Query: Defect engineering in thermoelectric materials: what have we learned?

Candidate papers:

abstract: Thermoelectric energy conversion is an all solid state technology that relies on exceptional semiconductor materials that are generally optimized through sophisticated strategies involving the engineering of defects in their structure. In this review, we summarize the recent advances of defect engineering to improve the thermoelectric (TE) performance and mechanical properties of inorganic materials. First, we introduce the various types of defects categorized by dimensionality, i.e. point defects (vacancies, interstitials, and antisites) dislocations, planar defects (twin boundaries, stacking faults and grain boundaries) and volume defects (precipitation and voids) Next, we discuss the advanced methods for characterizing defects in TE materials. Subsequently, we elaborate on the influences of defect engineering on the electrical and thermal transport properties as well as mechanical performance of TE materials. In the end, we discuss the outlook for the future development of defect engineering to further advance the TE field.
author_names: Tyler J Slade

Lei Hu

Xian Yi Tan

Yubo Luo

Zhong-Zhen Luo

Jianwei Xu

Qingyu Yan

Mercouri G Kanatzidis
title: Defect engineering in thermoelectric materials: what have we learned?
venue: Chemical Society reviews
year: 2021

abstract: For decades, zone melted Bi2Te3 based alloys have been the most widely used thermoelectric materials with an optimal operation regime near room temperature. However, the abundant waste heat in the mid temperature range poses a challenge; namely, how and to what extent the service temperature of Bi2Te3 based alloys can be upshifted to the mid temperature regime. We report herein a synergistic optimization procedure for Indium doping and hot deformation that combines intrinsic point defect engineering, band structure engineering and multiscale microstructuring. Indium doping modulated the intrinsic point defects, broadened the band gap and thus suppressed the detrimental bipolar effect in the mid temperature regime; in addition, hot deformation treatment rendered a multiscale microstructure favorable for phonon scattering and the donor like effect helped optimize the carrier concentration. As a result, a peak value of zT of ~1.4 was attained at 500 K, with a state of the art average zTav of ~1.3 between 400 and 600 K in Bi0.3Sb1.625In0.075Te3. These results demonstrate the efficacy of the multiple synergies that can also be applied to optimize other thermoelectric materials. A popular material for converting heat into electricity can now operate at elevated temperatures associated with industrial machinery. Bismuth tellurium is a thermoelectric alloy that works at room temperature and finds use in refrigeration and powergeneration, but much waste heat is created in the so called middle temperature range of 100 300 degrees Celsius. Tiejun Zhu from Zhejiang University and colleagues doped indium atoms into bismuth tellurium to provide a balance to the excess, thermally activated charge carriers that normally materialize when this alloy is heated to middle temperatures. Hot deformations of the alloy during fabrication introduced missing atom defects and micrograins that worked together with dopants to scatter heat transporting phonon waves and optimize carrier concentrations. Thermoelectric and X ray testing revealed that the doped alloyhad a higher working temperature and better mechanical properties. We herein report a synergistic optimization procedure that combines point defect engineering, band structure engineering and multiscale microstructuring in p type (Bi,Sb)2Te3 thermoelectric materials by Indium doping and hot deformation. As a result, a peak value of zT ~1.4 was attained in Bi0.3Sb1.625In0.075Te3 at 500 K, along with a state of the art average zTav of ~1.3 between 400 and 600 K. These results demonstrate the efficacy of the multi synergies that can also be applied to optimize other thermoelectric materials.
author_names: Zhaojun Xu

Haijun Wu

Tiejun Zhu

Chenguang Fu

Xiao-hua Liu

Lipeng Hu

Jian He

Jiaqing He

Xinbing Zhao
title: Attaining high mid temperature performance in (Bi,Sb)2Te3 thermoelectric materials via synergistic optimization
year: 2016

abstract: Numerous endeavors have been made to advance thermoelectric SnTe for potential applications. Effective strategies focus on the manipulation of transport properties, including valence band convergence, resonate state, and defect engineering. It has been demonstrated that alloying trivalent Bi or chalcogenide SnSe alone in SnTe can trigger an inherent enhancement of thermoelectric performance. However, what the critical role in the transport valence band co doping Bi and Se in SnTe plays is still unclear. Particularly, fully evaluating the effect of band convergence on the carrier concentration dependent weighted mobility, which dominates the electronic performance, is primary and essential for designing excellent thermoelectric materials. Here, we report that Bi doping in SnTe SnSe alloys can derive a distinct decrease in the energy offset between the two valence bands, thus improving the density of state effective mass by only slightly deteriorating the mobility. The well established theoretical model reveals that the Bi doping induced band convergence and the optimized carrier concentration actually enhance the weighted mobility, contributing to the improvement of electronic performance. Moreover, the Debye Callaway model demonstrates the origin of the reduced lattice thermal conductivity. The present results confirm the potential of transport engineering in promoting thermoelectric performance.
author_names: Xuming Guo

