JPH10300551A - Acoustic surface planimeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an acoustic surface planimeter by which the surface area of an object can be measured quickly and simply in the air by a method wherein the phase difference between outputs of a plurality of microphones is measured and the surface area of the object is computed on the basis of the phase difference when the object is put into a measuring container. SOLUTION: A conductor 18 and a conductor 19 are connected to a loudspeaker 6 via a terminal 8 and a terminal 9. A sine-wave driving signal at an angular frequency is supplied from a signal generator 16 through the conductors. An alternating volume change is given differentially to a measuring container 2 and a reference container 1 according to the surface or the rear of the diaphragm 7 of the loudspeaker 6. As a result, pressure changes, i.e., sound pressures, are generated at the inside of the measuring container 2 and the reference container 1. A microphone 11 detects the sound pressure at the inside of the reference container 1, its output is amplified by an amplifier 13 so as to become a sound-presure signal e1 , and the signal is fetched by a signal processing device 15. A microphone 12 detects the sound pressure at the inside of the measuring container 2, its output reaches an amplifier 14 through a terminal 10 so as to be amplified here, and it becomes a sound-presure signal e2 so as to be fetched by the signal processing device 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the surface area of an object of any shape or the internal surface area of a container of any shape by acoustic means.

[0002]

2. Description of the Related Art As a method for measuring the surface area of an object having an arbitrary shape, a so-called gas adsorption method has conventionally been used. This is done by putting an object in a measuring container and evacuating it.
Next, a method is used in which the object is heated to release the gas adsorbed on its surface, and the surface area is determined by obtaining the amount of the released gas from the pressure increase in the measuring container at that time.

[0003]

The above-mentioned gas adsorption method is
In addition to the trouble and time required for the measurement, there is also a problem that it cannot be applied to a living body such as a human, for example, because the inside of the measurement container is once evacuated or the object to be measured is heated.

[0004]

According to the present invention, when an object to be measured is placed in a measuring container and the inside of the container is acoustically driven,
The gas in the thermal boundary layer in contact with the surface of the object transfers heat to and from the object, causing a loss of acoustic energy. As a result, the real part of the acoustic impedance as seen from the mouth of the container is proportional to the surface area of the object. The change in the real part is detected as the phase change of the sound pressure inside the container, and the surface area of the object is obtained.

That is, one form of the surface area meter of the present invention is as follows.
A reference container, a measurement container, a speaker that differentially applies an alternating volume change to these two containers, two microphones that detect a pressure change inside each of these two containers,
The signal processing device measures the phase difference between the outputs of the two microphones.The signal processing device measures the phase difference between the outputs of the two microphones. Calculate the surface area.

[0006]

According to the surface area meter of the present invention as described above, the surface area can be obtained within a few seconds after an object is placed in the measuring container. Further, since there is no need to evacuate the inside of the measurement container or heat the object, the method can be applied to a living body. Further, since the main components used are acoustic components such as speakers and microphones, the manufacturing cost is low and the size of the device is smaller than that of the conventional device. Hereinafter, the working principle of the present invention will be described with reference to examples.

[0007]

First Embodiment In FIG. 1, reference numeral 2 denotes a measuring container having an empty internal volume V ₀ and an internal surface area S ₀ in which an object 3 having a volume V and a surface area S is placed. ing. 2
Assuming that the volume of the space between and 3 is V ₂ and the internal surface area of the space is S ₂ , they are expressed as follows.

(Equation 1)

(Equation 2)

[0008] 4 is a lid, and on the reference container of the internal volume V ₁ is attached to that. Containers 1 and 2 on top of lid 4
A communication pipe 5 is attached to a part forming a partition wall between
The insides of the containers 1 and 2 are communicated. A speaker 6 as a sound source is also attached to the partition. Reference numeral 7 denotes a speaker diaphragm. Conductors 18 and 19 are connected to the speaker 6 through terminals 8 and 9, and a sine wave drive signal having an angular frequency ω is supplied from the signal generator 16 through these conductors.
And the reference container 1 is given an alternating volume change differentially. As a result, the pressure changes inside the measurement container 2 and the reference container 1,
That is, a sound pressure is generated. Reference numeral 11 denotes a microphone for detecting a sound pressure inside the reference container 1, and its output is amplified by an amplifier 13 to become a sound pressure signal e ₁ , which is taken into a signal processing device 15. 12 is a microphone for detecting the measurement container 2 inside the sound pressure, the output of which written taken sound pressure signal e ₂ next signal processing device 15 is amplified here reaches the amplifier 14 through the terminal 10.

