The advent of prototype manufacturing is ideally suited to constructing freeform optical systems. Freeform system will in general have both reflective and transmissive surfaces or lenses that are arranged with unique, non-concentric geometric forms. Prototype printers are ideally suited to manufacturing very complex, three dimensional shapes by converting Computer Aided Design, or CAD files into Stereolithography or STL files. The freeform optical geometry can be a very complex design and thus is very well suited to prototype printing. Prototype printers also have the major advantage of reducing the time from design concept to a complete workable product by over an order of magnitude. This reduced time to turn-around from a concept to a working model is often considered one of the major advantages of prototype manufacturing. It should be recognized therefore that there are several very positive advantages of adapting 3-D printers to making optical freeform structures. There are however problems that are outlined below that address surface quality for reflective optics made with prototype printers. Transmissive optics are considered even more difficult although there is a company that claims to have solved surface issues and will in their shop create optics from your designs; both surface quality and structural integrity are reported as optically acceptable. See below.
The optical surfaces from commercial prototype printers are not yet of a quality necessary for optical systems: the problem is surfaces are stepped by the deposition made by the print head media and the surface is not typically smooth to optical requirements in either RMS or peak heights. The roughness of the surface will require post-printing processing which negates some of the advantages of using a prototype printer. Philips in the Netherlands and Osram AG in Augsburg, Germany both touch up surfaces after printing for post-processing to improve surface quality. It is proposed here to study freeform reflective optics made for illumination systems. We propose two ways to create surfaces that are of sufficient optical quality: first is to investigate index matching material that can be deposited as a liquid and then polymerized to improve surface quality. The issues of wetting, surface tension, polymerization shrinkage and index matching on stepped surfaces are important directions to pursue in this research phase; prototype surfaces with a prescribed slope will be constructed and then processed as outlined above for step heights and smoothness.
There are also companies such as LUXeXcel, http://www.luxexcel.com that claims to use surface tension in smoothing surfaces for their “Printoptical Technology.” This is a processing approach that is said to allow single-step manufacturing with optical quality. This process claims to avoid the use of molds and any post-processing of the optic. The claim is no molds need be created, no intermediate steps are necessary and no post-processing is needed. The surface is smooth because the polymer is in a liquid state and surface tension draws the surface smooth after it is deposited but before it is polymerized. Their proprietary polymer is used for making lens in their system. This company processes CAD files but does not disclose any details of their processes nor sell additive printers. All work orders and end products are made in their shops. In many ways this negates the advantages of a shop trying freeform designs and optimizing the optic after rapid experimental results are obtained.
The University of Rochester will have a very high end Stratasys/Objet additive printer that prints a clear transparent polymer. In addition, we also have 2 OptiPro Systems for post processing an optic: an XF grinder and a UFF polisher. These instruments will aid in this research as well as the University’s extensive surface characterization instrumentation: Zygo’s NewView 3-D optical surface profiler, surface white light interferometers, profilometers, scanning electron microscopes, conventional and laser 3-D microscopes, etc.
In summary, the proposed research is to improve surface quality in additive printing by researching the materials used in the printer and the print head design. The surfaces constructed will be characterized after printing and after post-processing by thermal and optical polymerization especially with optical matching liquids.
Research Project: Two Chamber Model of the Cochlea
(Joint project with Prof. Jong-Hoon Nam)
Motivation: Two Chamber Model of the Cochlea Supervised by Profs. Gracewski and Nam Motivation: The mammalian cochlea is a frequency analyzer. External sound stimuli are encoded at different locations along the cochlear coil (35 mm in human cochlea) according to their frequency. The human ear can resolve 3.6 Hz in the frequency range between 1000 and 2000 Hz. Without such remarkable resolution, we could not distinguish our friends’ voices over the phone. Interaction between the fluid in the cochlear duct and the basilar and tectorial membranes is believed to be responsible for the tonotopy—the relation between the frequency and the location of maximum basilar membrane response. Most current models of the fluid-membrane interaction model the basilar and tectorial membrane as a single structure. However there is experimental evidence that these membranes move independently, often oscillating out of phase. Therefore, the goal of this project is to develop a two-chamber model to investigate whether the independent motion has a significant effect on the frequency tuning.
