Ultrasonic sensor platforms for non-destructive evaluation

Robotic vehicles are receiving increasing attention for use in Non-Destructive Evaluation (NDE), due to their attractiveness in terms of cost, safety and their accessibility to areas where manual inspection is not practical. A reconfigurable Lamb wave scanner, using autonomous robotic platforms is presented. The scanner is built from a fleet of wireless miniature robotic vehicles, each with a non-contact ultrasonic payload capable of generating the A0 Lamb wave mode in plate specimens. An embedded Kalman filter gives the robots a positional accuracy of 10mm. A computer simulator, to facilitate the design and assessment of the reconfigurable scanner, is also presented. Transducer behaviour has been simulated using a Linear Systems approximation (LS), with wave propagation in the structure modelled using the Local Interaction Simulation Approach (LISA). Integration of the LS and LISA approaches were validated for use in Lamb wave scanning by comparison with both analytical techniques and more computationally intensive commercial finite element/diference codes. Starting with fundamental dispersion data, the work goes on to describe the simulation of wave propagation and the subsequent interaction with artificial defects and plate boundaries. The computer simulator was used to evaluate several imaging techniques, including local inspection of the area under the robot and an extended method that emits an ultrasonic wave and listens for echos (B-Scan). These algorithms were implemented in the robotic platform and experimental results are presented. The Synthetic Aperture Focusing Technique (SAFT) was evaluated as a means of improving the fidelity of B-Scan data. It was found that a SAFT is only effective for transducers with reasonably wide beam divergence, necessitating small transducers with a width of approximately 5mm. Finally, an algorithm for robot localisation relative to plate sections was proposed and experimentally validated

Experimental validation of a two-dimensional shear-flow model for determining acoustic impedance

Tests were conducted to validate a two-dimensional shear-flow analytical model for determining the acoustic impedance of a liner test specimen in a grazing-incidence, grazing-flow environment. The tests were limited to a test specimen chosen to exhibit minimal effects of grazing flow so that the results obtained by using the shear-flow analytical model would be expected to match those obtained from normal-incidence impedance measurements. Impedances for both downstream and upstream sound propagation were generally consistent with those from normal-incidence measurements. However, sensitivity of the grazing-incidence impedance to small measurement or systematic errors in propagation constant varied dramatically over the range of test frequencies

Design and Operation of a Microwave Flow Cytometer for Single Cell Detection and Identification

Microwave dielectric sensing has become a popular technique in biological cell sensing for its potential in online, label-free, and real-time sensing. At microwave frequencies probing signals are sensitive to intracellular properties since they are able to penetrate cell membranes, making microwave flow cytometry a promising technology for label-free biosensing. In this dissertation a microwave flow cytometer is designed and used to measure single biological cells and micro particles. A radio frequency (RF)/microwave interferometer serves as the measurement system for its high sensitivity and tunability and we show that a two-stage interferometer can achieve up to 20 times higher sensitivity than a single interferometer. A microstrip sensor with an etched microfluidic channel is used as the sensing structure for measuring single cells and particles in flow. The microwave flow cytometer was used to measure changes in complex permittivity, , of viable and nonviable Saccharomyces cerevisiae and Saccharomyces pastorianus yeast cells and changes in complex permittivity and impedance of two lifecycle stages of Trypanosoma brucei, a unicellular eukaryotic parasite found in sub-Saharan Africa, at multiple frequencies from 265 MHz to 7.65 GHz. Yeast cell measurements showed that there are frequency dependent permittivity differences between yeast species as well as viability states. Quadratic discriminate analysis (QDA) and k-nearest neighbors (KNN) were employed to validate the ability to classify yeast species and viability, with minimum cross-validation error of with cross validation errors of 19% and 15% at 2.38 GHz and 265 MHz, respectively. Measurements of changes in permittivity and impedance of single procyclic form (PCF) and bloodstream form (BSF) T. brucei parasites also showed frequency dependence. The two cell forms had a strong dependence on the imaginary part of permittivity at 2.38 GHz and below and a strong dependence on the real part of permittivity at 5.55 GHz and above. Three PCF cell lines were tested to verify that the differences between the two cell forms were independent of cell strain. QDA gave maximum cross-validation errors of 15.4% and 10% when using one and three PCF strains, respectively. Impedance measurements were used to improve cell classification in cases where the permittivity of a cell cannot be detected. Lastly, a microwave resistance temperature detector (RTD) is designed, and a model is developed to extract the temperature and complex permittivity of liquids in a microfluidic channel. The microwave RTD is capable of measuring temperature to within 0.1°C. The design can easily be modified to increase sensitivity be lengthening the sensing electrode or modified for smaller volumes of solute by shortening the electrode

