Liquid density detection device and detection method based on capacitive micromechanical ultrasonic transducer

Abstract

The invention discloses a liquid density detection device and detection method based on a capacitive micromechanical ultrasonic transducer, and belongs to the technical field of ultrasonic detection and sensors. The detection device is mainly composed of a liquid detection tank, an aluminum block, a CMUT, an ultrasonic pulse generation receiver, an oscilloscope, a data processing module and a display storage unit. According to the detection method disclosed by the invention, the liquid density is calculated according to a preset frequency-density calibration curve by measuring the change of the resonant frequency of the CMUT in liquids with different densities according to the fact that the change of the liquid density can influence the diaphragm damping of the CMUT. The detection device has the advantages of being high in precision, high in portability, high in response speed, good in real-time performance and the like in liquid density detection, has the characteristic of being suitable for various liquids, and can be widely applied to the fields of industry, environment monitoring, biomedicine and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrasonic detection and sensors, and in particular to a liquid density detection device and a detection method based on a capacitive micromechanical ultrasonic transducer. Background Art

[0002] Liquid density is an important parameter in current industrial, environmental and medical testing, and its changes are often used to analyze the purity, concentration and physical and chemical properties of liquids. Traditional liquid density detection methods mainly include hydrometer method, vibration tube method and buoyancy method. However, these methods usually require a large equipment space, complicated operation steps, and in some cases cannot achieve real-time and portable detection. For on-site detection or liquid density measurement in special environments, the limitations of traditional methods are gradually emerging.

[0003] In recent years, ultrasonic technology has received widespread attention in the field of liquid detection. By measuring the propagation speed or reflection characteristics of ultrasonic waves in liquids, the density of the liquid can be inferred. However, traditional ultrasonic sensors are large in size, difficult to miniaturize, and not sensitive enough to changes in the acoustic impedance of liquids, so their application in density detection is limited.

[0004] As an emerging ultrasonic sensor device, capacitive micromachined ultrasonic transducer (CMUT) has the advantages of high sensitivity, wide bandwidth, and compact structure, and is suitable for detecting the acoustic properties of liquids. CMUT transmits and receives ultrasonic waves through a vibrating film, and its resonant frequency is affected by the mass of the liquid load and the acoustic impedance. When the CMUT is immersed in liquids of different densities, the density of the liquid changes the vibration characteristics of the diaphragm, thereby affecting the resonant frequency. By measuring the change in the resonant frequency, the liquid density can be indirectly inferred.

[0005] The advantages of CMUT are that it is small in size and easy to integrate, which can meet the needs of portable and on-site detection. At the same time, CMUT is highly sensitive to changes in acoustic impedance and can accurately capture small changes in liquid density. This makes CMUT-based liquid density detection technology have a wide range of application potentials, not only suitable for industrial and environmental monitoring, but also for medical testing and biochemical analysis, providing a new method for liquid detection technology. Summary of the invention

[0006] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and provide a liquid density detection device based on a capacitive micromachined ultrasonic transducer. The device can achieve liquid density measurement with a smaller range and higher sensitivity, thereby meeting the real-time detection of liquid density in an industrial environment.

[0007] The present invention is achieved through the following technical solutions: A liquid density detection device based on a capacitive micromachined ultrasonic transducer comprises a liquid detection tank, an aluminum block, a CMUT, an ultrasonic pulse generator receiver, an oscilloscope, a data processing module and a display storage unit; the aluminum block and the CMUT are arranged in the liquid detection tank, the aluminum block and the CMUT are spaced apart and the spacing is a fixed value; the CMUT is connected to the ultrasonic pulse generator receiver, the ultrasonic pulse generator receiver is connected to the oscilloscope, the oscilloscope is connected to the data processing module, and the data processing module is connected to the display storage unit.

[0008] As a preferred technical solution, the detection device also includes a temperature sensor, which is placed in the liquid detection tank and connected to the data processing module.

[0009] As a preferred technical solution, a density-resonance frequency calibration database is provided in the data processing module, and a pre-established frequency-density calibration curve is stored in the density-resonance frequency calibration database. The frequency-density calibration curve is established based on the test results of liquids with known density.

[0010] As a preferred technical solution, the CMUT is composed of an upper electrode, a vibration film, an insulating layer, a silicon substrate and a lower electrode stacked in sequence.

[0011] As a preferred technical solution, the CMUT is mounted on a PCB, wherein the lower electrode of the CMUT is connected to the PCB by bonding with conductive silver paste, and the upper electrode of the CMUT is connected to the PCB by gold wire bonding.

[0012] As a preferred technical solution, the CMUT is encapsulated using PDMS.