Zhiyu Chen

Jingyou Tang

Fu Chun Zhang

Yan Zhong

Hangtian Liu

Ran Ang
title: Thermoelectric transport properties in Bi doped SnTe SnSe alloys
year: 2020

abstract: R Trailblazer. Maverick. These are adjectives often used to describe celebrities and politicians, but rarely attributed to scientists. However, in the case of Mildred Dresselhaus, who died earlier in 2017 at age 86, these superlatives were spot on. Dresselhaus, known as the "queen of carbon," was a pioneer in the fi eld of nanoscience. She carried out a series of experiments that led to a fundamental understanding of the electronic structure of semi metals, especially graphite, along with carbon nanotubes and graphene. A Massachusetts Institute of Technology (MIT) professor emerita of physics and of electrical engineering and computer science, she was also well known for being the fi rst to exploit the thermoelectric effect at the nanoscale, effi ciently harvesting energy from the temperature differences in materials that conduct electricity. The co author of eight books and some 1700 papers, she supervised more than 60 doctoral students in her 50 years on the MIT faculty. To those in the materials science and engineering community, she was a prolifi c and innovative scientist, a well loved mentor, and a role model to hundreds of women (and men) in science and engineering. "Professor Dresselhaus embodied what a scientist should be: bold, pioneering, kind, and dedicated to making the world a better place," says Jennifer Dionne, an associate professor of materials science and engineering at Stanford University and 2017 MRS Outstanding Young Investigator Award recipient. "She was a huge inspiration for me, and I hope we all can help carry on her legacy for years to come." Alongside Dresselhaus's outstanding research accomplishments was her long standing commitment to promoting gender equity in science and engineering. In 1971, she and a colleague organized the fi rst Women's Forum at MIT to discuss the roles of women in science and engineering. She received a Carnegie Foundation grant in 1973 to support her efforts to encourage women to enter traditionally male dominated fi elds of science and engineering. For a number of years, she led an MIT seminar in engineering for fi rst year female students designed to build their confi dence. In 2015, Dresselhaus delivered the keynote address at a three day workshop for female graduate students and postdocs considering careers in academic research, "Rising Stars." Her remarks, on the importance of persistence, described her interactions with Nobel laureate Enrico Fermi during morning walks to the laboratory at The University of Chicago. Previously, she said during a 2012 interview with the Kavli Foundation, "What I learned from him [Fermi] was the importance of having a very broad understanding of science, so you can take advantage of new science opportunities so that you can really serve society." In comparison, Dresselhaus noted in the same interview, which she gave when she received the Kavli Prize, "my advisor didn't know what I was working on until two weeks before I submitted my PhD thesis. He never talked with me because he didn't think women should be in science." Her primary message to the workshop attendees was persistence. "It was what you did that counted, and that followed me through life," she said.
author_names: Aditi S Risbud
title: Millie Dresselhaus: Our science celebrity
year: 2017

