France



Tunneling magnetoresistive (TMR) sensors can easily be used for magnetic sensing due to high sensitivity, small size, and low power consumption. [1] They also have extremely short response times and are suitable for precise sensing applications. The magnetic hysteresis in the sensing layer of TMR sensors usually has a negative effect on the linearity and reversibility of the sensors. Therefore, reduced magnetic hysteresis, as well as low power and low noise, is favored in low magnetic field measurement. Previous research has shown that the magnetic hysteresis in TMR sensors can be reduced using AC modulation magnetic fields. [2] In this study, a much smaller AC modulation amplitude is used for lower overall power consumption of TMR sensors and the linear response range of the sensors under a small modulation field is investigated.&lt;br/&gt;The magnetic tunnel junction (MTJ) stack in the studied TMR sensor was designed as Si/150 SiO&lt;sub&gt;2&lt;/sub&gt;/ 1.5 Ta/25 Ru/7 Ir&lt;sub&gt;20&lt;/sub&gt;Mn&lt;sub&gt;80&lt;/sub&gt; / 2.2 Co&lt;sub&gt;30&lt;/sub&gt;Fe&lt;sub&gt;70 &lt;/sub&gt;/0.85 Ru/ 2.8 Co&lt;sub&gt;40&lt;/sub&gt;Fe&lt;sub&gt;40&lt;/sub&gt;B&lt;sub&gt;20&lt;/sub&gt;/ 2 MgO /1.3 Co&lt;sub&gt;40&lt;/sub&gt;Fe&lt;sub&gt;40&lt;/sub&gt;B&lt;sub&gt;20&lt;/sub&gt; / 0.6 MgO/ 50 Co&lt;sub&gt;40&lt;/sub&gt;Fe&lt;sub&gt;40&lt;/sub&gt;B&lt;sub&gt;20&lt;/sub&gt; /2 Ta/15 Ru (in nm). The TMR ratio is about 180 % and the coercivity of the free layer is about 0.5 mT after magnetic annealing at 340 &lt;sup&gt;o&lt;/sup&gt;C for 2 hour. The MTJs were connected into a Wheatstone bridge to form a sensor. An alternating current driven modulation coil was added surrounding the TMR sensor during magnetic field measurement with the AC modulation field applied along the sensing direction.&lt;br/&gt;The DC voltage output of the TMR sensor with different measurement conditions is shown in Fig. 1. The sensor was powered by a 1.5 Volt battery and a sinusoidal modulation field was applied with a frequency of 1 kHz and an amplitude of 0.3 mT. The output voltage of the sensor was measured in these DC magnetic field ranges: (a) -3 mT to 3 mT, marked in black in the figure, (b) -1.8 mT to 1.8 mT, marked in green, (c) -0.6 mT to 0.6 mT, marked in blue, and (d) -0.1 mT to 0.1 mT, marked in red. The figure shows that magnetic hysteresis in TMR sensor was effectively reduced if measured in a small range of DC magnetic field. With the amplitude of AC modulation field being as small as 0.3 mT, the sensor exhibits a linear response in the range of -0.6 mT to 0.6 mT, where the sensitivity is 20.6%/mT. It’s demonstrated that based on a simple construction, TMR sensors with small AC modulation fields can be used for low field sensing with good linearity.&lt;br/&gt;&lt;br/&gt;ACKNOWLEDGMENT&lt;br/&gt;This work was supported by Ministry of Science and Technology of Taiwan under grant number: 108-2314-B-003 -001 and 109-2314-B-003 -004. The MTJ samples were prepared in the Nebraska Nanoscale Facility: National Nanotechnology Coordinated Infrastructure and the Nebraska Center for Materials and Nanoscience, which are supported by the National Science Foundation under Award ECCS: 2025298, and the Nebraska Research Initiative.

**References:**

[1] Zheng, C. et al. Magnetoresistive Sensor Development Roadmap (Non-Recording Applications). IEEE Trans. Magn. 2019, 55, 1–30.&lt;br/&gt;[2] S. Liao et al., &quot;Hysteresis Reduction in Tunneling Magnetoresistive Sensor with AC Modulation Magnetic Field,&quot; IEEE Transactions on Magnetics,(2020) doi: 10.1109/TMAG.2020.3009900.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/064c1f75dc42a064ec6e3200b38de2c4.jpg)
Fig.1 The output voltage of the sensor as a function of the applied DC magnetic field in the range of four conditions: -0.1 mT to 0.1 mT, -0.6 mT to 0.6 mT, -1.8 mT to 1.8 mT, and -3 mT to 3 mT. The sensor was powered by a 1.5 Volt battery and a AC modulation field was applied with a frequency of 1 kHz and an amplitude of 0.3 mT for all conditions of DC field range.



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 A study of hysteresis reduction of small AC magnetic field modulated tunneling magnetoresistive sensor

