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This paper reports on a quantitative technique based on the Magnetic Flux Leakage (MFL) method, for the detection and interpretation of the MFL signals caused by rectangular hairline cracks in pipeline structures. This was achieved through visualization and 3D imaging of the leakage field. This research is aimed at detecting hairline cracks caused by granular bond separation, which occurs during manufacturing, leaving pipelines and steel structures with miniature cracks. The investigation compared finite element numerical simulation with experimental data. The response of the MFL probe scanned above a hairline crack was first predicted using an optimized 3D finite element model. The MFL signals associated with both the surface and far-surface cracks were compared. The results show that the depth, width and length of the various hairline cracks can be estimated by using the distribution pattern and strength of the (Bx), (By) and (Bz) components of the MFL signals.

Previous investigations of the Matteucci effect in amorphous microwires have yielded a basic understanding of the underlying physical mechanism. However, a complete quantitative model is still elusive particularly in explaining the role of magnetoelastic interactions. This is important because the Matteucci effect is an under-utilized phenomenon with promising potential for exploitation in stress sensing applications. In this work, we have studied the influence of tensile stress on the Matteucci effect in two types of amorphous wires (Fe77.5Si7.5B15 and Co68.15Fe4.35Si12.5B15). This paper shows how the axial stress significantly affects the Matteucci voltage and that this behaviour is dependent upon the sign of the magnetostriction constant. Measuring the Matteucci voltage as a function of stress in magnetostrictive wire produced an equivalent gauge factor over two orders of magnitude greater than that obtained in a conventional resistive strain gauge. This offers the potential for the development of a new type of wire-based strain sensor.

The majority of power transformers are usually energized by sinusoidal excitation. However, there is a growing demand for using PWM excitation on power electronics devices for energy savings. As awareness of the environment also increases, the importance of noise and vibration issues becomes more significant. Increasing non-linear loads over time affect the ageing and lifetime of transformers. Such cases also cause to change the nominal values ​​of transformers. It is important that mechanical parameters such as vibration and noise can be accurately measured and examined so that all necessary functions can be entirely performed as other electromagnetic performances. For this reason, it is necessary to analyse the vibration movements of transformers and determine their characteristics, especially locally under changing operating conditions. Magnetostrictive is known as the main source of vibration and noiseof the transformer core. This paper presents localized magnetostriction of transformer core measured by strain gauges under sine and PWM voltage excitations. For validation of the study in this paper, a no-load strain measurement was performed experimentally on a real 20kVA three-phase three-limb T-joint transformer assembled in a laboratory.\ud\udLocalized magnetostriction in the rolling and transverse directions of the lamination under sinusoidal and PWM voltage excitations was carried out. The results of the experiment were compared with each other in terms of the location of the sensors.\ud\udThe Finite Element Analysis (FEA) was used to simulate the magnetic behavior of the transformer based on time-dependent analysis of magnetic field density, force, e.t. distributions under no-load conditions, respectively.\ud\udIn conclusion, evaluating the localized magnetostriction characteristic, especially under PWM voltage excitation, is essential for interlamination electromagnetic and electromechanical behaviors.\ud\ud Previous article in issue

Assessing the effect of defect induced stresses on magnetic flux leakage (MFL) signals is a complicated task due to nonlinear magnetomechanical coupling. To facilitate the analysis, a multi-physics finite elemental simulation model is proposed based on magnetomechanical theory. The model works by quasi-statically computing the stress distribution in the specimen, which is then inherited to solve the nonlinear magnetic problem dynamically. The converged solution allows identification and extraction of the MFL signal induced by the defect along the sensor scanning line. Experiments are conducted on an AISI 1045 steel specimen, i.e. a dog-bone shaped rod with a cylindrical square-notch defect. The experiments confirm the validity of the proposed model that predicted a linear dependency of the peak-to-peak amplitude of the normalized MFL signal on applied stress. Besides identifying the effect of stress on the induced MFL signal, the proposed model is also suitable for solving the inverse problem of sizing the defects when stress is involved.

