JPH05273224A - Measuring apparatus for flow velocity - Google Patents

Abstract

PURPOSE:To easily and correctly measure the absolute value of the flow velocity irrespective of the concentration of a fluid in a flow velocity measuring apparatus which forms an image of particles in the fluid onto a detecting aperture of a predetermined size and measures the flow velocity of the fluid from several fluctuations of the image of particles passing the aperture. CONSTITUTION:The illuminating light for measuring purpose projected from a non-laser light source 18 which has an amplifying action of light illuminates the ocular fundus Er of a to be inspected eye E via an optical system including a lens 19 and the like. An image of particles in the blood flow of blood vessel of the fundus of the eye formed by the scattered light is focused on a detecting aperture 26 through a lens 17 to a mirror 25. The light of the image of particles passing the aperture is detected by a photomultiplier 27. The frequency of the numerical fluctuation of the image in the detecting aperture is analyzed by a frequency analyzer 28 from the output signals of the photomultiplier 27, and the flow velocity is calculated by a signal processor 29 based on the analyzing result. Since the illuminating light is not a laser light, the measurement is carried out correctly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow velocity measuring device for measuring an absolute value of a flow velocity of a fluid represented by particle velocity in the fluid by using light.

[0002]

2. Description of the Related Art Conventionally, as a method of non-invasively measuring the flow velocity of a fluid by using light, a method based on a laser Doppler phenomenon, a method based on a laser speckle phenomenon, and a number fluctuation of a particle image in a detection aperture are used. A method using is proposed.

When an absolute value is measured by a velocity meter based on the laser Doppler phenomenon, the amount of Doppler shift depends on the scattering geometry, so the scattering geometry must be limited, and when configuring a highly accurate laser Doppler velocity meter. Is required to be strictly limited to the scattering geometry, which is known to be difficult to manufacture and practically use.

The method utilizing the laser speckle phenomenon has a drawback in that the absolute value cannot be measured in principle, and some calibration is required, so that the calibration takes time.

On the other hand, the method utilizing the number fluctuation of the particle image in the detection aperture is an absolute measurable method in which optical adjustment is easy because it is sufficient to satisfy the imaging relationship. This method will be described with reference to FIG.

In FIG. 1, when laser light emitted from a laser light source 1 is applied to an optically transparent tube 2 in which a fluid to be measured flows, the laser light is scattered by particles 3 in the fluid flowing in the tube 2. The scattered light is diaphragm 4, lens 5
An image is formed on the rectangular detection aperture 6 by the image forming optical system.
That is, the image of the particle 3 is formed. Then, the light of the particle image that crosses the detection aperture 6 is detected by the photomultiplier tube 7, and the calculation processing based on the photon correlation method is performed by the detection signal. In this case, the autocorrelation function of the intensity of the detected signal is

[0007]

[Equation 1]

[0008] Where M: measurement volume / volume of coherent region, N: number of particles existing in detection aperture, | g (τ) | square: intensity due to phase fluctuation caused by scattering of laser light by particles Fluctuation autocorrelation function, f (τ): Autocorrelation function of intensity fluctuation due to fluctuations in the number of particles caused by particles crossing the detection aperture.

The second term of the above equation (1)

[0010]

[Equation 2]

Is a term generated when the phase of the laser beam is scattered and fluctuated by the particles and depends on the moving speed of the particles.

The third term

[0013]

[Equation 3]

Is a term produced by the number of particles present in the measurement volume varying with time as the particles pass through the measurement volume, which is also dependent on the moving speed of the particles.

The second term is multiplied by the reciprocal of the coherence degree M and the square of the number N of particles in the measurement volume as a coefficient,
The number of particles N is applied to the third term as a coefficient. Therefore, the better (smaller) the coherence degree M and the larger the number N of particles, the more dominant the term of phase fluctuation. Since the term of phase fluctuation is the speckle phenomenon itself, if the phase fluctuation becomes dominant, absolute measurement becomes impossible.

On the other hand, when the term of the number fluctuation becomes dominant, as shown in FIG. 2, the image 2'of the tube 2 is formed on the detection aperture 6 having the aperture size d, and the particle image 3'makes up the aperture 6 '. In the case of crossing, an autocorrelation function of triangular intensity fluctuation as shown in FIG. 3 is obtained. By measuring τ0 in FIG. 3, the particle velocity, that is, the flow velocity can be very easily measured from the relationship of (particle velocity) = (aperture size d) / τ0 (2).