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Tunneling magnetoresistive (TMR) sensors can easily be used for magnetic sensing due to high sensitivity, small size, and low power consumption. [1] They also have extremely short response times and are suitable for precise sensing applications. The magnetic hysteresis in the sensing layer of TMR sensors usually has a negative effect on the linearity and reversibility of the sensors. Therefore, reduced magnetic hysteresis, as well as low power and low noise, is favored in low magnetic field measurement. Previous research has shown that the magnetic hysteresis in TMR sensors can be reduced using AC modulation magnetic fields. [2] In this study, a much smaller AC modulation amplitude is used for lower overall power consumption of TMR sensors and the linear response range of the sensors under a small modulation field is investigated. The magnetic tunnel junction (MTJ) stack in the studied TMR sensor was designed as Si/150 SiO2/ 1.5 Ta/25 Ru/7 Ir20Mn80 / 2.2 Co30Fe70 /0.85 Ru/ 2.8 Co40Fe40B20/ 2 MgO /1.3 Co40Fe40B20 / 0.6 MgO/ 50 Co40Fe40B20 /2 Ta/15 Ru (in nm). The TMR ratio is about 180 % and the coercivity of the free layer is about 0.5 mT after magnetic annealing at 340 oC for 2 hour. The MTJs were connected into a Wheatstone bridge to form a sensor. An alternating current driven modulation coil was added surrounding the TMR sensor during magnetic field measurement with the AC modulation field applied along the sensing direction. The DC voltage output of the TMR sensor with different measurement conditions is shown in Fig. 1. The sensor was powered by a 1.5 Volt battery and a sinusoidal modulation field was applied with a frequency of 1 kHz and an amplitude of 0.3 mT. The output voltage of the sensor was measured in these DC magnetic field ranges: (a) -3 mT to 3 mT, marked in black in the figure, (b) -1.8 mT to 1.8 mT, marked in green, (c) -0.6 mT to 0.6 mT, marked in blue, and (d) -0.1 mT to 0.1 mT, marked in red. The figure shows that magnetic hysteresis in TMR sensor was effectively reduced if measured in a small range of DC magnetic field. With the amplitude of AC modulation field being as small as 0.3 mT, the sensor exhibits a linear response in the range of -0.6 mT to 0.6 mT, where the sensitivity is 20.6%/mT. It’s demonstrated that based on a simple construction, TMR sensors with small AC modulation fields can be used for low field sensing with good linearity. ACKNOWLEDGMENT This work was supported by Ministry of Science and Technology of Taiwan under grant number: 108-2314-B-003 -001 and 109-2314-B-003 -004. The MTJ samples were prepared in the Nebraska Nanoscale Facility: National Nanotechnology Coordinated Infrastructure and the Nebraska Center for Materials and Nanoscience, which are supported by the National Science Foundation under Award ECCS: 2025298, and the Nebraska Research Initiative.

**References:**

[1] Zheng, C. et al. Magnetoresistive Sensor Development Roadmap (Non-Recording Applications). IEEE Trans. Magn. 2019, 55, 1–30. [2] S. Liao et al., "Hysteresis Reduction in Tunneling Magnetoresistive Sensor with AC Modulation Magnetic Field," IEEE Transactions on Magnetics,(2020) doi: 10.1109/TMAG.2020.3009900.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/064c1f75dc42a064ec6e3200b38de2c4.jpg)
Fig.1 The output voltage of the sensor as a function of the applied DC magnetic field in the range of four conditions: -0.1 mT to 0.1 mT, -0.6 mT to 0.6 mT, -1.8 mT to 1.8 mT, and -3 mT to 3 mT. The sensor was powered by a 1.5 Volt battery and a AC modulation field was applied with a frequency of 1 kHz and an amplitude of 0.3 mT for all conditions of DC field range.

poster

Fluxgate sensors are among the most sensitive devices for the detection of weak magnetic fields (in the range of 10-6 T) with resolutions of 100 pT at room temperature [1]. In conventional configuration, a fluxgate magnetometer consists of two ferromagnetic cores around which two coils for excitation and two coils for detection are wound and differentially connected. The residence times difference (RTD) fluxgate sensor first proposed by Bruno Andò, et al [1] consist of a single soft ferromagnetic core and two coils (one for excitation and one for detection). The sensor detects the external magnetic field strength through its corresponding relationship with the residence times difference of the induced peeks that appear when the excitation field cycles the magnetization of the core. One of the materials showing potential for the development of RTD sensors is represented by the glass-coated microwires exhibiting large Barkhausen effect, i.e., magnetization switching in a single step when the external excitation field is reversed. Recently, a new method to switch the axial magnetization in bistable glass-coated microwires has been reported [2, 3]. The method, detailed in [2], consists in applying a current directly through a magnetic sample subjected to controlled torsion. Using this method as a basis, we report here the development of a new RTD magnetic sensor that does not require an excitation coil. The sensor electronics was built using a dsPIC microcontroller which generates the signal for sensor excitation and measures the time difference between induced peaks (Fig.1). The time resolution of the electronics is about 1/(384x106) s. The sensor performance was studied comparatively using as sensitive elements glass-coated microwires with nominal compositions of the magnetic core Fe77.5Si7.5B15, Co68.18Fe4.32Si12.5B15 and Fe73.5Si13.5B9Cu1Nb3 (FINEMET), having metallic core diameters (Φmetal) of 10, 20 and 30 mm, respectively, and 7 mm glass coating thickness. The transfer functions (time difference versus applied field) were measured for different configuration of the sensor excitation current and torsion values. The value of the sensor sensitivity (S) decreases, and the dynamic range (DR) increases when the excitation current amplitude (I) increases. For annealed Co68.18Fe4.32Si12.5B15 microwires, having a metallic core diameter of 20 μm, we obtained a sensitivity value of 84 μs/(A/m), with a dynamic range of 17 A/m, for an excitation current amplitude of 10 mA. For an excitation current with an amplitude of 40 mA we obtained a sensitivity value of 11.7 μs /(A/m) and a dynamic range of 180 A/m. For current amplitudes of 50 mA and above, the dynamic range decreases due to the fact that the induced peaks become poorly defined, with low amplitudes, and cannot be easily distinguished by the electronic detection system. The annealed Co68.18Fe4.32Si12.5B15 microwires show wider measuring range and higher linearity of the transfer function as compared to all the other analyzed compositions (DR = ± 130 A/m for Φmetal = 20 μm and I=30 mA). The Fe77.5Si7.5B15 microwires show a fairly high noise on the measured transfer graph and lower dynamic range as compared to the Co68.18Fe4.32Si12.5B15 microwires (DR = ± 32 A/m for Φmetal = 20 μm and I=30 mA). The annealed Fe73.5Si13.5B9Cu1Nb3 wires show an extremely low linear variation transfer function (± 9 A/m for Φmetal = 20 μm and I=30 mA) as compared to the other compositions analyzed. For annealed Co68.18Fe4.32Si12.5B15 microwires with different core diameters, we observed that for the same excitation current of 30 mA and the same torsion of 483 Rad/m, the sensitivity of the sensor decreases from 27.7 μs/(A/m) for wires with a diameter of 10 μm, to 12.7 μs/(A/m) for wires having 30 μm in diameter, the dynamic range increasing at the same time from 41 A/m for wires with 10 μm in diameter, to 200 A/m for the samples with 30 μm in diameter (Fig 2). This behavior follows the evolution of the switching field of the same samples, which decreases from 45 A/m for wires with a diameter of 10 μm to 21 A/m for wires with a diameter of 30 μm. The influence of torsion on the transfer function of the sensor is relatively low. Thus, for Co68.18Fe4.32Si12.5B15 wires with a diameter of 30 μm we obtained a sensitivity of 12 μs/(A/m) for a torsion of 120 Rad/m (one end rotation of 450 on a wire with a length of 6.5 mm) and 12.7 μs/(A/m) for 483 Rad/m (one end rotation 1800 on a wire with a length of 6.5 mm). For higher torsion values, a sharp decrease in field sensitivity is observed, most likely due to the strong increase of the mechanical stresses induced in the wire. Work supported by the Nucleu Programme (Project PN 19 28 01 01) and Contract No. 11PFE/16.10.2018 financed by the Romanian Ministry of Education and Research.

