JPH03194470A - Flow velocity measuring instrument - Google Patents

Abstract

PURPOSE:To measure a slow flow velocity and discriminate the direction of the flow by irradiating a reflection body with ultrasonic wave beams which differ in frequency in an intersecting state, receiving a reflected wave which has a beat signal corresponding to the movement of the reflection body due to an interference standing wave, and analyzing its frequency. CONSTITUTION:The ultrasonic waves beam which are generated by a 1st oscillator 11 and a transmitter 1, and a 2nd oscillator 12 and a transmitter 2 and differ in frequency by a frequency shift DELTAf intersect each other and the interference standing wave is generated at the intersection part. The reflected ultrasonic wave beam which has the beat signal corresponding to the movement of the moving reflection body based upon the interference standing wave from the flow 4 is received by a receiver 5, and processed by a detector 14 and a Fourier transformer (FFT) 15 to analyze its frequency, thereby deciding the flow velocity from the movement position of a beat frequency waveform part moving from the frequency DELTAf part and the flow direction from the moving direction. Thus the slow flow velocity can be measured and even the direction of the slow flow velocity is also surely detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a flow velocity measuring device using ultrasonic waves, and more particularly to a flow velocity measuring device using interference standing waves of ultrasonic waves.

(Prior Art) When the optical paths of light emitted from two laser light sources intersect, a standing wave is generated. When a moving object passes through this standing wave, it causes frequency fluctuations that are proportional to the speed of the object. A method for determining the flow velocity by applying this phenomenon to ultrasonic waves has been announced. The principle of flow rate measurement using this phenomenon will be explained with reference to FIG. In the figure, the first transmitter 1
When continuous wave ultrasound beams of wavelength λ emitted from the first transmitter 1 and the second transmitter 2 intersect at an angle of 2θ, the ultrasound beam from the first transmitter 1 and the ultrasound beam from the second transmitter 2 intersect. A standing wave is generated at the intersection 3, and interference fringes with an interval d shown in the following equation are formed.

λ Now, if we consider that one moving object 4 passes through the intersection 3 where this standing wave exists at a speed of ■, the moving object 4
When the receiver 5 receives an echo signal from the waveform, the envelope becomes a signal with fluctuations corresponding to the shape of the standing wave. The period T of this fluctuation signal of the envelope line, that is, the beat signal, is as shown in the following equation.

T=λ/V・・・・・・(2)(2)
As clearly seen from the equation, the period T becomes shorter if the moving speed of the moving object 4 is faster, and becomes longer if the moving speed is slower. FIG. 4 shows the waveform of a received signal having a beat signal due to this echo. The period T of this beat signal is as shown in the figure. Flow velocity measurement using this method has the following advantages compared to the Doppler method.

With the Doppler method, it is possible to measure extremely low flow velocities that are difficult to determine n1.

Unlike the Losperacle velocity measurement method, there is no probabilistic factor in measurement accuracy, so it can be measured in a short time.

In the hasberacle velocity measurement method, the scatterer density is sufficiently high to form a speckle region.
However, with this method, measurement is possible even when a single scatterer passes through.

(Problem to be Solved by the Invention) By the way, in the flow velocity measurement method that utilizes interference standing waves generated by the intersection of two identical frequencies as described above, it is possible to measure the flow velocity or the moving speed of an object (hereinafter referred to as flow velocity). However, unlike the Doppler measurement method, it is not possible to know the direction of movement. Knowing the direction of flow is an important issue in medical ultrasound systems.

The present invention has been made in view of the above points, and its purpose is to realize a current velocity measuring device that can measure the direction of flow without losing the advantages of the current velocity measurement method using interference standing waves. be.

(Means for Solving the Problems) The present invention for solving the above problems includes a first oscillator that generates a signal with a frequency higher than a certain reference frequency by a certain deviation frequency, and an output of the first oscillator. a first transmitter that generates an ultrasonic wave according to a signal and irradiates the ultrasonic beam at a certain angle to a target; a second oscillator that generates a signal of a certain reference frequency; and the second oscillator. a second transmitter that generates a frequency of a signal from the first transmitter and emits an ultrasonic beam that intersects at a certain angle near the target with respect to the irradiation beam of the first transmitter; The speed and direction of movement of the reflector from the reflector present at the intersection are determined based on the moving standing waves generated at the intersection between the ultrasonic beams emitted from the wave transmitter and the second transmitter. a receiver that receives a reflected wave having a beat signal derived from the waveform, a reception amplifier that amplifies the reflected wave signal from the receiver, a detector that detects the received signal, and a frequency The method is characterized by comprising an FFT for analysis.

(Function) At the intersection of the ultrasonic beam from the first transmitter and the ultrasonic beam from the second transmitter with a slightly different frequency, a constant beam moves at a speed proportional to the frequency difference. Wave presence occurs. The reflected signal from the fluid passing through this intersection is
Since the beat frequency has a certain relationship between the moving speed of the standing wave and the flow velocity, the flow velocity can be determined from the position of the reflected signal in the frequency spectrum.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of a circuit according to an embodiment of the present invention and a diagram showing standing waveforms. In the figure, parts equivalent to those in FIG. 3 are given the same reference numerals. In the figure, 11 is the frequency f1+
A first oscillator 12 oscillates a signal of frequency f and supplies the signal to the first transmitter 1, and a second oscillator 12 oscillates a signal of frequency f and supplies the signal to the second transmitter 2. In this case, the reference frequency f and the deviation frequency Δf are appropriately selected as necessary. 13 is a receiving amplifier that amplifies the echo signal from the moving object 4 or a fixed object at the intersection 3 which the receiver 5 receives and converts into an electrical signal; 14 is a detector that detects the output signal of the receiving amplifier 13; , its output is FF
The frequency is analyzed at T15 and output to the next circuit.

