JP2007108099A - Acoustic velocity measuring method and instrument of high resolution for fluid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acoustic velocity measuring method and an instrument of high resolution capable of measuring an acoustic velocity at 1 ppm of resolution even under a pressurized condition, and capable of knowing clearly a delicate change in the volume or elasticity of a substance or a substance contained therein. <P>SOLUTION: A sound wave is generated and detected in a resonator by the same transducer, an acoustic cavity (acoustic resonator) is thereby compactified and a measuring system is thereby simplified. A required sample amount is reduced further (sound path length 3 mm, sample amount 10 μl), and a temperature is easily stabilized in addition thereto. When generating/detecting a signal compatibly by the same transducer, a sound wave signal propagated through a route other than an input signal or the sample is favorably removed to detect only a resonance sound wave signal in the sample. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a high-resolution sound velocity measuring method and apparatus for fluid.

  In recent years, in the field of new materials and biological sciences, it has been required to measure changes in volume and elastic modulus of substances with extremely high accuracy for physical property research and material evaluation methods. For example, a sound velocity resolution of about 1 ppm is required to detect a state in which a protein molecule in a 0.1% protein aqueous solution changes in volume by 0.1% depending on pressure and temperature. When high resolution becomes possible, real-time interactions between antigens and antibodies without labeling can be observed. The realization is a powerful physical property research and material evaluation method.

Therefore, various methods and apparatuses are currently being used to measure subtle changes in the volume and elastic modulus of a substance and the substance contained therein. For high-accuracy measurement, the resonance method based on sound velocity measurement is usually used. For example, a commercially available device for high resolution and high pressure has the following examples.
(1) Resonic ResoScan type sample volume is 0.2mL, resolution is 10ppm, high pressure support is a special specification, can be up to 250MPa, and the operating temperature is 5-85 ℃.
(2) Ultrasonic Scientific HR-US102 type sample volume is 1mL (custom order 0.03mL is acceptable), resolution 0.1ppm, high pressure 0.5MPa is possible, working temperature: -40 ~ + 150 ℃.

In addition, there has been proposed an acoustic cell that measures the resonance frequency in the acoustic cell and determines the sound velocity and the acoustic impedance based on the measured values. (Patent Document 1)
US Patent Publication No. 2005 / 0043906A1

However, the conventional methods and apparatuses have the following problems especially when trying to use them under high pressure, and it has been extremely difficult to measure with high accuracy.
(1) It is difficult to improve the temperature stability and uniformity in the high-pressure vessel.
In a conventional commercially available device in which the vibration source and the detector are composed of separate transducers, the sound wave generation unit and the detection unit become complicated in order to increase the resolution, the entire device becomes larger, and temperature stability is impaired. Result.

Further, in the apparatus of Patent Document 1, the resonance frequency to be measured is a composite acoustic cell including a container, not a single sample, but the sound path length is fixed, and a large number of resonance frequencies are obtained up to higher order. In order to determine the sound velocity and the acoustic impedance from the characteristics of the frequency region where the resonance frequency shift occurs due to the reflection effect on the wall, it is necessary to separately know the acoustic impedance of the tube material, and it is not possible to obtain a high-resolution sound velocity.

(2) A large amount of sample is required for measurement.
Furthermore, in the conventional method / apparatus, since it is difficult to measure with high accuracy for a very small amount of measurement sample, the sample to be measured is limited.
(3) The acoustic cell is deformed by high pressure.
In addition, for example, under an ultrahigh pressure of 200 MPa or more, the acoustic cell is deformed, and high-precision measurement becomes difficult.

The present invention has been made in view of such circumstances, and it is possible to measure the speed of sound with 1 ppm resolution even under pressure, and to clearly know the subtle changes in the volume and elastic modulus of the substance and the substance contained therein. It is an object of the present invention to provide a high-resolution sound speed measurement method and apparatus that can be used.

In order to achieve the above object, the present inventor has paid attention to the following points as a result of intensive studies.
(Points of interest)
Sound waves are generated and detected in the acoustic cavity (acoustic resonator) by the same transducer, which makes the acoustic cavity small and simplifies the measurement system. By reducing the size of the acoustic cavity, the amount of sample required for measurement can be reduced, and temperature stabilization can be facilitated. Therefore, since the generation and detection of the signal is also performed by a single transducer, the configuration is such that only the resonance sound wave signal in the sample can be detected by successfully removing the input signal and the sound wave signal propagating through the path outside the sample.

