T. Uchiyama

Giant magneto-impedance in Co-rich amorphous wires and films

A comprehensive analysis of magneto impedance (MI) phenomena in Co-rich amorphous materials is presented on the basis of skin effect in combination with dynamical magnetization processes. We consider a MI effect for which the domain walls are perpendicular to the current and field direction. Thus, the magnetization induced by current proceeds, via both the wall movement and moment rotation. The magnetic responses of impedance in wires and films have some common features and can be understood from the same mechanism. The sensitivity of the magnetic response in a small sample (1 mm length and a few micrometer thickness) is about 10%/Oe in wires and 5%/Oe in films. The model describes well the existing experimental data for moderate frequencies, There is some quantitative discrepancy for the case of a very strong skin effect, where the position dependence of basic magnetostatic parameters is important. >

Recent advances of micro magnetic sensors and sensing application

Abstract Principle and basic performance of micro magnetic sensors such as the Hall element, the magneto-resistance (MR) element, the giant magneto-resistance (GMR) element, the thin-film fluxgate sensor (FGS), and the magneto-impedance (MI) element are summarized. Their basic properties are compared with each other considering a new sensing target in various modern industrial fields. A new micro-sized magnetic field sensor with a high sensitivity and a quick response is developed using the MI effect in amorphous wires and thin films. The MI sensor having a micro-sized zero-magnetostrictive amorphous wire head of about 1 mm installed in self oscillation circuits such as the Colpitts oscillator and a multivibrator circuit shows a high sensitivity with a resolution of 10 −6 Oe for ac fields and 10 −5 Oe for dc fields, quick response with a cutt-off frequency of about 1 MHz, and a high temperature stability of less than 0.05%FS °C −1 up to 70°C. A very low power consumption and highly stable MI sensor is constructed using a CMOS multivibrator. A stable measurement for a surface-flux distribution around a 2000-pole ring magnet with a diameter of 19 mm for a high density rotary encoder was carried out using the MI sensor. A small pin hole of 100 mm diameter in an iron sheet was detected at non destructive testing (NDT) using a gradient-field detection type MI sensor cancelling back ground disturbance fields. A sample of clustered magnetic particles was magnetically detected using the MI sensor probe in a simulation of detection of a brain tumor at which an injected sol was induced with the magnetic particles.

Magneto-impedance element

The magneto-impedance (MI) effect is a phenomenon in which the voltage induced by a high frequency current source in a ferromagnetic wire changes with the application of an external field. A giant MI effect was found in amorphous magnetic wires having a composition of (Fe/sub 0.06/Co/sub 0.94/)/sub 72.5/Si/sub 12.5/B/sub 15/ and a magnetostriction of (-10/sup -7/). The amplitude of the wire voltage decreased by 40% at 1 MHz, 60% (600 kHz) and 50% (150 kHz), for wires having diameters 30 /spl mu/m, 50 /spl mu/m and 124 /spl mu/m, respectively, under the influence of an external longitudinal field of about 10 Oe (800 A/m). A highly sensitive and quick-response field sensor was constructed using a 200 MHz resonant multivibrator bridge-circuit combining two MI-effect elements of 1 mm length with two field effect transistors (FET). Highly sensitive flux detection was carried out by using the small MI sensor head on a rotary encoder magnet having 512 poles and a diameter of 30 mm. Discussion of a mechanism for the MI effect considers the skin effect in an amorphous wire with high circumferential anisotropy. >

Sensitive and quick response micro magnetic sensor utilizing magneto-impedance in Co-rich amorphous wires

New high performance micro magnetic heads and sensors are presented utilizing the giant magneto-impedance (GMI) in the Co-rich amorphous wire. Typical performances or advantageous features of the head and sensor-are as follows; (i) head size can be reduced to about 1 mm maintaining a flux detection sensitivity of about 10/sup -5/ Oe, (ii) a rapid response with the cut-off frequency of 20/spl sim/30 MHz using a wire current of 200/spl sim/300 MHz, (iii) high temperature stability of about 0.01 %FSspl deg/C with a maximum operating temperature of about 180/spl deg/C using a negative feedback loop in the sensor circuit, and (iv) small power consumption of less than 10 mW using a self-oscillation circuit, in which a MI element voltage decreases to zero (100% change) with an external field of about 2 Oe. The basic properties and mechanism of the GMI, the head construction, the sensor construction principle, sensor circuits and sensing applications are discussed. >

Sensitive micro magnetic sensor family utilizing magneto-impedance (MI) and stress-impedance (SI) effects for intelligent measurements and controls

Abstract Recent development in the field of highly sensitive, quick response and small power consumption micro magnetic sensor family (MI sensors and SI sensors) utilizing the magneto-impedance (MI) and stress-impedance (SI) effects mainly in amorphous wires is summarized. The MI and SI sensors are constituted with CMOS inverter IC and MI and SI heads magnetized with the sharp pulse current generating the skin effect, which realize the application specified integrated circuits (ASIC) sensors. Various pocketable or handy micro sensors have been developed, such as the handy terrestrial field sensor and the electronic compass for automobiles using the amorphous zero-magnetostrictive (FeCoSiB) wire MI chips combined with the CMOS IC circuit. Highly sensitive micro stress (strain) sensors and micro acceleration sensors are also developed using the amorphous magnetostrictive (CoSiB) wire SI elements combined with the CMOS IC circuit. Various small oscillatory motions in human bodies, such as the finger tip blood vessel pulsation (FTP) and the mechano-encephalogram, and road bridge oscillation during car passing are sensitively detected using the SI acceleration sensor.

