Disclosure of Invention
In view of this, the invention provides a strain sensor composed of three LGS surface acoustic wave resonators and a test method thereof, which solve the problem in the related art that the strain sensor composed of the surface acoustic wave resonators performs strain test in an environment with large temperature variation.
According to an aspect of the present invention, there is provided a strain sensor composed of three LGS surface acoustic wave resonators, including: a first LGS surface acoustic wave resonator, a second LGS surface acoustic wave resonator, and a third LGS surface acoustic wave resonator; the first LGS surface acoustic wave resonator is arranged on an object to be detected along the same direction of the surface acoustic wave propagation direction and the main strain of the object to be detected, the second LGS surface acoustic wave resonator is arranged on the object to be detected along the vertical direction of the surface acoustic wave propagation direction and the main strain of the object to be detected, and the third LGS surface acoustic wave resonator is arranged on the object to be detected along the direction of the surface acoustic wave propagation direction and the main strain of the object to be detected in any angle direction, wherein any angle refers to an angle except the same direction and the vertical direction; the three LGS acoustic surface wave resonators are arranged at the same horizontal position of an object to be detected; the three LGS surface acoustic wave resonators comprise an LGS piezoelectric substrate, and interdigital fingers and electrodes arranged on the LGS piezoelectric substrate; the piezoelectric substrate materials of the three LGS surface acoustic wave resonators have the same tangential direction.
According to another aspect of the present invention, there is provided a method of testing a strain sensor composed of three LGS surface acoustic wave resonators, including the steps of:
step 1: the strain sensor composed of the three LGS surface acoustic wave resonators provided by the invention is firstly bonded on the same horizontal position of an object to be detected by using high-temperature-resistant inorganic glue.
Step 2: and connecting the three LGS surface acoustic wave resonators with a vector network analyzer by using a high-temperature coaxial line with an SMA connector at one end. One end with an SMA joint is connected with a vector network analyzer, the other end of the SMA joint is coaxially stripped and divided into three strands, and the three strands are respectively connected with three LGS surface acoustic wave resonators; under the condition of normal temperature, the initial resonant frequencies of three LGS surface acoustic resonators displayed by a vector network analyzer are respectively recorded: the first LGS SAW resonator is f0-0The second LGS SAW resonator is f0-90The third LGS SAW resonator is f0-x。
And step 3: when the temperature rises to T, applying strain to a strain sensor consisting of an object to be measured and the three LGS surface acoustic wave resonators, and respectively recording the resonant frequencies of the three LGS surface acoustic wave resonators displayed by the vector network analyzer: the first LGS SAW resonator is f0-0', the second LGS SAW resonator is f0-90', the third LGS SAW resonator is f0-x′。
And 4, step 4: subtracting the initial resonant frequency corresponding to the step 2 from the resonant frequency recorded in the step 3, and respectively calculating the resonant frequency change value delta f of the first LGS surface acoustic wave resonator0And a resonance frequency variation value Deltaf of a second LGS surface acoustic wave resonator90And a resonance frequency variation value Deltaf of a third LGS surface acoustic wave resonatorx。
Step 5, calculating the change result delta f of the resonant frequency according to the step 40、Δf90And Δ fxEstablishing relational expressions (4), (5) and (6) of resonant frequencies of the first, second and third LGS surface acoustic wave resonators with temperature change and strain change, respectively:
first LGS surface acoustic wave resonator:
second LGS surface acoustic wave resonator:
third LGS surface acoustic wave resonator:
wherein: Δ ε represents the change in strain, Δ f0、Δf90And Δ fxRespectively representing the variation values of the resonant frequencies of the first LGS surface acoustic wave resonator, the second LGS surface acoustic wave resonator and the third LGS surface acoustic wave resonator; f. of0-0、f0-90And f0-xRespectively representing initial resonant frequencies of the first, second and third LGS surface acoustic wave resonators; c. C0、c90And cxConstant terms representing strain variations of the first, second, and third LGS surface acoustic wave resonators, respectively; d0,d90,dxConstant terms respectively representing coupling terms of temperature change and strain change of the first LGS surface acoustic wave resonator, the second LGS surface acoustic wave resonator and the third LGS surface acoustic wave resonator; a Δ T2Represents a second order temperature term; b Δ T represents a first order temperature term; Δ T Δ ∈ is expressed as a temperature change and strain change coupling term.
Step 6: eliminating the second order temperature term a delta T of each relation in step 5 by solving the system of equations2And a first order temperature term b Δ T, and then eliminating a temperature change and strain change coupling term Δ T Δ ε to obtain formula (11):
the strain change delta epsilon of the object to be measured can be obtained through the formula (11), and therefore the strain magnitude epsilon of the object to be measured can be obtained.