abstract: Our colleague and friend, Fu Zhai Cui, has decided to step down from his position as Co Editor in Chief of Biomedical materials (BMM) at the end of the year due to other commitments. BMM would not be the journal that it is, and we two would not have served as participants in its development, were it not for Fu Zhai. It was his vision and hard work that gave birth to BMM. Fu Zhai's e mail to Dr Mingfang Lu at IOP Publishing in June of 2005 initiated the process that led to the new journal being established. Underscoring the importance of such an endeavor, Fu Zhai noted that biomedical materials and tissue engineering and their applications had been rapidly developing in recent years and the trend was likely to continue for many years, that there were relatively few journals capable of handling these subjects, and even fewer journals that faced East as well as West. There are several features of Fu Zhai's professional life which have added to the character of BMM and which reflect, and perhaps even help to explain, his country's remarkable development: resourcefulness, innovation, and drive. When we first met Fu Zhai at Tsinghua University more than 15 years ago, the facilities available to him were notably limited, especially in comparison to those that we had access to at our respective institutions. There was almost a complete absence of biomaterials related journals at Tsinghua, prompting us to consider ways in which we could send our surplus issues to him. But Fu Zhai made the most of what resources he did have and directed his students in important and productive research that was published in leading English language journals. Fu Zhai never let his thinking and efforts be constrained by limited resources. The projects undertaken by Fu Zhai and his students at Tsinghua have always displayed engineering innovation born of scientific understanding. He is either investigating biomaterials for new applications or taking novel approaches for the production of new types of biomaterials. In both cases, his work is founded on knowledge drawn from an array of scientific studies and his success is due in large part to the multidisciplinary teams that he assembles. For example, Fu Zhai's group was one of the first in the world to employ biomaterial implants (hyaluronic acid hydrogels) for the treatment of brain defects, thus pioneering the area of brain tissue engineering. For other biomaterials applications, such as bone tissue engineering, Fu Zhai took the biomimetic approach of producing mineralized collagen scaffolds. But he did so in the novel way of co precipitating collagen and hydroxyapatite to favor self assembly and a hierarchical microstructure. Fu Zhai's insights into the mineralization process were derived in part from his own studies with Heng De Li, one of the pioneers of biomineralization. Biomaterials researchers frequently think about the potential clinical applications of their developments, but rarely find or make the opportunity to commercialize their products. Fu Zhai acted on translational research before that term entered the researcher's lexicon. He orchestrated the compilation of pre clinical data and engaged his clinical colleagues in the necessary human trials to demonstrate the safety and efficacy of his mineralized collagen scaffolds for spine fusion and other applications. After having been approved by the China medical device regulatory process, the product is now being used in clinics. A journal like BMM would like to be known for publishing papers which exemplify some of the same traits that Fu Zhai has demonstrated in his own career: resourcefulness, innovation, and clinical utility. Moreover, Fu Zhai has shown by his own example why he was so right to have seen the importance of establishing a truly international biomaterials journal. We both look forward to continuing in the capacity of Co Editors in Chief, with the confidence that comes with knowing that our friend, Fu Zhai Cui, will be available to advise us.
author_names: In-seop Lee

Myron Spector
title: Fu Zhai Cui's vision and leadership
year: 2010

abstract: Including students in special practice curriculums, such as the one initiated by University of Agricultural Sciences and Veterinary Medicine Cluj Napoca, they become more aware of the entire process in the food industry, from the acquisition, reception, management of primary and auxiliary materials, to the importance of hygiene, protective equipment, the temperature and operating mode and the sales of the final products. The aim of the study is to evaluate the impact of practical train ing and its role in transforming students in future eng ineers better prepared for the labor market. Introduction While the university remains a cultural instituti on, creating value, not for a moment forget that the purpose for which it r eceives funding or that students pay taxes is not to form people of culture, but to provide speci alists in certain economic and social fields (Mihailescu, 2007) The aim of the study is to evaluate the impact of p ractical training for Food Science and Technology students in terms of overall impact on competences in the European food industry to produce safe, high quality and varied f oods that meet the needs of consumers. Materials and Methods. For the study we have analyzed and evaluated the s tudents during their practice programs. We had short discus sions with them individually about their likes and dislikes related to the individual progra ms. Students of the Faculty of Agriculture from UASMV Cluj Napoca are performing practice programs during the 2nd and 3rd year of ba chelor program, through fully equipped Pilot plants such as Milk dairy products, Meat and meat products, Brewery Plant and Bread bakery belonging to the Food Engineering Department. In these pilot plants the students are trained by technicians and academic staff to partic ipate in food technology production. This is important because the young students learn about al l the processes, becoming responsible in turn with: evaluate the raw materials inputs, purch asing, receiving and controlling the production in authorized laboratory, HACCP monitoring, labeling, delivery, sale. All these play an important role in supporting the knowledge accumulated in courses and laboratories and providing an overview on produ ction and its problems, on responsibilities that they might have as Engineers Food control specialist. They improve their competences learning these things by own, inc luding methods to correct problems or manufacturing defects that can occur. This is important because in the current economy we should check students especially at the output, not just at the input, ho w they are prepared for the labor market. The practical training is intended to improve the old w ay of teaching. Each teacher is normally concerned only with his discipline. Teachers do not gather together to tell the student "Look in your job, you do this and that. For this, take w hat you learned from the field X and combine what you learned in the field Y and find a solution Our education is focused towards
author_names: Andrei Borsa

