JPH0467132B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an automatic speed of sound measuring device using ultrasonic waves.

[Technical background of the invention and its problems]

BACKGROUND ART Conventionally, in order to determine the speed of sound passing through electronic component materials, etc., a method is known in which ultrasonic waves are injected into a sample and the reflected waves from the bottom of the sample are detected to determine the speed of sound. In particular, there is a method based on an ultrasonic phase comparison method that utilizes ultrasonic interference as a sound speed measurement position for determining the sound speed with high accuracy. Such a device is
A burst signal with a constant pulse width excites an ultrasonic transducer attached directly to one end of the sample or via a buffer load to emit a burst-shaped ultrasonic wave (incident wave), and this incident wave is transmitted to the sample. The waves are reflected off the bottom surface and received by an ultrasonic transducer. Then, by appropriately widening the pulse width of the burst signal, multiple reflected waves obtained from the bottom of the sample are superimposed one after another to cause interference, and the sound velocity of the sample is determined by determining the wave number of the carrier wave of the burst signal contained in the sample. . Specifically, the amplitude of the portion where reflected waves are multiplexed varies with the frequency of the carrier wave, and the wave number in the sample is an integral multiple (n-1,
n), the amplitude takes its minimum value, and the frequencies of the carrier waves of the corresponding burst signals are _o-1 and _o.The sound velocity of the sample, υ, is given by the thickness of the sample, υ=2l( _o − _{o- 1} )...It is expressed as (1).

Conventional sound speed measurement devices have a structure that reads the amplitude of the overlapping part of the combined waves by visually observing the combined waves drawn on an oscilloscope, and calculates the sound speed υ by finding the frequency at which the amplitude is minimum. Therefore, an error occurs due to visual inspection.

Therefore, the present inventors previously proposed an automatic speed of sound measuring device.

This automatic sound velocity measuring device is shown in FIG. This device is connected to a gate amplifier 3 of an oscillation circuit 1 consisting of an ultrasonic transducer 5, a gate amplifier 3, and a synthesizer of a conventional sound velocity measurement device, and has an envelope detector 8 for detecting reflected waves received by the transducer. A wave height detector 9 is provided, which is connected to the envelope detector 8 and detects the state of change in the amplitude of the reflected wave. The synthesizer 2
An oscillation circuit controller 10 for controlling the frequency of the gate amplifier 3 and the pulse width of the gate amplifier 3 is provided, and a storage circuit 11 connected to the oscillation circuit controller 10 and storing a frequency-converted signal to be output to the synthesizer 2 is provided. The structure includes a sound speed analyzer 12 which is connected to a storage circuit 11 and calculates the sound speed of the sample based on a predetermined frequency conversion signal stored in a storage circuit 11.
The characteristic point is that when the change state of the amplitude of the reflected wave detected by the wave height detector gradually decreases, a signal is sent from the wave height detector 9 to the oscillation circuit controller 10 such that the last amplitude takes the minimum value. Based on the signal, the storage circuit 11 reads out a frequency conversion signal corresponding to the signal, and the sound velocity analyzer 12 determines the sound velocity of the sample. If the amplitude of the reflected wave does not gradually decrease, the oscillation circuit control is performed. The speed of sound is determined by sending signals for controlling the frequency to the synthesizer 2 and the pulse width to the gate amplifier 3 using the device 10, and repeating the operation until the amplitude gradually decreases.

This device uses the frequency at which the amplitude reaches its minimum value.
_o-1 , _o , _o+1 ,... are stored in a memory circuit, and the sound speed is calculated using the following formula.

υ=2l・< _o − _o-1 > l: Thickness of the sample < _o − _o-1 >: Average value of the frequency interval when the amplitude shows the minimum value In order to take the average value of the frequency interval in this way ,
Measurement accuracy can be improved by performing measurements in as wide a frequency range as possible. However, ultrasonic transducers have a unique resonant frequency,
Transmission and reception sensitivity is excellent in the frequency range in the vicinity, but the sensitivity decreases as the frequency deviates from the resonance frequency. Therefore, the frequency range that can be used in sound speed measurements is limited, and there is a limit to the reduction in sound speed measurement errors that can be obtained.

[Purpose of the invention]

The present invention has been made in consideration of the above points, and
An object of the present invention is to provide an automatic sound speed measurement device that can automatically and accurately measure the sound speed of a sample.

