A low-noise magnetoresistive-superconducting hybrid magnetic sensor

Abstract

This invention provides a low-noise magnetoresistive-superconducting composite magnetic detector, comprising a superconducting layer and a magnetoresistive element. The superconducting layer consists of a closed superconducting loop, which includes two parallel current-compressing structures. The width of both current-compressing structures is smaller than the width of the superconducting loop, with the width of the current-compressing structure on the outer side of the superconducting loop being smaller than that on the inner side. Two electrodes are connected to the current-compressing structure on the outer side of the superconducting loop, and a high-frequency alternating current is passed through them. The magnetoresistive element is located above the current-compressing structure on the outer side of the superconducting loop. This invention overcomes the problem of excessive low-frequency noise in existing magnetoresistive-superconducting composite magnetic detectors and proposes a novel low-noise magnetoresistive-superconducting composite magnetic detector.

Description

Technical Field

[0001] This invention belongs to the field of weak magnetic field detection technology, specifically relating to a low-noise magnetoresistive-superconducting composite magnetic detector. Background Technology

[0002] Weak magnetic field detection technology has important applications in industrial production, biomedicine, national defense, and geological exploration. Among all types of magnetic field detectors, SQUID devices based on the superconducting Josephson effect and optically pumped atomic magnetometers that utilize the interaction between nucleons and magnetic fields to achieve magnetic field detection are currently the most sensitive magnetic detectors, with magnetic field detection accuracy reaching the pT or even fT level. However, these magnetic detectors face challenges such as the difficulty in fabricating core components (the Josephson junction of SQUID devices and the bubble chamber of optically pumped atomic magnetometers require sophisticated fabrication processes), complex system structures (SQUIDs require a flux-locked loop, and optically pumped atomic magnetometers require an optical path), and high operating costs (SQUIDs need to operate in the liquid helium temperature range). In recent years, a novel magnetoresistive-superconducting composite magnetic detector has attracted widespread attention. This detector uses a closed superconducting ring as a magnetic concentrator and amplifies the magnetic field of the magnetoresistive sensor. The thermal noise level of the device in the liquid nitrogen temperature range is close to that of high-temperature SQUID devices. Due to its simple structure, high sensitivity, and low thermal noise, it has the potential for large-scale application in the field of pT and even fT level magnetic field detection. However, the device currently exhibits significant 1 / f noise at low frequencies, making it difficult to further improve the detection accuracy of the magnetoresistive-superconducting composite magnetic detector. Summary of the Invention

[0003] To overcome the problem of high low-frequency 1 / f noise in existing magnetoresistive-superconducting composite magnetic detectors, this invention proposes a low-noise magnetoresistive-superconducting composite magnetic detector, which is a novel type of magnetoresistive-superconducting composite magnetic detector. The low-noise magnetoresistive-superconducting composite magnetic detector proposed in this invention can solve the problem of high low-frequency 1 / f noise in existing magnetic detectors, and therefore can be used for the measurement of weak low-frequency magnetic field signals.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] The present invention discloses a low-noise magnetoresistive-superconducting composite magnetic detector comprising a superconducting layer and a magnetoresistive element. The superconducting layer consists of a closed superconducting loop; the superconducting layer includes two current-compression structures, a first current-compression structure and a second current-compression structure, arranged in parallel. The width of the first current-compression structure outside the superconducting loop is smaller than that of the second current-compression structure inside the superconducting loop, and the magnetoresistive element is located above the first current-compression structure outside the superconducting loop.

[0006] The superconducting layer is used to sense the magnetic field perpendicularly passing through the superconducting loop and generate a superconducting shielding current in the closed superconducting loop. When the superconducting shielding current flows through the current compression structure of the superconducting layer, the superconducting shielding current density increases, and an enhanced induced magnetic field is generated above the two parallel current compression structures. The first current compression structure on the outer side of the superconducting layer has two electrodes connected and an alternating current is passed through it. The amplitude of the alternating current is greater than the critical current of the first current compression structure on the outer side of the superconducting layer and less than the critical current of the second current compression structure on the inner side of the superconducting layer. The magnetoresistive field is used to detect the magnetic field strength above the first current compression structure on the outer side of the superconducting layer. Under the action of the alternating current, the first current compression structure on the outer side of the superconducting loop loses its periodic quench, which can modulate the low-frequency magnetic field signal induced by the magnetoresistive field to a high frequency and be detected by the magnetoresistive field.

[0007] The superconducting layer is made of yttrium barium copper oxide high-temperature superconducting material, and the magnetoresistance is made of giant magnetoresistance or tunnel magnetoresistance.

[0008] Compared with existing technologies, the present invention has the following advantages:

[0009] This invention utilizes the characteristic that superconductors exhibit quenching above the critical current. It modulates the shielding current induced by the superconducting loop with a high-frequency current, thereby modulating the frequency of the magnetic field to be measured on the surface of the superconducting loop current compression structure from low to high frequency. Because magnetoresistive-superconducting composite magnetic detectors exhibit significant 1 / f noise at low frequencies, which decreases significantly with increasing frequency, this invention significantly reduces the 1 / f noise of the device by modulating the magnetic field to be measured from low to high frequency. Therefore, it overcomes the difficulty of further improving the detection accuracy of existing magnetoresistive-superconducting composite magnetic detectors due to their significant 1 / f noise at low frequencies. Attached Figure Description

[0010] Figure 1 This is a top view of the low-noise magnetoresistive-superconducting composite magnetic detector of the present invention.

[0011] Figure 2 This is a side view of the low-noise magnetoresistive-superconducting composite magnetic detector of the present invention.

[0012] Figure 3 The image shows a comparison of the noise spectra of a conventional magnetoresistive-superconducting composite magnetic detector and the low-noise magnetoresistive-superconducting composite magnetic detector of this invention.

