Seth D. Cohen, Entered 2007/08
Office Location: 183 Physics
Office Phone: 919-660-2512
Email Address: sdc18@phy.duke.edu
Specialties:
Nonlinear dynamics and complex systems
Education:
BS, University of Rochester, 2007
Research Categories: Complex and Nonlinear Circuits, Ultra Wideband RF Transmission, Wave-Chaos, Sub-wavelength Imaging Techniques
Research Description: The transfer of information between identical chaotic elements is of great interest in understanding the dynamics of large coupled networks. To explore the characterizations of such a network, I have begun examining methods for radio frequency signal transmission between high-speed nonlinear oscillators. Coupling through radio transmission, rather than hard-wire connections, will allow for through-wall transmission as well as additional elements to be more easily added into the network.
Due to the broadband nature of the chaotic signal, the frequency spectrum of the high-speed chaos can fall under the category of FCC regulation 47CFR15.503 for Ultra Wideband (UWB) signals. I have been researching antennas and modulation methods that will enable bi-directional coupling between identical elements, as well as keep our transmission within legal limits. This transfer of information will be used to couple two or more of these elements in an area for further study. With small affordable devices operating within FCC regulations, the dynamics of a many bodied chaotic network can be studied in real time to evaluate current theories and explore applications in commercial technologies.
Broadband chaos has been observed previously in a simple transistor-based nonlinear circuit with time-delayed feedback through a single coaxial cable. We have replaced this coaxial cable with a multipath delay system consisting of broadband antennas placed inside a stadium-shaped cavity. This creates a new nonlinear-feedback system where the multipath reflections of the radio waves inside the cavity become the delayed-feedback loops of the dynamical system.
By moving a sub-wavelength scatterer that is also placed in the cavity, the path lengths and coupling strengths of these feedback delays change. From small scatterer movements, we observe bifurcations in the system’s output voltage between periodic, quasiperiodic, and chaotic attractors. In between bifurcations, the dynamics respond with small shifts in peak frequency values. This enables the sub-wavelength object to be tracked to within λ/10,000. By exploiting this novel technique for sub-wavelength sensitivity, we hope to improve traditional methods of intrusion detection systems and tracking devices with through-wall capabilities. Furthermore, in scaling this system down to the optical domain, we predict potential applications in biological microscopy.
Recent Publications
- Seth D. Cohen, Hugo L. D. de S. Cavalcante, and Daniel J. Gauthier, Subwavelength Position Sensing Using Nonlinear Feedback, Physical Review Letters, vol. 107 no. 25 (December, 2011) [PhysRevLett.107.254103], [doi] [abs].