JP3507308B2 - Method and apparatus for measuring magnetic field of magnetic head - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the measurement of a magnetic field obtained from a magnetic field generator of a magnetic head, for example, and in particular to a magnetic field capable of measuring the magnetic field strength generated from the magnetic head in a high frequency band and further the magnetic field waveform with high accuracy. The present invention relates to a magnetic field measuring method for a head and a magnetic field measuring apparatus.

[0002]

2. Description of the Related Art As a method for measuring a magnetic field generated from a magnetic head or the like, a method using a Hall element and a method using a magnetic flux detecting coil have been generally used.
There are methods such as R element and MFM. 5A and 5B show a conventional magnetic field measuring method, FIG. 5A is a circuit configuration diagram showing a detection method using a Hall element, and FIG. 5B is a circuit configuration diagram using a detection coil.

The measuring method using the Hall element is the most commonly used method. When a current I is applied to one end of the Hall element 1 shown in FIG. 5A and a magnetic field having a magnetic flux density B is applied from a direction perpendicular to the current I, a voltage is applied to the other end of the Hall element 1 by the Hall effect. Occur. The electromotive force V generated at this time is represented by V = Rh · B · I / d [v], where Rh is the Hall coefficient and d is the thickness of the Hall element.
The measured magnetic field can be converted into a voltage value for measurement. In addition, since the DC amplifier is less stable than the AC amplifier, the current I flowing through the hall element 1 is generally used.
Is obtained from the AC constant current generator 2, and even if the magnetic field to be measured is DC, the voltage generated in the Hall element 1 becomes an AC signal having the same frequency as the current, and its amplitude matches the magnitude of the magnetic field to be measured. By amplifying this voltage with the amplifier 3 and synchronously detecting it with the alternating current signal in the synchronous rectifier 4, the magnitude and polarity of the magnetic field can be known. When the magnetic field to be measured is an alternating current, the magnetic field is modulated at the frequency of the alternating current. However, by amplifying the voltage generated in the Hall element 1 and performing synchronous detection, the magnitude of the alternating magnetic field can be measured. It is possible.

On the other hand, in the method using the magnetic flux detecting coil shown in FIG. 5B, the detecting coil 5 having the number of turns n is used, and when the detecting coil 5 is interlinked with the magnetic flux φ within a unit time t,
According to the law of electromagnetic induction, V = − is applied to both ends of the detection coil 5.
A voltage of n · dφ / dt is generated. By amplifying this voltage V by the amplifier 6, the voltage V proportional to the strength of the magnetic field
Can be obtained. Further, according to the law of electromagnetic induction, the voltage V induced in the detection coil 5 is proportional to the changing speed of the magnetic field, that is, the frequency f, so that the number of turns n of the detection coil 5 can be reduced in the high frequency region. .

[0005]

However, when attempting to measure the magnetic field strength of the magnetic head by the above-mentioned methods, there are the following problems. Since the measurable frequency band is as low as several KHz, the method using the Hall element 1 has a problem that it cannot be applied to a recent magnetic head driven in the several tens MHz band.

Further, the method using the detection coil 5 theoretically enables effective measurement in a high frequency band. However, in the above-described measuring device and method using the detection coil 5, the higher the frequency band is, the more susceptible it is to radiation noise. For example, in the frequency band of 10 MHz or more, it is generally known that the influence of radiation noise is so great that it becomes difficult to know whether the magnetic field is being measured or the noise is being measured. That is, the drive frequency band of the magnetic head and the frequency band of the radiation noise are both equal to
Since they coincide with each other in the frequency band of 0 MHz, there is a problem that the magnetic field strength in the tens of MHz band that is most desired to be detected cannot be measured with high accuracy.

In particular, when a coil with a very small number of turns such as one turn is used as the detection coil, the detection sensitivity is improved in the higher frequency band and a slight change in magnetic flux can be detected. Since radiation noise from the drive coil of the magnetic head is also detected with a relatively large value, the magnetic field output from the detection coil 5 is largely affected by noise.

Although it is possible to remove the noise by using a filter or the like, it is difficult to accurately remove only the noise because the magnetic field output signal and the noise output signal are in the same frequency band. Is. Therefore, the above-mentioned conventional measuring device and measuring method cannot measure the magnetic field strength with high accuracy. Furthermore, in the measurement method using the detection coil, since a differential waveform is obtained,
It is not possible to properly grasp the change state of the magnetic field generated from the magnetic field generation unit of the magnetic head.

The present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a magnetic field measuring method and a magnetic field measuring apparatus for a magnetic head capable of measuring the magnetic field strength in the high frequency band and further the magnetic field waveform with high accuracy. I am trying.

