Magnetomechanical Sensors Research Articles

Miniature magneto-mechanical resonators for wireless tracking and sensing.

Sensor miniaturization enables applications such as minimally invasive medical procedures or patient monitoring by providing process feedback in situ. Ideally, miniature sensors should be wireless, inexpensive, and allow for remote detection over sufficient distance by an affordable detection system. We analyze the signal strength of wireless sensors theoretically and derive a simple design of high-signal resonant magneto-mechanical sensors featuring volumes below 1 cubic millimeter. As examples, we demonstrate real-time tracking of position and attitude of a flying bee, navigation of a biopsy needle, tracking of a free-flowing marker, and sensing of pressure and temperature, all in unshielded environments. The achieved sensor size, measurement accuracy, and workspace of ~25 centimeters show the potential for a low-cost wireless tracking and sensing platform for medical and nonmedical applications.

Correlative structural refinement-magnetic tunability, and enhanced magnetostriction in low-temperature, microwave-annealed, Ni-substituted CoFe2O4 nanoparticles

The preparation of nanomaterials by conventional methods involves multiple steps that are time- and energy-consuming; hence, it must be replaced by clean, environment-friendly processes. Nanostructured mixed spinel ferrites have wide applicability given their electrical, magnetic, and magnetostrictive properties. Herein, we present an ultrafast, eco-friendly, and thermally efficient microwave (MW)-heating technique to replace the conventional strategies for the preparation of Ni-doped CoFe2O4 ferrite nanoparticles. Mixed spinel ferrite nanoparticles are obtained through an MW technique carried out for 20 min at 600 °C. The cubic nature of the MW-processed, Ni-substituted CoFe2O4 spinel ferrite is demonstrated by Rietveld refinement. Composition-dependent tunable magnetic properties associated with cation distribution and average crystallite size variation are realized by the substitution of Ni2+ at Co2+ in the CoFe2O4 lattice. The highest values of saturation magnetization and coercivity are noted for the Co0.9Ni0.1Fe2O4 ferrite at 5 K and the average crystallite size is ~ 20 nm; the octa to tetra transition of Co2+ is observed owing to substitution by Ni2+ ions. The highest values of magnetostrictive coefficient and strain sensitivity are detected for CoFe2O4; the Ni2+-substituted Co0.9Ni0.1Fe2O4 also exhibits nearly identical behavior. Thus, Ni2+-substituted CoFe2O4 is a remarkable magnetostrictive material suitable for developing magnetoelectric composites and magneto-mechanical sensor applications. Moreover, it is observed that efficient, fast, and eco-friendly microwave processing can be adopted as an alternative approach for low-temperature processing such kinds of nanostructured materials for future electromagnetic device applications.

The effect of heat treatment parameters on the microstructure and torque response of a 13 wt% Cr steel

Shafts intended for magnetomechanical sensors require a combination of mechanical properties and/or characteristics in addition to good magnetic properties. In the case of X46Cr13, this can be attained by the appropriate selection of heat treatment parameters. In fact this study discusses the effect of these parameters on the microstructure, mechanical and magnetic properties of this material.The B-H curves showed that irrespective of the heat treatment condition, the material was harder to magnetize in the axial direction than circumferentially. Also, quenched and tempered structures were harder to magnetize than those in the annealed condition. Changes in the austenitising temperature or time were not observed to lead to major changes in the B-H curve. On the other hand, increasing the tempering temperature from 350 °C to 500 °C, led to a significant drop in coercivity, attributed to a decrease in M3C precipitates. This change in coercivity was comparable to that observed as the tempering temperature increased from 500 °C to 600 °C, in which case the matrix structure changed from martensite to ferrite.Martensitic structures showed a lower magnetic response to a given applied torque than their annealed counterparts. On the other hand, with martensitic structures, the signal to torque relationship remained linear even at high torque values. This was not the case with the annealed structures.The study concludes that austenitising at 1040 °C for 45 min and tempering at 350 °C and 375 °C for 2 h yields an optimal combination of properties and performance.

