JPS6326349B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic generation and detection device that electromagnetically generates and detects ultrasonic waves.

Conventionally, when transmitting and detecting ultrasonic waves into metal materials for the purpose of inspection, etc., a piezoelectric vibrator or the like is vibrated and brought into contact with the material through a couplant such as water or oil. , it was necessary to achieve acoustic coupling. For this reason, it has been difficult to apply it to high-temperature materials, materials with rough surfaces, etc. Therefore, there has been a desire for a device that can transmit and detect ultrasonic waves into materials without contacting them.

Such a device is already known and details are described in Japanese Patent Laid-Open No. 52-92781. A device based on this is shown in FIG. In FIG. 1, 1 is a material having a conductive surface, 2 is an iron core of an electromagnet for generating a magnetic field in the vicinity thereof, and an excitation coil 3 is wound around this iron core 2. The excitation coil 3 is adapted to be supplied with power from a current source 4. Further, an excitation coil 5 and a detection coil 6 are arranged at the lower end of the iron core 2. The excitation coil 5 is used to generate an eddy current in the material 1, and the detection coil 6 is used to generate an eddy current in the material 1. It is for detecting current.

7 is a high-frequency pulse power supply, which includes a high-voltage DC power supply 8, a charging resistor 9, a capacitor 10, and a discharge tube 11.
The output of this high frequency pulse power source 7 is sent to the excitation coil 5.

Further, the output signal of the detection coil 6 is amplified by an amplifier 12 and then displayed on an oscilloscope 13. In FIG. 1, the excitation coil 5
Although the detection coil 6 is depicted realistically, the second
The figure shows the connection relationship, and the output ends of the high frequency pulse power source 7 are connected to both ends of the excitation coil 5, and the detection coil 6 is electromagnetically coupled to the output ends of the excitation coil 5.

Next, the operation of the conventional ultrasonic wave generation and detection device will be explained. When a current is passed through the excitation coil 3 by the current source 4, a magnetic field is generated by the electromagnetic iron core 2 near the surface of the material 1 having a conductive surface.

On the other hand, the excitation coil 5, discharge tube 11, and capacitor 10 are connected in series. capacitor 10
is charged by the high voltage DC power supply 8 through the charging resistor 9. When the voltage across the terminals of the capacitor 10 is charged to a certain voltage or higher, discharge occurs within the discharge tube 11, causing the excitation coil 5, the discharge tube 11, and the capacitor 1 to
0 constitutes a series resonant circuit, and a high frequency pulse current flows through the excitation coil 5.

This pulsed current causes an eddy current to flow on the surface of the material 1. This eddy current generates ultrasonic waves due to interaction with the magnetic field generated by the iron core 2. The generated ultrasonic waves are reflected from the bottom surface of the material 1, reach the vicinity of the surface again, and generate eddy currents due to interaction with the magnetic field. After this eddy current is detected by the detection coil 6, it is amplified by the amplifier 12 and displayed on the oscilloscope 13.

The conventional ultrasonic generation/detection device has an excitation coil 5
and the detection coil 6 are arranged in parallel, a voltage is directly induced in the detection coil 6 by the high-frequency pulse current flowing through the excitation coil 5, and if the high-frequency pulse current is increased in order to increase the sensitivity. The voltage induced in the detection coil 6 becomes extremely large and destroys the input section of the amplifier 12. Alternatively, a protection circuit is required to prevent this. Further, there is a drawback that the cables between the detection coil 6 and the amplifier 12 are required to withstand high voltage.

In order to solve these problems, a method has already been devised and is disclosed in Japanese Patent Application Laid-open No. 143388/1983.