[0013] Furthermore, the present invention also provides a detection method for the liquid density detection device based on the capacitive micromachined ultrasonic transducer, which specifically comprises the following steps: S1. Sample preparation Load the liquid sample to be tested into the liquid detection tank to ensure that the packaged CMUT is completely immersed in the liquid to ensure the accuracy of the measurement.

[0014] S2. Resonance frequency measurement A set of broadband signals is emitted through the ultrasonic pulse generator receiver to stimulate the CMUT, causing its vibrating film to vibrate. The CMUT emits ultrasonic waves, which are reflected back to the CMUT after hitting the surface of the aluminum block after flying a specific distance. The ultrasonic pulse generator receiver then receives the ultrasonic signal, converts the received ultrasonic signal into an electrical signal, and connects it to an oscilloscope through a BNC cable. The received signal is Fourier transformed through the oscilloscope to convert the time domain signal into a frequency domain signal. The optimal vibration frequency of the CMUT at this liquid density is the resonant frequency at this time, so the horizontal coordinate corresponding to the point with the maximum value of the frequency domain signal at this time is the resonant frequency.

[0015] S3. Data processing and density calculation The resonant frequency recorded by the oscilloscope is transmitted to the data processing module, and the data processing module converts the measured frequency change into the corresponding density value according to the pre-established frequency-density calibration curve.

[0016] S4. Display and storage The data processing module sends the calculated density value result to the display storage unit and stores the data in the display storage unit at the same time; the user can view the real-time density data on the display storage unit, and the data can be used for subsequent analysis, recording and comparison.

[0017] S5. Temperature compensation The temperature sensor measures the liquid temperature in real time and inputs the temperature data into the data processing module for temperature compensation correction.

[0018] The technical principle of the above-mentioned liquid density detection device and detection method based on capacitive micromachined ultrasonic transducer provided by the present invention is that since the change of liquid density will affect the diaphragm damping of CMUT, the liquid density is calculated according to the preset frequency-density calibration curve by measuring the change of the resonant frequency of CMUT in liquids of different densities.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1) The detection device of the present invention has high sensitivity. Since the vibration characteristics of the vibrating film in the CMUT are very sensitive to the liquid load, the CMUT can accurately detect small changes in liquid density and is suitable for application scenarios with high precision requirements. In contrast, traditional methods, such as the hydrometer method and the vibrating tube method, although effective, are difficult to achieve high precision in small-scale or trace sample detection.

[0020] 2) The detection device of the present invention has the advantages of compact structure and easy integration. The CMUT is manufactured based on the MEMS process, has a small size and high integration, and is very suitable for portable devices and embedded applications. In contrast, traditional density detection equipment is usually large in size, not convenient for on-site use, and difficult to meet portability requirements.

[0021] 3) The detection process of the detection device of the present invention is fast and real-time. By measuring the change of the resonant frequency of the CMUT, the CMUT can obtain liquid density information in a very short time, which is very suitable for real-time monitoring. Compared with the longer operation of the hydrometer or laboratory detection method, the real-time performance of the CMUT is significantly improved.

[0022] 4) The detection device of the present invention is applicable to a variety of liquids and does not require contact measurement. This non-invasive feature reduces the risk of sample contamination, making it more advantageous in sensitive fields such as biomedicine and chemical engineering. In summary, the detection device of the present invention has the advantages of high precision, strong portability, fast response speed, good real-time performance, etc. in liquid density detection, is adaptable to the characteristics of various liquids, and can be widely used in industry, environmental monitoring, biomedicine and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 It is a schematic diagram of the structural connection of the detection device of the present invention.

[0025] Figure 2 It is a schematic diagram of the structure of CMUT in the detection device of the present invention.

[0026] Figure 3 It is a schematic diagram of the resonant frequency of the ultrasonic signal received after Fourier transformation when the detection device of the present invention performs detection.

[0027] In the figure: 1-liquid detection tank, 2-aluminum block, 3-temperature sensor, 4-CMUT, 5-ultrasonic pulse generator receiver, 6-oscilloscope, 7-data processing module, 8-display storage unit, 9-PCB board. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In the description of the present invention, unless otherwise clearly specified and limited, the terms "installation", "connection", "placement" and the like should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Example 1

[0031] like Figure 1 As shown, this embodiment provides a liquid density detection device based on a capacitive micromachined ultrasonic transducer, including a liquid detection tank 1, an aluminum block 2, a temperature sensor 3, a CMUT 4, an ultrasonic pulse generator receiver 5, an oscilloscope 6, a data processing module 7 and a display storage unit 8.

[0032] The liquid detection tank 1 is used to load the liquid sample to be detected.

