Nikkei Electronics Asia -- February 2007
Tech Feature
Aichi Steel Develops Low-Cost, Miniature Magnetism Sensor

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Jan 26, 2007 16:01 Nikkei Electronics Asia
Aichi Steel Corp and Aichi Micro Intelligent Corp, both of Japan, have jointly developed a miniature magnetism sensor capable of detecting magnetic fields with 1nT resolution. In addition to improving resolution about 1,000 times over conventional sensors, the new sensor is also significantly cheaper than the available sensors offering 1nT resolution already.   
The new sensor utilizes the magneto-impedance (MI) sensor device, based on the MI effect causing the impedance of an amorphous wire to change when an external magnetic field changes.
The device was developed by Aichi Steel, and targets practical applications including motion sensors and electronic compasses for mobile equipment. The resolution was improved through measures including modifications to the device structure and suppression of noise from electrical circuits.
The small size and low cost were achieved through the use of micro-electromechanical system (MEMS) technology, a source at the firm said (see Fig). The sensor is about 4mm in length, compared to about 1cm square for a flux gate (FG) sensor device, for example. The price of the new sensor is about US$100, or roughly one-twentieth that of an FG sensor.

New Development
Aichi Steel expects the new MI sensor to drive new application development.
One such development is under way now at Nagoya University, where researchers are developing a system to detect quantity, size and speed of vehicles in motion. They plan on using it to control traffic light switch timing based on speed detection, to ensure smooth vehicle flow. The higher resolution makes it possible to detect a vehicle from about 5m, and it can be installed along roadsides, such as in guardrails. The systems proposed by competing firms use lower-resolution magnetism sensors, making it necessary to mount them as close to the vehicles as possible and increasing construction costs. The high-resolution FG sensor is possible, but the high power consumption makes it inappropriate for battery-driven applications. A system using the MI sensor would operate for about one week from a battery.
The Toyohashi University of Technology of Japan, in cooperation with firms including Advance Food Technology of Japan, has developed a system to detect foreign materials in foodstuff. It is capable of detecting foreign materials in foodstuffs that are difficult for conventional systems to handle, such as those in aluminum wrapping or with high salt content.

by Tadashi Nezu