Magnetic Microsensors Research Articles

Micro magnetic field sensor based on bifunctional diodes

Multiple-quantum well (MQW) diodes can be used as bifunctional diodes due to the emission-detection spectral overlap. When integrated with magnetic fluids (MFs) that have tunable refractive index, they can be designed as micro magnetic field sensors. The sapphire substrate of the MQW diode chip that consists of an MQW transmitter and receiver that is directly exposed to the MF, and the external magnetic field strength is used to change the refractive index at the boundary between the sapphire and the MF, thus modulating the reflected light and realizing external magnetic field sensing. Verified by experimental measurements, the micromagnetic field sensor has a detection range of 0.001-0.05 T, a sensitivity of 127.3 µA/T, and a resolution of 4.5×10−5 T, with excellent stability and repeatability. Additionally, the sensor demonstrates good velocity resolution under dynamic magnetic fields and can detect the direction of magnetic field motion, providing significant application value.

A resonant magnetic microsensor based on magnetic torque with piezoresistive readout

A resonant magnetic microsensor based on magnetic torque with piezoresistive readout

Magnetic field detection utilizing soft magnetic ribbons and a rectangular solenoid

An effective approach to high-sensitivity magnetic field detection under low-frequency excitation by soft magnetic ribbons and a rectangular solenoid is proposed and certificated. The solenoid wound by nonmagnetic copper wire is located at the geometric center region of the soft magnetic ribbons that act as the magnetic core. The proposed magnetic sensor utilizes the nonlinear magnetization of soft magnetic ribbons and the magneto-inductive effect and proximity effect of the solenoid, exhibiting significant impedance variation at a relatively low frequency. The impedance ratio and impedance sensitivity of the prototype reaches the maximum value of 5630% and 570% Oe−1 at 500 kHz, which is far superior to the conventional giant magneto-impedance (GMI) magnetic sensor and planar coil laminated GMI magnetic sensor. The investigation indicates the fabricated magnetic sensor with optimal dimension parameters can provide a sensitivity of 3329 mV Oe−1 at 500 kHz. More importantly, the proposed prototype is particularly suitable for micromachining, providing the possibility for manufacturing high-sensitivity micro-magnetic sensors.

Synthesis, characterization, and feasibility investigation of dysprosium-doped samarium iron oxide nano-powder/polydimethylsiloxane (Dy-SmFeO/PDMS) nano-composite for dynamic magneto-mechanical stability

In this study, the synthesis and characterization of a dysprosium-doped samarium iron oxide nano powder/polydimethylsiloxane (Dy-SmFeO/PDMS) nano-composite are described. The sol-gel citrate method was employed for the synthesis, yielding highly polycrystalline nano powders with a polymorphic distribution, as revealed by X-ray diffraction and Rietveld analysis. Raman spectroscopy was utilized to investigate the chemistry of the nano powders. Notably, the readings obtained using a vibrating sample magnetometer highlighted the intriguing ferromagnetic-to-antiferromagnetic coupling behavior of the samples. The field-emission scanning electron microscopy analysis indicated that the orthorhombic crystal surfaces were uniformly encapsulated by PDMS. Furthermore, a dynamic mechanical analysis was conducted under the influence of a magnetic field (1000 mT) revealed the excellent mechanical stability of the composite. This research highlights the potential of the Dy-SmFeO/PDMS composite as a promising magnetic material with desirable properties, opening up possibilities for various applications in fields such as micro-magnetic devices, sensors, spin valves, and actuators.

Optical Magnetic Field Microsensors Based on GaN Diode Optopairs Integrated With Magnetic Fluids

In this work, the development of optical magnetic microsensors based on chip-scale GaN-on-sapphire diode optopairs integrated with magnetic fluids is demonstrated. The submillimeter-sized optopairs function as light emitters and detectors and the transparent sapphire substrate as light-guiding media is covered with magnetic fluids using PDMS recesses. The magnetic fluid strength introduces the optical reflection introduces changes in optical reflection at the boundary between the sapphire and the magnetic fluid, thus varying the amount of light received by the photodetector. Verified through experimental measurements, the micro-sensor exhibits a wide detection range of 50-2000 Gs and a fast response time of 0.06 s. The developed magnetic sensor provides remarkable features of rapid response, wide measurement range, high compactness, and simplicity of operation, making it well-suited for use in practical applications.

