Points of interest on the "MA-Q pitching analysis ball" realized with a built-in MI-sensor from the viewpoint of Sensor Magnetics

On September 4, 2017, Aichi Steel Co., Ltd. and sports company Mizuno Co., Ltd. simultaneously announced the results of joint development in the media. On TBS TV’s World Business Satellite that night, a former professional baseball pitcher actually performed a pitch which was caught by a catcher, and at the same time, a scene in which the "speed, rotation speed, and angle of the rotation axis" of the ball was displayed on the smartphone screen was shown. Publications with technical materials from both companies and electronic editions of newspaper companies can be read on-line, so we can see a variety of views, some stating "baseball balls are I-o-T," a wide variety of other responses. It seems some feel that because it appears on the smartphone screen, it becomes "I-o-T" because the digital data will be loaded on the internet.

In this section, we will summarize the characteristics of magnetic sensors and magnetic sensing techniques (Sensor Magnetics).

Amorphous wire CMOS IC Magnetic Impedance Effect Sensor (MI Sensor) is a novel high-sensitivity, high-performance micromagnetic sensor based on the Magnetic Impedance Effect (Magneto-Impedance effect; 1993) that realizes "High-Impedance Magnetic Element for High-Speed Magnetization Operation with Magnetic Rotation" by energizing a high-frequency current or an equivalent sharp-rising pulsed current that produces a "skin effect" on a high-resistivity (130 μΩ-cm) amorphous wire (zero magnetostrictive FeCoSiB). (Because of the low impedance of the conventional high-sensitivity magnetic sensor elements, it became impossible to operate as an element of the sensor electronic circuit when shrunk to micro dimensions.) The MI sensor is based on the novel configuration principle (magnetic impedance effect) of the high-sensitivity magnetic sensor, so that many high-performance characteristics (① to ⑪) shown below are simultaneously exhibited.

• (1) Ultra-high Sensitivity Characteristics: Because it operates with magnetization rotation from the wire circumferential direction of the amorphous wire surface layer, magnetic noise (Barkhausen noise) is not generated, making a magnetic sensor with a high detected magnetic field signal-to-noise (SN ratio), the theoretical accuracy of the magnetic material itself is of ultra-high sensitivity at about 10 fT (= 10-10 G). The noise of the magnetic sensor is the sum of the noise of the sensor electronic circuit, the accuracy of 1 pT (= 10-8 G) in the case of AC magnetic field detection of several Hz or more has been obtained in the experiment.
• (2) Micro-dimensional magnetic heads: due to skin effects, the impedances (Z = (1 + j) Rdc (ɑ/(8ρ)1/2)(ωμ) 1/2 ; Rdc, ɑ, ρ: the direct current resistivity, radius, and conductivities of amorphous wires, ω, μ: the energizing angular frequency and circumferential differential permeability of amorphous wires, respectively) are high, thus micro-dimensioning sensor magnetic heads that can operate as sensor electronics elements.
  　 　Specifically, 3-axis electronic compass chips for cellular phones built with MI geomagnetic sensors with external dimensions of 2mm×2mm×1mm are mass-produced by Aichi Steel.
• (3) Ultra-low power consumption: The power consumption is extremely small because the high-speed magnetization operation is performed by the magnetization rotation of the surface layer of the amorphous wire. Specifically, the power consumption of the electronic compass chip for wristwatches is sub-mW.
• (4) Wide Dynamic Range: Due to the high signal to noise ratio, a Dynamic Range (within range of linearity) of 10,000 times or more of the detection accuracy can be set. Therefore, it is possible to operate the electronic compass even in places such as a vehicle where disturbance DC magnetic fields of several Gauss can be found.
• (5) High-speed response: It is a high-speed response micromagnetic sensor with extremely small magnetization losses because the magnetization operation is in the magnetization rotation of the amorphous wire surface layer. In an exemplary magnetic impedance-effect experiment on thin-film magnets, M. Senda, O. Ishii, Y. Koshimoto, and T. Toshima, "Thin film high frequency magneto-impedance (HFMI) effect," IEEE Trans. on Magnetics, Vol.30, N,o.6, pp.4611-4613, 1994. reported measurement results at 11GHz energization (Barkhausen zero noise, zero hysteresis of magnetic field detection characteristics). Until now, there was no magnetic sensor with high sensitivity and high-speed response. It is capable of detecting from DC to GHz magnetic signals.
• (6) Highly directional: The aspect ratio of the thin wire shape of the amorphous wire is further increased by the skin effect, and the horizontal the directivity measurement value when the in-plane angle resolution is 0.1° agrees with the theoretical value.
• (7) Temperature stability: Temperature stability is high due to the use of amorphous wire, a highly reliable thin-wire bulk magnetic material which has a Curie temperature of 550°C, zero magnetostriction, low magnetic loss due to magnetization rotation operation, strong elasticity, and corrosion resistance.
• (8) Maximum operating temperature: In common with ⑥, the maximum operating temperature of an electronic compass chip is 80°C.
• (9) Magnetic shock resistance: This is a new requirement specification that emerged in the age of wearable geomagnetic sensors. For example, an electronic compass built into a wristwatch frequently experiences instantaneous proximity to a strong magnet (instantaneous magnetic field exposure of several to several tens of Gauss) due to human free arm motion, but the MI sensor reliably returns to the operating point because the voltage detection method utilizes a pick-up coil. In other magnetic sensors where the operating point is set by a bias magnet, there are cases where the operating point is changed.
• (10) High reliability: In common with ⑥ and highly reliable against disturbances such as mechanical, thermal, and electromagnetic shock.
• (11) Integrated Circuit Mass Productivity: From the magneto-impedance effect (analog effect; 1993) of high-frequency energization to the "pulsed magneto-impedance effect" (digital-analog (hybrid) effect of pulse energization; 1997), a sensor circuit capable of integrated circuits was realized by combining a micro-magnetic sensor with a CMOS IC digital electronic circuit.