In this work, Bi1-xHoxFeO3 (with x = 0, 0.05, 0.10, 0.15 and 0.20) thin films were successfully grown on Si (100) substrates using pulsed laser deposition and the effect of Ho doping on the crystal structure, dielectric and magnetic properties were studied. X-ray diffraction studies on undoped BiFeO3 confirmed the presence of a rhombohedral phase with crystallite sizes in the 14–24 nm range. The surface morphology and microstructure of the thin films were analysed by field emission scanning electron microscopy and atomic force microscopy. The results reveal that the grain size decreases as the Ho doping concentration increases. X-ray photoemission spectroscopy was used to identify the chemical bonding, valance band and core levels of Ho doped BiFeO3 thin films. Dielectric constant and loss in Ho doped samples has been measured using a vector network analyzer and shows good dielectric behaviour compared to undoped BiFeO3. A vibrating sample magnetometer was used to investigate the magnetic properties for Ho doping with concentrations of x ≥ 0.15. In comparison to undoped BiFeO3, the doped films exhibited larger remanence and saturation magnetization. The enhancement of these properties due to Ho doping is discussed along with their relevance in designing multiferroic materials based on Bi1-xHoxFeO3 films for magnetic field sensors, multiple-state memories and spintronic elements.

This paper presents a study on attempting to substitute Gd into a Ca-Ba M-type hexaferrite (Ca0.5Ba0.5GdxFe12−xO19, where x = 0, 0.05, 0.1, 0.15, 0.2, 0.25) using the sol–gel method. The structural, magnetic and microwave properties of the resultant material were investigated. Since Gd has a much larger ionic radius than Fe, substitution is not straightforward as revealed by the structural analysis. X-ray diffraction (XRD) patterns revealed some substitution into the M-type phase due to a changing lattice parameter; however, significant quantities of additional phases of hematite (α-Fe2O3) and gadolinium orthoferrite started to form at concentrations of up to Gd = 0.10 and at higher Gd concentrations, respectively. High-resolution transmission electron microscopy of selected compositions showed d-spacings corresponding to the three phases observed in XRD, confirming the incomplete substitution of Gd. Scanning electron microscopy showed platelet-shaped grains. Vibrating sample magnetometry at room temperature showed varied results owing to a myriad of interactions from the hexaferrite and secondary phases. The microwave complex permittivity and permeability in the frequency range of 2–11 GHz showed little frequency dependence with nominal values for the complex permeability. All the compositions exhibit low magnetic losses with frequency except Gd = 0.10. Such type of materials can be used for microwave devices in the low-GHz range and as well as permanent magnets.

As their eye movements are limited, many birds respond to continuous movement of their visual world by a reflexive oscillation of their heads, analogous to optokinetic nystagmus eye movement in primates. To elicit this optocollic response (OCR), we have placed homing pigeons in the centre of a circular arena of high-resolution monitors and then presented horizontally drifting vertical gratings while recording their head movements. If the combination of the spatial frequency and contrast of the grating is beyond their visual capabilities, the reflexive movements cease, allowing us to establish what the animals can and cannot see. The results successfully replicated a previously published spatial contrast sensitivity curve obtained by more invasive electrophysiological methods. In addition to defining the limits of spatial vision, this psychophysical approach can permit an investigation of the effect of stimulus velocity on the OCR. The presentation of a higher velocity drifting pattern only elicited OCR after a prolonged warm up period, which became longer with higher velocities. In humans, such a delay in the development of optokinetic nystagmus is normally only observed in young infants. Moreover, when the drifting pattern is turned off and the bird left in darkness, there is a prolonged after-OCR. This noninvasive approach is clearly applicable to exploring different aspects of visual performance of any animal in which gaze stabilization is achieved by head rather than eye movements.

The development of techniques for monitoring finger movement is becoming increasingly important in areas, such as robotics, virtual reality, and rehabilitation. To date, various techniques have been proposed for tracking hand movements, but the majority suffer from poor accuracy and repeatability. Inspired by the articulated structure of finger joints, we propose a novel 3-D printed optical sensor with a compact hinged configuration for tracking finger flexion. This sensor exploits Malus' law using the attenuation of light transmitted through crossed polarizers. The sensor consists of a single LED, two pieces of linear polarizing film, and a photodetector that detects the changes in polarized light intensity proportional to the angle of finger flexion. This paper presents the characterization of the proposed optical sensor and compares it with a commonly used commercial bend sensor. Results show that the bend sensor exhibits hysteresis error, low sensitivity at small angles, and significant temporal drift. In contrast, the optical sensor is more accurate (±0.5°) in the measuring range from 0° to 90°, and exhibits high repeatability and stability, as well as a fast dynamic response. Overall, the optical sensor outperforms the commercial bend sensor, and shows excellent potential for monitoring hand movements in real time.