Micromachined Two-Dimensional Weak Magnetic Field Sensors of Soft Magnetic Film/Planar Coil Laminated

Two-dimensional magnetic sensors of soft magnetic film/planar coil laminated have outstanding advantages in miniaturization and integration. However, due to the cumbersome process and complicated structure of the sensor, its yield rate is extremely low, and the gap between magnetic films is large, resulting in increased leakage flux and low sensitivity. Therefore, a high-performance soft magnetic film with through-holes/ planar coil laminated micro-magnetic sensor with mutual inductance is designed and the sensor is fabricated by Micro-Electro-Mechanical System technology. The micro-magnetic sensor can be processed in 15 steps, with a yield rate of more than 95%, and the gap between magnetic films can be effectively reduced, resulting in reduced leakage flux and improved sensitivity. Moreover, the effect of coil resistance is eliminated, the noise level of the proposed mutual inductance micro-magnetic sensor is reduced and the detectivity can be significantly enhanced. The experiment result shows that the sensitivity of the proposed mutual inductance micro-magnetic sensor is 46.5 mV/Oe in the range of 0 Oe~0.3 Oe, the voltage noise is as low as 0.8 μV/√Hz, and the noise level reaches 17.2 μOe/√Hz. Therefore, the detectivity of the proposed mutual inductance micro-magnetic sensor can reach 17.2 μOe (1.72 nT), which has significant potential in several areas, such as biosensing and geomagnetic navigation.

High-Performance Two-Dimensional MEMS Micro-Magnetic Sensor With Magnetic Circuit Differential

Two-dimensional magnetic sensors of soft magnetic film/planar coil laminated have the advantages of low power consumption and high sensitivity, which has great potential in developing miniaturized high-performance magnetic sensors. However, the miniaturization of magnetic sensors increases the noise level resulting in limited detection ability. In this letter, a novel two-dimensional MEMS soft magnetic film/planar coil laminated micro-magnetic sensor with magnetic circuit differential is proposed. Magnetic circuit differential technology effectively reduces the common-mode noise of the micro-magnetic sensor, so the intrinsic noise of the proposed micro-magnetic sensor is significantly suppressed. Moreover, the geometric parameters of the proposed micro-magnetic sensor are optimized by MEMS technology, and the sensitivity is improved. Consequently, the detectivity of the two-dimensional MEMS micro-magnetic sensor with magnetic circuit differential is significantly enhanced. Experimental results show that the two-dimensional MEMS micro-magnetic sensor with magnetic circuit differential has a detection limit of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> Oe-level, which presents a good development prospect in the weak magnetic field.

Coupled microscopic and micromagnetic depth-specific analysis of plastic deformation and phase transformation of metastable austenitic steel AISI 304L by flow forming

Abstract This paper presents the characterization of the microstructure evolution during flow forming of austenitic stainless steel AISI 304L. Due to plastic deformation of metastable austenitic steel, phase transformation from γ-austenite into α’-martensite occurs. This is initiated by the formation of shear bands as product of the external stresses. By means of coupled microscopic and micromagnetic investigations, a characterization of the microstructure was carried out. In particular, this study shows the distribution of the strain-induced α’-martensite and its influence on material properties like hardness at different depths. The microstructural analyses by means of electron backscattered diffraction (EBSD) technique, evidence a higher amount of α’-martensite (ca. 23 %) close to the outer specimen surface, where the plastic deformation and the direct contact with the forming tool take place. In the middle area (ca. 1.5 mm depth from the outer surface), the portion of transformed α’-martensite drops to 7 % and in the inner surface to 2 %. These results are well correlated with microhardness and micromagnetic measurements at different depths. EBSD and atomic force microscopy (AFM) were used to make a detailed characterization of the topography and degree of deformation of the shear bands. Likewise, the mechanisms of nucleation of α’-martensite were discussed. This research contributes to the development of micromagnetic sensors to monitor the evolution of properties during flow forming. This makes them more suitable for closed-loop property control, which offers possibilities for an application-oriented and more efficient production.

