Systems Design Engineering

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This is the collection for the University of Waterloo's Department of Systems Design Engineering.

Research outputs are organized by type (eg. Master Thesis, Article, Conference Paper).

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Now showing 1 - 18 of 18

Asynchronous Optical Flow and Egomotion Estimation from Address Events Sensors
(University of Waterloo, 2022-05-18) Azzi, Charbel; Abdel-Rahman, Eihab; Fakih, Adel
Motion estimation is considered essential for many applications such as robotics, automation, and augmented reality to name a few. All cheap and low cost sensors which are commonly used for motion estimation have many shortcomings. Recently, event cameras are a new stream in imaging sensor technology characterized by low latency, high dynamic range, low power and high resilience to motion blur. These advantages allow them to have the potential to fill some of the gaps of other low cost motion sensors, offering alternatives to motion estimation that are worth exploring. All current event-based approaches estimate motion by considering that events in a neighborhood encode the local structure of the imaged scene, then track the evolution of this structure over time which is problematic since events are only an approximation of the local structure that can be very sparse in some cases. In this thesis, we tackle the problem in a fundamentally different way by considering that events generated by the motion of the same scene point relative to the camera constitute an event track. We show that consistency with a single camera motion is sufficient for correct data association of events and their previous firings along event tracks resulting in more accurate and robust motion estimation. Towards that, we present new voting based solutions which consider all potential data association candidates that are consistent with a single camera motion for candidates evaluation by handling each event individually with- out assuming any relationship to its neighbors beyond the camera motion. We first exploit this in a particle filtering framework for the simple case of a camera undergoing a planar motion, and show that our approach can yield motion estimates that are an order of magnitude more accurate than opti- cal flow based approaches. Furthermore, we show that the consensus based approach can be extended to work even in the case of arbitrary camera mo- tion and unknown scene depth. Our general motion framework significantly outperforms other approaches in terms of accuracy and robustness.
Combined Electrostatic/Electromagnetic MEMS Actuators
(University of Waterloo, 2016-08-10) Alneamy, Ayman; Abdel-Rahman, Eihab; Heppler, Glenn
In this work, one and two degrees of freedom (DOF) lumped mass models of Micro- Electro-Mechanical System (MEMS) actuators are introduced, investigated, and compared to experimental results. A one degree of freedom system representing the actuators out-of plane bending motion under the electrostatic excitation is demonstrated. The capacitive gap between the movable plate and stationary electrode decreases when the microplate inclination angle is accounted for in the model. We investigate experimentally the primary, superharmonic of order two, and subharmonic of order one-half resonances of an electrostatic MEMS actuator under direct excitation. We identify the parameters of a 1-DOF generalized Duffing oscillator, model that represents it. The experiments were conducted in soft vacuum in order to reduce squeeze- film damping and the actuator response was measured optically using a laser vibrometer. The predictions of the identified model were found to be in close agreement with the experimental results. We also identified the power level of process (actuation voltage) and measurement noise. A one DOF model of the actuator's torsional motion under the electrostatic torque is also introduced. It was found that utilizing electrostatic actuation in torsional motion is not e ffective. The maximum angle obtained was 0.04 degrees at high voltage. Finally, a novel two DOF model of the MEMS actuator's torsion and bending under electrostatic and electromagnetic excitation was demonstrated analytically and compared to experimental results. Torsional motions were driven by a torque arising from a Lorentz force. It succeeded in generating a large torsion angle, 1 degree at 1.35 T magnetic field density, and a current of 3.3 mA.
Design and Development of a Training System for Manual Handling Tasks in Masonry
(University of Waterloo, 2021-09-24) McFarland, Tasha; Abdel-Rahman, Eihab; Haas, Carl
The construction industry is one of the industries with the highest rates of musculoskeletal disorders (MSDs). Masons are particularly susceptible to overexertion and back injuries due to the physical demands of their jobs. In the past, optoelectronic motion capture has been considered the ‘gold standard’ for motion capture in biomechanics; however, it is often not feasible for onsite data collection. Therefore, most onsite assessment tools in the industry rely on observational techniques of postures to estimate risk that cannot accurately estimate internal joint demands. Advancements in inertial measurement unit (IMU) technology have led to the development of data collection systems comparable to that of the aforementioned ‘gold standard’, thereby enabling the quantification of joint loads and forces on masons in the working environment. Previous research has reported that “technique” during manual handling tasks, such as lifting, can have a large impact on spinal loads. The comparison of expert and novice working techniques reveals that experts use distinct working strategies, which can lead to both lower joint forces and increased productivity. Furthermore, training based on expert work strategies has been shown to reduce exposures to biomechanical risks. Despite frequency of injuries, MSD risks are often under-prioritized in terms of safety training. Researchers emphasize a need to integrate ergonomics training within apprentices’ skill training classes. This thesis focuses on the development of an enhanced training tool and program to reduce MSD risk in apprentice masons. A novel quantitative scoring system was developed to estimate MSD risk based on the peak joint loads of expert masons. This scoring system was integrated into the enhanced training tool to better assess risk based on onsite measurement of joint loads. Furthermore, the movement patterns of novice, apprentice and expert masons were analysed to determine key characteristics of inexpert and expert techniques. These characteristics were compared to high-risk postures in the literature to establish clear postural guidelines, which were then implemented into the enhanced training tool. The tool was designed to provide evidence-based recommendations to improve posture and technique based on kinematic analyses of masons’ movements. User interviews were conducted with masonry instructors to evaluate challenges, needs, and values for the training program. These insights directed the design of the accompanying educational module and overall training program. The training program and tool has the capacity to reduce biomechanical exposures of apprentice masons and increase productivity.