FIG. 2 shows an example of the configuration of the signal processing device 15. The sound pressure signals e ₁ and e ₂ are converted into digital quantities by analog / digital converters 151 and 152, respectively, and are taken into the digital computer 150. A frequency multiplier 155 multiplies the frequency of a synchronizing signal supplied from the signal generator 16 through the conductor 17 into a sampling pulse, and performs analog-to-digital conversion in synchronization with the sampling pulse. However, a clock pulse generator is provided inside the signal processing device 15, and the analog-to-digital conversion is performed independently of the signal generator 16.
It may be performed in synchronization with this internal clock pulse. In this case, the frequency multiplier 155 and the conductor 1
7 becomes unnecessary. The start of the analog-to-digital conversion starts from the digital computer 150 via the leads 153 and 15.
4 is controlled by the start pulse sent.

The digital computer 150 performs a Fourier transform of the sound pressure signals e ₁ and e ₂ , measures the phase difference θ of e ₂ with respect to e ₁ , and outputs the signal e if the measurement of the volume of the object is required. ₁ and respective amplitudes E ₁ and E ₂ of e ₂ is also measured. That is, in the digital computer 150, assuming that time is represented by t, the waveforms of the sound pressure signals e ₁ (t) and e ₂ (t) are represented by t
= T ₀ to t = t ₀ + T, and the Fourier transform is performed by integrating the product of the captured waveform with sinωt and cosωt with respect to t, but e ₁ (t) sinω
The integral of t is E _1S , the integral of e ₁ (t) cosωt is E _1C , e
₂ (t) sin .omega.t of the integral value E _2S, When E _2C an integral value of e ₂ (t) cosωt, the phase difference with respect to e ₁ (t) of e ₂ (t) from these values θ, e ₁ ( The amplitude E _{1 of} t) and the amplitude E ₂ of e ₂ (t) are obtained by the following equations, respectively.

(Equation 3)

(Equation 4)

(Equation 5)

In the above equation, G ₁ and G ₂ are constants including the gain of the analog-to-digital converter and the integration time T. The measurement of the phase difference and the amplitude is not limited to the above-described method using the Fourier transform, and various other known methods can be applied.

The communication pipe 5 functions to balance the static pressures inside the reference vessel 1 and the measurement vessel 2 and to equalize the components of the gas in the two vessels, but when the working gas is air,
Components such as humidity have little difference between the two containers. Therefore, instead of the communication tube 5, a capillary tube only for balancing the static pressure can be used. Also, unless the container is particularly tightly sealed, the static pressure inside the containers 1 and 2 is usually equal to the outside atmospheric pressure through the gap between the assembled device components. However, communication tubes and capillaries are not essential.

Assuming that the acoustic impedance when the internal space of the measuring container 2 is viewed from the speaker 6 is Z ₂ , when the size of the measuring container is sufficiently smaller than the wavelength of sound, Z ₂ is approximately as follows. Is represented.

(Equation 6)

(Equation 7)

(Equation 8)

In these equations, j is the unit imaginary number, γ is the specific heat ratio of the gas (about 1.4 in the case of air), P ₀ is the static pressure of the gas in the vessel, κ is the thermal conductivity of the gas, ρ Is the density of the gas,
c _p is the specific heat at constant pressure of the gas. [delta] _t denotes the thickness of the thermal boundary layer, but if the standard state of air, f = ω / 2π = 2
At 5 Hz, δ _t is about 0.5 mm.

If the argument of the acoustic impedance Z _{2 in} the equation (6) is αrad, it is as follows.

(Equation 9)

Since ε is very small compared to 1, the above equation is approximately obtained as follows.

(Equation 10)

The change in the argument α of the acoustic impedance appears as a change in the phase of the sound pressure inside the measuring container 2, but as shown in the equation (7), ε changes in proportion to the surface area S _2. 2 puts the measured object 3 in S
_{When 2} changes, the argument α changes, and the phase of the sound pressure inside the container 2 changes accordingly. Therefore, the surface area S of the measured object 3 can be known from the phase change of the sound pressure. This is the basic principle of the surface area meter of the present invention.

As described above, what is measured in this embodiment is that the phase difference between the signal e _{2 and} the signal e ₁ when the object 3 having the volume V and the surface area S is placed in the measuring container 2 is measured. Assuming that θ when the container 2 is emptied is θ ₀ , the following expression is derived from Expressions (1), (2), (7), and (10).

