Michiharu Yamamoto

Amorphous wire and CMOS IC-based sensitive micromagnetic sensors utilizing magnetoimpedance (MI) and stress-impedance (SI) effects

New sensitive quick-response and low-power-consumption micromagnetic sensors, namely, the magnetoimpedance (MI) sensor utilizing the MI effect in zero-magnetostrictive amorphous wires and the stress-impedance (SI) sensor utilizing the SI effect in negative-magnetostrictive amorphous wires, are presented. The field detection resolution of the CMOS IC-type MI sensor is about I /spl mu/Oe for ac fields and 100 /spl mu/Oe for a dc field with the full scale of /spl plusmn/3 Oe using a 2- or 0.5-mm-long amorphous wire with 30- or 15-/spl mu/m diameter as a sensor head. The possible response speed is about 1 MHz, and the power consumption is about 10 mW. The magnetoimpedance integrated circuit (MIIC sensor was developed in 2002 by the Aichi Steel Company, Japan, for mass production. The stress detection resolution of the SI sensor is about 0.1 Gal in acceleration Sensing, which is suitable for detection of microdisplacement in the medical field. More than 100 themes are proposed for application of MI and SI sensors.

Recent Advances of Amorphous Wire CMOS IC Magneto-Impedance Sensors: Innovative High-Performance Micromagnetic Sensor Chip

We analyzed and organized the reasons why the amorphous wire CMOS IC magneto-impedance sensor (MI sensor) has rapidly been mass-produced as the electronic compass chips for the smart phones, mobile phones, and the wrist watches. Comprehensive advantageous features regarding six terms of (1) microsizing and ultralow power consumption, (2) high linearity without any hysteresis for the magnetic field detection, (3) high sensitivity for magnetic field detection with a Pico-Tesla resolution, (4) quick response for detection of magnetic field, (5) high temperature stability, and (6) high reversibility against large disturbance magnetic field shock are based on the magneto-impedance effect in the amorphous wires. We have detected the biomagnetic field using the Pico-Tesla resolution MI sensor at the room temperature such as the magneto-cardiogram (MCG), the magneto-encephalogram (MEG), and the self-oscillatory magnetic field of guinea-pig stomach smooth muscles (in vitro) that suggest the origin of the biomagnetic field is probably pulsive flow of Ca2

Improved pulse carrier MI effect by flash anneal of amorphous wires and FM wireless CMOS IC torque sensor

A figure of merit (FOM) for the magneto-impedance (MI) effect is defined by the product of the MI ratio and the cut-off frequency for ac field detection as (|/spl part/Z//spl part/Hex|/Z/sub 0/)/spl middot/f/sub cutoff/. The FOM for almost zero-magnetostrictive amorphous wire of 30 /spl mu/m diameter was about improved 2.5 times by twisting and flash annealing using a pulse current of 80 mA, 1 second. A sensitive, quick response, and low power consumption wireless FM type MI sensor is constituted using the high FOM amorphous wire head combined with all CMOS IC sensor circuit. The wireless MI sensor is successfully applied to a torque sensor fixed on an automobile power steering steel.

High-Resolution Magneto-Impedance Sensor With TAD for Low Noise Signal Processing

We propose a new measurement system using a magnetoimpedance (MI) sensor with a time analog-to-digital (TAD) converter for a very weak magnetic field measurement and for a low noise signal processing. To demonstrate magnetic characteristics of the proposed measurement system of MI sensor with TAD, we measured the magnetic field sensitivity of the new MI sensor measurement system. In addition, we also investigated the noise level of this proposed measurement system owing to verification on the possibility of the detection of very weak magnetic signals. The gradiometer of MI sensor with TAD was applied to reduce extrinsic noise, such as geomagnetism and commercial power supply noise. We demonstrated that the newly developed MI sensor measurement system has 3 pT/LSB resolution without an amplifier. This shows that the proposed measurement system of MI sensor with TAD is suitable for a low-noise measurement.

3-axis amorphous wire type giant magneto-impedance sensors

In the previous, the author reported a 2-axis mass-production of an amorphous wire GMI (giant magneto-impedance) sensor with 10,000 times the sensitivity of the MR sensor. This paper presents a newly developed 3-axis amorphous wire type GMI sensors by adding a new Z axis. The 3D GMI sensor has three orthogonally arranged micro GMI sensor elements and a CMOS signal conditioning IC in a small resin-mold package. And the length of GMI sensor element was shortened from 1.5 mm to 0.8 mm. The worlds smallest, quick response and low power consumption 3D sensor can be used in mobile phones with GPS capability as an electronic compass.

Accelerometer using MI sensor

Recently accelerometer attracts much attention from industries for its vast potential to the applications in the field of automobile, mobile computers, robotics and so on. Most of the newly developed accelerometers are Si based sensors with the aid of the MEMS technology. They suffer either weakness against mechanical shock or slow response to the acceleration, so some improvement is needed to apply them to the applications such as cell phones. So far the authors have developed micro MI sensor (magneto-impedance sensor) element that incorporates amorphous magnetic wire and micro-pickup coil. This paper presents a new type of accelerometer using MI element which satisfies mechanical endurance and fast response, as well as miniature size.

Mass produced amorphous wire type MI sensors

Summary form only given. The MI sensor, originally discovered by Mohri et al. (1992), has 10,000 times the sensitivity of the MR sensor. Mass-production of an amorphous wire sensor without loss of characteristics during bonding of the amorphous wire has been a considerable challenge. Here, the successful mass production of an amorphous wire type MI sensor is introduced. A summary of the sensor performance, and the technical points important to mass production are given.

Real-time brain activity measurement and signal processing system using highly sensitive MI sensor

Superconducting Quantum Interference Devices (SQUIDs) are the most used sensor to detect the extremely weak magnetic field of brain. However, the sensor heads need to be kept at very low temperature to maintain superconductivity, and that makes the devices large-scale and inconvenient. In order to measure brain activity in normal environment, we had constructed a measurement system based on highly sensitive Magneto-Impedance (MI) sensor, and reported the study of measuring Auditory Evoked Field (AEF) brain waves. In this study, the system was improved, and the sensor signals can be processed in real-time to monitor brain activity. We use this system to measure the alpha rhythm in the occipital region and the Event-Related Field (ERF) P300 in the frontal, the parietal and both the temporal regions.

Development of high sensitivity multi core MI element

MI sensor is a magnetic sensor based on the Magneto Impedance (MI) effect discovered by Mori et al. in 1993[1]. A small and highly sensitive magnetic sensor (AMI 306) based on above MI effect and used as an electromagnetic compass mainly in mobile phones and smart phones has been developed and commercialized by AICHI MICRO INTELLIGENT[2]. According to theoretical analysis, the MI sensor is foreseen to show the fT/√Hz level of noise density[3], and its performance would even be equal to SQUID. MI element (AMI306) with pickup coil fabricated by a plating process is used in electromagnetic compasses. Although it shows magnetic resolution in the micro Tesla order[4], higher performance in sensitivity and noise level is required.

Development of highly-sensitive mi sensor used for foreign particles inspection

Depending on applications, there were some problems that the sensor output will be easily saturated with geomagnetism owning to its high sensitivity. Therefore we present the design of MI sensor which is not saturated with geomagnetism, while retaining low noise density of 10 pT/Hz0.5 at 10 Hz . Then we verify that the particle with a size of 0.3 mm would be enough detected. In our presentation, we also introduce a demo unit for foreign body detection.