Dynamic Scanning Probe Lithography and Its Applications
(University of Waterloo, 2022-01-25) Saritas, Resul; Abdel-Rahman, Eihab; Yavuz, Mustafa
This dissertation presents a novel, benchtop, low-cost, high-throughput direct surface patterning method dubbed dynamic-Scanning Probe Lithography (d-SPL). It employs a scriber mounted via a spring-damper mechanism to a nano-resolution 3D stage. As the scriber traverses the substrate surface, non-uniformity in the surface morphology leads to time-variation in the magnitude and direction of the contact force, which in turn generates scriber vibrations. The spring-damper mechanism dissipates those vibrations and stabilizes the contact force, thereby enabling long and uniform micro and nano patterns on a wide variety of substrates and preventing scriber tip failure. An analytical model was developed to investigate the dynamics of d-SPL and determine its safe operation conditions and limitations. It was used to investigate and explain, for the first time, a small micro-scale chatter phenomenon observed in the response of d-SPL. The model was validated through comparison to experiments. d-SPL was utilized for high velocity fabrication of micro and nanochannels at 1 mm/s. The channel dimensions are controlled by the scriber surface contact force. d-SPL also provided the basis for a novel rapid fabrication method that enhances the output power of triboelectric nanogenerators (TENGs) by simultaneously creating centimeter-long nano grooves (NGs) and nano triangular prisms (NTPs) on the surface of polymeric triboelectric materials. The output power of the nano structured TENGs was 12.2 mW compared to 2.2 mW for flat TENGs. A coupled electromechanical model was developed to describe the energy flow through the TENGs. Analytical and experimental results for the proposed TENGs show that they can harvest low-frequency and wide-band vibrations below 10 Hz. d-SPL can also fabricate long micro and nano wires through a continuous chip removal process. The wire dimensions can be controlled via the tip-substrate contact force while taking into account the substrate material. Continuous chip removal produced millimeter long, helical shaped gold nano wires out of a 600 nm thick gold layer on a dielectric substrate. Continuous flexible helical polymeric micro wires were obtained by chip removal from a Poly (methyl methacrylate) (PMMA) substrate. The wires were coated with 50nm Silver (Ag) layer to produce flexible conductive micro-helical wires. It was found that these wires can behave as freely standing cantilever beams. A low-cost and rapid fabrication of back-gated field effect transistors (BGFETs) was also developed based on d-SPL. A silver layer pre-coated on top of another SiO2 layer was patterned into interdigitated electrodes (IDEs) to form the source and drain of a FET with a channel length of 20 µm. A glycol-graphene mixture was then deposited to create the channel between the source and drain using a nanostage integrated microplotter and allowed to dry naturally. The Ion/Ioff ratio of the fabricated BGFET was calculated from the I-V curve as a 10^3.
Electrostatic MEMS Bifurcation Sensors
(University of Waterloo, 2018-08-24) ALGHAMDI, MAJED; Abdel-Rahman, Eihab
We report experimental evidence of a new instability in electrostatic sensors, dubbed quasi-static pull-in, in two types of micro-sensors operating in ambient air. We find that the underlying mechanism and features of this instability are distinct from those characterizing hitherto known static and dynamic pull-in instabilities. Specifically, the mechanism instigating quasi-static pull-in is a global Shilnikov homoclinic bifurcation where a slow-varying waveform drives the sensor periodically through a saddle-node bifurcation. Based on these findings, we propose a new taxonomy of pull-in instabilities in electrostatic sensors. Experimental evidence of nonlinear chaotic behaviors were observed in an electrostatic MEMS sensor. Period doubling bifurcation (P-2), period three (P-3), and period six (P-6) were observed. A new class of intermittency subsequent to homoclinic bifurcation in addition to the traditional intermittencies of type-I and type-II were demonstrated. Quasiperiodicity and homoclinic tangles leading to chaos were also reported. All of these nonlinear phenomena instigate either banded chaos or full chaos and both are observed in this work. Based on our knowledge, this is the first observation such chaotic behaviors in electrostatic MEMS sensors. All of the experimental observations have been measured optically via a laser Doppler-vibrometer (LDV) in ambient pressure. Also, a new class of intermittencies was found in the oscillations of an electrostatic sensor. These intermittencies involve a dynamic system spending irregular time intervals in the vicinity of the ghost of an orbit before undergoing bursts that are arrested by landing on a larger attractor. Re-injection into the vicinity of the ghost orbit is noise induced. As a control parameter is increased, switching intermittency of type-I leads to a stable periodic orbit, whereas switching intermittency of type-II leads to a chaotic attractor. These significant findings in nonlinear dynamic were used to develop novel MEMS sensors. An electrostatic MEMS gas sensor is demonstrated. It employs a dynamic-bifurcation detection technique. In contrast to traditional gas or chemical sensors that measure (quantify) the concentration of an analyte in analog mode, this class of sensors does not seek to quantify the concentration. Rather, it detects the analyte's concentration in binary mode, reporting ON-state (1) for concentrations above a preset threshold and OFF-state (0) for concentrations below the threshold. The sensing mechanism exploits the qualitative difference between the sensor state before and after the dynamic pull-in bifurcation. Experimental demonstration was carried out using a laser-Doppler vibrometer to measure the sensor response before and after detection. The sensor was able to detect ethanol vapor concentrations as 100\,ppb in dry nitrogen. A closed-form expression for the sensitivity of dynamic bifurcation sensors was derived. It captured the dependence of sensitivity on the sensor dimensions, material properties, and electrostatic field. An analog dynamic bifurcation mass sensor is developed to demonstrate a sensing mechanism that exploits a quantitative change in the sensor state before and after depositing added mass. A polymeric material was deposited on the top surface of the sensor plate to represent added mass. A variation in the frequency and current amplitude were utilized to demarcate the added mass optically and electrically. A chemical sensor was also developed to detect mercury in deionized-water in a fashion of analog detection. A polymeric sensing material that has high selectivity to mercury was utilized to captured mercury molecules in water. The sensor was submerged completely in water with a pre-defined flow-rate. The sensor was excited electrostatically. A variation in the frequency response due to added mass was measured electrically using a lock-in amplifier. A frequency-shift was observed while releasing the mercury to the water.
