RSS 1.0Sensing, Magnetism and Microsystems Lab
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Recent Submissions
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Magnetic Catheter Placement in Neonates: A Handheld Solution to Radiation Exposure and Operational Delays(Advanced Sensor Research, Wiley, 2022-12-13) [Article]The use of subcutaneous devices has greatly advanced the field of medicine and surgery. However, localizing these devices internally requires imaging techniques such as X-ray or ultrasound. A novel magnetic tracking system for subcutaneous medical devices is presented, providing the capability for precise device localization in an extremely compact and portable pocket-size format. It is entirely benign, avoids X-rays, and can be used to immediately confirm the proper instrument placement. It is implemented on umbilical catheters and endotracheal tubes and is characterized by bench-test, cadaveric, and in vivo studies. The systems consist of a magnetic tip fixed to the distal end of the subcutaneous device, as well as a Magnetic Sensing-Array Device that utilizes a matrix of magnetic field sensors to localize the magnetic tip. The bench-tests show a high localization accuracy for a distance up to 4 cm. The accuracy is slightly reduced during cadaveric and in vivo tests, due to factors impacting the application, such as the dermal surface topography. Regardless, the magnetic subcutaneous medical device tracking system is shown to be robust in performance and functionality in real-world clinical applications, and with its intuitive approach and portability, it has the potential to make real-time subcutaneous device tracking widely accessible.
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Current-induced zero-field domain wall depinning in cylindrical nanowires(Scientific Reports, Springer Science and Business Media LLC, 2022-11-14) [Article]Multi-segmented cylindrical nanowires have properties that make them attractive for high-density, high-speed logic and memory applications. Investigations of the current-induced domain wall motion in cylindrical nanowires have, so far, typically been conducted with a background magnetic field. However, if performed at zero external field, they would be much more viable for their use in prospective electronic devices. Here, we present an all-magneto electrical method to consistently pin domain walls in multi-segmented nanowires and induce their de-pinning using current pulses. The experiments were conducted with compositionally modulated three-segmented nickel/cobalt/nickel and two-segmented cobalt/nickel nanowires of 190 and 150 nm diameter, respectively, where the soft/hard magnetic texture has been fairly studied. We find that for the 3 segmented nanowire, the domain wall can be de-pinned independent of the polarity of the pulse, while for the 2 segmented nanowire the domain wall de-pins only for one polarity. Applying current pulses of 1 × 1012 A/m2, we use a pulse width of 22 ns to estimate a lower boundary for the domain wall speed of 634.54 m/s in cobalt. We study the resistive heating effect from the DC measurement current to find a temperature increase of no more than 2 °C after more than 20 h of tests.
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Domain Wall Propagation and Pinning Induced by Current Pulses in Cylindrical Modulated Nanowires(arXiv, 2022-10-04) [Preprint]The future developments of three-dimensional magnetic nanotechnology require the control of domain wall dynamics by means of current pulses. While this has been extensively studied in planar magnetic strips (planar nanowires), few reports exist in cylindrical geometry, where Bloch point domain walls are expected to have intriguing properties. Here we report this investigation in cylindrical magnetic Ni nanowires with geometrical notches. Experimental work based on synchrotron X-ray magnetic circular dichroism (XMCD) combined with photoemission electron microscopy (PEEM) indicates that large current densities induce domain wall nucleation while smaller currents move domain walls preferably against the current direction. In the region where no pinning centers are present we found domain wall velocity of about 1 km/s. The domain wall motion along current was also detected in the vicinity of the notch region. Pinning of domain walls has been observed not only at geometrical constrictions but also outside of them. Thermal modelling indicates that large current densities temporarily raise the temperature in the nanowire above the Curie temperature leading to nucleation of domain walls during the system cooling. Micromagnetic modelling with spin-torque effect shows that for intermediate current densities Bloch point domain walls with chirality parallel to the Oersted field propagate antiparallel to the current direction. In other cases, domain walls can be bounced from the notches and/or get pinned outside their positions. We thus find that current is not only responsible for the domain wall propagation but is also a source of pinning due to the Oersted field action.
