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Open AccessArticle

Magneto-Impedance Sensor Driven by 400 MHz Logarithmic Amplifier

Industrial Technology Institute, Miyagi Prefectural Government, Sendai 981-3206, Japan
Micromachines 2019, 10(6), 355; https://doi.org/10.3390/mi10060355
Received: 30 April 2019 / Revised: 23 May 2019 / Accepted: 28 May 2019 / Published: 29 May 2019
A thin-film magnetic field sensor is useful for detecting foreign matters and nanoparticles included in industrial and medical products. It can detect a small piece of tool steel chipping or breakage inside the products nondestructively. An inspection of all items in the manufacturing process is desirable for the smart manufacturing system. This report provides an impressive candidate for realizing this target. A thin-film magneto-impedance sensor has an extremely high sensitivity, especially, it is driven by alternatiing current (AC) around 500 MHz. For driving the sensor in such high frequency, a special circuit is needed for detecting an impedance variation of the sensor. In this paper, a logarithmic amplifier for detecting a signal level of 400 MHz output of the sensor is proposed. The logarithmic amplifier is almost 5 mm × 5 mm size small IC-chip which is widely used in wireless devices such as cell phones for detecting high-frequency signal level. The merit of the amplifier is that it can translate hundreds of MHz signal to a direct current (DC) voltage signal which is proportional to the radio frequency (RF)signal by only one IC-chip, so that the combination of a chip Voltage Controlled Oscillator (VCO), a magneto-impedance (MI) sensor and the logarithmic amplifier can compose a simple sensor driving circuit. View Full-Text
Keywords: magneto-impedance sensor; thin-film; high frequency; logarithmic amplifier; nondestructive inspection magneto-impedance sensor; thin-film; high frequency; logarithmic amplifier; nondestructive inspection
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Nakai, T. Magneto-Impedance Sensor Driven by 400 MHz Logarithmic Amplifier. Micromachines 2019, 10, 355.

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