Two-channel Lamb wave sensor, dew point sensor and method

Abstract

The invention provides a two-channel Lamb wave sensor, a dew point sensor and a method, and belongs to the field of micro electro mechanical systems and humidity measurement. The gas dew point measuring method solves the problem that a working surface electrode and a piezoelectric material of an MEMS resonant dew point sensor in the prior art are easily corroded by the environment, and the gas dew point measuring method is provided. A dual-channel Lamb wave sensor comprises two Lamb wave sensors which are arranged on the same chip and are close in position; the temperature sensor is provided with a temperature reference channel and a sensing channel. The dew point sensor comprises a dual-channel Lamb wave sensor, wherein the electrode side of the dual-channel Lamb wave sensor is attached to a printed circuit board; the upper side of the semiconductor chilling plate is connected with the printed circuit board, and the lower side of the semiconductor chilling plate is connected with the radiating fins; the refrigeration assembly is arranged on the lower portions of the heat dissipation fins. The device is mainly used for measuring dew points.

Description

Technical Field

[0001] The invention belongs to the field of micro-electromechanical systems and humidity measurement, and in particular relates to a dual-channel Lamb wave sensor, a dew point sensor and a method. Background Art

[0002] Dew point sensors play an important role in key national economic fields such as semiconductors, agriculture, aerospace, biomedicine, and environmental monitoring. Dew point is defined as the temperature at which air is cooled to saturation when the water vapor content and atmospheric pressure in the air are constant. At this time, the condensation rate of water molecules is greater than the vaporization rate, and liquid water appears on the surface of the sensor. There are temperature changes and gas-liquid phase changes in the process, and the measurement is relatively complex.

[0003] In recent years, with the development of micro-electromechanical system (MEMS) processing technology, sensors have been miniaturized. MEMS resonant dew point sensors have the advantages of small size, high sensitivity, and easy integration, and have been rapidly developed. Its working principle is the mass load effect. The tiny condensation on the surface will affect the resonant state of the piezoelectric microsensor, thereby changing the resonant frequency. Common types include surface acoustic wave (SAW), quartz crystal microbalance (QCM) and cantilever beam type.

[0004] The prior art has the following problems:

[0005] The above-mentioned devices have exposed electrodes or piezoelectric materials on their working surfaces, and are in direct contact with condensate during the dew point measurement process. Inert electrodes (such as gold) are relatively stable but expensive; aluminum electrodes are low in cost but unstable, and long-term use can easily lead to electrode corrosion or detachment. In addition, some piezoelectric materials such as zinc oxide are not resistant to acids and alkalis and are easily corroded by condensate.

[0006] In summary, a Lamb wave resonant dew point sensor device with electrode self-protection and a measurement method thereof are proposed. Summary of the invention

[0007] In view of this, the present invention aims to propose a dual-channel Lamb wave sensor, a dew point sensor and a method to solve the problem in the prior art that the working surface electrodes and piezoelectric materials of the MEMS resonant dew point sensor are susceptible to environmental corrosion, and to propose a gas dew point measurement method.

[0008] To achieve the above object, the present invention adopts the following technical solution. According to one aspect of the present invention, a dual-channel Lamb wave sensor is provided, comprising:

[0009] Lamb wave sensors, two of which are provided on the same chip;

[0010] A protective component is used to isolate one of the Lamb wave sensors from the air to form a temperature reference channel; and to isolate the electrode side of another Lamb wave sensor from the air to form a sensing channel;

[0011] Among them, when condensation occurs, the offset of the resonant frequency of the sensing channel is greater than the resonant frequency of the temperature reference channel, and the temperature when the resonant frequencies of the temperature reference channel and the sensing channel deviate is the dew point temperature.

[0012] Furthermore, the Lamb wave sensor is provided with interdigital electrodes, a piezoelectric layer, a bottom electrode, a structural layer, a silicon dioxide layer and a support layer in sequence from top to bottom.