**References:**

1. B. Andò, S. Baglio, A.R. Bulsara et al., IEEE Instrum Meas Mag, Vol.8(4), 2005 2. S. Corodeanu, H. Chiriac, A. Damian et al., Scientific Reports, Vol. 9, No. 5868, 2019. 3. V. Zhukova, J. M. Blanco, A. Chizhik et al., AIP Adv. 7, 056026, 2017.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/bfb14137e3ddfb99b934821adb3b5624.jpg)
Fig. 1. Schematic representation (a) and picture (b) of the RTD fluxgate sensor and the typical output voltage for a sinusoidal excitation signal (c).

![](https://assets.underline.io/uploads/markdown_image/1/image/232054e41dfbb608104ce6b41997f805.jpg)
Fig. 2. The transfer graph obtained for Co68.18Fe4.32Si12.5B15 microwires, annealed at 3000C-1h, having different diameters of the metallic core.

 RTD fluxgate sensors based on current induced magnetization reversal in twisted glass-coated microwires

I. Introduction To achieve a higher power density of power electronic modules, the switching frequency of the power electronic devices is increasing significantly. Especially, the next-generation power electronic devices utilizing wide-bandgap semiconductor materials such as SiC and GaN which can realize the switching frequency in megahertz [1]. The current sensing is essential for the control purpose, condition monitoring, protection, and power management in power electronic modules. Although the shunt resistor can be used to measure the current, it is non-isolated and the parasitic impedance introduced may incur extra power losses and jeopardize the reliability of power electronic modules [2]. The Hall-effect current transducers are extensively exploited for current measurement in power electronic modules. Nevertheless, they are inapplicable in high-bandwidth current sensing due to the limited bandwidth of typically less than 200 kHz [3]. Since the magnetic sensor such as magnetoresistive (MR) sensor can measure current up to several megahertz non-invasively [4], there are researches on using the MR sensors for current measurement in power electronics [5-8]. Due to the skin effect, the high-bandwidth current tends to be distributed on the surface of a conductor and the skin depth decreases with the frequency. Thus, the main challenge is that the magnetic field of current varies with frequency causing the nonlinearity of MR sensors. It was studied that the frequency response can be improved by placing a copper sheet around the MR sensor [5]. Although the planar copper concentrator can concentrate the magnetic field [6], the magnetic flux density (B) still varies with the frequency. The copper foil is used to wrap the MR sensor to achieve a unity normalized gain until 83.3 kHz, but the gain increases for higher frequency [7]. Besides, the field summing and decoupling methods are adopted to reduce the phase shift and extend the bandwidth to 1 MHz with an error of 5 % by using two MR sensors [8]. Therefore, the technique for a single magnetic sensor to measure a high-bandwidth current is still lacking. In this paper, a technique using a specially designed wire loop and differential amplifier based calibration circuit is developed for the magnetic sensor to measure high-bandwidth current. The skin effect of rectangular wire on the printed circuit board (PCB) is analyzed mathematically. The effects of concentrators in various structures on B are investigated based on simulation results. The effectiveness of the proposed wire loop on concentrating magnetic field of current up to 10 MHz is evaluated. The experimental results verify that the proposed technique using the wire loop and differential amplifier based calibration circuit can sense the high-bandwidth current in high accuracy. II. Analysis of High-Bandwidth Current Sensing Technique Generally, the PCB trace of a power electronic module is rectangular as shown in Fig. 1 (a). Considering a 1 oz copper trace in a width of 2.54 mm, the height is 35 μm which is much less than the width. Thus, magnetic vector potential (A) of the position (x, y) can be calculated by [9] A=Iμo/8πw{(w+x)log[(w+x)2+y2]+(w-x)log[(w-x)2+y2]+2y[tan-1(w+x)/y+tan-1(w-x)/y]-4w} where 2w and 2h are the width and height of the PCB wire respectively, μo is the vacuum permeability. When the trace is carrying a high-bandwidth current, the skin effect should be considered. The skin depth can be calculated by δ=√(2ρ/ωμo) where δ is the skin depth, ρ is the electrical resistivity of copper, ω is the angular frequency. The skin depth decreases with the frequency. This affects the A and thus the B since B = ▽×A. As shown in Fig. 1 (b) and (c), the magnetic sensor is located on the top layer of the PCB and the trace with a current of 1 A is on the bottom layer, the average B of the magnetic sensor located region (Bavg) decreases from 0.0746 mT to 0.0725 mT when the frequency increases from 1 kHz to 1 MHz. A copper sheet of 25.4 μm can be used to concentrate the Bavg to 0.141 mT at 1 MHz as shown in Fig. 1 (d). However, in this case, the Bavg increases with the frequency. The problem that Bavg varies with frequency still exists. A wire loop is designed to reduce the variation of Bavg with frequency as shown in Fig. 2 (a). The bottom-layer current passes through a rectangular wire with a cross-section of 0.2 mm × 0.2 mm located 0.35 mm above the magnetic sensor and then passes to the top layer. In this way, the Bavg is 0.242 mT when the frequency is 1 kHz and 100 kHz as shown in Fig. 2 (b) and (c). It only decreases by 0.826 % to 0.240 mT at 10 MHz. Thus, a stable B can be achieved by this method, and thus current can be sensed accurately by the magnetic sensor despite the high frequency. In the full paper, the influence of skin effect on high-bandwidth current sensing will be analyzed. The effects of concentrators in various structures on B will be investigated and presented. The principle of the proposed wire loop and differential amplifier based calibration circuit will be elaborated. The effectiveness of the proposed technique for high-bandwidth current sensing will be verified and evaluated experimentally.