[0013] Wherein: 1-superconducting layer, 2-magnetoresistive, 3-first current compression structure, 4-second current compression structure, 5-electrode. Detailed Implementation

[0014] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0015] like Figure 1 , Figure 2 As shown, the low-noise magnetoresistive-superconducting composite magnetic detector of this embodiment includes a superconducting layer 1 and a magnetoresistive element 2. The superconducting layer 1 consists of a closed superconducting loop. The superconducting layer 1 includes two current compression structures, a first current compression structure 3 and a second current compression structure 4, which replace part of the closed loop of the superconducting layer 1 and are arranged in parallel. The widths of the first current compression structure 3 and the second current compression structure 4 are both much smaller than the width of the closed superconducting loop of the superconducting layer 1. The width of the first current compression structure 3 on the outer side of the superconducting loop is smaller than the width of the second current compression structure 4 on the inner side of the superconducting loop. The magnetoresistive element 2 is located directly above the first current compression structure 3 on the outer side of the superconducting layer 1.

[0016] like Figure 1 , Figure 2 As shown, the superconducting layer 1 is used to induce a magnetic field perpendicularly passing through the superconducting loop and generate a superconducting shielding current in the closed superconducting loop. When the superconducting shielding current flows through the two parallel first current compression structures 3 and second current compression structures 4 of the superconducting layer 1, since the widths of the two current compression structures are much smaller than the width of the closed loop of the superconducting layer 1, the superconducting shielding current density will increase, and an enhanced induced magnetic field will be generated on the surfaces of the first current compression structure 3 and the second current compression structure 4.

[0017]

[0018] In formula (1), B ext Let μ0 be the magnetic field to be measured, μ0 be the free permeability, S be the effective area of ​​the superconducting layer, w be the width of the current-compressed structure, and L be the closed-loop inductance of superconducting layer 1. It can be seen that the superconducting shielding current density is inversely proportional to the width of the current-compressed structure. Therefore, the superconducting shielding current density of the first current-compressed structure 3 on the outside of the superconducting loop is greater than the shielding current density of the second current-compressed structure 4 on the inside of the superconducting loop. Simultaneously, the critical current of the first current-compressed structure 3 on the outside of the superconducting loop is less than that of the second current-compressed structure 4 on the inside of the superconducting loop. Two electrodes 5 are connected to the first current-compressed structure 3 on the outside of the superconducting layer 1, and an alternating current is passed through it. The frequency of the alternating current is higher than 1 kHz, and the amplitude of the alternating current is greater than the critical current of the first current-compressed structure 3 but less than the critical current of the second current-compressed structure 4. The magnetoresistive resistor 2 is used to detect the magnetic field strength above the first current-compressed structure 3.

[0019] Under the action of alternating current, the first current compression structure 3 periodically loses quench. Therefore, the frequency of the external magnetic field induced by the magnetoresistive 2 is modulated from low frequency to high frequency by the first current compression structure 3 periodically losing quench. The function of the second current compression structure 4 is to ensure that the superconducting shielding current flows through the second current compression structure 4 on the inner side when the first current compression structure 3 on the outer side loses quench, so that it will not disappear. Figure 3 The image shows a comparison of the noise spectra of a conventional magnetoresistive-superconducting composite magnetic detector and the low-noise magnetoresistive-superconducting composite magnetic detector of this invention. It can be seen that the low-noise magnetoresistive-superconducting composite magnetic detector proposed in this invention can significantly reduce low-frequency noise and improve the accuracy of magnetic field detection.

[0020] like Figure 1 , 2 As shown, the superconducting layer 1 can be prepared using low-temperature superconducting materials such as niobium, niobium-titanium, and niobium-tritin, as well as high-temperature superconducting materials such as yttrium barium copper oxide, and the magnetoresistance 2 can be prepared using giant magnetoresistance and tunneling magnetoresistance.

[0021] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-noise magnetoresistive-superconducting hybrid magnetic sensor, characterized by: The low-noise magnetoresistive-superconducting composite magnetic detector includes a superconducting layer (1) and a magnetoresistive element (2); the superconducting layer (1) is composed of a closed superconducting loop; the superconducting layer (1) includes two current compression structures, a first current compression structure (3) and a second current compression structure (4), which are arranged in parallel. The width of the first current compression structure (3) on the outside of the superconducting loop is smaller than that of the second current compression structure (4) on the inside of the superconducting loop. The magnetoresistive element (2) is located above the first current compression structure (3) on the outside of the superconducting layer (1); the superconducting layer (1) is used to sense a magnetic field that passes perpendicularly through the superconducting loop and to generate a superconducting shielding current in the closed superconducting loop; when the superconducting shielding current flows through the first current compression structure (3) of the superconducting layer (1)... When the compression structure (3) and the second current compression structure (4) are connected, the superconducting shielding current density increases and an enhanced induced magnetic field is generated above the first current compression structure (3) and the second current compression structure (4). The first current compression structure (3) of the superconducting layer (1) is connected to two electrodes (5) and an alternating current is passed through it. The amplitude of the alternating current is greater than the critical current of the first current compression structure (3) and less than the critical current of the second current compression structure (4). The magnetoresistive (2) is used to detect the magnetic field strength above the first current compression structure (3) on the outside of the superconducting layer (1). Under the action of the alternating current, the first current compression structure (3) loses periodic quench, modulates the low-frequency magnetic field signal to be measured to a high frequency, and is detected by the magnetoresistive (2).

2. The low-noise magnetoresistive-superconducting composite magnetic detector according to claim 1, characterized in that: The superconducting layer (1) is made of yttrium barium copper oxide high-temperature superconducting material; the magnetoresistance (2) is made of giant magnetoresistance or tunnel magnetoresistance.

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