JPH01167686A - Magnetostriction measuring instrument - Google Patents

Abstract

PURPOSE:To accurately measure the magnetostriction strain of a material by using laser light, giving periodic magnetic field variation to a sample, and measuring reflected light due to curvature by an optical position detecting element. CONSTITUTION:The sample 4 on which laser light from a laser light source 2 is projected is placed in the center and a couple of coils 5 for magnetic field production are provided. A couple of coils 6 for magnetic field production are provided above and below the sample 4. A current which varies alternately is supplied to the coils 5 and 6 by a coil power source 7 and a phase shifter 8. A magnetic field which varies with time is applied to the sample 4 made of a thin film and a substrate, the magnetism state in the thin film varies period ically, and 'curvature' due to magnetic strain also varies periodically. Conse quently, the resulting displacement of laser reflected light is measured by the optical position detecting element 3 as a voltage signal, which is amplified by an amplified 9 and recorded on a recorder 11 many times. Consequently, the magnetostriction of the sample 4 is accurately measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an apparatus for measuring magnetostrictive properties of magnetic materials.

[Prior Art] In magnetic materials used in transformers, motors, VTRs, etc., the phenomenon of magnetostriction is generally observed.

Magnetostriction is a phenomenon in which materials expand and contract as the magnetization state changes, but this expansion and contraction is extremely small, and 1al
For a material with a length of , a change in length of lO→~10-'am occurs. Conversely, this phenomenon appears as a phenomenon in which the magnetization state inside the material changes when a mechanical force that causes expansion and contraction is applied from the outside.

Therefore, it is necessary to measure the magnetostriction phenomenon in detail for magnetic materials used in various harsh environments.

Until now, magnetostriction has been measured using differential transformers, strain gauges, etc. attached to magnetic materials.

However, recently, magnetic materials are often used in thin film applications, that is, in thicknesses of several micrometers (1 micrometer = 0.0001 am), and moreover, magnetic materials are often used in thin film applications, such as glass and ceramic plates (several tens of micrometers thick).
0μ■ to several mm). In such cases, differential transformers and strain gauges are much larger than the thin film, and when bonded to the thin film, the minute expansion and contraction of the thin film is almost eliminated, making measurement impossible using conventional methods. Become.

However, when a change in magnetostriction occurs in a thin film, the thin film expands and contracts, so when it is in close contact with a plate, the film as a whole will "warp".
can be seen. By measuring this "warpage", the expansion and contraction of the thin film can be calculated from the elastic constants of the thin film and plate.

Therefore, the most important technique is to measure this "curvature" with high precision.

The present invention relates to a device for measuring this "warpage".

As a method for measuring "warpage", an apparatus that utilizes changes in capacitance as shown in FIG. 6 is used. In other words, an electrode plate 1c is placed very close (about several hundred pm) parallel to the surface of a thin film 1b that is in close contact with a plate (substrate) la, and the amount by which the capacitance between this and the thin film changes due to "warping" is calculated. is measured by capacitance change measuring device 1d.

[Problems to be Solved by the Invention] The above measurements are performed electrically, but since the change in capacitance is extremely small, errors in adjusting the distance between the thin film and the electrode plate, electrical noise, and instability occur. This is a major hurdle and requires very precise and expensive electrical equipment. Moreover, there are many variations in the measured values, and the measurement accuracy is 10-4 to 10".
It was just am.

[Means for Solving the Problems] As shown in FIG. 1, the present invention irradiates the surface of the thin film 1b that is in close contact with the plate (substrate) la from a laser light source 2 with laser light focused within 1 inch, for example. , the displacement due to the "warpage" of the reflected light is measured by an optical position detection element 3 that generates a voltage proportional to the position when irradiated with narrowly focused light. That is, 1 the present invention uses a laser beam to detect the magnetostrictive displacement of a magnetostrictive material by using an optical position detection element to detect the change in the position of the reflected light, and further eliminates noise generated during the measurement. In order to do this, measurements were carried out many times (for example, from 2 to 37 times) while the measurement sample was fixed and the direction of the magnetic field applied to it was changed.

It also attempts to block mechanical and electrical noise by using a phase detection method (lock-in amplifier) to enable precise measurements.

As described above, the present invention relates to an apparatus for optically measuring magnetostriction by installing a laser beam and an optical position detection element.
Compared to conventional capacitance methods, this device uses changes in light to measure, so there is no electrical noise or instability.
, m-determining accuracy can be improved to about 10-'am, and errors in thin film position can also be eliminated by a simple calibration method.

[Effect] As mentioned above, in the present invention, laser light is used.

Since magnetostriction is optically measured by attaching an optical position detection element, there is no electrical noise or instability, and errors in thin film position can be eliminated by a simple calibration method.

[Example] Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory diagram showing the basic configuration of the present invention, FIG. 2 is a configuration diagram showing the specific configuration of the present invention, and FIG. 3 is an explanatory diagram showing the relationship between the detection configuration and detected waveform in FIG. Fig. 4 is a diagram showing an embodiment of the present invention, (a) is a plan view, (b) is a front view, (c) is a side view, and Fig. 5 is a control 1 display device of the device shown in Fig. 4. front view.