**References:**

[1] E. Santi, K. Peng, and H. A. Mantooth, IEEE Transactions on Electron Devices., Vol. 62, pp. 434-442 (2015). [2] S. Ziegler, R. C. Woodward, and H. H.-C. Iu, IEEE Sensors Journal., Vol. 9, pp. 354-376 (2009). [3] A. Patel and M. Ferdowsi, IEEE Transactions on Vehicular Technology., Vol. 58, pp. 4108-4119 (2009). [4] J. Lenz and S. Edelstein, IEEE Sensors Journal., Vol. 6, pp. 631-649 (2006). [5] P. E. Schneider, M. Horio, and R. D. Lorenz, IEEE Transactions on Industry Applications., Vol. 48, pp. 1432-1439 (2012). [6] S. J. Nibir and B. Parkhideh, IEEE Transactions on Industrial Electronics., Vol. 65, pp. 2766-2774 (2018). [7] S. Shao, N. Yu, and X. Xu, IEEE Transactions on Power Electronics., Vol. 35, pp. 10930-10944 (2020). [8] M. Sheng, M. H. Alvi, and R. D. Lorenz, IEEE Journal of Emerging and Selected Topics in Power Electronics., (2020). [9] K. J. Binns and P. J. Lawrenson, Analysis and Computation of Electric and Magnetic Field Problems. Elsevier (2013).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/ed98288a51e289100f50bc2581a3c0e8.jpg)
Fig. 1. PCB trace. (a) Cross-section. Magnetic flux at (b) 1 kHz, (c) 1 MHz, and (d) 1MHz with a copper concentrator.

![](https://assets.underline.io/uploads/markdown_image/1/image/30af824e42f7b3345abdd284eed45dd0.jpg)
Fig. 2. Wire loop. (a) Layout. Magnetic flux at (b) 1 kHz, (c) 100 kHz, and (d) 10 MHz.

 High-Bandwidth Current Sensing Technique Based on Magnetic-Field Sensing Using a Wire Loop and a Differential Amplifier Calibration Circuit

In recent years, magnetoelectric (ME) composites consisting of magnetostrictive and piezoelectric phases mechanically coupled to each other have received widely attention due to the tremendous potential applications for functional devices such as magnetic sensors, phase shifters, transformers or gyrators, current sensors and energy harvesters. In the field of magnetic sensors, the ME magnetic sensors are composed of ME composites that show many excellent advantages, such as low cost, high sensor performances (sensitivity, linearity, resolution), small volume perfect and simplified electronic circuits [1]. These advantages offer the potential of ME magnetic sensor to be a new generation of magnetic sensors. There are enormous investigations activities in recent years on ME magnetic sensor. Previous research shows that ME magnetic sensor exhibit high AC/DC magnetic sensor performances at room temperature under resonance conditions [2]. Additionally, the ME magnetic field sensors have been drawn significant interests for numerous applications, such as bio-magnetism detecting apparatuses, earth magnetic field detection, non-destructive material testing, and aerospace instruments[3]. However, these ME magnetic sensor need to be strictly parallel to the magnetic field when measuring the magnetic field due to the ME laminates of configurations of square, or rectangular geometries have high anisotropy, otherwise will cause enormous deviation and affect the stability of ME magnetic sensors. It is thus desirable to develop ME magnetic sensor with ultra-lower anisotropy, along with high sensor performances. In this study, a toroidal ME magnetic sensor in composite of strictly concentric ferrites/piezoelectric rings with toroidal solenoid wound around was fabricated and developed. Compared with the previously reported ME magnetic sensor of configurations of square, or rectangular geometries, the toroidal ME magnetic sensor has ultra-lower shape-induced anisotropy, high stability and high sensor performances, which voltage output is almost unaffected by the angle between the ME magnetic sensor and the magnetic field. These excellent stability and sensor performances characteristics offer unique possibilities for possible use of ME magnetic sensor.

**References:**

[1] J. Zhai, Z. Xing, S. Dong, Appl. Phys. Lett. Vol. 88, p.062510 (2006). [2] H. Xi, M. Lu, Q. Yang, Sensor Actuat A-Phys. Vol. 311, p.112064 (2020). [3] J. Gao, L. Shen, Y. Wang, J. Appl. Phys. Vol. 109, p.074507 (2011).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/ec5e0db2329771e70db9c72da54c82bb.jpg)
Fig.1. Schematic diagram of the presented magnetic field sensor.

