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A novel method relying on strain engineering to realize arrays of on-chip-integrated giant magneto-impedance (GMI) sensors equipped with pick-up coils is put forth. The geometrical transformation of an initially planar layout into a tubular 3D architecture stabilizes favorable azimuthal magnetic domain patterns. This work creates a solid foundation for further development of CMOS compatible GMI sensorics for magnetoencephalography., (© 2015 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this study, we demonstrate closed-loop motion control of self-propelled microjets under the influence of external magnetic fields. We control the orientation of the microjets using external magnetic torque, whereas the linear motion towards a reference position is accomplished by the thrust and pulling magnetic forces generated by the ejecting oxygen bubbles and field gradients, respectively. The magnetic dipole moment of the microjets is characterized using the U-turn technique, and its average is calculated to be 1.3x10⁻¹⁰ A.m² at magnetic field and linear velocity of 2 mT and 100 µm/s, respectively. The characterized magnetic dipole moment is used in the realization of the magnetic force-current map of the microjets. This map in turn is used for the design of a closed-loop control system that does not depend on the exact dynamical model of the microjets and the accurate knowledge of the parameters of the magnetic system. The motion control characteristics in the transient- and steady-states depend on the concentration of the surrounding fluid (hydrogen peroxide solution) and the strength of the applied magnetic field. Our control system allows us to position microjets at an average velocity of 115 µm/s, and within an average region-of-convergence of 365 µm.

Asymmetry of magnetic objects in a fluid under an oscillating magnetic field leads to a wealth of nonequilibrium dynamics phenomena including a novel ratchet effect without an asymmetric substrate. These nonlinear dynamics are explained in the framework of the Stokes' model by a drag coefficient, which depends on the direction of motion. This approach is general and is independent of the physical mechanism responsible for this directional dependence of the drag coefficient as well as the size of the object. The theoretical model is experimentally verified for two systems, a nonrigid magnetic microcoil and a chiral magnetic macroobject immersed in a bounded fluid.

We present fuel-free locomotion of magnetic spherical Janus motors driven by magnetically induced thermophoresis--a self-diffusive propulsion of an object in any liquid media due to a local temperature gradient. Within this approach an ac magnetic field is applied to induce thermophoretic motion of the objects via heating a magnetic cap of the particles, while an additional dc magnetic field is used to orient Janus motors and guide their motion on a long time scale. Full control over the motion is achieved due to specific properties of ultrathin 100-nm-thick Permalloy (Py, Fe₁₉Ni₈₁ alloys) magnetic films resulting in a topologically stable magnetic vortex state in the cap structure of Janus motors. Realized here magnetically induced thermophoretic locomotion does not require catalytic chemical reactions that imply toxic reagents. In this respect, we addressed and successfully solved one of the main shortcomings in the field of artificial motors, namely being fully controlled and remain biocompatible. Therefore, our approach is attractive for biotechnological in vitro assays and even in vivo operations, since the functioning of Janus motors offers low toxicity; it is not dependent on the presence of the fuel molecules in solution. Furthermore, the suggested magnetic ac excitation is superior compared to the previously proposed optically induced heating using lasers as it does not require transparent packaging.

For transportation of molecules or biological cells using artificial motors, the control over their motion, i.e. direction and speed of transfer, is important. Here, we demonstrate that modification of the velocity and orientation of a magnetic Janus particle can be efficiently controlled by tuning the strength of an applied homogeneous magnetic field. Interestingly, by keeping the same orientation of the magnetic field but changing its magnitude not only the velocity of capped particles can be altered but even their direction of motion can be reversed. We put forth a simple qualitative model, which allows us to explain this intriguing observation.

Magnetic sensors are widely used in our daily life for assessing the position and orientation of objects. Recently, the magnetic sensing modality has been introduced to electronic skins (e-skins), enabling remote perception of moving objects. However, the integration density of magnetic sensors is limited and the vector properties of the magnetic field cannot be fully explored since the sensors can only perceive field components in one or two dimensions. Here, we report an approach to fabricate high-density integrated active matrix magnetic sensor with three-dimensional (3D) magnetic vector field sensing capability. The 3D magnetic sensor is composed of an array of self-assembled micro-origami cubic architectures with biased anisotropic magnetoresistance (AMR) sensors manufactured in a wafer-scale process. Integrating the 3D magnetic sensors into an e-skin with embedded magnetic hairs enables real-time multidirectional tactile perception. We demonstrate a versatile approach for the fabrication of active matrix integrated 3D sensor arrays using micro-origami and pave the way for new electronic devices relying on the autonomous rearrangement of functional elements in space. State-of-the-art magnetic skins can only sense in one or two-dimensions, at small spatial resolutions. By combining the ancient art of paper folding, origami, with advanced semiconductor technology, here, authors present cutting edge three-dimensional magnetic sensors. [ABSTRACT FROM AUTHOR]

