A portable ultrasonic sound pressure measurement device based on the principle of acoustic capillary effect

Abstract

The present invention relates to a portable ultrasonic sound pressure measuring device based on the principle of acoustic capillary effect, comprising a detection part and a main body, wherein the detection part comprises an outer sleeve and a capillary, the capillary is arranged in the outer sleeve, the capillary is connected with the inner cavity of the outer sleeve, and is filled with incompressible liquid from which bubbles have been excluded; a capillary jack is arranged at the front end of the main body, the bottom end of the capillary extends into the capillary jack of the main body, a piezoelectric film is arranged at the bottom end of the capillary jack; and a single chip microcomputer is arranged in the main body. The present invention can measure the continuous real-time change value of ultrasonic power through the pump pressure at the capillary mouth caused by ultrasonic waves, and can also directly perform data analysis through the single chip microcomputer to obtain the maximum value, minimum value and average value of ultrasonic power within the period of time, which plays a very important role in the medical field and the field of sonochemical reaction.

Description

Technical Field

[0001] The invention relates to an ultrasonic sound pressure measuring device, in particular to an ultrasonic power, ie, sound pressure detection device designed by utilizing the principle of acoustic capillary effect. Background Art

[0002] At present, ultrasound is increasingly widely used in various fields, and excessive ultrasonic power is the main reason for its harm to the human body. It is of great significance to detect whether the ultrasonic power is within the safety threshold. At the same time, sonochemical reactors are widely used, but in complex sonochemical environments, ultrasonic power will inevitably dissipate over time. Detecting whether it is stable at the expected output value is also of great significance to improving the accuracy of the experiment. However, the commonly used measurement methods for ultrasonic power, such as the acoustic-optical effect to measure sound intensity, have equipment that is too complex and bloated. It is necessary to use a computer to process the diffraction image using complex algorithms. Users need to understand a wealth of image processing and computer-related code writing capabilities. The threshold for use is high and not easy to popularize, and the degree of uncertainty is large. Another commonly used measuring instrument, the hydrophone, is difficult to make smaller than the wavelength of the sound wave, so it will cause sound field distortion, which will inevitably affect the measurement accuracy, and can only be used in water. Therefore, there is a need for a detection device for ultrasonic power, i.e., sound pressure, which is small in size, highly sensitive, and has a simple and easy-to-operate measurement method. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a portable ultrasonic sound pressure measuring device based on the principle of acoustic capillary effect, comprising a detection part and a main body, wherein the detection part is arranged at the front end of the main body, the detection part comprises an outer sleeve and a capillary, the bottom end of the outer sleeve is fixedly connected to the main body, the capillary is arranged in the outer sleeve, the capillary is communicated with the inner cavity of the outer sleeve, and is filled with incompressible liquid from which bubbles have been eliminated; a capillary jack is arranged at the front end of the main body, the bottom end of the capillary extends into the capillary jack of the main body, and a piezoelectric film is arranged at the bottom end of the capillary jack; a single-chip microcomputer is arranged in the main body, a button and a display screen are arranged on the surface of the main body, and the single-chip microcomputer is respectively connected to the piezoelectric film, the button and the display screen;

[0004] A power source is also arranged in the main body, and the power source is connected to the single chip computer to provide electric energy; the power source includes a battery and a voltage stabilizing circuit.

[0005] The top end of the outer sleeve is provided with a soft membrane surface.

[0006] A limiting groove is arranged in the outer sleeve, and the capillary is fixed in the limiting groove.

[0007] Choose a suitable angle and extend the detection part into the ultrasonic field to be measured. The PVDF piezoelectric film measures the external force exerted on the liquid when it enters and exits the capillary channel and converts it into a voltage signal. The weak voltage signal is amplified and the high impedance output is converted into a low impedance output in the single-chip microcomputer. The sliding average filter is used for filtering. The single-chip microcomputer then performs analog-to-digital conversion. The electrical signal is connected to the pin of the ADC channel that can be reused by the single-chip microcomputer. The sampling period is set, the conversion resolution is set to 16 bits, and continuous conversion is turned on. After conversion into a digital signal, the number obtained is x, and the obtained number is calculated:

[0008]

[0009] Among them, V 1 This is the actual voltage value at this time, V ref is the reference voltage;

[0010] Combined with the sensitivity characteristics of the piezoelectric film at this time, the pressure at this time can be calculated, and the pressure to be measured can be obtained by removing the area. Substitute into the formula:

[0011]

[0012] Where ρ is the fluid density, a is the kinetic energy correction coefficient, and u 1 is the instantaneous flow velocity at the capillary tube mouth, α is the expansion coefficient, α>1, A 1 is the inner diameter of the capillary, A 2 is the outer diameter of the capillary, Z 1 is the height at the capillary opening, Z 2 is the height of the piezoelectric film, g is the gravitational acceleration, σ is the water tension coefficient, θ is the contact angle, r is the inner diameter of the capillary, P 气 The pressure caused by the rising of bubbles generated by ultrasonic cavitation effect. is the head loss in the pipe;

[0013] The instantaneous flow velocity u at the capillary tube mouth is obtained from the above formula: 1 The average vibration velocity u of the fluid at the nozzle in one cycle can be calculated, and then the average vibration velocity u is substituted into the formula:

[0014] P=ρcu

[0015] Calculate the sound pressure value P here, where c is the propagation speed of sound.

