John Burkhardt

Jitterbot: A Mobile Millirobot Using Vibration Actuation

Microrobotics is a rapidly growing field with promising applications in microsurgery and microassembly. A challenge in these systems is providing power and control signals to the robot. This project explores crawling robots that are powered and controlled through a global mechanical vibration field. Structures within the robot will cause it to respond to particular frequencies with different motion modalities. A prototype, dubbed the “jitterbot”, was cut out of a 0.75 mm sheet of steel using electric discharge machining (EDM), and has a total footprint of approximately 30 mm × 20 mm in the xy-plane. The “robot” has a tripod body (8 mm × 16 mm) with three small legs, and two suspended masses that are designed for specific resonance frequencies. The robot was tested on a plate that was vibrated vertically at frequencies ranging from 20 to 2,000 Hz. For particular resonant frequencies, the robot moves forward and turns in either a clockwise or counterclockwise direction. Finite element modeling confirms that the mechanism for motion is a rocking mode that is influenced by two arms that are suspended mass springs tuned to different frequencies. This lays the groundwork for further miniaturization.

The Effectiveness of Additional Class Contact Time on Student Performance in Statics

The effect of additional class contact time on student performance in statics is investigated. Comparisons are made between the final exam grades and final course grades of at-risk students placed on two versions of the same statics course. A standard version of the statics course meets for three hours per week over the course of a 15-week semester, while a second version meets for four hours per week. During the 11-year timeframe covered by this study, the four-hour statics course has been populated by students identified as ‘at risk’ using an informal screening procedure. For comparison purposes, using the same enrollment data, a second group of at-risk students was identified from within the standard three-hour course using a more formal screening procedure based on logistic regression. A comparison between the two groups shows that the extra contact hour had a minor, statistically insignificant effect on final exam and final course grades.

Student teams and jigsaw techniques in an undergraduate CSE project course

The use of jigsaw techniques in a multidisciplinary, project-oriented, introductory computational science and engineering course is described. The course revolves around the study and completion of four projects, each devised and taught by a team of faculty drawn from several departments. This paper discusses the execution of a single project in the course and the use of a jigsaw team structure in its execution. Jigsaw techniques are implemented by forming project teams composed of members with designated areas of expertise. Project team members with common areas of expertise are then formed into secondary expert teams. The project team maintains responsibility for completion of the project while the expert teams are responsible for mastering their designated areas as well as developing a strategy for teaching the members of their project team what they have learned. All students are evaluated equally in each area of expertise. The effectiveness of the jigsaw technique is determined through the use of peer, group, and individual assessment.

Transport in multi-coupled Anderson localizing systems

Abstract The time-domain behavior of a multi-coupled disordered system is studied by numerical simulation. A two-dimensional mesh with periodic boundary conditions in a short, circumferential, direction, and fixed boundary conditions in a long, axial, direction, is subjected to a tone-burst load on the central ring. The resulting narrow-band process has an energy density which evolves in space and time. On short time scales it diffuses classically. On long time scales the transport ceases and the profile approaches an exponential. Localization lengths and transport time scales are compared with earlier predictions.

The Center for Computational Science and Engineering at the U.S. Naval Academy

There is a strong and increasing desire for more multidisciplinary activities within mathematical, scientific and engineering education. This has found particularly strong voice in the rise of graduate programs in Computational Science and Engineering. The growth of such programs and centers is only just beginning to take root in the undergraduate curriculum. In this paper, the authors describe the proposal, founding and development of a Center for CSE at an undergraduate school. The center grew from an initial proposal to planning and running its first multidisciplinary course in one year. In the paper, they describe the chronology of this process as well as giving some pointers on how to go about creating the right environment for such a development in undergraduate colleges. The development of a special team-taught multidisciplinary course is also described.

Spectral statistics in damped systems: Diffuse field decay curvature for materials characterization

A new nondestructive technique is proposed which exploits the unique decay characteristics of diffuse fields in nonproportionally damped systems. A power-law decay model is derived and advanced as the basis for the inverse estimation of both the strength and spatial extent of the dissipative region in nonproportionally damped systems. In materials where mechanical damage results in increased internal friction, a common effect in many engineering metals, this technique is proposed as a nondestructive technique for characterizing such damage. The results of numerical experiments on nonproportionally damped acoustic systems are presented which support the proposed technique.