Ultralow Mechanical Damping with Meissner-Levitated Ferromagnetic Microparticles

Levitated nanoparticles and microparticles are excellent candidates for the realization of extremely isolated mechanical systems, with a huge potential impact in sensing applications and in quantum physics. Magnetic levitation based on static fields is a particularly interesting approach, due to the unique property of being completely passive and compatible with low temperatures. Here, we show experimentally that micromagnets levitated above type-I superconductors feature very low damping at low frequency and low temperature. In our experiment, we detect 5 out of 6 rigid-body mechanical modes of a levitated ferromagnetic microsphere, using a dc SQUID (Superconducting Quantum Interference Device) with a single pick-up coil. The measured frequencies are in agreement with a finite element simulation based on ideal Meissner effect. For two specific modes we find further substantial agreement with analytical predictions based on the image method. We measure damping times $\tau$ exceeding $10^4$ s and quality factors $Q$ beyond $10^7$, improving by $2-3$ orders of magnitude over previous experiments based on the same principle. We investigate the possible residual loss mechanisms besides gas collisions, and argue that much longer damping time can be achieved with further effort and optimization. Our results open the way towards the development of ultrasensitive magnetomechanical sensors with potential applications to magnetometry and gravimetry, as well as to fundamental and quantum physics.

Improved magnetostrictive properties of cobalt ferrite (CoFe2O4) by Mn and Dy co-substitution for magneto-mechanical sensors

The present study explores the effect of Dy3+ rare-earth ion substitution on the crystal structure, morphology, and magnetic properties of magnetostrictive Co0.7Mn0.3Fe2O4 spinel ferrite and demonstrates their potential applications in magnetomechanical sensors. The intrinsic CoFe2O4 and Dy-substituted Co0.7Mn0.3Fe2−xDyxO4 (x = 0.0–0.1) were prepared by the standard solid-state chemical reaction method. X-ray diffraction studies along with the Rietveld refinement confirm that all the samples exhibit single-phase cubic spinel structure with space group Fd3¯m. Raman and Mössbauer data analyses reveal that the cation redistribution with Mn and Dy cosubstitution in CoFe2O4 and confirm the presence of a mixed spinel structure. Electron microscopy analysis indicates the significant effect of Mn, Dy cosubstitution on the microstructure of CoFe2O4. All the samples exhibit the magnetic hysteresis (M-H) loops at 5 K and 300 K. Saturation magnetization (Ms) and the cubic anisotropy constant (K1) values increase with Mn substitution, while with Dy substitution, Ms reduces due to the decrease of magnetic interactions with Dy substitution. However, the coercive field decreases with Mn and increases with Dy substitution. Higher values of magnetostriction coefficients (λ11 = −95 ppm and λ12 = 52 ppm) and the strain derivative (dλ/dH=0.075ppm/Oeat600Oe) observed make Co0.7Mn0.3Fe1.95Dy0.05O4 a suitable candidate for designing torque/stress sensors and a magnetostrictive phase for making magnetoelectric composite. Chemical composition optimization yields higher values Ms (89 emu/g, i.e., 3.73 μB) at lower coercivity (Hc = 241 Oe) for Co0.7Mn0.3Fe2O4 and higher values of λ11, λ12, and dλ/dH at a lower magnetic field (below 800 Oe) for Co0.7Mn0.3Fe1.95Dy0.05O4. The results suggest and demonstrate that Co0.7Mn0.3Fe2O4 and Co0.7Mn0.3Fe1.95Dy0.05O4 are the potential candidates for designing magnetomechanical sensor applications.

Sintering of Cermets: A Case Study of Sintering Ni–Co Ferrite with Ag-, Cu- and Ni-Dispersed Alloy Particles

Literature has shown that the development of ferrite cermets makes possible the enhancement of the mechanical properties of these ceramics for applications in electronics, magnetomechanical sensors, and inert anodes. In this work, a Ni–Co ferrite powder was mixed with metallic powders, compacted, and sintered. The metallic powders used were Ag–Ni and Cu–Ni, prepared by mechanical alloying, and commercial Ag and Ag–Cu powders. The microstructures, crystal structures, and chemical compositions of the sintered samples were analyzed. The Cu–Ni cermet did not present traces of second phases in its XRD pattern, and the experimental results indicate a high reactivity between the ferrite and the Cu–Ni alloy. In the Ag–Cu and Ag–Ni cermets, the composition of the metallic particles was nearly 100% Ag after sintering. It was observed that, for the production of ferrite particulate cermets, the composition, particle size, and melting point of the metallic phase must be carefully adjusted in order to obtain a material with proper chemical composition and microstructure (uniform distribution of the metallic phase and no cracks in the metal–ceramic interfaces).