[0016] Beneficial effects of the present invention:

[0017] The detection device provided by the present invention is easy to operate, and the main analysis process relies on a single-chip microcomputer, so the cost is relatively low; compared with the commonly used hydrophone that converts the mechanical vibration signal of water through a piezoelectric transducer, the device is not affected by the distortion of the ultrasonic field, does not change the original sound field, and measures more accurately; at the same time, the device can be used in most environments, not limited to water or air, and only needs to place the detection part in the sound field environment to be measured. Through the pump pressure at the capillary mouth caused by ultrasound, the real-time change value of the continuous ultrasonic power can be measured, and the maximum, minimum and average values ​​of the ultrasonic power during this period can also be obtained directly through data analysis by a single-chip microcomputer, and these values ​​can be directly displayed on the display screen of the device. The device plays a very important role in the medical field and the field of sonochemical reactions. It can not only monitor in real time whether the medical ultrasonic power exceeds the threshold value that is harmful to the human body, but also ensure that the ideal and stable ultrasonic power is maintained in a complex sonochemical reactor environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0019] Figure 2 It is a schematic diagram of the internal structure of the present invention;

[0020] Figure 3 It is a schematic diagram of the micro-element structure of a cylindrical fluid;

[0021] Figure 4 This is a schematic diagram of the cross-sectional structure taken at the pipe mouth.

[0022] 1. Detection part; 2. Main body; 3. Outer sleeve; 4. Capillary; 5. Piezoelectric film; 6. Single chip microcomputer; 7. Button; 8. Display screen; 9. Power supply; 10. Soft film surface; 11. Limiting groove. DETAILED DESCRIPTION

[0023] The present invention provides a portable ultrasonic sound pressure measuring device based on the principle of acoustic capillary effect. Figure 1 , 2As shown: it includes a detection part 1 and a main body 2, the detection part 1 is arranged at the front end of the main body 2, the detection part 1 includes an outer sleeve 3 and a capillary 4, the bottom end of the outer sleeve 3 is fixedly connected to the main body 2, the capillary 4 is arranged in the outer sleeve 3, the capillary 4 is connected to the inner cavity of the outer sleeve 3, and is filled with incompressible liquid from which bubbles have been eliminated; a capillary jack is provided at the front end of the main body 2, the bottom end of the capillary 4 extends into the capillary jack of the main body, and a PVDF piezoelectric film 5 is provided at the bottom end of the capillary jack 3 mm away from the bottom of the capillary 4; a single-chip microcomputer 6 is provided in the main body 2, and the single-chip microcomputer 6 model is 6STM32F103C8T6 single-chip microcomputer; a button 7 and an OLED display screen 8 are provided on the surface of the main body 2, and the single-chip microcomputer is respectively connected to the PVDF piezoelectric film 5, the button 7 and the OLED display screen 8.

[0024] The button 7 includes five function keys and an on / off key. The five function keys are respectively start / stop counting, zero adjustment, maximum value, minimum value and average value keys.

[0025] A power supply 9 is also provided in the main body 2, and the power supply 9 is connected to the single chip computer 6 to provide electric energy; the power supply 9 includes a battery and a voltage stabilizing circuit.

[0026] A soft membrane surface 10 is provided at the top of the outer sleeve 3 to provide an allowable space for liquid vibration.

[0027] A limiting groove 11 is provided at the inter-tube gap 40 mm to 70 mm from the tube bottom in the outer sleeve 3 , and the capillary tube 4 is fixed in the limiting groove 11 to prevent the capillary tube 4 from moving.

[0028] The present invention is based on the acoustic capillary effect, that is, the ultrasonic wave causes the fluid to oscillate, thereby causing the difference in energy loss between the fluid entering and exiting the pipe at the four openings of the capillary tube to generate pump pressure. When the ultrasonic wave propagates in the fluid, it causes the fluid to vibrate periodically in time and space, which can make the fluid at the pipe opening enter and exit the pipe at a high frequency. It is known from fluid mechanics that when water flows into a suddenly narrowed pipe and flows out of the pipe, the local resistance is different, and the energy loss is different. The difference in local resistance and energy loss between the inflow pipe and the outflow pipe generates the pump pressure of the ultrasonic pump.

