Arrival of a New Era of Magnetic Sensors

On November 27, 2017, this author spoke at the Iwasaki Conference of the Magnetics Society of Japan. At the request of the steering committee, the address was titled, “High-performance micromagnetic sensors supporting new developments for the information society.”

As discussed at the start of the address, production of smartphones and other cell phones has exceeded one billion units per year for the past few years. Every one of those phones was equipped with an electronic compass, and every one of the electronic compasses was equipped with a micromagnetic sensor (MI sensor) as a key component. Just looking at these numbers, it is easy to feel the arrival of the magnetic sensor era. However, even greater than this boom in electronic compasses is the enormous Internet of Things (IoT) magnetic sensor era, for which Aichi Steel Corporation has been busy announcing the development of new MI sensor application technologies and products. These include the development of a Magnetic Positioning System (MPS) for autonomous buses (2016 National Project of the Ministry of Land, Infrastructure, Transport and Tourism, with verification trials conducted November 11–17, 2017, in mountainous areas at the roadside station at Okueigenji, Higashiomi, Shiga Prefecture) and the joint development with Mizuno Corporation of the MA-Q baseball rotation analysis system for professional baseball pitchers (announced to the media on September 4, 2017). In every case, the high performance of amorphous wire MI sensors, which are based on MI element technologies developed through mass production of electronic compasses, was fully demonstrated, making these sensors the clear leaders with limitless potential.

In the first development example above—the MPS for autonomous buses—affordable ferrite magnets were embedded in the road surface every two meters. The weak magnetic fields generated by the magnets were used by a high sensitivity, multiplex differential MI sensor array that is installed on the bottom of the bus to pinpoint the position of the magnetic markers to a high degree of accuracy. Coupled with the excellent environmental performance (robustness) of the MI sensors, this system enabled the trials to be conducted without issues.

The trials demonstrated that GPS-based systems face social credibility issues due to problems like buses running off course when bad weather causes failures, while the magnetic positioning method is trouble-free and provides safety and peace of mind to society. It is particularly important that technologies like these for autonomous public transport vehicles have a social license to operate and give the public peace of mind that is more than just science and technology.

In the second development example above—the baseball rotation analysis system for professional baseball pitchers—MI sensor-based electronic compass technologies were used to develop a high-performance system able to detect rotational speeds of up to 50 rps with high response detection of relative geomagnetism. The problem previously was that gyro sensors commonly used to measure the rotation of free bodies were only able to detect speeds of up to about 17 rps, which made them impractical for this application. Using this system, the pitching speed, rotational speed, and rotational axis of the pitched ball are immediately displayed on a smartphone screen, with the IoT sensing measurements posted as digital data on the internet.

Another important requirement was for the magnetic sensors to withstand the strong impact that the catcher is subjected to when catching a ball pitched by a professional pitcher. During impact resistance testing, the sensors were able to withstand 3,000 pitches. In this respect as well, amorphous wire MI sensors demonstrated superior properties that verified their suitability for use as harsh environment-resistant IoT sensors. As well as the direct effect of the robust elastic structure of amorphous wire, testing demonstrated the minuteness of size and mass of the MI sensors themselves.

The electronic compass mentioned above is a system that provides a heading service to rotate a road map on a user’s smartphone screen into a direction that is easy for the user to see. It does this by using the Global Positioning System (GPS) to identify the global position of the smartphone user on a city map, and then using geomagnetism, as measured by an MI sensor in the phone, and angle of gravitational force of the phone, as measured with an accelerometer, to identify the orientation of the phone within the horizontal plane. This enables the electronic compass to create the illusion of being able to sense direction by detecting geomagnetic lines of force, which normally cannot be detected by people. This can then be provided as augmentation, or an augmented reality information service. With provision of intelligent yet virtual services such as these, demand for electronic compasses can be expected for a while to come because they offer more than physical services. However, the real potential for growth lies in perceiving their use as a checkpoint on the way to IoT sensors, not just use as magnetic sensors. Amorphous wire MI sensors are magnetic sensors with an enormous amount of capability and potential to drive this developmental viewpoint going forward.

