Patent Grant
9128009
This application is the United States national stage of International Application No. PCT/KR2010/007708, filed Nov. 3, 2010, and claims priority to Korean Patent Application No. 10-2009-0121039, filed Dec. 8, 2009, the disclosures of which are hereby incorporated in their entirety by reference.
1. Field of the Invention
The present invention relates to a ΔE measuring device minimizing external magnetic disturbance, and more particularly, to a ΔE measuring apparatus measuring a change (ΔE) in elastic modulus under a magnetic field by removing a bias effect by the earth's magnetic field and a magnetic tool and device and using a magneto acoustic resonance method.
2. Description of Related Art
Generally, in order to form a space not having a magnetic field by reducing a change amount in the earth's magnetic field, a method (hereinafter, referred to as a magnetic shielding method) of shielding a magnetic field using a magnetic material having high magnetic permeability, a method of measuring a change amount in external magnetic field and applying magnetic fields having the same magnitude as each other and the opposite directions to each other to offset a magnetic field (hereinafter, a magnetic field offsetting method), and the like, have been suggested.
An example of the latter may include an apparatus as shown in
To this end, each of large three-axis Helmholtz coil apparatuses 102, 104, and 106 is adjusted and installed in a non-magnetic building 10 in a vertical direction, a north-south direction, and an east-west direction, and small Helmholtz coils 122, 124, and 126 are adjusted to coincide with each other in each direction and are connected in series with each other in an observing chamber 12 positioned at a point spaced apart from the building to the south by 50 m. Three current sources 142, 144, and 146 for offsetting a DC earth's magnetic field are installed in a measuring chamber 15 spaced apart from the non-magnetic building 10 to the north by 50 m.
In addition, in order to allow coil constants of two Helmholtz coils offsetting a vertical component to coincide with each other, a branch resistor (RV), a branch resistor (RN) connected in a north-south (N-S) direction, and a branch resistor (RE) connected in an east-west (E-W) direction are used. In addition, since the east-west direction is the same direction as that of a solenoid that is a precise magnetic field generator, branch resistors RE1 and RE2 are used in order to improve uniformity in a central space of the Helmholtz coils and allow coil constants of two large Helmholtz coils to coincide with each other.
In the case of each of the Helmholtz coils, a DC coil and a coil offsetting a variance according to a time are wound around the same coil bobbin in order to simultaneously offset a DC component and a component according to a time.
Two Helmholtz coils should be installed in a state in which they are spaced apart from each other by 30 m or more in order to exclude mutual interference. The two Helmholtz coils have different sizes, but have the same coil constant (a size of a magnetic field according to current) and are connected in series with each other to simultaneously offset the earth's magnetic fields at two places.
Next, in order to remove a component changed according to a time, a magnetic resonance frequency that is in proportion to a change amount in earth's magnetic field is measured using a magnetic resonance measurer and is compared with a first set reference frequency to generate current (voltage) corresponding to a difference between the above-mentioned two frequencies (a difference between magnetic fields) using a phase comparator, and the current (voltage) is applied to the Helmholtz coils to generate magnetic fields that is in proportion to a magnitude of the earth's magnetic field in an opposite direction to that of the earth's magnetic field, thereby offsetting the earth's magnetic field.
Since the apparatus shown in
However, according to the related art, in order not to have any external effect on the non-magnetic building, the non-magnetic building should be built without using a magnetic material such as iron.
In addition, there is a spatial limitation in that the non-magnetic building should be spaced apart from a road by a predetermined distance or more in order to remove interference from the outside.
Therefore, disturbance is easily generated due to a surrounding environment (for example, home appliances, a steel-frame building, or the like) having magnetism as well as an external magnetic field at a place except for the non-magnetic building.
Further, since a soft magnetic material is easily affected by the appliances, the steel-frame structure, or the like, having magnetism in the vicinity thereof, it is difficult to perform precise measurement.
An object of the present invention is to provide an apparatus capable of removing a bias effect due to the earth's magnetic field and minimizing external magnetic disturbance due to magnetism of home appliances and a steel-frame structure.
Another object of the present invention is to provide an apparatus capable of precisely measuring a change amount in elastic modulus under a magnetic field of a magnetic material (particularly, a soft magnetic material) by minimizing external magnetic disturbance.
In one general aspect, a ΔE measuring device minimizing external magnetic disturbance includes: three-axis Helmholtz coils arranged in x, y, and z axis directions to remove the earth's magnetic field; a three-axis magnetic sensor installed at one side of the three-axis Helmholtz coils to measure magnetic fields formed in the three-axis Helmholtz coils; a second power supply unit supplying offset current offsetting the measured magnetic fields to the three-axis Helmholtz coils according to the measured magnetic fields; a tertiary coil inserted into and seated in the three-axis Helmholtz coils; a secondary coil inserted into and seated in the tertiary coil; a primary coil inserted into and seated in the secondary coil and having a sample inserted thereinto and seated therein, the sample corresponding to an object to be measured; a signal generator applying an AC current signal to the secondary coil; a first power supply unit applying a DC current signal to the tertiary coil; a signal measuring unit measuring a magneto acoustic resonance frequency detected in the primary coil; and a calculating unit calculating an elastic modulus using the magneto acoustic resonance frequency and commanding the second power supply unit to supply the offset current.
