Abstract
In order to further improve noise performance and achieve higher sensitivity, we have investigated a highly sensitive MI element by controlling anisotropy, and have analyzed noise components of a MI sensor by using a femto-tesla MI sensor system with a synchronized peak-to-peak detector. According to the results, sensitivity of a MI element decreases when tension increases. Meanwhile, sensitivity of a MI element is also linearly proportional to the ratio of impedance change and anisotropy field (∆Z/Hk). The theoretical model shows the same effect as measurement results. Furthermore, the noise of a MI sensor is considered to be mainly due to circuit noise, fluctuation of wire magnetic moment (thermal magnetic noise), and irreversible movement of a domain wall trapped by impurities and scratches on a wire surface (Barkhausen noise). The lowest thermal magnetic noise of amorphous wire calculated in our study is approximately 60 fT. Meanwhile, thermal magnetic noise and magnetic noise due to irreversible movement of a domain wall have been demonstrated as a function of the magnetic anisotropy.
Highlights
As a high-performance magnetic sensor, the magnetoimpedance (MI) sensor has attracted considerable attention and has wide prospects in geomagnetic detection and bio-sensing.1 Compared with other magnetic sensors, a MI sensor has very high sensitivity and pico-tesla resolution which is coming up with Superconducting Quantum Interference Devices
The noise of a MI sensor is considered to be mainly due to circuit noise, fluctuation of wire magnetic moment, and irreversible movement of domain wall trapped by impurities and scratches on a wire surface (Barkhausen noise)
Hrms is the magnetic noise field due to fluctuation of wire magnetic moment. en is circuit noise. ew is the noise due to irreversible movement of domain wall trapped by impurities and scratches on wire surface (Barkhausen noise)
Summary
As a high-performance magnetic sensor, the magnetoimpedance (MI) sensor has attracted considerable attention and has wide prospects in geomagnetic detection and bio-sensing. Compared with other magnetic sensors, a MI sensor has very high sensitivity and pico-tesla resolution which is coming up with Superconducting Quantum Interference Devices. In a MI sensor, the impedance change of Co-based amorphous wire increases with the frequency of excitation current.. In 1995, a pulse driven MI sensor was developed with good linearity by using a pick-up coil and higher change rate of impedance in amorphous wire of more than 100%.3,4. In 2002, for distinguishing the poles of external magnetic fields, a pick-up coil was wound around the amorphous wire for detecting the induced voltage proportional to the impedance change (direction change of a magnetization vector) in pick-up coil. According to Eq (1), the intrinsic magnetic field noise of 30-um Co-based amorphous wire is about 10 fT measured over a bandwidth of 1 Hz, with a length of 1 cm at room temperature. We have investigated the sensitivity of MI element by controlling anisotropy, and investigated the intrinsic noise of MI element, analyze the noise components of MI sensor
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