[0033] The aluminum block 2 is placed in the liquid detection tank 1. The aluminum block 2 is used to reflect the ultrasonic signal, and the reflected ultrasonic signal is then received by the CMUT 4; since the aluminum block 2 has a high acoustic impedance, when the ultrasonic wave enters the aluminum block 2 from the liquid medium, most of the sound waves will be reflected at the interface, resulting in a high reflectivity.

[0034] The temperature sensor 3 is arranged in the liquid detection tank 1, and the temperature sensor 3 is connected to the data processing module 7. The temperature sensor 3 is used to compensate for the influence of temperature on the resonance frequency, so as to make the detection result more accurate.

[0035] CMUT 4 is placed in the liquid detection tank 1. CMUT 4 and aluminum block 2 are spaced relative to each other and the spacing is fixed to ensure the detection accuracy. CMUT 4 is connected to ultrasonic pulse generator and receiver 5. CMUT 4 is used to transmit and receive ultrasonic signals and measure their resonant frequency. The design and preparation process of CMUT 4 ensure that it can provide stable ultrasonic propagation characteristics in liquids of different densities. Figure 2As shown, CMUT 4 is composed of an upper electrode, a vibration film, an insulating layer, a silicon substrate and a lower electrode stacked in sequence. CMUT 4 is mounted on a PCB board 9. The lower electrode of CMUT 4 is connected to the PCB board 9 by pasting with conductive silver paste, and the upper electrode of CMUT 4 is connected to the PCB board 9 by gold wire bonding. CMUT 4 and PCB board 9 are packaged as a whole with PDMS, so that CMUT 4 can be tested in liquid, and due to the flexible nature of PDMS, the influence on the vibration of the vibration film is small.

[0036] The ultrasonic pulse generator receiver 5 is connected to the oscilloscope 6. The ultrasonic pulse generator receiver 5 is used to excite the CMUT 4 and amplify it by a certain multiple, which is conducive to observing the signal, so as to make it vibrate within a specific frequency range and emit ultrasonic signals.

[0037] The oscilloscope 6 is connected to the data processing module 7 and is used to display the received ultrasonic signal and perform Fourier transform on the received signal to obtain the resonant frequency of the CMUT 4 at this time. The resonant frequency is the frequency corresponding to the highest point of the received signal after Fourier transform.

[0038] The data processing module 7 is connected to the display storage unit 8. A density-resonance frequency calibration database is provided in the data processing module 7. A pre-established frequency-density calibration curve is stored in the density-resonance frequency calibration database. The frequency-density calibration curve is a standard curve established based on the test results of a liquid with a known density. The data processing module 7 is used to observe the ultrasonic signal after Fourier transformation, analyze the relationship between the resonant frequency and the liquid density, calculate the liquid density according to the preset frequency-density calibration curve, and transmit the calculated density data to the display storage unit 8.

[0039] The display storage unit 8 is used to display the liquid density detection result in real time and store the detection data.

[0040] The detection device of the present invention adopts CMUT 4 as a core component. According to different excitation signals when CMUT 4 is working, its working mode can be divided into a transmitting mode and a receiving mode. When CMUT 4 works in the transmitting mode, the vibrating film vibrates under the action of the excitation voltage, thereby causing the medium in the sound field to vibrate, thereby realizing the conversion of the electrical signal to the ultrasonic signal; when CMUT 4 works in the receiving mode, the ultrasonic signal acts on the vibrating film to make it vibrate, causing the change of the capacitor charge to generate current, thereby realizing the conversion of the ultrasonic signal to the electrical signal; when CMUT 4 is immersed in liquid, the density of the liquid will change its equivalent load mass and affect the resonant frequency of CMUT 4; by measuring the change in the resonant frequency, combined with a pre-set frequency-density calibration curve, the density of the liquid can be inferred. Example 2

[0041] This embodiment provides a detection method for the liquid density detection device based on the capacitive micromachined ultrasonic transducer described in Embodiment 1, which specifically includes the following steps: S1. Sample preparation The liquid sample to be tested is loaded into the liquid detection tank 1 to ensure that the packaged CMUT 4 is completely immersed in the liquid to ensure the accuracy of the measurement.

[0042] S2. Resonance frequency measurement A group of broadband signals are emitted by the ultrasonic pulse generator receiver 5 to stimulate the CMUT 4, so that its vibrating film vibrates. The CMUT 4 emits ultrasonic waves, which are reflected back to the CMUT 4 after hitting the surface of the aluminum block 2 after flying a specific distance. The ultrasonic pulse generator receiver 5 then receives the ultrasonic signal, converts the received ultrasonic signal into an electrical signal, and connects it to the oscilloscope 6 through a BNC connection line. The received signal is Fourier transformed by the oscilloscope 6 to convert the time domain signal into a frequency domain signal. The optimal vibration frequency of the CMUT 4 under the liquid density is the resonant frequency at this time, so the horizontal coordinate corresponding to the point of the maximum value of the frequency domain signal at this time is the resonant frequency.

