Method for measuring a magnetic field using magnetoelectric sensors

• US 9,383,417 B2
• Filed: 01/13/2012
• Issued: 07/05/2016
• Est. Priority Date: 01/18/2011
• Status: Active Grant

• Current Assignee: Christian-Albrechts-Universität zu Kiel
• Original Assignee: Christian-Albrechts-Universität zu Kiel
• Inventors: Jahns, Robert, Knoechel, Reinhard, Quandt, Eckhard
• Primary Examiner(s): Le, John H
• Application Number:
  US13/992,474
• Publication Number:
  US 20130289913A1
• Time in Patent Office: 1,635 Days
• Field of Search: 702/38, 702/65, 702/75, 702/76, 702/106, 702/115, 324/244, 324/249, 455/41.1
• US Class Current: 1/1
• CPC Class Codes: G01R 33/02 Measuring direction or magnitude of magnetic fields or magnetic flux G01R33/20 takes precedence
• CPC Class Codes: G01R 33/06 using galvano-magnetic devices
• CPC Class Codes: G01R 33/18 Measuring magnetostrictive properties

Abstract

A method for measuring a time-variant magnetic field using a magnetoelectric sensor having mechanical resonant frequency f_R, wherein the magnetic field has at least one component having harmonic time dependence with the measuring signal amplitude to be determined H_mess0 and the measuring signal frequency to be determined f_mess in a known frequency interval f_min<f_mess<f_max. The method includes: a. superimposing the magnetic field with a modulation magnetic field having harmonic time dependence with the known modulation amplitude H_mess0 and a selectable modulation frequency on the sensor, b. varying (wobbling) the modulation frequency over a complementary frequency interval determined by the known interval limits f_min, f_max and the resonant frequency of the sensor, c. measuring the sensor signal for each selected modulation frequency, d. searching for the at least one modulation frequency f_mod, which results in a sensor signal in the mechanical resonance of the sensor, e. calculating the measuring signal frequency f_mess from the previously determined modulation frequency f_mod and from the resonant frequency of the sensor f_R, f. transmitting the sensor signal at the modulation frequency f_mod into the superimposed magnetic field amplitude H_sup, and g. calculating the measuring signal amplitude H_mess0 from the superimposed magnetic field H_sup and the modulation amplitude H_mod0.

Claims

1. A method for measuring a time-variant magnetic field using a magnetoelectric sensor having a mechanical resonant frequency f_R, the magnetic field comprising at least one component having a harmonic time dependence

with the measuring signal amplitude H_mess0 to be determined and the measuring signal frequency f_mess to be determined in a known frequency interval f_min<

f_mess<

f_max, characterized by the following steps;

a. superimposing the magnetic field with a modulation magnetic field having a harmonic time dependence with the known modulation amplitude H_mod0 and a selectable modulation frequency on the sensor,

b. varying (wobbling) the modulation frequency over a complementary frequency interval determined by the known interval limits f_min, f_max and the resonant frequency of the sensor f_R,

c. measuring the sensor signal for each selected modulation frequency,

d. searching for the at least one modulation frequency f_mod, which results in a sensor signal in the mechanical resonance of the sensor,

e. calculating the measuring signal frequency f_mess from the previously determined modulation frequency f_mod and from the resonant frequency of the sensor f_R

f. translating the sensor signal at the modulation frequency f_mod into the superimposed magnetic field amplitude H_sup,

g. calculating the measuring signal amplitude H_mess0 from the superimposed magnetic field amplitude H_sup and the modulation amplitude H_mod0.

2. The method according to claim 1, wherein the operating point of the sensor in its magnetostriction characteristic is established such that its frequency response in the leading order is a square function of the magnetic field strength.

3. The method according to claim 2, wherein the complementary frequency interval is established according to f_R−

f_max<

f_mod<

f_R−

f_min or f_R+f_min<

f_mod<

f_R+f_max and the at least one component of the magnetic field with the harmonic time dependence is calculated according to f_mess=|f_R−

f_mod| and H_mess0=H_sup/H_mod0.

4. The method according to claim 1, wherein the magnetic field exhibits a plurality of components having a harmonic time dependence with different magnetic field component amplitudes and/or magnetic field component frequencies in the interval f_min<

f_mess<

f_max and a plurality of modulation frequencies are determined in a complementary frequency interval that leads the sensor into the mechanic resonance, each determined modulation frequency being assigned precisely one magnetic field component frequency and each magnetic field strength measured in resonance precisely one magnetic field component amplitude.

5. The method according to claim 1, wherein the absolute value of H_mod0 is set up to be smaller than or equal to the absolute value of a field strength H_B, the magnetostriction characteristic of the sensor having its inflection points at the field strength±

H_B.

6. The method according to claim 1, wherein said method is carried out using a device for measuring a magnetic field having an arrangement comprising a number N of magnetoelectric sensors, the sensors possessing known mechanical resonant frequencies f_R(i), i=1, . . . , N and the magnetic field having a harmonic time-dependence with the known frequency f_M, wherein the sensor designated by the index i is determined for detecting the magnetic field by superimposing the magnetic field with a modulation magnetic field having the frequency of f_mod=f_R(i)+f_M or f_mod=f_R(i)−

f_M.

7. A method for measuring a time-variant biologically produced magnetic field having a frequency of from 1 Hz up to approximately 100 Hz using a magnetoelectric sensor having a mechanical resonant frequency f_R, the magnetic field comprising at least one component having a harmonic time dependence

with the measuring signal amplitude H_mess0 to be determined and the measuring signal frequency f_mess to be determined in a known frequency interval f_min<

f_mess<

f_max, characterized by the following steps;

a. superimposing the magnetic field with a modulation magnetic field having a harmonic time dependence with the known modulation amplitude H_mod0 and a selectable modulation frequency on the sensor,

b. varying (wobbling) the modulation frequency over a complementary frequency interval determined by the known interval limits f_min, f_max and the resonant frequency of the sensor f_R,

c. measuring the sensor signal for each selected modulation frequency,

d. searching for the at least one modulation frequency f_mod, which results in a sensor signal in the mechanical resonance of the sensor,

e. calculating the measuring signal frequency f_mess from the previously determined modulation frequency f_mod and from the resonant frequency of the sensor f_R

f. translating the sensor signal at the modulation frequency f_mod into the superimposed magnetic field amplitude H_sup,

g. calculating the measuring signal amplitude H_mess0 from the superimposed magnetic field amplitude H_sup and the modulation amplitude H_mod0.