Electrostatic Micro-Tweezers
(University of Waterloo, 2020-06-25) Alneamy, Ayman; Abdel-Rahman, Eihab; Heppler, Glenn
This dissertation presents a novel electrostatic micro-tweezers designed to manipulate particles with diameters in the range of 5-14 μm. The tweezers consist of two grip-arms mounted to an electrostatically actuated initially curved micro-beam. The tweezers offer further control, via electrostatic actuation, to increase the pressure on larger objects and to grasp smaller objects. It can be operated in two modes. The first is a traditional quasi-static mode where DC voltage commands the tweezers along a trajectory to approach, hold and release micro-objects. It exploits nonlinear phenomena in electrostatic curved beams, namely snap-through, snap-back and static pull-in and the bifurcations underlying them. The second mode uses a harmonic voltage signal to release, probe and/or interact with the objects held by the tweezers in order to perform function such as cells lysis and characterization. It exploits additional electrostatic MEMS phenomena including dynamic pull-in as well as the orbits and attractors realized under harmonic excitation. Euler-Bernoulli beam theory is utilized to derive the tweezers governing equation of motion taking into account the arm rotary inertia, the electrostatic fringing field and the nonlinear squeeze-film damping. A reduced-order model (ROM) is developed utilizing two, three and five straight beam mode shapes in a Galerkin expansion. The adequacy of the ROM in representing the tweezers response was investigated by comparing its static and modal response to that of a 2D finite element model (FEM). Simulation results show small differences between the ROM and the FEM static models in the vicinity of snap-through and negligible differences elsewhere. The results also show the ability of the tweezers to manipulate micro-particles and to smoothly compress and hold objects over a voltage range extending from the snap-back voltage (89.01 V) to the pull-in voltage (136.44 V). Characterization of the curved micro-beam show the feasibility of using it as a platform for the tweezers. Evidence of the static snap-through, primary resonance and the superharmonic resonances of orders two and three are observed. The results also show the co-existence of three stable orbits around one stable equilibrium under excitation waveforms with a voltage less than the snap-back voltage. Three branches of orbits are identified as a one branch of small orbits within a narrow potential well and two branches of medium-sized and large orbits within a wider potential well. The transition between those branches results in a characteristic of double-peak frequency-response curve. We also report evidence of a bubble structure along the medium sized branch consisting of a cascade of period-doubling bifurcations and a cascade of reverse period-doubling bifurcations. Experimental evidence of a chaotic attractor developing within this structure is reported. Odd-periodic windows also appear within the attractor including period-three (P-3), period- five (P-5) and period-six (P-6) windows. The chaotic attractor terminates in a cascade of reverse period-doubling bifurcations as it approaches a P-1 orbit.
Fabrication, Testing and Characterization of MEMS Gyroscope
(University of Waterloo, 2017-05-16) Almikhlafi, Ridha; Abdel-Rahman, Eihab
This thesis presents the design, fabrication and characterization of two Micro-Electro-Mechanical Systems (MEMS) vibratory gyroscopes fabricated using the Silicon-On-Insulator-Multi-User-MEMS Process (SOIMUMPs) and Polysilicon Multi-User-MEMS-Process (Poly-MUMPs). Firstly, relevant literature and background on static and dynamic analysis of MEMS gyroscopes are described. Secondly, the gyroscope analytical model is presented and numerically solved using Mathematica software. The lumped mass model was used to analytically design the gyroscope and predict their performance. Finite element analysis was carried out on the gyroscopes to verify the proposed designs. Thirdly, gyroscope fabrication using MEMSCAP's SOIMUMPs and PolyMUMPs processes is described. For the former, post-processing was carried out at the Quantum Nanofab Center (QNC) on a die-level in order to create the vibratory structural elements (cantilever beam). Following this, the PolyMUMPs gyroscopes are characterized optically by measuring their resonance frequencies and quality factor using a Laser Doppler Vibrometer (LDV). The drive resonance frequency was measured at 40 kHz and the quality factor as Q = 1. For the sense mode, the resonance frequency was measured at 55 kHz and the unity quality factor as Q = 1. The characterization results show large drive direction motions of 100 um/s in response to a voltage pulse of 10 V. The drive pull-in voltage was measured at 19 V. Finally, the ratio of the measured drive to sense mode velocities in response to a voltage pulse of 10 V was calculated at 1.375.