Further, as a merit of using the number fluctuation, the time for the phenomenon to change is ten times or more as long as the phase fluctuation. Therefore, when detecting by the photon correlation method, the sampling time for counting photoelectron pulses is set to 1
It can be set to be 0 times or more longer, a sufficient number of detection counts can be obtained, the influence of counting fluctuation in photoelectron statistics can be suppressed, and the signal S / N ratio can be easily improved.
Therefore, it is more advantageous to use the phenomenon of the number fluctuation than the phase fluctuation.

[0018]

As described above, the method utilizing the number fluctuation of the particle image in the detection aperture is advantageous for measuring the flow velocity. However, when measuring a fluid using coherent light such as laser light with this method, the effect of the phase fluctuation component occurs depending on the concentration of the target fluid (particle number density), even when trying to measure the number fluctuation. There was a problem that caused an error.

Therefore, an object of the present invention is to provide a flow velocity measuring device for measuring a flow velocity by utilizing the number fluctuation of the particle image,
It is an object of the present invention to solve the above problems and provide a structure capable of accurately measuring a flow velocity regardless of the concentration of a fluid.

[0020]

In order to solve the above-mentioned problems, according to the present invention, an illumination light for measurement is generated in a flow velocity measuring device for measuring the flow velocity by utilizing the number fluctuation of the particle image. A non-laser light source, an optical system that guides the illumination light to a fluid to be measured, an optical system that forms a particle image of the scattered light of the illumination light scattered by the fluid on a detection aperture, and the optical system. Photoelectric conversion means for detecting the light of the image of the particle image, means for frequency-analyzing the frequency of the number fluctuation in the detection aperture of the particle image by the output signal of the photoelectric conversion means, and based on the result of the frequency analysis A structure having a calculation means for calculating the flow velocity of the fluid is adopted.

[0021]

According to such a configuration, by making the measurement illumination light non-laser light, it is possible to eliminate the influence of the phase fluctuation component based on the coherence of light that causes a measurement error. You can make accurate measurements.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. Here, a flow velocity measuring device for measuring the flow velocity of the fundus blood flow of the human eye is shown.

FIG. 4 shows a schematic structure of the flow velocity measuring device of the embodiment. In FIG. 4, reference numeral 8 is a fundus E of the eye E to be examined.
It is a halogen lamp which is a light source of observation illumination light for the examiner to observe r, and is arranged on a plane conjugate with the cornea of the eye E to be inspected. The light emitted from the halogen lamp 8 passes through the lens 9, the diaphragm 10 and the lens 11, is reflected by the color separation mirror 12 and forms an image on the ring slit 13. Then, the light passing through the ring-shaped opening of the ring slit 13 passes through the lenses 14 and 15 and is reflected by the perforated mirror 16, and the objective lens 17 forms a ring-shaped image in the vicinity of the cornea Ep of the eye E to be inspected. The fundus Er of E is illuminated.

On the other hand, reference numeral 18 is a non-laser light source having a light amplification function which is a light source of the illumination light for measurement and is similarly arranged on the corneal conjugate plane. As the non-laser light source 18, for example, a super luminescent diode L3302 (trade name) manufactured by Hamamatsu Photonics KK can be used. The light emitted from the non-laser light source 18 passes through the lenses 19, 20, and 21 and is guided from the color separation mirror 12 to the illumination optical system of the ring slit 13 to the objective lens 17, and similarly illuminates the fundus Er of the eye E to be examined. ..

The color separation mirror 12 is, as shown in FIG.
The light source for measurement, that is, the non-laser light source 18, transmits light in the emission wavelength range and reflects the other wavelength bands.

The scattered light of the observation illumination light and the measurement illumination light scattered by the fundus Er of the eye E to be examined is reflected by the objective lens 17,
The wavelength separation mirror 23 is reached through the hole of the perforated mirror 16 and the lens 22.

As shown in FIG. 6, the wavelength separation mirror 23 reflects the emission wavelength range of the measurement light source, that is, the non-laser light source 18, and the other wavelength bands (including the emission wavelength range of the halogen lamp 8). It shall have the property of transmitting.

The scattered light of the measuring illumination light is separated by the color separation mirror 23.
And is imaged on a rectangular detection aperture 26 of a predetermined size arranged on the fundus conjugate plane via the lens 24 and the mirror 25. That is, a particle image in the bloodstream is formed. Then, the light of the particle image that crosses the detection opening 26 is received by the photomultiplier tube 27 and photoelectrically converted, and the output signal is output from the frequency analyzer 2.
8, the frequency analysis of the number fluctuation of the particle image is performed, and the blood flow velocity is calculated by the signal processing device 29 based on the analysis result.

