MI Column 2
High-performance micromagnetic sensor Amorphous wire MI sensor invention
I The Advent of Smartphones and Electronic Compasses for Watches
From temporary tent dwellings where the electrical grid doesn’t reach to the huts on the shores of the lakes in the jungles of Africa, mobile phones and smartphones have become an essential item for everyone. As of 2017, the world's population of 6.3 billion people had approximately 1 billion mobile phones and smartphones produced annually. Even conservative calculations see every human in the world owning a smartphone in six years. An explosive social phenomenon that has occurred worldwide since 2010 is called the Wearable Information Terminal Equipment Age (based on the Internet). Since 2015, Aichi Steel Corporation and ROHM Corporation have been using a large number of MI sensors manufactured by both Aichi Steel Corporation and ROHM Corporation, in a two-company production system, as geomagnetic sensor elements for electronic compasses in these mobile phones and smartphones.
This electronic compass is a standard chip embedded with a GPS terminal on a smartphone or other device. The user can know his position via GPS and "know the direction" (east, west, south, or north) he faces via an electronic compass. "Knowing the direction" is a specific service that displays a map on the screen and automatically turns (heading) the map screen in the direction you are facing.
Geomagnetic sensor chips are used as a means of detecting this orientation. The magnetic field lines of geomagnetism are stable stationary magnetic fields that originate from near the Antarctic point and are drawn up near the Arctic point, covering the Earth's surface. The magnetic field strength near the Antarctic and Arctic poles is approximately 680 milligaus (mG) with a dip angle of near 90° (vertical). The magnetic field is approximately 330 mG at the equator with a dip angle of 0° (horizontal) and in Nagoya and Tokai regions the magnetic field is approximately 480 mG with a dip angle of approximately 45°. Because mobile phone and smartphone users tilt their screens to their desired angle away from the horizontal plane, the built-in geomagnetic sensor requires a three-axis geomagnetic vector sensor. This sensor calculates the magnetic field of the horizontal plane using signal processing technology from this detected magnetic field, and then determines the orientation in the horizontal plane. At this time, the azimuth detection accuracy must be 0.1° so that heading can be smoothed, and the detection accuracy of the magnetic field must be 0.1 mG. This magnetic field detection accuracy can be easily cleared with a flux gate magnetic sensor (FG sensor), which is a highly sensitive magnetic sensor, but generally FG sensors are not built into smartphones because the length of the magnetic element head is long (5mm or more) and the power consumption is large (10mW or more).
On the other hand, conventional micro-dimensional magnetic sensors, such as MR and Hall elements, require a large amount of signal processing power because of their low magnetic field detection sensitivity, making them difficult to use. New magnetic sensors (GMR elements and TMR elements) with relatively high sensitivity in micro dimensions use bias micromagnets for setting the operating point, so the operating point deviates when subject to a strong disturbance magnetic shock, which makes them also difficult to use. This "disturbance magnetic shock" occurs when the magnetic field of the device comes close to nearby magnets in our daily lives. Electronic compasses are also incorporated into watches, but in this case, the free movement of the human arm (wrist) will result in frequent, unconscious exposure to intense magnetic stimuli. In addition, magnetic sensors require a wide dynamic range because they constantly receive dynamo magnetism and body remanent magnetism when used in a vehicle. Otherwise, the highly sensitive magnetic sensor will be saturated with a strong disturbance magnetic field, resulting in zero sensitivity as a geomagnetic sensor.
The amorphous wire MI sensor is a sensor capable of simultaneously clearing eight or more types of specifications such as high sensitivity, high accuracy, wide dynamic range, ultra-micro power consumption, micro dimensions, magnetic shock resistance, high-speed response, and temperature stability. With its sophisticated specifications, it is not an exaggeration to say that this is a sensor running in its own lane. Especially for electronic compasses for wristwatches since 2013, the specification level required is much higher, and other than the MI sensor there is none available.
The worldwide, explosive spread of electronic compasses for smartphones and mobile phones can be thought of as having the following characteristics in the history of science and technology civilization.
- (1) Geomagnetism is the first social phenomena in the history of mankind to be utilized routinely for ordinary peoples. Geomagnetics research was first published by the British physician Gilbert in the 1600-year-old book De Magnete (published 25 years after its discovery), and demonstration data was used to elucidate that geomagnetism does not come from the arctic stars as previous Medieval Christians claimed, but from the Earth itself because the Earth is a magnet. 400 years since geomagnetics was discovered by Gilbert, we now use geomagnetics everyday in electric compasses for smartphones. With this big discovery, Gilbert is considered to be a forefather of European and American sciences (European and American sciences were born in 1600). Today, geology and biology explain that geomagnetism occurred about 2.7 billion years ago (Earth's birth was 4.3 billion years ago) and that shielding the earth's surface from cosmic ray exposure enabled organisms in the ocean to generate on the surface. Specifically, it has been explained that proton (H+) flows injected toward the Earth in solar activity (nuclear fusion) are wound around the geomagnetic field lines (the left-hand rule of electromagnetism) and stay (form an ionosphere) in the magnetosphere. The "magnetic storm" mechanism is when the magnitude of the geomagnetism is reduced by more than 1mG by the winding of this large amount of protons with geomagnetic field lines. (Protons injected from the sun, filling the solar system, was confirmed in measurements performed by Voyager 1, a space probe that escaped the solar system in 2016.) Humans also ingest this proton into the body and use the proton flow in the cell's mitochondria to generate biocell energy ATP (ATP physiology), thus clarifying the mechanism by which all organisms utilize solar energy. (The mechanism by which protons of magnetospheric retention reach the earth's surface can be explained by the hydrogen binding energy of protons and the formation of clouds by water vapor (positive charging of clouds, lightning generation) and the occurrence of rain.) In can be said that electronic compass/GPS is an information science and technology use of the magnetic environment, which is most important for living things, by advanced micromagnetic sensors.
- (2) The electronic compass for smartphones has been a crucible for the advancement of magnetic sensors. As a result of the rapid progress of the information society, we have entered an era in which electronic information devices are carried in the pockets of the general public on a daily basis. However, this social phenomenon has resulted in an unexpected situation where electronic equipment is subjected to unprecedentedly harsh specifications. That is to say, the human body has evolved to be extremely tough, yet highly sensitive and ultra-flexible in function. The human body does not react even when it come into close contact with NdFeB ultra-strong magnets for a short time. (MIC, ICNIRP, IEEE human exposure standards) Humans are a class of mammals that have evolved over several tens of thousands of years. The electronic compass has not only changed where information and electronic equipment is used, it is used as an electronic equipment which combines various applications which are consistent with human behavior. For example, both electric compasses and humans are ultra-strong, ultra-high sensitivity, and ultra-flexible, and up until now it enforces the fundamental consciousness reform of electronic equipment researchers and engineers. Even in the field of magnetic sensors, it is necessary to be aware that the conventional single-ability evaluation sensors are facing a situation where they are simply not enough.
- (3) The usage of the electronic compass is thought to reflect the sense of personal security in advanced urban societies. Together with the European and American countries, Japan has ended a period of high economic growth, and as a result, people are becoming overly concentrated in large cities. There is a lot of information flooding in on a daily basis, and people are forced to live by making full use of various convenient and comfortable public transportation and cheap but high-performance private cars. Business behaviors in large cities also need to respond immediately to instantaneous environmental changes. Walking also needs to be judged instantaneously, and the electronic compass of smartphones is also becoming a necessity. Getting lost while walking in a big city causes instant panic and mental stress. In metropolitan areas control over one’s stress levels is becoming more and more important, and the electronic compass is a personal security tool that helps maintain mental health.