[0013] Furthermore, the structural layer is made of silicon.

[0014] Furthermore, the protection component includes a front protection structure and a back protection mechanism, the front protection structure is arranged on the electrode side of the two Lamb wave sensors, and the back protection mechanism is arranged on the opposite side of the electrode side of any one of the Lamb wave sensors.

[0015] According to another aspect of the present invention, there is provided a dew point sensor, further comprising:

[0016] A printed circuit board connected to the electrode side of the dual-channel Lamb wave sensor;

[0017] A semiconductor cooling chip, one side of which is connected to the printed circuit board, the calibration sensor and the temperature sensor, and the other side of which is connected to the heat sink fins;

[0018] The refrigeration component is arranged on a side of the heat dissipation fins away from the semiconductor refrigeration plate.

[0019] Furthermore, the cold end of the semiconductor refrigeration plate is connected to a dual-channel Lamb wave sensor.

[0020] Furthermore, the calibration sensor and the temperature sensor are arranged adjacent to the dual-channel Lamb wave sensor.

[0021] Furthermore, the resonant frequency of the dual-channel Lamb wave sensor is 1 MHz-1 GHz.

[0022] According to another aspect of the present invention, a method for measuring gas dew point is provided, using the above-mentioned dew point sensor, and the specific steps are as follows:

[0023] S1, cooling, using the semiconductor refrigeration sheet to reduce the temperature of the dual-channel Lamb wave sensor and the calibration sensor until condensation appears on the surface of the sensing channel, and continue measuring for a certain period of time to collect data;

[0024] S2. Record data, measure and record the change of the resonant frequency of the dual-channel Lamb wave sensor over time in real time, and use the host computer to read and record the change of the calibration sensor output over time and the change of the temperature sensor output over time, that is, the temperature and condensation state at each frame moment;

[0025] S3, establish a training set, repeat S1 and S2 steps multiple times, the obtained data is used as the training set data, and the frame data are aligned by time;

[0026] S4, model training, using random forest algorithm to obtain classification model based on training set data, taking the resonant frequency of the sensing channel and the resonant frequency of the temperature reference channel as input, and the condensation state as output, to complete model training and calibration; linearly fitting the measured temperature of the temperature sensor and the resonant frequency of the temperature reference channel, and calculating TCF;

[0027] S5, test, repeat steps S1 and S2 without a calibrated sensor, measure the change of the resonant frequency of the sensing channel and the temperature reference channel, and determine the data frame at the time of dew point occurrence through the model; calculate the dew point according to the resonant frequency of the data frame of the temperature reference channel at the time of dew point occurrence and the TCF fitted in step S4.

[0028] Furthermore, the training set data includes the resonant frequency and temperature of the sensing channel and the resonant frequency and condensation state of the temperature reference channel.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The back of the Lamb wave sensor sensing channel is used as the measurement working surface. The back side is relatively stable and insensitive to corrosion. At the same time, the interdigital electrodes required for Lamb wave excitation and reception are protected in a closed chamber and do not directly contact the condensate, which is beneficial to protect the Lamb wave sensor;

[0031] 2. The prior art usually uses the method of calculating the resonant frequency difference between the sensing channel and the reference channel. If it is greater than a set threshold, it is judged that condensation occurs on the surface, but the optimization of threshold selection is not considered. The present invention uses machine learning to identify the resonant frequency point when condensation occurs, reducing the error introduced by threshold selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0033] Figure 1 This is a schematic diagram of the structure of the dual-channel Lamb wave sensor of the present invention;

[0034] Figure 2 This is a schematic diagram of the structure of the Lamb wave sensor of the present invention;

[0035] Figure 3 This is a schematic diagram of the structure of the Lamb wave resonant dew point sensor with electrode self-protection according to the present invention;

[0036] Figure 4 A model training and calibration flow chart of a gas dew point measurement method according to the present invention;

[0037] Figure 5 This is a measurement process diagram of a gas dew point measurement method according to the present invention.

