Measuring coercive force in local domains of a sample

A method has been proposed for determining the coercive force in local domains of bulk samples magnetized normally to the surface. The method is based on local measurement of the normal magnetic-field component at the sample surface, in the gap between the sample and the pole of a magnetizing device. The coercive force is determined by the magnetic field for which local magnetization in the measured domain becomes zero. Conditions for the correctness of coercive-force measurements have been established.     

The influence of biaxial elastic deformation on the coercive force and local remanent magnetization of construction steels

The influence of biaxial elastic tension-compression and tension-tension deformation on the coercive force and remanent magnetization of Cτ3 steel and 09Γ2C pipe steel cross-shaped specimens is studied. It is shown that coercive force grows monotonically with increasing load in the direction of compression under elastic tension-compression deformation and almost does not change under elastic tension-tension deformation. The local remanent magnetization decreases for all the considered types of biaxial elastic deformation. The possibility of using these methods for the evaluation of the stressed state of complexly deformed carbon steel products is discussed.     

A hardware-software system for the magnetographic inspection of ferromagnetic objects

A hardware-software system, which incorporates a scanning unit of a standard magnetographic flaw detector attached to a personal computer and computer programs that allow one to obtain signal records and visualize defect fields that are recorded on a magnetic tape on the screen of a monitor, has been developed for magnetographic nondestructive testing.     

Correlation of the impact elasticity of cast steels with their coercive force

The character of the correlation of the impact elasticity of cast and subsequently normalized and thermostrengthened steels 08XΓΦЛ and 08XΓTЛ with their coercive force is studied. Such a correlation in the form of a curve characterized by a maximum is observed for both low-carbon and low-alloyed hot-rolled steels.     

Study of arrangement efficiency of hall sensors of an attachable magnetic instrument used for recording the coercive force of a local area of an article

The use as a tested parameter of a coercimeter of the demagnetizing current that is measured at the moment of zero crossing of the magnetic flux in the magnet core by Hall sensors arranged under the electromagnet poles is shown to have an advantage over the use of the demagnetizing current measured at equal readings of Hall sensors placed in the neutral plane of the electromagnet in the leakage flux at different distances from an article.     

Inductive impedance transducer for recording displacements of ferromagnetic and nonferromagnetic conductive objects

The paper describes an inductive magnetic transducer for on-line recording of translations and vibrations. The transducer consists of an iron cored sensor coil and simple accompanying circuitry. The main features which are peculiar to the present transducer are (a) facility for linearizing the voltage versus displacement characteristic for certain regions of distances, (b) ability to measure vibrations and translations of both ferromagnetic objects and nonferromagnetic conductive objects, (c) relative simplicity of circuitry, and (d) the fact that only passive components are used for the transducer and an output voltage enhancement is attained by the employment of resonance. The paper is introduced by a comprehensive review of various types of magnetic transducers.     

Development of an improved Kelvin probe force microscope for accurate local potential measurements on biased electronic devices

An improved setup for accurate near‐field surface potential measurements and characterisation of biased electronic devices using the Kelvin Probe method has been developed. Using an external voltage source synchronised with the raster‐scan of the KPFM‐AM, this setup allows to avoid potential measurement errors of the conventional Kelvin Probe Force Microscopy in the case of in situ measurements on biased electronic devices. This improved KPFM‐AM setup has been tested on silicon‐based devices and organic semiconductor‐based devices such as organic field effect transistors (OFETs), showing differences up to 25% compared to the standard KPFM‐AM lift‐mode measurement method.     

Regularities of the change in the coercive force under biaxial asymmetric deformation of steel 3

The change in the coercive force under biaxial asymmetric (tension and compression in mutually perpendicular directions) cyclic deformation of cross-shaped steel 3 specimens in the elastic region of deformations was studied. Specimens were deformed beforehand under biaxial asymmetric loading to various degrees of plastic deformation. It was demonstrated that the elastic-deformation dependences of the coercive force measured along the tension and compression directions are qualitatively similar to those under uniaxial tension or compression. It was also shown that, under cyclic elastic loading, these dependences are reversible for well-annealed steel and have a hysteresis that expands with increasing degree of plastic deformation for plastically deformed steel. The possible causes of the hysteresis in the dependence of the coercive force on the elastic cyclic deformations under biaxial loading are discussed. It was supposed that the hysteresis of the coercive force was caused by the appearance of free (not bound in carbide phases) carbon atoms playing the role of interstitial impurity atoms for the α-iron lattice in plastically deformed carbon steels. The possibility of estimating the stressed-strained state of steel under biaxial loading using a magnetic method was discussed.     