[Equation 11]

(Equation 12)

Equation (11) is an equation for measuring the surface area, and FIG. 3 is a graph of the equation. The empty volume V ₀ is obtained by measuring the internal dimensions of the measuring container 2, and the container 2 is empty. If the phase difference θ _{0 at this time} is measured in advance, the equation (1) is obtained by calibration using two standard objects whose volumes and surface areas are known.
The coefficient of 1) can be determined. That is, the volume V _A
In defining a point A in the graph of FIG. 3 the first standard object surface area S _A by measuring the phase difference theta _A at that time placed in a container 2, then the surface area S _B by volume V _B If the second standard object is put in the container 2 and the phase difference θ _B at that time is measured to determine the point B on the graph, a straight line connecting the two points A and B has a measurement formula in which the coefficient is determined. Represents This formula is generated and stored in the digital computer 150. If the volume V of the measured object 3 is known and its surface area S is unknown, the object 3 is placed in the measuring container 2 and the phase difference θ at that time is measured, and the value and the value of the volume V are stored in the above-described memory. The S / V can be determined by applying the measurement formula, and thus the value of the surface area S can be obtained.

In the above description, the internal volume V of the measuring container 2
_{Although 0} and the volume V of the measured object 3 are measured and known in advance by other methods such as dimensional measurement and the underwater gravimetric method based on Archimedes' principle, the surface area meter of the present invention has an arbitrary shape. It can also have a function as a volume meter that measures the volume of an object by acoustic means, displays the value of the volume of the object obtained using this function, and uses that value to measure the surface area of the object can do. Hereinafter, the function of the volume measurement will be described.

When the speaker 6 is driven by the signal from the signal generator 16 and the diaphragm 7 is pushed out at a certain moment and the volume V ₂ of the internal space of the measuring container 2 is compressed by a minute volume ΔV _S , The internal volume V ₁ of the container 1 is Δ
Inflate by V _S. Also, if [Delta] V _P becomes very small volume of gas into the measurement vessel 2 through the communicating pipe 5 flows, [Delta] V _P becomes the volume of gas flowing through the communicating pipe 5 from the reference container 1. At this time, the pressure changes occurring inside the reference container 1 and the measurement container 2 are -ΔP ₁ and ΔP ₂ , respectively.

(Equation 13)

The following is obtained from the relational expression of adiabatic change of gas.

[Equation 14]

(Equation 15)

From the above two equations, the following equation is obtained.

(Equation 16)

From the equations (1) and (16), the volume V of the measured object is expressed as follows.

[Equation 17]

In the above equation, since V ₀ and V ₁ are constant values, the volume V of the object is represented by the ratio ΔP ₁ / Δ
It will be obtained from the P _2.

In the digital computer 150, the amplitude ratio E ₁ / E ₂ of the sound pressure signal measured by the Fourier transform is used as a quantity corresponding to ΔP ₁ / ΔP ₂ in the above equation, and the volume of the object is calculated by the following volume measurement equation. Calculate the volume V.

(Equation 18)

FIG. 4 is a graph of the above equation. The coefficients V ₀ and V ₁ in this equation can be determined by calibration using a standard object whose volume is known. First, the measurement container 2 is emptied and V =
And 0 states, determine the R ₀ points on E ₁ / E _2-axis by the value R ₀ of the amplitude ratio E ₁ / E ₂ at that time, and then placed a standard object of volume V _C in the container 2 The value R of the amplitude ratio at that time
Be determined point C by _C, represents R _0, measurement equation linear coefficient connecting the two points C has been determined, that the straight line crosses the ordinate represents the value of V _0. Volume V of measured object 3
When both the surface area S and the surface area S are unknown, the object to be measured 3 is put into the measuring container 2 and V is first determined from the ratio E ₁ / E ₂ of the amplitudes of the signals e ₁ and e _{2 at} the time by the above volume measurement equation. Then, the phase difference θ between e ₁ and e ₂ is measured, the surface area S is calculated by the surface area measurement formula of the equation (11) using the value and the obtained volume V value, and the value is displayed. .

The method of measuring the volume described above is equivalent to measuring the absolute value | Z ₂ | of the acoustic impedance when the inside of the measuring container 2 is viewed from the speaker 6. As is clear from equation (6), | Z ₂ | is slightly affected by the surface area S ₂ , so that the volume V of the measured object 3 in the measurement container 2 is proportional to the surface area S, (Γ-1)
It is measured smaller than the true volume by δ _t S / 2. Therefore, the error is corrected using the value of the object surface area obtained by the method described above to obtain a more accurate volume measurement value, and the more accurate surface measurement value is obtained using the corrected volume measurement value. Can be obtained.

