Preparation method and application of high-dielectric flexible composite film suitable for small-size patch antenna sensor

Abstract

The invention belongs to the technical field of sensors, and particularly relates to a preparation method and application of a high-dielectric flexible composite film suitable for a small-size patch antenna sensor. Due to the unique structure of the patch antenna sensor, strain measurement and crack detection can be carried out on key metal structural components in the fields of aerospace crafts, automobiles and the like on line. In order to solve the problems that an existing patch antenna sensor is large in size, the structural size is difficult to effectively match with a component with a complex curved surface and the like, a polyvinylidene fluoride zirconium oxide composite film is used as a dielectric layer material, and the limitation of device preparation on size is broken through in combination with a printing technology; a high-dielectric flexible thin film material for a high-sensitivity small-size rectangular patch antenna sensor is prepared, so that the length and the width of a single patch antenna sensor do not exceed 10mm, the thickness of the single patch antenna sensor does not exceed 1mm, and the sensitivity of crack detection on a metal structural member is nearly 200MHz / mm.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology, specifically relating to a method for preparing a high-dielectric flexible composite film suitable for small-size patch antenna sensors and its application. Background Technology

[0002] Key load-bearing structures in major technological equipment such as aerospace vehicles, automobiles, ships, and industrial robots are often subjected to harsh environments such as high temperature, low temperature, high pressure, and fatigue loads during long-term use. This often leads to strain concentration and damage accumulation, resulting in crack initiation and ultimately structural failure. Since crack initiation regions mainly occur at strain concentration points, strain and crack size are important indicators of structural health. Real-time strain measurement and monitoring of critical structures to promptly detect potential crack initiation areas is crucial for ensuring the safety of major technological equipment and engineering facilities. Traditional non-destructive testing methods, such as ultrasonic testing, X-ray testing, and eddy current testing, are widely used for crack detection. However, these methods suffer from limitations such as blind spots, limited accuracy, and operational complexity in certain special situations.

[0003] Wireless passive patch antenna sensors exhibit high sensitivity for detecting microcracks, enabling rapid detection and early warning of crack initiation stages. They are also more adaptable to harsh environments, exhibiting strong resistance to interference from environmental contaminants and high reliability in engineering applications. While existing antenna sensors can meet the damage detection needs of many engineering facilities, for critical structural components of major technical equipment, particularly their complex and intricate parts, existing antenna sensors suffer from insufficient flexibility or excessive size, making it difficult to adhere to the surface of complex components. This results in devices malfunctioning due to size mismatch or installation difficulties, exhibiting low sensitivity, unstable signals, or excessively weak signals. This makes it difficult to accurately extract minute damage from delicate structures, directly impacting the assessment of the in-service safety and reliability of precision and complex engineering structures.

[0004] Domestic and international researchers have made significant progress in advancing the high sensitivity, miniaturization, and flexibility of patch antenna sensors. However, the research focus has largely been on optimizing the antenna sensor's structure and improving its sensitivity. For example, one antenna sensor based on an H-shaped structure uses H-shaped slots on the patch antenna. When the surface current passes through the slot, it bends, thus extending the surface current of the antenna. Simulation analysis shows that the size of the antenna sensor has been reduced to 34.12% under the same conditions. Manohar combines fractal and slotting techniques to perform fractal design on a star antenna and creates U-shaped slots on the ground plane, further reducing the size of the antenna sensor. However, the smaller and more complex the device, the more difficult it is to manufacture, which poses many obstacles to structural design, thus limiting the improvement in miniaturization and device sensitivity.

[0005] Recent research indicates that the size and sensitivity of patch antenna sensors are closely related to the electrical properties of their dielectric layer material. High-dielectric, low-loss flexible dielectric materials are highly beneficial for obtaining highly sensitive, small-sized patch antenna sensors. However, the matrix materials commonly used to fabricate antenna sensors are mostly polypropylene films, polytetrafluoroethylene resins, and polyimide films. While these materials offer good flexibility, their dielectric properties are generally poor (typically a dielectric constant of 2–5). Consequently, the size of the corresponding devices needs to reach a certain level to achieve sensitive response and be used for detection, which is highly disadvantageous for crack detection in small, delicate structures. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention uses polyvinylidene fluoride zirconia composite film as the dielectric layer material and combines printing technology to overcome the size limitations of device fabrication. It provides a method for preparing a high-dielectric flexible composite film for a high-sensitivity small-size rectangular patch antenna sensor, so that the length and width of a single patch antenna sensor do not exceed 10mm and the thickness does not exceed 1mm. The sensitivity for detecting cracks on metal structures is close to 200MHz / mm.

[0007] This invention is achieved through the following technical solution:

[0008] (1) Hydroxylation treatment of zirconium oxide (ZrO2) powder: Weigh out nano zirconium oxide powder and add it to deionized water. Stir the nano zirconium oxide powder to completely disperse it in the water. After stirring, collect the lower precipitate, wash it with methanol and centrifuge it. After centrifugation, collect the centrifuged product and dry it under vacuum to obtain hydroxylated nano zirconium oxide (ZrO2-OH) powder.