On the causes of the formation of a maximum in the dependences of the coercive force of simple carbon steels on the tempering temperature

The dependences of the coercive force H _c of quenched specimens made of simple carbon steels on the tempering temperature T _t were measured at room and liquid-nitrogen temperatures. These studies showed that the formation of the character of H _c(T _t) dependences for the mentioned steels within the region of medium and high tempering temperatures is caused by the content of cementite and its magnetic hysteresis properties.     

Irreversible changes in the magnetization as indicators of stressed-strained state of ferromagnetic objects

The changes in the magnetic properties of low-carbon steels connected with reversible and irreversible magnetization reversal processes under the action of elastic stresses are studied. It is shown that, on the curve of return from the coercive force, the maximal irreversible increment in the magnetization corresponds to the zero values of applied stresses. The application of compressive stresses leads to a sharp decrease in the irreversible component of the magnetization increment. Tensile stresses influence slightly the proportion between reversible and irreversible processes. New possibilities for the multiparametric quasi-static evaluation of stressed-strained states of ferromagnetic objects are revealed.     

A permanent-magnet-based attached instrument used to inspect articles on the basis of their coercive force

An attached magnetic instrument that uses two permanent magnets to magnetize and demagnetize an article is considered. When one of the magnets is set at a fixed angle, the rotation angle of the other magnet is proportional to the coercive force of an article and is used as the tested parameter.     

Easy and direct method for calibrating atomic force microscopy lateral force measurements

We have designed and tested a new, inexpensive, easy-to-make and easy-to-use calibration standard for atomic force microscopy (AFM) lateral force measurements. This new standard simply consists of a small glass fiber of known dimensions and Young's modulus, which is fixed at one end to a substrate and which can be bent laterally with the AFM tip at the other end. This standard has equal or less error than the commonly used method of using beam mechanics to determine a cantilever's lateral force constant. It is transferable, thus providing a universal tool for comparing the calibrations of different instruments. It does not require knowledge of the cantilever dimensions and composition or its tip height. This standard also allows direct conversion of the photodiode signal to force and, thus, circumvents the requirement for a sensor response (sensitivity) measurement.     

Compact cantilever force probe for plasma pressure measurements

A simple, compact cantilever force probe (CFP) has been developed for plasma pressure measurements. It is based on the pull-in phenomenon well known in microelectromechanical-system electrostatic actuators. The probe consists of a thin (25 mum) titanium foil cantilever (38 mm of length and 14 mm of width) and a fixed electrode separated by a 0.75 mm gap. The probe is shielded by brass box and enclosed into boron nitride housing with a 9 mm diameter window for exposing part of cantilever surface to the plasma. When the voltage is applied between the cantilever and the electrode, an attractive electrostatic force is counterbalanced by cantilever restoring spring force. At some threshold (pull-in) voltage the system becomes unstable and the cantilever abruptly pulls toward the fixed electrode until breakdown occurs between them. The threshold voltage is sensitive to an additional externally applied force, while a simple detection of breakdown occurrence can be used to measure that threshold voltage value. The sensitivity to externally applied forces obtained during calibration is 0.28 V/microN (17.8 VPa for pressure). However, the resolution of the measurements is +/-0.014 mN (+/-0.22 Pa) due to the statistical scattering in measured pull-in voltages. The diagnostic temporal resolution is approximately 10 ms, being determined by the dynamics of pull-in process. The probe has been tested in the tokamak ISTTOK edge plasma, and a plasma force of approximately 0.07 mN (plasma pressure approximately 1.1 Pa) has been obtained near the leading edge of the limiter. This value is in a reasonable agreement with the estimations using local plasma parameters measured by electrical probes. The use of the described CFP is limited by a heat flux of Q approximately 10(6) W/m(2) due to uncontrollable rise of the cantilever temperature (DeltaT approximately 20 degrees C) during CFP response time.     