A series of co-precipitated Zn1−xCoxGdyFe2−yO4 spinel ferrites (x =0.0–0.5, y=0.00–0.10) sintered at 1000 °C were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), vibrating sample magnetometery (VSM) and microwave cavity perturbation (MCP). XRD patterns and FTIR spectra reveal formation of the spinel phase along with few traces of GdFeO3 second phase. The lattice constant decreases with an increasing amount of CoGd ions due to the segregation of Gd3+on the grain boundaries and due to replacement of lager Zn2+ ions with smaller Co2+ ions. SEM shows grain size to decrease with the increase of CoGd contents due to grain growth inhibition by the second phase. VSM results show remanence and saturation magnetization to exhibit an increasing trend due to Co substitution on octahedral sites and presence of a second phase. The coercivity increases with the increase of CoGd contents due to anisotropic nature of Co. MCP shows the complex magnetic permeability to increase with CoGd concentration while the complex permittivity decreases.

The investigation of planar coils of differing topologies, when combined with a magnetostrictive amorphous ribbon to form a stress-sensitive self-inductor, is an active research area for applications as stress or pressure sensors. Four topologies of planar coil (Circular, Mesh, Meander, and Square) have been constructed using copper track on 30 mm wide PCB substrate. The coils are energized to draw 0.4 A and the resulting magnetic field distribution is observed with a newly developed three-dimensional magnetic field scanner. The system is based on a variably angled Micromagnetics® STJ-020 tunneling magneto-resistance sensor with a spatial resolution of 5–10 µm and sensitivity to fields of less than 10 A/m. These experimental results are compared with the fields computed by ANSYS Maxwell® finite element modelling of the same topologies. Measured field shape and strength correspond well with the results of modelling, including direct observation of corner and edge effects. Three-dimensional analysis of the field shape produced by the square coil, isolating the components H(x) and H(z), is compared with the three-dimensional field solutions from modelling. The finite element modelling is validated and the accuracy and utility of the new system for three-dimensional scanning of general stray fields is confirmed.

The usage of planar sensors is widespread due to their non-contact nature and small size profiles, however only a few basic design types are generally considered. In order to develop planar coil designs we have performed extensive finite element modelling (FEM) and experimentation to understand the performance of different planar sensor topologies when used in inductive sensing. We have applied this approach to develop a novel displacement sensor. Models of different topologies with varying pitch values have been analysed using the ANSYS Maxwell FEM package, furthermore the models incorporated a movable soft magnetic amorphous ribbon element. The different models used in the FEM were then constructed and experimentally tested with topologies that included mesh, meander, square coil, and circular coil configurations. The sensors were used to detect the displacement of the amorphous ribbon. A LabView program controlled both the displacement stage and the impedance analyser, the latter capturing the varying inductance values with ribbon displacement. There was good correlation between the FEM models and the experimental data confirming that the methodology described here offers an effective way for developing planar coil based sensors with improved performance.

A bilayer sensor consisting of a stress sensitive magnetoelastic layer mounted onto a support substrate has been developed utilizing its change in curvature when subjected to gas flow forces. Two different materials, aluminium and HAVAR, with various thicknesses were used as the support layer to investigate the effect of bilayer stiffness on sensor sensitivity. Selection of the support layer was also important in determining the location of the neutral bending axis of the composite bilayer ensuring maximum stress sensitivity within the magnetic layer. Change in magnetic permeability proportional to stress was detected by measuring the inductance of a pickup coil positioned around one end of the bilayer sensor. The sensor was subjected to various airflow speeds and delivered consistent signal outputs for flow speeds up to 25 ms $^{\mathrm {\mathbf {-1}}}$ while proving to be extremely robust in turbulent conditions.

A new versatile scanning hardware based on a Micromagnetics® STJ-020 MgO-based tunnelling magnetoresistance (TMR) sensor has been developed to volumetrically scan the thin boundary layer above a given sample. An (x, y) planar scan of the surface of a 7.5 mm × 7.5 mm sample of grain-oriented (3% Si) electrical steel is presented. Stray fields normal to the surface between −116 and 272 A/m are measured. At 10 q, m/pixel domain and micro-domain structures are seen. At 5 q, m/pixel the micro-domain structures resolve into clear Lancet domains. The domain images presented have greater qualitative similarity with Kerr effect observations than with Bitter technique results. An (x, z) vertical scan along a 2.35 mm transect reveals the perpendicular extent of the stray fields, with the normal components shown to emanate from the domain bodies and extend approximately 40–100 q, m from the sample surface. With the aim of investigating how the stray fields close back onto the surface, the (x, z) transect is repeated with the sensor at 5, 10, 15 and 20 degrees from the vertical. For the first time, the stray fields from surface domains viewed by other techniques in only a planar (x, y) projection have been studied in the (x, z) plane perpendicular to the surface.