[0029] Ultrasonic pump principle:

[0030] The fluid inside and outside the capillary 4 is analyzed in the cylindrical coordinate system, and the fluid is differentiated into cylindrical microelements. Figure 3 and 4 shown.

[0031] The Bernoulli equation is used to analyze the fluid at the mouth of capillary tube 4 to obtain the relationship between the instantaneous cross-sectional flow velocity and the pressure difference between the 1-1 section and the 2-2 section:

[0032]

[0033] Among them, P 1 is the pressure at section 1-1, P 2 is the pressure at section 2-2, u 1 is the instantaneous velocity of the fluid at the 1-1 section, i.e. the nozzle, u 2 is the instantaneous velocity of the fluid outside the tube at section 2-2, ρ is the fluid density, g is the gravitational acceleration, a is the kinetic energy correction coefficient, is the local resistance, ζ is the local resistance coefficient;

[0034] From the table, we can see that when entering the capillary 4, ζ=0.5(1-A 1 / A 2 ), denoted as ζ 入 ; Outflow capillary tube mouth, ζ = (1-A 1 / A 2 ) 2 , denoted as ζ 出 ;

[0035] Among them, A 1 is the inner diameter area of ​​capillary 4, A 2 is the outer diameter area of ​​capillary 4;

[0036] Considering that water may overflow when impacting the capillary tube 4, it is necessary to expand the research scope from the cylindrical outer diameter range of the capillary tube 4 to R'. The expanded area is A' 2 And introduce the expansion coefficient α; after this part of water hits the capillary, the area it is in will become smaller (originally there was only water, after hitting the capillary mouth, part of the area is the capillary wall, and part of the area is water), and the area of ​​the reduced water is A′ 1 , the formula is as follows:

[0037]

[0038] Among them, α is measured by experiment. When the ratio of inner diameter to outer diameter is 1:3, α is about 1.2; A′ 1 To enlarge the research object and then reduce the area, A′ 2 To enlarge the posterior cylindrical area of ​​the research object;

[0039] Introduce the continuity equation:

[0040] A 1 V 1 =A 2 V 2 (3)

[0041] Combining equations (1), (2) and (3), we can obtain:

[0042]

[0043]

[0044] Among them, ΔP 入 is the pressure entering capillary 4, ΔP 出 is the pressure out of the capillary 4;

[0045] Under high-frequency vibration, the macroscopic manifestation is the average pressure, that is:

[0046]

[0047] Substituting (4) and (5) into (6), the average pressure of the fluid is:

[0048]

[0049] The fluid flowing in the pipe is analyzed and the Bernoulli total flow equation is introduced:

[0050]

[0051] Here, P 气 is the pressure caused by the bubbles rising due to ultrasonic cavitation effect, Z 1 is the height of the capillary tube orifice, Z 2 is the height of the piezoelectric film, Z 毛 is the height of the liquid column due to capillary action, is the head loss in the pipe;

[0052]

[0053] Among them, σ is the water tension coefficient, θ is the contact angle, and r is the inner diameter of the capillary;

[0054] Combining equations (7), (8) and (9) we can obtain:

[0055]

[0056] By measuring the pressure The instantaneous flow velocity u at the capillary tube mouth can be obtained 1 , the average vibration velocity u of the fluid at the nozzle in one cycle can be calculated and substituted into the formula:

[0057] P=ρcu (11)

[0058] Among them, ρ is the fluid density, c is the propagation speed of sound, and the sound pressure value P here can be calculated.

[0059] Since the bubble pressure is unstable due to the cavitation effect of ultrasound, the present invention uses the internal liquid environment to ensure the relative stability of the bubble pressure and determines the relative stability of the bubble pressure through pressure measurement. value:

[0060] Since the capillary tubes are of the same length and have the same resistance along the way, the pressure at the point where the liquid enters and exits the capillary tube is replaced by the pressure at the bottom of the measuring tube. The pressure measurement utilizes the PVDF piezoelectric film 5 for pressure measurement.

[0061] The PVDF piezoelectric film 5 converts the external force into voltage, has high sensitivity, fast response speed, and can measure small pressure changes; but its impedance is high and its energy is small, so it needs to be connected to a preamplifier with high input impedance to amplify the weak signal and convert the high impedance output into a low impedance output; because there is too much noise after conversion into an electrical signal reflecting the pressure, the signal needs to be filtered, and a sliding average filter is used here for filtering. The sliding average filter has a good inhibitory effect on periodic interference and has high smoothness. It is suitable for high-frequency oscillation systems, can filter out noise more accurately, and the sliding window can better realize real-time filtering.

