Weak current sensor based on magnetoelectric effect

Abstract

The invention belongs to the field of sensors, and particularly relates to a weak current sensor based on a magnetoelectric effect. The sensor comprises a current magnetic field conversion circuit, a magnetoelectric sensing unit and a preamplifier, the current magnetic field conversion circuit converts a current signal to be detected into a magnetic field signal, the magnetoelectric sensing unit is used for detecting the magnetic field signal, and the output of the magnetoelectric sensing unit is connected with the input end of the preamplifier. The magnetoelectric sensing unit comprises a piezoelectric layer and magnetostrictive layers on the two sides of the piezoelectric layer, and magnetic field signals are converted into electric signals, so that the magnetoelectric sensing unit can work in a room temperature environment, and equivalent current noise reaches or approaches the fA / [square root of] Hz magnitude.

Description

Technical Field

[0001] The invention belongs to the field of sensors, and in particular relates to a weak current sensor based on magnetoelectric effect. Background Art

[0002] Professor Wang Daheng, a famous Chinese scientist, pointed out that "metrology is the science of improving the quantification precision of physical quantities and is the foundation and frontier of physics". The modern International System of Units is based on seven basic units: second, meter, kilogram, ampere, kelvin, mole and candela. So far, it has achieved great success in ensuring the consistency and reproducibility of global measurements. As one of the seven basic units, the ampere is also the basic unit of electromagnetic metrology. The precision and accuracy of current metrology and measurement are extremely important in scientific research and production life.

[0003] Weak current sensors sense the current information in the measured circuit and convert it into an electrical signal that meets certain standards according to certain physical transformation laws to meet the requirements of current measurement, transmission, display, and control. They play a vital role in various applications such as power systems, industrial automation, renewable energy systems, automotive electronics, and medical equipment. With the development of industrial technology, the development of current sensors has gone through the stages of shunts, current transformers, Rogowski coils, and fluxgate sensors from the 19th century to the early 20th century. The rapid development of semiconductors in the 1950s promoted the birth of new current sensors. Hall current sensors, magnetoresistive current sensors, etc. have gradually been used to meet the accuracy requirements, current ranges, response times, and isolation requirements of different scenarios.

[0004] Existing current sensors can be divided into two categories according to direct measurement and indirect measurement methods: the first category mainly includes shunts, that is, the shunt is directly connected in series in the circuit to be measured. The principle is based on the proportional relationship between voltage and current in Ohm's law. When measuring large currents, the loss is large and there is no electrical insulation; the second category is indirect measurement. The measurement principle is based on Ampere's loop law, which converts the measured current information into the measured magnetic induction intensity, and then obtains the current through the conversion formula. Representative sensors include Hall effect current sensors, fluxgate current sensors, current transformers, magnetoresistive current sensors, Rogowski coil current sensors, etc. With the increasing demand for weak current signal measurement, there is an urgent need to promote the development of high-precision current sensors by adopting new materials, new methods and high-end integrated technologies. Weak current measurement technology that combines magnetic field with other physical principles or effects has gradually developed, such as fiber optic current sensors based on magneto-optic effect, nuclear magnetic resonance NMR (nuclear magnetic resonance) current sensors, magnetoelectric current sensors, quantum Hall effect (quantum Hall effect) current sensors, and current sensors based on SQUID (Superconducting Quantum Interference Device). The above new sensors are all indirect measurement methods. Taking the Hall current sensor as an example, it uses a high magnetic permeability magnetic core as a magnetic gathering element to surround the current to be measured, and places the Hall sensitive unit at the opening of the magnetic core to measure the magnetic field changes caused by the current; while the magnetoresistive current sensor, ME and SQUID current sensor need to be connected in series to the circuit to be measured. When the current to be measured passes through the sensor coil, a magnetic field is first established around it, and then the magnetic induction element is used to detect the value of the magnetic field, and finally the current information is obtained through a linear conversion relationship. Non-invasive measurement does not require direct contact with the circuit and is easy to install, but may be interfered by external magnetic fields. The invasive measurement method has high measurement accuracy, may increase the complexity of the circuit, and is suitable for application scenarios with high-precision measurement requirements.