[Summary of the invention]

The present invention provides an oscillation circuit comprising a synthesizer and a gate amplifier connected to the synthesizer, an ultrasonic transducer connected to the gate amplifier and sending a burst signal to a sample, and an ultrasonic transducer connected to the ultrasonic transducer and configured to transmit a burst signal to a sample. a reflected wave amplifier that amplifies the reflected wave received by the acoustic wave transducer; an envelope detector that is connected to the reflected wave amplifier and detects the reflected wave;
A wave height detector is connected to the envelope detector and detects changes in the vibration of the reflected wave; and a wave height detector is connected to the wave height detector and controls the amplification factor of the reflection amplifier based on the wave height detected by the wave height detector. With the output from the amplification factor controller and the wave height detector,
an oscillation circuit controller that controls the frequency of the synthesizer and the pulse width of the gate amplifier; a storage circuit that is connected to the oscillation circuit controller and stores a frequency-converted signal to be output to the synthesizer; This is an automatic sound speed measurement device characterized by comprising a sound speed analyzer that determines the sound speed of a sample based on a predetermined frequency conversion signal stored in the storage circuit.

The present invention is characterized by providing an amplification factor controller. If the first amplitude H ₁ of the group of reflected waves detected by the wave height detector is smaller than the set value H ₀ , the amplification factor of the reflected wave amplifier is adjusted by the amplification factor controller so that this H ₁ becomes greater than or equal to H ₀ . change.
If H ₁ ≧H ₀ , the amplification factor of the reflected wave amplifier is not changed, for example, the amplification factor is set to 1, and the process directly proceeds to the next operation. FIG. 2a shows the change in amplitude _H1 with frequency when such amplification factor control is performed. When the amplitude H ₁ is greater than or equal to the set value H ₀ , it is the same as when there is no reflected wave amplifier, and when H ₁ <H ₀ , H ₁ is held at H ₀ . Note that the solid line in the figure shows the change in H ₁ according to the present invention, and the broken line shows the change in H ₁ when no reflected wave amplifier is provided. F ₀ is the resonant frequency of the ultrasonic transducer. In addition, Fig. 2b shows the change in the peak value H _N of the Nth reflected wave in the group of reflected waves in the vicinity of the minimum frequency F _N (range H ₁ < H ₀ in Fig. 2 a). shows. In the present invention, since the amount of change in H _N can be increased, both the efficiency and accuracy when finding the minimum value of H _N are improved. Note that the solid line in the figure shows the change in H _N in the case of the present invention, and the dotted line shows the case where no amplification factor controller is provided.

By changing the amplification factor of the reflected wave in this way, it becomes possible to measure the sound speed in a wider frequency range than in the past, and it is possible to reduce errors in sound speed measurements. Further, by amplifying the reflected wave only when H ₀ <H ₁ or less, a uniform error can be maintained in a wide frequency range, and the measurement accuracy of the apparatus is further improved. In other words, in the conventional method, the accuracy is good near the resonant frequency of the ultrasonic transducer, but the accuracy decreases as you move away from this resonant frequency. Since the way in which errors are included changes,
The overall measurement error has increased.
However, in the present invention, when H ₀ < H ₁ , the amplification factor of the reflected wave is increased to improve accuracy, so it is possible to maintain a uniform error in a wide frequency range, reduce overall variation, and improve the accuracy of sound speed measurements. Improves accuracy.

〔Effect of the invention〕

As described above, according to the present invention, the speed of sound can be measured in a wide frequency range with a low error range, so the speed of sound of a sample can be measured accurately and automatically.

[Embodiments of the invention]

An embodiment of the present invention will be described based on FIG.
In the figure, the same numbers are used for the same parts as in FIG. 1. 1 in the figure is an oscillation circuit, which includes a synthesizer 2 that generates a continuous wave with a stable frequency;
It is comprised of a gate amplifier 3 connected to the synthesizer 2 and amplifying the continuous wave into a burst signal having a constant pulse width. An ultrasonic transducer 5 for sending a burst signal to the sample 4 is connected to the gate amplifier 3, and the ultrasonic transducer 5 is fixed onto the ultrasonic buffer load 6 on the sample 4 with adhesive. ing. Further, the gate amplifier 3 and the ultrasonic transducer 5 include an ultrasonic transducer 5.
An oscilloscope 13 is connected to draw the waveform of the reflected wave received by the oscilloscope 13. The oscilloscope is provided for waveform observation, and is not particularly necessary in the apparatus of the present invention.