[0038] Interdigitated electrode 1; piezoelectric layer 2; bottom electrode 3; structural layer 4; silicon dioxide layer 5; supporting layer 6; front protection structure 7; temperature reference channel 8; sensing channel 9; back protection mechanism 10; calibration sensor 11; temperature sensor 12; dual-channel Lamb wave sensor 13; chip fixing device 14; printed circuit board 15; semiconductor cooling sheet 16; heat sink fins 17; cooling assembly 18. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely explain the technical solutions in the embodiments of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict, and the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0040] It should be noted that the descriptions of the present invention regarding directions such as "left", "right", "left side", "right side", "upper", "lower", "top", "bottom", etc. are all defined based on the relationship between the orientations or positions shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the structure described must be constructed and operated in a specific orientation, and therefore, cannot be understood as a limitation on the present invention. In the description of the present invention, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0041] In the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral 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 ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] Referring to the accompanying drawings, this embodiment is described, providing a dual-channel Lamb wave sensor, comprising:

[0043] Lamb wave sensors, two of which are provided on the same chip;

[0044] The protective component isolates one of the Lamb wave sensors from the air to form a temperature reference channel 8; the electrode side of the other Lamb wave sensor is isolated from the air to form a sensing channel 9, wherein when condensation occurs, the resonant frequency offset of the sensing channel 9 is greater than the resonant frequency of the temperature reference channel 8, and the temperature when the resonant frequencies of the temperature reference channel 8 and the sensing channel 9 deviate is the dew point temperature. The Lamb wave is excited by the front cross-finger electrode of the sensor, and there are normal vibration components on the front and back surfaces of the device, which are sensitive to attached liquids; the temperature reference channel 8 and the sensing channel 9 are located close to each other and are on the same chip, so it is believed that the temperatures of the two channels are approximately equal, and the contribution of the ambient temperature to the resonant frequency offset is the same. Therefore, in the initial cooling stage without condensation, the resonant frequency offsets of the two channels are approximately equal; after condensation occurs, the resonant frequency offset of the sensing channel 9 is greater than the temperature reference channel 8, and the moment when the resonant frequencies of the two channels deviate is the moment when condensation occurs, and the temperature at this time is the dew point, and the specific data frame is determined by the subsequent dew point identification method. Because the temperature reference channel 8 is only affected by the ambient temperature, its resonant frequency is approximately linear in a small range of 0-40 degrees Celsius, and can be converted into a temperature measurement result, ie, a dew point measurement result, by pre-calibration.

[0045] In this embodiment, the Lamb wave sensor is provided with interdigital electrodes 1, piezoelectric layer 2, bottom electrode 3, structural layer 4, silicon dioxide layer 5 and support layer 6 from top to bottom. The piezoelectric layer 2 is prepared on the SOI (Silicon-On-Insulator) substrate based on magnetron sputtering technology or wafer bonding technology, the interdigital electrodes 1 are prepared by metal stripping process, and the back support layer 6 and silicon dioxide layer 5 are processed by deep reactive ion etching technology and wet etching process respectively to prepare the back cavity. If the wavelength of the interdigital electrode 1 is greater than the thickness of the propagation medium, that is, the sum of the thickness of the piezoelectric layer 2, the bottom electrode 3 and the structural layer 4, Lamb waves can be excited.

[0046] In this embodiment, the structural layer 4 is made of silicon.

[0047] In this embodiment, the piezoelectric materials used in preparing the dual-channel Lamb wave device are aluminum nitride, zinc oxide, and lithium niobate.

