CN111077170B - High-sensitivity microwave microfluidic sensor based on electromagnetic band gap structure - Google Patents
High-sensitivity microwave microfluidic sensor based on electromagnetic band gap structure Download PDFInfo
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- CN111077170B CN111077170B CN201911364213.1A CN201911364213A CN111077170B CN 111077170 B CN111077170 B CN 111077170B CN 201911364213 A CN201911364213 A CN 201911364213A CN 111077170 B CN111077170 B CN 111077170B
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N22/00—Investigating or analysing materials by the use of microwaves or radio waves, i.e. electromagnetic waves with a wavelength of one millimetre or more
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2617—Measuring dielectric properties, e.g. constants
Abstract
The invention discloses a high-sensitivity microwave microfluidic sensor based on an electromagnetic band gap structure. The invention comprises a coplanar waveguide transmission line, a dielectric layer and an electromagnetic band gap structure from top to bottom in sequence, wherein the electromagnetic band gap structure is a periodic structure, and all unit structures are connected through microstrip lines. The micro-fluid channel is arranged at the lower side of the electromagnetic band gap structure, and respectively covers the gaps at the left side and the right side of the electromagnetic band gap unit structure in a branch path mode, each branch path is respectively converged at an upper port and a lower port, and a liquid sample is injected into one port by a pinhole and then flows out from the other port. The structure of the invention is based on an electromagnetic band gap structure, and the microfluidic channel is designed into a plurality of shunt branches, thereby obviously increasing the path around the electric field, improving the conditions of lower sensitivity and lower quality factor Q value of the existing microfluidic sensor, improving the sensitivity, having higher Q value and ensuring the high resolution and accuracy of measurement.
Description
Technical Field
The invention belongs to the technical field of microwaves, and particularly relates to a high-sensitivity microwave microfluidic sensor structure based on an electromagnetic band gap structure, which is used for representing the dielectric constant of liquid.
Background
With the continuous development of microwave technology, microwave sensors are increasingly used in electronics, biomedicine and industrial applications, and are the first choice for microfluidics and biosensing applications due to the advantages of high sensitivity, good robustness, low manufacturing and measuring costs, and the like.
The dielectric constant is one of important physical properties of electromagnetic properties of a reaction substance, and is an important link of interaction between the substance and an electromagnetic field, and the response of a material to electromagnetic waves depends on the dielectric constant, so that the accurate measurement of the dielectric constant is important for applications such as antenna, microwave circuit design and nondestructive testing. A microfluidic sensor, whose microfluidic channel is usually considered to be in the gap region of a designed structure, has a strong local electric field when at resonance, which is very sensitive to changes in nearby dielectric materials, can change the resonance frequency and the quality factor by placing a liquid sample in the microfluidic channel, and determines the complex dielectric constant of the liquid sample from the measured changes in resonance frequency and peak attenuation. At present, in the design and application of a microfluidic sensor, the sensitivity of the microfluidic sensor based on the existing resonance principle is low, the Q value is continuously reduced along with the increase of the dielectric constant of liquid, and few microfluidic sensors designed based on the electromagnetic band gap structure are available. At present, the maximum Sensitivity of a Microwave sensor based on an electric small resonator is 6.81MHz, and is proposed by an Amir Ebrahimi journal article 'ultra high-Sensitivity Microwave sensor for microfluidics complex Sensitivity Measurement'. In view of this, the structure of the invention provides a microfluidic sensor based on an electromagnetic band gap structure, and a plurality of microfluidic channel branches are designed in Polydimethylsiloxane (PDMS), so that an electric field path of a measurement area is greatly increased, the detection sensitivity is greatly improved (6.97MHz), a higher Q value is provided, and the measurement accuracy and resolution are improved.
Disclosure of Invention
The invention mainly aims to overcome the defects of the prior art and provides a microwave microfluidic sensor with reasonable structure, high sensitivity and high Q value.
In order to achieve the purpose, the invention is realized according to the following technical scheme:
the invention relates to a microwave micro-fluid sensor based on an electromagnetic band gap structure, which is characterized in that a coplanar waveguide (CPW) transmission line, a dielectric layer and the electromagnetic band gap structure are sequentially arranged from top to bottom, wherein the electromagnetic band gap structure is a periodic structure, the unit structure size is 28mm multiplied by 28mm, and all the unit structures are connected through a rectangular microstrip line.
