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A 3-Axis Miniature Magnetic Sensor Based on a Planar Fluxgate Magnetometer with an Orthogonal Fluxguide.

Lu CC, Huang J - Sensors (Basel) (2015)

Bottom Line: Experimental characterization of the miniature fluxgate device demonstrates satisfactory spatial magnetic field detection results in terms of responsivity and noise spectrum.As a result, at an excitation frequency of 50 kHz, a maximum in-plane responsivity of 122.4 V/T appears and a maximum out-of-plane responsivity of 11.6 V/T is obtained as well.The minimum field noise spectra are found to be 0.11 nT/√Hz and 6.29 nT/√Hz, respectively, in X- and Z-axis at 1 Hz under the same excitation frequency.

View Article: PubMed Central - PubMed

Affiliation: Institute of Mechatronic Engineering, National Taipei University of Technology, Taipei 106, Taiwan. cclu23@ntut.edu.tw.

ABSTRACT
A new class of tri-axial miniature magnetometer consisting of a planar fluxgate structure with an orthogonal ferromagnetic fluxguide centrally situated over the magnetic cores is presented. The magnetic sensor possesses a cruciform ferromagnetic core placed diagonally upon the square excitation coil under which two pairs of pick-up coils for in-plane field detection are allocated. Effective principles and analysis of the magnetometer for 3-D field vectors are described and verified by numerically electromagnetic simulation for the excitation and magnetization of the ferromagnetic cores. The sensor is operated by applying the second-harmonic detection technique that can verify V-B relationship and device responsivity. Experimental characterization of the miniature fluxgate device demonstrates satisfactory spatial magnetic field detection results in terms of responsivity and noise spectrum. As a result, at an excitation frequency of 50 kHz, a maximum in-plane responsivity of 122.4 V/T appears and a maximum out-of-plane responsivity of 11.6 V/T is obtained as well. The minimum field noise spectra are found to be 0.11 nT/√Hz and 6.29 nT/√Hz, respectively, in X- and Z-axis at 1 Hz under the same excitation frequency. Compared with the previous tri-axis fluxgate devices, this planar magnetic sensor with an orthogonal fluxguide provides beneficial enhancement in both sensory functionality and manufacturing simplicity. More importantly, this novel device concept is considered highly suitable for the extension to a silicon sensor made by the current CMOS-MEMS technologies, thus emphasizing its emerging applications of field detection in portable industrial electronics.

No MeSH data available.


Field noise spectra of the magnetometer with 2-mm core width under different excitation frequencies in X- and Z-axis: (a) at 25 kHz; (b) at 50 kHz.
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sensors-15-14727-f011: Field noise spectra of the magnetometer with 2-mm core width under different excitation frequencies in X- and Z-axis: (a) at 25 kHz; (b) at 50 kHz.

Mentions: In addition to responsivity characterization, field noise analysis of the micro-fluxgate sensor under a magnetically shielded environment is also vital to assess the feasibility of a magnetometer. The field noise spectra was measured under a magnetically shielded environment by using a lock-in amplifier and a power amplifier to generate excitation current for the fluxgate sensor, and adopting a spectrometer to measure the voltage noise vs. frequency from 0.1 Hz to 10 Hz. The field noise is defined as the ratio of the voltage noise to the responsivity under specific excitation voltage. All noise measurements were implemented with core width of 2 mm under 25 kHz and 50 kHz, respectively. As shown in Figure 11, it is evident that the field noise density descends while the excitation frequency increases from 25 kHz to 50 kHz, which may help trim down field noise spectra at low-frequency fields (<10 Hz). As a result, experiments shown in Figure 11a reveal that the minimum field noise spectra in the X-axis direction observed at 1 Hz of magnetic fields were 0.53 nT/√Hz under a 25 kHz excitation and 0.11 nT/√Hz under a 50 kHz excitation, correspondingly. Likewise, as shown in Figure 11b, the lowest field noise spectra in the Z-axis direction at 1 Hz of magnetic fields were measured as 21.91 nT/√Hz and 6.29 nT/√Hz under 25 kHz and 50 kHz of excitation frequency. In fact, in the relatively low frequency bandwidth (~10 Hz), one can observe that the magnetic sensor demonstrates a relatively improved field noise density against the frequency variation. In addition, by taking Figure 9, Figure 10 and Figure 11 into account, it is noteworthy that the responsivity values of X- and Z-axis measured at 25 kHz and 50 kHz differ by a factor of 10-fold, and the field noise values of X- and Z-axis, for example at 1 Hz, differ by about a factor of 40–60 folds with respect to 25 kHz and 50 kHz, respectively. This fact implies that an additional factor of 4–6 fold is introduced then. We thus consider the reinforced effect in the field noise could be attributed to the following reasons: (1) different gain constants may be employed for the X-axis and Z-axis voltage noise measurements; and (2) the correlation between the field noise induced by the magnetic core and the orientation of excitation fields. For instance, the sensing direction of in-series pick-up coils while running the X-axis sensing mode may reduce portion of the voltage noise. In contrast, the sensing direction of in-series pick-up coils while running the Z-axis sensing mode may amplify the voltage noise in parts. These facts may have a partial influence on the field noise we measured.