Sevastita Muste

Maria Tofana

Andruta Elena Muresan
title: The impact of practical training and professional development for students in enhancing European competences in Food Science and Technology
year: 2012

abstract: Nature is the largest laboratory that ever existed and ever will. In addressing its challenges through evolution Nature tested every field of science and engineering leading to inventions that work well and last. Nature has "experimented" with various solutions and over billions of years it has improved the successful ones. It has always served as a model for mimicking and inspiration to humans in their efforts to improve their life. Adapting mechanisms and capabilities from nature and using scientific approaches led to effective materials, structures, tools, mechanisms, processes, algorithms, methods, systems and many other benefits. The subject of copying, imitating, and learning from biology was coined Biomimetics by Otto H. Schmitt in 1969. This field is increasingly involved with emerging subjects of science and engineering and it represents the studies and imitation of nature's methods, designs and processes. Biologically inspired technologies are making it possible to consider developing such devices as prosthetics that feel and operate like the "real thing" as well as engineering robots that look and behave as human and animals. Mimicking Nature involves many challenges and requires significant technology advances. To promote advances in the field of electroactive polymers (EAP) that is know as artificial muscles, the author posed in 1999 an armwrestling challenge for a match between human and a robotic arm that is driven by these materials. A contest is now held annually and it is providing a measure of the advances in the field of EAP and the ability to mimic the performance of muscles. A review will be given of selected areas that were inspired by nature with emphasis on EAP and an outlook for potential future development in biomimetics. Program Guide and Abstracts 6 Blackledge, Todd A. Spider silk: a 400 million year experiment in materials science Department of Biology, University of Akron, Akron, OH 44325 3908, USA Abstract: Spider dragline silk has a number of enticing properties for the production of biomimetic fibers, in particular high tensile strength and extreme toughness. However, silk also plays an integral role in the ecology of spiders including protection against predators or the environment, capture of prey, dispersal, communication, and reproduction. Furthermore, orb weaving spiders can produce at least seven different types of silk that are composed of different sets of proteins. The material properties of these silk fibers result from how the constituent proteins of silk fibers are assembled and Spider dragline silk has a number of enticing properties for the production of biomimetic fibers, in particular high tensile strength and extreme toughness. However, silk also plays an integral role in the ecology of spiders including protection against predators or the environment, capture of prey, dispersal, communication, and reproduction. Furthermore, orb weaving spiders can produce at least seven different types of silk that are composed of different sets of proteins. The material properties of these silk fibers result from how the constituent proteins of silk fibers are assembled and interact with one another and are likely to have been shaped by natural selection on the ways in which each silk interacts with the environment. Therefore, the biomechanical study of spider silk can potentially link together research ranging from the evolution of silk genes through the ecological function of webs or other silk structures. Here, I discuss how research on the biological diversity of silks spun by spiders can facilitate efforts to synthesize biomimetic fibers. Program Guide and Abstracts 7 Bras, Bert. Inclusion of biologically inspired design into mechanical engineering design classes School of Mechanical Engineering, Georgia Institute of Technology Abstract. In this talk, we will present our experiences with including biomimetic In this talk, we will present our experiences with including biomimetic principles into mechanical engineering design classes. The goals are 1) to expose engineering students and practitioners to biomimicry and 2) to gain insight into the efficiency and effectiveness of using biomimetic approaches to solving engineering design problems. Specifically, our experience with ME 4182 