![](https://assets.underline.io/uploads/markdown_image/1/image/c6f133ff964c062f2b382cef753f9eca.jpg)
Fig.2. The effect of DC magnetic field angle on the ME output voltage measured for toroidal ME sensor. The inset indicates the direction of the DC magnetic fields in a top view

 Ultra-lower anisotropy magnetic field sensor in ferrite/piezoelectric toroidal magnetoelectric composites

1. Background and problem considered Metal tube and wire are used in variety parts of infrastructures. Defects like holes and cracks in the products can cause serious accidents. They are inspected in manufacturing processes by using Non-Destructive Techniques (NDTs). The inspection speed and sensitivity are important because the tube and wire are long. The Eddy Current Testing (ECT) is one of NDTs and widely used in the processes. The ECT is better than the ultrasonic testing, the X-ray testing and other NDTs on the speed and sensitivity. However tube and wire manufacturers need faster inspection speed and better inspection sensitivity, because the speed is closely related to the production speed. The speed is determined by the vibration of the inspection sample caused by the transport of the sample. The vibration has an impact on detection signals of the ECT [1]. In previous studies, signals caused by vibration are removed from the detection signal by suppressing the vibration of the transport device, and/or signal processing [2-4]. We propose a new ECT probe to suppress the vibration component in the detection signal. The novelty of the proposed probe is that it has two outer coils for electromagnetically suppressing the vibration components outside of the two inner coils for flaw detection. The principle that the proposed method reduces the detection signal due to the vibration is explained. 2. Vibration Signal Suppression Probe The proposed probe has four coils and is used with a variable amplifier and a phase shifter which is known as an all-pass filter. It is possible that effect of the vibration in the detection signal can be equal to zero by using the variable amplifier and phase shifter which adjust the amplitude and the phase of the excitation current flowing through the outer coil. Fig. 1 shows the structure of the probe with four coils. L2 and L3 are defined as the inner coils. L1 and L4 are defined as the outer coils. The inside coils form a self-induced differential sensor. The outer and inner coils form a mutually induced differential sensor with the outer coil as excitation and the inner coil as detection. The detection signals of the sensors due to the displacement of the rod is defined as the displacement signal. The displacement signal of the probe is equal to the total output of the self-induced and mutual-induced sensors. We simplify discussion by limiting static displacement. The displacement is defined the offset between axes of the rod and coils and rotation of the rod. As shown in Fig. 1, axis of the rod has the offset from axis of coils to the radius direction. The rod rotates around a point on the plane containing the axes of the rod and coil. To demonstrate the effectiveness of the method, the displacement signals of the ECT were simulated by the 3D finite element method. In the simulation, excitation current was 10 mA at 16 kHz, a brass rod with a conductivity of 1.26×107 S/m was used, and dCoils was 6 mm. Simulated detection signals are shown in Fig. 2. The detection signal of the ECT is obtained as a point on the complex plane. The horizontal and vertical axes of the plane represent in-phase and quadrature components of the signals for the excitation current. The solid and dotted lines in Fig. 2 show simulated results of displacement signals when the inner or outer coils are used as the excitation coils. The lines show the displacement signals generated when the balance of the electromotive force was lost due to the displacement. The phases of the displacement signals were constant. The amplitudes of the displacement signals were proportional to the rod of offset and rotation. The dash dot line shows that displacement signal with the amplitude and phase of the outer excitation signal adjusted using a variable amplifier and phase shifter. The amplitude and phase were adjusted so that it is equal to the inverted phase of the inner excitation signal and the amplitude of the inner excitation signal. The displacement signals cancel each other when inner and outer coils are used as excitation coil at the same time. In this case, the gain of the amplifier was 4.59 and the phase of the phase shifter was -44.8 degrees. The detail of the experimental method and results will be presented in our presentation.

**References:**

[1] C. Reboud, D. Prémel, G. Pichenot, and D. Lesselier, International Journal of Applied Electromagnetics and Mechanics, Vol. 25, No. 1-4, pp. 313-317(2007) [2] Cheng-Chi Tai, James H. Rose, and John C. Moulder, In Review of Progress in Quantitative Nondestructive Evaluation, pp. 1593-1600(1997). [3] L. Janousek, Z. Chen, N. Yusa, and K. Miya, NDT & E International, Vol. 38, No. 6, pp. 508-515(2005) [4] W. Yin, and A. J. Peyton, NDT & E International, Vol. 40, No. 1, pp. 43-48(2007)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/374558b7ee841ebcdba2ff4816bbbf11.jpg)
Fig. 1. Structure of the vibration suppression probe. The inside coils, L2 and L3, form a self-induced differential sensor. The outer, L1 and L4, and inner coils form a mutually induced differential sensor with the outer coil as excitation and the inner coil as detection.

![](https://assets.underline.io/uploads/markdown_image/1/image/256978b252c8d9537c973c2b60778bbb.jpg)
Fig. 2. Simulated displacement signals. The solid line is the signal with the inner excitation. The dot line is the signal with the outer excitation. The dash dot line is the signal adjusted from the outer excitation signal. The total signal of inner and adjusted outer signals is equal to zero.

 New Eddy Current Probe for Vibration Signal Suppression

Many ferromagnetic substances are naturally magnetized under the influence of the geomagnetic field, and information about the corresponding objects can be obtained based on the analysis of monitoring the magnetic fields generated around magnetic targets. The detection and tracking of magnetic targets is the current research hotspot, and the target monitoring based on magnetic signals as well as widely used in various fields. Currently, the magnetic target localization method is commonly used to obtain the relative position of the target by inversion of the magnetic field gradient tensor matrix. However, this method has a detection blind spot, and even if the final results are corrected by mean filtering, there is still a certain amount of error. Therefore, the correction of the localization results needs to be based on the information of the magnetic field gradient matrix collected at the detection point. This paper uses the magnetic field gradient tensor target localization algorithm as the basis of single-point localization, analyzes its error in detection, and proposes a weighted route fitting method based on magnetic field gradient matrix information for the characteristics of route calculation which is vulnerable to great errors. After simulation experiments, the method can reduce the fluctuation of detection results to a certain extent, and can effectively propose the influence of the extreme error generated by the detection blind area on the positioning results. To investigate the sources of error in target localization, we designed a series of experiments for the magnetic field gradient matrix-based localization method. The location of the detection blind zone is verified by changing the relative position of the magnetic target to the detection point. When the position vector is perpendicular to the magnetic moment vector, the error rate increases significantly. The experimental results are consistent with the theoretical formula, and the higher the accuracy of the magnetic sensor, the smaller its detection blind zone. When the detection point out is in the detection blind area, its magnetic field gradient matrix is a non-full-rank matrix, so the accuracy of target detection is often inversely proportional to the dispersion of its matrix eigenvalues. Therefore, by introducing a weighted fitting method based on the gradient matrix, the detection error can be reduced to a certain extent and the interference caused by abnormal data can be eliminated. Experiments are designed to verify the feasibility of the method. The schematic diagram of the positioning detection experiment is shown in Figure 1 below, where ABCED represents the location of different detection points, and the oval dashed line is its detection range. The magnetic target is set to come out from the coordinates (-0.5m,0m) and advance along a straight line to (0.5m,0m), and the comparison of its route monitoring results is shown in Figure 2 below. Based on the results, it can be concluded that the error-corrected route is closer to the set simulation route.