An example of this is shown in FIG. 2A. This 2A
In the figure, 5 is an excitation coil, and 61 and 62 are a detection coil A and a detection coil B provided to sandwich the excitation coil 5, and these coils are placed facing the material 1 to be inspected. In this way, the two flat detection coils 61 and 62 are stacked parallel to the surface of the material to be inspected 1 with a space between them, and the two detection coils 61 and 62 are Since the connection is arranged so that the direction of the power source is opposite, and the detection outputs of both detection coils 61 and 62 are summed, the voltage induced in the detection coil by the excitation coil 5 can be canceled when viewed from the output terminal. For this purpose, induction by the excitation coil 5 must occur equally in each of the detection coils 61 and 62. This can be achieved by making the distances from the excitation coil 5 to the detection coils 61, 62 the same if the detection coils 61, 62 have the same shape and size. However, in this case, if the distance between the excitation coil 5 and the detection coils 61 and 62 is narrow, the detection coil 61 approaches the detection coil 62 and operates differentially with respect to the ultrasonic signal to be detected. , the detection efficiency will decrease. Furthermore, if the distance between the excitation coil 5 and the detection coils 61, 62 is widened, the excitation coil 5 will be separated from the surface of the material to be inspected 1, and the efficiency of ultrasonic wave generation will be reduced. Providing and differentially connecting two detection coils in this way is effective in canceling the induction caused by the excitation signal, but has the disadvantage of lowering the efficiency of the transducer. Since electromagnetic ultrasonic waves have extremely low efficiency, devices configured to reduce efficiency as described above have a major drawback in practice.

This invention was made to eliminate the above-mentioned conventional drawbacks, and by providing a transformer whose primary side is connected in series with the excitation coil and whose secondary side is connected in series with the detection coil, the excitation coil is connected in series with the detection coil. It is an object of the present invention to provide an ultrasonic generation/detection device that can prevent high voltage from being induced in a detection coil due to a high-frequency pulse current flowing through the coil.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the ultrasonic wave generation and detection device of the present invention will be described below with reference to the drawings. FIG. 3 is a circuit diagram showing only the excitation coil 5, the detection coil 6, and their vicinity in one embodiment, and the same parts as in FIG. 2 are given the same reference numerals. In FIG. 3, the part of the magnetic field generating device including the iron core 2, excitation coil 3, and current source 4 in FIG. 1 is not shown, but this part is constructed in the same manner as in FIG. 1.

In this FIG. 3, a transformer 14 is a newly added part according to the present invention.
has a primary winding 15 and a secondary winding 16, and 1
The secondary winding 15 and the excitation coil 5 are connected in series. Both ends of the series circuit formed by the primary winding 15 and the excitation coil 5 are connected to the output end of the high frequency pulse power source 7.

Similarly, the secondary winding 16 and the detection coil 6 are connected in series, and both ends thereof are connected to the input end of the amplifier 12. The other parts are constructed in the same manner as in FIG. 2.

The transformer 14 is sufficiently far away from the excitation coil 5, the detection coil 6, and the surface of the material 1, so that there is no electromagnetic coupling therewith.

Next, the operation of the ultrasonic wave generation and detection device of the present invention configured as described above will be explained. The operation of the ultrasonic generation and detection device of the invention will be explained with reference to the waveform diagrams shown in FIGS. 4a to 4d.
4a to 4d are waveform diagrams of e _a to e _d in FIG. 3, respectively, with the horizontal axis representing time and the vertical axis representing voltage. Detection coil 6 and transformer 1
The voltage across the terminals of the series circuit with the secondary winding 16 of 4 is ( _ed + e _{c )} , but the voltage across the secondary winding 16 is
The coupling of the transformer 14 is connected to the excitation coil 5 so that the phases of the voltage e _c and the voltage e _b across the detection coil 6 are opposite to each other.
By reversing the connection between the voltage and the detection coil 6, the voltage _ed across the series circuit can be made smaller than the voltage _eb .

Further, if the coupling strength of the transformer 14 is adjusted so that the absolute value of the voltage e _c becomes equal to the absolute value of the voltage e _b , the voltage e _d becomes zero.

Next, the ultrasonic waves that have arrived at the surface of the material 1 generate eddy currents by the action of a magnetic field generated separately by a magnetic field generator, and this eddy current is transmitted to the detection coil 6.
Detected by The signal detected by the detection coil 6 is input to the amplifier 12 through the secondary winding 16 of the transformer 14 . At this time, the primary side of the transformer 14 includes a capacitor 10, a discharge tube 11, and a primary winding 1.
5. The excitation coils 5 are connected in series, but are cut by the discharge tube 11. Therefore, the circuit of the detection coil 6, secondary winding 16 and amplifier 12 is completely unaffected by the state of the primary side of the transformer 14.

