Engineering (Faculty of)

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Now showing 1 - 20 of 27

Assessment Methods for Advanced Masonry Work Systems
(University of Waterloo, 2021-03-19) Ryu, JuHyeong; Haas, Carl; Abdel-Rahman, Eihab
The physically strenuous and demanding nature of construction tasks exposes workers to injury risks, can reduce productivity, and contributes to undesirable early retirement. In spite of these risks, human performance in the workplace is often managed by over-simplified standards. Complex construction sites require continuous manual labor intervention. Site complexity also preclude objective and reliable quantification of labor exposure to ergonomic risk factors. It also impedes the introduction of automation and robotics in construction industry despite recent advancements in other construction technologies. The overarching goal of this dissertation is to identify opportunities for human-centric advanced work assessment systems that can 1) objectively and simultaneously evaluate ergonomic risk levels and productivity in construction tasks involving heavy material handling, 2) effectively identify safe and productive working postures and techniques that workers develop as they gain experience, and 3) evaluate the impact of introducing new, semi-automated work systems on health and productivity in a construction context. To achieve these goals, this research adopts wearable inertial measurement unit (IMU) based motion capture systems as means of data collection in construction worksites. It analyzes the resultant whole-body kinematic data using analytical tools including combined biomechanical-productivity analysis, rule-based postural ergonomic risk assessment, statistical analysis, and data clustering algorithms. This research specifically focuses its efforts on the masonry field, one of the most labor-intensive trades in construction. Over the span of four years, 45 masons at various levels of experience participated in field experiments within the framework of this study. The acquired data was used to develop automated ergonomic assessment systems to evaluate risk levels via various rule-based assessment tools as well as biomechanical analysis. This approach enabled us to objectively evaluate ergonomic risk level in construction tasks, then analyze the relationships among body loads, experience, and work methods to quantitatively investigate differences in joint loads between experts and apprentices. Furthermore, motion data-driven identification of expert work technique was proposed as a guide to proper working methods and apprentice training. These approaches allowed us to identify proper work techniques adopted by experts and suggested the utilization of expert' techniques in apprentice training to reduce the prevalence of occupational injuries and to improve productivity. Leveraging these insights, this study proposed a systematic and objective methodology to assess the value of a semi-automated work system in a construction context. The proposed methodology fills an important technology gap by representing a proactive approach for the evaluation of semi-automated work systems in terms of reduction in exposure to health risks and improvements of productivity. Ultimately, the present research seeks to maximize occupational performance by minimizing the level of human efforts in construction.
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.
Design of an Integrated Electrostatic Atomic Force Microscope
(University of Waterloo, 2018-05-22) Nafissi, Hamidreza; Abdel-Rahman, Eihab; Mansour, Raafat
The need for investigation and characterization of physical, chemical and structural properties of material surfaces at the micro and nano scales led to the invention of Atomic Force Microscopy (AFM) in 1986 as a successor to the well-known Scanning Tunneling Microscopy (STM) to overcome the main shortcoming of STM, which worked only on conducting or semiconducting materials. In fact, the idea of AFM is predicated on the measurement of inter-atomic interaction forces between the molecules of a sharp stylus at the end of a silicon probe and the molecules of a specimen, when the tip comes to close proximity (less than $100$nm) of the sample. It detects the height of the probe hovering above the specimen surface by measuring the tip deflection, or the amplitude and frequency of its vibration. In each case (mode), the interaction forces between the sharp tip and the specimen govern the measured parameter which is detected optically by a laser beam reflected of the probe back side. A piezoelectric actuator drives the probe vibrations and Z-axis motions. Optical detection and piezoelectric actuation contribute significantly to the price and complexity of traditional AFM systems. In this research effort, we use electrostatic actuation and capacitive motion detection of off-shelf AFM probes via electrodes printed on a Printed Circuit Board (PCB), thereby eliminating the optical and piezoelectric components of traditional AFMs, drastically reducing its cost, size and complexity as well as enabling new AFM operating modes. Two configurations for the probe-electrode system were modeled, simulated and demonstrated experimentally. The actuation voltage contains DC and AC components while the actuation frequency is set close to the probe natural frequency. Model and experimental results show that the DC component controls the operating point (static gap between the electrode and the probe) and the AC component controls the sensitivity of the AFM. The detector output current is first amplified using a low-noise transimpedance amplifier. Next, a lock-in amplifier measures the magnitude and phase of the current at the second harmonic of the actuation frequency which is directly related to the tip-sample separation. This detection method overcomes the effect of large parasitic capacitance. It enables us to sketch two-dimensional maps of the current's magnitude or phase representing the specimen's topography. To improve sensitivity, the static distance between the probe\textquoteright s tip and the specimen was set to operate the AFM in intermittent (tapping) mode. A nano-stage was developed for this purpose. It allows us to raster scan the specimen surface. In future work, automatic closed-loop feedback control should be deployed to manage the height of the AFM tip over the specimen. A resonant drive and detection scheme should also be used to miniaturize the footprint of the AFM system to a few centimeters.