Capstone Design will be highlighted. The initial experiment consisted of including biology undergraduate students as project consultants for the engineering design teams. Experiences from the engineering students (through surveys and informal feedback) biology students and faculty will be presented. Selected projects will be highlighted to illustrate the effectiveness, shortcomings, and barriers to biomimetic approaches. Lessons learned and suggestions for future experiments, implementations and expansion will be given. Program Guide and Abstracts 8 Clark, Robert. Biologically Inspired Materials and Material Systems Duke University. Abstract. It is clear that our biological and medical community is now at a point of incredible opportunity. The collective biological sciences (biological, biophysical, biochemical, biocomputational, and biomedical) have generated a plethora of information regarding complex biological systems, especially at the microcellular and nanomolecular levels. It is time to bring these research advances into the core curriculum for all students interested in careers that require a more detailed and mechanistic understanding of the biological world, disease, and medicine. It is clear that our biological and medical community is now at a point of incredible opportunity. The collective biological sciences (biological, biophysical, biochemical, biocomputational, and biomedical) have generated a plethora of information regarding complex biological systems, especially at the microcellular and nanomolecular levels. It is time to bring these research advances into the core curriculum for all students interested in careers that require a more detailed and mechanistic understanding of the biological world, disease, and medicine. We recognized several years ago that a more rigorous mapping of engineering onto the biological sciences might yield more mechanistic information about nature's own technologies. Our approach is to recognize that Biology (Nature) itself can be viewed as an "engineered system" and that much of Biology's systems function (and dysfunction) at cellular (micro) and molecular (nano) scales. At these scales we explore a more formal "Mapping of Engineering onto Biology," for both health and disease, and new technological innovation. This defines our approach towards bioinspiration. Framing this approach, we recognize: (1) Biology as a series of cellular products, nano components, energy consuming processes, and functioning devices that are "manufactured" with a limited set of materials, that nevertheless overcome the same physical and chemical limitations (force, temperature, pressure, E fields, time, solubility, diffusion, etc. as other inorganic materials, but do it to support life; (2) disease, either due to defects in manufacturing, (genetic based) or toxic insult (environmental based) as an opportunity to detect and characterize what has changed compared to the "normal state" (3) medicine, as a tool for prevention or cure, again at the gene based manufacturing level, or by drug or biocompatible prosthetic intervention. This mapping framework is directed towards organizing and generating extensive information that at present is missing concerning the physical and chemical properties of cellular, intracellular, and membrane components that will lead to a greater understanding of how the molecular machines that drive healthy processes are built and function. From this knowledge, we can then understand failures in these components that lead to disease or gain inspiration in the design of new materials and devices for humanity. Such an approach places existing (and future) knowledge, especially of cell and molecular biology, fairly and squarely in the realm of engineering materials and design methodology. It is, then, a formal Engineering Design Methodology, and a better understanding of the complex relationships between cellular and molecular material's composition, structure, properties and performance (CSPP) that is the cornerstone of our reverse and forward engineering exercises motivated by basic questions in the biological sciences. The Center for Biologically Inspired Materials and Material Systems at Duke University was founded to establish an integrative educational and research environment for students, faculty, and staff. The structure of the Center, mechanisms for fostering research and collaborative educational activities, and a few examples of results from these efforts will be
author_names: Kartik Sundar

