正帰還回路によるアモルファスワイヤＣＭＯＳ ＩＣスイッチ形ＭＩ磁界センサ

Sensitive, quick response and low power consumption micro-magnetic sensors have been developed utilizing the magneto-impedance (MI) and stress-impedance (SI) effects in zero-magnetostrictive (zero-/spl lambda/) and negative-magnetostrictive amorphous wires connected with CMOSFET IC sensor circuits. The MI magnetic field sensor using zero-/spl lambda/ amorphous wires of 30 /spl mu/m diameter and 2 mm length represents the resolution of about 1 /spl mu/G for AC fields and about 100 /spl mu/G for the DC field with /spl plusmn/3 G in the full scale, the cut-off frequency of about 1 MHz, and low power consumption of about 10 mW for the CMOS MI sensor. The SI sensor using a 20 /spl mu/m diameter negative-/spl lambda/ amorphous wire shows the gauge factor of about 4000 for stress (strain) sensors and the resolution of 0.1 Gal for acceleration sensors. The principles, basic features, and applications of MI and SI sensors are summarized.

In order to achieve the alpha rhythm and visual event-related fields (ERFs) measurements at room temperature, we have newly proposed a high-performance magneto-impedance (MI) sensor system with peak-to-peak voltage detector by synchronized switching, which utilizes the time-differential measurement in each MI element for suppressing the low-frequency noise components and increasing the stability of the sensor system. A high field detection sensitivity with good linearity is obtained via new MI sensor system, which is approximately $1.3\times $ higher than that of the previous MI gradiometer. The noise level we achieved here is lower than 2 pT/Hz $^{1/2}$ in an unshielded environment, for the frequency range of 1–100 Hz. Meanwhile, we have demonstrated the new MI sensor system for room temperature alpha rhythm and visual ERFs measurements. We have achieved a clear sensitivity for spontaneous brain activity with SNR of about 8. As expected, the alpha rhythm signals simultaneously measured by EEG and MI sensor are significantly attenuated when the subject opens eyes and intensified with closed eyes. The considerable enhancement of alpha rhythm measured by MI sensor when the subject had closed eyes further evidences the signals recorded are emanating from spontaneous brain activity. For visual ERFs measurements, we have achieved a clear sensitivity for P300 brain activity for all subjects and demonstrated the tendency of P300 latency to increase with the target/standard discrimination difficulty.

A new car sensing system using an amorphous wire CMOS magneto-impedance (MI) sensor built into a disk set on the road is presented. When a car passes above the disk, the MI sensor detects stray fields from the car body. The speed and length of a car can be estimated processing the signals from two MI sensors. A prototype disk with two MI sensors, a microcomputer, and a semiconductor IC memory built-in has been developed. The disk system can record the length, the velocity and the time when a car passed for two thousand cars. The proposed sensing system is useful for automatic traffic measurements.

In this study, a programmable Magneto-Impedance (MI) sensor circuit has been designed by using a Field-Programmable-Gate-Arrays (FPGA), and an operational amplifier integrator has been used to replace the peak hold circuit in the conventional system to sample the entire output of the sensor. Since there is no need to adjust the sampling timing to match different MI sensor’s outputs, it is more suitable for mass production than conventional circuits. It was also found that the output of the sensor has the same sensitivity on the rising and falling edges of the excitation current. The output of two parts of the sensor is sampled by an asynchronous sampling frequency, and the noise level of the system proposed is reduced. In comparison with the conventional system, the proposed system in this work has higher sensitivity and lower noise level when utilizing the same sensor, so it might be applied to the bio-medical signal measurement in the future.

