TMR Sensor Circuit for Microwave Magnetic Field Measurement
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Solution Overview
Problem
Conventional methods struggle to accurately measure in-plane high-frequency magnetic fields generated by microwave-assisted magnetic heads, particularly due to the high frequency range of 10 GHz to 40 GHz and the need for precise measurement of fields exceeding 2 kOe, which is challenging with existing sensors like GMR and TMR heads.
Innovation Solution
A magnetic field measuring apparatus utilizing a TMR element with a narrow-range band-pass filter and amplifier configuration, allowing for precise measurement of in-plane high-frequency magnetic fields by ensuring a Signal-to-Noise Ratio (SNR) of 3 dB or greater, and enabling scanning of the magnetic field intensity across a predetermined region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional magnetic heads are used to generate perpendicular recording magnetic field, then recording magnetic field can be generated, but the recording magnetic field is insufficient to achieve saturation magnetization when using magnetic particles with large magnetic anisotropic energy
Solution Approach 1:
The patent combines perpendicular recording magnetic field generation with in-plane high-frequency magnetic field generation by integrating a supplementary coil system. The main coil generates the perpendicular field while the supplementary coil generates the in-plane microwave band field, merging two field generation functions into one magnetic head structure to achieve both saturation magnetization and reduced field requirements
Solution Approach 2:
The patent applies periodic action by generating in-plane high-frequency magnetic fields at microwave frequencies (10-40 GHz) that oscillate rapidly. This periodic field application enables resonance with the ferromagnetic recording layer, significantly reducing the perpendicular field strength needed for saturation magnetization while maintaining reliable recording
2Reliability
If magnetic particles with large magnetic anisotropic energy are used, then thermal fluctuation resistance is improved, but the coercive force becomes large making saturation recording difficult
Solution Approach 1:
The patent uses periodic high-frequency magnetic fields at microwave frequencies to resonantly interact with the ferromagnetic recording layer. This resonance effect temporarily reduces the effective coercive force, enabling saturation magnetization even when using particles with inherently large magnetic anisotropic energy and coercive force
Solution Approach 2:
The patent changes the frequency parameter of the applied magnetic field to match the ferromagnetic resonant frequency of the recording layer (10-40 GHz). This parameter change enables resonance that significantly reduces the field strength needed for magnetization reversal, allowing use of high-coercivity particles while achieving successful recording
3Power
If the gap between main magnetic pole and auxiliary magnetic pole is reduced to around 30 nm, then in-plane high-frequency magnetic field can be generated, but the measurement region becomes extremely tiny making measurement difficult
Solution Approach 1:
The patent moves the measurement function to a different spatial dimension by positioning the magnetic sensor in the air bearing surface region above the gap, rather than attempting to measure within the tiny gap itself. This dimensional shift allows access to the magnetic field at a measurable distance while still capturing the field generation effect
4Measurement precision
If GMR or TMR heads are used for measurement, then magnetic field can be detected, but the frequency response is insufficient for microwave band measurements
Solution Approach 1:
The patent changes the frequency parameter of the measurement system by using a magnetic sensor capable of responding to microwave frequencies (10-40 GHz). This parameter change enables the sensor to detect the in-plane high-frequency magnetic field at the correct frequency range, overcoming the frequency response limitation of conventional GMR/TMR heads
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 apparatus enables reliable and precise measurement of in-plane high-frequency magnetic fields, ensuring high-density recording and improved recording quality, while simplifying and reducing the cost of shipping inspections.
Implementation Method 1
a magnetic sensor having a tunneling magnetoresistive (TMR) element for measuring the in-plane high-frequency magnetic field intensity generated from the microwave generation mechanism
Implementation Method 2
the band-pass filter is a narrow-range band-pass filter such that a peak pass frequency of the filter that is a center is a basic frequency selected from a range of 10 to 40 GHz and a band width centered around the basic frequency is a narrow range of ±0.5 to ±4 GHz
Implementation Method 3
an in-plane alternating magnetic field is generated by driving the alternating current of the microwave band in the supplementary coil
Data Source
AI summary
A measuring circuit system in a magnetic field measuring apparatus of the invention has an amplifier and a band-pass filter connected in sequence on an output terminal side of the TMR element, the band-pass filter is a narrow-range band-pass filter such that a peak pass frequency of the filter that is a center is a basic frequency selected from a range of 10 to 40 GHz and a band width centered around the basic frequency is a narrow range of ±0.5 to ±4 GHz; and with the measuring circuit system, an SIN ratio (SNR) of 3 dB or greater is obtained, the SNR being defined by a ratio of an amplitude S of a high-frequency generated signal induced by the TMR element to a total noise N that is a sum of a head noise generated by the TMR element and a circuit noise generated by the amplifier. With such a configuration, an in-plane high-frequency magnetic field generated by a microwave-assisted magnetic head is reliably and precisely measured.