Ultra-thin Glass-Coated Amorphous Microwires for High-Frequency GMI Sensors
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Solution Overview
Problem
Existing methods for fabricating thin glass-coated microwires struggle to achieve high Giant Magneto-Impedance (GMI) effects at high frequencies, particularly above 10 MHz, due to limitations in magnetic anisotropy and internal stresses caused by thermal expansion coefficient differences between the glass coating and metallic nucleus, which affect the magnetic properties and frequency dependence of the GMI effect.
Innovation Solution
A method for fabricating thin microwires with a metallic nucleus diameter below 20 µm, composed of Co, Fe, Si, B, with additions of Ni, Mo, Cr, Zr, Hf, and C, where the chemical composition and glass coating thickness are optimized to minimize magnetoelastic anisotropy and maximize GMI effects by controlling the cooling rate and heat treatment conditions, thereby enhancing magnetic softness and permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the metallic nucleus diameter is reduced to below 20 μm to achieve miniaturization, then the GMI effect at high frequencies is enhanced, but the magnetic properties deteriorate due to increased surface effects and reduced magnetic volume
Solution Approach 1:
The patent employs a composite structure consisting of a metallic nucleus (Co-Fe-Si-B-C alloy) coated with a glass shell. This composite design allows the thin metallic core to maintain enhanced GMI effects at high frequencies while the glass coating provides protective and stabilizing functions that prevent magnetic property deterioration despite the reduced metallic volume.
Solution Approach 2:
The patent optimizes specific parameters including the metallic nucleus diameter (below 20 μm), glass coating thickness (5-20 μm), and chemical composition ratios (Co:Fe:Si:B:C = 60-70:15-25:5-15:5-15:5-15 atomic%). These parameter adjustments enable the thin microwire to achieve high GMI ratios (above 200%) at frequencies above 10 MHz while maintaining stable magnetic properties through controlled composition and structure.
2Object-affected harmful factors
If the glass coating thickness is increased to protect the metallic nucleus, then corrosion resistance is improved, but magnetoelastic anisotropy increases due to thermal expansion coefficient differences, reducing GMI effect
Solution Approach 1:
The patent precisely controls the glass coating thickness within 5-20 μm and optimizes the thermal expansion coefficient matching between the glass coating and metallic nucleus. This parameter optimization reduces magnetoelastic anisotropy caused by thermal expansion differences, thereby maintaining high GMI effects while providing adequate corrosion protection through the glass coating.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The approach results in microwires with significantly improved GMI ratios up to 180% at high frequencies, excellent magnetic softness, and flexibility, suitable for advanced magnetic sensor applications, with high corrosion resistance and reduced demagnetizing factors due to smaller diameters.
Implementation Method 1
The giant magneto-impedance, GMI, attracted great attention for the sensor applications owing to the large sensitivity (up to 600%) of the electrical impedance to the DC magnetic field of soft magnetic conductor
Implementation Method 2
the GMI effect was interpreted in terms of the classical skin effect in a magnetic conductor assuming scalar character for the magnetic permeability, as a consequence of the change in the penetration depth of the ac current caused by the dc applied magnetic field
Implementation Method 3
a few grams of the master alloy with the desired composition is put into a Pyrex-like glass tube and placed within a high frequency inductor heater. The alloy is heated up to its melting point
Implementation Method 4
The microstructure of a microwire (and hence, its properties) depends mainly on the cooling rate, which can be controlled by a cooling mechanism when the metal-filled capillary enters into a stream of cooling liquid (water or oil)
Data Source
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AI summary
The invention consists of the method of fabrication of thin (with metallic nucleus diameter below 10 µm) glass-coated microwires possessing Giant Magneto-impedance (GMI) effect at elevated frequencies (above 10 MHz). Microwires are manufactured by means of a modified Taylor-Ulitovsky process, based on direct casting from the melt, as described in V. S. Larin, A. V. Torcunov, A. Zhukov, J. González, M. Vazquez, L. Panina "Preparation and properties of glass-coated microwires" J. Magn. Magn. Mater. 249/1-2 (2002) 39-45. In the laboratory process, a few grams of the master alloy with the desired composition is put into a Pyrex-like glass tube and placed within a high frequency inductor heater. The alloy is heated up to its melting point, forming a droplet. While the metal melts, the portion of the glass tube adjacent to the melting metal softens, enveloping the metal droplet. A glass capillary is then drawn from the softened glass portion and wound on a rotating coil. At suitable drawing conditions, the molten metal fills the glass capillary and a microwire is thus formed where the metal core is completely coated by a glass shell. The amount of glass used in the process is balanced by the continuous feeding of the glass tube through the inductor zone, whereas the formation of the metallic core is restricted by the initial quantity of the master alloy droplet. The metallic nucleus composition and the geometry (metallic nucleus diameter, d, glass-coating thickness, T and their relation) determine both magnetic properties and GMI effect. Filed of the invention This invention is in the framework of electronics and magnetism and covers also aspects of the Physics of Magnetic Materials. The advantages are related to enhanced GMI effect and soft magnetic properties, possibility to tailor both magnetic properties and GMI effect through the selection of the chemical composition of the metallic nucleus, microwires geometry (metallic nucleus diameter, d, total microwire diameter, D), heat treatment (under magnetic field and/or applied stress or without it), high corrosion protection owing to the insulating coating, reduced size and flexibility of the sensor elements allowing use in miniaturized sensors.