Deep learning technology is generally applied to analyze periodic data, such as the data of electromyography (EMG) and acoustic signals. Conversely, its accuracy is compromised when applied to the anomalous and irregular nature of the data obtained using a magneto-impedance (MI) sensor. Thus, we propose and analyze a deep learning model based on recurrent neural networks (RNNs) optimized for the MI sensor, such that it can detect and classify data that are relatively irregular and diverse compared to the EMG and acoustic signals. Our proposed method combines the long short-term memory (LSTM) and gated recurrent unit (GRU) models to detect and classify metal objects from signals acquired by an MI sensor. First, we configured various layers used in RNN with a basic model structure and tested the performance of each layer type. In addition, we succeeded in increasing the accuracy by processing the sequence length of the input data and performing additional work in the prediction process. An MI sensor acquires data in a non-contact mode; therefore, the proposed deep learning approach can be applied to drone control, electronic maps, geomagnetic measurement, autonomous driving, and foreign object detection.

This paper describes a compact three-phase electric current sensor using a magneto-impedance (MI) sensor for wide-range current sensing. The MI sensor is composed of a thin-film MI element and a bias coil. Double shields are used for high shielding performance maintaining compact size. Two kinds of alternating bias are used in the system to achieve a wide measurement range of 1:600. Furthermore, using optimized carrier electric current is shown to decrease the temperature dependence of the MI sensor

This paper demonstrates the performance of magnetoimpedance (MI) sensors for biomagnetic field recording. The rms noise of an amorphous wire MI sensor with 600 turns of pick‐up coil was estimated as approximately 3 pT/Hz1/2 at 1 Hz. Here, we demonstrate that this sensitivity is enough to clearly detect magnetic cardiogram signals. We also measured the biomagnetic field around a smooth muscle tissue sample taken from a guinea‐pig. We discovered that the magnetic‐field waveform of a small tissue sample is similar to the voltage waveform measured by a microelectrode array in a smooth muscle sheet sample. The results suggest that the localized biomagnetic field generated by smooth muscle cells can be detected by an MI sensor. We concluded that the MI sensor is a promising device for use as a noninvasive tool to test cell activity or function through magnetic‐field measurement. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The magneto‐impedance (MI) effect was discovered about 30 years ago and a microsize magnetic sensor utilizing this effect has become commercially available. We make some modifications to the commercially available MI sensors to cover the dynamic range of the geomagnetic field. The total cost of three MI sensors for the two horizontal components and one vertical component including the modification is approximately one‐third of the standard price of triaxial fluxgate magnetometer sensors. For the period of 30 March to 27 April 2018, we conducted experimental observations of geomagnetic field variations with the MI sensor magnetometer (MIM) at the Mineyama observatory, which is located about 100 km northwest of Kyoto, Japan. Data obtained with the MIM are compared with those from the fluxgate magnetometer (FGM) that has been working at the observatory. Results show that the MIM can record geomagnetic field variations such as geomagnetic storm, solar quiet variations, low‐latitude positive bays, storm sudden commencement, and long‐period geomagnetic pulsations with a peak‐to‐peak amplitude of ≤1 nT that is also detected with the FGM. Power spectra of the geomagnetic field variations measured with the MIM and FGM are almost the same. It is found that the MIM has a larger temperature drift than the FGM. The present study reveals that the MIM is comparable to the FGM in measuring the geomagnetic field variations in a period from a few tens of seconds to a few hours and is useful for researches in upper atmospheric physics or space physics.

We investigated the effects of induced helical anisotropy and application of dc bias current IB on longitudinal magnetoimpedance (MI) in amorphous microwires both separately and together. We demonstrated that when both parameters are present, i.e., a dc bias current IB is applied to the microwire with induced helical anisotropy, the longitudinal MI sensor range can be considerably extended up to the fields considerably higher than its anisotropy field as the slope of MI curve dZ/dHE remains rather high. A highly asymmetric longitudinal MI dependence with a rather high slope at the zero-field point was obtained. Reversing the bias current IB causes reversal of the bias field direction and results in a mirroring of the MI dependence. This gives a possibility to determine both the sign and the magnitude of the external magnetic field. The obtained results can be used in development of the longitudinal MI sensors with increased sensitivity and/or range.