Design of A Multifunctional Micro-Magnetic Testing Instrument

Micro-magnetic testing technology is capable of non-destructively evaluating the mechanical properties and residual stress in ferromagnetic components. In the applications of micro-magnetic testing technology, several types of magnetic signals, such as magnetic Barkhausen noise, incremental permeability, tangential magnetic field and eddy current, etc., are used to characterize the target properties (mechanical properties and residual stress). In this paper, a unique framework for multifunctional micro-magnetic sensor design is proposed. Accordingly, a multifunctional micro-magnetic instrument is developed. Intermittently superimposed magnetic fields of high (several kHz) and low frequencies (several Hz) are used for material magnetization. Combined magnetic sensors are employed to measure a total of five types of signals, including the magnetic Barkhausen noise, incremental permeability, eddy currents, tangential magnetic field and main flux. Especially, twisted-pair wiring was used for winding two identical sensing coils. One of the sensing coils is used for eddy current or incremental permeability detection and the rest one acts as a compensatory coil to suppress the strong mutual induction voltage in detection coil. The entire instrument is composed of a multi-channel signal generator, a power amplifier, signal processing circuits embedded into the multifunctional sensor and a four-channel signal acquisition device. The multi-channel signal generator is constructed based on FPGA and high speed D/A converters. The direct digital synthesizer and state machine are programed in FPGA to enable the excitation of intermittently superimposed signals of high and low frequencies. Carefully experiments were performed to test the performances of the developed instrument. The results obtained from different types of steels proved that the developed instrument can acquire five types of magnetic signals with high SNR. The features of the five types of magnetic signals can used to distinguish the material and its mechanical properties such as surface hardness.

Design of advanced micro-magnetic sensors for various applications

The state of the microstructures determines both the mechanical properties (hardness, yield strength, elongation, etc.) and micro-magnetic properties (magnetic Barkhausen noise (MBN), incremental permeability (IP), etc.). The non-destructive nature of the micro-magnetic testing technology facilitate it be a valuable tool for quality control in the manufacturing of ferromagnetic components. In the implementation of micro-magnetic testing, the functions and the geometry of the sensors need be customized for specific target properties and components. In this paper, four types of advanced or multifunctional sensors are presented and applied for micro-magnetic testing. First, a multifunctional sensor is developed for flat surface. Unique intermittent magnetizing method using superimposed magnetic fields of high and low frequencies enable the sensor to measure the magnetic Barkhausen noise, incremental permeability, eddy currents, tangential magnetic field and main flux. Second, to conduct magnetic Barkhausen noise testing at the inner corner of V-shape bending plate, a miniaturized sensor with U-shape roller magnetizer is designed to perfect contact with the corner region. Third, read head of a magnetic tape player is revised to act as high-lateral-resolution (up to 500μm) sensor for magnetic Barkhausen noise measurement in ferromagnetic film. Fourth, a slender probe is developed and embedded into an anti-bulking fixture that is clamped onto the flat specimen. With the slender probe together with the special fixture, the dependency of the magnetic Barkhausen noise on the compressive and tensile stress is first experimentally observed in a single flat specimen under continuous load.

Highly sensitive low field Lorentz-force MEMS magnetometer

We present a highly sensitive Lorentz-force magnetic micro-sensor capable of measuring low field values. The magnetometer consists of a silicon micro-beam sandwiched between two electrodes to electrostatically induce in-plane vibration and to detect the output current. The method is based on measuring the resonance frequency of the micro-beam around the buckling zone to sense out-of-plane magnetic fields. When biased with a current of 0.91 mA (around buckling), the device has a measured sensitivity of 11.6 T−1, which is five orders of magnitude larger than the state-of-the-art. The measured minimum detectable magnetic field and the estimated resolution of the proposed magnetic sensor are 100 µT and 13.6 µT.Hz−1/2, respectively. An analytical model is developed based on the Euler–Bernoulli beam theory and the Galerkin discretization to understand and verify the micro-sensor performance. Good agreement is shown between analytical results and experimental data. Furthermore, the presented magnetometer is promising for measuring very weak biomagnetic fields.

Manufacturing and Characterization of Three-Axis Magnetic Sensors Using the Standard 180 nm CMOS Technology.