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Gmr Biosensing with Magnetic Nanowires as Labels for the Detection of Osteosarcoma Cells(Elsevier BV, 2022-07-05) [Preprint]Magnetic nanowires (MNWs) were explored as potential magnetic tags for cell detection with giant magnetoresistance (GMR) biosensors based on a handheld system. Due to size, shape anisotropy and higher moment materials, the signal detected from a single MNW was 2500 times larger than that from a single magnetic iron oxide nanobead, which is important for ultra-low concentration cell detection. A model was used to determine how the MNW orientation with respect to the GMR sensor impacts detection performance, and the results aligned well with the experimental results. As a proof of concept OSCA-8 cells tagged with Ni MNWs were also detected using the same handheld system. The limit of detection (LOD) in aqueous solution appeared to be 133 cells, and single-cell detection can be realized if the cell is in direct contact with the sensor surface. Since MNWs are already employed in magnetic separation of cells, directly using MNWs as tags in cell detection eliminates the need of additional functionalization with other labels. This largely simplifies the detection process and reduces the risk of contamination during sample preparation.
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Modulated nanowire scaffold for highly efficient differentiation of mesenchymal stem cells(Journal of Nanobiotechnology, Springer Science and Business Media LLC, 2022-06-16) [Article]Background: Nanotopographical cues play a critical role as drivers of mesenchymal stem cell differentiation. Nanowire scaffolds, in this regard, provide unique and adaptable nanostructured surfaces with focal points for adhesion and with elastic properties determined by nanowire stiffness. Results: We show that a scaffold of nanowires, which are remotely actuated by a magnetic field, mechanically stimulates mesenchymal stem cells. Osteopontin, a marker of osteogenesis onset, was expressed after cells were cultured for 1 week on top of the scaffold. Applying a magnetic field significantly boosted differentiation due to mechanical stimulation of the cells by the active deflection of the nanowire tips. The onset of differentiation was reduced to 2 days of culture based on the upregulation of several osteogenesis markers. Moreover, this was observed in the absence of any external differentiation factors. Conclusions: The magneto-mechanically modulated nanosurface enhanced the osteogenic differentiation capabilities of mesenchymal stem cells, and it provides a customizable tool for stem cell research and tissue engineering.
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Distinguishing Local Demagnetization Contribution to the Magnetization Process in Multisegmented Nanowires(Nanomaterials, MDPI AG, 2022-06-08) [Article]Cylindrical magnetic nanowires are promising materials that have the potential to be used in a wide range of applications. The versatility of these nanostructures is based on the tunability of their magnetic properties, which is achieved by appropriately selecting their composition and morphology. In addition, stochastic behavior has attracted attention in the development of neuromorphic devices relying on probabilistic magnetization switching. Here, we present a study of the magnetization reversal process in multisegmented CoNi/Cu nanowires. Nonstandard 2D magnetic maps, recorded under an in-plane magnetic field, produce datasets that correlate with magnetoresistance measurements and micromagnetic simulations. From this process, the contribution of the individual segments to the demagnetization process can be distinguished. The results show that the magnetization reversal in these nanowires does not occur through a single Barkhausen jump, but rather by multistep switching, as individual CoNi segments in the NW undergo a magnetization reversal. The existence of vortex states is confirmed by their footprint in the magnetoresistance and 2D MFM maps. In addition, the stochasticity of the magnetization reversal is analysed. On the one hand, we observe different switching fields among the segments due to a slight variation in geometrical parameters or magnetic anisotropy. On the other hand, the stochasticity is observed in a series of repetitions of the magnetization reversal processes for the same NW under the same conditions.
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Competition between chiral energy and chiral damping in the asymmetric expansion of magnetic bubbles(ACS Applied Electronic Materials., 2021-10) [Article]Magnetic chirality is an important knob in spintronics and can be engineered through structural symmetry breaking of magnetic thin film multilayers. The dynamics of chiral domain walls is determined by the cooperation of chiral contributions in the magnetic energy functional as well as in the dissipation tensor which need to be better controlled for the sake of the device applications. In this work, we performed a systematic study of magnetic field-induced magnetic bubble expansion in structural inversion asymmetric multilayers with different Pt thicknesses using polar magneto-optical Kerr microscopy. Asymmetric expansion of magnetic bubble is investigated in the creep regime as a function of in-plane and out-of-plane magnetic fields. The results reveal the competition between two key mechanisms governing the asymmetry in the field-driven domain wall expansion, namely the Dzyaloshinskii-Moriya interaction and the chiral magnetic damping. The interplay between these two effects leads to the seemingly counterintuitive experimental signature, depending on the strength of the external magnetic field. The effective control on the bubble asymmetry expansion can be of great importance for future memory and multiplexer-based applications.