Mechanical, Magnetic, and Microstructural Characterization of Ni0.9Co0.1Fe2O4 Produced by the Ceramic Method

Ni-Co ferrites, especially the ones with lower cobalt fractions, are candidate materials for applications in magnetomechanical sensors and electromagnetic wave absorbers. This work studied the microstructure, magnetostriction, flexural strength, and complex magnetic permeability of Ni0.9Co0.1Fe2O4, presenting data that weren't covered by previous literature on this composition. It was found that sieving the calcined powder before the forming operation increased the flexural strength of the ceramic. The Ni-Co ferrite had a saturation magnetostriction of 36ppm. The real part of the complex magnetic permeability varied between 2.2-2.3 in frequencies from 100MHz to 1GHz. In frequencies higher than 1GHz, µ' decreased sharply and reached 1 at 3.9GHz. It was found that the grinding media provided a small fraction of Al to the ferrite composition, which apparently affected the complex magnetic permeability of the material but the magnetostriction results were very close to Al-free Ni-Co ferrites with similar composition.

Processing and characterization of a Ni-Co ferrite for sensor applications

AbstractNi-Co ferrites are magnetostrictive ceramics that have potential application in magnetostrictive/ magnetoelastic sensors, as well as in magnetoelectric composites. Ni-rich Ni-Co spinel ferrite samples were processed by the ceramic method and bulk samples were sintered at 1350 ºC in the solid state and at 950 ºC with Bi2O3 liquid phase. The sintered samples were characterized by light microscopy, scanning electron microscopy, Raman spectroscopy, vibrating sample magnetometry and capacitance dilatometry. With Bi2O3 additions as small as 0.6 mol% it was possible to sinter the Ni-Co ferrite at 950 ºC, obtaining high-density samples; however, such liquid-phase sintered samples presented iron oxide particles. The studied samples presented magnetoelastic sensitivities very close to CoFe2O4, with significantly lower magnetic hysteresis. The results thus indicate that the magnetic properties of the samples analyzed are suitable for applications in magnetomechanical sensors.

Magnetic and magnetoelastic properties of Zn-doped cobalt-ferrites—CoFe2−xZnxO4 (x=0, 0.1, 0.2, and 0.3)

Cobalt-ferrite (CoFe2O4) based materials are suitable candidates for magnetomechanical sensor applications owing to a strong sensitivity of their magnetostriction to an applied magnetic field. Zn-doped cobalt-ferrites, with nominal compositions CoFe2−xZnxO4 (x=0–0.3), were synthesized by auto-combustion technique using Co- , Fe- , and Zn-nitrate as precursors. X-ray spectra analysis and Transmission electron microscopy studies revealed that the as-prepared powders were comprised of nano-crystalline (∼25–30nm) cubic-spinel phase with irregularly-shaped grains morphology along with minor impurity phases. Calcination (800°C for 3h) of the precursor followed by sintering (1300°C for 12h) resulted in a single phase cubic-spinel structure with average grain size ∼2–4 μm, as revealed from scanning electron micrographs. The magnitude of coercive field decreases from ∼540Oe for x=0 to 105Oe for x=0.30. Saturation magnetization initially increases and peaks to ∼87emu/g for x=0.2 and then decreases. The peak value of magnetostriction monotonically decreases with increasing Zn content in the range 0.0–0.3; however the piezomagnetic coefficient (dλ/dH) reaches a maximum value of 105×10−9Oe−1 for x=0.1. The observed variation in piezomagnetic coefficient in the Zn substituted cobalt ferrite is related to the reduced anisotropy of the system. The Zn-doped cobalt-ferrite (x=0.1) having high strain derivative could be a potential material for stress sensor application.