The theoretical analysis of the invention is as follows:
in the prior art, a strain sensor composed of two LGS surface acoustic wave resonators is used for strain testing in an environment with large temperature change, a coupling item can appear between the temperature and the strain, so that a measurement result and a result obtained by reacting a standard strain gauge are greatly different, and therefore the strain sensor composed of the two LGS surface acoustic wave resonators is not suitable for the strain testing in the environment with large temperature change. Based on the result of analyzing the experimental data of the strain sensor consisting of the two LGS surface acoustic wave resonators, the relationship between the change of the resonant frequency along with the temperature and the change of the strain is re-determined, and the formula (1) is obtained:
in the formula (1), a.DELTA.T2Representing a second-order temperature term, b Δ T a first-order temperature term, s a strain frequency coefficient of the surface acoustic wave resonator, Δ ε a strain change, f0Representing the resonant frequency of the SAW device at room temperature and deltaf representing the change in resonant frequency. Meanwhile, the strain frequency coefficient of the surface acoustic wave resonator and the change of the temperature present a linear relation, and the relation is specifically shown in formula (2):
s=c+dΔT (2)
in the formula (2), c represents a constant term of a strain change, and d represents a constant term of a coupling term of a temperature change and a strain change.
The formula (2) is substituted for the formula (1), and the relation formula (3) of the resonant frequency of the surface acoustic wave resonator along with the temperature change and the strain change can be obtained:
according to the formula (3), the relations (4), (5) and (6) of the resonant frequencies of the first, second and third LGS surface acoustic wave resonators with the changes of temperature and strain are respectively established:
first LGS surface acoustic wave resonator:
second LGS surface acoustic wave resonator:
third LGS surface acoustic wave resonator:
subtracting the formula (5) from the formula (4), subtracting the formula (5) from the formula (6), and eliminating the second-order temperature term a Δ T2And the first order temperature term b Δ T, yielding formula (7) and formula (8):
constant term d obtained by dividing temperature change and strain change coupling term by equation (7)0-d90Equation (8) divided by the constant term d of the temperature change and strain change coupling termx-d90To give formulae (9) and (10):
subtracting the formula (10) from the formula (9), eliminating the coupling term delta T delta epsilon of the temperature change and the strain change, and finally eliminating the influence of the temperature change in the strain test to obtain a relational expression (11) of the resonant frequency and the strain change of the object to be tested:
the strain change delta epsilon of the object to be measured can be obtained through the formula (11), and therefore the strain magnitude epsilon of the object to be measured can be obtained.
In the formula (11), the unknown coefficient has Δ f0、Δf90、ΔfxAnd Δ ε;wherein Δ f0、Δf90And Δ fxThe strain change delta epsilon of the object to be tested can be obtained from the vector network analyzer through the test result, and can be obtained only by substituting the test result into the formula (11).
In summary, a strain sensor and a test method using three LGS surface acoustic wave resonators establish a relational expression of three resonant frequencies with temperature change and strain change by using the three LGS surface acoustic wave resonators, and then according to the characteristics that the three LGS surface acoustic wave resonators have the same temperature coefficient and different strain coefficients in the same temperature environment, the influence of temperature and temperature change on strain test is eliminated, and the accuracy of the strain test is improved. Is suitable for any temperature environment, and is simple and easy to operate.
Detailed Description
For better understanding of the present invention, the technical solution of the present invention will be described in detail with specific examples, but the present invention is not limited thereto.
The surface acoustic wave resonator comprises an LGS piezoelectric substrate, and an electrode 4 and an interdigital 5 which are arranged on the LGS piezoelectric substrate; the piezoelectric substrate is made of LGS (lanthanum gallium silicate) material with the tangential direction of (0 degrees, 138.5 degrees and 26.6 degrees), the size of the substrate is 6mm multiplied by 6mm, and the thickness of the substrate is 0.5 mm; and growing an Au electrode on the substrate by adopting an electron beam evaporation technology. The specific sensing mode of the surface acoustic wave resonator is the piezoelectric effect.