Differential force microscope for long time-scale biophysical measurements

Force microscopy techniques including optical trapping, magnetic tweezers, and atomic force microscopy (AFM) have facilitated quantification of forces and distances on the molecular scale. However, sensitivity and stability limitations have prevented the application of these techniques to biophysical systems that generate large forces over long times, such as actin filament networks. Growth of actin networks drives cellular shape change and generates nano-Newtons of force over time scales of minutes to hours, and consequently network growth properties have been difficult to study. Here, we present an AFM-based differential force microscope with integrated epifluorescence imaging in which two adjacent cantilevers on the same rigid support are used to provide increased measurement stability. We demonstrate 14 nm displacement control over measurement times of 3 hours and apply the instrument to quantify actin network growth in vitro under controlled loads. By measuring both network length and total network fluorescence simultaneously, we show that the average cross-sectional density of the growing network remains constant under static loads. The differential force microscope presented here provides a sensitive method for quantifying force and displacement with long time-scale stability that is useful for measurements of slow biophysical processes in whole cells or in reconstituted molecular systems in vitro.     

Development of measurement frame for detailed measurements of hysteresis cycles of ferromagnetic sheets

This paper describes the electromagnetic design of a new concept of permeameter capable of providing a measurement of the magnetic permeability of sheet strips up to 1.5 mm thick. The measurements are performed in DC. A specific feature of the device is its ability to follow the history of the excitation, representing an ideal tool to experimentally characterize hysteresis cycles as a function of the initial magnetization status of the material. The first preliminary results taken with measurement frame are also presented.     

Coercive force of ferromagnetic steels under the biaxial symmetrical tension of a material

Patterns of coercive force variations of Ct.3 and X70 ferromagnetic steels under biaxial symmetrical tension within both elastic and plastic ranges of deformation were studied using X-shaped specimens. It was shown that the coercive force of isotropic polycrystalline materials increased during plastic deformation under biaxial symmetrical tension and was proportional to applied stresses (loads). Plastic deformation of materials with high initial coercive-force anisotropy along the principal directions (X70 steel) leads to an abrupt decrease in anisotropy and subsequent alternation of its sign. The patterns of a material’s coercive force behavior allow the coercive force to be used for estimating the stress-strain state (from both an increase in the coercive force and its variations during loading as compared to that of the initial material) of articles made from the studied steels under biaxial symmetrical tensile deformation.     

The effect of the plastic tension of steels on the dependences of the coercive force on elastic compressive stresses

The effect of compressive stresses σ^? on the coercive force H _c of annealed isotropic low-carbon steels, which were preliminarily subjected to plastic tension ? _pl ⁺ of different values, has been studied. It was shown that the shape of hysteresis loops H _c (σ^?) and their changes with increasing ? _pl ⁺ are related to induced residual compressive and tensile stresses, which result from plastic tension, and also to the occurrence of plastic compressive deformations ? _pl ^? because of the Bauschinger effect. The causes of the openness of the first cycle of the H _c (σ^?) dependence and also for the occurrence of maximum of the H _c (σ^?) function in the ascending branch of this cycle are considered. A procedure for determining the residual tensile stresses, which result from the preliminary plastic tension, has been suggested and achieved experimentally. It was shown that the magnetoelastic change of magnetization, which is observed in the plastic compression, can serve as an indicator of these deformations σ _pl ^? .     

The detection of real defects in ferromagnetic objects using a magnetic-field imaging film

Tracer patterns of real defects during magnetic monitoring of ferromagnetic objects using a magnetic-field imaging film are presented. The results of production tests on the monitoring of a real object are demonstrated.     

Calibration of lateral force measurements in atomic force microscopy with a piezoresistive force sensor

We present here a method to calibrate the lateral force in the atomic force microscope. This method makes use of an accurately calibrated force sensor composed of a tipless piezoresistive cantilever and corresponding signal amplifying and processing electronics. Two ways of force loading with different loading points were compared by scanning the top and side edges of the piezoresistive cantilever. Conversion factors between the lateral force and photodiode signal using three types of atomic force microscope cantilevers with rectangular geometries (normal spring constants from 0.092 to 1.24 N/m and lateral stiffness from 10.34 to 101.06 N/m) were measured in experiments using the proposed method. When used properly, this method calibrates the conversion factors that are accurate to +/-12.4% or better. This standard has less error than the commonly used method based on the cantilever's beam mechanics. Methods such of this allow accurate and direct conversion between lateral forces and photodiode signals without any knowledge of the cantilevers and the laser measuring system.     

Choice of place of magnetic-flux registration in the magnetic core of an attachable electromagnet for inspection of articles using their coercive force

The demagnetizing current I _dc is measured in different areas of an electromagnet-article magnetic circuit at the moment of zero crossing of the magnetic flux as the gap between the electromagnet and article changes. The weaker dependence of the I _dce magnitude measured in close proximity to the article on the gap width and the possibility of using the parameter in measuring the coercive force of the article with an attachable transducer (in particular, with a Hall sensor) are demonstrated.