Now, in FIG. 3, the excitation coil 5, the primary winding 15 of the transformer 14, the discharge tube 11, and the capacitor 10 are connected in series, and when the voltage between the capacitor terminals exceeds a certain voltage, the discharge tube 11, a series resonant circuit is formed, and a high-frequency pulse current flows through the excitation coil 5 and the primary winding of the transformer 14. The waveform of the voltage e _a between the terminals of the excitation coil 6 at this time is as shown in FIG. 4a.

Since the excitation coil 5 is provided near the surface of the material 1 having a conductive surface, it functions exactly the same as the excitation coil 5 in a conventional ultrasonic generation/detection device, and generates an eddy current in the material 1. Ultrasonic waves are generated by interaction with a separately generated magnetic field.

At this time, since the detection coil 6 is provided near the excitation coil 5, a voltage is applied to the detection coil 6.
e _b is induced. On the other hand, the primary winding 1 of the transformer 14
5 induces a voltage e _c in the secondary winding 16 closely coupled to it.

The above explanation has been made separately for excitation and detection, but when the voltage at each part is plotted with time on the horizontal axis, it becomes as shown in Figure 4, which is clear from Figure 4. In this way, during excitation, no high voltage is induced between the detection coil 6 and the terminals of the secondary winding 16 of the transformer 14, and only the signal that detects the ultrasonic wave appears as an output.

By the way, the voltage e _b induced in the detection coil 6 during excitation depends on the physical characteristics of the material 1, etc., even if the applied voltage e _a and the geometric arrangement of the excitation coil 5 and the detection coil 6 are constant. Therefore, if the coupling coefficient between the primary winding 15 and the secondary winding 16 of the transformer 14 can be adjusted, it can be applied to various materials.

In the above embodiments, the generation of ultrasonic waves was shown to be due to the interaction between the eddy current caused by the high-frequency pulsed current and a separately generated magnetic field. It may be due to action.

Although the transformer 14 is shown in FIG. 3 as being provided near the excitation coil 5 and the detection coil 6, it may also be provided near the high voltage pulse radio wave 7 and the amplifier 12. Further, the discharge tube 11 has a withstand voltage,
The switching element is not limited to a discharge tube as long as it has a specification that satisfies the withstand current.

As described above, according to the ultrasonic generation and detection device of the present invention, the primary winding of the transformer is connected in series with the excitation coil to supply the output of the high-frequency pulse power source, and the secondary winding of the transformer and the detection coil are connected in series to suppress the induction of high voltage, especially on the detection coil side, which prevents damage to the receiver and eliminates the need for a protective device. In addition, a weak electric signal cable can be used from the detection coil to the receiver, resulting in low cost and high reliability.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of a conventional electromagnetic-mechanical ultrasonic generation/detection device, and Fig. 2 is a diagram clearly showing the connection between the excitation coil and detection coil of the conventional ultrasonic generation/detection device. , FIG. 2A is a diagram showing the relationship between a conventional excitation coil and a detection coil, FIG. 3 is a circuit diagram of a portion excluding magnetic field generation in an embodiment of the ultrasonic generation/detection device of the present invention, and FIGS. FIG. 4d is a diagram showing voltage waveforms at various parts in FIG. 3. 1... Material, 2... Iron core, 3... Excitation coil,
4...Current source, 5...Excitation coil, 6...Detection coil, 7...High frequency pulse power supply, 12...Amplifier, 14...Transformer, 15...Primary winding, 16...
...Secondary winding. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A magnetic field generator provided near a material having a conductive surface, an excitation coil that generates an eddy current using a pulse current from a high-frequency pulse power source, an ultrasonic wave in the material, and the magnetic field generator. A detection coil and a primary winding are connected in series with the excitation coil, and the output of the pulse power source is supplied to both ends of the series circuit. and a transformer in which the secondary winding is connected in series with the detection coil so that the voltage induced in the secondary winding is in the opposite direction to the voltage induced in the detection coil; 2
An ultrasonic generation and detection device comprising means for amplifying and displaying an induced voltage across a series circuit of a next winding and the detection coil. 2. The ultrasonic generation and detection device according to claim 1, characterized in that the coupling coefficient between the primary winding and the secondary winding of the transformer is made variable.