A three-axis micro magnetic sensor (MS) is developed based on the standard 180 nm complementary metal oxide semiconductor (CMOS) technology. The MS designs two magnetic sensing elements (MSEs), which consists of an x/y-MSE and an z-MSE, to reduce cross-sensitivity. The x/y-MSE is constructed by an x-MSE and an y-MSE that are respectively employed to detect in the x- and y-direction magnetic field (MF). The z-MSE is used to sense in the z-direction MF. The x/y-MSE, which is constructed by two magnetotransistors, designs four additional collectors that are employed to increase the sensing current and to enhance the sensitivity of the MS. The Sentaurus TCAD software simulates the characteristic of the MS. The measured results reveal that the MS sensitivity is 534 mV/T in the x-direction MF, 525 mV/T in the y-direction MF and 119 mV/T in the z-axis MF.

Development of a methodical approach for uncertainty quantification and meta-modeling of surface hardness in white layers of longitudinal turned AISI4140 surfaces

Abstract The formation of thermally and mechanically induced near-surface microstructures in the form of white layers leads to different hardness properties in these areas. Therefore, this paper conducts systematic surface hardness measurements and uncertainty quantification utilizing the Monte Carlo Method (MCM) in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM). Furthermore, several meta-models describing the hardness course in relationship to the material depth are used to model this nonlinear relationship via machine learning. The evaluation and selection of the optimal model considers the trade-off between measurement uncertainty and prediction quality in terms of mean squared error (MSE). The resulting measurement uncertainty is to be used for the calibration of a non-destructive micromagnetic material sensor. This will then be implemented for in-process monitoring in the outer diameter longitudinal turning process. This should make it possible to detect white layers during machining and to avoid them accordingly by controlling the machine parameters. By means of a soft sensor, the corresponding target value is to be derived from the micromagnetic material sensor measurement.

Mutual inductive magnetic sensor consisting of a pair of coplanar parallel winding spiral coils sandwiched by soft magnetic ribbons

The paper proposed a mutual inductive magnetic sensor composed of a pair of parallel winding spiral coplanar coils sandwiched by soft magnetic ribbons. Because the layout of coils is in a single individual layer, the gap between the magnetic ribbons up and down is decreased compared with the previous multilayer laminated magnetic sensor. Therefore, the magnetic leakage is ameliorated, and the electromagnetic coupling between the coils and ribbons is strengthened, which in turn enhances the sensitivity. The magnetic sensor can provide a sensitivity of 5.73 mV/Oe at an excitation frequency of 500 kHz, exhibiting an enhancement of 5 times relative to the multilayer laminated sensor. In addition, the resolution of the magnetic sensor is 0.18 nT. More importantly, the structure is particularly suitable for micromachining, providing the possibility for manufacturing high-performance micro-magnetic sensors with simpler planar technology.

Highly sensitive Mach-Zehnder interferometric micromagnetic field sensor based on 3D printing technology.

A two-photon 3D printed polymer magnetic sensing device based on a Mach-Zehnder interferometer (MZI) is proposed. One arm of the MZI contains a hollow cavity and two connecting open channels that can be filled with magnetic fluids (MFs) and sealed by the UV curable adhesive, forming a magneto-optical component of the interferometer. As the magnetic field changes, the refractive index (RI) of the MF changes, and the effective RI of the guiding mode of the waveguide changes accordingly, which results in a change in the phase of the MZI. The interferometric spectra can be used to evaluate the sensing sensitivity. The MZI structure with a hollow length of 40 µm is fabricated, and the microstructure is encapsulated with MF, demonstrating a highly sensitive magnetic field device. The experimental results show that the magnetic field sensitivity of the fabricated magnetic field device is -1.675nm/Oe. For a spectrometer with a resolution of 1 pm, the minimal detectable magnetic field resolution of the sensor is up to 59.7 nT with good stability.