Fast Stress Detection via ECG
(University of Waterloo, 2019-05-23) Malinovic, Aleksandar; Abdel-Rahman, Eihab
Nowadays stress has become a regular part of life. Stress is difficult to measure because there has been no definition of stress that everyone accepts. Furthermore, if we do not get a handle on our stress and it becomes long term, it can seriously interfere with our health. Therefore, finding the method for stress detection could be beneficial for taking control of stress. Electrocardiogram (ECG) is the measurement of the electrical activity of the heart and represents an established standard in determining the health condition of the heart. The PQRST1[55] complex of ECG conveys information about each cardiac-cycle, where the R-peak is placed in the middle of the PQRST complex and represents the maximum value of the PQRST. Since the PQRST depicts the entire cardio-cycle, the R–peak determines half of the cardio-cycle. The distance between two adjacent R-peaks is defined as a heart rate (HR). The variation of the HR in the specific time frame, defined as heart rate variability (HRV), can reflect the state of the autonomic nervous system (ANS). The ANS has two main divisions, the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). The SNS occurs in response to stress while the PNS results from the function of internal organs. The activity of ANS can cause an acceleration (SNS) or deceleration (PNS) of the HR. The SNS activity is associated with the low-frequency range while, the PNS activity is associated with the high frequency component of the HRV. Therefore, the power ratio of the low and high-frequency components of the spectrum of HRV can potentially show whether the subject is exposed to stress or not [48] [50]. In this research, we introduced three new indices, with one of them proposed as a proxy to provide equivalent results in the detection of stress or no-stress states while avoiding complex measurement devices as well as complex calculations. The goal was to find a more time efficient method for fast stress detection which could potentially be used in the applications that run on devices such as a wearable smartwatch in tandem with a smartphone or tablet. The experiment was established to measure the literature proposed index for stress measurement [48][50] as well as our introduced indices. In the experiment, we induced stress to the participants by using mental arithmetic as a stressor [51][53]. Theexperiment contained two kinds of trials. In the first one, the participant was exposed to different amounts of cognitive load induced by doing mental-arithmetic while, in the second one, the participant was placed in a relaxed environment. Each participant in the experiment gave feedback in which period of the experiment he/she felt stress. During the entire experiment, we recorded theparticipant‘s ECG. The ECG was used to calculate HRV which consequently was used for the calculation of the values of the index as proposed from the literature for calculating the level of the stress. The same data was used for the calculation of our introduced indices. The values of our proposed index was compared with the index and the participant‘s feedback. Finally, the data analyses showed that our proposed index is suitable to determine whether a participant is exposed to stress.
Graphene Nanoparticle-Polymer Composite Fabricated by Pulsed Laser Ablation in Liquid
(University of Waterloo, 2016-06-09) ALAMRI, MERVAT; Abdel-Rahman, Eihab; Yavuz, Mustafa; Brzezinski, Andrew
Graphene is an attractive alternative material for diverse applications in electronic devices, fuel cells, biomedical sensors, energy storage, and super-capacitors due to its exceptional thermal, electrical, optical and mechanical properties. This material can be synthesized by many effective methods such as chemical vapor deposition (CVD), micromechanical exfoliation of graphite, and reduction of graphene oxide. Each of these methods has its advantages and disadvantages. This thesis investigates a novel and clean approach to grow graphene directly from bulk graphite by Pulsed Laser Ablation in Liquid, whereas the graphite sheets are immersed in different polymeric solutions (deionized Water, Ethanol, and Toluene) and exposed to two types of lasers (nanosecond and femtosecond lasers). This technique is simple, and fast; a one-step procedure to fabricate pure and stable graphene nanoparticles (GNPs) by short ablation time. It results in controllable-size products, high mass production, high stability, less aggregation, and absence of chemical agents, a known disadvantage observed in other approaches for graphene production. The ablation parameters had been optimized for the best formation efficiency of Pulsed Laser Ablation in Liquid (PLAL) process, after controllably varied trials, which are: 532 nm and 800 nm λ -wavelength for the nanosecond laser and femtosecond laser respectively, with pulse width of 150 ns for ns-laser and 35 fs for fs-laser. The pulse energy are 800 µJ and 250 μJ for the ns-laser and fs-laser respectively, 1kHz is the repetition rate for both lasers. Ablation times are 20 minutes for ns-laser and 1-2 hours for fs-laser, and 5 cm focal length for the focusing lens. Confirming the presence of graphene in solutions or in fabricated thin films is carried out by several characterization techniques including Raman; UV-VISIBLE; atomic force microscopy (AFM); scanning electron microscope (SEM); and transmission electron microscopy (TEM). These techniques allow an insight into the morphological and structural properties of the produced graphene, confirming the purity; particle size uniformity; as well as the number of graphene layers. This thesis attempts to interpret three main aspects of graphene growth: the advantages of the use of the PLAL approach and how it overcomes some of the reported challenges in graphene growth processes; the function of the contribution of different polymers which enhances the formation efficiency, and prevents agglomeration of carbon-based materials of the prepared GNP. Finally, the potential recipe that had been used for growing high quality graphene, with controllable thickness and particle size, was employed in the results section of this thesis.