Here, when the AC current signal is applied to the secondary coil using the signal generator and an output signal of the primary coil measuring the magneto acoustic resonance signal is measured using the signal of the signal generator as a reference signal while a frequency of the signal is increased, the magneto acoustic resonance signal as shown in
The elastic modulus may be calculated by the following Equation:
E=4l2fr2ρ
(where E indicates an elastic modulus depending on the magneto acoustic resonance frequency (fr), l indicates a length of the sample, fr indicates the magneto acoustic resonance frequency, and ρ indicates density).
The first power supply unit may stepwise increase the current applied to the tertiary coil to change a magnetic field applied to the sample, and the second power supply unit may supply both of the DC and AC current signals
The calculating unit may include an analog to digital converting unit transmitting a signal to and receiving the signal from at least any one of the three-axis magnetic sensor, the first power supply unit, the second power supply unit, the signal generator, and the signal measuring unit.
Coils of each axis of the three-axis Helmholtz coils may be configured of two coaxial coils which are positioned to be spaced apart from each other by a radius thereof.
According to the exemplary embodiment of the present invention, a space minimizing external magnetic disturbance using the three-axis Helmholtz coils, the elastic modulus is measured in a magneto-acoustic resonance scheme, and an elastic modulus and ΔE measuring device having a plurality of coil structures capable of measuring a change in elastic modulus under a magnetic field is inserted into the space, thereby making it possible to minimize external magnetic field disturbance.
The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
In Korea, a magnitude of the earth's magnetic field on the earth's surface is about 0.5 G (Gauss). A magnetic material (for example, an amorphous material) having low coercive force and high magnetic permeability is significantly magnetized even with this earth's magnetic field. In addition, a magnetic material (particularly, a soft magnetic material) is affected even by an external environment having magnetism.
1) of
2) of
3) of
In
(a) magnetic material 611 having strong anisotropy
(b) magnetic material 610 having weak anisotropy
That is, a gradient (a)>(b). The reason is that stronger anisotropy acts on the magnetic material having the strong anisotropy.
When an elastic modulus (E) and a change (ΔE) in elastic modulus are calculated based on the graph shown in
Where Ed indicates an elastic modulus in a demagnetized state, εel indicates elastic strain generated in any material regardless of magnetism, εme indicates magnetic elastic strain corresponding to a value due to rearrangement of a magnetic domain vector by applied stress, and σ indicate stress.
Where Es indicates an elastic modulus in a saturated state or an elastic modulus in a non-magnetic material.
The following Equation 3 is derived from Equation 1 and Equation 2.
As an example of a value of ΔE/Eeff, nickel (Ni) has a value of ΔE/Eeff of about 6% and iron has a value of ΔE/Eeff smaller than 1%.
Therefore, referring to
As described above, in order to perform precise measurement of the magnetic material, a ΔE effect should be measured in a state in which the earth's magnetic field and the external magnetic field are removed.
A configuration of a ΔE effect measuring device is shown in
That is,
The three-axis Helmholtz coils 271, 272, and 273 includes x-axis coils 271 and 271′, y-axis coils 273 and 273′, z-axis coils 272 and 272′, and the like. Here, the y-axis coil 273′ is not shown. In the case of the Helmholtz coils, two coaxial coils are positioned so as to be spaced apart from each other by a diameter thereof to make a magnetic field therebetween substantially constant, which is shown in
Further, in order to measure a magnetic field in the three-axis Helmholtz coils 271, 272, and 273, the three-axial magnetic sensor 230 is provided at the center of the three-axis Helmholtz coils 271, 272, and 273. The three-axis magnetic sensor 230 serves to measure the magnetic field in the three-axis Helmholtz coils 271, 272, and 273. This three-axis magnetic sensor 230 measures strength of the magnetic field to transmit the measured strength to the computer 200 through the multi-functional DAQ board 210.
Therefore, after the strength of the magnetic field at the center of the Helmholtz coil is measured using the three-axis magnetic sensor 230, a signal is transmitted from the multi-functional DAQ board 210 to the second power supply unit 270 so that a magnetic field having the same magnitude as that of the magnetic field at the center of the Helmholtz coil and the opposite direction to that of the magnetic field at the center of the Helmholtz coil is generated, and the second power supply unit converts the signal into current to apply the current to the three axis Helmholtz coils, such that external magnetic disturbance is offset, whereby a magnetic field value becomes “0”. In order to facilitate the understanding, only the x-axis coil will be described by way of example.