Design, fabrication and characterization of ferroelectret energy harvester
(University of Waterloo, 2019-04-22) Kayaharman, Muhammed; Yavuz, Mustafa; Abdel-Rahman, Eihab
Energy harvesters gained significant interest over the last decade with the reduce in power requirements of today’s electrical devices and with the fast developments in low-power electronics. Limited battery life is one of the weak spots that constrains the potential of possible applications. There are only two options for remote applications when the battery is died. Either charging the battery or replacing the battery with a new one. And both of these solutions are time-consuming and expensive. On the other hand, for some of the remote applications, such as health monitoring for aircrafts, battery replacement or charging may not even be an option because of dangerous or inaccessible area conditions. In this research, a one-layer ferroelectret energy harvester is designed and fabricated. Ferroelectret energy harvester is modeled as a mass-spring-damper under harmonic base excitation. d33 piezoelectric constant of the harvester is measured with laser interferometry method. Natural frequency of the harvester is measured experimentally with a frequency sweep up to 1 kHz. Optimum resistance of the three energy harvesters measured with impedance matching to maximize the transduction from mechanical domain into electrical domain. The effect of constant stress and stress-cycling on the stability of ferroelectret energy harvester is analyzed. According to our experiment results, constant stress significantly increased the d33 piezoelectric charge constant and the natural frequency (wn) of the harvester. Increased d33 constant also increased the the power output of the harvester under constant stress compared to stress-cycling and stress-free. Also output voltage and the capacitance value of the energy harvesters are affected by constant-stress and stresscycling. And last, mathematical model is compared with experimental results to validate the piezoelectricity of ferroelectret energy harvesters.
Design, Fabrication and Characterization of MEMS Gyroscopes Based on Frequency Modulation
(University of Waterloo, 2018-07-24) Effa, Dawit (David); Yavuz, Mustafa; Abdel-Rahman, Eihab
Conventional amplitude modulated (AM) open loop MEMS gyroscopes experience a significant performance trade-off between having a large bandwidth or high sensitivity. It is impossible to improve both metrics at the same time without increasing the mass of the gyroscope or introducing a closed loop (force feedback) system into the device design. Introducing a closed loop system or increasing the proof mass on the other hand will surge power consumption. Consequently, it is difficult to maintain consistently high performance while scaling down the device size. Furthermore, bias stability, bias repeatability, reliability, nonlinearity and other performance metrics remain primary concerns as designers look to expand MEMS gyroscopes into areas like space, military and navigation applications. Industries and academics carried out extensive research to address these limitations in conventional AM MEMS gyroscope design. This research primarily aims to improve MEMS gyroscope performance by integrating a frequency modulated (FM) readout system into the design using a cantilever beam and microplate design. The FM resonance sensing approach has been demonstrated to provide better performance than the traditional AM sensing method in similar applications (e.g., Atomic Force Microscope). The cantilever beam MEMS gyroscope is specifically designed to minimize error sources that corrupt the Coriolis signal such as operating temperature, vibration and packaging stress. Operating temperature imposes enormous challenges to gyroscope design, introducing a thermal noise and drift that degrades device performance. The cantilever beam mass gyroscope system is free on one side and can therefore minimize noise caused by both thermal effects and packaging stress. The cantilever beam design is also robust to vibrations (it can reject vibrations by sensing the orthogonally arranged secondary gyroscope) and minimizes cross-axis sensitivity. By alleviating the negative impacts of operating environment in MEMS gyroscope design, reliable, robust and high-performance angular rate measurements can be realized, leading to a wide range of applications including dynamic vehicle control, navigation/guidance systems, and IOT applications. The FM sensing approach was also investigated using a traditional crab-leg design. Tested under the same conditions, the crab-leg design provided a direct point of comparison