The unit structure of the electromagnetic band gap structure is a square annular structure, a small square plane plate is embedded in a hollow-out area in the center of the unit structure, and a gap is reserved between the square plane plate and the square annular structure; etching a rectangular gap on the upper side and the lower side of the smaller square, and leading out a microstrip line from the middle point of the bottom of the rectangular gap to be connected with the inner wall of the square annular structure;
the CPW microstrip line structure is arranged on the upper surface of the dielectric layer and comprises an input port and an output port which are respectively positioned on two sides of the dielectric layer, the two ports are used for connecting SMA connectors, and the SMA connectors are connected with the vector network analyzer;
the width of the CPW microstrip line is 1.56mm, and the distance between the CPW microstrip line and ground planes on two sides is 0.8 mm;
the microfluidic channel is arranged on the lower side of the electromagnetic band gap structure and respectively covers gaps on the left side and the right side of the electromagnetic band gap unit structure in a branch path mode, each branch path is respectively converged at an upper port and a lower port, and a liquid sample is injected into one port by a pinhole and then flows out of the other port;
the height, the width and the length of the whole PDMS channel are respectively 5mm, 25mm and 54mm, and the height of the microfluidic channel inside the PDMS channel is 0.2 mm;
the microfluidic channel is formed by processing PDMS (polydimethylsiloxane), 4 branch circuits are arranged in total, the width of each branch circuit is 2.6mm, the branch circuits pass through the groove rings on the left side and the right side of the central area of the electromagnetic unit structure respectively, the electric field intensity of the area is the largest, the microfluidic channel is very sensitive to the dielectric constant change of a dielectric material, and the microfluidic channel is suitable for being placed to measure the dielectric constant of a liquid sample;
the dielectric layer is made of RogersRO4350 material, the relative dielectric constant of the dielectric layer is 3.66, the thickness of the dielectric layer is 0.762mm, and the loss tangent value is 0.004.
The sensitivity of the sensor determines the resolution ratio of the liquid dielectric constant measurement, the Q value determines the measurement precision, and the miniaturization and anti-interference capability determine the practicability of the sensor;
compared with the prior art, the structure of the invention is as follows:
the structure of the invention is based on an electromagnetic band gap structure, and the microfluidic channel is designed into a plurality of shunt branches, thereby obviously increasing the path around the electric field, improving the conditions of lower sensitivity and lower quality factor Q value of the existing microfluidic sensor, improving the sensitivity, having higher Q value and ensuring the high resolution and accuracy of measurement.
Drawings
FIG. 1 is a schematic top-to-bottom view of the inventive structure;
FIG. 2 is a schematic diagram of the structure of the present invention, wherein (a) is a parametric illustration of the CPW transmission line; (b) marking a parameter of the electromagnetic band gap structure with a figure;
FIG. 3 is a schematic diagram of the S parameter of the inventive structure;
FIG. 4 is a schematic diagram of the electric field intensity distribution of the structure of the present invention;
FIG. 5 is a schematic diagram of a PDMS microfluidic channel of the inventive structure, wherein (a) is a front view of the PDMS microfluidic channel and (b) is a top view of the PDMS microfluidic channel;
FIG. 6 is a schematic diagram showing the relationship between the S parameter of the structure of the present invention and the liquid sample to be tested;
wherein, 1 is GND; CPW microstrip line; a Rogers RO4350 dielectric layer; 4. an electromagnetic bandgap structure.
Detailed Description
The structure of the present invention will be described in further detail with reference to the following detailed description of the preferred embodiments of the invention.
Fig. 1 is a schematic diagram of the structure of the present invention, and the top layer structure to the bottom layer structure are a CPW transmission line 2, a dielectric layer 3 and an electromagnetic bandgap structure 4. The electromagnetic band gap structure is formed by two periodic structures, the unit structure size is 28mm multiplied by 28mm, and all the unit structures are connected through a rectangular microstrip line.
The CPW microstrip line structure is arranged on the upper surface of the dielectric layer and comprises an input port and an output port which are respectively positioned on two sides of the dielectric layer, the two ports are used for connecting SMA connectors, and the SMA connectors are connected with the vector network analyzer; the width of the CPW microstrip line is 1.56mm, and the distance between the CPW microstrip line and the ground planes 1 on the two sides is 0.8 mm;
fig. 2(a) and 2(b) are parameter labeling diagrams of the CPW transmission line and the electromagnetic band gap structure, respectively, where two ports of the transmission line are used for connecting the SMA connector, a unit structure of the electromagnetic band gap structure is a square ring structure, a small square planar plate is embedded in a hollow central region of the unit structure, and a gap is left between the square planar plate and the square ring structure; etching a rectangular gap on the upper side and the lower side of the smaller square, and leading out a microstrip line from the middle point of the bottom of the rectangular gap to be connected with the inner wall of the square annular structure;
FIG. 3 is a schematic diagram of S-parameter of the structure of the present invention, wherein the resonant frequency is 2.447GHz and the Q-value is 122.
Fig. 4 is a schematic diagram showing the electric field intensity distribution of the structure of the present invention, in which the electric field intensity around the gap in the central region of the electromagnetic bandgap structure is the largest, and the microfluidic channel is suitable for being placed for measuring the dielectric constant of the liquid sample.