[0010]

The magnetic head magnetic field measuring method of the present invention is characterized by including the following steps.
Of. (A) provide an alternating current to the magnetic head, the magnetic sensing means
The step of the first detection value by detecting the magnetic field output of the magnetic heads do we in one position, to give the same alternating current (a) and step (b) the magnetic head
As it is, the magnetism detecting means is set to the magnetism with respect to the first position.
Air head so that the detected magnetic field output is at a constant level.
The position of the magnetic detection means when it converges to the second position.
And the magnetic field from the magnetic head at this position
A step of setting an output as a second detection value, and (c) a step of obtaining a difference between the first and second detection values .

[0011]

That is, in the present invention, the magnetic field is measured at least twice by the magnetic detection means. In the two measurements, the detected magnetic field strengths are made different and the same level of noise can be detected. The noise is canceled by taking the difference between the two detection values. Therefore, when obtaining the second detection value, it is preferable to sufficiently separate the magnetic field detection means from the magnetic field generation unit so that only the noise is detected as the second detection value.

In the above, the magnetic detection means is a magnetoresistive effect element or a detection coil having one or more turns.

By using these elements, it is possible to detect a magnetic field having an extremely high frequency in the MHz band, for example.

If the magnetic detection means is a detection coil and the detection output of this detection coil is integrated to detect the magnetic field waveform from the magnetic field generator, a magnetic field in a high frequency band can be detected and The magnetic field waveform can be detected. That is, it is possible to detect with high accuracy the waveform of the magnetic field generated at a high frequency such as the MHz band, which has been impossible in the past.

[0016]

[0017]

Further, the magnetic field measuring apparatus of the present invention comprises a magnetic head installation portion, a drive circuit for applying an alternating current to the magnetic head, a detection coil having one or more turns for detecting a magnetic field output from the magnetic head , Pair the detection coil with the magnetic head .
The first position by, and the first magnetic heads than the position
The magnetic field output from the magnetic head is
A coil support portion facing a second position where it converges to a constant level, and detection by the detection coil at the first position.
Magnetic detected by the detection coil in the first detection value indicative of the magnitude and the second position of the magnetic field output from the magnetic head
An analysis circuit that takes a difference from a second detection value indicating the magnitude of the magnetic field output from the air head and integrates the detection value;
Is provided.

[0019]

The present invention is based on Faraday's law of electromagnetic induction. That is, the higher the drive frequency of the magnetic head, the higher the rate of change (dφ / dt) of the magnetic flux generated from the magnetic head. Therefore, the rate of change of the total magnetic flux interlinking in the detection coil also increases, and the electromotive force generated due to this also increases. Further, since this electromotive force is proportional to the number of turns of the detection coil, it is possible to obtain a sufficient magnetic field output even when the number of turns of the coil is 1 in an extremely high frequency band.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a magnetic head magnetic field measuring apparatus according to the present invention. In the magnetic field measuring apparatus shown in FIG. 1, an oscillator 12 is connected to an amplifier 12, and a magnetic head H which is a magnetic field to be measured is connected to the amplifier 12. The oscillator 11 and the amplifier 12 constitute a drive circuit that gives an AC magnetic field to the magnetic head H. The magnetic head H is, for example, for a magneto-optical disk device, in which a core is embedded in a slider and the facing gap part of the core serves as a magnetic field generating part. The magnetic head H is a predetermined holding jig (ground part). ) Is fixedly held via the slider.

A detection coil 13 is provided near the magnetic head H as a magnetic detection means for measuring the magnetic field strength. The detection coil 13 is supported by the coil supporting portion. The coil support portion is a manipulator or the like that moves in the same distance in two steps. Due to the movement operation of the coil support portion, the detection coil 13 is extremely close to the magnetic field generation portion of the magnetic head H, and from that position. It can be moved to a slightly separated position. The detection coil 13
The output terminal of is connected to the waveform recording means 14. In addition, the output of the amplifier 12 is acquired by the current probe 15,
It is input to the waveform recording means 14. An analyzing means 16 is connected to the waveform recording means 14.

The oscillator 11 is, for example, a pulse generator or the like, and one that can output a square wave from DC to several tens MHz is used. The magnetic head H includes an oscillator 1
The output signal from 1 is driven by receiving the drive signal amplified by the amplifier 12. Alternatively, when the drive signal of the oscillator 11 can supply a predetermined drive current, the magnetic head H may be directly driven by the output signal from the oscillator 11. The current waveform of the drive signal acquired by the current probe 15 is used as the trigger signal of the magnetic field output signal from the detection coil 13. Therefore, even if the magnetic field output of the detection coil 13 is a weak signal, the synchronization can be reliably achieved. In addition, instead of the current output of the amplifier 12,
For example, the output signal of the oscillator 11 may be directly input to the waveform recording means 14.