[0062] After filtering, the single-chip microcomputer 6 performs analog-to-digital conversion, connects the electrical signal to the pin of the ADC channel that can be reused by the single-chip microcomputer 6, sets the sampling period, sets the conversion resolution to 16 bits, and starts continuous conversion. After conversion to a digital signal, the number obtained is x, and the obtained number is calculated:

[0063]

[0064] Among them, V 1 This is the actual voltage value at this time, V ref is the reference voltage;

[0065] Combined with the sensitivity characteristics of the piezoelectric film 5 at this time, the pressure at this time can be calculated, and the pressure to be measured can be obtained by removing the area.

[0066] Turn on the device, select a suitable angle, extend the detection part 1 into the ultrasonic field to be tested, press the zeroing button, and after zeroing, try to keep the tilt angle of the device from changing significantly; press the start / stop counting button, and after starting counting, the pressure value can be displayed in real time on the OLED display 8. Press the stop counting button again to stop counting, and the number on the OLED display 8 will no longer be updated; the pressure value between two key presses is stored in an array, and the maximum and minimum values ​​can be compared by traversing all the values ​​in this array, and the average value of all the numbers in the array can be calculated. Pressing the maximum value button, the minimum value button and the average value button will display the maximum, minimum and average values ​​of the ultrasonic pressure during this period.

Claims

1. A portable ultrasonic sound pressure measuring device based on the principle of acoustic capillary effect, characterized in that: It comprises a detection part and a main body, wherein the detection part is arranged at the front end of the main body, and comprises an outer sleeve and a capillary tube, wherein the bottom end of the outer sleeve is fixedly connected to the main body, and the capillary tube is arranged in the outer sleeve, and the capillary tube is communicated with the inner cavity of the outer sleeve, and is filled with incompressible liquid from which bubbles have been eliminated; a soft membrane surface is arranged at the top end of the outer sleeve; a capillary tube jack is arranged at the front end of the main body, and the bottom end of the capillary tube extends into the capillary tube jack of the main body, and a piezoelectric film is arranged at the bottom end of the capillary tube jack; a single-chip microcomputer is arranged in the main body, and buttons and a display screen are arranged on the surface of the main body, and the single-chip microcomputer is respectively connected with the piezoelectric film, the buttons and the display screen.

2. A portable ultrasonic sound pressure measuring device based on the principle of acoustic capillary effect according to claim 1, characterized in that: A power source is also arranged in the main body, and the power source is connected to the single chip computer to provide electric energy; the power source includes a battery and a voltage stabilizing circuit.

3. A portable ultrasonic sound pressure measuring device based on the principle of acoustic capillary effect according to claim 1, characterized in that: A limiting groove is arranged in the outer sleeve, and the capillary is fixed in the limiting groove.

4. A portable ultrasonic sound pressure measuring device based on the principle of acoustic capillary effect according to claim 1, characterized in that: Choose a suitable angle and extend the detection part into the ultrasonic field to be measured. The piezoelectric film measures the external force exerted on the liquid when it enters and exits the capillary and converts it into a voltage signal. The weak voltage signal is amplified and the high impedance output is converted into a low impedance output in the single-chip microcomputer. The sliding average filter is used for filtering. The single-chip microcomputer then performs analog-to-digital conversion. The conversion resolution is set to 16 bits and continuous conversion is turned on. After conversion into a digital signal, the number obtained is x, and the obtained number is calculated: Among them, V1 is the actual voltage value at this time, V ref is the reference voltage; Combined with the sensitivity characteristics of the piezoelectric film at this time, the pressure at this time is calculated, and the pressure to be measured is obtained by removing the area. Plug into the formula; Wherein, ρ is the fluid density, a is the kinetic energy correction coefficient, u1 is the instantaneous flow velocity at the capillary mouth, α is the expansion coefficient, α>1, A1 is the inner diameter area of ​​the capillary, A2 is the outer diameter area of ​​the capillary, Z1 is the height at the capillary mouth, Z2 is the height at the piezoelectric film, g is the gravitational acceleration, σ is the water tension coefficient, θ is the contact angle, r is the inner diameter of the capillary, P 气 The pressure caused by the rising of bubbles generated by ultrasonic cavitation effect. is the head loss in the pipe; The instantaneous flow velocity u1 at the capillary tube mouth is obtained from the above formula, and the average vibration flow velocity u of the fluid at the tube mouth in one cycle is calculated, and then the average vibration flow velocity u is substituted into the formula: P=ρcu Calculate the sound pressure value P here, where c is the propagation speed of sound.

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