Sperm-driven micromotors, consisting of a single sperm cell captured in a microcap, utilize the strong propulsion generated by the flagellar beat of motile spermatozoa for locomotion. It enables the movement of such micromotors in biological media, while being steered remotely by means of an external magnetic field. The substantial decrease in swimming speed, caused by the additional hydrodynamic load of the microcap, limits the applicability of sperm-based micromotors. Therefore, to improve the performance of such micromotors, we first investigate the effects of additional cargo on the flagellar beat of spermatozoa. We designed two different kinds of microcaps, which each result in different load responses of the flagellar beat. As an additional design feature, we constrain rotational degrees of freedom of the cell's motion by modifying the inner cavity of the cap. Particularly, cell rolling is substantially reduced by tightly locking the sperm head inside the microcap. Likewise, cell yawing is decreased by aligning the micromotors under an external static magnetic field. The observed differences in swimming speed of different micromotors are not so much a direct consequence of hydrodynamic effects, but rather stem from changes in flagellar bending waves, hence are an indirect effect. Our work serves as proof-of-principle that the optimal design of microcaps is key for the development of efficient sperm-driven micromotors. [ABSTRACT FROM AUTHOR]

Embryo transfer (ET) is a decisive step in the in vitro fertilization process. In most cases, the embryo is transferred to the uterus after several days of in vitro culture. Although studies have identified the beneficial effects of ET on proper embryo development in the earlier stages, this strategy is compromised by the necessity to transfer early embryos (zygotes) back to the fallopian tube instead of the uterus, which requires a more invasive, laparoscopic procedure, termed zygote intrafallopian transfer (ZIFT). Magnetic micromotors offer the possibility to mitigate such surgical interventions, as they have the potential to transport and deliver cellular cargo such as zygotes through the uterus and fallopian tube noninvasively, actuated by an externally applied rotating magnetic field. This study presents the capture, transport, and release of bovine and murine zygotes using two types of magnetic micropropellers, helix and spiral. Although helices represent an established micromotor architecture, spirals surpass them in terms of motion performance and with their ability to reliably capture and secure the cargo during both motion and transfer between different environments. Herein, this is demonstrated with murine oocytes/zygotes as the cargo; this is the first step toward the application of noninvasive, magnetic micromotor‐assisted ZIFT. [ABSTRACT FROM AUTHOR]

This letter reports the transformation of large-area planar metal–insulator–metal (MIM) nanomembrane capacitors into compact tubular 3-D architectures. By combining the powerful approach of strain-induced nanomembrane self-assembly with an external magnetic field, a stable winding process over a large distance in the range of centimeters is demonstrated. A wet release platform based on encapsulated methyl cellulose allows to release the planar structures with rates of several $100~\mu \text{m}$ /s from their substrate. Footprint shrinkage factors up to 230 are shown by assembling 24-mm long planar structures into 3-D architectures having 82- $\mu \text{m}$ diameter and ~120 windings. The fabricated capacitors feature a capacitance per footprint up to $1.3~\mu \text{F}$ /mm2 for a 15-nm Al2O3 dielectric with less than 100-nA/ $\mu \text{F}$ leakage at 6 V and improved frequency characteristics. This technology is a promising candidate for bridging the gap between discrete multilayer ceramic capacitor (MLCC) and ON-chip trench capacitor technologies. [ABSTRACT FROM AUTHOR]

We studied curvature-driven modifications to the magnetostatic coupling of vortex circulation and polarity in soft-magnetic closely packed cap arrays. A phase diagram for the magnetic remanent/transition states at room temperature as a function of diameter and thickness was assembled. For specimens with vortex remanent state (40 nm-thick Permalloy on 330 nm spherical nanoparticles), both vortex circulation and polarity were visualized. Intercap coupling upon vortex nucleation leads to the formation of vortex circulation patterns in closely packed arrays. The remanent circulation pattern can be tailored choosing the direction of the applied magnetic field with respect to the symmetry axis of the hexagonal array. An even and random distribution of vortex polarity indicates the absence of any circulation-polarity coupling. [ABSTRACT FROM AUTHOR]