We have investigated the basic characteristics and applicability of the LC high pass filter configuration for signal conditioning of the magnetoimpedance (MI) sensor. The MI sensor elements were fabricated through photolithography and lift‐off process of CoZrNb/Au/CoZrNb multilayer, and the LC high pass filters were configured using the fabricated sensor elements and surface mount capacitors. To confirm the high frequency performance of the sensor elements, frequency dependence of the impedance was measured as function of external magnetic field using a network analyzer. The output increased to reach the peak value with increase of magnetic field to around 20 Oe, which was almost the same with the anisotropic field of the multilayer film pattern, and the measured maximum change ratio is 49%. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetoimpedance (MI) in Co-based amorphous alloys has been shown to be a very sensitive, quick-response new method for measurements of magnetic fields. At present, the experimental results on MI in amorphous wires are obtained for frequencies f<200 MHz. For quick-response magnetic heads used in high density magnetic recording, the carrier current frequency of the MI element is needed to be increased up to 1 GHz to detect recorded signals of 50–100 MHz. Here we present the experimental data on MI in CoFeSiB amorphous wires for a broad waveband of 1–1200 MHz. The experimental technique is based on the measurement of the complex reflection coefficient from a coaxial waveguide having an amorphous wire as an internal conductor. This method avoids the radiation effects, inevitable at high frequencies, f≳100 MHz, in simpler techniques utilizing an oscilloscope or an impedance analyzer with a lead wire. From the data on reflection coefficient, the real and imaginary parts of the wire impedance Z and permeability μ are found as functions of a frequency and an external longitudinal field. The impedance versus field behavior changes with increasing the frequency. For f<1 MHz the absolute value of the impedance ‖Z‖ decreases with increasing the field. As the frequency is increased, a maximum appears in the impedance-field dependence. In the case of high frequencies, f≳800 MHz, ‖Z‖ increases with the field. For all frequencies, a higher sensitivity is seen in small fields less than 2 Oe. The sensitivity has a maximum of about 100%/Oe at the frequency of 600 MHz, and it is still very high (∼20%/Oe) up to f∼1 GHz. These results are in satisfactory agreement with the theoretical ones based on the skin effect in a magnetic wire with a tensor rotational permeability.

We designed a novel field-programmable gate-array circuit for a magneto-impedance (MI) sensor system. The noise level of the system, measured with different MI sensors, is about 10 pT, which is lower than that of conventional systems. Thus, the system has greater flexibility for different MI sensors and is suitable for low-noise measurements.

Comparative study of the sensing performance of orthogonal fluxgate sensors with different amorphous sensing elements

A new method of obtaining the asymmetrical magneto-impedance (MI) effect in a zero-magnetostrictive FeCoSiB amorphous wire is presented, where in a wire coil is used to apply a wire pulse current. The mechanism for the generation of the asymmetrical MI effect is qualitatively explained by means of a magnetization rotation model for the surface layer of a wire with a spiral magnetization. A linear magnetic-field sensor circuit uses the amorphous-wire asymmetrical MI element magnetized with a sharp pulse train current in a C-MOS multivibrator circuit.

The magneto-impedance (MI) effect attracts an increasing interest due to its high value in comparison to magnetic resistance (MR) effects, opening possible applications as e.g., high-sensitivity magnetic field detectors, magnetic recording heads, etc. However, for most samples employed in MI measurements in the literature, i.e., amorphous wires, magnetic multilayers and ribbons, the real three-dimensional domain structure remains unknown. In order to find the relation between the magnetic domain structure and the respective value of the MI effect, permalloy (Ni81Fe19) nanowires and thin films were produced by electron-beam lithography (EBL), lift-off technique and focused ion beam (FIB) milling. Wires and other structures (rectangles, circles), and domain pinning sites (notches) were manufactured with optimized dimension (size, thickness, etc.). The magnetic structure of our samples and the MI effects were analyzed by magnetic force microscopy and transport measurements.