That is, the frequency analyzer 28 calculates the autocorrelation function of the intensity fluctuation due to the number fluctuation of the particle image from the output signal of the photomultiplier tube 27, and the signal processing device 29 uses the obtained autocorrelation function of the intensity fluctuation. Τ0 shown in Fig. 2
Then, the blood flow velocity is calculated from the equation (2). The calculation result is displayed on the monitor 30.

On the other hand, the scattered light of the illumination light for observation passes through the color separation mirror 23, reaches the eye S of the examiner through the mirrors 31, 32 and the lens 33, and observes the fundus Er of the eye E to be examined. You can

According to the present embodiment as described above, the influence of the phase fluctuation component based on the coherence of light which causes the above-mentioned measurement error is eliminated by making the measurement illumination light non-laser light. Is possible. In addition, when a normal non-laser light source such as a halogen lamp is used as the light source for the measurement illumination light, the brightness per unit area (or per unit solid angle) is low. However, by using the non-laser light source 18 having a light amplification function, it is possible to illuminate with high brightness and sufficient power, and obtain a sufficient amount of detected light. Therefore, the absolute value of the flow velocity can be easily and accurately measured even for a high-concentration fluid such as the blood flow in the fundus blood vessel.

[0032]

As is apparent from the above description, according to the present invention, a particle image in a fluid to be measured is imaged on a detection aperture having a predetermined size, and the number fluctuation of the particle image traversing the detection aperture is fluctuated. In a flow velocity measuring device for measuring the flow velocity of the fluid, a non-laser light source for generating illumination light for measurement, an optical system for guiding the illumination light to a fluid to be measured, and the illumination scattered by the fluid An optical system for forming a particle image by the scattered light of light on the detection aperture, a photoelectric conversion means for detecting the light of the formed particle image, and detection of the particle image by an output signal of the photoelectric conversion means. Since a structure having a means for frequency-analyzing the frequency of the number fluctuations in the aperture and a means for calculating the flow velocity of the fluid based on the result of the frequency analysis is adopted, the phase based on the coherence of light that causes a measurement error is adopted. Effect of fluctuation component It is possible to eliminate the absolute value excellent effect of easily and accurately performed measurements regardless flow rate on the concentration of the fluid to be measured can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a conventional schematic configuration for measuring a flow velocity using a number fluctuation of a particle image in a detection aperture.

FIG. 2 is an explanatory diagram showing a state in which a particle image crosses over a detection aperture.

FIG. 3 is a diagram showing an autocorrelation function of intensity fluctuation when a particle image crosses a detection aperture.

FIG. 4 is a configuration diagram showing a configuration of a flow velocity measuring device according to an embodiment of the present invention.

5 is a diagram showing the reflectance / transmittance characteristics of the color separation mirror 12 in FIG. 4 depending on the wavelength of light.

FIG. 6 is a diagram showing reflectance / transmittance characteristics of the wavelength separation mirror 23 in FIG. 4 depending on the wavelength of light.

[Explanation of symbols]

 8 Halogen Lamp 9, 11 Lens 10 Aperture 12 Color Separation Mirror 13 Ring Slit 14, 15 Lens 16 Perforated Mirror 17 Objective Lens 18 Non-laser Light Source with Optical Amplification 19-22 Lens 23 Wavelength Separation Mirror 24 Lens 25 Mirror 26 Detection Aperture 27 Photomultiplier tube 28 Frequency analyzer 29 Signal processing device 30 Monitor

Claims (2)

[Claims] 1. A flow velocity measuring device for forming a particle image in a fluid to be measured on a detection aperture having a predetermined size, and measuring the flow velocity of the fluid by the number fluctuation of the particle image traversing the detection aperture. A non-laser light source that generates illumination light, an optical system that guides the illumination light to a fluid to be measured, and a particle image formed by scattered light of the illumination light scattered by the fluid is formed on the detection aperture. An optical system, photoelectric conversion means for detecting the light of the formed particle image, means for frequency-analyzing the frequency of the number fluctuations in the detection aperture of the particle image by the output signal of the photoelectric conversion means, A flow velocity measuring device comprising a calculation means for calculating the flow velocity of the fluid based on the result of frequency analysis. 2. The flow velocity measuring device according to claim 1, wherein the non-laser light source is a light source having a light amplification function.