Furthermore, an envelope detector 8 for detecting the reflected wave (composite wave) received by the ultrasonic transducer 5 is provided so as to be connected to the gate amplifier 3 and the ultrasonic transducer 5 via the reflected wave amplifier 7a. . A wave height detector 9 is connected to the envelope detector 8 to detect a change in the amplitude of the composite wave. An oscillation circuit controller 10 is connected to this wave height detector 9 via an amplification factor controller 7b, and when the amplitude of the composite wave gradually decreases, the last amplitude becomes the minimum value. A signal corresponding to the signal and other amplitudes are sent. Moreover, this oscillation circuit controller 10
are connected to the synthesizer 2, the gate amplifier 3, and a storage circuit 11 for storing frequency-converted signals output from the oscillation circuit controller 10 to the synthesizer 2, respectively. When the oscillation circuit controller 10 receives a signal from the wave height detector 9 in which the amplitude of the composite wave gradually decreases and the final amplitude does not become the minimum value, the oscillation circuit controller 10 transmits a frequency conversion signal to the synthesizer 2 and a frequency conversion signal to the gate amplifier 3. It sends a pulse width converted signal. Furthermore, when a signal is input from the wave height detector 9 in which the amplitude of the composite wave gradually decreases and the amplitude of the amount becomes the minimum, the oscillation circuit controller 10 stores the signal in advance in the storage circuit 11 corresponding to the signal. This function reads out the frequency-converted signal that has been converted. A sound velocity analyzer 12 for measuring the sound velocity of the sample 4 is connected to the memory circuit 11 . This sound speed analyzer 12
is the speed of sound analyzer 12 from the oscillation circuit controller 10.
It is read out using a frequency converted signal that is read out. Furthermore, the amplification factor controller 7b compares the set value H ₀ and the first wave height value H ₁ of the reflected wave, and determines that H ₁ <
If H ₀ , a signal is sent to the reflected wave amplifier 7a to change the amplification factor so that H ₁ ≧H ₀ . When H ₁ ≧H ₀ , the amplification factor is kept at 1.

The operation of the automatic speed of sound measuring device configured as described above will be explained. First, the oscillation circuit controller 10 sends a predetermined wind wave number conversion signal to the synthesizer 2 and a signal with a predetermined pulse width to the gate amplifier 3, respectively. Note that these signals are stored in the memory circuit 11.
Remember it. In response to the signal, the oscillation circuit 1 generates a burst signal having a predetermined frequency and pulse width. Next, the ultrasonic transducer 5 is excited by this burst signal to emit a burst-shaped ultrasonic wave (incident wave), and this incident wave is reflected by the bottom surface of the sample 4 through an ultrasonic buffer load 6 and synthesized. The ultrasonic transducer 5 receives the waves as waves. Next, the reflected wave amplifier 7a amplifies the combined wave. However, this amplification factor is controlled by an increase factor controller 7b. Subsequently, the envelope detector 8 detects the composite wave to draw an envelope with a predetermined pulse width, and the oscilloscope 18 observes the waveform of the composite wave. Figure 4 shows the relationship between amplitude and time. Here, as the envelope curve is shown in FIG. 4a, the pulse width W of the burst signal is 2l/υ (however,
(l is the thickness of the sample, υ is the sound velocity of the sample), and if W<2l/υ, the oscillation circuit controller 1
0, a signal with a pulse width such that W>2l/υ is sent to the gate amplifier 3. In addition, t ₀ in Figure 4 a
indicates the time for the ultrasonic waves to travel back and forth through the ultrasonic buffer road 2, and the Nth reflected wave that appears every 2l/υ is called the Nth reflected wave, and its peak value is H _N.

As shown in FIG. 2a, H ₁ decreases as it deviates from the resonant frequency F ₀ . Here, the wave height detector 9
Accordingly, the amplification factor controller 7b operates, a signal is sent to the reflected wave amplifier 7a, and the amplification factor of the reflected wave amplifier 7a is increased until H ₁ ≧H ₀ . If H ₁ ≧H ₀ , the amplification factor controller 7b does not operate.

If it is confirmed by the wave height detector 9 that the amplitude of the reflected wave (synthesized wave) does not gradually decrease as shown in the envelope shown in FIG. Continue feeding until the amplitude of the envelope gradually decreases as shown in FIG. 4c. In this case as well, the amplification factor controller 7b operates so that H ₁ ≧H ₀ . In addition, in Fig. 4 b and c, the Nth reflected wave, that is, t ₀ + (χ + 1)
×2l/υ time to t ₀ +χ×2l/υ time (χ=1,
The envelope of the composite wave appearing in 2, 3...N) is the first
The amplitude and phase of the reflected waves from the next to the χth order are synthesized. In particular, when the amplitude gradually decreases as shown in FIG. 4c, the range of fluctuation in the amplitude of the N×2l/υ-th composite wave is the largest, and the amplitude thereof is the smallest. Then, when an envelope as shown in FIG. 4c is drawn by the frequency conversion signal, a signal that minimizes the amplitude of the composite wave is sent from the wave height detector 9 to the oscillation circuit controller 10. Memory circuit 1
The frequency converted signal stored in step 1 is read out to the sound speed analyzer 12. However, the sound speed analyzer 12 determines the sound speed of the sample when the amplitude of the composite wave becomes the minimum value.

