Abrasive finishing is a machining process which alters the surface of a workpiece to achieve a specific property. Typical abrasive finishing processes focus on geometric tolerances and surface topography. Abrasive finishing is primarily dependent on finishing forces, relative velocities, and abrasive size. The material removal rate in finishing is inversely related to the surface finish. Magnetic and electric fields have been used to control the force applied to abrasives which finish the workpiece. These processes show an increase in performance when the field is used to control the process. Field assisted finishing processes can be energy intensive and expensive. A novel finishing media is proposed which does not require a field to achieve a similar force response. This media has inherent thickening mechanisms driven by shear jamming. This shear jamming mechanism can deliver forces an order of magnitude higher than shear thickening mechanisms. This novel slurry is demonstrated as a viable finishing media with performance similar to magnetic abrasive finishing. / Thesis / Master of Applied Science (MASc)

Bats using their biosonar while flying in dense swarms may face significant bioacoustic challenges, in particular mutual sonar jamming. While possible solutions to the jamming problem have been investigated multiple times in literature, the severity of this problem has received far less attention. To characterize the acoustics of bat swarms, a simple model of the acoustically relevant properties of a bat swarm has been set up and evaluated. The model contains only four parameters: bat spacial density, biosonar beamwidth, duty cycle, and a scalar measure for the smoothness of the flight trajectories. In addition, a threshold to define substantial jamming was set relative to the emission level. The simulations results show that all four model parameters can have a major impact on jamming probability. Depending on the combination of parameter values, situations with or without substantial jamming probabilities could be produced within reasonable ranges of all model parameters. Hence, the model suggests that not every bat swarm does necessarily impose grave jamming problem. A fitting process was introduced to describe the relationship between the four parameters and jamming probability, hence produce a function with jamming probability as output and four parameters as input. Since the model parameters should be comparatively easy to estimate for actual bat swarms, the simulation results could give researchers a way to assess the acoustic environment of actual bat swarms and determine cases where a study of biosonar jamming could be worthwhile. / Master of Science

abstract: Interference constitutes a major challenge for communication networks operating over a shared medium where availability is imperative. This dissertation studies the problem of designing and analyzing efficient medium access protocols which are robust against strong adversarial jamming. More specifically, four medium access (MAC) protocols (i.e., JADE, ANTIJAM, COMAC, and SINRMAC) which aim to achieve high throughput despite jamming activities under a variety of network and adversary models are presented. We also propose a self-stabilizing leader election protocol, SELECT, that can effectively elect a leader in the network with the existence of a strong adversary. Our protocols can not only deal with internal interference without the exact knowledge on the number of participants in the network, but they are also robust to unintentional or intentional external interference, e.g., due to co-existing networks or jammers. We model the external interference by a powerful adaptive and/or reactive adversary which can jam a (1 &#8722; &#949;)-portion of the time steps, where 0 < &#949; &#8804; 1 is an arbitrary constant. We allow the adversary to be adaptive and to have complete knowledge of the entire protocol history. Moreover, in case the adversary is also reactive, it uses carrier sensing to make informed decisions to disrupt communications. Among the proposed protocols, JADE, ANTIJAM and COMAC are able to achieve &#920;(1)-competitive throughput with the presence of the strong adversary; while SINRMAC is the first attempt to apply SINR model (i.e., Signal to Interference plus Noise Ratio), in robust medium access protocols design; the derived principles are also useful to build applications on top of the MAC layer, and we present SELECT, which is an exemplary study for leader election, which is one of the most fundamental tasks in distributed computing. / Dissertation/Thesis / Ph.D. Computer Science 2012

Three novel approaches that are based on a recent communication technique called time compression overlap-add (TC-OLA), are introduced into pulse compression (PC) radar systems to improve the radar waveform shaping and enhance radar performance. The first approach lays down a powerful framework for combining the TC-OLA technique into traditional PC radar system. The new TC-OLA-based radar obtained is compared with other radars, namely traditional linear frequency modulation (LFM), and wideband LFM which has the same processing gain under different background situations. The results show the superiority of the proposed radar over the others. The second approach combines a random phase noise signal with a selected radar signal to build a new radar system, SSLFM radar, that enjoys the low-probability of intercept property, and, therefore, has higher immunity against noise jamming techniques compared with other radar systems. The properly recovery of the transmitted signal, however, requires a synchronization system at the receiver side. In this dissertation, we propose three synchronization systems each having different pros and cons. The last approach takes the radar waveform design methodology in a different direction and proposes a novel framework to combine any number of radar signal and transmit them simultaneously. Instead of trying to achieve universality through waveform shaping optimization, we do so via pluralism. As a proof of concept, all the proposed radars have been implemented and tested on software-defined radar (SDR). The theoretical and the experimental results showed the superiority of all proposed radar systems. Since TC-OLA is fundamental to this work, we add a chapter to propose a new technique called downsample upsample shift add (DUSA) to address the limitations of the existing implementation of TC-OLA. / Graduate

