10/20/2021
By Sokny Long

The Francis College of Engineering, Department of Mechanical Engineering, invites you to attend a doctoral proposal defense by Joshua Morris on “Design, Characterization, and Analysis Methods for Low Frequency Mechanical Metamaterials.”

PhD Candidate: Joshua Morris
Defense Date: Friday, Oct. 29, 2021
Time: 10 to 11 a.m.
Location: Southwick 240 and virtually via Zoom. Those interested in attending via Zoom should contact joshua_morris@student.uml.edu and committee advisor, alireza_amirkhizi@uml.edu, at least 24 hours prior to the defense to request access to the meeting.

Committee Chair (Advisor): Alireza Amirkhizi, Associate Professor, Mechanical Engineering, UMass Lowell

Committee Members:

  • Christopher Hansen, Associate Professor, Mechanical Engineering, UMass Lowell
  • Alessandro Sabato, Assistant Professor, Mechanical Engineering, UMass Lowell
  • Farhad Pourkamali, Assistant Professor, Computer Science, UMass Lowell
  • Thomas Plaisted, Materials Engineer, Lab’s Project Lead, Army Research Lab

Brief Abstract:
Mechanical metamaterials (MM) are effective tools for attenuating wide frequency bands through the introduction of a microstructure with carefully tailored effective properties. Recent advances in MM design demonstrate that architectures with subwavelength periodicity and low-mass can have excitation frequencies at acoustic and ultrasonic frequencies. A design, analysis, and characterization toolset is demonstrated that accounts for practical bounds such as manufacturing limitations. Models with finite boundaries expose length and dispersion effects that afflict performance and predictive analysis. Examination of shear modes reveals coupling with longitudinal waves that can limit total attenuation though the MM. A characterization experiment is developed from these observations which employs a transfer matrix approach for the extraction of effective properties with no prior knowledge of the MM composition and geometry. Phase information from multiple measurement points allows the reflections to be separated, greatly reducing the needed length scale of the experiment. The accelerated design and characterization methods lend to optimization techniques capable of tuning performance through geometric or material variation. A reduced order model and automated decision-making algorithm explore the manufacturable design space for optimized attenuation performance and new MM applications, such as pass band type behavior. The proposed practical techniques serve to bridge the gap between theoretical MM analysis and their potential technological applications.

All interested students and faculty members are invited to attend.