The research objective of this Faculty Early Career Development (CAREER) project is creating and understanding new metamaterials based on engineered, ordered granular crystals. Metamaterials are artificially composite systems, having their fundamental components (for example spherical grains) arranged in precise geometrical structures, that present properties not found in other natural systems. It will study how stress waves propagate in these new materials with experiments, and will develop numerical and analytical models to predict their behavior. It will research wave behavior at interfaces and will study the interplay of discrete effects and periodicity, disorder and localization, creating parallels with other physical phenomena. The understanding provided by studying these new materials will allow the creation of novel devices like tunable acoustic lenses, vibration absorbers, energy traps and actuators.
The societal impact of this work can be identified with the potential discovery of new systems that will affect everyday life (i.e. new acoustic methods for imaging/surgery, protective systems and signal transformation/redistribution in communication). It will also offer a great educational platform: creating and understanding new mechanical systems requires learning how to balance in depth fundamental physics with imagination, inspiring young generation to ?think out-of-the-box?. It will engage graduate, undergraduate, and high school students in several cooperative activities combining groundbreaking studies with the development of practical applications and patentable devices. It will particularly emphasize undergraduate education, motivating women and underrepresented groups toward science. The multidisciplinary aspects of this work will foster collaborations with other research institutions, with industry and with the broader community. The proposed plan will create two new academic courses and will organize summer schools with strong international emphasis.
The prime goal of this five-year integrated research and educational program was to establish an experimental mechanics group in the Graduate Aeronautical Laboratories (GALCIT) at the California Institute of Technology, to study highly nonlinear dynamical systems and structures. The research objective of this proposal was to develop a fundamental understanding of how stress waves propagate in highly nonlinear, heterogeneous, ordered media (granular crystals) and to exploit such knowledge for creation of new materials and devices. Building from well-studied local phenomena (i.e., the Hertzian contact interaction between particles), it created complex global systems with unprecedented mechanical properties. In the elastic limit, one? dimensional chains of particles solicited by dynamic impulses had been shown to present an interesting nonlinear response and support the formation and propagation of compact acoustic waves. This 5-year research project was aimed at continuing the experimental, computational and analytical studies of granular crystals in one-, two- and three-dimensions. The fundamental understanding obtained from our work, provided fundamental tools to design, fabricate and test new materials viable for engineering applications. It has made possible to engineer solid systems with tunable dynamic responses that can present resonances, dispersion and localization phenomena, acoustic band gaps and compact discrete waves. The resulting novel materials and acoustic devices presented can now be further investigated and developed to be used for a wide range of applications, including shock and vibration absorbers, noise insulating materials, earthquake protective systems, energy harvesting devices and acoustic lenses. In the course of the project, several patents were filed, both in the USA and internationally. Some of these patents have been used to fund a Start-up company (Solitonik), which develops acoustic testing systems for evaluating materials properties using nonlinear waves. The proposal supported, in part or in full, the scientific and academic training of 33 graduate students and post docs, as well as 31 undergraduate students and 4 high-school students, which were involved in research activities in the PI’s lab. In addition, the PI’s commitment to teaching extended from the classroom to the general public. The PI delivered numerous prestigious general audience lecture (e.g., the Caltech Watson Lecture Series), interviews culminating in a live appearance in CNN, to describe the findings related to the discovery of a new acoustic lens capable of generating sound bullets (see image). The research results obtained as part of this effort received extensive recognitions from both the academic community, as well as the general audience. Many of the high-profile research publications resulting form this work were highlighted in news media (CNN, Discovery Channel, Popular Science, MSNBC, etc.). Prof. Daraio and her students received numerous awards, including the Presidential Early Career Award (PECASE), which Prof. Daraio received in 2012 from President Obama.