**References:**

Zhao G, Han Q, Tong X, et al. Adaptive filtering method for magnetic anomaly detection[J]. Journal of Applied Remote Sensing, 2018, 12(2):1-10. Kim K Y, Jeong E, Kim S, et al. Magnetic Anomaly Detection Using Continuous Angle Alignment of Three-Axis Magnetic Signal[J]. IEEE sensors journal, 2019, 19(2):743-750. Zheng J, Fan H, Zhang Q, et al. Magnetic Anomaly Target Recognition Based on SVD and SVMs[J]. IEEE Transactions on Magnetics, 2019, 55(9):1-8. Shen Y, Wang J, Shi J, et al. Interpretation of Signature Waveform Characteristics for Magnetic Anomaly Detection Using Tunneling Magnetoresistive Sensor[J]. Journal of Magnetism and Magnetic Materials, 2019, 484(AUG.):164-171. Huang Y, Wu L H, Sun F. Underwater Continuous Localization Based on Magnetic Dipole Target Using Magnetic Gradient Tensor and Draft Depth[J]. IEEE Geoscience and Remote Sensing Letters, 2014, 11(1):178-180. Nara T, Ito W. Moore–Penrose generalized inverse of the gradient tensor in Euler's equation for locating a magnetic dipole[J]. Journal of Applied Physics, 2014, 115(17PT.3):3646-3648.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/c3e0fd30c505b2a24e40c70d1a568e97.jpg)
Fig.1 Schematic diagram of magnetic target movement route monitoring

![](https://assets.underline.io/uploads/markdown_image/1/image/18c7f44678b5fffecd2245e1eb1c5fc9.jpg)
Fig.2 Comparison chart of route fitting correction results

 Magnetic Target Motion Monitoring Based on Weighted Route Fitting

Low frequency and weak magnetic field sensors based on magnetoelectric effect have received extensive attention due to their valuable characteristics, such as low-cost materials and fabrication, room-temperature response, low size, self-powered and non-contact sensing, high sensing resolution and large dynamic range1. In order to improve the sensitivity of magnetoelectric sensors, it is necessary to use soft magnetic materials (such as magnetic amorphous alloys, nickel, permendur, galfenol, Terfenol, ferrites) with low coercivity, low residual magnetization and high permeability as magnetostrictive phase2. The characteristics of soft magnetic field determine that the magnetoelectric sensor can quickly respond to the change of the external magnetic field, obtain the induced electromotive force, and timely recover to the state of complete demagnetization when the external magnetic field disappears. However, the output voltage generated by the magnetoelectric composite is an ambiguous function of the applied DC magnetic field due to non-negligible hysteresis loss in soft magnetic materials. The intrinsic hysteresis loop of magnetic materials is a multivalued function, which causes the magnetoelectric composites to output an uncertain voltage under the same external DC magnetic field. The non-negligible hysteresis behavior of magnetic media leads to the absolute measurement error of DC magnetic field sensor and reduces the signal-to-noise ratio (SNR). This will limit the measurement stability and accuracy of magnetoelectric sensors. Therefore, the use of magnetostrictive materials with smaller remanence may be a way to further improve the working stability of magnetoelectric sensors. In this study, by comparing three typical magnetostrictive materials with different properties, the effect of intrinsic hysteretic properties of the materials on the stability of the sensor will be studied. Furthermore, the advantages of permalloy such as low coercivity and low remanence have been used to fabricate a ME sensor with high stability. Each vibration mode of permalloy shows consistency for at least 110 hours without any demagnetization. The stable vibration mode indicates that the stability of magnetoelectric sensor based on permalloy will reach a higher order of magnitude than NZFO and Terfenol-D. Compared to previously reported counterparts, this ME sensor can achieve higher precision measurement and produce higher stability signal.

**References:**

1 Hu J M, Chen L Q and Nan C W, Adv. Mater., Vol. 28, p.15-39 (2016) 2 Burdin D A, Chashin D V and Ekonomov N A, J. Magn. Magn. Mater., Vol. 449, p.152-156 (2018)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/325c0e3bc1c866f9e9b23231c59ea03d.jpg)
Three different magnetostrictive material magnetization curves. The insert shows initial part of the curve in expanded scale.

![](https://assets.underline.io/uploads/markdown_image/1/image/c6859ec992e58cfac796facb7c4412d0.jpg)
The dynamic d33 spectrum which sampled under the condition of resonance and the same applied magnetic field for 120h.