Smart FRP Composite Sandwich Bridge Decks in Cold Regions

INE/AUTC 12.0

Low cost sonar based on echolocation: an embedded system approach

Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do ParanáOne of the greatest challenges of mobile robot applications is obstacle detection and its localization. Most systems applied to address this problem can be branched into two segments: vision-based and non-vision based. In the former, camera detection and image processing are sensitive to variations in environmental conditions as well as their high cost. For this reason, this option is not interesting. In the second segment, on the other hand, ultrasonic sensors stand out for their attractive features at an affordable cost and, unlike other systems, are capable of operating in a variety of environments. The main problem using these devices is the difficulty of correctly handling the data acquired, limiting their efficiency. The present work focuses on the improvement and employment of a low cost location system based on ultrasonic sensors, combining trigonometric and signal processing techniques. The work is divided into two parts: processed version in MATLAB and application of embedded system. For the version in MATLAB, two optimal techniques — envelope detection and cross-correlation — were evaluated. For the embedded system approach, the technique with the best performance was implemented. In both parts, the validation of results obtained occurred through a set of measurements with various objects in assorted configurations.Um dos maiores desafios das aplicações de robôs móveis é a detecção de obstáculos e sua localização. A maioria dos sistemas aplicados para solucionar esse problema pode ser ramificada em dois segmentos: baseado em visão e em não visão. No primeiro, a detecção por câmera e o processamento de imagens são sensíveis as variações nas condições ambientais, além de possuírem alto custo. No segundo segmento, por outro lado, os sensores ultrassônicos se destacam por seus recursos atraentes a um custo acessível e, ao contrário de outros sistemas, são capazes de operar em uma variedade de ambientes. O principal problema do uso desses dispositivos é a dificuldade de manipular corretamente os dados adquiridos, limitando sua eficiência. O presente trabalho enfoca na melhoria e no emprego de um sistema de localização de baixo custo, baseado em sensores ultrassônicos, combinando técnicas trigonométricas e de processamento de sinais. O trabalho está dividido em duas partes: versão processada em MATLAB e aplicação do sistema embarcado. Para a versão em MATLAB, duas técnicas ótimas — detecção de envelope e correlação cruzada — foram avaliadas. Para a abordagem de sistema embarcado, foi implementada a técnica com o melhor desempenho. Em ambas as partes, a validação dos resultados obtidos ocorreu através de um conjunto de medidas com vários objetos em configurações variadas

Synesthesia: Detecting Screen Content via Remote Acoustic Side Channels

We show that subtle acoustic noises emanating from within computer screens can be used to detect the content displayed on the screens. This sound can be picked up by ordinary microphones built into webcams or screens, and is inadvertently transmitted to other parties, e.g., during a videoconference call or archived recordings. It can also be recorded by a smartphone or "smart speaker" placed on a desk next to the screen, or from as far as 10 meters away using a parabolic microphone. Empirically demonstrating various attack scenarios, we show how this channel can be used for real-time detection of on-screen text, or users' input into on-screen virtual keyboards. We also demonstrate how an attacker can analyze the audio received during video call (e.g., on Google Hangout) to infer whether the other side is browsing the web in lieu of watching the video call, and which web site is displayed on their screen