Lena H Ting
title: Program Guide and Abstracts GENERAL INFORMATION All sessions will be held in Auditorium 236 in the
year: 2006

abstract: Pattern formation and evolution in liquid crystal polymers is studied in both static situation as well in applied magnetic and flow fields. Observations of nucleation and growth of nematic domains in an isotropic matrix under static conditions were used to establish the origins of the most common types of point defects. The patterns describing the director field distribution were revealed using a solidification induced banding method on quenched samples. At a low percent conversion of isotropic to nematic, the defect density is dominated by domain density and by anchoring conditions between the nematic domains and the isotropic matrix. At higher percent conversions, the defect density is controlled by domain domain interaction events. The defect density rises as the domains nucleate and impinge but decreases after the generation of defects of negative strengths and an annihilation process begins. Larger domains created in the coalescence process can then grow and impinge and continue defect generation via domain interaction. The absence of negative strength defects during the preimpingement phase indicates these defects arise solely due to the domain domain coalescence during the growth process. The subsequent effects of both magnetic fields and flow fields on defect structure are also examined. With respect to the former, a solution of the director orientation distribution function is presented for N6el inversion walls created in a liquid crystal by application of a magnetic field. The theoretical model is used to simulate director trajectories across walls as a function of both the elastic anisotropy and the orientation of the wall with respect to the applied field. The gradual transition of the defect structures from Neel bend walls to Neel splay walls as the angle between the wall and the magnetic field is varied is also presented. Experimental micrographs obtained via atomic force microscopy on a thermotropic liquid crystalline polymer are used to test and evaluate the theoretical model. Visualization of director textures using the lamellar decoration technique shows the theoretical and experimental results to be in good agreement. The results were used to determine that the sample had an elastic anisotropy of 0.5, implying that k, 3k 33 The effects of flow on the disclination textures were studied with an optical shearing cell. Flow visualization experiments were used to study curvature driven motion in disclination loops created during flow. Theories of differential geometry were used to predict the way the line curvature should evolve over time. Theoretically the relationship between velocity and local curvature is linear. Experimentally, deviations from the theory sometimes occurred due to forces of attraction between nearby disclinations. Even though disclination evolution in both small molecular and polymer liquid crystals obeyed similar physical laws, several significant differences were observed. Disclinations in the polymer systems generally displayed initially highly contorted contours. In the small molecule liquid crystals however, the loop contours consistently displayed very simple shapes. In the polymer system, the complex line shape reflects the many prior loop loop coalescence events due to the greater density of loops than in the low molar mass liquid crystal. Moreover, the reduction of regions of high loop curvature is inherently slower in the polymer liquid crystal due to the higher viscosity of the medium. In addition, the motion of the disclination contour may also be affected by a possible reduction in the mobility of disclinations due to the presence of lower molecular weight components at the defect core which themselves must diffuse along with the line defect. Thesis Supervisor: Edwin L. Thomas Title: Morris Cohen Professor of Materials Science and Engineering Acknowledgments: It is hard to believe that my 8+ years at MIT are coming to an end! Before departing there are many people I would like to thank. First I would like to express my appreciation to my advisor Professor Edwin Thomas, for his enthusiasm and support over the years. His excitement for scientific research made an indelible impression on me when I came to him as a sophomore in September of 1989 to inquire about undergraduate research opportunities in his group. Since that time he has taken great care in my professional development, something that has added significantly to my positive experience at MIT. As I reflect on the last 8 years I have worked for him, I am beginning to understand the advice given to me by one of his former students. One person in particular suggested that if I wanted to start research as a undergraduate I should "go work for Ned Thomas" That was it. No "ifs" "ands" or "buts" just "do it" When I look back now, if I had to do it over again I wouldn't have done anything differently. The lessons I have learned from Ned about academics, research, and group management are invaluable and will serve a foundation for some day in the future when I start my own research group. I am also very grateful to Professor Michael Rubner for his support, especially of my desires to become involved with teaching. The first time we worked together was in the Fall of 1992 when I was a grader for his course in Polymer Chemistry. He gave me his full support when I expressed an interest in also running review sessions and holding office hours in addition to my regular duties. I was honored when he asked me to become a fulltime graduate teaching assistant for him in the fall of 1995. The marvelous example he set in the classroom is something to which I aspire. His continued advice over the years is something that I have appreciated a great deal. There are many other people that have been instrumental in my career at MIT. I am very grateful to Professor Robert Rose for his guidance and support over the years. He has been one of the most influential professors I have interacted with and has been instrumental in my decision to become a professor. I would also like to thank the members of my committee: Professors Robert Armstrong, Ken Russell and Chris Scott for their advice and suggestions. Professor Sam Allen was also very instrumental in my research on curvature driven motion of disclination loops. Scott Clingman (Cornell University, Professor Chris Ober's group) was a main driving force in this research through the superb polymers he synthesized for me. I don't know what I would have done without him. I owe you one Scott! I also could not have done this without the continual support of my friends and family. I would like to thank Leslie Lawrence, Marshall Hughes, Dongsik Yoo and Barbara Dirsa for their friendship over the years. A big thank you is also due to Kevin McGinty, my piano teacher, who was not only a superb teacher but a good friend as well. He was one of the main people who helped me maintain my sanity while finishing my degree. The love and support of my parents, Paul and Lynda Gunther, helped pull me through the difficult moments. To all my brothers and sisters: Jordan, Jenessa, Jilenne, Julia, Jansen, Justus, and Jesse..yes! I am now Dr. Gunther! I am deeply indebted to my brother Jordan who spent nearly one week of his summer vacation helping me finish the final corrections on my thesis. I couldn't have done it without you! Finally, I would like to thank the Lord for his love and blessings and without whom none of this would have been possible.
author_names: Jane Davis Gunther
title: Defects in liquid crystal polymers their origins and behavior in magnetic and flow fields
year: 1997