Amorphous wire and CMOS IC-based sensitive micromagnetic sensors utilizing magnetoimpedance (MI) and stress-impedance (SI) effects

New sensitive quick-response and low-power-consumption micromagnetic sensors, namely, the magnetoimpedance (MI) sensor utilizing the MI effect in zero-magnetostrictive amorphous wires and the stress-impedance (SI) sensor utilizing the SI effect in negative-magnetostrictive amorphous wires, are presented. The field detection resolution of the CMOS IC-type MI sensor is about I /spl mu/Oe for ac fields and 100 /spl mu/Oe for a dc field with the full scale of /spl plusmn/3 Oe using a 2- or 0.5-mm-long amorphous wire with 30- or 15-/spl mu/m diameter as a sensor head. The possible response speed is about 1 MHz, and the power consumption is about 10 mW. The magnetoimpedance integrated circuit (MIIC sensor was developed in 2002 by the Aichi Steel Company, Japan, for mass production. The stress detection resolution of the SI sensor is about 0.1 Gal in acceleration Sensing, which is suitable for detection of microdisplacement in the medical field. More than 100 themes are proposed for application of MI and SI sensors.

Hypoxia Induces Transcription of the Plasminogen Activator Inhibitor-1 Gene Through Genistein-Sensitive Tyrosine Kinase Pathways in Vascular Endothelial Cells

A decline in oxygen concentration perturbs endothelial function, which promotes local thrombosis. In this study, we determined whether hypoxia in the range of that observed in pathophysiological hypoxic states stimulates plasminogen activator inhibitor-1 (PAI-1) production in bovine aortic endothelial cells. PAI-1 production, measured by ELISA, was increased by 4.7-fold (P<0.05 versus normoxic control, n=4) at 12 hours after hypoxic stimulation. Northern blot analysis showed the progressive time-dependent increase in the steady-state level of PAI-1 mRNA expression by hypoxia, which reached a 7.5-fold increase (P<0.05 versus control, n=4) at 12 hours. Deferoxamine, which has been known to bind heme protein and to reproduce the hypoxic response, induced PAI-1 production at both the mRNA and protein levels. The half-life of PAI-1 mRNA, as determined by a standard decay assay, was not affected by hypoxia, suggesting that induction of PAI-1 mRNA was regulated mainly at the transcriptional level. Transient transfection assays of the human PAI-1 promoter-luciferase construct indicates that a hypoxia-responsive region lies between -414 and -107 relative to the transcription start site, where no putative hypoxia response element is found. The hypoxia-mediated increase in PAI-1 mRNA levels was attenuated by the tyrosine kinase inhibitors genistein (50 micromol/L) and herbimycin A (1 micromol/L), whereas PD98059 (50 micromol/L, MEK1 inhibitor), SB203580 (10 micromol/L, p38 mitogen-activated protein kinase inhibitor), and calphostin C (1 micromol/L, protein kinase C inhibitor) had no effect on the induction of PAI-1 expression by hypoxia and deferoxamine. Genistein but not daidzein blocked the production of hypoxia- and deferoxamine-induced PAI-1 protein. Thus, we conclude that hypoxia stimulates PAI-1 gene transcription and protein production through a signaling pathway involving genistein-sensitive tyrosine kinases in vascular endothelial cells.

Asymmetrical magneto-impedance effect in twisted amorphous wires for sensitive magnetic sensors

An asymmetrical and sensitive magneto-impedance effect was realized in twisted FeCoSiB and CoSiB amorphous wires magnetized with a dc-biased ac current, in impedance up to about 120%/Oe. The asymmetrical magneto-impedance (AMI) is useful to construct linear field sensors without any dc bias field. Mechanisms of the AMI are also discussed.

Sensitive Stress-impedance Micro Sensor Using Amorphous Magnetostrictive Wire

A giant stress-impedance (GSI) effect with the strain-gauge factor more than 1200 was found in negative magnetostrictive amorphous CoSiB wires of 30-/spl mu/m diameter magnetized with a high frequency current or a sharp pulse current. A sensitive stress sensor is constructed using a CMOS IC multivibrator circuit in which the amorphous wire is magnetized with a sharp pulse train current. The amorphous wire GSI sensor will be applied for detection of such as pressure, tension, stream speed for liquid and gases and mechano-cardiogram with the sensitivity of 5-6 times higher than that of the semiconductor stress sensors utilizing the piezo-resistance effect showing a gauge factor of about 200.

Magneto-impedance in sputtered amorphous films for micro magnetic sensor

The magneto-impedance (MI) effect in RF sputtered (CoFe)/sub 80/B/sub 20/ zero-magnetostrictive amorphous films are presented. The relation between annealing conditions and MI characteristics was investigated. Impedance Z monotonously decreased with increasing applied field Hex when a high frequency sinusoidal current was applied to the sample annealed in a rotational field. In case of the samples having transverse anisotropy, Z sharply increases with Hex for the region Hex<Hk (anisotropy field). MI ratio (/spl Delta/|Zl/lZ/sub 0/l/Oe) of 8%/Oe was obtained for the sample annealed in a dc field (or applying dc current) after annealing in the rotational field. The Colpitts oscillator type field sensor was constructed using the film element. A direction sensing utilizing the terrestrial field was carried out using the MI-colpitts sensor.