CN107655902A - A kind of circular microwave resonant cavity sensor solution concentration measuring method - Google Patents

Abstract

The invention relates to a method for measuring the solution concentration of a circular microwave resonant cavity sensor, comprising the following steps: constructing a solution measurement system, the optimized size of the resonant cavity is as follows: the radius of the bottom surface of the cavity is 28.24mm, the height is 56.48mm, and the wall thickness is 3mm; The outer diameter of the tube is 3mm, the inner diameter is 2mm; the radius of the coupling hole is 3mm; the SMA port of the waveguide is connected to the vector network analyzer to obtain resonance information; when the circular resonant cavity sensor solution tube is a cavity, the measured resonant frequency f ₀ is a reference frequency; after the solution tube is put into the solution to be tested, measure the resonant frequency f of solutions with different concentrations; the mathematical model of the above-mentioned resonant cavity parameters is Substitute f ₀ and f to calculate the dielectric constant ε _r of the solution, so as to determine the concentration of the solution.

Description

A method for measuring the solution concentration of a circular microwave resonant cavity sensor

technical field

The invention belongs to microwave measurement technology and relates to a solution concentration measurement method.

Background technique

With the continuous development of microwave technology, microwave measurement technology has shown a wide range of applications in society, technology and economy. Applications of microwave technology include military, industrial, medical, scientific research, precision testing, communication systems, etc. Concentration is an important parameter of medium characteristics. The ratio of component concentration and the ratio of additive content in food industry safety, dust emission and chemical material content in chemical industry, the content of a certain gas in the atmospheric environment and the detection of pollutants, all of these are To be characterized by concentration. On-line detection of solution concentration occupies an important position in the fields of food, medicine, and chemical industry.

As a sensor based on microwave technology, the circular microwave resonant cavity has the advantages of high quality factor, low loss, high sensitivity and stable measurement. Invention patent application 201210009379.3, a circular microwave resonant cavity is given, and various parameters are simulated and optimized for solution measurement. The dimensions are as follows: the cavity bottom radius is 28.24mm, the height is 56.48mm, and the wall thickness is 3mm; The outer diameter of the tube is 3mm, the inner diameter is 2mm; the radius of the coupling hole is 3mm; currently in the field of scientific research using microwave resonator measurement research methods (documents [1]-[5]) there is no clear mathematical model as a guide. The present invention is based on mathematical derivation and provides a solution concentration measurement method on the given optimized size.

Citation:

[1] S.Kim, H.Melikyan, J.Kim, A.Babajanyan, J.H.Lee, L.Enkhtur, B.Friedmanand K.Lee, "Noninvasive in virto measurement of pig-blood D-glucose by using microwave cavity sensor , "Diabetes Res. Clinical Pract., pp.379-384, Jan. 2012.

[2] R.Dobson, R.Wu and P.Callaghan, "Blood glucose monitoring using microwave cavity perturbation," Electronics Letters., vol.48, no.15, pp.1-2, May2012.

[3] S.Kim, J.Kim, K.Kim et al. "In vitro monitoring of goat-bloodglycemia with a microwave biosensor," Current Applied Physics, 14, pp.563-569, Jan 2014.

[4] G.Gennarelli, S.Romeo, M.R.Scarfi and F.Soldovieri, "A microwaveresonant sensor for concentration measurements of liquid solutions," IEEE Sensors J., vol.13, no.5, pp.1857-1864, May 2013

[5] Suttie N, Shaw J, Hill M J, "Direct demonstration of microwave demagnetization of a whole rock sample with minimal heating," Earth and Planetary Science Letters, vol.3, no.292, pp.357-362, Feb 2010

Contents of the invention

The invention simulates and optimizes the geometric size of a circular microwave resonant cavity sensor, and further proposes a solution concentration measurement method based on the optimized size.

A method for measuring the solution concentration of a circular microwave resonant cavity sensor, comprising the following steps:

(1) Build a solution measurement system, the solution tube holds the solution, the waveguide and the cavity are coupled and connected through small holes, and the parameters are optimized by simulation. The dimensions are as follows: the radius of the bottom of the cavity is 28.24mm, the height is 56.48mm, and the wall thickness is 3mm ; The outer diameter of the solution tube is 3mm, the inner diameter is 2mm; the radius of the coupling hole is 3mm;

(2) The SMA port of the waveguide is connected to a vector network analyzer to obtain resonance information;

(3) When the circular resonant cavity sensor solution tube is a cavity, the measured resonant frequency _f0 is the reference frequency;

(4) After the solution tube is put into the solution to be tested, measure the resonance frequency f of solutions with different concentrations;

(5) The mathematical model of the above resonant cavity parameters is

Substitute f ₀ and f to calculate the dielectric constant ε _r of the solution, so as to determine the concentration of the solution.