This thesis developed a novel theory of fiber jamming and experimentally verified it. The theory relates the performance, which is the ratio between the stiff and soft states of a fiber jamming chamber, to three relative design parameters: the ratio of the wall thickness to the membrane inner diameter, the ratio of the fiber diameter to membrane inner diameter, and the number of fibers. These three parameters, when held constant across different chamber sizes, hold the performance constant. To test the theory, three different types of fiber jamming chambers were built in three different sizes. Each chamber was set up as a cantilever beam and deflected 10mm in both the un-jammed (soft) and jammed (stiff) states. When the three design parameters were held constant, the performance of the chamber was consistent within 10\%. In contrast, when the parameters were altered, there was a statistically significant $p < .0001$ and noticeable effect on chamber performance. These two results can be used in tandem to design miniaturized fiber jamming chambers. These results also have a direct application in soft robots designed for minimally invasive surgery.

The pervasiveness of wireless communications in modern society is unprecedent. Using numerous wireless technologies, including cellular, WiFi, WiMax and others, users gain ubiquitous access to a wealth of information services relevant to their everyday lives. These include communication services (voice, email, text), commercial transactions (e-banking, e-trading), location-based services (points of interest, navigation), social networking, web access, and others. Further proliferation of mobile services and applications provided via wireless communications is contingent upon the network's reliability and security. As this wireless revolution continues to unfold, users have grown increasingly concerned with the amount of sensitive information that leaks to unauthorized parties. They have also become more skeptical to the abilities of current technologies in providing a reliable and secure environment. The problem of ensuring network reliability and security is particularly challenging in the wireless domain. The open nature of the wireless medium leaves it accessible to any device equipped with a transceiver. Wireless networks remain vulnerable to numerous attacks, including eavesdropping, packet modification and injection, replay, impersonation, and jamming. Moreover, the poor physical security of the majority of wireless stations (mobile devices, sensor, etc.) makes them susceptible to physical compromise. Such compromised devices become a launchpad for internal attacks from adversaries with intimate knowledge of network secrets and protocol specifications. Internal attacks are much harder to counter than external ones since the adversary can bypass typical cryptographic methods that authorize user access. In this dissertation, we investigate attacks on wireless communications launched by internal adversaries. In particular, we are concerned with sophisticated intentional interference (jamming) attacks against broadcast communications. Such attacks have been shown to be detrimental to network operation. We further consider the problem of distributed node coordination in dynamic spectrum networks. To address these problems, we design novel communication protocols that protect broadcast communications from internal attacks via a combination of randomization, redundancy and cryptographic techniques. We propose new security metrics to quantify the ability of the adversary to deny access to the broadcast channel. We introduce a randomized distributed scheme that allows nodes to establish and maintain the broadcast channel in the presence of the jammer. Also this scheme uniquely identifies the set of compromised nodes, both when nodes are acting independently and when they are colluding. To protect broadcast communication performed on control channel, we propose a secure broadcast scheme called TDBS, which implements the broadcast operation as a series of unicast transmissions, distributed in frequency and time. Finally, we address the problem of dynamically assigning the control channel in CRNs based on time- and space-varying spectrum opportunities. We propose a cluster-based architecture that allocates different channels for control at various clusters in the network. The clustering problem is formulated as a bipartite graph problem, for which we develop a class of algorithms to implement. Extensive simulations are conducted to verify the validity of the proposed mechanisms.

Highly nonlinear structures exhibit complex responses to external loads, and often become unstable. In this thesis, I consider structures with either a nonlinear geometric response or material response. Geometrically nonlinear bistable shells have two stable configurations and can reversibly change between them via snap-through instabilities. This snap-through behavior can cause large geometric deformations in response to small changes in loading, and thus is ideal for designing various devices. For materially nonlinear structures, one recent focus is the potential to utilize granular jamming to construct structures. However, it is not yet fully understood how the stability of such nonlinear structures is governed by geometric and materials properties. This thesis aims to answer this question and propose design guidelines for engineering applications. This research will focus on the statics and dynamics of spherical shells, prestressed bistable shells and elastogranular columns. For spherical shells, we aim to find out under what geometric criteria can a shell be turned inside out, and as the shell goes through the snap-through instability, what dictates the shape and speed of it. Geometric criteria to predict whether a spherical shell is bistable or monostable is proposed based on precisely fabricated soft spherical shells. Point load indentation tests were performed to determine how stable a spherical shell is in its everted configuration. The results show a distinct difference between shallow shells and deep shells, which led to further studies on the snapping dynamics of spherical shells. High speed videos are recorded to track the motion of the apex of an everted spherical shell during its snap-through process, and we find that as the spherical shell goes from shallow to deep, the axisymmetric snapping will transform into asymmetric snapping. This change in snapping modes greatly affects the snapping dynamics of the everted spherical shells, and the shapes they adopt through the instability. Besides spherical shells, we also analyzed prestressed, bistable, cylindrical shells. Prestressed bistable shells fabricated by stretching and bonding multiple layers of elastomers can have various geometric shapes and can snap under external stimuli, but the governing parameters for the fabrication and snapping are not known yet. An analytical model was proposed based on non-Euclidean Plate Theory to predict the mean curvature of the prestressed shell, and the amount of stimulus that is needed to trigger the snapping. Numerical simulations are performed to compare with the analytical results. Based on the proposed theory, for given fabrication parameters and material properties, the final mean curvature of the bistable prestressed shell can be predicted accurately, as well as the amount of stretch that is needed to trigger snapping. This study can be used to design smart actuators or other soft, smart devices. To study material nonlinear structures, we use a mixture of grains and rods to enable the formation of stable structures via granular jamming. Understanding how these constituents govern the mechanical properties of the jammed structures is crucial for devising relevant engineering designs. We examine freestanding columns composed of rocks and string, and propose a simple physical model to explain the resulting structure’s mechanical behavior. The results indicate that exterior fiber mainly contributes to stiffness, while interior fiber increases the stored elastic energy and absorbed total energy of the structures under certain external load. By assembling the grains and strings in an engineer way, structures with robust mechanical properties can be formed. The results provide guidelines that allow the design of jammed elastogranular structures with desired mechanical properties. The research results of this thesis will open and guide a variety of possibilities in designing functional responsive devices or jamming structures.