The three LGS surface acoustic wave resonators are combined into a strain sensor, and the strain sensor comprises: a first LGS surface acoustic wave resonator, a second LGS surface acoustic wave resonator, and a third LGS surface acoustic wave resonator. The three LGS surface acoustic wave resonators are arranged on an object to be detected according to the diagram shown in figure 1, wherein a first LGS surface acoustic wave resonator 1 is arranged on the object to be detected along the surface acoustic wave propagation direction of the first LGS surface acoustic wave resonator and the main strain direction of the object to be detected at an angle of 0 degrees; the second LGS surface acoustic wave resonator 2 is arranged on the object to be detected, and forms an angle of 90 degrees with the main strain vertical direction of the object to be detected along the surface acoustic wave propagation direction; and the third LGS surface acoustic wave resonator 3 is arranged on the object to be detected, and forms an angle of 30 degrees with the main strain direction of the object to be detected along the surface acoustic wave propagation direction of the third LGS surface acoustic wave resonator. The three LGS acoustic surface wave resonators are arranged at the same horizontal position of an object to be detected; the three LGS surface acoustic wave resonators comprise an LGS piezoelectric substrate, and interdigital fingers and electrodes arranged on the LGS piezoelectric substrate; the piezoelectric substrate materials of the three LGS surface acoustic wave resonators have the same tangential direction.
In order to simplify the testing process, three LGS surface acoustic wave resonators are usually connected in parallel by a platinum wire or high-temperature silver paste, and then are respectively connected to the same vector network analyzer, and the resonant frequency changes of the three LGS surface acoustic wave resonators are obtained at the same time. In addition, the three LGS surface acoustic wave resonators may not be connected at all, and in this way, the three LGS surface acoustic wave resonators need to be connected to a vector network analyzer respectively to obtain three surface acoustic wave resonant frequency changes. However, when a strain sensor composed of three LGS surface acoustic wave resonators is used for strain testing, the three LGS surface acoustic wave resonators are required to be in the same temperature environment regardless of the manner used.
In this embodiment, a method for testing a strain sensor including three LGS surface acoustic wave resonators is also provided, and the strain of a rectangular alloy plate is tested by the method, and the specific test steps are as follows:
step 1: the strain sensor composed of three LGS surface acoustic wave resonators provided by the invention is firstly bonded on the same horizontal position of a rectangular alloy plate by using high-temperature-resistant inorganic glue.
Step 2: and connecting the three LGS surface acoustic wave resonators with a vector network analyzer by using a high-temperature coaxial line with an SMA connector at one end. One end with an SMA joint is connected with a vector network analyzer, the other end of the SMA joint is coaxially stripped and divided into three strands, and the three strands are respectively connected with three LGS surface acoustic wave resonators; under the condition of normal temperature, vector is recorded respectivelyInitial resonance frequencies of three LGS surface acoustic resonators as displayed by the quantum network analyzer: initial resonant frequency f of first LGS surface acoustic wave resonator0-0221.286MHz, the initial resonant frequency f of the second LGS SAW resonator0-90227.583MHz, the initial resonant frequency f of the third LGS SAW resonator0-30Is 224.356 MHz.
And step 3: when the temperature rises to 225 ℃, applying strain to a strain sensor consisting of an object to be tested and three LGS surface acoustic wave resonators; the resonant frequencies of the three LGS surface acoustic resonators displayed by the vector network analyzer at this time were recorded separately: first LGS surface acoustic wave resonator f0-0' 221.313MHz, second LGS SAW resonator f0-90' 227.606MHz, third LGS SAW resonator f0-30′=224.382MHz。
And 4, step 4: correspondingly subtracting the initial resonant frequency obtained in the step 2 from the resonant frequency obtained by the three LGS surface acoustic wave resonators in the step 3 to obtain a resonant frequency change value delta f of the first LGS surface acoustic wave resonator0And a resonance frequency variation value Deltaf of a second LGS surface acoustic wave resonator90And a resonance frequency variation value Deltaf of a third LGS surface acoustic wave resonator30。
Step 5, changing the resonant frequency change value delta f of the three LGS surface acoustic wave resonators calculated in the step 40、Δf90And Δ f30Formula (11):
the calculation was carried out to obtain the magnitude of the strain change Δ ∈ of the rectangular alloy sheet, and finally the magnitude of strain ∈ of the rectangular alloy sheet was 491.459863 μ ∈.
To verify the correctness and feasibility of equation (11), the test of a standard strain gauge was added to the above example and the error between the two was calculated. The standard strain gauge shows that the strain of the rectangular alloy plate is 493 mu epsilon at the temperature T of 225 ℃; comparing the two, the error of the calculation result is only 0.3% by adopting the method provided by the invention. It can be seen that the strain calculated by the theoretical expression of the present invention substantially matches the results shown by the standard strain gauge.
For the present embodiment, the strain sensor is tested at different temperatures, and the results of strain change and frequency change are shown in fig. 2, and when the temperature changes, the relationship between the resonant frequency and the strain is still linear, which indicates that the strain sensor and the testing method provided by the present invention, which are composed of three LGS surface acoustic wave resonators, completely eliminate the influence of temperature change, and the results are more accurate compared with the prior art.