The study of finger kinematics has developed into an important research area. Various hand tracking systems are currently available; however, they all have limited functionality. Generally, the most commonly adopted sensors are limited to measurements with one degree of freedom, i.e., flexion/extension of fingers. More advanced measurements including finger abduction, adduction, and circumduction are much more difficult to achieve. To overcome these limitations, we propose a two-axis 3D printed optical sensor with a compact configuration for tracking finger motion. Based on Malus’ law, this sensor detects the angular changes by analyzing the attenuation of light transmitted through polarizing film. The sensor consists of two orthogonal axes each containing two pathways. The two readings from each axis are fused using a weighted average approach, enabling a measurement range up to 180 ∘ and an improvement in sensitivity. The sensor demonstrates high accuracy (±0.3 ∘ ), high repeatability, and low hysteresis error. Attaching the sensor to the index finger’s metacarpophalangeal joint, real-time movements consisting of flexion/extension, abduction/adduction and circumduction have been successfully recorded. The proposed two-axis sensor has demonstrated its capability for measuring finger movements with two degrees of freedom and can be potentially used to monitor other types of body motion.

The ability to orientate and navigate is critically important for the survival of all migratory birds and other animals. Progress in understanding the mechanisms underlying these capabilities and, in particular, the importance of a sensitivity to the Earth’s magnetic field has, thus far, been constrained by the limited number of techniques available for the analysis of often complex behavioural responses. Methods used to track the movements of animals, such as birds, have varied depending on the degree of accuracy required. Most conventional approaches involve the use of a camera for recording and then measuring an animal's head movements in response to a variety of external stimuli, such as changes in magnetic fields. However, video tracking analysis (VTA) will generally only provide a 2D tracking of head angle. Moreover, such a video analysis can only provide information about movements when the head is in view of the camera. In order to overcome these limitations, the novel invention reported here utilises a lightweight (

The wearing process of an ultrahigh molecular weight polyethylene (UHMWPE) bearing surface in orthopaedic surgical implants cannot be tracked at present; hence, implant failure only becomes apparent when the patient experiences some discomfort. In exploring the integration of wireless stress sensors into UHMWPE, this paper describes the first step in achieving in vivo monitoring of implant wear using magnetostrictive amorphous ribbons.

Electrodeposited FeCoNiB nanowires with 10% boron in the electrolyte have been investigated. The focus is on studying the effect of their size on the magnetic characteristics. Both the coercivity and the squareness decreased with the increase in the nanowire diameter. The coercivity for out-of-plane (OOP) measurements varied from 41 to 277 Oe for nanowire arrays of different diameters. For nanowires of 20 and 200 nm in diameter the easy axis is in the OOP direction whereas it is in the in-plane (IP) direction for nanowires of 100 nm in diameter. For most of the samples, the OOP coercivity was higher than the IP coercivity, suggesting lower magnetostatic interactions amongst the nanowires. The OOP axis switched from easy to hard when the nanowire length increased beyond a critical value. EDX investigations showed that the atomic concentration of Fe and Co for the templates with pore diameters of 20 and 100 nm did not vary as much as the change observed for the template with a 200 nm pore diameter. The thermal stability of the FeCoNiB nanowires deposited at 9 mA pulsed current was studied over the temperature range 10–300 K. The OOP coercivity increases from 45 Oe at 300 K to 76 Oe at 10 K. Similarly, the squareness increased from 0.01 at 300 K to 0.023 at 10 K. The obtained results are important for the fabrication of nanowire arrays to be used in integrated microsystems.