In the present invention, the peak value of the first reflected wave
By raising H ₁ to a certain level, it becomes possible to measure the speed of sound with the same error level over a wide frequency range. In particular, when detecting the peak value as a digital quantity, if the difference between the detected peak values is large,
When the peak value is small, that is, when it deviates from the resonant frequency, the error is large, and when it is near the resonant frequency, the error is small. However, as in the present invention, by raising H ₁ to a certain level and matching the levels, the errors can be made small and uniform, and the overall measurement accuracy is improved.

Using this device, the following measurements were performed. Length 200mm as ultrasonic buffer load 6,
A quartz columnar body with a diameter of 25 mm was prepared, and each end face was machined to be flat and parallel. Next, a taper was formed on one end so that the diameter of the end face was 15 mm and the angle with the side surface of the cylinder was 30°, and further,
Annular grooves with a depth of 1 mm were formed at 1 mm intervals on the outer peripheral surface of the cylinder including the tapered portion. As the ultrasonic transducer 5, a 20 MHz x-cut crystal oscillator with a diameter of 20 mm is used, and the sound speed of a cylindrical x-cut crystal (sample) with a thickness of 10 mm and a diameter of 30 mm is set to a frequency of 16 to 24 MHz.
When measured over a wide frequency range, the actual value was 5720.
It was confirmed that automatic measurement was possible within an error range of about ±5 m/sec. Although this is not equipped with a reflected wave amplifier or amplification factor controller, this is ±10m/
Compared to sec, we were able to improve the accuracy further.

In addition, in the above example, when measuring the sound velocity of the sample,
Although we have described the case where an ultrasonic buffer load is used between the sample and the ultrasonic transducer, it is not limited to this.
The sound velocity of the sample may be measured by attaching an ultrasonic transducer directly to the sample.

In addition, although an oscilloscope was used in the above example, this was only for checking the waveform of the composite wave received by the ultrasonic transducer, and it is expected that the same effect as in the above example can be obtained even without using an oscilloscope. can.

Furthermore, when an ultrasonic buffer load is used, heat is not directly transferred to the ultrasonic transducer, making it possible to measure the sound velocity over a wide temperature range, for example, from room temperature to about 950°C.

Since the ultrasonic transducer is bonded to the ultrasonic buffer load, it is easier to handle than when it is bonded to the measurement sample.

There are advantages such as

Also, when used for ultrasonic buffer load,
In order to prevent reflection from the side surface of the buffer load, it is preferable to provide a groove around the buffer load. Furthermore, by making the bonded portion with the sample tapered to reduce the bonding area, there is no risk of sample damage due to differences in thermal expansion. Further, it is preferable to provide a groove in this tapered portion as in this embodiment.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an automatic sound speed measurement device previously proposed by the inventor, Fig. 2 is a frequency-peak value characteristic curve, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4. is an amplitude-time curve diagram. 1...Oscillation circuit, 2...Synthesizer, 3...
Gate amplifier, 5... Ultrasonic transducer, 7a... Reflected wave amplifier, 7b... Amplification factor controller, 8... Envelope detector, 9... Wave height detector, 10... Oscillation circuit controller, 11 ...Memory circuit, 12...Sonic speed analyzer.

Claims (1)

[Claims] 1. An oscillation circuit consisting of a synthesizer and a gate amplifier connected to the synthesizer, an ultrasonic transducer connected to the gate amplifier and sending out a burst signal to the sample, and an ultrasonic transducer connected to the ultrasonic transducer. a reflected wave amplifier that amplifies the reflected wave received by the
an envelope detector that detects a reflected wave; a wave height detector that is connected to the envelope detector and detects a state of change in the amplitude of the reflected wave; and a wave height detector that is connected to the wave height detector;
When the first amplitude H ₁ of the group of reflected waves detected by this wave height detector is smaller than the set value H ₀ , the amplification factor of the reflected wave amplifier is controlled so that H ₁ ≧H ₀ , and the state an amplification factor controller that detects a changing state of the amplitude of the reflected wave with the wave height detector; and an oscillation circuit controller that controls the frequency of the synthesizer and the pulse width of the gate amplifier based on the output from the wave height detector; A memory circuit connected to the oscillation circuit controller and storing a frequency conversion signal to be output to the synthesizer; An automatic sound speed measuring device characterized by comprising a sound speed analyzer for determining the speed of sound.