Implementation of optical depth scanning and wide-field imaging in photoacoustic remote sensing (PARS) microscopy
(University of Waterloo, 2022-09-15) Mukhangaliyeva, Lyazzat; Haji Reza, Parsin; Abdel-Rahman, Eihab
Optical resolution photoacoustic microscopy (OR-PAM) is a hybrid biomedical imaging technique that utilizes acoustic detection and optical absorption contrast. It is based on the photoacoustic effect, where the excitation light energy absorbed by biomolecules is converted into heat. The initial temperature rise causes thermo-elastic expansion in tissues, resulting in the generation of acoustic waves detected by an ultrasound transducer. OR-PAM takes advantage of tightly focused light as the excitation source to achieve micron to submicron optical lateral resolution at superficial depths (~1mm). Additionally, it provides high contrasts to endogenous chromophores allowing for label-free in-vivo imaging. As a result, OR-PAM is a powerful tool for morphological, functional, and molecular imaging of biological organisms and their vital processes. However, conventional OR-PAM architectures are usually limited by the need for an ultrasound transducer to be in direct contact with the sample through a coupling medium. This condition introduces complexity to optical design and implementation and might become a source of infection or contamination in applications where physical contact is undesirable or impossible. Photoacoustic remote sensing (PARS) microscopy is an all-optical, label-free technique first introduced in 2017. But unlike OR-PAM, PARS does not require physical contact with the sample. PARS microscopy employs an interrogation beam as an alternative to the conventional ultrasonic transducer. There are, however, two limitations to PARS that will be addressed in this thesis dissertation. Firstly, PARS lacks an inherent 3D imaging capability since photoacoustic pressures induced by pulsed lasers are detected at their origin. Instead, volumetric imaging is achieved by mechanical scanning, which presents some drawbacks, such as slow scanning rates and motion artifacts, as well as being bulky and expensive. Optical focus shifting may allow PARS to image larger volumes at higher speeds and with higher resolution. In this work, a novel continuous micro-electromechanical systems (MEMS) deformable mirror (DM) was integrated into a PARS microscope for imaging at varying depths. The first step was to create an optical model using the DM characteristics and use Zemax to predict the focal shift. Next, an experimental investigation of the focus shifting ability of the DM was conducted using a 532-nm scattering microscope, and a focal shift of 240 µm was achieved. Afterward, carbon fiber imaging was conducted to demonstrate the axial scanning capabilities of DM-based PARS microscopy. Lastly, the focal plane was optically shifted to perform in-vivo PARS imaging of blood vessels in chick embryo chorioallantoic membrane (CAM) models at different depths. The second limitation of PARS microscopy is its inability to provide fast wide field of view (WFOV) imaging. WFOV imaging is achieved by mechanically scanning small areas laterally at different positions and then stitching them together. Mechanical scanning, however, is slow, prone to motion artifacts, and might agitate sensitive samples. As part of this work, we demonstrated how an optical approach using a scan lens could be used to achieve 8.58.5 mm2 FOV imaging of carbon fibers in PARS. Moreover, the system was utilised in in-vivo studies by imaging CAM vasculature and reaching up to 3.343.34 mm2 FOV. Further system enhancements are needed to expand the FOV, increase imaging speeds, and improve resolution. This potentially can be realized by integrating adaptive optics elements to actively correct for system- and specimen-induced aberration and adjust focus over a large FOV.
Incorporation of Pressure Insoles into Inverse Dynamic Analysis
(University of Waterloo, 2022-01-27) Mahmassani, Ahmad; Abdel-Rahman, Eihab; Haas, Carl
Estimation of body loads during industrial tasks, such as lifting and weight bearing, is central to workplace ergonomics and the study of the safety and risk factors in work techniques. Evaluating those loads requires data collection of body kinematics and the external forces prevailing during the task under evaluation. Current practice calls for kinematic data to be gathered using optical motion capture systems (OMC) and external forces, primarily ground reaction forces (GRFs), to be gathered using force plates. However, this experimental methodology is confined to laboratory settings. Modern motion capture systems, such as those based on Inertial Measurement Units (IMUs), pave the way to more versatile motion analysis techniques not confined to labs. Inverse dynamics models have been developed based on IMU kinematic data. In order to eliminate the need for force plates and to make the experimental apparatus fully portable, those models estimate GRFs from measured accelerations. This study aimed to advance the state-of-the-art on IMU-based inverse dynamics analysis by incorporating pressure insoles as the source of the vertical components of the GRFs, with a view to improving the model fidelity while keeping the experimental apparatus portable. Specifically, it enabled the development of a synchronized and automated inverse dynamics model, comprised of an inertial motion capture suite and pressure insoles, that can estimate net joint forces and moments during manual handling activities. An experiment was designed to examine whether the GRFs measured by the pressure insole can detect and differentiate among various sizes (and weights) of concrete masonry units (CMUs). The instrumented pressure insoles were consistently able to identify three different CMU block weights (8 kg, 16kg, and 24 kg) during various gait patterns (along circular, square, and linear paths). On the other hand, the results were inconclusive in distinguishing between one-handed and two-handed manual handling of CMUs. An improved inverse dynamic model was introduced to calculate the joint loads workers experience during material manual handling based only on measurements by IMU motion capture suits and pressure insoles. The outcome of this thesis was the development of a weight detection algorithm with a detection accuracy of 89% across all three sizes of CMUS as well as an integrated inverse dynamic model incorporating data collected by IMUs motion suits and pressure insoles.