A flexible bismuth-based Hall sensor is realized with a total thickness of only 80 $\mu $ m including encapsulation. After wiring, the sensors have a maximum height of 280 $\mu $ m and could be mounted onto curved surfaces with radii down to 5 mm without degradation of its performance. These flexible sensors allow one to measure time-varying magnetic fields and are applied to realize flux-based control strategies for magnetically suspended systems, which is demonstrated by means of a single-axis magnetic levitation setup. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the precise localization of spherical Pt-Silica Janus micromotors (diameter 5 µm) under the influence of controlled magnetic fields. First, we control the motion of the Janus micromotors in twodimensional (2D) space. The control system achieves precise localization within an average region-of-convergence of 7 µm. Second, we show that these micromotors provide sufficient propulsion force, allowing them to overcome drag and gravitational forces and move both downwards and upwards. This propulsion is studied by moving the micromotors in three-dimensional (3D) space. The micromotors move downwards and upwards at average speeds of 19.1 µm/s and 9.8 µm/s, respectively. Moreover, our closed-loop control system achieves localization in 3D space within an average region-of-convergence of 6.3 µm in diameter. The precise motion control and localization of the Janus micromotors in 2D and 3D spaces provides broad possibilities for nanotechnology applications. [ABSTRACT FROM AUTHOR]

Diluted magnetic ZnCoO films with 5 at.% Co have been fabricated by pulsed laser deposition on c-plane sapphire substrates and Schottky and Ohmic contacts have been prepared in top-top configuration. The diode current is significantly reduced after the diode has been subjected to an external magnetic field. In the reverse bias range the corresponding positive magnetoresistance is persistent and amounts to more than 1800% (50 K), 240% (30 K), and 50% (5 K). This huge magnetoresistance can be attributed to the large internal magnetic field in depleted ZnCoO with ferromagnetic exchange between stable bound magnetic polarons. [ABSTRACT FROM AUTHOR]

We demonstrate the closed-loop motion control of self-propelled microjets inside a fluidic microchannel. The motion control of the microjets is achieved in hydrogen peroxide solution with time-varying flow rates, under the influence of the controlled magnetic fields and the self-propulsion force. Magnetic dipole moment of the microjets is characterized using the U-turn and the rotating field techniques. The characterized magnetic dipole moment has an average of \1.4\times \10^-13 A.m ^2 at magnetic field, linear velocity, and boundary frequency of 2 mT, 100 \mum/s, and 25 rad/s, respectively. We implement a closed-loop control system that is based on the characterized magnetic dipole moment of the microjets. This closed-loop control system positions the microjets by directing the magnetic field lines toward the reference position. Experiments are done using a magnetic system and a fluidic microchannel with a width of 500 \mum. In the absence of a fluid flow, our control system positions the microjets at an average velocity and within an average region-of-convergence (ROC) of 119 \mum/s and 390 \mum, respectively. As a representative case, we observe that our control system positions the microjets at an average velocity and within an average ROC of 90 \mum/s and 600 \mum and 120 \mum/s and 600 \mum when a flow rate of 2.5 \mul/min is applied against and along the direction of the microjets, respectively. Furthermore, the average velocity and ROC are determined throughout the flow range (0 to 7.5 \mul/min) to characterize the motion of the microjets inside the microchannel. [ABSTRACT FROM PUBLISHER]

We demonstrate precise closed-loop control of microjets under the influence of the magnetic fields in three-dimensional (3D) space. For this purpose, we design a magnetic-based control system that directs the field lines towards reference positions. Microjets align along the controlled field lines using the magnetic torque exerted on their magnetic dipole, and move towards the reference positions using their self-propulsion force. We demonstrate the controlled motion of microjets in 3D space, and show that their propulsion force allows them to overcome vertical forces, such as buoyancy forces, interaction forces with oxygen bubbles, and vertical flow. The closed-loop control localizes the microjets within a spherical region of convergence with an average diameter of 406±220 μm, whereas the self-propulsion force allows them to swim at an average speed of 222±74 μm/s within the horizontal plane. Furthermore, we observe that the controlled microjets dive downward and swim upward towards reference positions at average speeds of 232±40 μm/s and 316±81 μm/s, respectively. [ABSTRACT FROM AUTHOR]

