JPH0310072B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting plate waves caused by electromagnetic ultrasound.

A conventional device of this type is shown in FIG. In the figure, 1 indicates the first excitation coil 2 and the first
A first electromagnet with an inner core that receives current from a first DC power source 4 and generates a magnetic field, and 5 has a rectangular wave shape in which the coil sides are connected in series as shown in FIG. The vibration generating coil shown in the drawing has a grid-like shape in which the coil sides are connected in parallel and receives a signal from the pulser 6, and the first electromagnet 1 and the vibration generating coil 5 form a transmission transducer 7. Further, 8 is a second electromagnet 12 in the form of an inner core, which is composed of a second excitation coil 9 and a second iron core 10 and receives current from a second DC power supply 11 to generate a magnetic field in the same direction as the first electromagnet 1 described above. is Figure 2a,
A vibration detection coil that has one of the shapes shown in FIG.
and form a receiving transducer 15.
Further, reference numeral 16 denotes a sample plate made of a conductive material, and the transmitting transducer 7 and the receiving transducer 15 are provided on the sample plate 16 at a predetermined distance apart, and a transmitting signal is transmitted between them as indicated by an arrow 17. The plate wave 18 is configured to propagate from the transducer 7 side to the receiving transducer 15 side.

Note that FIGS. 3a to 3d show the states of the magnetic field, eddy current, etc. when a plate wave is generated in the plate wave transmitter/receiver. Among them, FIGS. 3a and 3b relate to plate waves generated by the longitudinal wave generation method, and FIGS. 3c and d relate to plate waves generated by the transverse wave generation method.

In FIG. 3a, H is the magnetic field given by the first electromagnet 1 and horizontal to the sample plate 16, Ji
(i=1, 2, 3, 4) means that when a pulse current is applied as shown in the vibration generating coil 5 having the shape shown in FIG. 2a and having four coil sides, the sample plate 16
Eddy current induced in the surface layer, Fvi (i=1, 2,
3 and 4) are the directions according to Fleming's left hand rule due to the horizontal magnetic field H and eddy current Ji, that is, the direction of the sample plate 16
With the Lorentz force acting in the vertical direction as shown in the figure,
The Lorentz force Fvi excites a plate wave 18 as shown in FIG. 3b.

On the other hand, in FIG. 3c, unlike FIG. 3a, the direction of the magnetic field V is perpendicular to the sample plate 16 as shown. Therefore, even if the direction of the eddy current Ji (i=1, 2, 3, 4) induced by the conduction of the vibration generating coil 5 is the same as that in FIG. 3a, the magnetic field V and the eddy current Lorentz force whose direction is determined by the direction of Ji
Fhi (i=1, 2, 3, 4) appears in alternating directions on a plane parallel to the plane of the sample plate 16, as shown in FIG. 3c. However, this Lorentz force
Fhi excites a plate wave 18 as shown in FIG. 3d.

The vibration modes of the plate wave 18 excited in this way are the a mode in which the front and back surfaces of the sample plate 16 vibrate as shown in FIG. 4a, and the a mode as shown in FIG. 4b. An s-mode in which the front and back surfaces of the sample plate 16 are symmetrically vibrated is considered.

Next, the operation of the conventional plate wave electromagnetic ultrasonic detection device having the above-described configuration will be explained. In the following explanation, a case will be explained in which plate waves are generated by a longitudinal wave generation method, but it goes without saying that the same explanation can be made in a case where a transverse wave generation method is used.

In order to excite the plate wave, first, the first DC power supply 4
Using the first electromagnet 1, a static magnetic field V is generated in a direction perpendicular to the surface of the sample plate 16. After that,
When a pulse current P is supplied from the pulser 6 to the vibration generating coil 5, the coil pitch D of the vibration generating coil 5 is
Eddy currents J ₁ , J ₂ , J ₃ , J ₄ are induced in the surface layer of the sample plate 16 at equal intervals, and the Lorentz force Fhi (i=
1, 2, 3, 4) occur in the direction of the arrow shown in FIG. 3c. Among these Lorentz forces, Lorentz forces Fh ₁ and Fh ₂ and Fh ₃ and Fh ₄ compress the composition particles of the sample plate 16, respectively, while Lorentz forces Fh ₂ and Fh ₃ compress the composition particles of the sample plate 16. By pulling the particles, the surface layer of the sample plate 16 expands and contracts, causing vibrations as shown by the broken line in FIG. 3d, which propagate in the direction of the arrow 17 shown in FIG. 1 and in the opposite direction.

Note that if the coil pitch D of the vibration generating coil 5, the material and plate thickness of the sample plate 16 are kept constant, and the frequency of the transmitted pulse current P is changed, the a mode, the s mode as shown in FIGS. 4a and 4b, and even the Various higher-order mode plate waves can be generated and propagated.

On the other hand, plate wave detection can be performed by a receiving transducer having the same configuration as the transmitting transducer 7, based on the opposite principle to plate wave generation and according to Fleming's right-hand rule.