  As a result of focusing on the above, the present invention is configured as follows. According to the first aspect of the present invention, an acoustic cavity having a known length is filled with a sample to be measured, the inside of the acoustic cavity is vibrated by sound wave generating means disposed at both ends of the acoustic cavity, and the frequency of the vibration is The resonance frequency at which resonance in the acoustic cavity is generated is detected by the sound wave detection means, the sound path length of the acoustic cavity is modulated by the means for modulating the acoustic cavity length, and the resonance frequency is And a method of measuring the speed of sound in a sample, characterized by measuring the speed of sound based on the modulated sound path length.

  The invention according to claim 2 proposes a method of measuring the speed of sound in a sample according to claim 1, wherein the sound wave generating means and the sound wave detecting means arranged in the acoustic cavity are performed by the same transducer.

The invention according to claim 3 is characterized in that the reflection wall of the acoustic cavity is vibrated at a low frequency, the acoustic cavity container length is modulated, and the output signal is synchronously detected at the modulation frequency. We propose a method for measuring the speed of sound in a sample.

  According to a fourth aspect of the invention, there is provided the method for measuring a sound velocity in a sample according to any one of the first to third aspects, wherein a flexible piezo transducer is used as a reflector for the modulation of the acoustic cavity container length. suggest.

  The invention according to claim 5 is characterized in that the acoustic cavity is disposed in a high-pressure vessel to eliminate a pressure difference between the acoustic cavity and the high-pressure vessel. A method for measuring the speed of sound in a sample is proposed.

  The invention according to claim 6 sweeps the acoustic cavities filled with the sample to be measured, transducers for generating sound waves disposed at both ends of the acoustic cavities, and the frequencies of sound waves generated by the transducers for generating sound waves. Means for detecting the resonance frequency at which resonance in the acoustic cavity occurs, and means for modulating the length of the acoustic cavity, the detected resonance frequency and the modulated acoustic cavity being included. We propose a device for measuring the speed of sound in a sample characterized by measuring the speed of sound by the length of a tee.

  The invention according to claims 7 to 10 relates to the sound speed measuring device in the sample according to claim 6, and is a sound speed measuring device in the sample that performs the sound speed measuring method in the sample according to any of claims 2 to 6. .

According to the present invention configured as described above, the above-described problems are solved as follows.

(1) Resolution of issues 1 and 2
In this method, generation and detection of sound waves in the resonator are performed by the same transducer. This allows for a smaller acoustic cavity and simplifies the measurement system. By making the acoustic cavity extremely small, the amount of sample required for measurement can be reduced (in the embodiment, the sound path length is 3 mm, the sample amount is 100 μl), and temperature stabilization is facilitated.

However, when the signal generation / detection is also performed by a single transducer, it is necessary to detect only the resonance sound wave signal in the sample by successfully removing the input signal and the sound wave signal propagating through the path outside the sample. For this reason, a method is adopted in which the acoustic cavity is modulated by vibrating the reflecting wall of the resonant container at a low period, and the output signal is synchronously detected at the modulation frequency. This improved the SN and improved the signal selectivity. For the modulation of the acoustic cavity, a flexible piezo transducer was used as the reflector.

(2) Solution to Problem 3
The acoustic cavity according to the present invention used under high pressure has a flow hole connecting the inside and the outside. With this structure, there is no static pressure difference between the inside and outside of the acoustic cavity, and it is possible to manufacture the resonator thinly. Deformation is minimized and temperature control is easy.
(3) Summary As described above, according to the present invention, the generation and detection of sound waves in the acoustic cavity are performed by the same transducer, and the input signals and the sound wave signals propagated through the path outside the sample are successfully removed. Only the resonant sound wave signal in the sample is detected. For this reason, the above problem is solved with a very simple configuration by adopting a method and apparatus that modulates the acoustic cavity by vibrating the reflecting wall of the resonant container at a low period and synchronously detects the output signal at the modulation frequency. can do.

Embodiments of the present invention (hereinafter referred to as the present invention) will be described below with reference to the drawings.