[0005] Superconducting quantum interference SQUID is currently the magnetic sensor with the highest detection accuracy, with advantages such as high sensitivity, high resolution, and wide frequency response range. Its working principle is based on the superconducting Josephson effect and the phenomenon of magnetic flux quantization. SQUID current sensors often work in extremely low temperature environments (<4.2K), with complex preparation processes, high costs, and are easily disturbed by external environmental magnetic fields and vibrations. At present, the equivalent input current noise level of commercial low-temperature SQUID sensors is approximately 1pA / √Hz within the white noise range. With the development of micro-nano material processing technology and integrated circuit technology, the sensor sensitivity of SQUID has been further improved.

[0006] Drung, Storm and Beyer designed a differential amplification readout circuit based on two identical SQUID sensor units. The readout circuit works in an environment of 77-300K, and the measurement noise effectively suppresses the common-mode interference in the SQUID sensor (Drung, D., Storm, J., and Beyer, J.. (2013). Squid current sensor with differential output. IEEE Transactions on Applied Superconductivity, 23(3),

[0007] 1100204-1100204.). Schmelz et al. proposed a high-precision SQUID current sensor based on a sub-micrometer cross-type Josephson tunnel junction, which can measure the equivalent input current noise level of fA / √Hz in a 4.2K environment (Schmelz M, Zakosarenko V, Schoenau T, et al. A new family of field-stable and highly sensitive SQUID current sensors based on sub-micrometer cross-type Josephson junctions [J]. Superconductor Science and Technology, 2017, 30 (7): 074010-. DOI: 10.1088 / 1361-6668 / aa7216.). Although the SQUID current sensor has an equivalent current noise of fA / √Hz, it is still limited by the harsh ultra-low temperature working conditions. Magnetoelectric sensors deeply couple magnetostriction and piezoelectric effects, and achieve highly sensitive detection of magnetic fields through this combined effect. They are very suitable for preparing portable, ultra-sensitive, and weak current sensors at room temperature. Dong et al used a small quasi-ring-type ME composite material to sandwich a PZN-4.5PT crystal ring layer between two TERFENOL-D rings, and sensed tiny currents or vortex magnetic fields through a low-altitude non-contact mode. The equivalent current noise reached 0.1μA / √Hz (Dong Shuxiang, Bai, John, G., Zhai Junyi, et al. (2005). Circumferential-mode, quasi-ring-type, magnetoelectric laminate composite—a highly sensitive electric current and / or vortex magnetic fields sensor. Applied Physics Letters, 86, 182506.).Zhang and Or used a pair of magnetoelectric composite materials to develop a gradient-type magnetoelectric current sensor, which combines the advantages of small nonlinearity of current-induced MFG effect and high sensitivity and high common-mode noise suppression rate in MFG effect. The results show that in the frequency range of 1Hz to 170kHz, the intrinsic equivalent current noise of the gradient-type current sensor is 0.6μA / √Hz to 14.3mA / √Hz (Zhang, Mingji; Or, Siu (2018). Gradient-Type Magnetoelectric Current Sensor with Strong Multisource Noise Suppression. Sensors, 18 (2), 588.). Bauer et al. prepared an ultra-low power current sensor using magnetoelectric lead zirconate titanate / nickel zinc ferrite (PZT-NZF) nanoantennas, with an equivalent current noise of 8.4nA / √Hz@1kHz (Bauer, MJ, Thomas, A., Isenberg, B., Varela, J., & Andrew, JS.).

[0008] (2020). Ultra-low-power current sensor utilizing magnetoelectric nanowires. IEEE Sensors Journal, PP (99), 1-1.).

[0009] In summary, current sensors that can work in room temperature environments and whose equivalent current noise reaches or approaches fA / √Hz have always been a hot topic in academic research and have broad application prospects. However, according to the currently publicly reported technologies, the equivalent current noise of weak current sensors based on magnetoelectric effect is often in the order of μA / √Hz or nA / √Hz. The present invention provides a weak current sensor based on magnetoelectric effect, whose equivalent current noise reaches or approaches the order of fA / √Hz. Summary of the invention

[0010] The technical problem to be solved by the present invention is to provide a weak current sensor based on magnetoelectric effect, so that it can work in a room temperature environment and the equivalent current noise reaches or approaches the fA / √Hz level.

