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Recent Submissions
Microstructure control and property enhancement of NiTi-stainless steel dissimilar joints
(University of Waterloo, 2025-03-21) Zhang, Kaiping
Dissimilar joining between Nickel-Titanium (NiTi) and stainless steel (SS) is of significance in many areas especially biomedical applications, however, achieving reliable NiTi-SS joints is highly challenging due to the formation of brittle intermetallic compounds (IMCs) in the fusion zone (FZ) or the interface. Two strategies can be summarized to address this issue: (1) restricting the mixing of molten metals and (2) replacing the most harmful Laves (Fe,Cr)2Ti with ductile phases. The former one poses large processing complexity and may lead to NiTi plastic deformation degrading the functional properties. The latter struggles to eliminate brittle IMCs entirely in the FZ and may introduce toxic elements. This research investigated both aspects to control the microstructure and properties of NiTi-SS joints by leveraging the flexibility of laser beam and the thermomechanical process of resistance welding.
The combination of laser beam defocus and large offset enabled the laser weld-brazing of NiTi and SS wires. This approach successfully eliminated the IMCs network in the FZ, shifting the conventional and complex FZ brittleness issue to a focus on controlling the brazed interface. Additionally, laser welding mode significantly influenced the macrosegregation and porosity in the FZ of NiTi-SS joints. Low laser power density and long welding time mitigated the macrosegregation and porosity by weakening the laser keyhole effect and prolonging the molten pool duration. In NiTi-SS laser weld FZ, large pores were caused by the instability or collapse of the laser keyhole, while small pores originated from the Ni vaporization.
Both IMCs control strategies were investigated in resistance spot welding (RSW) of NiTi and SS for the first time. The use of Nb interlayer resulted in a unique sandwich-structured joint, where two FZs were separated by solid-state Nb, suppressing the mixing of dissimilar molten metals. Nb-containing eutectics formed at both interfaces, enhancing the joint strength with a 38% increase in fracture load and a remarkable 460% increase in energy absorption. In another approach, increasing Ni concentration via a melted Ni interlayer effectively replaced Fe2Ti with relatively ductile Ni3Ti in the FZ. However, high Ni content also induced large pores and cracks, limiting the effectiveness of this strategy in NiTi-SS RSW.
A novel processing approach leveraging interfacial liquid control was proposed, achieving a solid-state joined interface in NiTi-SS fusion welding (e.g., resistance microwelding) without any additional interlayers. The produced NiTi-SS joints showed superior strength, superelasticity and corrosion resistance compared to NiTi joints or base metal. The ultrathin reaction layer at the solid-state joined interface contributed to a strong metallurgical bonding, while Joule heating effects and interfacial reactions enhanced superelasticity and corrosion resistance of the joint. Notably, a face-centered-cubic (FCC) reorientated layer (ROL) was found between SS and IMC layer at the controlled ultrathin interface. The formation of this ROL was uncovered based on an epitaxial growth model. This ROL introduced a strong crystallographic mismatch with the textured SS, resulting in the fracture at this interface. These phenomenal findings offer valuable insights for studying material interface and controlling dissimilar-metal welding process.
Influence of Absorbency and Additives on Performance of Battery-Free IoT Water Leak Sensors
(University of Waterloo, 2025-03-19) MacGregor, Oluwadamilola Solomon
Leak detection is a reliable solution for controlling the potentially destructive outflow and wastage of water. Several types of devices are used in domestic and industrial spaces; however, most have their power sources run out, and thus require battery change. The associated costs add to overhead expenditure of the user. This necessitates the use of leak detectors that are self-powered, having no use for external sources of power.
Integrating water leak detection systems with Internet of Things (IoT) technology such as Bluetooth low energy (BLE) and long-range (LoRa) protocols provides advantages such as real-time monitoring, which informs incidents and ultimately saves huge cost. The use of IoT-enabled sensors and cloud-based data analytics offers pre-emptive control mechanisms for prompt identification and containment of localized leaks. This helps reduce wastage of water and damage to property, both of which reduce costs as remote access through IoT networks guarantee instant notifications for preventative measures. Scalability fosters effortless deployment in residential, commercial, and industrial environments.
In a self-powered IoT water leak device, parameters such as capillary action and electrochemical reactions directly impact power generation and beacon activation. Energy generation and harvesting happen as water interacts with active materials within the sensor device. There must be a cathode and an anode, to interact with the leaking water which would be the electrolyte. Therefore, the materials selected to play such roles in the device are crucial for the desirable chemical interactions, once in contact with the leaking water.
