Alexandria N. Marchi

A graphite oxide (GO)-based remote readable tamper evident seal

This paper presents a prototype of a remotely readable graphite oxide (GO) paper-based tamper evident seal. The proposed device combines the tunable electrical properties offered by reduced graphite oxide (RGO) with a compressive sampling scheme. The benefit of using RGO as a tamper evident seal material is the sensitivity of its electrical properties to the common mechanisms adopted to defeat tamper-evident seals. RGOs electrical properties vary upon local stress or cracks induced by mechanical action (e.g., produced by shimming or lifting attacks). Further, modification of the seals electrical properties can result from the incidence of other defeat mechanisms, such as temperature changes, solvent treatment and steam application. The electrical tunability of RGO enables the engraving of a circuit on the area of the tamper evident seal intended to be exposed to malicious attacks. The operation of the tamper evident seal, as well as its remote communication functionality, is supervised by a microcontroller unit (MCU). The MCU uses the RGO-engraved circuitry to physically implement a compressive sampling acquisition procedure. The compressive sampling scheme provides the seal with self-authentication and self-state-of-health awareness capabilities. The prototype shows potential for use in low-power, embedded, remote-operation non-proliferation security related applications.

Structural Health Monitoring of Additively Manufactured Parts Using Fiber Bragg Gratings

Many industries are moving toward the opportunities afforded by additive manufacturing (AM) techniques as a primary manufacturing method for components. Additionally, AM continues to be an effective option for rapid prototyping in many applications. Some advantages AM processes have over traditional manufacturing include the ability to create highly complex and multi-material parts with little or no restriction on the geometry of the object at a relatively low price point. However, one of the main challenges that from AM techniques is the relatively high variation, in both material properties and exact geometry, from part to part. This variation calls for structural health monitoring of each individual part. In this paper, fiber Bragg gratings (FBGs) -- chosen because they can be embedded with minimal effect on the desired structure -- are inserted into AM geometries between layers, allowing for strain readings to be taken in situ. These measurements provide empirical data of incipient failure as AM parts tend to fail between layers. Fused deposition modeling (FDM) is used, as it is relatively common and inexpensive, to create parts into which the FBGs are embedded. Measurements taken under a variety of tests are compared to analogous finite element as well as analytical models allowing for model accuracy evaluation for AM parts. This work provides experimental data to validate models, in addition to forming a better understanding of the validity and procedure of embedding FBGs into FDM parts. Additionally, this work serves as a proof of concept and calls for more work to be done in the field.

Material Characterization of Self-Sensing 3D Printed Parts

Additive manufacturing has seen a resurgence in recent years, mainly driven by its ability to produce parts with complex designs and incorporate multiple components into a single manufactured part. However, additive manufacturing still needs improvements to fabricate consistent and reliable parts. Some of the shortcomings of the process include the effects of build orientation on the material properties. Current structural health monitoring methods, such as visual photography and thermography, provide limited data to quantify the quality and reliability of printed part. In this study, 3D printed novel sensors were embedded within a part and were evaluated as an alternative method for structural health monitoring. The embedded sensors were composed of conductive filament and are intended as a non-intrusive method to monitor the structural health of the part during its service life. Filaments using novel materials, e.g. conductive polylactic acid, were evaluated for their material characteristics and suitability for sensor verification and validation. Specifically, the novel conductive filaments were evaluated for their performance in terms of mechanical and electrical properties. The Young’s modulus of the additively manufactured, polylactic acid part was determined by both tensile testing and cantilever testing; and temperature sensitivity was determined by resistance measurements during thermal cycling. Embedding of the sensor into the service part during the printing process can reduce the cost and production time for structural health monitoring and provide a new application area for additive manufacturing.

Performance assessment of a remotely readable graphite oxide (GO)-based tamper-evident seal

Tamper-evident seals are commonly used for non-proliferation applications. A properly engineered tamper-evident seal enables the detection of unauthorized access to a protected item or a secured zone. Tamper-evident seals must be susceptible to malicious attacks. These attacks should cause irreversible and detectable damage to the seals. At the same time, tamper-evident seals must demonstrate robustness to environmental changes in order to minimize false-positive and false-negative rates under real operating conditions. The architecture of the tamper-evident seal presented in this paper features a compressive sampling (CS) acquisition scheme, which provides the seal with a means for self- authentication and self-state of health awareness. The CS acquisition scheme is implemented using a micro-controller unit (MCU) and an array of resistors engraved on a graphite oxide (GO) film. CS enables compression and encryption of messages sent from the seal to the remote reader in a non-bit sensitive fashion. As already demonstrated in our previous work through the development of a simulation framework, the CS non-bit sensitive property ensures satisfactory reconstruction of the encrypted messages sent back to the reader when the resistance values of the resistor array are simultaneously affected by modest changes. This work investigates the resistive behavior of the reduced GO film to changes in temperature and humidity when tested in an environmental chamber. The goal is to characterize the humidity and temperature range for reliable operation of a GO-based seal.

Phase Control of RF Cavities

Particle accelerators use superconducting radio frequency (RF) cavities that create extremely large electromagnetic fields to accelerate charged particles. The latest accelerators require an unprecedented level of precision in terms of particle energy, which translates into accelerating field amplitude and phase within error bounds of 0.01 % and 0.01°, respectively. To save money, it is possible to split the output of one high power controlled RF source to multiple cavities. However, in practice, all cavities are slightly different and experience different disturbances in operation. Because of an inability to quickly modulate the phase and amplitude of the individual split high power RF signals, the fields of an entire multi-cavity system are averaged and treated as one entity on which feedback control is performed at the low power input to the high power RF amplifier. The issue is compounded by the severe electrical loading that the RF cavity experiences during operation. Radiation pressure causes Lorentz force detuning, which shifts each cavity’s resonance peak, amplitude, and phase of its accelerating field in a unique way. Piezo tuners have been used to counteract Lorentz force detuning of individual cavities. This paper studies RF cavity phase control via piezo tuners. The controller designed is capable of quickly modifying the natural frequency of a cavity as a tool for modulating the phase of an RF signal. The approach is validated in hardware with a Niobium coated single-cell copper TESLA-type RF cavity.

A Remotely Readable, Self-authenticating Tamper Evident Seal Based on Graphene-based Materials and Compressive Sensing

Low-cost, high-precision patterning of flexible electrical components have gained special attention in many applications where multi-functional materials fuse structural support with electrical sensing. In particular, a number of structural health monitoring (SHM) applications call for the development of “sensing skin” technologies. One application that uses these technologies includes the development of next-generation tamper-evident seals (TES) that are capable of being read remotely. In our design, the state of the TES’s physical structure is monitored through an electrical circuit based on a conductive material. Electrical changes in the TES’s circuit correspond to material property changes induced by humidity, temperature, or chemical changes. Intrinsically unifying material and electrical properties, graphene and graphite derivatives promote simplistic manufacturing of flexible materials with unique electrical properties that are attractive for sensing skin applications. In addition to developing a functional graphenebased material, an encryption scheme to transmit the state of the material is devised utilizing compressive sensing. Our work focuses on the production of printable graphene-based materials and graphene-based/polymeric composites proficient for sensing environmental changes. Printing of functional complex graphene-based materials requires specific formulation while balancing electrical conductivity, formulation simplicity, solution viscosity, and printing compatibility. Production of electrically stable components on flexible substrates with programmable electrical properties will be key to using printed graphene-based materials in sensing skin applications. doi: 10.12783/SHM2015/269

A remote-readable graphite oxide (GO) based tamper-evident seal with self-reporting and self-authentication capabilities

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.