Looking into the origins of electronic compasses, which represent the battleground of this current race for development of magnetic sensors, 1985 stood out as a significant year. It was the year when the telecommunications industry was deregulated in Japan. As part of the structural reform of the country, 1985 was the year that Nippon Telegraph and Telephone Public Corporation (NTT) and Kokusai Denshin Denwa Co., Ltd. (KDD) were privatized. The year marked 40 years after Japan’s defeat in the Pacific War, and the final years of the postwar boom. It was a time of rapid popularization of cell phones triggered by the development of car phones in 1979. And with the U.S.-driven internet projects, as well as the occurrence of other developments, it was an exciting period of global expansion of the postwar information society.

In 1983, the Global Positioning System was made available for civilian use after the shooting down of a Korean Air Lines flight. Out of this came an idea for an electronic compass for cell phones put forward by Japan’s Information Society Promotion Group, with the core device for realizing this idea being a high-sensitivity micromagnetic sensor. This led to the guiding principle of “creating high-impedance magnetic elements with high magnetic sensitivity” being established by KDD Chairman Shintaro Oshima and Kyushu University Professor (now Professor Emeritus) Kousuke Harada for the creation of high-sensitivity micromagnetic sensors. (Incidentally, this guiding principle, which was the temporary title, was not officially announced by either party anywhere, but was the unofficial title of the research being conducted by close friends and junior researchers in applied magnetism.)

It was not an easy matter to develop the magnetic elements mentioned in this guiding principle. At the time, research was at the level of creating composite wire magnetic elements with phosphor-bronze wire permalloy plating. While sensitivity of magnetizing properties was increased using external magnetic fields, the research determined that low impedance meant it was not possible to develop MI sensors that would function in magnetic sensor electronic circuits when the elements were miniaturized to 1 mm or less. Research continued around the world with the guiding principle in mind, but no-one was able to achieve success for several years.

Then in 1993, high-impedance magnetic elements with high magnetic sensitivity were finally created in this author’s laboratory at Nagoya University using amorphous wire high-frequency energization and the skin effect method (the magneto-impedance effect). This was later developed into the pulse magneto-impedance effect using pulse energization and the skin effect method (1997–1999), from which high-performance micromagnetic sensors (MI sensors) that could be incorporated into integrated circuits were developed using pickup and analogue switch methods. Through a Japan Science and Technology Agency (JST) high-tech consortium, Aichi Steel succeeded in finding a practical application for these MI sensors. This led to a succession of different uses, including use in mass production of magnetic compasses for smartphones and in the development of IoT sensors for an autonomous driving MPS, which led to the current new era of magnetic sensors. With at least 10 properties required of electronic compasses and IoT-oriented high-performance micromagnetic sensors (including sensitivity and signal-to-noise ratio, micro-dimensional properties, power consumption, dynamic range, magnetic shock resistance, linearity and orientation, temperature stability, maximum operating temperature, suitability to mass production of integrated circuits, and production costs), there is a need to achieve an optimal combination of magnetic material and magnetic effect.

Amorphous wire has a significant presence as a magnetic material in amorphous wire MI sensors. Amorphous wire itself is a new material developed in Japan in 1981 using an underwater ultra-rapid quench spinning method in the laboratory of Professor Tsuyoshi Masumoto at Tohoku University. This technology led to the ability to produce, on the order of kilometers, wire that is corrosion resistant, robust and elastic, with a cross section of perfect, ultra-uniform circularity. With the addition of the wire drawing technology of Unitika Ltd., production of micro-dimensional magnetic elements became possible. MI sensors were finally created through a combination of this remarkable new material and the skin effect-based magnetic impedance effect. The production systems and technology for this amorphous wire was transferred to Aichi Steel in 2014, after which the wire was further enhanced and developed into powerful magnetic material used for IoT magnetic sensors (MI sensors) today.

2017.12.5