In a water leak detector where the most crucial feature is sensitivity to water, capillary action is one of the most significant parameters to consider. Both the design of the sensor casing and channels through which the water travels, are to foster a seamless flow. Also, within the sensor chamber, each material in the stack must demonstrate capillarity. Therefore, porosity is key, as their pore sizes determine what material passes through and what might otherwise be trapped to impede the flow of the water being transmitted. Therefore, capillary action is explored for absorbent materials and the sensor casing. Both filter paper (FP) and fabric materials are examined, to ascertain which one gives optimally combined advantages for absorbency and repeatability. FP showed superior performance, due to its pore size. This advantage becomes particularly useful where additives are considered for the powder mixture.
Without additives, the stacked materials have only water to interact with. While this is sufficient to power BLE, it is not enough for LoRa technologies which require higher power. To account for this, additives can be included in the materials within the sensor stack. Salts are among such additives that can provide active ions when interacting with water. Subsequently, these ions facilitate electricity generation due to increased current. Therefore, the power output of the device can be increased when additives are introduced.
In previous similar works, it was shown that pure materials without any additives produce an open-circuit voltage (OCV) of 2 V and short-circuit current (SCC) of only 10 mA. This combination was able to power the sensor for beacon activation through 7 cycles of wetting-drying rounds of repeatability, but only for the BLE protocol. To solve for this limitation, NaCl was added in varied proportions. 10 wt.% NaCl was found to outperform other samples. After several rounds of repeatability, the values of current and voltage were observed to diminish. A sensor without NaCl typically lasts 7 rounds of repeatability, sensors containing NaCl last only about 3 rounds. The primary concern with the use of such additives may be an imminent trade-off between the increased power generation and possible corrosion which compromises shelf life.
One of the downsides of using additives to enhance power generation is the corrosion of metallic materials in the sensor. To study the effect of NaCl on the corrosion of the metallic material, and thus the shelf life of the sensor, electrochemical corrosion tests were performed. As expected, it was observed that higher salt content resulted in higher corrosion rate. Therefore, repeatability was significantly reduced in higher salt contents, thereby limiting the overall shelf life of the sensor. Ultimately, the use of salts should be limited and be specific to the target use case.
Multi-Object Tracking using Mamba and an Investigation into Data Association Strategies
(University of Waterloo, 2025-03-19) Khanna, Dheraj
Multi-Object Tracking (MOT) is a critical component of computer vision, with applications spanning autonomous driving, video surveillance, sports analytics, and more. Despite significant advancements in tracking algorithms and computational power, challenges such as maintaining long-term identity associations, handling dynamic object counts, managing irregular movements, and mitigating occlusions persist, particularly in complex and dynamic environments. This research addresses these challenges by proposing a learning-based motion model that leverages past trajectories to improve motion prediction and object re-identification, and we also investigate how to maximize the performance of trackers with data association.
Inspired by recent advancements in state-space models (SSMs), particularly Mamba, we propose a novel learning-based architecture for motion prediction that combines the strengths of Mamba and self-attention layers to effectively capture non-linear motion patterns within the Tracking-By-Detection (TBD) paradigm. Mamba's input-dependent sequence modeling capabilities enable efficient and robust handling of long-range temporal dependencies, making it well for complex motion prediction tasks. Building on this foundation, we explore hybrid data association strategies to improve object tracking robustness, particularly in scenarios with occlusions and identity switches. By integrating stronger cues such as Intersection over Union (IoU) for spatial consistency and Re-Identification (Re-ID) for appearance-based matching, we enhance the reliability of object associations across frames, reducing errors in long-term tracking. Fast motion and partial overlaps often lead to identity mismatches in object tracking. Traditionally, spatial association relies on IoU, which can struggle in such scenarios. To address this, we enhance the cost matrix by incorporating Height-based IoU to handle partial overlaps more effectively. Additionally, we extend the original bounding boxes with a buffer to account for fast motion, thereby improving the robustness and accuracy of the spatial association process. Additionally, we study the impact of dynamically updating the feature bank for Re-ID during the matching stage, culminating in a refined weighted cost matrix. To further address challenges in identity switching and trajectory consistency, we introduce the concept of virtual detections in overlapping scenarios and explore its effectiveness in mitigating ID switches.
Developing a robust and accurate MOT tracker demands a critical interplay between accurate motion modeling and a sophisticated combination of stronger and weaker cues in data association. Through extensive experimental evaluations on challenging benchmarks such as DanceTrack and SportsMOT, the proposed approaches achieve significant performance gains, with HOTA scores of 63.16% and 77.26% respectively, surpassing multiple existing state-of-the-art methods. Notably, our approach outperforms DiffMOT by 0.9% on DanceTrack and 0.06% on SportsMOT, while achieving 3- 7% improvements over other learning-based motion models. This work contributes to advancing MOT systems capable of achieving high performance across diverse and demanding scenarios.