Fig. 5 is a schematic diagram of a PDMS microfluidic channel of the structure of the present invention, in which the length, width, and height of the whole body are 54mm, 25mm, and 5mm, respectively, the height of the microfluidic channel is 0.2mm, there are 4 branches in total, which cover the gaps on the left and right sides of the electromagnetic bandgap unit structure, respectively, the width of each branch is 2.6mm, the 4 branches converge at the upper and lower ports, respectively, and a liquid sample is injected into one port with a pinhole and then flows out from the other port;
the values of the parameters of the structure of the invention are shown in table 1:
TABLE 1 values of the parameters
| Parameter(s) | w1 | w2 | w3 | w4 | w5 |
| Numerical value (mm) | 1.56 | 12.42 | 0.4 | 0.4 | 0.4 |
| Parameter(s) | a1 | a2 | g1 | g2 | d1 |
| Numerical value (mm) | 28 | 13.42 | 1 | 2.6 | 9.82 |
| Parameter(s) | d2 | d3 | d4 | c | l1 |
| Numerical value (mm) | 18.98 | 2.6 | 13.42 | 1 | 62 |
| Parameter(s) | s1 | t1 | t2 | t3 | h1 |
| Numerical value (mm) | 6 | 0.8 | 0.55 | 3 | 5 |
| Parameter(s) | h2 | ||||
| Numerical value (mm) | 0.2 |
As shown in FIG. 6, which is a graph of the relationship between the S parameter of the structure of the present invention and the liquid sample to be measured, when the dielectric constant of the liquid sample to be measured is increased from 1 to 80, the resonant frequency of the sensor is changed from 2.385GHz to 1.785GHz, wherein the corresponding frequency offset is 488MHz when the dielectric constant of the liquid is increased from 10 to 80, the sensitivity of the structure of the present invention is 6.97MHz, and the structure has a high Q value, thereby ensuring the resolution and the accuracy of the measurement.
The invention has been described above with reference to the accompanying drawings, it is obvious that the invention is not limited to the specific implementation in the above-described manner, and it is within the scope of the invention to apply the inventive concept and solution to other applications without substantial modification, or with substantial modification.
Claims (6)
1. The high-sensitivity microwave microfluidic sensor based on the electromagnetic band gap structure is characterized by sequentially comprising a coplanar waveguide microstrip line, a dielectric layer and the electromagnetic band gap structure from top to bottom, wherein the electromagnetic band gap structure is a periodic structure, and all unit structures are connected through a rectangular microstrip line;
the unit structure of the electromagnetic band gap structure is a square annular structure, a small square plane plate is embedded in a hollow area in the center of the unit structure, and a gap is reserved between the small square plane plate and the square annular structure; etching a rectangular gap on the upper and lower sides of the smaller square plane plate, and leading out a microstrip line from the middle point of the bottom of the rectangular gap to be connected with the inner wall of the square annular structure;
the coplanar waveguide microstrip line is arranged on the upper surface of the dielectric layer and comprises an input port and an output port which are respectively positioned on two sides of the dielectric layer, the two ports are used for connecting SMA connectors, and the SMA connectors are connected with the vector network analyzer;
the width of the coplanar waveguide microstrip line is 1.56mm, and the distance between the coplanar waveguide microstrip line and ground planes on two sides is 0.8 mm;
the micro-fluid channel is arranged at the lower side of the electromagnetic band gap structure, and respectively covers the gaps at the left side and the right side of the electromagnetic band gap unit structure in a branch path mode, each branch path is respectively converged at an upper port and a lower port, and a liquid sample is injected into one port by a pinhole and then flows out from the other port.
2. A high sensitivity microwave microfluidic sensor based on an electromagnetic bandgap structure as claimed in claim 1 wherein the height of the microfluidic channel is 0.2 mm.
3. The electromagnetic bandgap structure based high sensitivity microwave microfluidic sensor as claimed in claim 1, wherein said microfluidic channel has 4 branches, each branch having a width of 2.6mm, passing through the left and right slot rings of the central region of the unit structure of two electromagnetic bandgap structures.
4. The high-sensitivity microwave microfluidic sensor based on an electromagnetic band gap structure as claimed in claim 1, wherein the dielectric layer is a RogersRO4350 material, the relative dielectric constant is 3.66, the dielectric thickness is 0.762mm, and the loss tangent value is 0.004.
5. The electromagnetic bandgap structure based high sensitivity microwave microfluidic sensor as claimed in claim 1, wherein said electromagnetic bandgap structure unit structure size is
。
6. A high sensitivity microwave microfluidic sensor based on an electromagnetic bandgap structure as claimed in claim 1 wherein the unit cell structures of the electromagnetic bandgap structure are spaced apart by 6 mm.
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