abstract: Well, the theory of scattering of elastic waves is difficult. I don't want to minimize that, but I thought I might make a few diversionary introductory remarks. My first reference will be the Los Angeles Times of today, the astrology column. It advises those born under the sign of Leo to choose their words carefully to avoid trouble. That happens to be applicable to yours truly. I hope I do it. Disciplines Materials Science and Engineering Structures and Materials This 3. ultrasonic scattering 1 is available at Iowa State University Digital Repository: http:/lib.dr.iastate.edu/ cnde_yellowjackets_1975/21 BASIC tHEORY OF ULTRASONIC SCATTERING BY DEFECTS: NUMER ICAL STUDIES FEATURES FOR EXPERIMENTAL APPLICATION* i* J. A. Krumhansl Cornel l University Ithaca, New York Well, the theory of scattering of elastic waves is difficult. I don't want to minimize that, but I thought I might make a few diversionary introductory remarks. My first reference will be the Los Angeles Times of today, the astrology column. It advises those born under the sign of Leo to choose their words carefully to avoid trouble. That happens to be applicable to yours truly. I hope I do it. The second technique which has been found useful in the unruly audiences at Cornell is to show your last slide first or you'll never get there. So, that's what I want to do. Figure l (see Fig. 1 of the Appendix) is a threedimensional plot of elastic wave cross sections which we have calculated from 0 to 180deg as a function of ka. This is for a longitudinal plane wave incident on a spherical cavity in titanium, and this is the differential scattering cross section for the transverse component. The calculation is for all ka from 0 to 6. The experimentalist can, for example, if he prescribes the frequency spectrum, which is, of course, a range of ka, take a cut across this with his computer and estimate the total difference across section for a transversely polarized receiving transducer, with this incident longi tudinal wave We're cost conscious at the un iversity. This data presentation costs about a dollar and took three mi nutes. Now, given the end of the story, I don't know whether anybody is interested in my filling in the details but that's what I'm here for. So, let me proceed. We're doing this in the solid state theory group at Cornell. The people listed in the Appendix are the participants. We began in September 1974. Jim Gubernatis really deserves special mention for giving technical leadership to the program and seeing that it moved, and particularly for supervi sing a number of the computations. Without this help I don't think we would have gotten where we are. The rest of us are active participants. One l ast bit of perspective: the cost of this total program for this year is about that of two Tektronix scopes with ordinary software. It' s an interesting academic experiment. Can some denizens of a university theoretical physics group interact with engi neers? We've had a good time, and also learned a lot by interactions with Prof. Pao in the Cornel l Mechanics Department during the course of the past year. We tried to look around and see where we might make a contribution in the overall NDE program and the contribution we chose to make was to update the theory of scattering, and we found that it was sort of a cold water shock when you move from the simplicity of quantum mechani cs with its scalar fields To supplement th1s paper wh1ch was presented at the symposium, a technical surrmary article, "Theory of the Scattering of Ultrasound by Flaws" by J. E. Gubernatis, E. Domany, t~ Huberman, and J. A. Krumhansl, is incorporated as an Appendix. t Research sponsored by ARPA/AFML Center for Advanced NDE.
author_names: James A Krumhansl
title: Basic Theory of Ultrasonic Scattering by Defects: Numerical Studies and Features for Experimental Application
year: 1975

