The blossoming of sensing solutions based on the use of carbon materials and the pervasive exploration of compressed sensing (CS) for developing structural health monitoring applications suggest the possibility of combining these two research areas in a novel family of smart structures. Specifically, the authors propose an architecture for security-related applications that leverages the tunable electrical properties of a graphite oxide (GO) paper-based tamper-evident seal with a compressed-sensing (CS) encryption/authentication protocol. The electrical properties of GO are sensitive to the traditional methods that are commonly used to remove and replace paper-based tamper-evident seals (mechanical lifting, solvents, heat/cold temperature changes, steam). The sensitivity of the electro-chemical properties of GO to such malicious insults is exploited in this architecture. This is accomplished by using GO paper to physically realize the measurement matrix required to implement a compressive sampling procedure. The proposed architecture allows the seal to characterize its integrity, while simultaneously providing an encrypted/authentication feature making the seal difficult to counterfeit, spoof, or remove/replace. Traditional digital encryption/authentication techniques are often bit sensitive making them difficult to implement as part of a measurement process. CS is not bit sensitive and can tolerate deviation caused by noise and allows the seal to be robust with respect to environmental changes that can affect the electrical properties of the GO paper during normal operation. Further, the reduced amount of samples that need to be stored and transmitted makes the proposed solution highly attractive for power constrained applications where the seal is interrogated by a remote reader.
It has been argued that the isolation of monolayer graphene is among the most important discoveries in the last half century. Graphene has led to new thinking about how to address persistent challenges faced by traditional material systems. A long-standing problem faced by the particle accelerator community is that of limited lifetime of electron sources. These sources launch the electron beam which is bunched and accelerated to high energies for many different applications, ranging from next generation user facilities for discovery science to directed energy systems for defense and environmental needs. Addressing limited lifetime of electron sources is a complicated problem, but we have made progress toward developing a methodology to use multiple graphene layers as a monolayer ruggedizing shield which does not appreciably disrupt photoemission but does provide a barrier isolation which could increase cathode lifetime. We present key results to date which enable graphene to function as a monolayer shield for sensitive photocathode films.
In crack detection applications large sensor arrays are needed to be able to detect and locate cracks in structures. This paper analyzes different sensor shapes and layouts to determine the layout which provides the optimal performance. A “snaked hexagon” layout is proposed as the optimal sensor layout when both crack detection and crack location parameters are considered. In previous work we have developed a crack detection circuit which reduces the number of channels of the system by placing several sensors onto a common bus line. This helps reduce data and power consumption requirements but reduces the robustness of the system by creating the possibility of losing sensing in several sensors by a single broken wire. In this paper, sensor bus configurations are analyzed to increase the robustness of the bused sensor system. Results show that spacing sensors in the same bus out as much as possible increases the robustness of the system and that at least 3 buses are needed to prevent large segments of a structure from losing sensing in the event of a bus failure.
The carbon nanotube photoexcitation spectrum is dominated by excitonic transitions, rather than interband transitions
between continuum states. There are eight distinct excitonic transitions (four singlet and four triplet), each with two-fold
degeneracy. Because the triplet excitons are spin polarized with electron and hole spins both pointing in the same
direction, they are optically inactive, and optical spectroscopy has revealed no evidence for their existence. Here, we
show that by the interaction with a spin filter ferromagnetic semiconductor, photoexcitation of the carbon nanotube
triplet exciton is possible, and its contribution to the photocurrent can be detected. The perturbation provided by the spin
filter allows for inter-system mixing between the singlet and triplet excitonic states, and relaxes the spin selection rules.
This supplies the first evidence for the existence of the triplet exciton, and provides an avenue for the optical excitation
of spin polarized carriers in carbon nanotubes.
Conference Committee Involvement (1)
New Concepts in Solar and Thermal Radiation Conversion and Reliability
19 August 2018 | San Diego, California, United States