Interaction Forces in Coupled Magnetic Pendulums
(University of Waterloo, 2022-09-22) Lahlou, Mariam; Heppler, Glenn; Abdel-Rahman, Eihab
In this research, we investigated the non-linear motion and magnetic forces in a chain of magnetic pendulums with cylindrical magnets to eventually better understand the be- haviour of Josephson junction-effect devices. We studied the nonlinear motions of our system through the interaction forces between the magnets and analytically derived the equations of motion with the aim of simulating the dynamics of the system. To obtain the natural frequencies of our analytical system, we used the Fast Fourier transform. Finally, we validated the accuracy of our simulated system’s response by comparing its behaviour to that of an experimental setup consisting of two coupled magnetic pendulums. Ultimately, we solved for the equations of motions of our magnets and integrated the magnetic forces from the magnetic field function. We also experimentally validated the nonlinear response of the system as well as its equilibrium points and natural frequency. The results we obtained through comparing the simulated system response and the de- signed experiment response indicated that our analytical model can accurately predict the behaviour of such a system.
Interactions of Magnetic Pendulums
(University of Waterloo, 2019-09-03) Saeidi Hosseini, Razieh Sadat; Heppler, Glenn; Abdel-Rahman, Eihab
In recent years, coupled magnetic oscillators have received remarkable attention due to their application in vibration energy harvesting techniques and also its promising ability to help researchers to have a better understanding of atoms in a lattice behaviour. Energy harvesters scavenge ambient vibration energy and convert it into useful electrical energy. According to previous studies nonlinear mechanical attachments have received significant interest as the basis for energy harvesting systems. Another substantial field that coupled nonlinear oscillators and specifically coupled magnetic oscillators may play a crucial role in is atomic physic. Due to the qualitative similarity of the magnetic field and the electromagnetic field governing the atoms in the lattice structure in crystalline solids, investigating the coupled magnetic oscillators could help researchers to better perceive the lattice behaviour. In this thesis, a chain of two-dimensional magnetic pendulums using an ideal point mass model as well as a rigid body model of a pendulum is investigated. The pendulums proposed in the model are to simulate the vibration of atoms in the lattice structure of crystalline solids and the attached magnets are chosen to represent the electromagnetic field governing the atoms. The nonlinear dynamics of the models through the interaction forces between the magnets has been investigated. With the aim of demonstrating the dynamics of the system completely, the equations of motion of the pendulum magnets have been analytically derived and by linearizing the equations of motion, the natural frequencies of the system have been found. The behaviour of the simulated system has been examined experimentally to assure the accuracy of the analytical approach. To achieve the intent, a simple experimental setup consisting of an array of two coupled magnetic pendulums has been introduced. Ultimately, the equations of motions of a rigid body model including the determined magnetic forces have been numerically solved and the nonlinear response of the system along with the equilibrium points and the system's frequency have been validated experimentally. The results obtained through comparing the simulated system response and the designed experiment response indicates that the simulated model can predict the behaviour of such system in reality.
Open-Loop Transient Atomic Force Microscopy
(University of Waterloo, 2023-02-01) Olfat, Seyed-Mahdi; Abdel-Rahman, Eihab
The Atomic Force Microscope (AFM) is an instrument for measuring, in fact “seeing”, phenomena at nanoscale (10^(-9) m) and all the way down to the atomic scale (<10^(-10) m). It was borne out of a need to observe physical reality below the resolution of optical microscopes. Invented in 1986 by Binnig, it has aided scientists, researchers, and engineers spanning many scientific and industrial domains. The typical sensing apparatus of the AFM is a very sharp tip (a few atoms wide) attached to the free-end of a fixed-free micro-beam. The tip is brought close to the desired specimen to initiate localized force interactions between the top-most atoms of the specimen and the bottom-most atoms of the tip. The tip-sample coupled system introduces a relative shift in the deflection of the microcantilever, this shift is interpreted as the magnitude of the interaction force and used for topographical mapping as well as mechanical/electrical/thermal characterization of a single point on the specimen. By recording the cantilever deflections while laterally scanning the sample, an area is “imaged”. According to resonant sensing theory, the sensitivity of the deflection of an oscillating cantilever beam driven at its resonant frequency is increased by a factor proportional to its quality factor (Q). As such, it is very common for an AFM cantilever to be driven at (or near) its first resonant mode in order to increase the Signal-to-Noise ratio (SNR). Whilst away from the sample, the steady-state response is perfectly harmonic with a force-response phase difference of 90 degrees: the very definition of resonance. However, near the sample, the response becomes anharmonic, nonlinearly modulated by the tip-sample interactions. This anharmonic response needs to be demodulated to quantify the interaction forces. The deviation from the harmonic response is only instantly described if the instantaneous frequency and amplitude are known. Alas, this is not possible. System design engineers are confronted with the ultimate compromise, namely, the Heisenberg uncertainty principle. More specifically, the energy spread of any time-frequency transformed signal forms a rectangle in the time-frequency plane, this "Heisenberg resolution box" has a minimum surface area of 1/2 that ultimately limits the attainable time-frequency resolution. This thesis proposes a framework for a holistic approach to an open-loop bottom-up AFM system design. Design decisions and compromises are discussed and analyzed based on the desired requirements such as the SNR, the minimum acceptable noise floor, the demodulation scheme, and the maximum/minimum response times. An electrothermally driven and piezo-resistively sensed single-chip AFM (sc-AFM) is used for testing and verification. System Identification is carried out in the frequency domain to characterize the noise and establish the best linear approximation (BLA) transfer function of the AFM cantilever. For imaging, the AFM cantilever is continuously driven by an excitation signal while the cantilever deflection signal is sampled and filtered digitally. An analysis window is selected to adequately capture both transient and steady-state responses of the cantilever deflection signal. Moreover, a complete digital processing pipeline is proposed and implemented using the STFT for nonlinear time-varying spectral signal processing. Finally, imaging results based on amplitude-modulation AFM (AM-AFM) are demonstrated.