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Robust, Long-Term, and Exceptionally Sensitive Microneedle-Based Bioimpedance Sensor for Precision Farming(Advanced Science, Wiley, 2021-06-17) [Article]Precision farming has the potential to increase global food production capacity whilst minimizing traditional inputs. However, the adoption and impact of precision farming are contingent on the availability of sensors that can discern the state of crops, while not interfering with their growth. Electrical impedance spectroscopy offers an avenue for nondestructive monitoring of crops. To that end, it is reported on the deployment of impedimetric sensors utilizing microneedles (MNs) that can be used to pierce the waxy exterior of plants to obtain sensitive impedance spectra in open-air settings with an average relative noise value of 3.83%. The sensors are fabricated using a novel micromolding and release method that is compatible with UV photocurable and thermosetting polymers. Assessments of the quality of the MNs under scanning electron microscopy show that the replication process is high in fidelity to the original design of the master mold and that it can be used for upward of 20 replication cycles. The sensor's performance is validated against conventional planar sensors for obtaining the impedance values of Arabidopsis thaliana. As a change is detected in impedance due to lighting and hydration, this raises the possibility for their widespread use in precision farming.
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Magnetic sensors – A review and recent technologies(Engineering Research Express, IOP Publishing, 2021-06-15) [Article]Magnetic field sensors are an integral part of many industrial and biomedical applications, and their utilization continues to grow at a high rate. The development is driven both by new use cases and demand like internet of things as well as by new technologies and capabilities like flexible and stretchable devices. Magnetic field sensors exploit different physical principles for their operation, resulting in different specifications with respect to sensitivity, linearity, field range, power consumption, costs etc. In this review, we will focus on solid state magnetic field sensors that enable miniaturization and are suitable for integrated approaches to satisfy the needs of growing application areas like biosensors, ubiquitous sensor networks, wearables, smart things etc. Such applications require a high sensitivity, low power consumption, flexible substrates and miniaturization. Hence, the sensor types covered in this review are Hall Effect, Giant Magnetoresistance, Tunnel Magnetoresistance, Anisotropic Magnetoresistance and Giant Magnetoimpedance.
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A Microneedles Balloon Catheter for Endovascular Drug Delivery(Advanced Materials Technologies, Wiley, 2021-05-28) [Article]Disorders of the inner parts of blood vessels have been significant triggers of cardiovascular diseases (CVDs). Different interventional methods have been employed, from complex surgeries to balloon angioplasty techniques to open the narrowed blood vessels. However, CVDs continue to be the lead cause of death in the world. Delivering a therapeutic agent directly to the inner wall of affected blood vessels can be a transformative step toward a better treatment option. To open the door for such an approach, a catheter delivery system is developed based on a conventional balloon catheter where a fluidic channel and microneedles (MNs) are integrated on top of it. This enables precise and localized delivery of therapeutics directly into vessel walls. Customizable MNs are fabricated using a high-resolution 3D printing technique where MN's height ranges from 100 to 350 µm. The MNs penetration into a synthetic vascular model is investigated with a computerized tomography scan. Ex vivo tests on rabbit aorta confirm the MN-upgraded balloon catheter's performance on real tissue. Delivery of fluorescent dye is accomplished by injecting it through the fluidic channel and MNs into the aortic tissue. The dye is observed at up to 180 µm of depth, confirming site-specific endovascular delivery.
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A Facile Magnetic System for Tracking of Medical Devices(Advanced Materials Technologies, Wiley, 2021-05-05) [Article]The largest disadvantage of modern day minimally invasive surgery is the required use of X-ray or fluoroscopic imaging for locating or tracking medical catheters and tubes. The implications are increased costs and effort, limited availability for instance in less developed countries, and the cumulative exposure to contrast dyes and ionizing radiation are detrimental to health, especially in young patients and neonates with increased sensitivity. In order to reduce the use of X-ray imaging and provide a wider accessibility, a facile magnetic system is proposed for subcutaneous medical device localization. It consists of a lightweight and flexible, biocompatible, and permanent magnet at the tip of the subcutaneous device and a sensing device to scan the dermal surface and locate the magnetic tip. The mechanical and magnetic properties of the magnetic tip are tailored to fit the requirements of the delicate catheter application. Evaluation of the tracking system using a 5 Fr magnetic tip resulted in a depth-dependent position and orientation error of 0.75 mm and 3.7°. Additionally, a maximum placement depth error of 0.96 mm is achieved. Evaluation of the system in vivo revealed its practicality and accuracy as well as the influence of potential user errors.