The influence of hydrostatic pressure and transverse magnetic field on the electric conductivity of the magnetorheological elastomers

Two sets, each of five samples, of magnetorheological elastomers (MREs) based on silicone rubber and carbonyl iron were prepared. One set of samples was obtained by polymerization of the silicone rubber with additives in the absence of the magnetic field, while the other by polymerization of the silicone rubber with additives in the presence of the magnetic field (840 kA/m). The samples from each set differ by volume concentration of the magnetic phase. By means of an experimental setup described in the paper, the electrical resistance R of the samples was measured as a function of the force F applied on the surface of the samples, for fixed values of the transverse magnetic field strength H. From the as-measured dependence R = R( F) H , the dependence σ = σ( p) H of the electric conductivity σ on the applied pressure p was determined. The experimental results are discussed in view of possible applications like magneto-mechanical sensors working in hostile media.

Advances in Magnetic Field Sensors

The most important milestone in the field of magnetic sensors was when AMR sensors started to replace Hall sensors in many applications where the greater sensitivity of AMRs was an advantage. GMR and SDT sensors finally found applications. We also review the development of miniaturization of fluxgate sensors and refer briefly to SQUIDs, resonant sensors, GMIs, and magnetomechanical sensors.

Advanced simulation tool for the design of sensors and actuators

Sensors, actuators, and sensor-actuator systems are often based on the mutual interaction of physical fields, e.g., the mechanical field with the electromagnetic field. The accurate modeling of such transducers leads to so-called multi-field problems, which are described by a system of non-linear partial differential equations. These systems cannot be solved analytically and thus numerical calculation schemes have to be applied. Therewith, we have developed the simulation tool CFS++(Coupled Field Simulation in C++) based on the Finite Element (FE) method, which is capable of efficiently solving the arising partial differential equations. The program is applicable for simulating capacitive micromachined transducers, piezoelectric transducers, electromagnetic and magnetomechanical sensors and actuators. It also contains models for (aero-)acoustics and ultrasound transducers. Furthermore, we offer advanced material models including hysteretic behaviors.

The modeling of magnetomechanical sensors in laminated structures

A non-linear magnetomechanical plate model has been developed to predict the magneticinduction, elastic and magnetostrictive strain and mechanical stress in a laminatedstructure with magnetostrictive and non-magnetic layers under the simultaneous effect ofquasi-static mechanical stress and the magnetic field. This model was obtained by couplingclassical laminated plate theory to an energy-based statistical magnetomechanical model.The model was used to study a unimorph structure having a magnetostrictive iron–gallium(Galfenol) patch attached to a non-magnetic aluminum substrate. The sensingresponses from the patch were obtained for in-plane axial and shear forces as well asbending and twisting moments acting on the unimorph. The effect of the DC biasmagnetic field and the ratio of patch thickness to substrate thickness on the sensorperformance was studied. The results demonstrate that the model can capture thenon-linearity in the magnetomechanical process and the different structural couplings.

A Survey in Mathematics for Industry An efficient method for the numerical simulation of magneto-mechanical sensors and actuators

The dynamic behaviour of magneto-mechanical sensors and actuators can be completely described by Maxwell's and Navier-Lamé's partial differential equations (PDEs) with appropriate coupling terms reflecting the interactions of these fields and with the corresponding initial, boundary and interface conditions. Neglecting the displacement currents, which can be done for the classes of problems considered in this paper, and introducing the vector potential for the magnetic field, we arrive at a system of degenerate parabolic PDEs for the vector potential coupled with the hyperbolic PDEs for the displacements.Usually the computational domain, the finite element discretization, the time integration, and the solver are different for the magnetic and mechanical parts. For instance, the vector potential is approximated by edge elements whereas the finite element discretization of the displacements is based on nodal elements on different meshes. The most time consuming modules in the solution procedure are the solvers for both, the magnetical and the mechanical finite element equations arising at each step of the time integration procedure. We use geometrical multigrid solvers which are different for both parts. These multigrid solvers enable us to solve quite efficiently not only academic test problems, but also transient 3D technical magneto-mechanical systems of high complexity such as solenoid valves and electro-magnetic-acoustic transducers. The results of the computer simulation are in very good agreement with the experimental data.