[0048] In this embodiment, the protection assembly includes a front protection structure 7 and a back protection mechanism 10, wherein the front protection structure 7 is arranged on the electrode side of the two Lamb wave sensors, and the back protection mechanism 10 is arranged on the opposite side of the electrode of one Lamb wave sensor. The front protection structure 7 is used to isolate the front of the dual-channel sensor from the air, and the back protection structure 10 is used to isolate the back of the temperature reference channel 8 from the air. The back of the sensing channel 9 is in direct contact with the air for condensate generation and dew point detection. Therefore, the front of the dual-channel sensor is isolated from the outside air, and the electrodes and piezoelectric materials only exist on the front of the sensor and are not in contact with the condensate, which plays a protective role; wherein, the temperature reference channel 8 is completely isolated from the environment on both sides, so it has no response to the mass load effect caused by the condensate, and its resonant frequency shift is completely caused by the change of ambient temperature; the back of the sensing channel 9 is unprotected, and when condensation occurs, its mass load effect causes the resonant frequency to shift, and the ambient temperature also causes its resonant frequency to shift. The front protection structure 7 and the back protection mechanism 10 are selected according to the actual needs. The material and corresponding structure. Specific implementation method 2:

[0050] A dew point sensor, including the dual-channel Lamb wave sensor mentioned in the first embodiment, further comprising:

[0051] The printed circuit board 15 is bonded to the electrode side of the dual-channel Lamb wave sensor; the dual-channel Lamb wave sensor 13 is tightly bonded to the printed circuit board 15 via the chip fixing device 14, with the back side facing upward, that is, the back side of the sensing channel 9 is in contact with the gas, which can promote heat exchange. The printed circuit board 15 is used to facilitate electrical connection and is connected to the dual-channel Lamb wave sensor 13 using an ultrasonic gold wire ball bonding machine.

[0052] A semiconductor cooling sheet 16, one side of which is connected to the printed circuit board 15, the calibration sensor 11 and the temperature sensor 12, and the other side of which is connected to the heat dissipation fins 17;

[0053] The cooling assembly 18 is arranged on the side of the heat dissipation fins 17 away from the semiconductor cooling sheet 16 ; the temperature control is achieved by the semiconductor cooling sheet 16 , the heat dissipation fins 17 and the cooling assembly 18 .

[0054] In this embodiment, the cold end of the semiconductor refrigeration sheet 16 is attached to the dual-channel Lamb wave sensor 13. The semiconductor refrigeration sheet 16 works based on the Peltier effect, and its cold end is attached to the dual-channel Lamb wave sensor 13 for cooling to measure the dew point.

[0055] In this embodiment, the calibration sensor 11 and the temperature sensor 12 are arranged adjacent to the dual-channel Lamb wave sensor 13. The calibration sensor 11 and the temperature sensor 12 are mainly used for additional configuration in the model training and calibration process, but not in the subsequent measurement process. The adjacent arrangement can reduce the temperature error.

[0056] In this embodiment, the resonant frequency of the dual-channel Lamb wave sensor 13 is 1 MHz-1 GHz. Specific implementation method three:

[0058] A gas dew point measurement method is provided, using the above-mentioned dew point sensor, and the specific steps are as follows:

[0059] First, perform the calibration process:

[0060] S1, cooling, using the semiconductor refrigeration sheet 16 to reduce the temperature of the dual-channel Lamb wave sensor 13 and the calibration sensor 11 until condensation appears on the surface of the sensing channel 9, and continue measuring for a certain time to collect data; the measurement time can be 3-5 minutes.

[0061] S2. Record data, use a vector network analyzer to measure and record the change of the resonant frequency of the dual-channel Lamb wave sensor 13 over time in real time, and use a host computer to read and record the change of the output of the calibration sensor 11 over time and the change of the output of the temperature sensor 12 over time, that is, the temperature and condensation state at each frame moment;

[0062] S3, establish a training set, repeat steps S1 and S2 multiple times, and use the obtained data as the training set. The frames of data are time aligned. The purpose is to establish a mapping relationship between the resonant frequency of the dual-channel Lamb wave sensor 13 and the condensation state, and extract the characteristics of the moment when the resonant frequency of the two channels deviates, that is, the moment when condensation occurs, so as to improve the measurement accuracy.