A first embodiment of the present invention is shown in the figure.
(1) Overall Configuration FIG. 1 shows a configuration diagram (block diagram) of a high-resolution sound velocity measuring method and apparatus according to the present invention. Use the resonance method. The sample is filled in the sample chamber 5 of the acoustic cavity shown in FIG. 2, and the signal generator SG vibrates one end wall of the acoustic cavity at the frequency f to detect the vibration state in the acoustic cavity. A frequency fr at which resonance occurs in the acoustic cavity by sweeping the frequency f is measured by a lock-in amplifier. The speed of sound is determined from the measured resonance frequency and tube length. The electrical circuit configuration for this purpose will be described in (3) below.

(2) Configuration of acoustic cavity Further, a schematic diagram of the acoustic cavity is shown in FIG. An X-cut quartz piezoelectric element 1 (in the example, a fundamental frequency of 10 MHz, a diameter of 7 mm, a thickness of 0.3 mm, and an electrode diameter of 3 mm) was used for generation and detection of a sound wave having a frequency f. A piezoelectric flexible metal plate 2 (Murata Manufacturing Co., Ltd. 7BB-12-9, diameter 12 mm, thickness 0.2 mm) was used as a reflector.
The acoustic cavity consists of a metal resonance tube (outer diameter 13 mm, inner diameter 6 mm, length 0.30 mm). At one end, the X-cut quartz piezoelectric element 1 is attached as a sound wave generating / detecting element driven by the electrode 3. A piezoelectric flexible metal plate 2 is attached to the end as a reflection plate. The piezoelectric flexible metal plate 2 is bent and deformed by an external voltage, thereby changing the sound path length of the acoustic cell. In the embodiment, an AC voltage (frequency f _m = 1 kHz, voltage 0.1 V _pp ) is applied to the piezoelectric flexible metal plate 2 to modulate the sound path length. A small hole (diameter 0.6 mm in the embodiment) 4 is opened in the body of the acoustic cavity so that the sample to be measured can enter and exit from the sample chamber 5.

(3) Configuration of electrical signal system FIG. 3 shows an electrical connection diagram of the present invention. A signal generator SG is used to apply a voltage of frequency f to the crystal resonator R (X-cut crystal piezoelectric element 1 in this embodiment). The coil L establishes electrical matching between the signal generator SG and the crystal resonator R. A high frequency acoustic frequency in the voltage output from the acoustic cavity is detected by a diode D. The detected signal is synchronously detected at the modulation frequency f _m of the sound path length, and the voltage and phase are measured. For this measurement, a commercially available lock-in amplifier LA (NF Co. LI-575 type in this example) was used. As shown in FIG. 1, sweep of the excitation frequency f, recording of the detection signal, and temperature control are controlled by one PC.

(4) When performing measurement under high pressure or changing the pressure, an acoustic cavity is installed in the high pressure container (not shown). Since the fluid can enter and exit through the holes 4 of the acoustic cavity body, no pressure difference is generated inside and outside the acoustic cavity even under high pressure.

(5) Temperature control According to the study by the present inventors, it is necessary to stabilize the temperature of the sample and the acoustic cavity within ± 0.01 K in order to measure the sound velocity with 1 ppm resolution. Since this device is small, a temperature stability of ± 1 mK can be easily achieved by installing it in a constant temperature bath ((7) Reference 1 below).

(6) Measurement Result Example In the present invention configured as described above, FIG. 4 shows a graph of the modulation signal intensity A of the measurement results when the frequency is swept. This figure shows six resonance spectra (resonance frequencies fr: 9.1633, 9.3911, 9.6056, 9.810, 10.015, and 10.235 MHz) of the crystal-water composite resonance system. Using these resonance frequencies, we were able to determine the sound velocity of water (1500 m / s) that was consistent with the literature value from the analytical formula of the composite resonator model derived by Miller and Bolef (reference document 2). By determining the value of the resonance frequency fr with a resolution of 10 Hz, a change in sound velocity of 1 ppm can be detected. However, in order to improve the accuracy of the measured sound speed, it is necessary to increase the number of effective digits of the sound path length.
(7) References References related to the above (5) and (6) are presented below.
1) K. Tozaki, C Ishii, O. Izuhara,
N. Tsuda, Y. Yoshimura, H. Iwasaki, Y. Noda and A. Kojima: Rev. Sci. Instrum. 69
(1998) 3298.
2)
JGMiller and JGBolef: J. Appl.Phys., 39 (1968) 4589.