Since 2003, Aichi Steel has demonstrated the above mentioned performance of the MI sensors in the practical application and mass production of electronic compasses for cellular phones, smartphones, and watches. Therefore, the development of MA-Q using the MI sensors can be said to be technically “promising”. Since a pitched baseball is an object that moves freely in space, only a weak force is generated during movement, such as aerodynamic drag and the force of the Magnus effect due to the relationship between rotation and airflow. Therefore, the rotation measurement by the accelerometer takes a considerable amount of signal processing and is not practical. Generally, the rotation of a free-moving object is measured by a gyroscopic sensor. However, the gyroscopic sensor utilizing the dynamic self-excited vibration of an electrostrictive rod is difficult to miniaturize, and it is difficult to detect a rotational speed of approximately 17 rps (rotation per second) or higher with MEMS gyro sensors that could be built into a ball. In response to this challenge of high-speed rotational detection, it is noteworthy that the potential of MI sensors is being exploited explicitly in developing MA-Q. In other words, a professional baseball pitcher can expect a high-speed ball revolution of up to 50 rps, so the built-in MI geomagnetic sensor will detect a relative geomagnetic change of 50 rps (Hz). This condition corresponds to rotating the electronic compass itself at 50 rps . The geomagnetic change waveform applied to this geomagnetic sensor is not a sine wave, and the maximum amplitude is the magnitude of geomagnetism (±500mG in the Japanese Islands). Therefore, the response speed of the MI sensor requires several hundred Hz, but it is sufficiently possible for the MI sensor.

It has been difficult for magnetic sensors to detect geomagnetism at high speed, but it was impossible to predict that they would be installed in the minute area at the center of a baseball and withstand the large impact shock of being caught.. MA-Q has been proven by undergoing 3000 impact tests. This can also be said to be a new use of magnetic sensors.

The impressive feature of MA-Q is the originality of "precisely measuring the complex high-speed rotational motion of high-speed objects on the earth with a relatively high-speed change relative to geomagnetism." It is unprecedented that geomagnetism has been used in this way, and it reminds us that we are living in a magnetic field.

The air surrounding us is also invisible, but we can feel the existence of it as a wind. Gravity can also be felt as weight. On the other hand, geomagnetism cannot be sensuously felt. However, geomagnetic field rays prevent the direct descent onto the earth's surface of solar wind cosmic rays (protons) by wrapping them around, thereby protecting all living organisms on the earth. At the same time, it forms the positive charged ionosphere enabling the short-wave propagation method.

It is estimated from rock remanent magnetic measurements and other methods that geomagnetism occurred 1.7 billion years ago , and it is estimated that life on the earth had been submerged in the sea to avoid exposure to solar wind cosmic rays until then. The mechanism of generation of geomagnetism was published in Le Magnete by Gilbert, UK, published in 1600, correcting the Dogma of the Middle Christian Church that "geomagnetism comes from the Arctic star". In other words, we covered the distribution of magnetic lines on the Earth based on data from compass measurements by a large number of sailors and showed that geomagnetism matches the distribution of magnetic lines on the Earth's surface when the Earth is seen as a single large magnet. This geomagnetic dipole generates geomagnetism in a size of about 760mG vertically from the Antarctic. The geomagnetism is horizontal at about 330mG in an equatorial zone halfway toward the north. The geomagnetism penetrates into the Arctic at three locations (near the Arctic, north of Lake Baikal, Siberia, and north of Hadson Bay, Canada) at a size of about 760mG vertically. Now, we know that the north-south of this magnetism is reversed about every 1 million years.

The consistent modeling based on this instrumentation data is an unprecedented method, and accepted by a large number of people, Gilbert is positioned as the "founder of modern science." And modern Western science is said to have started with Gilbert's "discovery of geomagnetism" in 1600.

The original idea of using geomagnetism, which is the origin of modern Western sciences, is not the traditional comprehensive use, but the precise measurement of high-speed free-running micro-objects to wirelessly transmit data to a smartphone. This is an innovative idea that makes use of geomagnetism for super-advanced information technology. It can be said that the development of MA-Q will foresee the emergence of various novel information measurement methods, starting with the analysis of pitchers for professional baseball pitchers.