[0063] S4, model training, using random forest algorithm to obtain classification model based on training set, with the resonant frequency of sensing channel 9 and the resonant frequency of temperature reference channel 8 as input, and condensation state as output, to complete model training and calibration; the role of the classification model is to establish the mapping relationship between the resonant frequency of dual-channel Lamb wave sensor 13 and the condensation state, so that in practical applications, only the dual-channel resonant frequency of dual-channel Lamb wave sensor 13 needs to be measured to estimate the current condensation state. Linearly fit the measured temperature of temperature sensor 12 and the resonant frequency of temperature reference channel 8, calculate TCF frequency temperature coefficient, its role is to establish the functional relationship between the resonant frequency of temperature reference channel 8 and actual temperature, so that in step S5, the dew point is calculated by the measured resonant frequency, and the calculation formula is as follows:

[0064]

[0065] Where △f is the frequency offset, △T is the corresponding temperature change, and f0 is the initial resonant frequency.

[0066] The model training steps are as follows:

[0067] Construct training set Τ n =[X n×p ,Y n×1 ]. The matrix X has n rows and p columns, and each row is the resonant frequency change (time series) of the sensing channel 9 and the temperature reference channel 8 during a cooling-condensation process, each taking 5 seconds, and sampling once every 0.25 seconds, with a total of 40 data points, that is, p = 40. Some of the data are near the moment of condensation, and some are data when there is no condensation. The number of rows n represents the number of repeated experiments, which is 100. The matrix Y has n rows and 1 column, which is the measurement result of the high-precision calibrated dew point sensor 11. It is considered that condensation begins when the relative humidity reaches saturation, otherwise it is considered that there is no condensation. Based on this mark, the data in Y is 1 or 0. The minimum leaf size MLS is 1, and the number of decision trees N is 200. Repeat the following steps (1)-(3) N times, each corresponding to the i-th decision tree (i=1,2...N), so as to construct all 200 decision trees:

[0068] (1) From Τ n Select n rows from the matrix to form a temporary matrix, denoted as Σ n =[X' n×p ,Y' n×1 ]. (2) Define a set Λ, which only contains Σ n An element. Define Λ f Is an empty set.

[0069] (3) If Λ is not an empty set, repeat the following steps until Λ is an empty set: Let the first element of set Λ be the matrix E. If the number of rows contained in matrix E is less than or equal to MLS, or the rows of matrix E are completely identical, then remove E from Λ and add E to Λ f Otherwise, randomly select n×p Select 7 columns to form X" n×7 Subset, select the feature with the smallest Gini coefficient and its corresponding value as the split point to complete the segmentation [X" n×7 ,Y' n×1 ], and then divide the matrix E into matrix E1 and matrix E2, then delete the element E from Λ, and add E1 and E2 as elements.

[0070] The test process after calibration is completed is as follows:

[0071] S5, test, repeat S1 and S2 steps without calibration sensor 11, measure the resonant frequency change of sensing channel 9 and temperature reference channel 8, divide by time, and combine to form x 1×p , and import it as input into each Λ fCalculate the results of 200 decision trees and calculate the average output value. If it is greater than 0.5, it is considered to be condensation, otherwise it is considered to be no condensation, and then judge the dew point occurrence time; calculate the dew point according to the resonant frequency F of the data frame at the dew point occurrence time of the temperature reference channel 8 and the TCF fitted in step S4. The calculation formula is as follows:

[0072]

[0073] Where T is the dew point, T0 is the initial temperature of the sensor (room temperature), and f0 is the initial resonant frequency.

[0074] In this embodiment, the training set data includes the resonant frequency of the sensing channel 9 and the resonant frequency and condensation state of the temperature reference channel 8 .

[0075] The embodiments of the present invention disclosed above are only used to help illustrate the present invention. The embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. According to the content of this specification, many modifications and changes can be made. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well.