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Integrated magnetohydrodynamic pump with magnetic composite substrate and laser-induced graphene electrodes(Polymers, MDPI AG, 2021-04-01) [Article]An integrated polymer-based magnetohydrodynamic (MHD) pump that can actuate saline fluids in closed-channel devices is presented. MHD pumps are attractive for lab-on-chip applications, due to their ability to provide high propulsive force without any moving parts. Unlike other MHD devices, a high level of integration is demonstrated by incorporating both laser-induced graphene (LIG) electrodes as well as a NdFeB magnetic-flux source in the NdFeB-polydimethylsiloxane permanent magnetic composite substrate. The effects of transferring the LIG film from polyimide to the magnetic composite substrate were studied. Operation of the integrated magneto hydrodynamic pump without disruptive bubbles was achieved. In the studied case, the pump produces a flow rate of 28.1 µL/min. while consuming ~1 mW power.
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A Wideband Magnetic Frequency Up-Converter Energy Harvester(Advanced Engineering Materials, Wiley, 2021-03-05) [Article]Many sensor applications require small and noninvasive methods of powering, such as marine animal tracking and implantable healthcare monitoring. In such cases, energy harvesting is a viable solution. Vibrational energy harvesting is abundantly available in the environment. These vibrations usually are low in frequency and amplitude. Conventional vibrational harvesters convert the environmental vibrations into electrical signals; however, they suffer from low-voltage outputs and narrow bandwidths, limiting the harvesting to a small range of frequencies. Herein, a new mechanical harvester is introduced using a magnetic frequency up-converter. It is implemented using attractive-force magnetic coupling between a soft magnet and a permanent magnet to convert low-frequency vibrations into high-frequency pulses. Combined with a piezoelectric generator, the harvester generates a high output voltage for an extended bandwidth of operation. The proposed harvester shows a 50.15% increase in output voltage at the resonant frequency (12.2 Hz), resulting in 14.79 V at 1.0 g, with a maximum peak voltage of 16.28 V. The bandwidth of operation ranges from 10.77 to 22.16 Hz (11.39 Hz), which when compared with a single-beam harvester shows an increase of 3250% in the bandwidth, where the average power is greater for 92.56% of this bandwidth.
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Flexible Hall sensor made of laser-scribed graphene(npj Flexible Electronics, Springer Nature, 2021-02-15) [Article]Graphene has shown considerable potential for sensing magnetic fields based on the Hall Effect, due to its high carrier mobility, low sheet carrier density, and low-temperature dependence. However, the cost of graphene in comparison to conventional materials has meant that its uptake in electronic manufacturing has been slow. To lower technological barriers and bring more widespread adoption of graphene Hall sensors, we are using a one-step laser scribing process that does not rely on multiple steps, toxic chemicals, and subsequent treatments. Laser-scribed graphene Hall sensors offer a linear response to magnetic fields with a normalized sensitivity of ~1.12 V/AT. They also exhibit a low constant noise voltage floor of ~ 50 nV/Hz−−−√ for a bias current of 100 µA at room temperature, which is comparable with state-of-the-art low-noise Hall sensors. The sensors combine a high bendability, come with high robustness and operating temperatures up to 400 °C. They enable device ideas in various areas, for instance, soft robotics. As an example, we combined a laser-scribed graphene sensor with a deformable elastomer and flexible magnet to realize low-cost, compliant, and customizable tactile sensors.
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Cylindrical Magnetic Nanowires Applications(IEEE Transactions on Magnetics, Institute of Electrical and Electronics Engineers (IEEE), 2021-01-28) [Article]Cylindrical magnetic nanowires feature unique properties, which make them attractive for fundamental research as well as novel applications. These one-dimensional structures introduce a pronounced shape anisotropy that together with material selection can strongly affect the magnetic properties and can be tuned by incorporating segments of different materials or diameters along the length. They attract a large interest in the scientific community, ranging from physicists to material scientists to bioengineers. Consequently, these nanowires are developed for and employed in very diverse applications in medicine, biology, data and energy storage, catalysis or microwave electronics, among others. In this review we investigate the most active emerging applications of cylindrical nanowires grown in alumina templates by electrochemical deposition. This method has several key features, including low cost and a high level of control over the design. A fundamental property that distinguishes those applications is the operating frequency, which we chose to apply as an underlying structure for this review. With this we attempt to provide a wide and organized view of applications based on cylindrical magnetic nanowires with a focus on tailored physical and chemical properties.