[0029]

Second Embodiment FIG. 5 shows an example in which the present invention is applied to the measurement of the internal surface area of a container. The reference container 1 and the speakers 6, the microphones 11, 12, the communication tube 5, the signal generator 16, and the signal processing device 15 attached thereto are the same as those in FIG. In the apparatus of FIG. 5, an adapter 22 having an internal volume V ₀ is fixedly attached below the reference container 1. Then, the reference container 1 is coupled to the measured container 23 having the internal volume V by placing the adapter 22 down on the container 23.
Here, the internal space and the internal space of the container to be measured 23 of the adapter 22 through the measurement hole 21 of the cross-sectional area S _H, constituting the acoustically closed one space inside the volume V ₀ + V.

The situation described above is equivalent to the situation in FIG. 1 where the object 3 in the measuring container 2 has a negative volume of -V. Therefore, the surface area measurement formula of the apparatus of FIG. 5 is obtained by substituting -V for V in formula (11). That is, the internal surface area S of the container 23 to be measured is measured by the following equation.

[Equation 19]

(Equation 20)

In the above, S ₀ is the internal surface area of the adapter 22 when the container 23 to be measured is taken and the measurement hole 21 is closed with a flat plate, and θ ₀ is the phase difference between the signal e _{2 and} the signal e _{1 at} this time. It is. S _X is the increment of the internal surface area when bound to the container to be measured 23 by taking the above flat plate 23
The internal surface area S of this _X
To become plus the cross-sectional area S _H of the measurement hole 21 obtained by separately measured. Further, similarly to the case of the equation (11), the internal volume V ₀ of the adapter 22 is known,
If θ ₀ is measured in advance, Equation (19) is determined by sequentially connecting two standard containers having known internal volumes and internal surface areas in place of the container 23 to be measured and performing calibration. Then, the measured container 23 whose internal volume V is known is connected, the phase difference θ at that time is measured, and the value and the value of V are applied to the above-described measurement formula to calculate S _X , Then, the internal surface area S of the container 23 to be measured is obtained by the equation (20).

As in the case of the apparatus of FIG. 1, the internal volume V _{0 of the} adapter 22 and the internal volume V of the container 23 to be measured can be obtained by the apparatus of FIG. The volume measurement equation at this time is the following equation obtained by substituting -V for V in equation (18).

(Equation 21)

As in the case of equation (18), the above measurement equation is determined by calibration using a standard container having a known internal volume. Then, a signal e ₁ when the measured container 23 is connected.
By the fitting ratio E ₁ / E ₂ of the amplitude of e ₂ in this-determined volumetric, displays the measured internal volume V of 23, also, the value used to calculate the internal surface area S of 23 Can be

[Brief description of the drawings]

FIG. 1 is a surface area meter according to an embodiment of the present invention.

FIG. 2 is an example of a configuration of a signal processing device in FIG. 1;

FIG. 3 is a graph of a surface area measurement formula.

FIG. 4 is a volume measurement type graph.

FIG. 5 is an application example of the present invention for measuring the internal surface area of a container.

[Explanation of symbols]

1 Reference container with internal volume V ₁ 2 Measurement container with empty internal volume V ₀ and internal surface area S ₀ 3 Object to be measured with volume V and surface area S 4 Lid 5 Communication tube 6 Speaker 7 Speaker vibration plate 8,9,10 terminals 11 and 12 microphones 13, 14 amplifier 15 signals measurement hole 22 inside the volume of the processing unit 16 the signal generator 17, 18, 19 lead 21 sectional area S _H is the internal surface area V ₀ S ₀ Adapter 23 Measurement container with internal volume V and internal surface area S

Claims (2)

[Claims] 1. A reference container, a measurement container, means for differentially applying an alternating volume change to the two containers, and means for detecting a pressure change inside each of the two containers,
Means for measuring a phase difference between the two detected pressure change signals, wherein the surface area of the object to be measured is determined by the phase difference when the object to be measured is placed in the measurement container. And a surface area meter. 2. A reference container coupled to the container to be measured, means for differentially applying an alternating volume change to the two containers, and means for detecting a pressure change inside each of the two containers. Means for measuring a phase difference between the two detected pressure change signals, and determining an internal surface area of the measured container by the phase difference when the reference container is coupled to the measured container. A surface area meter characterized in that: