Miniaturized sensor for measuring dielectric constant of dielectric material

Abstract

The invention discloses a miniaturized sensor for measuring the dielectric constant of a dielectric material, and belongs to the technical field of microwave sensing. The sensor structure comprises a top metal patch signal layer, a middle dielectric substrate layer and a bottom metal grounding layer, wherein the top-layer metal patch structure comprises five parts, namely a 50-ohm microstrip line, a 1 / 4 wavelength impedance change line, a coplanar waveguide with a coupling slot, a substrate integrated waveguide and a sensing unit, and the top layer and the grounding layer are connected through a metalized through hole of the middle layer; and a complementary split-ring resonator sensing unit of a stepped impedance fractal structure is etched on the top metal layer and is used as a sensing area for placing a solid material for dielectric constant measurement. According to the sensor, the purpose of miniaturization of the sensor is achieved through loading of the resonant ring unit, the measurement sensitivity is high, the measurement error is small, and the sensor is suitable for dielectric constant measurement of dielectric materials.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave sensing and relates to a miniaturized sensor for measuring the dielectric constant of a dielectric material. Background Art

[0002] The dielectric constant describes the dielectric polarization characteristics of a medium under the action of an external electric field, and is an important property of dielectric materials. The dielectric constant measurement of dielectric materials is of great significance in the field of RF microwave device manufacturing: for example, RF filters, antennas, high-speed PCB board production, etc. all require the use of dielectric materials with specific dielectric constants. With the development of microwave sensing technology, dielectric measurement sensors in the microwave frequency band are also constantly developing. There are three mainstream methods for measuring the dielectric constant of plates using microwave technology: the free space method, the waveguide method, and the electromagnetic resonance method. The free space method has a wide measurement range but is only applicable to large-sized materials; the waveguide method has high measurement accuracy but its measurement system is bulky and only applicable to thin sheet materials; the electromagnetic resonance method can realize the sampling and identification of small-sized plates, the overall measurement device is simple, and the accuracy is moderate, so the sensor based on the electromagnetic resonance method is very suitable for the dielectric constant measurement of dielectric materials.

[0003] However, most of the dielectric constant measurement sensors currently implemented based on the electromagnetic resonance method are electrically large in size and have low measurement sensitivity. The electrically large size increases the sampling area of ​​the object to be measured, causing unnecessary material loss during sampling, and also increases the manufacturing cost of the sensor; the low measurement sensitivity makes it difficult to distinguish between plates with similar dielectric constant values, limiting the measurement resolution of the sensor.

[0004] Therefore, in order to further improve the sensor test sensitivity, achieve enhanced test resolution, and achieve miniaturization of sensor electrical dimensions, and reduce the overall sensor manufacturing cost and measurement sampling cost. The present invention proposes a miniaturized sensor for dielectric constant measurement of dielectric materials, which uses a step impedance fractal resonant ring sensing unit with a SIW structure to achieve device miniaturization and sensitivity enhancement. Compared with the dielectric measurement sensor of the traditional coupled microstrip transmission line and waveguide structure, it has higher test resolution and smaller overall size, and has the potential to be integrated into radio frequency circuit components and systems. Summary of the invention

[0005] The purpose of the present invention is to provide a miniaturized sensor for measuring the dielectric constant of a dielectric material.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A miniaturized sensor for measuring the dielectric constant of a dielectric material. The sensor has a three-layer structural design, which comprises, from top to bottom, a metal patch signal layer (10), an intermediate dielectric substrate layer (5), and a bottom metal grounding layer (9).

[0008] Furthermore, the top metal patch signal layer (10) is composed of five parts: a 50-ohm microstrip line (1), a 1 / 4-wavelength impedance transformation line (2), a coplanar waveguide with a coupling slot (3), a substrate integrated waveguide (6), and a sensing unit (7). The sensing unit (7) realizes miniaturization design by generating a new low-frequency resonance point using a stepped impedance resonator structure.

[0009] Furthermore, the inner and outer rings of the sensing unit (7) are square structures with side lengths br and ar respectively; the opening widths of both the inner and outer rings are g; the width of the thin part of the stepped impedance slot is W s , and the thick part has a width of W r , and are rectangular structure slot grooves with four sizes of lengths Lr1, Lr2, Lr3, and Lr4 respectively.