{circle around (1)} A magnetic field in the x-axis coils 271 and 271′ is first measured.
{circle around (2)} In the case in which the measured magnetic field is not “0”, the second power supply unit 270 applies current to the x-axis coils 271 and 271′. In this case, a direction and strength of the current are adjusted so that the current has the same magnitude as and the opposite direction to the magnetic field measured in {circle around (1)}. These adjustment values are calculated by the computer 200 and transmitted to the second power supply unit 270 through the multi-functional DAQ board 210, and the second power supply unit 270 converts the adjustment values into the current to allow the current to the x-axis coils 271 and 271′.
{circle around (3)} A magnetic field in the x-axis coils 271 and 271′ is again measured.
{circle around (4)} When the measured magnetic field becomes “0”, it means that the external magnetic disturbance is offset.
When processes of {circle around (1)} to {circle around (4)} are similarly applied to remaining y-axis and z-axis coils 272 and 273, the three-axis space magnetic disturbance is offset.
Continuously describing
The sample 290 which is an object to be measured is inserted into the magneto acoustic resonance signal detecting coil 280a of the ΔE measurement coil 280. The sample 290, which is a magnetic material, may be a wire, a thick film, or the like.
The first power supply unit 260 applies DC current to the variable direct current magnetic field applying coil 280c.
The signal generator 250 serves to apply an AC current signal to the frequency variable alternate current magnetic field applying coil 280b. That is, the signal generator 250 may generate a sine wave signal having a frequency from 50 Hz to 3 MHz. Further, in the present invention, since only a small magnetic field is generated, a power amplifier is not used.
The signal measuring unit 240 serves to measure a magneto acoustic resonance signal detected in the magneto acoustic resonance signal detecting coil 280a. The signal measuring unit 240, which is a lock-in amplifier, compares frequencies of the signal generated in the magneto acoustic resonance signal detecting coil 280a and a reference signal (ref) with each other to remove noise and measure only a desired signal. A configuration diagram of the signal measuring unit 240 is shown in
Since the frequency variable alternate current magnetic field applying coil 280b is connected to the signal generator 250 to receive the AC signal, an AC magnetic field is generated in the magneto acoustic resonance signal detecting coil 280a. Therefore, a length of the sample 290 is also repeatedly increased and decreased finely by a magneto elastic effect and resonates at a specific frequency. This resonance is measured as a magneto acoustic resonance signal in the magneto acoustic resonance signal detecting coil 280a, which is shown in
The magneto acoustic resonance frequency 700 and the signal measured in the magneto acoustic resonance signal detecting coil 280a are adjusted as a signal capable of being received in the multi-functional DAQ board 210 using the signal measuring unit 240 and then transmitted to the multi-functional DAQ board 210, and the multi-functional DAQ board 210 digitally processes the received signal to transmit the processed signal to the computer 200.
Here, an elastic modulus may be calculated using the magneto acoustic resonance frequency 700, which may be represented by the following Equation 4.
E=4l2fr2ρ [Equation 4]
Where E indicates an elastic modulus depending on a magneto acoustic resonance frequency (fr), l indicates a length of a sample, fr indicates the magneto acoustic resonance frequency, and ρ indicates density.
In the case in which the elastic modulus is calculated, ΔE may be measured. ΔE may be measured by adjusting the DC current signal applied to the variable direct current magnetic field applying coil 280c, as described above. More specifically, in
That is, when the magnetic field is changed, the elastic modulus is also changed, which may be represented as a graph by
Here, in the graph shown in
Next, the signal measuring unit 240 shown in
The PSD unit 410 generates an output signal by a phase difference between the magneto acoustic resonance frequency signal and a phase shifted reference signal to transmit the output signal to the computer 200 through the multi-functional DAQ board 210 (See
Although the exemplary embodiment of the present invention has been described above with reference to the accompanying drawings, it may be appreciated by those skilled in the art that the scope of the present invention is not limited to the above-mentioned exemplary embodiment, but may be variously modified. Therefore, the scope of the present invention is to be defined by the accompanying claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2009-0121039 | Dec 2009 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR2010/007708 | 11/3/2010 | WO | 00 | 8/13/2012 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2011/071244 | 6/16/2011 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4165479 | Mansfield | Aug 1979 | A |
| 4442404 | Bergmann | Apr 1984 | A |
| 6404340 | Paradiso et al. | Jun 2002 | B1 |
| 8128564 | Kwon et al. | Mar 2012 | B2 |
| Number | Date | Country |
|---|---|---|
| 2002-232182 | Aug 2002 | JP |
| 10-0608110 | Apr 2006 | KR |
| Entry |
|---|
| International Search Report dated Jun. 29, 2011 in International Application No. PCT/KR2010/007708. |
| Number | Date | Country | |
|---|---|---|---|
| 20120310581 A1 | Dec 2012 | US |