 High-stability magnetic sensors in permalloy/piezoelectric magnetoelectric heterostructure using inappreciable hysteresis

With the development of the Internet of things, the demand for wearable flexible sensors is increasing. In order to research the new type of flexible magnetic sensors, in this paper, aiming at the vacancy of the application surface acoustic wave(SAW) devices in the field of wearable flexible magnetic sensors, the SAW magnetic sensors with ZnO/FeGa/PI structure are modeled and simulated[1,2], and the resonant characteristics and wave modes are studied. The frequency domain analysis of four kinds of devices with different thickness of 1.2 μm, 2 μm, 3.4 μm and 4 μm is carried out respectively. It is found that the device has multiple wave modes in each case, and the resonance peak of the device shifts to high frequency with the increase of the thickness of the piezoelectric layer. By comparing the modal deformation figure, it is found that the main modes of piezoelectric film with different thickness are various. For example, for 1.2 μm, the main mode is mode 2, while for 2 μm, the main mode is mode 4. The reason is that the device is composed of multi-layer thin films, in which the acoustic wave is not only affected by the piezoelectric medium, but also by the magnetostrictive layer and flexible substrate. Therefore, the optimal working mode is different for different thickness devices. In this paper, the flexible magnetic sensor is designed according to different thickness structure, and its optimal working mode is studied. When the maximum resonant mode is used as the working mode, the linear region of the magnetic sensor is basically unchanged, which is between 2 and 10 Oe. When the thickness of ZnO is 2 μm, the sensitivity in the linear region is the largest, about 253.3 kHz/Oe, and the working frequency is about 70MHz. When the thickness of ZnO is 3.4 μm, the sensitivity is only 30.5 kHz/Oe, but the working frequency is the highest, about 106MHz. This provides a theoretical basis for the development and application of flexible magnetic sensors. It is also found that when the thickness of ZnO is 1.2 μm, the maximum absolute value of admittance is only 0.0564, while for the structure with 4 μm, the maximum absolute value of admittance is 10.3413, which is of great significance for the subsequent design of impedance matching of wireless SAW magnetic sensor.

**References:**

[1] Datta S, Atulasimha J, Mudivarthi C, et al. Stress and magnetic field-dependent Young's modulus in single crystal iron-gallium alloys[J]. Journal of Magnetism and Magnetic Materials, 2010, 322(15): 2135-2144. [2] Chung G S, Phan D T. Finite Element Modeling of Surface Acoustic Waves in Piezoelectric Thin Films[J]. Journal of the Korean Physical Society, 2010, 57(3): 446-450.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/7b7faa45b7f12d0b6a8f402c537530e5.jpg)
FIG. 1 Absolute value of admittance and deformed shape plot of piezoelectric layers with different thickness (a) 1.2 μm (b) 2 μm (c) 3.4μm (d) 4 μm.

![](https://assets.underline.io/uploads/markdown_image/1/image/d20a6bf2d577a547df1976e022bde57b.jpg)
FIG. 2 (a) Relationship between resonant frequency of main mode and magnetic field intensity when the thickness of ZnO is 1.2 μm. (b) Sensitivity of main modes corresponding to different ZnO thickness.

 Simulation of wave mode of flexible SAW magnetic sensor based on ZnO/FeGa/PI structure

Magnetic field sensors using the magnetoelectric (ME) effect in the composite multiferroic structures have attracted intensive attention due to their convenient operating at room temperature and high sensitivity. Large works have focused on the improvement of sensitivity and linearity by designing novel device structures but put rare attention on the optimization of equivalent noise that is also an important parameter for actual device application. In this work, we present a DC magnetic field sensor consisting of PZT/Metglas/PZT composites. With applying a voltage bias on the bottom PZT piezoelectric layer, the ME coefficient of the top PZT/Metglas bilayers can be increased obviously, as shown in Fig.1(b). This effective increase of ME coefficient will benefit the improvement of the magnetic field-to-voltage transfer coefficient and the reduction of the noise in the magnetoelectric sensor that have been shown in Fig.1(b). By increasing the electric field from 0 V/mm to 360 V/mm, the sensitivity of the sensor can increase from 13.04 mV/Oe to 32.85 mV/Oe at the resonant frequency of 131.6 kHz, and the equivalent magnetic noise of the sensor will decrease from 20 nT/√Hz to 9.8 nT/√Hz, as shown Fig.1(c). This three times increase of sensitivity and two times reduction of equivalent noise in the DC magnetic field detection by using ME effect may offer a new route for the development of novel magnetic field sensors or arrays.

**References:**

1. J. L. Hockel, T. Wu, and G. P. Carman, Journal of Applied Physics, Vol. 109, p. 064106 (2011). 2. V. N. Serov, Y. K. Fetisov, and A. A. Berzin, IEEE Sensors Journal, Vol. 18, p. 8256 (2018). 3. Y. Shen, D. Ma, and J. Gao, IEEE Electron Device Letters, Vol. 39, p. 1417 (2018).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/4f90ba99bf370ba612a719e50bcc089f.jpg)
(a) Dependence of the output voltage with the DC magnetic field at different bias voltages; (b) Dependence of the sensitivity with the bias electric field for the proposed magnetic field sensor; (c) Frequency dependent equivalent noise density spectra at different bias electric fields of the proposed sensor.

 Optimization of Equivalent Noise in the DC Magnetic Field Sensor Based on Magnetoelectric Effect

Nowadays，the detection of the ultra-weak magnetic fields (&lt; 1 mOe) in micro- or nano-scope (&lt; 100 nm) is a hot research field. The magnetic sensor based on the principle of anisotropic magnetoresistance effect is attractive in the application of detecting the ultra-weak magnetic field in a contactless manner [1]. In this paper, a sensitive, 2-axis magnetic sensor based on anisotropic thin-film structure is proposed and fabricated. As the sensor’s induction layer, the anisotropic films of permalloy Ni (80%) Fe (20%) with different thicknesses (20 nm and 50 nm) are deposited by means of magnetron sputtering [2]. Seed layer under NiFe layer is used to control the grain size in the NiFe layer, which is an important parameter for magnetoresistance. In order to obtain the NiFe layer with good performance, tantalum is deposited as the seed layer, making the NiFe layer with &lt;111&gt; crystallographic texture with suitable grain size [3]. Figure 1 shows the schematic structure of the designed sensor for the ultra-weak magnetic field detection. The characterizations are conducted on the prepared layer, including surface roughness by atomic force microscope (AFM) and the crystalline structure by X-ray diffraction (XRD). According to the test results of AFM, it is found that the film with a thickness of 20 nm has a smoother surface with an average roughness of 1.985 nm, which is less than that of the film with a thickness of 50 nm with an average roughness of 3.005 nm. With the difference of surface roughness, the coercivity of the two thickness films is also different, and it ultimately has an effect on the film properties. Figure 2 shows the characterization results of the surface roughness of the deposited NiFe thin film. Based on the characterized results, the magnetoresistance related to the anisotropic effect is demonstrated and analyzed. The influence of the thickness of the anisotropic film on the characteristics of the magnetization and the dynamic range of the sensors, as well as the range of the magnetic field sensitivity is studied and analyzed in the paper [4]. The deposited film with 20 nm thickness shows obvious anisotropy with low coercivity, resulting in high sensitivity and outstanding detecting ability in the weak magnetic field.