A highly sensitive and wide-range resonant magnetic micro-sensor based on a buckled micro-beam

We experimentally demonstrate a miniature highly sensitive wide-range resonant magnetic Lorentz-force micro-sensor. The concept is demonstrated based on the detection of the resonance frequency of an in-plane electrothermally heated straight resonator operated near the buckling point. The frequency shift is measured with optical sensing (laser) and the device is operated at atmospheric pressure. The frequency shift of the micro-sensor becomes very sensitive to any external disturbances around the buckling zone as indicated by the analytical model and experimental data, which show high sensitivity. The magnetometer demonstrates a measured sensitivity (S) of 33.9/T, which is very high compared to the state of the art. In addition, the micro-sensor shows a bi-linear behaviour with good linearity in two magnetic field regimes, low and high, with low power consumption around 0.2 mW. These attractive features make the proposed micro-sensor promising for various low-cost magnetic applications.

Modifying magnetization behavior of magnetic films utilizing surface grooved grating patterns

The film-based magnetic sensors possess prominent superiorities in miniaturization and integration. Because of the presence of shape demagnetization, the magnetic film effective permeability is dramatically degraded, restricting the performance improvement of planar magnetic sensors. This study reports an efficacious approach to compensate for the shape demagnetization and actively increase effective permeability by introducing grooved grating patterns on a magnetic film surface. The grating patterned films are demonstrated that the maximum values of effective permeability and its variation rate with a magnetic field are increased by 446.03% and 606.77% compared with the same thickness smooth film. It is experimentally demonstrated that the magnetic behavior of the patterned film is modified. The magnetization curves of grooved films exhibit two magnetization rising stages. In addition, the anisotropy of the grooved films can be also tuned through the shape anisotropy of the gratings. Effective permeability and anisotropy field can be enhanced together by grooved grating patterns, which cannot be realized in smooth magnetic films. These results indicate that the surface grating etching strategy provides an effective method to modify the film magnetization behaviors. The grating-patterned films have enormous potential for ultra-sensitive and wide-range micro-magnetic sensors.

Highly Sensitive Resonant Magnetic Sensor Based on the Veering Phenomenon

We report a highly sensitive and miniature in-plane resonant Lorentz-force magnetic micro-sensor operating in air at atmospheric pressure. The concept is based on the detection of the resonance frequency shift of an electrothermally heated initially curved micro-beam experiencing the veering phenomenon (avoided crossing) between its first and third vibration modes. Finite element method (FEM) and experimental results show that the proposed micro-sensor exhibits high sensitivity around the veering regime for the third mode. When operated in the first mode, the micro-sensor shows a measured sensitivity (S) of 0.16/T, which is very high compared to the state of the art. At the veering phenomenon, the third mode is very sensitive to perturbations, and hence the micro-sensor becomes even more ultra-sensitive (S = 0.32/T) making it promising for various magnetic field applications. We report a minimum detectable magnetic field of 20 mT at atmospheric pressure.

Resonator-Based Bidirectional Lorentz Force Magnetic Sensor

We present a low power high sensitive in-plane resonant bidirectional Lorentz-force magnetic micro-sensor operating in air at ambient pressure. The concept is based on the detection of the resonance frequency shift of an electrothermally straight micro-beam resonator operated near the buckling point. Powered at 20 $\mu \text{W}$ , the micro-sensor shows a measured sensitivity (S) of 3.32/(mA.T), which is very high compared to the state of the art. The proposed method is simple in design making it promising for achieving practical low-cost magnetometer.

Magnetic Micro Sensors with Two Magnetic Field Effect Transistors Fabricated Using the Commercial Complementary Metal Oxide Semiconductor Process.

The fabrication and characterization of a magnetic micro sensor (MMS) with two magnetic field effect transistors (MAGFETs) based on the commercial complementary metal oxide semiconductor (CMOS) process are investigated. The magnetic micro sensor is a three-axis sensing type. The structure of the magnetic microsensor is composed of an x/y-MAGFET and a z-MAGFET. The x/y-MAGFET is employed to sense the magnetic field (MF) in the x- and y-axis, and the z-MAGFET is used to detect the MF in the z-axis. To increase the sensitivity of the magnetic microsensor, gates are introduced into the two MAGFETs. The sensing current of the MAGFET enhances when a bias voltage is applied to the gates. The finite element method software Sentaurus TCAD was used to analyze the MMS’s performance. Experiments show that the MMS has a sensitivity of 182 mV/T in the x-axis MF and a sensitivity of 180 mV/T in the y-axis MF. The sensitivity of the MMS is 27.8 mV/T in the z-axis MF.