[0010] Furthermore, the diameter of the metallized vias (4) on both sides of the dielectric substrate (5) is d1, the distance between adjacent vias is d2, the inner wall is a metal layer, and the vias (4) in the substrate are equivalent to the two side walls of a rectangular waveguide, restricting the electromagnetic field to propagate in the SIW.

[0011] Furthermore, the metallized vias (4) are cylindrical holes penetrating the dielectric substrate, and the inner wall of the holes is covered with a copper skin with a thickness of 0.0018 mm to connect the metal patch signal layer (10) and the bottom metal ground layer (9).

[0012] Furthermore, the dielectric substrate (5) is made of an F4B RF board with a thickness of h1, a dielectric constant of 3.5, and a loss tangent of 0.002, and the overall cross-sectional dimension is a×b.

[0013] Furthermore, the miniaturized dielectric constant measurement sensor for dielectric materials operates in the S band, and the relative electrical size of the sensor is 0.598λ g ×0.51λ g ×0.03λ g , λ g is the waveguide wavelength corresponding to the operating frequency point of 2.4 GHz. The peak sensitivity of the sensor is 5.25%, and the maximum measurement error is only 1.62%.

[0014] Compared with the prior art, the beneficial effects of the present invention are:

[0015] The miniaturized dielectric constant measurement sensor for dielectric materials of the present invention introduces a stepped open resonator sensing unit on the traditional substrate integrated waveguide structure, reducing the relative size of the sensor and improving the measurement sensitivity; in addition, the S of the sensor 21There are obvious transmission zeros near the resonant peaks of the sensing units in the transmission curve, which makes it difficult for the resonant peaks to be measured to be confused with the higher-order oscillation harmonics of the waveguide, and is more conducive to the extraction of the resonant frequency measurement; In summary, the present invention can not only measure the dielectric constant of the dielectric material, but also has the characteristics of small electrical size, high sensitivity, low measurement error, etc.

[0016] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following specification. Brief Description of the Drawings

[0017] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0018] Figure 1 is the top view of the structural dimensions of the sensor of the present invention.

[0019] Figure 2 is the 3D perspective structural disassembly diagram of the sensor of the present invention.

[0020] Figure 3 is the relationship diagram between the dielectric constant of the dielectric material and the resonant frequency of the sensor obtained by simulation in the embodiment of the present invention.

[0021] Figure 4 is the fitting relationship diagram between the dielectric constant of the dielectric material and the resonant frequency of the sensor obtained by simulation in the embodiment of the present invention.

[0022] Figure 5 is the comparison diagram between the measured data and the simulation data of the dielectric material with a known dielectric constant selected in the embodiment of the present invention. Detailed Embodiment

[0023] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0024] In order to make the objectives, features and advantages of the present invention more obvious and understandable, please refer to the accompanying drawings.

[0025] In the present invention, the operating frequency point of the miniaturized dielectric constant measurement sensor for the dielectric material without loading the sample of the dielectric material to be measured is 2.4 GHz.

[0026] Figure 1This is a top view of the structural dimensions of the miniaturized dielectric constant measurement sensor provided by the present invention, mainly showing the structural composition of the top metal patch signal layer (10). The feeding port and the output port are connected to the 50-ohm microstrip line (1). The transition structure consists of a 1 / 4-wavelength impedance transformation line (2) and a coplanar waveguide with a coupling slot (3), connecting the 50-ohm microstrip line (1) to the internal substrate integrated waveguide (6). Compared with the direct connection of the microstrip line (1) to the substrate integrated waveguide (6), the overall size is more compact. A sensing unit (7) is loaded at the center of the substrate integrated waveguide (6), which is a complementary split-ring resonator structure with stepped impedance fractal. The sensing unit (7) is a groove structure etched on the top metal layer, and the width of the thin part of the stepped impedance slot is W s , and the thick part has a width of W r , and rectangular structure slot gaps with 4 sizes of lengths Lr1, Lr2, Lr3, and Lr4 respectively.