Low-power and Radiation Hardened TSPC Registers
(University of Waterloo, 2025-03-19) Maheshwari, Yugal
Battery-operated systems require power and energy-efficient circuits to extend their battery life. Flip-flops (FFs) are a basic component of digital circuits, and their power consumption and speed significantly impact the overall performance of a digital system. A clock network in a complex System-on-Chip (SoC) consumes a substantial amount of power. Additionally, often pipelines are used to enhance the system throughput, which puts additional burden on the clock network. Arguably, a flip-flop with fewer clock transistors will reduce its power burden on the clock network. This research proposes three very low-power Single-edge Triggered (SET) True Single-phase Clock (TSPC) FFs with only two and three clock transistors. Moreover, a scan-chain of 256 FFs and AES-128 encryption engine were designed as a benchmark to further investigate the power savings of the proposed FFs. Additionally, we have also designed three very low-power Dual-edge Triggered (DET) latch-multiplexer
type TSPC FFs with only eight and ten clock transistors to sample the data at both positive and negative clock edges.
Furthermore, high-performance computations in Integrated Circuits (ICs) are increasingly needed for space and safety-critical applications. ICs are subjected to high-energy ionizing particles in the radiant space environment, which will cause the device performance to degrade or even fail. A Single Event Upset (SEU) occurs in the logic circuit when an ion strikes a device’s sensitive node, changing the output from 0 to 1 or from 1 to 0. In radiant applications, ICs contain storage cells like FFs, latches, or Static Random Access Memories (SRAM), and always experience SEU. Although package and process engineering can minimize alpha particles, cosmic neutrons cannot be physically blocked. Therefore, for high reliability systems, soft error tolerant circuit designs are crucial. Traditional Radiation Hardened By Design (RHBD) techniques have some trade-offs between area, speed, power, and energy consumption. Thus, new designs are required to reduce these penalties. This research proposes two high-performance, low-power, low-energy, and low-area RHBD TSPC FFs with only four and five clock transistors suitable for space and safety-critical applications.
Investigating Dual Embodiment in Recurring Tasks with a New Social Robot: Designing the Mirrly Platform
(University of Waterloo, 2025-03-19) Yamini, Ali
In many contexts, including education, therapy, and everyday tasks, assistive robots have demonstrated considerable promise for augmenting human capabilities and providing supportive interactions. By designing and building a new tabletop social robot, Mirrly, as well as empirically examining how different robotic embodiments affect user engagement and task compliance, this thesis tries to contribute to this field. In light of advances in human-robot interaction (HRI) and child-robot interaction (CRI), I investigated a comprehensive set of mechanical, electronic, and software requirements. As a result of these requirements, Mirrly was developed, a low-cost, compact platform that could be deployed in schools, therapy centers, or personal homes and it is anthropomorphic enough for supporting social interactions with people.
Following the design and implementation of Mirrly, I conducted a multi-session experiment to determine whether physical embodiment, virtual embodiment (mobile-based), or dual embodiment (both physical and virtual) promoted compliance with repetitive daily tasks, as relevant e.g. in clinical applications where patients need to comply with repetitive treatments. According to the results, physical presence is a strong motivator, leading to higher compliance and engagement, whereas dual embodiment enhanced participants' enjoyment (pleasure) of the interaction specifically. Interestingly, individual differences in the participant sample, such as personality traits and self-control, did not have a significant impact on adherence or user satisfaction. As at least within the short, relatively simple user tasks, these results emphasize the importance of design factors namely physical tangibility and interactive behaviors.
As part of the thesis, a review of relevant HRI and CRI literature is conducted to contextualize Mirrly's design within the context of current robotics. Following a detailed description of utilized methodology, I present the experimental conditions, measures, and analytical methods for assessing compliance, engagement, and perceived enjoyment. Finally, I discuss the implications of the findings for building more adaptive, child-centered robots, especially in clinical, therapeutic and educational settings. Several future directions are also proposed, including extending task complexity, integrating advanced sensors for personalized feedback, and conducting longitudinal studies.
As part of ongoing efforts in social and assistive robotics, this work introduces a novel robotic design. Moreover, in my study, I demonstrate that a robot with careful engineering, physical embodiment, and adaptability can significantly boost compliance. Consequently, this thesis lays a good foundation for future developments in CRI, highlighting how embodiment, anthropomorphism, and structured experimental design converge to support recurrent task compliance efficiently.