The temperature and composition dependence of magnetic properties of Co–Cr co-substituted magnesium ferrite, Mg1−xCoxCrxFe2−xO4 (x=0.0–0.5), prepared by novel polyethylene glycol assisted microemulsion method, are studied. The synthesized materials are characterized by the Mossbauer spectrometer and standard magnetic measurements. Major hysteresis loops are measured up to the magnetic field of 50 kOe at 300, 200 and 100 K. The high field regimes of these loops are modeled using the Law of Approach to saturation to determine the first-order cubic anisotropy coefficient and saturation magnetization. Both the saturation magnetization and the anisotropy coefficient are observed to increase with the decrease in temperature for all Co–Cr co-substitution levels. Also, both the saturation magnetization and the anisotropy coefficient achieved maximum value at x=0.3 and x=0.2, respectively. Explanation of the observed behavior is proposed in terms of the site occupancy of the co-substituent, Co2+ and Cr3+ in the cubic spinel lattice.

Recognizing and tracking articulations of the human hand is key to the development of areas such as robotics, virtual reality systems and physical rehabilitation. Based on the principle of crossed-polarization detection, a novel optical sensor with a hinge configuration, is proposed to monitor finger articulation. Using 3D printing technology, we fabricated a lightweight and compact sensor suited to attaching on fingers. The weighted average method was applied to the sensor's output data to determine angular positions corresponding to finger joint articulations. The experimental results show excellent consistency with theoretical predictions. The sensor features good accuracy (±0.5% of full scale) and repeatability, improved sensitivity, and an improved measuring range of 180°. The performance of the sensor is a promising development for monitoring finger articulation. Future work will focus on integrating multiple sensors as part of an instrumented glove to evaluate the true potential for monitoring hand articulation.

The effect of variation of composition on the structural, morphological, magnetic and electric properties of Mg1−xNixCrxFe2−xO4 (x = 0.0–0.5) nanocrystallites is presented. The samples were prepared by novel polyethylene glycol (PEG) assisted microemulsion method with average crystallite size of 15–47 nm. The microstructure, chemical, and phase analyses of the samples were studied by the scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray fluorescence (ED-XRF), and X-ray diffraction (XRD). Compositional variation greatly affected the magnetic and structural properties. The high-field regimes of the magnetic loops are modelled using the Law of Approach (LOA) to saturation in order to extract information about their anisotropy and the saturation magnetization. Thermal demagnetization measurements are carried out using VSM and significant enhancement of the Curie temperature from 681 K to 832 K has been achieved by substitution of different contents of Ni–Cr. The dc-electrical resistivity (ρRT) at potential operational range around 300 K is increased from 7.5 × 108 to 4.85 × 109 Ωcm with the increase in Ni–Cr contents. Moreover, the results of the present study provide sufficient evidence to show that the electric and magnetic properties of Mg-ferrite have been improved significantly by substituting low contents of Ni–Cr.

This paper presents our proposed design for a multi-core planar fluxgate sensor for low magnetic field measurements. It stands out from other fluxgate designs by using three core layers. This will increase flux concentration in the pickup coil and thus improve field sensitivity. The basic structure of the multi core fluxgate magnetic sensor is shown in Fig. 1. It consists of three-core flux concentrators, an excitation coil and a sensing coil. The actual implementation of the structure in PCB technology is shown in Fig. 1. The 20 turn planar excitation coil was constructed with a thickness of 30μm and sandwiched between the three-cores. The magnetic components were measured from the sensing coil, 400μm wide with 20 turns. The excitation and sensing coils were on separate PCB layers separated by a distance of 50 μm from each other.

The purpose of this research is to evaluate two types of sensor that can be applied to monitor human finger flexion in real time. Currently, flex sensors are the most commonly used resistance sensors in glove-based systems. However, measurements show that current flex sensors have problems associated with hysteresis error, low sensitivity at small angles, and considerable time drift with large bending angles which render them unsuitable for tracking hand motion at low speed. In contrast, the developed optical sensor prototype has good repeatability, sensitivity and low temporal drift, as well as offering the capability of accurate measurements in both clockwise and anticlockwise directions. The sensor is based on the principle of crossed-polarization detection, and consists of one LED, two rotatable polarizers and one photodiode amplifier which enables the detection of changes in polarized light intensity proportional to angular rotation.

The aim of this study is to deposit and then characterize a large quantity of magnetic materials and understand how the Novel Vacuum Coating Plant (VCP) system affects the properties of the materials. Ni60Fe40 and Ni80Fe20 were the compositions chosen for the investigation. The films were deposited on rigid and flexible substrates using the novel VCP. Data from Inductively Coupled Plasma Atomic Emission Spectrometry analysis performed on the source alloys confirmed that element concentrations were within 0.3% of the compositions. The X-ray diffraction patterns indicated that all films have face-centred cubic structure. Ni60Fe40 films evaporated on a polyimide (kapton™) substrate showed anisotropic behaviour due to the flexible nature of the substrate, aided by the relatively high magnetostriction caused by the composition, whereas the films produced on glass substrates exhibit only isotropic magnetisation irrespective of their compositions. Observations indicate that in-plane anisotropy and coercivity is dependent on the type of substrates and the compositions. All films showed planar magnetic anisotropy. It is seen that large film areas can be produced and their properties were affected by the deposition parameters in the VCP system.