[0027] Figure 2 This is a 3D perspective structural disassembly diagram of the sensor of the present invention. As shown in the figure, the main body of the sensor is divided into 3 layers of structures, from top to bottom are the metal patch signal layer (10), the middle dielectric substrate layer (5), and the bottom metal ground layer (9). During measurement, a sample of the dielectric material to be measured with dimensions of 9mm×9mm×1mm is placed directly above the central sensing unit (7) of the metal patch signal layer (10).

[0028] The present invention uses HFSS simulation software to simulate the above-mentioned miniaturized dielectric constant measurement sensor for the dielectric material. The optimized parameters after simulation are shown in Table 1. The simulation results are as Figure 3 , Figure 5 shown.

[0029] Table 1 Parameter table of the miniaturized dielectric constant measurement sensor for the dielectric material

[0030] Table 1 Specific dimensions of the sensor

[0031]

[0032] Figure 3 This is a graph showing the relationship between the dielectric constant of the dielectric material and the resonant frequency of the sensor obtained from the simulation of the embodiment of the present invention. From the simulation results, it can be seen that when the relative dielectric constant of the dielectric material to be measured changes from 1 to 11, the resonant frequency drops from 2.4 GHz to 1.6 GHz, the overall offset is 0.8 GHz, and the relative resonant frequency offset is 80 MHz / unit dielectric constant value, with relatively high sensitivity.

[0033] Figure 4This is the fitting relationship diagram between the dielectric constant of the dielectric material and the resonant frequency of the sensor obtained by simulation in the embodiment of the present invention. From the fitting results, it can be seen that as the relative dielectric constant of the object to be measured increases, the resonant frequency of the sensor decreases accordingly. The relationship between the relative dielectric constant and the resonant frequency satisfies the formula: ε r = 168.546Δf 3 - 18.112Δf 2 + 18.212Δf + 1.03. Based on this formula, a relative dielectric constant calculation model can be established under this circuit structure. When detecting the relative dielectric constant of a physical object, the sample to be measured is placed on the sensing unit (7), and the port is connected to a vector network analyzer. The resonant frequency is determined through the resonant curve within a specific frequency band, and then the relative dielectric constant of the object to be measured is calculated.

[0034] Figure 5 This is the comparison diagram between the measured data and the simulation data of the dielectric materials with known dielectric constants selected in the embodiment of the present invention. From the test results, it can be seen that the resonant frequency obtained by simulation is basically consistent with the measured points, verifying the feasibility of using the present invention to measure the dielectric constant of dielectric materials.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A miniaturized sensor for measuring the dielectric constant of a dielectric material, the sensor comprising three parts: a metal patch signal layer (10), an intermediate dielectric substrate layer (5) and a bottom metal grounding layer (9). The top layer structure is a signal transmission line composed of a 50 ohm microstrip feed line (1), a 1 / 4 wavelength impedance change line (2), a coplanar waveguide with a coupling slot (3), and a substrate integrated waveguide (6); a complementary open resonant ring unit (7) with an opening facing the feed source is loaded at the center of the top layer; the middle layer is a dielectric substrate (5) containing a metallized through hole (4); and the bottom metal grounding layer (9) is connected to the top layer through the metallized through hole (4).

2. According to claim 1, the metal ground layer (9) of the 50-ohm microstrip feed line (1) of the structure is welded to a common RF connector to serve as a feeding port and an output port for receiving external RF signals, wherein the negative half-axis portion of the y-axis is the feeding source of port 1, and the positive half-axis portion of the y-axis is the output source of port 2.

3. According to claim 1, except for the complementary open resonant ring unit (7), the structure is axially symmetrically distributed along the xoz plane and the yoz plane; the complementary open resonant ring unit (7) is a slot structure etched on the metal patch signal layer (10), and is axially symmetrically distributed along the yoz plane, wherein the outer large ring opening faces the feeding port direction, and the inner ring opening faces away from the feeding port direction.

4. According to claim 1, the intermediate layer dielectric substrate (5) is made of F4B radio frequency plate with a thickness of 2 mm, a dielectric constant of 3.5, and a loss tangent of 0.002; the inner diameter d1 of the metallized through hole (4); the interval between the two holes of the metallized through hole (4) is d2; and the horizontal row interval L0 of the metallized through hole (4).

5. According to claim 1, the dielectric material (8) to be tested is placed directly above the complementary split resonant ring unit (7), has a thickness of 1 mm, and a size slightly larger than ar×ar.

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