Resonant Drive Techniques for MEMS: A Comparative Study
(University of Waterloo, 2023-06-12) Abdelrahman, Rana; Abdel-Rahman, Eihab; Yavuz, Mustafa
Electrostatic actuation is popular in microelectromechanical systems (MEMS) because of its many advantages. However, it requires high voltage, typically provided by a power supply and a high voltage amplifier, which is limited in gain. As research interest has shifted to explore higher frequency MEMS, various methods have been proposed to amplify the voltage signal fed into the system by coupling it in series to an LC tank circuit. These methods are based on utilizing the electrical quality factor of an RLC circuit driven at its natural frequency. In this thesis, we analyzed and compared among these three resonant drive techniques. We also compared their performance to a voltage amplifier. The first resonant drive technique matches electrical and mechanical resonances and activates them simultaneously. The second technique drives the MEMS with a two-frequency signal. One frequency is set equal to the electric resonance, while the sum or difference of the two frequencies is set equal to the mechanical resonance. In the third method, an amplitude-modulated (AM) signal that contains an RF carrier frequency and a baseband frequency is used. The LC circuit is tuned to match the carrier frequency to the electrical resonance, and the baseband frequency is set equal to the mechanical resonance.
Resonant MEMS Deformable Mirror
(University of Waterloo, 2022-01-21) Kocer, Samed; Abdel-Rahman, Eihab; Yavuz, Mustafa
The performance of optical systems is often affected by aberrations that degrade the image resolution and contrast. These aberrations may be induced from atmospheric turbulence, imperfection in the optical alignment, or inhomogeneous refractive index distribution. Adaptive optics (AO) technology has been incorporated into different types of imaging instrument to correct optical aberrations. Deformable mirrors (DMs) are commonly used correction elements in AO due to their high optical performance, low cost, and reflective characteristics which enable to operate at different wavelengths. A DM can correct the aberrations by introducing a counter deformation to its reflective surface with respect to aberrated wavefront. Various DM designs have been developed over the last several decades to improve the state-of-the-art. Conventional DMs were invented to be used in astronomical observations. They are bulky, expensive, and required high voltages to operate. The development of micromachining introduced MEMS based DMs as an alternative to conventional ones and extended the utilization of AO in many areas including microscopy, laser machining, ophthalmoscopy, and optical coherence tomography (OCT). The design of DMs can be classified in two categories based on their reflective surface topology either segmented or continuous. Segmented DMs impose piston-tip-tilt motion to deform surface. They prevent cross coupling between actuators and provide high strokes, but the gaps between each segment scatter the light, and cause diffraction. Continuous DMs accomplish almost zero diffraction operation, however inter-actuator coupling occurs. MEMS DMs are preferred due to their compact size, low power consumption, and relatively fast response time. Piezoelectric, electrostatic, electrothermal, and electromagnetic actuation mechanisms are applied via a distributed actuator array underneath a mirror surface to deform its profile. Majority of the MEMS DM designs have mainly built on direct current (DC) electrostatic or piezoelectric actuation mechanisms. The former are encumbered with high electrode counts, special control algorithms and associated hardware. The latter are encumbered with hysteresis and complex structure which reduces their compatibility to micromachining. Besides, piezoelectric MEMS DMs might not be able to correct high and low order aberrations in a single actuator array design. Therefore, different electrode schemes might be necessary to replicate higher order aberrations, and each scheme requires different fabrication. Recent developments in AO have emphasized the demand for large stroke, low cost, easy-driven wavefront correction elements which built-in a simple miniaturized architecture to compensate optical aberrations rapidly in real-time. Thus, there is a need to develop such a system to advance the current state-of-the-art. In this thesis, we present a novel MEMS DM that can be used for AO to correct wavefront aberrations during real-time scanning. The DM employs resonant electrostatic actuation (REA) via 49 electrodes to deform a 1.6 mm circular plate dynamically. The DM surface was designed to be continuous to eliminate light diffraction across the facesheet. Unlike bias actuated and piezoelectric DMs, it can correct both low and high order aberrations within a simple device structure using a single actuator array by applying a single voltage waveform, thereby eliminating the need for individually addressable electrodes and the use of complex influence functions. REA drives the mirror at resonance and exploits dynamic amplification to increase the stroke with a minimal number of electrodes. The mirror depicts a low cost and high-performance alternative to previous MEMS DMs. The DM was designed and fabricated using a silicon-on-insulator (SOI) MEMS fabrication process. Finite element (FEM) simulations were conducted to determine natural frequencies and mode shapes of the DM geometry. Experimental characterization was carried out using laser Doppler vibrometer (LDV). To demonstrate mirror capability the DM was integrated into an optical system as a varifocal mirror to shift the focal point of a 532 nm incident pulsed laser beam. It is shown that an 8 cm focal shift was realized between the focal lengths of 11 cm and 19 cm. The DM surface was controlled easily by changing the phase angle $\phi$ between the pulse signal of the incident laser beam and the drive signal of the DM. The mirror promises to advance the current state-of-the-art aberration correction techniques and can be used as an adaptive element in AO systems for axial scanning and 3D multiwavelength imaging.
