser impact on the environment, though it adds moisture to the air. To avoid an increase in humidity, indirect evaporative cooling (IEC) can cool the primary air stream through a heat exchanger. In an IEC system, a working airflow passes through a channel with wet walls and causes evaporation. Due to the latent heat of evaporation, the wet channel walls are cooled down, causing cooling on the other side of the walls (the dry channel). The product air cools down when passing through this cold dry channel If the heat exchanger material has high in and out-of-plane thermal conductivities, along with the evaporative heat transfer (out-of-plane), it would also cool down the air through transferring sensible heat to the water reservoir through conduction (in-plane heat transfer). By applying a superwicking material pioneered by the PI as the heat exhanger, we propose here a disruptive indirect-hybrid-conductive-evaporative-cooling (IHCEC) system, where the surface of the heat exchanger is cooled by the combined effects of evaporative and conductive heat transfer. Our design can solve a range of key issues associated with conventional IEC systems, resulting in higher cooling efficiency and a larger coefficient-of-performance (COP) even in the humid environment (>60 %) with low-water consumption.
Research Project #2: Fabrication of Solar Thermal Tracking Panel for Efficient Solar-water Purification
Water, sanitation and hygiene (WASH) are essential to health, survival and sustainable development. About two-thirds of the world population is facing the problem of safe drinkable water and adequate sanitation causing around 842,000 diarrhoeal deaths each year. In general, an average of each person uses almost 80-100 gallons of water per day where the majority of it is being wasted as a flushing toilet, shower, laundry etc. Wastewater coming from different channels contains a number of hazardous chemicals such as heavy metals, dyes, detergents, nitrates, phosphates, urea etc., not only contaminates surface and groundwater but also become a part of our food-chain through their interaction with crops, and aquatic systems. The membrane-based filtration is not only inefficient but also wasting around four times of water into the sink, thus further increasing the water crisis. Evaporation or boiling of waste/contaminated/saline seawater has potential to address water crisis issue, but require thousands of kilowatt electricity or million gallons of fossil fuels, those have a negative impact on the environment, to fulfill daily US clean water demand.9 Moreover, the transportation of purified water from the facility in the coastal region to the cities in the non-coastal region also requires energy and infrastructure.
Wastewater and solar energy are available everywhere and can be combined to get safe and drinkable water at no cost. However, it requires a multi-functional surface that (i) can efficiently absorb solar energy to generate heat, (ii) transport water efficiently to wick its surface, and (iii) has the capability to directly face the sun, i.e. can track the sun to optimize solar irradiance on its surface. We developed superwicking and black metal technology, where a burst of laser pulses directly writes microcapillaries on the surface of a low-cost metal, like Al, where the surface of microcapillaries are covered with a range of hierarchical nano/microstructures those trap almost all incident photons incident on its surface to generate heat. At the same time, micro-capillaries are filled with a thin layer of water. Solar heat generation occurs at the bottom and walls of microcapillaries, where water is in abundance. The generated heat is confined in the capillary, thus efficiently evaporates water with high speed. For the practical realization, the superwicking black surface should track the sun. For example, its surface should be almost vertical during sunrise and angle of inclination from vertical should increase with time and become almost horizontal at noon.
The building of a solar tracking system that can mount superwicking black absorber to face the Sun without affecting water transport on its surface is the main purpose of this project. The entire system needs to be in a transparent hemispherical dome that will allow passing> 97 % of solar light and will help condensation of water-vapor into liquid-water. Liquid water droplets will nucleate, grow and finally follow the wall of the dome to get collected in a rim area, and finally will come out through an outlet.
Research Project #3: Enhancing Thermoelectric Generation Efficiency using Femtosecond Laser Treated Metals
Thermoelectric generation is a well-studied phenomenon that generates electricity by applying a temperature gradient across a thermoelectric material. The effect is sensitive to the temperature gradient and thus requires proper thermal management, e.g., to increase the temperature of the thermoelectric generator (TEG) hot side, or to decrease the temperature of the TEG cold side.
We have shown that using fs-laser ablation, the shiny metals can become pitch black. In fact, the creation of black metals using fs-laser ablation can create super light absorbers that absorb the visible, NIR, and MIR wavelength ranges.
Because absorptance and emittance are equivalent, for most materials, an efficient light absorber is an efficient thermal emitter that can effectively cool a surface via radiative cooling. We propose using fs-laser ablation of traditional heat sink materials, e.g., Al, as a heat exchanger which can increase the radiative cooling efficiency of a TEG and increase the TEG output power.
We will need one student to undertake this project for a period of 2 months. The student will be responsible to perform laser ablation and measure the absorptance of the fabricated samples. In addition, the student will perform thermoelectric generation measurements to evaluate TEG efficiency.
Research Project #4: Synergistic Energy Harvesting from the Sun and Outer Space using Femtosecond Laser Treatment of Semiconductors
Energy harvesting from the sun (~ 6,000 K) is the cornerstone of solar energy generation. In addition, radiative cooling relies on cooling objects by radiating energy out to the cold outer space (3 K) within the atmospheric transparency window. Recently, it has been proposed to combine these two resources for energy harvesting, i.e., using the same physical area it is possible to realize solar heating and radiative cooling. This can enable the operation of a heat engine that obtains the temperature difference between its hot and cold sides using infinitely available resources; the sun and the outer space. The challenge to large-scale deployment of this new technology is to find materials that can simultaneously and synergistically absorb the solar spectrum while transmitting the IR spectrum that corresponds to the atmospheric transparency window.
It is well-known that femtosecond (fs) laser ablation of semiconductors can increase their absorptance as well as the absorption spectral range. For example, treating Silicon with fs-laser ablation creates black Silicon which efficiently absorbs the entire solar spectrum. Moreover, many semiconductors have no absorption within the atmospheric window which corresponds to sub-bandgap energies. Consequently, treating semiconductors with fs laser ablation can create the desired synergistic solar absorber/ IR transparent material. We propose to use a femtosecond laser ablation of GaAs to demonstrate such a synergistic material due to its low sub-bandgap absorption. We will need one student to undertake this project for a period of 2 months. The student will be responsible to perform laser ablation and measure the reflection, scattering, and transmission of the fabricated samples.
Research Project: Surveying biological tissues with optical coherence elastography
Optical coherence tomography (OCT) is a high-resolution imaging modality that uses laser light to obtain volumetric scans of a sample. OCT elastography approaches can be used to obtain the biomechanical properties of tissue, and these approaches are also called optical coherence elastography (OCE). Numerous studies using OCE have been performed in cornea, skin, heart, muscle, and breast. This highly interdisciplinary project currently involves OCE scans of brain tissue to study injury, inflammation, aging, and neurodegenerative diseases. However, there is flexibility on applications depending on the student's specific interests. In this project, the student will be reviewing key literature paper and learn to summarize them for the team, and will be engaged in experiments including data collection, analysis, and participation in future publications as appropriate according to the student contribution.
Metrology of gradient index (GRIN) materials in the infrared wavelength spectrum. An opportunity to learn about measuring optical properties such as index of refraction, homogeneity, coefficient of thermal expansion, thermo-optics coefficient, and changes in index of refraction. The student will be using lab instrumentation to characterize GRIN materials and have an opportunity to learn about fabrication and design of GRIN optics. The work will focus on infrared materials, but may also overlap with 3D printed polymers, glasses, and other GRIN materials.