Project Description: Former Xerox Fellows developed passive time and frequency domain models of the cochlea. Most recently, a two-chamber model of the cochlear duct has been developed in the frequency domain that accounts for the independent motion of the tectorial and basilar membranes. This model will be used to investigate effects of the independent properties of the two membranes on the frequency response of the system. In addition, the passive systems in this model will be replaced with active components that should predict higher local sensitivity to frequency. To accomplish this task, a time domain model may need to be developed.
Research Project: Mixing and Transport in Energy & Ecology
Please click here for a description of available research projects.
Research Project #1: Measurement of Mechanical Properties of the Cochlear Partition
We study the mechano-transduction of the inner ear. The cochlea, the mammalian hearing organ, turns mechanical stimuli (sound) into neural signals. The identification of mechanical properties of cochlear sensory cells and tissues is crucial to better understand how we hear (or fail to hear). To measure the mechanical properties, we need to apply calibrated forces in the order of nanonewtons and measure displacements in nanometers at the speed of up to tens of kHz. Students will help with calibrating/developing force application methods such as acoustic sound pressure delivery to a micro-chamber system and magnetic tweezers (electro-magnetic force application through a micro bead). Through this project, students will experience how the principles of acoustics, electromagnetics, solid mechanics and vibrations are applied to micro-mechanical experiments with biological tissues.
Research Project #2: Different Modes of Propagating Waves in the Cochlea
(Joint project with Prof. Sheryl M. Gracewski)
The cochlea is an acoustic prism--it extracts different frequency components from sounds. The physical principle underlying this frequency analysis is mechanical resonance. The cochlear duct is a long tube filled with ionic solution and its cross-section is partitioned by two elastic membranes. As sound pressure is delivered to the cochlear duct through the ossicles (middle ear bones), the pressurized fluid field interacts with the elastic cochlear partitions to create propagating waves along the membrane. This finding of cochlear propagating wave gave the Nobel Prize to von Bekesy in 1961, and it was theoretically explained in the early 1970s. However, recently there were several observations that cannot be fully explained with the existing single-layer travelling wave theory. Students will help us explore different modes of propagating waves in the cochlear duct. Through this, students will experience how fundamental vibrations and fluid mechanics principles are applied to an intriguing biomechanical subject.
Research Project: Better Batteries
Our group is focused on building better batteries to improve sustainability in the years ahead.
As a Xerox summer research fellow, you will be working on the non-aqueous electrochemistry of low melting point metals. Using liquid carbonates as polar aprotic solvents that can dissolve ionic salts like NaCl and KCl, we will decompose the salts by electroplating the sodium and the potassium to make liquid eutectic Na-K alloys. The resulting Cl2 gas will be released. Other low melting alloys such as Roses metal, Galinstan, and Fields metal that are comprised of metals with multiple valences will be examined with respect to their electrochemistry as catalysts for oxidation. It is also known that Na and K form strongly bonded intermetallics, creating a situation where the chemical activity of these species is depressed. This means that dissolution of Na+ and K+ into these molten metals and their nanoscale or molten oxides should create an unusually complex chemistry with the potential for reversible energy storage. It is already known that sodium ions will enter tin dioxide crystals to leave metallic tin which can then react with additional sodium to form intermetallics. Thus, an electrode of heavily oxidized tin, itself a semiconductor, has several mechanisms of exothermically accepting sodium ions. In short, these are candidate system for liquid metal batteries that operate near room temperature.
Interestingly, the densities of these materials are such that the eutectic Na-K alloy floats in propylene carbonate (PC) and naturally, the Pb-Bi-Sn alloys, being very dense sink creating the opportunity to have a molten metal battery that operates at low, if not room temperature.
Critical to these experiments is the ability to build containers and set ups to PREVENT any moisture or air from contacting the system, as the alkali metals are extremely reactive. The fellow working on this project would be responsible for building a cell and making initial measurements on the charge discharge behavior of such liquid metal batteries.