**References:**

[1] N. A. Djuzhev, N. S. Mazurkin, and V. S. Pozdnyakov, Semiconductors, Vol. 49, no. 13, pp. 1739-1742 (2015) [2] M. Y. Chinenkov et al., NANOCON 2010 - 2nd International Conference, Conference Proceedings, pp. 270-273 (2010) [3] S. V. Luong, A. T. Nguyen, T. L. Nguyen, and A. T. Nguyen, IEEE Transactions on Magnetics, Vol. 54, no. 99, pp. 1-4 (2018) [4] D. Murzin, V. Belyaev, and F. Groß, Japanese Journal of Applied Physics, Vol. 59 (2019)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/7d4e34ba9f63b52244bdc965e672fa73.jpg)
The model of the magnetic sensor. Internal figure (a) Local top view of the model. (b) Enlarged view of permalloy stripes and parallelograms which are biased

![](https://assets.underline.io/uploads/markdown_image/1/image/ebdc03eef8f2668ca164a2570b87437a.png)
Results of Ni80Fe20 films' surface roughness with different thicknesses tested by atomic force microscope (AFM). (a) The thickness is 20nm. (b) The thickness is 50nm.

 A Sensitive, 2-Axis Magnetic Sensor Based on Anisotropic Magnetoresistance Effect

There are many different ways and methods for measuring displacement. The influence of the magnetic material on the inductance of the inductor in its vicinity has been well investigated and used for the realization of various sensors, as well as displacement sensors [1, 2]. However, it has been shown that an improvement in the inductance of the inductor can be achieved if the grooves are realized on the surface of the magnetic film [3], which gives the great potential for the realization of magnetic sensors with better characteristics. With advances in development of materials in recent years, 3D printing technology allows a very fast fabrication of prototypes. It can be used for development of electronic components, sensors and actuators. It is a very simple, high-quality and precise way to create complex geometric structures using different materials which enable the realization of sensors of different characteristics. This paper presents a wireless magnetic displacement sensor realized in heterogeneous integration technology. The sensor is realized using additive 3D printing technology and magnetic disc with improved design. The wireless measurement method enables simpler and more precise measurement and data collection compared to the classic wired method. The exploded 3D model of the sensor is shown in the Fig. 1. The proposed sensor consists of three parts: the inductor, the sensor’s casing with spacer and the ferrite disk with grooves. The inductor windings are turned downwards towards the ferrite. The inductor is realized in Printed Circuit Board Technology, in the form of a spiral with an outer diameter of 25 mm and 22 turns (the width of the conducting lines is 500 μm and the conductor spacing is 730 μm). Using the Mn0.5Zn0.5Fe2O4 powder, the ferrite disc with grooves is pressed and sintered at a temperature of 1275 °C for 2 hours in a chamber furnace. The ferrite disc has a diameter of 25 mm. It has three concentric rings and a circle in the center on its surface. The part of the sensor that allows the sensor to be sensitive to displacement is the spacer. The spacer is printed using a 3D technology. It was made of Ninjaflex, one of the leading flexible 3D filaments. It is in the shape of the ring with the thickness of 500 µm. Using a Polylactic acid (PLA) filament, the sensor’s housing is 3D printed in which the sensor parts are connected and fixed. The applicator of displacement that acts on the surface of the sensor is also 3D printed. Displacement measurement is performed wirelessly using an impedance analyzer HP4194A. A coil (antenna) is placed around the sensor and the impedance and the phase of the antenna-sensor system are measured, from which the resonant frequency is determined. The displacement operation on the sensor is performed using a manual translation stage which enables the precise movement of the sensor surface in the steps of 50 μm. The characteristic of the antenna-sensor is shown in the Fig. 2. During the action of the displacement, the spacer is compressed and the ferrite approaches the inductor, which causes an increase in inductance, i.e. a decrease in the resonant frequency of the antenna-sensor system.

**References:**

1. M. Kisic, N. Blaz, Lj. Zivanov and M. Damnjanovic, AIP Advances, Vol. 10, paper no. 015017, p. 1-4 (2020) 2. M. G. Kisic, N. V. Blaz, Lj. D. Zivanov and M. S. Damnjanovic, IEEE Transactions on Magnetics, Vol. 53, no. 11, Art no. 4004104, p. 1-4 (2017) 3. X. Zhou, Y. Wen, Y. Mu and P. Li, 64th Annual Conference on Magnetism and Magnetic Materials, MMM2019, November 4-8. 2019, Las Vegas, Nevada, Book of abstracts, paper no. DV-05, p. 437-438 4. Available online at: https://ninjatek.com/ninjaflex/, accessed 05.01.2021.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/eb2563e4c8b8f330d15ac98f997429ff.jpg)
Fig.1. The exploded 3D view of the sensor.

![](https://assets.underline.io/uploads/markdown_image/1/image/4dd0398f6f53d10c2624bcdc7dd3ddf0.jpg)
Fig. 2. The dependence of the resonant frequency on the displacement.

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