[0011] The present invention is implemented as follows: a weak current sensor based on magnetoelectric effect, the sensor comprising: a current magnetic field conversion circuit, a magnetoelectric sensing unit, and a preamplifier, wherein the current magnetic field conversion circuit converts the current signal to be measured into a magnetic field signal, the magnetoelectric sensing unit is used to detect the magnetic field signal, and the output of the magnetoelectric sensing unit is connected to the input end of the preamplifier.

[0012] Furthermore, the current-magnetic-field conversion circuit includes a matching impedance and a current-magnetic-field conversion coil. The matching impedance and the current-magnetic-field conversion coil are connected in parallel to convert the current signal to be measured into a magnetic field signal. The magnetic field noise generated by the intrinsic current noise of the current-magnetic-field conversion circuit is much lower than the intrinsic magnetic field noise of the magnetoelectric sensing unit.

[0013] Furthermore, the magnetoelectric sensing unit includes a piezoelectric layer and a magnetostrictive layer on both sides of the piezoelectric layer, which converts a magnetic field signal into an electrical signal. The piezoelectric layer includes N PZT piezoelectric fibers arranged in parallel, and two interdigitated electrodes with an electrode spacing of 850 μm are respectively bonded to the upper and lower sides of the piezoelectric layer with epoxy resin. The magnetostrictive layer uses an amorphous strip, and the magnetostrictive layer on each side is two pieces, which are bonded to the surfaces of the interdigitated electrodes on the upper and lower sides with epoxy resin. The interdigitated electrodes on one side are connected to the inverting input terminal of the preamplifier, and the interdigitated electrodes on the other side are grounded.

[0014] Furthermore, the non-inverting input terminal of the preamplifier is grounded, and a feedback capacitor C is connected in parallel between the inverting input terminal and the output terminal. f and feedback resistor R f .

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention proposes a weak current sensor based on magnetoelectric effect, which can work in a room temperature environment and the equivalent current noise reaches or approaches the fA / √Hz level. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A circuit schematic diagram of a weak current sensor based on magnetoelectric effect provided by an embodiment of the present invention;

[0018] Figure 2 A schematic diagram of the structure of a current-magnetic field conversion circuit provided by an embodiment of the present invention;

[0019] Figure 3 A schematic structural diagram of a magnetoelectric sensing unit provided in an embodiment of the present invention;

[0020] Figure 4 An equivalent magnetic field test diagram of a magnetoelectric sensor unit provided by an embodiment of the present invention;

[0021] Figure 5 An embodiment of the present invention provides an equivalent current noise test diagram of a weak current sensor. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] See also Figure 1 As shown, a weak current sensor based on magnetoelectric effect includes: a current magnetic field conversion circuit, a magnetoelectric sensing unit and a preamplifier, the current magnetic field conversion circuit converts the current signal to be measured into a magnetic field signal, the magnetoelectric sensing unit is used to detect the magnetic field signal, and the output of the magnetoelectric sensing unit is connected to the input end of the preamplifier. The current magnetic field conversion circuit includes a matching impedance and a current magnetic field conversion coil, the matching impedance and the current magnetic field conversion coil are connected in parallel to convert the current signal to be measured into a magnetic field signal, and the magnetic field noise generated by the intrinsic current noise of the current magnetic field conversion circuit is much lower than the intrinsic magnetic field noise of the magnetoelectric sensing unit.

[0024] In one embodiment, the structure adopted by the current magnetic field conversion coil is specifically to wind a copper wire on a cylindrical epoxy bracket, the copper wire has a wire diameter of 1 mm, the cylindrical epoxy bracket has an outer diameter of 40 mm, a length of 200 mm, and the coil has a total of 800 turns.

[0025] The magnetoelectric sensing unit includes a piezoelectric layer and a magnetostrictive layer on both sides of the piezoelectric layer, which converts the magnetic field signal into an electrical signal. Figure 3 As shown. The piezoelectric layer of the magnetoelectric sensor unit prepared by the present invention is composed of 5 PZT piezoelectric fibers with dimensions of 40mm (L) × 2mm (W) × 0.2mm (T) arranged in parallel. Two interdigitated electrodes with an electrode spacing of 850μm are bonded to the upper and lower sides of the piezoelectric layer with epoxy resin. Four Metglas amorphous ribbons with a length, width and thickness of 150mm × 15mm × 26μm are bonded to the surfaces of the upper and lower interdigitated electrodes with epoxy resin. Since the electrical signal directly output by the magnetoelectric sensor unit is very weak and the output impedance is large, a low-noise, high-input impedance preamplifier circuit is usually added after its output to achieve the functions of signal amplification and impedance conversion. The preamplifier used in the embodiment of the present invention is composed of a low-noise operational amplifier AD8065, a feedback capacitor C f , feedback resistor R f The positive input of the preamplifier is grounded, and the feedback capacitor C is connected in parallel between the negative input and the output. f and feedback resistor R f The operational amplifier has an input voltage noise of 7nV / √Hz, an input current noise of 0.6fA / √Hz, and an input impedance of 10 15 Ω, the feedback capacitor is 22pF, the feedback resistor is 10MΩ, and the circuit is powered by a ±5V lithium battery.