The present invention establishes a clear expression of solution permittivity and resonance frequency of resonant cavity sensor through mathematical derivation of cylindrical resonant cavity model. This expression is universal, and then according to the optimized resonant cavity size, specific Expression, so that the composition of various solutions can be measured, etc.

Description of drawings

Fig. 1 The resonant cavity cavity figure that the present invention adopts

Figure 2 Experimental measurement and theoretical calculation data of sugar solution

Specific implementation method

The solution concentration measurement principle of the present invention is realized according to the perturbation theory. According to the resonant cavity perturbation technology, the change of the resonant frequency of the sensor is:

ε and μ are the initial permittivity and permeability, Δε and Δμ are the changes in permittivity and permeability, and E ₀ and H ₀ represent the initial electric field and magnetic field vectors. The resonant cavity resonant frequency varies from the reference frequency _f0 to f.

Since the resonant cavity average time electromagnetic energy storage is equal, the frequency offset can be simplified as:

When measuring, when the sample is placed at the maximum electric field, the influence of the magnetic field can be ignored, and the frequency offset is:

When the resonator works in TE ₀₁₁ mode, the field components are:

l is the length of the resonant cavity, ω ₀ is the resonant angular frequency, μ ₀ is the magnetic permeability of the cavity, H ₀ is the magnetic field strength, k _c =3.832/a, a is the radius of the resonant cavity, and J ₀ is the zero-order Bessel function.

Therefore, the frequency offset of the resonant cavity sensor is

Where K ₁ and K ₂ are the constant values of the triple integral

From the commonly used integral formula:

For the detailed parameters of the resonant cavity, please refer to the invention patent application 201210009379.3. The parameters have been optimized by simulation, and the dimensions are as follows: the radius of the bottom surface of the cavity is 28.24mm, the height is 56.48mm, and the wall thickness is 3mm; the outer diameter of the solution tube is 3mm, and the inner diameter is 2mm; The coupling hole radius is 3mm.

Substituting the parameters into the integral formula gives

When the solution is placed in the cavity, the change of the resonance frequency caused by the change of the dielectric constant of the solution is:

The change in the composition of the sample to be tested in the resonant cavity sensor will lead to a change in the electromagnetic field distribution inside the resonant cavity, which intuitively shows the change of the resonant frequency, and then the sample to be tested can be determined according to the offset of the calculated resonant frequency ingredients.

Under the temperature of 298.15K, the system measures the dibasic sugar aqueous solution of 70-150 mg/dl, with a step size of 10 mg/dl, with fast measurement response and high precision. The experimental results are shown in Figure 2. The increase in the concentration of the sugar solution causes a linear increase in the resonance frequency. The experimental results match the mathematical model calculation results very well, with high accuracy and reliability.

Claims (1)

1. A circular microwave resonant cavity sensor solution concentration measurement method, comprising the following steps: (1) Build a solution measurement system, the solution tube holds the solution, the waveguide and the cavity are coupled and connected through small holes, and the parameters are optimized by simulation. The dimensions are as follows: the radius of the bottom of the cavity is 28.24mm, the height is 56.48mm, and the wall thickness is 3mm ; The outer diameter of the solution tube is 3mm, the inner diameter is 2mm; the radius of the coupling hole is 3mm; (2) The SMA port of the waveguide is connected to a vector network analyzer to obtain resonance information; (3) When the circular resonant cavity sensor solution tube is a cavity, the measured resonant frequency _f0 is the reference frequency; (4) After the solution tube is put into the solution to be tested, measure the resonance frequency f of solutions with different concentrations; (5) The mathematical model of the above resonant cavity parameters is <mrow><mfrac><mrow><mo>(</mo><mi>f</mi><mo>-</mo><msub><mi>f</mi><mn>0</mn></msub><mo>)</mo></mrow><msub><mi>f</mi><mn>0</mn></msub></mfrac><mo>&amp;ap;</mo><mo>-</mo><mn>0.00013</mn><mrow><mo>(</mo><msub><mi>&amp;epsiv;</mi><mi>r</mi></msub><mo>-</mo><mn>1</mn><mo>)</mo></mrow></mrow> Substitute f ₀ and f to calculate the dielectric constant ε _r of the solution, so as to determine the concentration of the solution.