Self-propelled microjet engines (microbots) can transport multiple cells into specific locations in a fluid. The motion is externally controlled by a magnetic field which allows to selectively load, transport and deliver the cells. [ABSTRACT FROM AUTHOR]

The authors report on topology dependent electron transport in tubular shaped two dimensional electron gas. These micron sized tubes are realized in strained InGaAs quantum wells as a first step towards investigating geometric potentials in low dimensional quantum systems. They investigate the topology induced change in magnetoresistance of the electronic system in a perpendicular magnetic field. At low magnetic field, an increased zero field magnetoresistance followed by a negative magnetoresistance is observed. They ascribe this effect to an increase in electron scattering along the curved regions. At high magnetic fields they observe a linear increase in resistance of the curved region as compared to planar regions. [ABSTRACT FROM AUTHOR]

The cover image represents an array of open superconductor nanostructured microtubes in a magnetic field (shown with arrows), which is perpendicular to the tubes' axes, in a transport current that flows from one edge of a slit to the other. A nontrivial topology of the screening currents in an open tube leads to the dynamic patterns of superconducting vortices that depend on the curvature, as reported by Roman Rezaev and co‐authors in article no. 1800251. A tube fabricated by the roll‐up technology is demonstrated to produce less dissipation as compared to a planar membrane under the same magnetic field and at the same transport current. The induced voltage as a function of the magnetic field provides a unique information about vortex patterns, which helps understand topology‐ and geometry‐driven effects on dissipation characteristics of nanostructured superconductor materials. [ABSTRACT FROM AUTHOR]

We present a new approach to monitor microbial population dynamics in emulsion droplets via changes in metabolite composition, using an inductively coupled LC resonance circuit. The signal measured by such resonance detector provides information on the magnetic field interaction with the bacterial culture, which is complementary to the information accessible by other detection means, based on electric field interaction, i.e. capacitive or resistive, as well as optical techniques. Several charge-related factors, including pH and ammonia concentrations, were identified as possible contributors to the characteristic of resonance detector profile. The setup enables probing the ionic byproducts of microbial metabolic activity at later stages of cell growth, where conventional optical detection methods have no discriminating power. [ABSTRACT FROM AUTHOR]

The article presents a study on the first imperceptible electronic skin (e-skin) with magnetic functionality that is capable of tracking body motions. Topics include the applications of imperceptible e-skins in wearable technology, navigation, and regenerative medicine, mechanical stability of two-dimensional (2D) magnetic field sensors, and encapsulation of polydimethylsiloxane (PDMS).

Radial-magnetized microhelix coils parametrically excited by a magnetic field reveal two distinct types of motion: a rotation at lower excitation frequencies ωmag ≤ 250° s-1 and an oscillatory-like rotative motion at higher frequencies ωmag ≥ 300° s-1, which have been detected experimentally [E. J. Smith, D. Makarov, S. Sanchez, V. M. Fomin, and O. G. Schmidt, Phys. Rev. Lett. 107, 097204 (2011)]. We provide a theoretical interpretation of this behavior within a model of nonlinear dynamics with parametric excitation by virtue of an interplay between the magnetic and the damping torques acting on the coil. A close fit to the experimental data is achieved if the shape factor of the coil increases from 0.173 for lower frequencies up to 0.276 at higher frequencies. We also predict a transition from the rotation to the oscillatory-like rotative motion that occurs via a regime, where periods of the rotative motion are interrupted by one or more hiccups (back-and-forth motions) of the coil. [ABSTRACT FROM AUTHOR]

Together with the well-known ferro- and antiferromagnetic ordering, nature has created a variety of complex helical magnetic configurations. Here, we design and investigate three-dimensional microhelix coil structures that are radial-, corkscrew-, and hollow-bar-magnetized. The magnetization configurations of the differently magnetized coils are experimentally revealed by probing their specific dynamic response to an external magnetic field. Helix coils offer an opportunity to realize microscale geometries of the magnetic toroidal moment, observed so far only in bulk multiferroic materials. [ABSTRACT FROM AUTHOR]

We describe the motion of self-propelled catalytic Ti/Fe/Pt rolled-up microtubes (microbots) in the microchannels of a microfluidics system. Their motion is precisely controlled by a small magnetic field, and the transport of multiple spherical micropartides into desired locations is achieved. The microbots are powerful enough to propel them- selves against flowing streams. The integration of smart and powerful" microbots into microchip systems can lead to multiple lab-on-a-chip functions such as separation of cells and biosensing. [ABSTRACT FROM AUTHOR]