Magnetostrictive materials have been utilized for the production of ultrasonic frequency vibrations for a number of years. This has particularly been the case in laminated nickel-based ultrasonic dental-scaler cleaning systems. In this study, a comparison has been made between the impedances of a number of magnetostrictive stacks of 50 mm×4 mm×∼0.3 mm strips at frequencies in the range of 10–50 kHz in a coil used for the excitation of a stack in a dental-scaler system. The magnetostrictive stacks tested comprised of potential replacement materials for standard nickel ones. The study showed that it was possible to compensate for the inductive ‘imaginary’ components of the impedance through the use of a tuned, series capacitance so that only the ‘real’ resistive component of the impedance remained. This reduced the electrical losses associated with the excitation of the magnetostrictive stacks as a result of the frequency-dependent inductance of the coil system. Consequently, the maximum power transfer from an amplifier to the transducer was increased. Also, the investigation showed how the ‘real’ component of impedance of the different stacks varied with frequency. In a tuned resonant electrical circuit, the resistive component of the impedance, if considered as a loss, would be the lowest that could be achieved with such a magnetic circuit. Consequently, the losses associated with resonant magnetostrictive devices, like dental scalers, can be reduced.

The Fe14.5Co16.5Ni55B15 and the Fe13Co15.5Ni51.5B20 ferromagnetic nanowires were deposited using the electrochemical deposition method. The structure of these nanowires was investigated using X-ray diffraction. Squid magnetometer was used to investigate the magnetic behavior. The hysteresis loops of 50 μm long nanowire arrays were studied as a function of boron concentration, nanowire diameter and field orientation. The competition between shape anisotropy and magnetostatic interactions played a vital role in determining the magnetic field necessary to saturate an array. The decrease in coercive field (Hc) and the squareness (SQ) of the hysteresis loop from 100 to 200 nm wire diameter for both types of compositions suggests the formation of multidomains in the nanowire.

The bi-layer thin film measurement system uses the principle of frequency modulation for the detection of displacement. The measuring system utilizes a personal computer based system using the LabVIEW® graphical programming package that provides the features necessary for acquiring the sensor signal, analyzing it and displaying the results. The results from the acquisition were compared with previously developed amplitude and phase modulation based systems to show that the frequency modulation technique provides a robust and accurate solution to evaluate magnetostrictive materials and their application in magnetic sensors. The performance of the bi-layer thin film sensor was examined and its thermal stability, over the temperature range of up to 180 ◦C, was tested in an environmental chamber. The temperature rise does cause inductance change, but the sensor signal remains unaffected due to the nature of the frequency modulation method. Thus, having two materials, with different thermal coefficients of expansion in a bi-layer thin film sensor does not adversely influence the sensor signals. This creates a temperature independent sensor that is needed for applications where there are temperature variations.

A novel bi-layer thin film sensor system was used for accurately registering physiological parameters associated with body movements, such as cardiac and respiratory activities. The bi-layer curvature sensor system can provide additional medical information about the cardiac activity of the patient by mapping the five characteristic waves of the normal heartbeat rate (P, Q, R, S and T wave). This system was also used for registering physiological parameters such as the monitoring of lung ventilation which can give a range of information about the patients health (normal respiration patterns, deep inhalation/exhalation and apnoea), easily distinguishable in the output signal. The bi-layer thin films used consist of a magnetic layer and a non-magnetic counter layer that is utilized to enhance the changes in the relative permeability of the material caused by tensile or compressive stresses during bending. The measuring system is based on a personal computer in conjunction with the LabVIEW® graphical programming package. The nature of this configuration provides the necessary features for sensor signal acquisition, analysis and data presentation. The results from the sensor application on patients demonstrate that this system can provide a robust, cost effective solution to monitoring cardio-respiratory activity with minimum inconvenience to the patient, which is necessary for prolonged, undisturbed monitoring.