Claims

1. A dual-channel Lamb wave sensor, characterized in that: include: Lamb wave sensors, two of which are provided on the same chip; A protective component is used to isolate one of the Lamb wave sensors from the air to form a temperature reference channel (8); and to isolate the electrode side of another Lamb wave sensor from the air to form a sensing channel (9); When condensation occurs, the offset of the resonant frequency of the sensing channel (9) is greater than the resonant frequency of the temperature reference channel (8), and the temperature at which the resonant frequencies of the temperature reference channel (8) and the sensing channel (9) deviate is the dew point temperature.

2. A dual-channel Lamb wave sensor according to claim 1, characterized in that: The Lamb wave sensor is provided with interdigital electrodes (1), a piezoelectric layer (2), a bottom electrode (3), a structural layer (4), a silicon dioxide layer (5) and a supporting layer (6) in sequence from top to bottom.

3. A dual-channel Lamb wave sensor according to claim 2, characterized in that: The structural layer (4) is made of silicon.

4. A dual-channel Lamb wave sensor according to claim 1, characterized in that: The protection component comprises a front protection structure (7) and a back protection mechanism (10), wherein the front protection structure (7) is arranged on the electrode side of the two Lamb wave sensors, and the back protection mechanism (10) is arranged on the opposite side of the electrode side of any one of the Lamb wave sensors.

5. A dew point sensor, comprising a dual-channel Lamb wave sensor as claimed in any one of claims 1 to 4, characterized in that: Also includes: A printed circuit board (15) connected to the electrode side of the dual-channel Lamb wave sensor; A semiconductor cooling sheet (16), one side of which is connected to the printed circuit board (15), the calibration sensor (11) and the temperature sensor (12), and the other side of which is connected to the heat dissipation fin (17); The refrigeration component (18) is arranged on a side of the heat dissipation fin (17) away from the semiconductor refrigeration plate (16).

6. A dew point sensor according to claim 5, characterized in that: The cold end of the semiconductor cooling sheet (16) is connected to the dual-channel Lamb wave sensor (13).

7. A dew point sensor according to claim 5, characterized in that: The calibration sensor (11) and the temperature sensor (12) are arranged adjacent to the dual-channel Lamb wave sensor (13).

8. A dew point sensor according to claim 5, characterized in that: The resonant frequency of the dual-channel Lamb wave sensor (13) is 1 MHz-1 GHz.

9. A method for measuring gas dew point, using a dew point sensor as claimed in any one of claims 6 to 8, characterized in that: The following steps are involved: S1, cooling, using the semiconductor cooling sheet (16) to reduce the temperature of the dual-channel Lamb wave sensor and the calibration sensor (11) until condensation appears on the surface of the sensing channel (9), and continuing to measure for a certain period of time to collect data; S2, recording data, measuring and recording the change of the resonant frequency of the dual-channel Lamb wave sensor over time in real time, using the host computer to read and record the change of the output of the calibration sensor (11) over time and the change of the output of the temperature sensor (12) over time, that is, the temperature and condensation state at each frame moment; S3, establish a training set, repeat steps S1 and S2 multiple times, and use the obtained data as the training set data, and align the data frames by time; S4, model training, using a random forest algorithm to obtain a classification model based on the training set data, taking the resonant frequency of the sensing channel (9) and the resonant frequency of the temperature reference channel (8) as input and the condensation state as output, completing model training and calibration; linearly fitting the measured temperature of the temperature sensor (12) and the resonant frequency of the temperature reference channel (8), and calculating TCF; S5, testing, repeating steps S1 and S2 without the calibration sensor (11), measuring the change of the resonant frequency of the sensing channel (9) and the temperature reference channel (8), and determining the data frame at the time of dew point occurrence through the model; and calculating the dew point based on the resonant frequency of the data frame of the temperature reference channel (8) at the time of dew point occurrence and the TCF obtained in step S4.

10. A gas dew point measurement method according to claim 9, characterized in that: The training set data includes the resonant frequency and temperature of the sensing channel (9) and the resonant frequency and condensation state of the temperature reference channel (8).

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