(About application)
In the present embodiment, a high-resolution sound velocity measuring method and apparatus using ultrasonic waves have been described. However, with a similar configuration, an underwater sound velocity meter in which water or a low-concentration aqueous solution is filled in an acoustic cavity formed by audible sound waves, It can be applied as a high-precision volume meter. In addition, since it can be made extremely small, the acoustic cavity can be put into a small container and remotely operated and measured like an IC tag, or it can be used for acoustic detection of NMR signals of substances in fluids in combination with a magnetic field. is there. Thus, it can be applied to various measuring devices and control devices.

  As described above, according to the present invention, the speed of sound can be measured with very high resolution under pressure and while changing the pressure. This makes it possible to clearly know the subtle changes in the volume and elastic modulus of a substance and the substance contained in it, enabling powerful physical property research and material evaluation methods, and is extremely useful.

Device configuration diagram Acoustic cavity Electrical connection diagram Example of measurement results (figure of measurement signal intensity with respect to excitation frequency f)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Quartz piezoelectric element 2 ... Piezoelectric flexible metal plate 3 ... Electrode 4 ... Sound cavity hole 5 ... Sample chamber
SG ... Signal generator
L ... Coil
D ... Diode
LA ... Lock-in amplifier R ... Quartz crystal

Claims (10)

Fill the acoustic cavity with the sample,
A sound wave is generated in the sample by a sound wave generating means disposed in the acoustic cavity;
Sweep the frequency of sound wave vibration,
Detect the resonance frequency of the frequency swept by the sound wave detection means,
Modulating the acoustic path length of the acoustic cavity by means for modulating the acoustic cavity length;
A method of measuring sound speed in a sample, characterized by measuring sound speed based on the resonance frequency and the modulated sound path length. 2. The method of measuring sound velocity in a sample according to claim 1, wherein the sound wave generating means and the sound wave detecting means arranged in the acoustic cavity are performed by the same transducer. The acoustic cavity length is modulated by vibrating the wall of the acoustic cavity at a low frequency,
3. The method of measuring the speed of sound in a sample according to claim 1, wherein the output signal from the transducer is synchronously detected at a frequency by the modulation. 4. The method for measuring the speed of sound in a sample according to claim 1, wherein said means for modulating the acoustic cavity length uses a flexible piezo transducer as a reflecting plate. Place the acoustic cavity in a high pressure vessel,
The method for measuring the speed of sound in a sample according to any one of claims 1 to 4, wherein a pressure difference between the acoustic cavity and the high-pressure vessel is eliminated by circulating the acoustic cavity and the high-pressure vessel. An acoustic cavity to fill the sample;
Transducers for generating sound waves disposed at both ends of the acoustic cavity;
Means for sweeping the frequency of the sound wave generated by the transducer for generating the sound wave;
Means for detecting a resonance frequency of a frequency swept by a transducer for generating the sound wave;
Means for modulating the length of the acoustic cavity,
An apparatus for measuring the speed of sound in a sample, wherein the speed of sound is measured based on the detected resonance frequency and the length of the modulated acoustic cavity. 7. The sound velocity measuring apparatus in a sample according to claim 6, wherein the transducer for generating the sound wave and the means for detecting the resonance frequency at which the resonance in the acoustic cavity is generated are the same. 7. The apparatus according to claim 6, further comprising means for vibrating the wall surface of the acoustic cavity at a low frequency, modulating the acoustic cavity length, and synchronously detecting an output signal from the transducer at a frequency by the modulation. 7. An apparatus for measuring the speed of sound in a sample according to any one of 7 above. 9. A sound velocity measuring apparatus in a sample according to claim 8, wherein said means for modulating the acoustic cavity length is a reflector using a flexible piezo transducer. The acoustic cavity is placed in a high pressure vessel,
10. The sound velocity measuring device in a sample according to claim 6, wherein a flow hole for eliminating a pressure difference between the acoustic cavity and the high-pressure vessel is disposed in the acoustic cavity.