Carrier-type Magnetic Field Sensor Research Articles

Two-terminal ultrahigh frequency carrier type thin-film magnetic sensor using impedance matching lines

This article reports on output and band characteristics of the two-terminal ultrahigh frequency (UHF) carrier type magnetic field sensor, which is based on impedance change due to magnetic field dependent permeability, and a magnetic field is detected as an amplitude modulation of a UHF carrier voltage. Two types of transmission line configurations (type-A and type-B) are proposed to make a two-terminal sensor rather than the four terminals of the conventional sensor operating on this principle, because the two-terminal sensor is more advantageous in terms of designing and fabricating of the sensor element and the transmission lines than the four-terminal sensor. In the type-A, a half-wave impedance matching line is added between the element and the carrier power supplying points. Also, in the type-B, a carrier power is supplied on the quarter-wave matching line located between the element and the load. The type-A sensor exhibits a lower output and a much narrower 3 dB-bandwidth of a few tens of MHz than the four-terminal sensor. In contrast, a higher output than that in the four-terminal sensor and a 3 dB-bandwidth of ∼100 MHz are confirmed in the type-B sensor by experiments and calculations.

A Measurement of Magnetocardiogram (MCG) by Planar Type Sensor using CoNbZr Film

We developed a very sensitive high-frequency carrier-type magnetic-field sensor with a sub-pT resolution using a transmission-line-type sensor. Meander-type sensor elements using amorphous CoNbZr films (4μm in thickness), Cu conductor with a meander pattern (30 mm in length, 1.0 mm in width, 18 μm in thickness), and a ground plane were fabricated. We obtained a magnetic field resolution of 9.1×10-13 T/Hz1/2 at 1 Hz. The detectable magnetic field was limited by the 1/f noise. We detected a magnetocardiogram (MCG) signal of heartbeats with the sensor.

形状磁気異方性を用いた高周波キャリア型磁界センサの磁性薄膜構造に関する検討

We attempted to control the magnetic anisotropy of a high-frequency carrier-type magnetic field sensor by means of shape anisotropy. We examined the size of element necessary to realize low anisotropy strength both experiment ally and theoretically. The theoretical results agreed well with the experimental ones, and we were able to calculate the size of an element with low anisotropy strength theoretically.

高周波キャリア型薄膜磁界センサを用いた心磁界測定

We developed a very sensitive high-frequency carrier-type magnetic field sensor with a pT resolution using a transmission-line-type sensor. Meander-type sensor elements using amorphous CoNbZr films were fabricated. We obtained a magnetic field resolution of 3.0 x 10-12 T/Hz1/2 at 1 Hz. The detectable magnetic field was limited by the 1/f noise. We detected the magnetocardiogram (MCG) signal by using the sensor.

形状磁気異方性による高周波キャリア型磁界センサの異方性制御

We tried to control the magnetic anisotropy of a high-frequency carrier-type magnetic field sensor by varying the shape of the magnetic film instead of the induced anisotropy. We confirmed that the impedance of the sensor was changed by applying a magnetic field, and showed that the properties of the sensor could be controlled through the design of the magnetic film’ s shape.

１０｀−１３´Ｔ台の磁界検出分解能を有する高周波伝送線路型薄膜磁界センサ

We developed a very sensitive high-frequency carrier-type magnetic field sensor with a sub-pT resolution using a resonating transmission line. Meander-type sensor elements using amorphous CoNbZr films were fabricated. We obtained a magnetic field resolution of 7.4 x 10-13 T/Hz1/2 at 501 kHz. The detectable magnetic field was limited bythe noise caused by nonlinear magnetic excitation. We analyzed the quality factor of the resonance for enhancementof the signal-to-noise ratio.

Detection of wide band signal by a high frequency carrier-type magnetic probe

A high frequency carrier-type magnetic field sensor [gaint magnetoimpedance (GMI) sensor] probe with a narrow magnetic strip was fabricated. High frequency field detection was performed by this probe. For specific dc bias fields, high sensitivity could be achieved in a wide range of frequency from 5kHzto1GHz. The sensitivity with a high dc bias field was lower than that with a low dc bias field. The outputs of the GMI probe were proportional to input power which generated the ac magnetic field.

高周波キャリア型磁界センサの磁界検出に及ぼすスイッチング電源ノイズの影響

The authors demonstrated experimentally an influence of power supply noise on the magnetic field sensing of a high-frequency carrier-type magnetic field sensor. In magnetic sensing using such a magnetic sensor, an external ac magnetic field signal is modulated in amplitude in accordance with a high-frequency carrier signal. When a switching power supply is used for the carrier signal circuit, the power supply noise is also modulated in amplitude by the carrier signal. Therefore, both the upper and lower sideband spectra in the vicinity of the carrier signal are due not only to the magnetic field component but also to the power supply noise component. The sensitivity and frequency bandwidth of magnetic field sensing depend strongly on the noise level and noise frequency of the switching power supply.

High-Frequency Carrier Type Thin-Film Sensor Using Low-Noise Crystal Oscillator

We have developed a very sensitive high-frequency carrier-type magnetic field sensor based on the giant magneto-impedance effect available at lower frequencies. Our approach is to optimize the sensor structure so as to obtain high impedance. In addition, we optimize the carrier suppressing circuit using a low-noise crystal oscillator to reduce the phase noise of the lower offset frequency (under 1 kHz) as a carrier source. When a small ac magnetic field is applied to the sensor element, a very small AM signal can be detected using a carrier suppressing circuit with a low-noise crystal oscillator. A resolution of 1.7/spl times/10/sup -8/ Oe/Hz/sup 1/2/ was obtained at 501 kHz. The detectable magnetic field is limited by the thermal noise of room temperature. Resolutions of 1.5/spl times/10/sup -7/ Oe/Hz/sup 1/2/ at 1 kHz and a resolution of 1.1/spl times/10/sup -6/ Oe/Hz/sup 1/2/ at 110 Hz were demonstrated. The resolution was basically limited by the phase noise of the crystal oscillator.

Remarkable improvement of sensitivity for high-frequency carrier-type magnetic field sensor with ferromagnetic resonance

Imaginary part of permeability becomes greater than real part in a special case of ferromagnetic resonance in thin films. The distribution of current density in the film arises a phase rotation with huge magnitude to the normal direction of the film. We confirm this phenomenon by experiments, and the application to the high-frequency carrier-type magnetic field sensor makes a remarkable improvement of sensitivity.

Micro-size magnetic strip for ultra high frequency carrier type magnetic field sensor

Magnetic strips aimed at high-frequency carrier-type magnetic field sensors were studied by using various strip widths in a carrier frequency range of gigahertz to obtain conditions for large impedance change. The impedance change was attributed to a magnetic resonance effect. It was shown that DC magnetic field regions at which the maximum change of impedance occur for wide strip elements were closely related to the applied carrier frequencies as expected theoretically. The DC magnetic field for the maximum sensitivity decreased as strips become narrow.

A high frequency carrier-type magnetic field sensor using carrier suppressing circuit

A highly sensitive high frequency carrier-type magnetic field sensor based on the giant magnetoimpedance effect has been developed. It has been combined with a high frequency carrier suppressing circuit to reduce carrier phase noise dramatically. Highly sensitive magnetic field resolution of 8.8/spl times/10/sup -7/ Oe (8.8/spl times/10/sup -11/ T) was demonstrated.