for assessing the performance of the cantilever beam gyroscope. To verify the feasibility of the FM detection method, these gyroscopes were fabricated using commercially available MIDIS™ process (Teledyne Dalsa Inc.), which provides 2 μm capacitive gaps and 30 μm structural layer thickness. The process employs 12 masks and hermetically sealed (10mTorr) packaging to ensure a higher quality factor. The cantilever beam gyroscope is designed such that the driving and sensing mode resonant frequency is 40.8 KHz with 0.01% mismatch. Experimental results demonstrated that the natural frequency of the first two modes shift linearly with the angular speed and demonstrate high transducer sensitivity. Both the cantilever beam and crab-leg gyroscopes showed a linear dynamic range up to 1500 deg/s, which was limited by the experimental test setup. However, we also noted that the cantilever beam design has several advantages over traditional crab-leg devices, including simpler dynamics and control, bias stability and bias repeatability. Furthermore, the single-port sensing method implemented in this research improves the electronic performance and therefore enhances sensitivity by eliminating the need to measure vibrations via a secondary mode. The single-port detection mechanism could also simplify the IC architecture. Rate table characterization at both high (110 oC) and low (22 oC) temperatures showed minimal changes in sensitivity performance even in the absence of temperature compensation mechanism and active control, verifying the improved robustness of the design concept. Due to significant die area reduction, the cantilever design can feasibly address high-volume consumer market demand for low cost, and high-volume production using a silicon wafer for the structural part. The results of this work introduce and demonstrate a new paradigm in MEMS gyroscope design, where thermal and vibration rejection capability is achieved solely by the mechanical system, negating the need for active control and compensation strategies.
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.
Electromagnetic Vibrational Energy Harvesters and Power Management
(University of Waterloo, 2016-01-14) Tunkar, Bassam; Yavuz, Mustafa; Abdel-Rahman, Eihab
The interest in scavenging various energy sources from the environment is rapidly increasing. Thanks to the advances in developing effective energy harvesters researches. Kinetic energy is a renewable source and it can be found numerously in the environment. One of the most popular class of the kinetic energy harvesters in this field is vibration energy harvesters (VEH). It is an electrical source that converts the vibrational energy into usable electrical energy to power up low-power portable or unreachable devices. The harvesting system can be self-powered as stand-alone or as alternative power source depending on the application. In this thesis, we have studied and developed two architectures for electromagnetic VEHs: a baseline VEH and a springless VEH. We introduced and studied power management circuits consisting of a full-wave bridge rectifier and a smoothing capacitor. Moreover, electromechanical model was developed and validated by the comparison to the experimental data. The basic electromagnetic VEH uses a mechanical mass-damper-spring oscillator to capture kinetic energy from vibrations. It has an electrical transducer using induction between a moving coil and a fixed magnets. It uses a cantilever suspension and operates at a frequency range of 57-59 Hz. We re-designed it using 80 turns coil-chip instead of 30-turns. The springless VEH works in a frequency range of 13-18 Hz. It was redesigned to carry 60-turns coil-chip. The re-design of the VEHs successfully increased the output voltage and power. The maximum power experimentally measured were 14.3mW and 12.27mW at optimal loads RL of 40 ohm and 3 ohm, respectively. The power management circuits introduced is consist of a MOSFET-based full-wave bridge rectifier and a smoothing capacitor to convert the VEH AC output waveform into a DC signal. We found that this rectifier can effectively convert the VEHs output with high voltage and power efficiencies > 93 %. The smoothing capacitor trades-in the signal ripples for lower voltage and power e efficiencies > 79 %. We identified the model parameters for the cantilever VEH, namely the natural frequency, mechanical Qm and total Qt quality factors, and effective average magnetic field density B. We solved the model equations numerically and analytically to find the eigenvalues, frequency response, output voltage and power. The model results agree with the obtained experimental results.