Tunable Permittivity Sensors
(University of Waterloo, 2021-09-02) Ahmed, Alaaeldin; Abdel-Rahman, Eihab; Basha, Mohamed
This thesis presents a novel electric permittivity sensor based on Bleustein- Gulyaev (BG) waves; waves that propagate along the surface of shear-poled piezoelectric materials. BG waves couple electromagnetic and acoustic waves, thereby reducing the speed of electromagnetic propagation to near acoustic speeds. Exploiting this property allows the development of permittivity sensors that feature several orders of magnitude reduction in size and operating frequency. This releases the limitations of RF complexity while reducing cost considerably. It also makes the sensor attractive for biological applications, as opposed to RF sensors that are limited by the water relaxation phenomenon at frequencies beyond 4 GHz. To date, sensors that used BG waves were limited to sensing mechanical properties, such as viscosity and density, which exploited the acoustic component of the wave only. To our best knowledge, this is the first attempt to probe and sense an electrical property acoustically using BG-waves. Towards that end, the nonlinear partial differential equations governing an electromechanical BG wave resonator are formulated. The permittivity of the medium-under-test was found to influence the sensor eigenvalues, enabling the implementation of a frequency-shift permittivity sensor. We also find that the sensor sensitivity is enhanced by increasing bias voltage to drive the sensor into the nonlinear regime, but this is limited by electrical breakdown. Sensor prototypes were fabricated on PZT4 and LiNbO3 shear-poled substrates. A novel method to characterize shear-horizontal surface acoustic waves, SHSAW, using a 1D Laser Doppler Vibrometer was developed to test the sensors. The method was also shown to be able to estimate the in-plane displacement field decay rate into the substrate. This technique provides researchers with a quick and effective method for the characterization of SH-SAW. The resonator model was validated using this experimental method. A Vector Network Analyzer was employed to observe the shift in the fundamental natural frequency of the fabricated permittivity sensors in the presence of various media-under-test. Measurements show deterministic and repeatable frequency shifts in the natural frequency in the presence of ethanol and deionized water compared to that of the bare surface, thereby demonstrating the permittivity sensor.
Use of Kinematics to Minimize Construction Workers' Risk of Musculoskeletal Injury
(University of Waterloo, 2017-03-29) Alwasel, Abdullatif; Abdel-Rahman, Eihab; Haas, Carl
Construction work requires more repetitive and highly physical effort than, for example, office work. Despite technological advancements in construction, the human factor is still an essential part of the industry. Hence, the need to maintain a healthy work environment is a shared interest between workers and industry. This thesis addresses the problem of cumulative injuries among construction workers, with emphasis on masons, and examines ways to improve safety and productivity simultaneously. Vision-based motion capture and sensor-based joint angle measurement techniques were tested against a state-of-the-art Optotrak system. Results show that the overall error in joint angle measurements was 10 deg for vision-based approaches compared to 3 deg for optical encoders. Moreover, a noninvasive fatigue detection method was developed by applying time-delay embedding and phase-space warping (PSW) techniques to a single joint angle, exerted force, and electromyography (EMG) data. Results indicate that the method can detect a slowly changing variable, fatigue in a limb, from a single kinematic signal, limb exerted force, or its EMG signals. Furthermore, twenty one masons distributed in four experience categories, ranging from novice to expert, took part in a study to evaluate safety and productivity in masonry work using inertial measurement units (IMUs). The study hypothesized that masons adopt safer and more productive work techniques with experience and that these techniques can be identified and used to train novice workers. Results indicate that journeymen appear to develop more productive and safer work techniques compared to other groups. On the other hand, the three-years experience group was found to sustain the highest joint compression forces and moments. Results also show that a clear distinction exists between expert and inexpert mason motion patterns. Support Vector Machine (SVM) classifiers were able to identify these differences with an accuracy of %92.04 in 13 seconds using a linear kernel. The thesis findings justify exploration of sensor fusion techniques to combine direct and indirect motion capture systems. The findings also suggest that PSW can be used in applications such as rehabilitation to access information about patient status hidden in the full-chain kinematics using a single kinematic signal. Finally, findings show the potential for training apprentices to excel in all three aspects: proficiency, productivity, and ergonomic safety by following the example of experts.

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