[0043] S3. Data processing and density calculation The resonant frequency recorded by the oscilloscope 6 is transmitted to the data processing module 7, and the data processing module 7 converts the measured frequency variation into a corresponding density value according to a pre-established frequency-density calibration curve.

[0044] S4. Display and storage The data processing module 7 sends the calculated density value result to the display storage unit 8, and stores the data in the display storage unit 8 at the same time; the user can view the real-time density data on the display storage unit 8, and the data can be used for subsequent analysis, recording and comparison.

[0045] S5. Temperature compensation The temperature sensor 3 measures the liquid temperature in real time and inputs the temperature data into the data processing module 7 for temperature compensation correction.

[0046] Figure 3 The figure is a schematic diagram of the resonance frequency of the ultrasonic signal received after Fourier transformation in the detection method of the present invention. It can be seen from the figure that after conversion into a frequency domain signal, the peak value of the received signal is 3.66MHz, which is the resonance frequency corresponding to the density at this time.

[0047] Obviously, the above embodiments are merely examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A liquid density detection device based on a capacitive micromachined ultrasonic transducer, characterized in that: It includes a liquid detection tank, an aluminum block, a CMUT, an ultrasonic pulse generator receiver, an oscilloscope, a data processing module and a display storage unit; the aluminum block and the CMUT are placed in the liquid detection tank, the aluminum block and the CMUT are spaced apart and the spacing is a fixed value; the CMUT is connected to the ultrasonic pulse generator receiver, the ultrasonic pulse generator receiver is connected to the oscilloscope, the oscilloscope is connected to the data processing module, and the data processing module is connected to the display storage unit.

2. The liquid density detection device based on capacitive micromachined ultrasonic transducer according to claim 1 is characterized in that: It also includes a temperature sensor, which is arranged in the liquid detection tank and connected to the data processing module.

3. The liquid density detection device based on capacitive micromachined ultrasonic transducer according to claim 2, characterized in that: The data processing module is provided with a density-resonance frequency calibration database, in which a pre-established frequency-density calibration curve is stored. The frequency-density calibration curve is established based on the test results of liquids with known densities.

4. The liquid density detection device based on capacitive micromachined ultrasonic transducer according to claim 3 is characterized in that: CMUT is composed of an upper electrode, a vibrating film, an insulating layer, a silicon substrate and a lower electrode stacked in sequence.

5. The liquid density detection device based on capacitive micromachined ultrasonic transducer according to claim 4, characterized in that: The CMUT is mounted on a PCB, wherein a lower electrode of the CMUT is connected to the PCB by bonding with conductive silver paste, and an upper electrode of the CMUT is connected to the PCB by gold wire bonding.

6. The liquid density detection device based on capacitive micromachined ultrasonic transducer according to claim 5, characterized in that: The CMUT is encapsulated with PDMS.

7. The detection method of the liquid density detection device based on the capacitive micromachined ultrasonic transducer according to claim 6, characterized in that: The steps include: S1. Sample preparation Load the liquid sample to be tested into the liquid detection tank, making sure that the packaged CMUT is completely immersed in the liquid to ensure the accuracy of the measurement; S2. Resonance frequency measurement A set of broadband signals is emitted through the ultrasonic pulse generator receiver to stimulate the CMUT, causing its vibrating film to vibrate. The CMUT emits ultrasonic waves, which are reflected back to the CMUT after hitting the surface of the aluminum block after flying a specific distance. The ultrasonic pulse generator receiver then receives the ultrasonic signal, converts the received ultrasonic signal into an electrical signal, and connects it to an oscilloscope through a BNC cable. The oscilloscope performs Fourier transform on the received signal, converting the time domain signal into a frequency domain signal. The optimal vibration frequency of the CMUT at this liquid density is the resonant frequency at this time, so the horizontal coordinate corresponding to the point of the maximum value of the frequency domain signal at this time is the resonant frequency. S3. Data processing and density calculation The resonant frequency recorded by the oscilloscope is transmitted to the data processing module, and the data processing module converts the measured frequency change into the corresponding density value according to the pre-established frequency-density calibration curve; S4. Display and storage The data processing module sends the calculated density value result to the display storage unit and stores the data in the display storage unit at the same time; the user can view the real-time density data on the display storage unit, and the data can be used for subsequent analysis, recording and comparison; S5. Temperature compensation The temperature sensor measures the liquid temperature in real time and inputs the temperature data into the data processing module for temperature compensation correction.

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