Application of magnetomechanical sensors for modal testing

A new modal testing technique using magnetomechanical sensors is proposed in this paper. To list some advantages of this technique, sensors are cost-effective and require no direct physical contact with a structure. The specific application made in this paper is the modal testing for the bending vibration of a solid circular beam. The theoretical analysis explaining the principle of the magnetostrictive sensor-based modal testing is presented for beam bending. The present results are compared with those obtained by the use of standard accelerometers. Although the application of this technique is made to relatively simple problems, the potential of magnetomechanical sensors for modal testing has been revealed.

The role of new materials in the development of magnetic sensors and actuators

Abstract Broadly magnetic sensors and actuators rely on only a few basic principles. These include the law of induction, for magneto-inductive devices; the Ampere force law, for magnetomechanical sensors; and changes in materials properties under the action of a magnetic field, such as magnetoresistance, magneto-optics or magnetoelasticity for sensors based on magnetoelectronics (Proceedings of the 5th Conference on Magnetic Materials, Measurements and Modeling: symposium on magnetic sensors materials and devices, Ames, Iowa, USA, May 16–17, 2002). The identification and characterization of new materials with enhanced magnetic properties is important for the development of improved sensors and actuators. In some cases the identification of new materials can open up new applications for magnetic sensors and actuators which were previously not possible.

Wave selection using a magnetomechanical sensor in a solid cylinder.

Magnetomechanical sensors have received much attention in recent years. However, investigations on the rejection of unwanted wave modes and thus the selection of a desired mode have not been reported. The purpose of this investigation is to present a technique to select only a desired wave mode in a solid ferromagnetic cylinder using a magnetomechanical sensor. To achieve this goal, we propose some bias magnet configurations for each of which either longitudinal or flexural waves alone can be extracted. A simplified theory relating bias magnet arrangement and measured wave modes is developed. Several experimental results confirm the validity of the present investigation.

Composite magnetostrictive materials for advanced automotive magnetomechanical sensors

In this paper we present the development of a composite magnetostrictive material for automotive applications. The material is based on cobalt ferrite, CoO⋅Fe2O3, and contains a small fraction of metallic matrix phase that serves both as a liquid-phase sintering aid during processing and enhances the mechanical properties over those of a simple sintered ferrite ceramic. In addition the metal matrix makes it possible to braze the material, making the assembly of a sensor relatively simple. The material exhibits good sensitivity and should have high corrosion resistance, while at the same time it is low in cost.

Metal-bonded Co-ferrite composites for magnetostrictive torque sensor applications

A new class of magnetomechanical sensor materials, Co-ferrite (CoO/spl middot/Fe/sub 2/O/sub 3/) and metal-bonded (Ag, Ni, Co) Co-ferrite composites, has been investigated. These materials exhibited magnetostriction in excess of 200 ppm and high d/sub 33/ (/spl part//spl lambda///spl part/H)/sub /spl sigma// coefficient, 1.3/spl times/10/sup -9/ A/sup -1/ m, at low applied field (<100 kA/m). Selected compositions were formed into test samples in the form of rings brazed to stainless steel through-shafts. Changes of surface axial magnetic field in response to applied torque as high as 64 AN/sup -1/ m/sup -2/ were observed for a demonstration sample of dimensions 25 mm OD, 12.5 mm ID, and 8 mm high. A hysteresis of /spl plusmn/0.5 N/spl middot/m was observed. These materials appear to be promising candidates for torque sensors, and other magnetostrictive sensor and actuator applications.

Material Properties and Related Considerations for Magnetomechanical Sensing Devices

AbstractSuitability of specific materials for use in magnetomechanical sensors more often depends on combinations of properties than on an outstanding value of a single property. These combinations include ratios and products of properties from different physical families. While magnetic, magnetoelastic, electrical and strength properties often play key roles in determining the performance of the sensor, non-physical characteristics such as manufacturability, available forms, environmental compatibility, toxicity and costs strongly influence the device design and may well dominate the final choice of material. The development of materials specifically for use in this class of sensors is encouraged by their already broad and growing range of applicability.