In FIG. 1, the magnetic field output of the detection coil 13 is directly input to the waveform recording means 14. Waveform recording means 1
4, a digitizing oscilloscope, a digital memory, or the like is used. When the waveform recording means 14 is a digitizing oscilloscope, the magnetic field output waveform (differential waveform) of the detection coil 13 and the current waveform of the current probe 15 after digital processing are directly displayed on the display screen. However, the magnetic field output waveform acquired by the detection coil 13 is the differential value represented by V = −n · dφ / dt described above converted into a voltage value. When the waveform recording means 14 is a digital memory,
Detection coil 1 after digital processing in waveform recording means 14
3, the magnetic field output waveform (differential waveform) and the drive current waveform data are temporarily stored.

The data of the magnetic field output of the detection coil 13 recorded in the waveform recording means 14 is used as the analyzing means (analyzing circuit) 16
Is taken in and analyzed. The analysis unit 16 is composed of, for example, a computer, and various kinds of analyzes can be performed by analysis software installed in the computer. For example, the data of the magnetic field output of the detection coil 13 stored in the waveform recording means 14 is fetched so that the waveform showing the magnetic field strength after the integration processing by the analysis software can be displayed on the display device on the computer. Has become.

[0026]

EXAMPLES A magnetic field measuring method using the magnetic field measuring apparatus according to the present invention will be specifically described below. In the examples described below, a fine conductor wire having a wire diameter of 15 μm is wound one turn and adhered to a glass substrate, a surface of which is covered with a protective sheet having a thickness of 20 μm, and an inner diameter of the coil 13 is 75 μm. Effective distance to the center of the coil is 30μ
The detection coil 13 formed in m is used as magnetic detection means.

FIG. 2A shows the magnetic field output of the detection coil, and the reference numeral represents the waveform of the first magnetic field output (first detection value) when the detection coil is brought close to the magnetic head (first position). In the figure, the reference numeral indicates the second magnetic field output (second position) when the detection coil is separated from the magnetic head (second position).
2B is a waveform diagram in which the second magnetic field output is subtracted from the first magnetic field output in FIG. 2A.

When the above-mentioned detection coil 13 is brought close to the magnetic head H, an output signal as shown in the first magnetic field output of FIG. 2A is detected. Further, when the detection coil 13 is gradually separated from the magnetic head, the magnetic field output also gradually decreases and converges to a substantially constant level. The magnetic field output measured at this constant level is presumed to be radiation noise generated from the coil of the magnetic head H, and it is impossible to completely shield only the magnetic head H. To be detected. Further, it can be confirmed that the radiation noise is generated more remotely than the magnetic field output is generated extremely close to the periphery of the magnetic head H. Therefore, the radiation noise can be detected by gradually separating the detection coil 13 from the magnetic head H and measuring the magnetic field output at a position where the level is constant. The distance (spacing) between the magnetic field generator of the magnetic head H and the detection coil of the magnetic detection means in this embodiment was 0.03 mm at the first position and 2.3 mm at the second position.

Therefore, from the first magnetic field output detected in the state where the detection coil 13 is approached, the second emission noise is detected.
By subtracting the magnetic field output of, the magnetic field output of the magnetic head itself excluding the radiation noise can be obtained.
Thus, only the difference is obtained is the magnetic field output waveform (differential waveform) shown in FIG. Since the first magnetic field output and the second magnetic field output acquired by the detection coil 13 are recorded as digital data in the above-mentioned waveform recording means, these data are taken into the analysis means and the difference for each time is calculated. By determining, the radiation noise can be removed. Therefore, the magnetic field output (differential waveform) of the magnetic head can be acquired with high accuracy up to the high frequency band. Further, as will be described later, it is possible to obtain the magnetic field strength by integrating this magnetic field output.

FIGS. 3 and 4 show examples of the analysis results when the driving frequency is 5 MHz and 30 MHz, respectively, in which (A) is the driving current waveform, (B) is the magnetic field strength waveform in the positive polarity, C) is a magnetic field strength waveform in reverse polarity. In this measurement, since it is similar to the actual drive signal of the magnetic head, a square wave is output from the oscillator 11, and the oscillator 11 or the amplifier 12 detected by the current probe is shown in FIGS. The current waveform of is shown. However, as shown in FIG. 4 (A), when the frequency becomes high, a blunt rising portion appears remarkably, and the square wave is not maintained.