That is, in the reception transducer 15, first, DC excitation is performed using the second DC power supply 11 and the second electromagnet 8, and a static magnetic field V perpendicular to the surface of the sample plate 16 is generated as in the transmission side. In this state, the sample plate 1 facing the vibration detection coil 12
When the plate wave 18 propagates to the part 6, an eddy current is generated by the interaction between the static magnetic field V and the vibration.
The alternating magnetic field generated by the eddy current interlinks with the vibration detection coil 12, and a voltage is induced in the vibration detection coil 12. This induced voltage is amplified by an amplifier 13, and a determiner 14 determines the propagation time and the magnitude of the received signal based on the amplified signal. Note that when the sample plate 16 vibrates with the maximum amplitude, the eddy current generated in the surface layer also reaches the maximum, so if the coil pitch D of the vibration detection coil 12 is matched to the wavelength of the plate wave, plate waves can be detected efficiently. be able to.

Furthermore, regarding the relationship between the pulse current P and the plate wave B generated by its energization, and the relationship between the plate wave B and the detection signal S captured by the vibration detection coil 12, please refer to FIGS. 5 and 6. Explain in detail.

Now, when a pulse current P corresponding to the coil side spacing as shown in FIG. Vibrations similar to the pulse current P are simultaneously excited in the opposite portions of the coil sides 5a to 5d of the coils 5, and these are propagated as waves in the x direction shown in FIG. Waves B5a to B5d excited by the coil sides 5a to 5d are shown in FIGS. 5c to 5f, respectively. As is clear from comparing these figures, each wave B5a to B5d starts excitation based on the position of each coil side, so the vibration points for the same pulse current value are different by the distance between the coil sides. There is. Therefore, the plate wave B, which is the composite wave, has a spatial spread as shown in FIG. 5g. In addition, in the meander line coil, the current direction of the adjacent coil sides is opposite, resulting in vibration waves B5a and B5c.
Although the phases of B5b and B5d are temporally inverted, they are spatially in the same phase, so that a plate wave B with a large amplitude as shown in FIG. 5g is formed.

This plate wave B (see FIG. 6b) propagates through the sample plate 16, and the vibration detection coil 1 as shown in FIG.
When reaching the opposite part of 2, according to the principle described above,
A voltage signal S is induced in the vibration detection coil 12 . FIGS. 6c to 6f show the waveforms of voltage signals S12a to S12d induced to the coil sides 12a to 12d of the vibration detection coil 12 at this time, respectively. As is clear from these figures, a voltage is induced in sequence from the coil side 12a on the transmitting side to the coil side 12d furthest from the transmitting side, shifted by a predetermined time period corresponding to the coil spacing. Therefore, the detection signal S, which is the composite wave, has a very large temporal spread as shown in FIG. 6g, and is sent to the determiner 14. Note that FIG. 7b shows a composite detection signal S when the number of coil sides of the vibration detection coil 12 is eight (see FIG. 7a). As is clear from this figure, when the number of coil sides is 8, the selectivity Q of the circuit is higher than when there are 4 coil sides.
Therefore, although the S/N ratio becomes good, the spread of the signal A becomes even larger.

Conventional plate wave electromagnetic ultrasonic detection devices are configured as described above, so if you try to increase the S/N ratio, the signal spreads and the resolution deteriorates, and if you try to increase the resolution, the S/N ratio decreases. , the drawback was that one had to be sacrificed.

The present invention has been made in view of the above points, and includes a plurality of sets of vibration detection coils having the same shape and parallel coil sides arranged in parallel, and signals from each vibration detection coil being arranged in parallel. The object of the present invention is to provide a plate wave electromagnetic ultrasonic detection device which has a configuration in which the signals are synthesized after passing through a delay circuit and sent to a determiner, and which can improve the S/N ratio without deteriorating the resolution.

Hereinafter, one embodiment of the present invention will be described with reference to FIG. 8, in which parts that are the same or have the same effect as those in FIG. 1 are given the same reference numerals. The configuration of the transmitting side of the apparatus of the present invention is the same as that of conventional apparatuses using electromagnetic or other methods, so only the configuration of the receiving side is shown in FIG. In the figure, reference numerals 19a to 19c are vibration detection coils each consisting of a meander line coil, and as shown in FIG. 9, the corresponding coil sides are arranged in parallel with each other. Also, 20a~
20c are vibration detection coils 19a to 19, respectively.
buffer amplifiers 21a, 21 for amplifying any one of the signals S19a to S19c from c;
b is a delay circuit that delays the signal from the buffer amplifier 20a or the buffer amplifier 21a, and 22 is an adder circuit that delays the signal from each vibration detection coil 19a to 19c to the delay circuits 21a and 2.
1b to make them in phase, and then add them.