The HydroBone is a variable stiffness load-bearing element, which utilizes jamming of granular media to achieve stiffness modulation, controlled by the application of positive pressure. Several compressive tests were conducted on the HydroBone in order to quantify the load-bearing capability of the system. It was determined that the stiffness of the HydroBone was a function of the internal pressure of the system. A controller was modeled based on this function to achieve automatic stiffness modulation of the HydroBone. An exoskeleton was designed based on the HydroBone and various actuators for the exoskeleton were considered. The HydroMuscle, a soft linear actuator was selected to provide knee actuation for the exoskeleton, based on several efficiency and force output test conducted. A knee brace was designed, capable of producing 15Nm of torque on the knee, actuated using Bowden cables coupled to the HydroMuscles.

"In a wireless network environment, all the users are able to access the wireless channel. Thus, if malicious users exploit this feature by mimicking the characteristics of a normal user or even the central wireless access point (AP), they can intercept almost all the information through the network. This scenario is referred as a Man-in-the-middle (MITM) attack. In the MITM attack, the attackers usually set up a rogue AP to spoof the clients. In this thesis, we focus on the detection of MITM attacks in Wi-Fi networks. The thesis introduces the entire process of performing and detecting the MITM attack in two separate sections. The first section starts from creating a rogue AP by imitating the characteristics of the legitimate AP. Then a multi-point jamming attack is conducted to kidnap the clients and force them to connect to the rogue AP. Furthermore, the sniffer software is used to intercept the private information passing through the rogue AP. The second section focuses on the detection of MITM attacks from two aspects: jamming attacks detection and rogue AP detection. In order to enable the network to perform defensive strategies more effectively, distinguishing different types of jamming attacks is necessary. We begin by using signal strength consistency mechanism in order to detect jamming attacks. Then, based on the statistical data of packets send ratio (PSR) and packets delivery ratio (PDR) in different jamming situations, a model is built to further differentiate the jamming attacks. At the same time, we gather the received signal strength indication (RSSI) values from three monitor nodes which process the random RSSI values employing a sliding window algorithm. According to the mean and standard deviation curve of RSSI, we can detect if a rogue AP is present within the vicinity. All these proposed approaches, either attack or detection, have been validated via computer simulations and experimental hardware implementations including Backtrack 5 Tools and MATLAB software suite. "

abstract: The rigidity of a material is the property that enables it to preserve its structure when deformed. In a rigid body, no internal motion is possible since the degrees of freedom of the system are limited to translations and rotations only. In the macroscopic scale, the rigidity and response of a material to external load can be studied using continuum elasticity theory. But when it comes to the microscopic scale, a simple yet powerful approach is to model the structure of the material and its interparticle interactions as a ball$-$and$-$spring network. This model allows a full description of rigidity in terms of the vibrational modes and the balance between degrees of freedom and constraints in the system. In the present work, we aim to establish a microscopic description of rigidity in \emph{disordered} networks. The studied networks can be designed to have a specific number of degrees of freedom and/or elastic properties. We first look into the rigidity transition in three types of networks including randomly diluted triangular networks, stress diluted triangular networks and jammed networks. It appears that the rigidity and linear response of these three types of systems are significantly different. In particular, jammed networks display higher levels of self-organization and a non-zero bulk modulus near the transition point. This is a unique set of properties that have not been observed in any other types of disordered networks. We incorporate these properties into a new definition of jamming that requires a network to hold one extra constraint in excess of isostaticity and have a finite non-zero bulk modulus. We then follow this definition by using a tuning by pruning algorithm to build spring networks that have both these properties and show that they behave exactly like jammed networks. We finally step into designing new disordered materials with desired elastic properties and show how disordered auxetic materials with a fully convex geometry can be produced. / Dissertation/Thesis / Doctoral Dissertation Physics 2018