On the other hand, (B) and (C) are obtained by removing the radiation noise from the magnetic field waveform detected by the detection coil by the above-mentioned method and integrating it to obtain the magnetic field strength. The magnetic field strength outputs in FIGS. 3 and 4B respectively show magnetic field strength waveforms when the polarity of the amplifier 12 connected to the input terminal of the magnetic head H is changed. The magnetic field waveform charts shown in (B) and (C) are obtained by digitally capturing data (averaging) obtained in advance and averaged a plurality of times in order to remove minute fluctuations with time. Originally, the same magnetic field strength should be measured even if the polarities of the input terminal of the magnetic head H and the output terminal of the amplifier 12 are reversed.

However, in this embodiment, the difference in the magnetic field strength waveform was measured only by the different polarities. It is considered that this is due to the earth around the oscillator 11 or the amplifier 12. In such a case, a highly accurate magnetic field strength waveform can be obtained by, for example, acquiring data for both the positive pole and the reverse pole and averaging the data. That is, it is possible to obtain a more accurate magnetic field strength waveform by recording the measured values of the positive pole and the reverse pole in the waveform recording means 14, respectively, and taking these data into the analyzing means and averaging them.

If an external integrator capable of responding to the driving frequency is provided between the output terminal of the detection coil 13 and the waveform recording means 14 in FIG. 1, the magnetic field is directly displayed on the display screen of the digital oscilloscope. The waveform can be displayed, or the magnetic field waveform can be obtained directly in digital memory. Therefore, it is possible to eliminate the need for integration processing in the analysis means 16. Further, the magnetic detection means in the present invention is not limited to the one-turn coil, and it is possible to use, for example, an MR element or the like. However, since the output of the MR element is already the magnetic field strength itself after the integration, the integration processing in the analysis device becomes unnecessary.

[0034]

According to the present invention described in detail above, several tens of millions
It is possible to measure the magnetic field strength characteristic of the magnetic head that is less affected by radiation noise up to the high frequency band of Hz.

Further, by averaging the magnetic field strength measured at the positive pole and the magnetic field strength at the opposite pole, it is possible to measure the magnetic field strength with higher accuracy.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a magnetic head magnetic field measuring apparatus according to the present invention;

2A is a magnetic field output waveform of a detection coil, FIG. 2B is a magnetic field output waveform of a difference between a close state and a separated state, FIG.

3A and 3B show analysis results when the drive frequency of the magnetic head is 5 MHz, where (A) is a drive current waveform, (B) is a positive magnetic field strength waveform, and (C) is a reverse polarity magnetic field strength waveform.

FIG. 4 shows analysis results when the magnetic head drive frequency is 30 MHz, (A) shows a drive current waveform, and (B) shows
Is a positive magnetic field strength waveform, (C) is a reverse polarity magnetic field strength waveform,

5A and 5B show a conventional magnetic field measurement method, FIG. 5A is a circuit configuration diagram showing a detection method using a Hall element, and FIG. 5B is a circuit configuration diagram using a detection coil.

[Explanation of symbols]

11 oscillator 12 amplifier 13 Detection coil 14 Waveform recording means 15 Current probe 16 Analytical means H magnetic head

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G11B 5/455 G01R 29/00-29/26 G01R 33/00-33/26

Claims (4)

(57) [Claims] 1. A magnetic field measurement of a magnetic head having the following steps :
Fixed method. (A) provide an alternating current to the magnetic head, the magnetic sensing means
The step of the first detection value by detecting the magnetic field output of the magnetic heads do we in one position, to give the same alternating current (a) and step (b) the magnetic head
As it is, the magnetism detecting means is set to the magnetism with respect to the first position.
Air head so that the detected magnetic field output is at a constant level.
The position of the magnetic detection means when it converges to the second position.
And the magnetic field from the magnetic head at this position
A step of setting an output as a second detection value, and (c) a step of obtaining a difference between the first and second detection values . Wherein said magnetic detecting means, the magnetic field measurement method of claim 1 Symbol placement of the magnetic head is a magnetoresistive effect element or one or more turns of the detection coil. Wherein the magnetic detection means is a detection coil,
3. The magnetic field measuring method for a magnetic head according to claim 2 , wherein the detection output of the detection coil is integrated to detect the magnetic field waveform from the magnetic field generator. 4. A magnetic head installation portion, a drive circuit for applying an alternating current to the magnetic head, and a magnetic field from the magnetic head.
A detection coil of one turn or more for detecting the output, and the detection
The first position against the coil in a magnetic head, and the first
The magnetic head is farther from the position 1 than the magnetic head.
Of the magnetic field output from the magnetic head detected by the detection coil at the first position, facing the second position where the detected magnetic field output from the device converges to a constant level .
The size of the magnetic field output from the magnetic head detected by the first detection value and the second of the detection coil at a position indicating the magnitude
A magnetic field measuring apparatus for a magnetic head, which is provided with an analysis circuit for taking a difference from a second detected value indicating the height and integrating the detected value.