Next, the operation of the receiving side having such a configuration is first explained.
This will be explained with reference to FIG. Inside the sample plate 16,
When a pulsed plate wave propagates from the transmitting side and reaches the receiving side under the influence of the magnetic field, an eddy current is generated in the surface layer of the sample plate 16, and this causes each vibration detection coil 19a to 19c to Electric signals S19a to S19c (see FIG. 10) corresponding to the eddy currents are induced, respectively. These guidance signals S19a to S19c
Although the corresponding coil sides of the coils 19a to 19c are arranged side by side, the positions of the coils are slightly different, so that the induction start times are made different as shown in the figure. That is, the vibration detection coil 19a disposed furthest from the transmitting side starts to induce vibration by a time ΔT ₂ earlier than the vibration detecting coil 19c disposed farthest from the transmitting side, and the intermediate vibration detecting coil 19b begins to induce vibration. Induction starts a time ΔT ₁ earlier than the detection coil 19c. Therefore, in order to make the composite plate wave efficient, first, the detection signal S19a and the detection signal S19b are sent to the delay circuits 21a and 2, respectively.
1b, the signals are delayed by time ΔT ₂ and time ΔT ₁ to bring all the detection signals into the same phase. Thereafter, the adding circuit 22 combines the signals that have become in phase and sends the synthesized signal to the determiner 14. By doing so, the signal used for determination will have an amplitude three times that of each detection signal, resulting in a good S/N ratio and favorable resolution. Note that the delay time △ set in each of the above-mentioned delay circuits 21a and 21b
T ₁ and △T ₂ are determined to satisfy the following formula.

△T ₁ = L ₁ /v, △T ₂ = L ₂ /v (However, L ₁ is the positional deviation distance between the vibration detection coil 19b and the vibration detection coil 19c, and L ₂ is the displacement distance between the vibration detection coil 19a and the vibration detection coil 19c. , and v is the propagation speed of the plate wave.

In the above embodiment, the outputs of the vibration detection coils are individually delayed and then added together. However, as shown in FIG. Good, similar effects can be expected. In addition, 22 in this Figure 11
a and 22b each represent an adder circuit. Also,
Although the above-mentioned embodiment shows an example in which three vibration detection coils are applied, it is needless to say that the number is not limited to this number as long as it is possible to implement the vibration detection coils. Furthermore, in the above embodiment,
Although a method of applying a vertical magnetic field to the surface of the sample plate has been shown, a method of applying a horizontal magnetic field may also be used. Furthermore, although we have shown a case where a linear meander line coil is used as the vibration generation/detection coil, various shapes such as a curved meander line coil as shown in Fig. 11, a linear or curved grid coil, etc. A curved meander line coil can be used to focus and diverge plate waves, and a grid coil can be used to improve the impedance of the coil. The effect can be expected that the current input type buffer amplifier can be easily used because of the low power consumption. Further, in the above embodiment, the coil sides are spaced at equal intervals, but depending on the purpose, they do not necessarily have to be at equal intervals.

As described above, according to the present invention, a plurality of vibration detection coils are arranged so that the corresponding coil sides are arranged in parallel, and a delay circuit is used to correct a waveform shift due to a shift in the arrangement position. Since the configuration is such that the signal is added and sent to the determination device, the amplitude of the signal used for determination is increased, and a plate wave electromagnetic ultrasonic detection device with good sensitivity and a good S/N ratio can be obtained. .

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional plate wave electromagnetic ultrasonic detection device, Fig. 2 is a schematic diagram showing the shape of the vibration generation/vibration detection coil in the device shown in Fig. 1, and Fig. 3 is an explanation of the principle of plate wave generation. Fig. 4 is an explanatory diagram showing a typical mode of plate wave vibration mode, Fig. 5 is an operation waveform diagram for explaining the process of plate wave generation, and Fig. 6 is an explanatory diagram for explaining the process of plate wave detection. Detection signal waveform diagram,
FIG. 7 is a waveform diagram similar to FIG. 6 when there are many coil sides, FIG. 8 is a block diagram showing a plate wave electromagnetic ultrasonic detection device according to an embodiment of the present invention, and FIG. 9 is a diagram showing the device shown in FIG. 8. 10 is a waveform diagram of the detection signal in the device shown in FIG. 8, FIG. 11 is a block diagram showing an embodiment of the detection signal processing section, and FIG. 12 is a vibration detection It is a schematic diagram showing various shapes of a coil. 8... Electromagnet, 11... DC power supply, 16... Sample plate, 19a to 19c... Vibration detection coil, 2
1a, 21b...delay circuit, 22...addition circuit.
In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A transmission transducer equipped with a vibration generating coil having coil sides arranged parallel to the sample plate surface and a magnet mechanism that applies a magnetic field horizontally or perpendicularly to the sample plate surface, and the above sample plate. A vibration detection coil having a coil side arranged parallel to the plate surface and a magnet mechanism that applies a magnetic field horizontally or perpendicularly to the sample plate surface, and comprising a receiving transducer provided at a distance, and a determiner receiving a signal from the vibration detection coil,
In the plate wave electromagnetic ultrasonic detection device, the vibration of the sample plate transmitted by the transmitting transducer is captured by the vibration detection coil, and the judge determines the properties of the sample plate based on the detection signal. Multiple sets of detection coils are provided with the same shape and the corresponding coil sides are arranged in parallel, and a delay circuit is provided corresponding to each vibration detection coil to respectively delay and output the detection signal from each vibration detection coil, and each delay circuit output is A plate wave electromagnetic ultrasonic detection device comprising: an adder that adds the sum and outputs the result to the determination device.