[0026] The performance test of the magnetoelectric sensor is carried out in a magnetic shielding room, and its magnetic shielding performance is 37dB@0.1Hz, 52dB@1Hz, and 73dB@10Hz. The magnetic field voltage conversion coefficient α of the magnetoelectric sensor ME The test method is as follows. The AC signal is input into the Helmholtz coil to generate a uniform test magnetic field B in its internal space. test , with an amplitude range of 0-1μT. The Helmholtz coil consists of two circular coils with a diameter of 20cm, 20 turns, and a spacing of 10cm. First, the Helmholtz coil generates a 100nT AC test magnetic field B test The magnetic field frequency gradually increases from 1kHz to 3MHz. The magnetoelectric sensor unit is placed in the Helmholtz coil, and the output voltage value of the magnetoelectric sensor is V out The voltage value V is measured by a dynamic signal analyzer or spectrum analyzer (4395A, Agilent, USA). out With test magnetic field B test The ratio is the magnetic field voltage conversion coefficient α of the magnetoelectric sensor ME In the absence of an external excitation magnetic field, the output voltage noise of the magnetoelectric sensor is measured by a dynamic signal analyzer. The voltage noise divided by the magnetic field voltage conversion coefficient is the equivalent magnetic field noise of the magnetoelectric sensor. The experimental measurement results are shown in Figure 4 and 5 As shown in the figure, the equivalent magnetic field noise at the resonant frequency of 15.7kHz reaches 30fT / √Hz. The performance test results of the weak current sensor show that the equivalent current noise at the resonant frequency of 15.7kHz reaches 4pT / √Hz.

[0027] The above description is only 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 in the protection scope of the present invention.

Claims

1. A weak current sensor based on magnetoelectric effect, characterized in that: The sensor comprises: a current-magnetic field conversion circuit, a magnetoelectric sensing unit, and a preamplifier, wherein the current-magnetic field conversion circuit converts the current signal to be measured into a magnetic field signal, the magnetoelectric sensing unit is used to detect the magnetic field signal, and the output of the magnetoelectric sensing unit is connected to the input end of the preamplifier.

2. A weak current sensor based on magnetoelectric effect according to claim 1, characterized in that: The current-magnetic-field conversion circuit includes a matching impedance and a current-magnetic-field conversion coil. The matching impedance and the current-magnetic-field conversion coil are connected in parallel to convert the current signal to be measured into a magnetic field signal. The magnetic field noise generated by the intrinsic current noise of the current-magnetic-field conversion circuit is much lower than the intrinsic magnetic field noise of the magnetoelectric sensing unit.

3. A weak current sensor based on magnetoelectric effect according to claim 1, characterized in that: The magnetoelectric sensing unit includes a piezoelectric layer and a magnetostrictive layer on both sides of the piezoelectric layer, which converts a magnetic field signal into an electrical signal. The piezoelectric layer includes N PZT piezoelectric fibers arranged in parallel. Two interdigital electrodes with an electrode spacing of 850 μm are respectively bonded to the upper and lower sides of the piezoelectric layer with epoxy resin. The magnetostrictive layer uses an amorphous strip. The magnetostrictive layer on each side is two sheets, which are bonded to the surfaces of the interdigital electrodes on the upper and lower sides with epoxy resin. The interdigital electrodes on one side are connected to the inverting input terminal of the preamplifier, and the interdigital electrodes on the other side are grounded.

4. A weak current sensor based on magnetoelectric effect according to claim 3, characterized in that: The positive input terminal of the preamplifier is grounded, and a feedback capacitor C is connected in parallel between the negative input terminal and the output terminal. f and feedback resistor R f .

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