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Physical Sensors Based on Laser-Induced Graphene: A Review(IEEE Sensors Journal, Institute of Electrical and Electronics Engineers (IEEE), 2020-10-29) [Article]Physical sensors form the fundamental building blocks of a multitude of advanced applications that detect and monitor the surroundings and communicate the acquired physical data. The everlasting need for more compliant, low-cost, and energy-efficient sensor solutions has led to considerable interest in enhancing their features and operation limits even further. While graphene has emerged as a promising candidate material, due to its outstanding electrical and mechanical properties, it is still not available in large volumes for practical applications. Meanwhile, Laser-Induced Graphene has opened new perspectives for a versatile, durable, printed physical sensing platform capable of detecting various physical parameters across a range of conditions and subjects. In this review, LIG physical sensors were categorized into four broad types based on their transduction mechanism: mechanical, thermal, magnetic, and electromagnetic. We summaries various design strategies established for preparing reliable physical sensors without the involvement of chemical treatments, synthesis, and multi-step fabrication processes. The review considers the effects of laser choice, lasing environment, and parameters on graphene properties. We also discuss a broad spectrum of applications of LIG physical sensors in fields ranging from healthcare, tactile sensing, environmental monitoring, energy harvesting, and soft robotics to desalination and THz modulation.
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An Assistive Magnetic Skin System: Enabling Technology for Quadriplegics(Advanced Engineering Materials, Wiley, 2020-10-27) [Article]People with quadriplegia no longer have control over their legs, neither the hands and cannot continue living their life independently. On top of that, severely injured quadriplegics (i.e., C1 and C2 injuries) suffer from speaking difficulties and minimal head and neck movements. With the advancement in wearable artificial skins and the Internet of Things, realizing comfortable and practical solutions for quadriplegics is more tangible than ever. Here, a comprehensive assistive magnetic skin system is presented that allows quadriplegics, including the severely injured ones, to move around individually and control their surroundings with ease. The system tracks facial expressions by tracking the movement of magnetic tattoos attached to the face, using magnetic field sensors incorporated into eyeglasses. The magnetic tattoos are made of highly flexible, stretchable, breathable, and biocompatible magnetic skins. In combination with smart-glasses, smart-wheelchair, and smart-gadgets, the users can move around and control their environment with their facial expressions. The system is also designed to allow quadriplegics to perform outdoor activities effortlessly. It supports line-of-sight communication and does not require pre-tethering to the smart-gadgets, unlike the existing solutions. Thus, enabling the user to walk on pathways, activate pedestrian lights, control public elevators, and perform various outdoor activities independently.
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Cellular network Marine Sensor Buoy(Institute of Electrical and Electronics Engineers (IEEE), 2020-10-12) [Conference Paper]Studies in the marine environment require devices to gather data in remote locations. These devices commonly use some form of data logging that require the user to retrieve the device after a period of time. This is not only a large effort, but often presents an unnecessary delay and risk in the event that the device malfunctions, goes missing or if the data collected is redundant. We propose a modular, remote and autonomous sensing solution that enables multi-sensor readout and wireless data communication, providing scientists with real time data. This sensor buoy is comprised of a primary module which is a data logger that connects to an online server via mobile network. The secondary portion is the hub that connects to an array of sensors that are customized to the needs of the marine scientists.
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Fabrication of Long-Range Ordered Aluminum Oxide and Fe/Au Multilayered Nanowires for 3-D Magnetic Memory(IEEE Transactions on Magnetics, Institute of Electrical and Electronics Engineers (IEEE), 2020-09-02) [Article]Large-scale long-range ordered anodic aluminum oxide and multilayered nanowires (NWs) are attractive to 3-D nanostructured material applications, such as high-density 3-D magnetic memory. This article demonstrates long-range ordered aluminum oxide made by simple and inexpensive double imprinting with line-patterned stamp and uniform iron-gold multilayered NWs fabricated by galvanostatic electrochemical deposition with a single electrolyte bath. These two structural features show potential for future high-density recording systems that require long-range ordered devices separated from each other by insulation to eliminate crosstalk.
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Strain-induced Differentiation of Mesenchymal Stem Cells(Institute of Electrical and Electronics Engineers (IEEE), 2020-08-28) [Conference Paper]Directing the fate of human mesenchymal stem/stromal cells (hMSCs) toward bone formation using mechanical strain is a promising approach in regenerative medicine related to bone diseases. Numerous studies have evaluated the effects of vibration or cyclic tensile strain on MSCs towards developing a mechanically-based method for stimulating differentiation. Here, we study the differentiation of hMSCs cultured on elastic polydimethylsiloxane (PDMS) membrane, which is magnetically actuated to induce periodically varying strain. The strain distribution across the membrane was calculated by finite-element modeling and demonstrates three main areas of different strain amplitudes. The strain effect on the hMSCs was evaluated by measuring the mineralization of differentiated hMSCs using Alizarin S red stain. The results indicate a strain-dependent differentiation of hMSCs, where the highest region of strain on the membrane resulted in the most accelerated differentiation. Osteogenic differentiation was achieved as early as two weeks, which is significantly sooner than control hMSCs treated with osteogenic media alone.