Diffuse wave energy transport in multicoupled, one‐dimensional Anderson localizing systems

The spatial and time domain evolution of energy density in a multicoupled, one‐dimensional disordered system is investigated. Scaling theory predictions are presented for both localization lengths and rates of diffuse transport. Scaling arguments suggest that localization lengths equal πρDo, where ρ is the modal density per unit length and Do is the bare diffusivity. Additionally, the rate of diffuse energy transport over a distance L is found to scale as ρL. These predictions are compared with the behavior of a numerical model for an Anderson localizing system. The system modeled is a cylindrical membrane disordered by the introduction of a random foundation of springs. [Work supported by ONR.]

Performance of at-risk students in dynamics following a statics class with additional recitation time

Comparisons are made between the final exam and final course grades of at-risk students in dynamics who took one of two versions of the same statics course. A standard version of the statics course met 3 hours per week over the course of a 15-week semester, while a second version met 4 hours per week. During the 11-year timeframe covered by this study, the 4-hour statics course was populated by students identified as ‘at risk’ using an informal screening procedure. For comparison with this group, using the same enrollment data, a second group of at-risk students was identified from the 3-hour statics class using a more formal screening procedure, based on logistic regression. A performance comparison of the two groups shows that the extra contact hour had a minor, statistically insignificant effect on student final exam and final course grades in dynamics. As a result of this study and a related study examining the effect of additional class time on statics performance, the 4-hour statics class is no longer offered.

Characterization of an acoustic actuation mechanism for robotic propulsion in low Reynolds number environments

With the end goal of medical applications such as non-invasive surgery and targeted drug delivery, an acoustically driven resonant structure is proposed for microrobotic propulsion. At the proposed scale, the low Reynolds number environment requires non-reciprocal motion from the robotic structure for propulsion; thus, a “flapper” with multiple, flexible joints, has been designed to produce excitation modes that involve the necessary flagella-like bending for non-reciprocal motion. The key design aspect of the flapper structure involves a very thin joint that allows bending in one (vertical) direction, but not the opposing direction. This allows for the second mass and joint to bend in a manner similar to a dolphin’s “kick” at the bottom of their stroke, resulting in forward thrust. A 130 mm x 50 mm x 0.2 mm prototype of a swimming robot that utilizes the flapper was fabricated out of acrylic using a laser cutter. The robot was tested in water and in a water-glycerine solution designed to mimic microscale fluid conditions. The robot exhibited forward propulsion when excited by an underwater speaker at its resonance mode, with velocities up to 2.5 mm/s. The robot also displayed frequency selectivity, leading to the possibility of exploring a steering mechanism with alternatively tuned flappers. Additional tests were conducted with a robot at a reduced size scale.

Analysis of flapping mechanism for acoustically actuated microrobotics

The field of microrobotics has vast applications including non-invasive surgery, targeted drug delivery, and telemetry. Many groups are developing or have developed magnetically based actuation methods for microrobotics. These magnetically based systems can potentially lead to undesirable effects on the human body. Acoustic control provides an interesting alternative to existing magnetic or electrostatic actuation in that acoustic signals include few harmful effects on the human subject. Furthermore, the use of acoustic signals allow for the possibility to leverage existing medical imaging technology. This paper describes an alternative method of actuation which utilizes double-jointed, flagella-like, flappers designed for whip-like, non-reciprocal motion. The flapper mechanism was investigated using COMSOL Multiphysics finite element software to determine eigenfrequencies. Flappers were then constructed from laser cut acrylic and styrene and joined with plastic cement. The flappers were excited to resonance and displayed behavior that was consistent with simulation. A 130 mm × 50 mm × 0.2 mm robot with the flapper tail was then constructed and tested in a tank containing water and an underwater speaker. The robot exhibited forward velocities as high as 2.5 mm/s as well as frequency selectivity, which could be exploited to achieve steering in the future by using multiple flappers with different resonance frequencies. This project lays the foundation for the development of an acoustically actuated microscale robot.