Next, the operation of the embodiment configured as described in item 1 will be explained, but first, the principle of this embodiment will be explained.

The frequency of the ultrasonic beams to be crossed is slightly shifted, and the first
If the frequency of the transmission signal from the transmitter 1 is f1 + Δf and the frequency of the transmission signal from the second transmitter 2 is f, and there is a difference of Δf between the two frequencies, the intersection 3 The resulting standing wave moves at a constant speed as shown by the arrow in the figure. It can be seen that this moving speed is equal to the value of the flow velocity at which no beat frequency occurs in the reflected wave from the flow. That is, when the moving speed of the standing wave is equal to the moving speed of the object, the intensity of the reflected wave from the object does not always change, so no beat frequency occurs.

In this case, a nasty side effect is that the fixed object's echo is modulated by the beat of its frequency difference, Δf. In this case, it is sufficient to make sure that there are almost no fixed reflection sources in the intersection 3, or else to remove the reflected waves using a strong notch filter. In the method of the embodiment in which the beams are intersected with a frequency difference of Δf, the fixed object has a certain beat frequency, that is, Δf, and a fluid flowing more slowly in the same direction as the moving direction of the standing wave. Since the fluid flowing in the opposite direction appears at a frequency lower than the beat frequency Δf, and the fluid flowing in the opposite direction appears at a frequency higher than the beat frequency Δf of the reflected wave from the fixed object, directional separation becomes possible.

Next, returning to the apparatus shown in FIG. 1, its operation will be explained. 1st
The oscillator 11 generates a signal with a frequency of f and +Δf to generate the first signal.
Supplied to the transmitter 1. The second oscillator 12 generates a signal of frequency f and supplies it to the second transmitter 2. The ultrasonic beam emitted from the first transmitter 1 and the ultrasonic beam emitted from the second transmitter 2 intersect at an intersection 3. The standing wave generated at this intersection 3 is directed from the first transmitter to the second transmitter 2 at a speed proportional to the frequency difference Δf between the transmitted beams emitted from the two transmitters. move towards. The receiver 5 receives a reflected signal from an object at the intersection 3 or a fluid flowing through the intersection 3, converts it into an electrical signal, and inputs the output signal to the reception amplifier 13. The signal amplified by the receiving amplifier 13 is detected by the wave detector 14, frequency-analyzed by the FFT 15, and output to the next circuit. The waveform of the signal subjected to frequency analysis in this FFT 15 is as shown in FIG. In the figure, 20 is an echo from a fixed target,
The beat frequency appears at Δf. Reference numeral 21 indicates an echo from the fluid, which indicates a case where the flow is moving in the opposite direction to the moving direction of the standing wave, and a beat frequency higher than Δf is output. Since the beat frequency due to the fluid having the same speed as the moving speed of the standing wave is O, the beat frequency due to the echo of the fluid in the same direction as the moving speed of the standing wave increases from Δf on the frequency axis toward 0 as the speed increases. The beat frequency due to echoes of the fluid that is moving and equal to the moving speed of the standing wave, i.e. 0
The beat frequency changes up to .

Therefore, Δf may be appropriately determined depending on the velocity of the flow to be measured.

As explained above, according to this embodiment, not only can extremely slow flow velocities starting from the velocity O be measured, but also the direction of the flow can be identified.

(Effects of the Invention) As explained in detail above, according to the present invention, it is possible to determine nj of an extremely low-velocity flow, and the flow velocity can be determined by observing the beat frequency caused by a slight movement. Measurement is possible. Moreover, in addition to the advantage that measurements can be made by the passage of just one scatterer, it is also possible to determine the direction of movement of the scatterer, which has a great practical effect.

[Brief explanation of drawings]

Figure 1 is a diagram showing a circuit according to an embodiment of the present invention and the standing waveform generated. Figure 2 is a diagram of the frequency spectrum obtained with the circuit in Figure 1. Figure 3 is an ultrasound beam of the same frequency. FIG. 4 is a diagram of the signal obtained from the crossed ultrasonic beams of FIG. 3. 1...First transmitter 2...Second transmitter 3.
...Intersection 4...Moving object (flow) 5
...Receiver 11...First oscillator 12
...Second oscillator 13...Reception amplifier 14.
...Detector 15...FFT2O...Echo from fixed target 21...Echo from fluid

Claims (1)

[Claims] A first oscillator (11) that generates a signal with a frequency higher than a certain reference frequency by a certain deviation frequency, and an ultrasonic wave generated by the output signal of the first oscillator (11). , a first transmitter (1) that irradiates an ultrasound beam at a certain angle to the target
), and a second oscillator (12) that generates a signal at a certain reference frequency.
and generating a frequency of a signal from the second oscillator (12);
a second transmitter (2) that emits an ultrasonic beam that intersects the irradiation beam of the first transmitter (1) at a certain angle near the target; and the first transmitter ( 1) and a moving standing wave generated at the intersection (3) by the ultrasonic beam irradiated from the second transmitter (2). a receiver (5) that receives a reflected wave having a beat signal derived from the moving speed and direction of the reflector; and a receiving amplifier (13) that amplifies the reflected wave signal from the receiver (5). , a detector (14) that detects the received signal, and an FFT (FFT) that frequency-analyzes the output signal of the detector (14).
15) A flow rate measuring device comprising: