Abstract
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.
Highlights
A thin-film magneto-impedance sensor [1,2,3,4,5,6] is useful for detecting magnetic materials nondestructively
For the measurement system which applied for a conveyer in manufacturing process and medical application the signal frequency range is expected to be from direct current (DC) to several Hz due to the movement speed of products or scanning speed of measurement probe
The merit of the amplifier is that it can transfer hundreds of MHz signal to a 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 MI sensor and the logarithmic amplifier can compose a simple sensor driving circuit
Summary
A thin-film magneto-impedance sensor [1,2,3,4,5,6] is useful for detecting magnetic materials nondestructively. The sensor has high sensitivity and has tolerance of normal magnetic field because of its demagnetizing force in the thickness direction. The thinner the sensor thickness the more tolerance appears against strong normal field, because of the demagnetizing field For driving such thin sensor, high frequency is essential for the skin-effect of magneto-impedance. An application of a logarithmic amplifier for detecting a level of the sensor signal at 400 MHz, which is proportional to the sensor impedance, is proposed. In this study the output frequency range was limited in which a signal of measured object carried on a conveyor This frequency was under several Hz, and the system will be designed without using a magnetic field shield structure. If a suitable device would be getting accessible the 500 MHz driving circuit can be made using the same design rule as this paper
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