It is.

As shown in FIG. 1, the present invention irradiates the surface of a thin film 1b that is in close contact with a plate (substrate) la with a laser beam focused within, for example, 1 square from a laser light source 2, and changes the direction of arrow A due to magnetostriction. The amount of displacement Q of the reflected light due to "warping" in the direction of arrow B is measured by the optical position detection element 3, which generates a voltage proportional to the position when a narrowly focused light is irradiated.

In order to increase the accuracy of this device, it is possible to increase the distance between the 7a film and the optical position detecting element, but due to non-uniform temperature changes from the outside, the laser light source, thin film, and optical position detecting element expand thermally. cause a slight change in position due to the "sled"
It appears as a signal equivalent to the change due to For this reason,
It is necessary to perform measurements in a much shorter time than the time required for temperature change.

In order to overcome this drawback, the present invention requires a device that generates a magnetic field that changes the magnetization state of the thin film at high speed.

As shown in Fig. 2, its specific configuration is such that a pair of magnetic field generating coils (or electromagnets) 5, 5 are provided on the left and right sides of the sample 4 onto which the laser light from the laser light source 2 is projected, and similarly A pair of magnetic field generating coils 6.6 are provided in the , and a coil power source 7 and a phase shifter 8 are connected to these two pairs of coils.
As a result, a temporally varying magnetic field is applied to the sample (material to be measured) 4, which consists of a thin film and a substrate, and the magnetization state within the thin film changes periodically, resulting in magnetostriction. “Sled” also causes periodic changes. The displacement of the laser reflected light caused by this is detected by the optical position detection element 3.
The voltage signal is measured as a voltage signal by the amplifier 9, and is enlarged by the amplifier 9 and recorded on the recorder 11 many times.

For the generation of a time-varying magnetic field, it is also possible to mechanically rotate only one pair of coils or electromagnets. As described above, in the present invention, a highly accurate magnetostriction measuring device can be obtained by using reflected laser light and providing a periodically changing magnetic field generating device.

In order to further improve accuracy, the present invention utilizes a phase detection method (lock-in amplifier 11) as shown in the figure. That is, a lock-in amplifier 11 is inserted between the amplifier (preamplifier) 9 and the recorder 10, which is an amplifier that has the function of amplifying and passing only signals of a specific frequency and blocking all other noise. Lock-in amplifier 1 uses a reference signal of the same frequency to determine this specific frequency.
1, but since a reference signal with the same frequency as this electric signal is generated in the coil power supply 7 that supplies periodic magnetic field current to the coils 5 and 6, if this is input into the lock-in amplifier 11, Only the necessary electrical signals pass through the lock-in amplifier 11, are expanded and rectified, and are recorded on the recorder 10 as DC signals.

Note that reference numeral 12 is an oscilloscope inserted into the circuit, FIG. 3 is for explaining how the signal waveform changes, and FIG. 4 shows an example of a specific device according to the present invention. In the figure, reference numeral 13 is a speaker for calibration, and Fig. 5 shows an example of the arrangement of measuring instruments. 17 is a function generator, 18 is an auto phase lock-in amplifier, 19.20 is a bipolar power supply, and 21 is a storage cabinet.

[Effects of the Invention] As described above, in the present invention, a laser beam is used to apply a periodic magnetic field change to a sample, and the reflected light due to the warpage caused in the sample is detected by an optical position detection element. Since it is converted into an electrical signal and measured, magnetostriction measurements of materials can be performed with high accuracy.
By installing a lock-in amplifier, other mechanical,
All electrical noise can be blocked, and even smaller "warpage" or magnetostriction can be measured.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the basic configuration of the present invention, FIG. 2 is a configuration diagram showing the specific configuration of the present invention, and FIG. 3 is an explanatory diagram showing the relationship between the detection configuration and detected waveform in FIG. 4 is a diagram showing an embodiment of the present invention, (a) is a plan view, (b) is a front view, (c) is a side view, and FIG. 5 is a control and display device for the device shown in FIG. 4. FIG. 6 is an explanatory diagram showing the basic configuration of the conventional device. 1a...Substrate, 1b...Thin film. 2... Laser light source, 3... Optical position detection element,
4... Sample (material to be measured), 5, 6... Coil, 7... Coil power supply, 8... Phase shifter,
9...Amplifier (preamplifier), 10...Recorder, 11...Lock-in amplifier.

Claims (2)

[Claims] (1) A pair or two pairs of magnetic field generators installed facing left and right or up and down with the material to be measured in between, a laser light source that irradiates toward the material to be measured placed in the magnetic field, and the material to be measured. A magnetostriction measurement device consisting of an optical position detection element that detects the displacement of laser reflected light due to magnetostriction displacement of a material. (2) A patent claim comprising a lock-up amplifier that detects the phase of a detection signal from an optical position detection element using a reference signal from a coil power supply that supplies a current that causes a synchronous magnetic field change to a magnetic field generator. The magnetostriction measuring device according to scope 1.