A 3-Axis Miniature Magnetic Sensor Based on a Planar Fluxgate Magnetometer with an Orthogonal Fluxguide.

Lu CC, Huang J - Sensors (Basel) (2015)

Field noise spectra of the magnetometer with 2-mm core width under different excitation frequencies in X- and Z-axis: (a) at 25 kHz; (b) at 50 kHz.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4507702&req=5

sensors-15-14727-f011: Field noise spectra of the magnetometer with 2-mm core width under different excitation frequencies in X- and Z-axis: (a) at 25 kHz; (b) at 50 kHz.
Mentions: In addition to responsivity characterization, field noise analysis of the micro-fluxgate sensor under a magnetically shielded environment is also vital to assess the feasibility of a magnetometer. The field noise spectra was measured under a magnetically shielded environment by using a lock-in amplifier and a power amplifier to generate excitation current for the fluxgate sensor, and adopting a spectrometer to measure the voltage noise vs. frequency from 0.1 Hz to 10 Hz. The field noise is defined as the ratio of the voltage noise to the responsivity under specific excitation voltage. All noise measurements were implemented with core width of 2 mm under 25 kHz and 50 kHz, respectively. As shown in Figure 11, it is evident that the field noise density descends while the excitation frequency increases from 25 kHz to 50 kHz, which may help trim down field noise spectra at low-frequency fields (<10 Hz). As a result, experiments shown in Figure 11a reveal that the minimum field noise spectra in the X-axis direction observed at 1 Hz of magnetic fields were 0.53 nT/√Hz under a 25 kHz excitation and 0.11 nT/√Hz under a 50 kHz excitation, correspondingly. Likewise, as shown in Figure 11b, the lowest field noise spectra in the Z-axis direction at 1 Hz of magnetic fields were measured as 21.91 nT/√Hz and 6.29 nT/√Hz under 25 kHz and 50 kHz of excitation frequency. In fact, in the relatively low frequency bandwidth (~10 Hz), one can observe that the magnetic sensor demonstrates a relatively improved field noise density against the frequency variation. In addition, by taking Figure 9, Figure 10 and Figure 11 into account, it is noteworthy that the responsivity values of X- and Z-axis measured at 25 kHz and 50 kHz differ by a factor of 10-fold, and the field noise values of X- and Z-axis, for example at 1 Hz, differ by about a factor of 40–60 folds with respect to 25 kHz and 50 kHz, respectively. This fact implies that an additional factor of 4–6 fold is introduced then. We thus consider the reinforced effect in the field noise could be attributed to the following reasons: (1) different gain constants may be employed for the X-axis and Z-axis voltage noise measurements; and (2) the correlation between the field noise induced by the magnetic core and the orientation of excitation fields. For instance, the sensing direction of in-series pick-up coils while running the X-axis sensing mode may reduce portion of the voltage noise. In contrast, the sensing direction of in-series pick-up coils while running the Z-axis sensing mode may amplify the voltage noise in parts. These facts may have a partial influence on the field noise we measured.

Bottom Line: Experimental characterization of the miniature fluxgate device demonstrates satisfactory spatial magnetic field detection results in terms of responsivity and noise spectrum.As a result, at an excitation frequency of 50 kHz, a maximum in-plane responsivity of 122.4 V/T appears and a maximum out-of-plane responsivity of 11.6 V/T is obtained as well.The minimum field noise spectra are found to be 0.11 nT/√Hz and 6.29 nT/√Hz, respectively, in X- and Z-axis at 1 Hz under the same excitation frequency.

View Article: PubMed Central - PubMed

Affiliation: Institute of Mechatronic Engineering, National Taipei University of Technology, Taipei 106, Taiwan. cclu23@ntut.edu.tw.

ABSTRACT
A new class of tri-axial miniature magnetometer consisting of a planar fluxgate structure with an orthogonal ferromagnetic fluxguide centrally situated over the magnetic cores is presented. The magnetic sensor possesses a cruciform ferromagnetic core placed diagonally upon the square excitation coil under which two pairs of pick-up coils for in-plane field detection are allocated. Effective principles and analysis of the magnetometer for 3-D field vectors are described and verified by numerically electromagnetic simulation for the excitation and magnetization of the ferromagnetic cores. The sensor is operated by applying the second-harmonic detection technique that can verify V-B relationship and device responsivity. Experimental characterization of the miniature fluxgate device demonstrates satisfactory spatial magnetic field detection results in terms of responsivity and noise spectrum. As a result, at an excitation frequency of 50 kHz, a maximum in-plane responsivity of 122.4 V/T appears and a maximum out-of-plane responsivity of 11.6 V/T is obtained as well. The minimum field noise spectra are found to be 0.11 nT/√Hz and 6.29 nT/√Hz, respectively, in X- and Z-axis at 1 Hz under the same excitation frequency. Compared with the previous tri-axis fluxgate devices, this planar magnetic sensor with an orthogonal fluxguide provides beneficial enhancement in both sensory functionality and manufacturing simplicity. More importantly, this novel device concept is considered highly suitable for the extension to a silicon sensor made by the current CMOS-MEMS technologies, thus emphasizing its emerging applications of field detection in portable industrial electronics.

No MeSH data available.