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.
Jerk as a Method of Identifying Physical Fatigue and Skill Level in Construction Work
(University of Waterloo, 2019-04-26) Zhang, Lichen; Haas, Carl; Abdel-Rahman, Eihab
Researchers have shown that physically demanding work, characterized by forceful exertions, repetition, and prolonged duration can result in fatigue. Physical fatigue has been identified as a risk factor for both acute and cumulative injuries. Thus, monitoring worker fatigue levels is highly important in health and safety programs as it supports proactive measures to prevent or reduce instances of injury to workers. Recent advancements in sensing technologies, including inertial measurement units (IMUs), present an opportunity for the real-time assessment of individuals' physical exposures. These sensors also exceed the ability of mature motion capture technologies to accurately provide fundamental parameters such as acceleration and its derivative, jerk. Although jerk has been used for a variety of clinical application to assess motor control, it has seldom been studied for applications in physically-demanding occupations that are directly related to physical fatigue detection. This research uses IMU-based motion tracking suits to evaluate the use of jerk to detect changes in motor control. Since fatigue degrades motor control, and thus motion smoothness, it is expected that jerk values will increase with fatigue. Jerk can be felt as the change in force on the body leading to biomechanical injuries over time. Although it is known that fatigue contributes to a decline in motor control, there are no explicit studies that show the relationship between jerk and fatigue. In addition, jerk as it relates to skill level of highly repetitive and demanding work has also remained unexplored. To examine these relationships, our first study evaluates: 1) the use of jerk to detect changes in motor control arising from physical exertion and 2) differences in jerk values between motions performed by workers with varying skill levels. Additionally, we conducted a second study to assess the suitability of machine learning techniques for automated physical fatigue monitoring. Bricklaying experiments were conducted with participants recruited from the Ontario Brick and Stone Mason apprenticeship program. Participants were classified into four groups based on their level of masonry experience including novices, first-year apprentices, third-year apprentices, and journeymen who have greater than five years of experience. In our first study, jerk analysis was carried out on eleven body segments, namely the pelvis, and the dominant and non-dominant upper and lower limb segments. Our findings show that jerk values were consistently lowest for journeymen and highest for third-year apprentices across all eleven body segments. These findings suggest that the experience that journeymen gain over the course of their career improves their ability to perform repetitive heavy lifts with smoother motions and greater control. Third-year apprentices performed lifts with the greatest jerk values, indicating poor motor performance. Attributed to this finding was the pressure that third-year apprentices felt to match their production levels to that of journeymen’s, leading third-year apprentices to use jerkier, less controlled motions. Novices and first-year apprentices showed more caution towards risks of injury, moving with greater motor control, compared to the more experienced third-year apprentices. However, the production levels of novices and first-year apprentices falter far behind the production levels of other experience groups. Detectable increases between jerk values during the beginning (rested) and end (exerted) of the task were found only for the journeymen, which is attributed to their greater interpersonal similarities in learned technique and work pace. In our second study, we investigated the use of support-vector machines (SVM) to automate the monitoring of physical exertion levels using jerk. The jerk values of the pelvis, upper arms, and thighs were used to classify inter-and intra-subject rested and exerted states. As expected, classification results demonstrated a significantly higher intra-subject rested/exerted classification than the inter-subject classification. On average, intra-subject classification achieved an accuracy of 94% for the wall building experiment and 80% for the first-course-of-masonry-units experiment. The thesis findings lead us to conclude that: 1) jerk changes resulting from physical exertion and skill level can be assessed using IMUs, and 2) SVMs have the ability to automatically classify rested and exerted movements. The investigated jerk analysis holds promise for in-situ and real-time monitoring of physical exertion and fatigue which can help in reducing work-related injuries and illnesses.
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.

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