abstract: Let me begin by saying that this is part of a program which is very much complementary to and is helped by the experimental program; so I'll repeat, in part, some of the overview comments that Bruce Thompson made this morning. We've regarded our role as one of trying to plug into the overall program those aspects of the theory of elastic wave scattering which can be developed in a utilitarian way in terms of modern analytical and computational techniques, in a form which I hope can be useful in signal processing, interpretation, design of experiment, etc. To outline our point of view, I'm going to first give a survey of what we have been doing and then give some of the results. It's rather shocking to think of the amount of money that goes into an experimental program and its interpretation, if the interpretation is done in terms of acoustic or scalar wave scattering theories, when the differences from proper elastic theory can be as great as those which Bruce Thompson pointed to this morning. Disciplines Materials Science and Engineering This 9. defect characterization: fundamentals is available at Iowa State University Digital Repository: http:/lib.dr.iastate.edu/ cnde_yellowjackets_1976/33 INTERPRETATION OF ULTRASONIC SCATTERING MEASUREMENTS BY VARIOUS FLAWS FROM THEORETICAL STUDIES J. A. Krumhansl Cornell University Ithaca, New York Let me begin by saying that this is part of a program which is very much complementary to and is helped by the experimental program; so I'll repeat, in part, some of the overview comments that Bruce Thompson made this morning. We've regarded our role as one of trying to plug into the overall program those aspects of the theory of elastic wave scattering which can be developed in a utilitarian way in terms of modern analytical and computational techniques, in a form which I hope can be useful in signal processing, interpretation, design of experiment, etc. To outline our point of view, I'm going to first give a survey of what we have been doing and then give some of the results. It's rather shocking to think of the amount of money that goes into an experimental program and its interpretation, if the interpretation is done in terms of acoustic or scalar wave scattering theories, when the d1fferences from proper elastic theory can be as great as those which Bruce Thompson pointed to this morning. Now, there certainly has been a tremendous amount done on elastic wave scattering. There are some methods, however, which have now become practical because of the advances in our understanding of an analytical techniques and computers. The work I'm reporting on has been done primarily by Jim Gubernatis of Los Alamos, Eytan Domany and others at Cornell, and myself. The experimental work we have interacted strongly with is that of Tittmann at Rockwell and Adler of Tennessee. We have received stimulus from the ARPA MRC, Materials Research Council program, arid from Tony Mucciardi at Adaptronics, and from the Rockwell program in general. As I said, our program objective is to be utilitarian, and utilitarian means not necessarily simple. The diagnostics of ultrasonic flaw detection involve two aspects: where is the defect (the existence of a defect) and what is the defect? Perhaps the real justification of the extent to which we try to carry the theory is in this latter regard, doing everything we can to squeeze out whatever characteristic information we can from ultrasonic scattering data. Let me briefly outline the theoretical methods. A traditional method with which most of us are familiar for problems of this sort is to use normal mode expansions. Now, in textbooks and teaching,this method is useful, but the geometries chosen are always spheres. Once you go beyond spherical harmonics you find that,if not hopeless, life is at least extremely difficult. Programming some of the calculations is cumbersome, and non intuitive. At least some of the training in modern theoretical physics has enriched 164 the bag of tools which can be used, particularly with integral equation methods which have the advantage that one plugs in information which can be related rather directly to the experimental featur"es of the si.tuation in question. They are also subject to approximation techniques such as iterationtry something, improve it ;try it again, improve itprinciple. With brute force large scale computers, one can hope to do some of these things inexpensively. Indeed, there are standard approximation methods that we use in nuclear scattering; Born approximation, variational methods, distorted wave methods and so forth,which provide a hunting license of sorts to see what one can do in the present context. Our first year's program, 1975, was largely concerned with establishing the theoretical base; the Cornell Materials Science Center report number 2654 presents a summary of the general theory, and provides detailed computer results for the Born approximation. The Born approximation simply inserts incident field displacement and strain at appropriate points in the integral formula as needed. This really doesn't solve the integral equation, but it's a first step, and has been very useful as an exploratory device. As the program has progressed we have tried to express the results of such a calculation concisely, and Jim Gubernatis has found that it's particularly useful to define something called an "f vector" which wi 11 give complete scattering data. It depends directly on the changes in material parameters, ~p, and directly on the changes in the elastic constant, ~c. In addition, we require a knowledge of the displacement and strain fields in the flaw region We are now in the process of using this approach. to examine carefully exact 1 imi ti ng behavior for low frequency. By utilizing all the information present in the longitudinal, transverse, and mode converted scattering,material parameter changes can be determined over and above any imaging or echo detection. Hopefully, microprocessors can eventually make the on line analysis cheap and easy. Now, I'd like to run through the main results we have obtained at Cornell during the past year. My colleagues have been Eytan Domany, Paul Muzikar, Steve Teitel, Dave Wood, and Jim Gubernatis, whose support came from Los Alamos. 1. General Summarv of 1975 76 Research Last year we presented an integral equation formulation of the ultrasonic scattering problem. We also compared the results of the Born approximation with exact results for spherical scatterers. From that study we learned much about the regions of applicability and validity of the Born approximation. In this year's research we have continued the theoretical workl, but placed special emphasis on attempts to make contact with the experimental situ~ tion for laboratory flaws prepared at Rockwell in determined geometries (a step closer to the "real world" In particular, we tried to identify some general features or indices that might be useful in evaluation of scattering data for NOT. In the course of many fruitful interactions with the experimental groups at Rockwell and Tennessee we learned about the needs and the formats most convenient for them, and developed a library of computer programs for various scattering situations. We have also investigated further approximations (static, quasi static) which may be better in certain limits, and started to compute and compare them with exact and experimental data. Finaliy, we h;;ve begun work to implement scattering theory for defects other than holes or inclusions, particularly scattering by flat cracks. We proceed with details of the studies. I I. Indices for NDT We have considered scattering by defects of two shapes, spheroids and cylinders, to seek information that indicates the deviat1on of the scatterer from spherical symmetry. The geometry of both scatterers can be characterized by a ratio b/a (see Fig. 1)
author_names: James A Krumhansl

Eytan Domany

P Musikar

Stephen Teitel

David Wood
title: Interpretation of Ultrasonic Scattering Measurements by Various Flaws from Theoretical Studies
year: 1977