The twisting of a pair of leads connecting to a search coil used for detection of magnetic field or flux density reduces errors due to stray magnetic fields. Although this method is commonly used, the influence of stray fields is often underestimated. This could lead to degradation of the accuracy of measurements. This paper presents an analysis of the influence of the quality of wire twisting and its possible influence on the signal-to-noise ratio. Twisted wires are approximated as a two-dimensional configuration, for which typical results of calculations are presented. The paper also reports the results from measurements using manually and machine-twisted pairs of wires. The analysis shows that the stray field influence can be reduced by up to 60% by proper twisting of a pair of wires connecting a sensor to measuring equipment.

A novel method has been used for accurately measuring low voltage signals (~10-4 V) associated with inductance changes of bilayer thin-film sensors under bending stress. In this paper the architecture of the system is first presented, and then the design ideas and key technologies are followed. Initially, the frequency modulated signals were simulated with superimposed noise signals to test the demodulation performance of the written program. From the results, the expected output of the program was confirmed. Following this, the frequency modulation technique was used with actual sensor signals to measure the displacement of a bilayer thin film sensor. The results from the acquisition were compared with a previously developed amplitude modulation based setup, and it proved that the frequency modulation system provided a robust and accurate solution to evaluate magnetostrictive materials and their application in magnetic sensors

All magnetostrictive types of soft magnetic materials show some weak sensitivity to processes of bending. However, as demonstrated here, a prerequisite for high sensitivity values is that the profile of material exhibits asymmetry with respect to physical characteristics. Specific technological processes yield ultra high sensitivity, a curvature of 1/m causing permeability changes of more than 50%.

The rotational power losses measured in the clockwise and anticlockwise directions differ noticeably. There are many factors that contribute to this difference, but these have not previously been explained in the literature. A discussion on the physical phenomena that contribute to the power loss along with the experimental measurements and analysis are presented.

It is well known that the rotational power loss differs if the flux vector is rotated in either a clockwise or an anticlockwise rotation direction. An analysis is presented that shows that averaging the clockwise and anticlockwise values introduces an additive error that is dependent on the angular misalignment between the measuring sensors. Equations to minimise this error are presented and validated by application to experiments on electrical sheet steel.

This paper concerns continuous nondisturbing estimation of blood pressure using mechanical plethysmography in connection with standard electrocardiography (ECG). The plethysmography is given by a novel magnetoelastic skin curvature sensor (SC-sensor) applied on the neck over the carotid artery. The sensor consists of a magnetoelastic bilayer partly enclosed by a coil. Bending the bilayer causes large changes of magnetic permeability which can be measured by the coil. The SC-sensor signal and the ECG signal are adaptively processed in order to estimate blood pressure according to a specifically established theoretical model. The model uses estimated vessel radius changes and pulse transit time as parameters. The results show cross correlation coefficients in the range 0.8 up to 0.9 between reference and estimated values of systolic blood pressure, diastolic blood pressure, and systolic/diastolic blood pressure change, whereas the estimation error was below 4 +/- 7 mmHg at rest and increased with the stress level. Limitations of the model applicability are given by a hysteretic behavior of both model parameters due to inert changes in artery stiffness. The SC-sensor and the ECG electrodes cause minimal inconvenience to the patient and offer an approach for a continuous nondisturbing monitoring of blood pressure changes, as being relevant for sleep monitoring or biomechanic feedback

The localised flux density measurements are practically limited to two methods: search coil and needle probe technique. The search coil requires drilling holes in the sample under test; therefore it is a destructive method. Needle probe technique is classified as a non-destructive technique. However, removing the coating affects the magnetic properties of the sample sharp needles introduce micro-damages to the surface of the specimen. At certain conditions, the electrical contacts between the needles and the sample could be replaced by capacitors made as pads manufactured from self-adhesive conductive tape or directly painted with conductive paint on the insulated surface of the sample. The paper presents theoretical analysis of the concept of the capacitive sensor. The simulations suggest that the described capacitive sensor would be suitable for detecting localised flux density in laminated material, especially at higher frequencies.

A novel loudspeaker design has been proposed that employs hundreds of micro transducers producing small displacements within the audible frequency range. The feasibility of employing a solenoid actuator as the loudspeaker transducer has been studied and discussed in this paper. Compared to its counterpart, voice coil motor, a solenoid actuator exhibits very non-linear behaviour. The theoretical description along with practical test on a commercial solenoid actuator reveals the limitations of solenoid operation at high acceleration and current.