[0009] (2) Preparation of printing solution: Weigh polyvinylidene fluoride (PVDF) powder and mix it with a polar solvent. After stirring and ultrasonic treatment, a PVDF solution is obtained. Then, the hydroxylated nano-zirconia powder prepared in step (1) is added. Stirring and ultrasonic treatment are continued (until the powder is completely dispersed in the PVDF solution) to obtain a PVDF / ZrO2-OH solution. Finally, acetone is added to obtain the printing solution.

[0010] (3) Printing device: The printing device includes a printing needle, a needle tube, a printing substrate, an XYZ three-axis moving mechanism, a high-voltage DC power supply, a pressure relief valve and an air compressor; the positive terminal of the high-voltage DC power supply is connected to the printing needle, and the negative terminal of the high-voltage DC power supply is connected to the printing substrate. The gas generated by the air compressor enters the needle tube through the pressure relief valve to realize printing.

[0011] (4) Thin film preparation: First, the three-dimensional dimensions of the composite thin film are modeled using Soildworks (the model slices obtained from the modeling are used to generate G-code files for printing); then, the printing liquid prepared in step (2) is added to the syringe, the distance between the printing needle and the printing substrate is adjusted, a high voltage DC voltage is connected, and the printing parameters and pressure relief valve are set. Then, the syringe is connected to the pressure relief valve, the air compressor is started, and the gas generated by the air compressor enters the syringe through the pressure relief valve for printing. The printed thin film is received by the printing substrate; after printing, the printing substrate with the thin film is vacuum dried, and the printed thin film is obtained after drying, which is the high dielectric flexible composite thin film. The thickness of the high dielectric flexible composite thin film is 0.8-1.0 mm, the β phase content is greater than 65%, and the relative permittivity is greater than 12.9.

[0012] Preferably, the zirconium oxide powder in step (1) has an average particle size of 0.5 to 1 μm and a purity of not less than 99.0%; the ratio of zirconium oxide powder to deionized water is 1 g: 100 to 600 ml.

[0013] Preferably, the stirring operation in step (1) is as follows: zirconium oxide powder and deionized water are magnetically stirred at a temperature of 20-30°C for 72-80 hours.

[0014] Preferably, the volume ratio of the precipitate to methanol in step (1) is 1:1 to 1.5.

[0015] Preferably, the vacuum drying temperature in step (1) is 60°C and the time is 60-100h.

[0016] Preferably, the polar solvent in step (2) is dimethylformamide (DMF), the amount of polyvinylidene fluoride (PVDF) powder is 20 wt.% to 40 wt.% of the polar solvent; the amount of hydroxylated nano-zirconia powder is 7 wt.% to 35 wt.% of the PVDF solution; and the amount of acetone is 1 wt.% to 10 wt.% of the PVDF / ZrO2-OH solution.

[0017] Preferably, in step (2), both stirring and ultrasonication are performed at room temperature. The stirring method is magnetic stirring, and the stirring time is 15-20 min. The ultrasonic treatment time is 30-45 min.

[0018] Preferably, in step (4), the high voltage DC power supply voltage is set to 4-10kV, the pressure of the gas relief valve is 0.2-2MPa, and the distance from the printing needle to the printing substrate is 2-5mm.

[0019] Preferably, the printing parameters in step (4) are set as follows: total thickness of the printed film is 0.8-1 mm, printing layer height is 0.2 mm, filling speed is 15 mm / s, filling method is linear, and filling density is 90%.

[0020] Preferably, the vacuum drying temperature in step (4) is 30-50°C and the time is 2-6 hours.

[0021] Preferably, the thickness of the printed film in step (4) is 0.8 to 1 mm.

[0022] Application: The high-dielectric flexible composite film obtained based on the above steps is used in the fabrication of a patch antenna sensor. The steps are as follows: The patch antenna sensor consists of three parts, including an antenna on the upper surface, a dielectric layer in the middle, and a metal ground plane at the bottom. The high-dielectric flexible composite film is used as the middle dielectric layer, and a gold film is sprayed on the surface of the dielectric layer as the antenna (radiating patch). Then, the film with the antenna is bonded to the metal plate to be tested, and the metal plate to be tested serves as the ground plane of the antenna sensor. After adding a feed point, it is connected by a coaxial feed wire to form the patch antenna sensor.

[0023] Preferably, the thickness of the gold film sprayed on the surface of the dielectric layer in the step is 15-30 μm, and the area of ​​the gold film sprayed is 60-90% of the area of ​​the dielectric layer.

[0024] Preferably, the patch antenna sensor described in the steps has a length and width of 5-10 mm and a thickness of 0.8-1 mm.

[0025] The patch antenna sensor prepared by this invention can be used to detect cracks in metal components, especially suitable for detecting cracks in fine metal components with a crack size of 1mm to 5mm; where fine metal components refer to metal parts produced by high-precision manufacturing processes, which have the characteristics of complex structure, high-precision dimensions and strict requirements for material properties.

[0026] The beneficial effects of this invention are as follows:

[0027] By applying the technical solution of this invention, at least the following beneficial effects have been achieved:

[0028] (1) The interface formed between zirconia nanoparticles and the polymer matrix leads to the accumulation of a large number of charges, increases interfacial polarization, and improves the dielectric properties of the film. Compared with pure PVDF film, the relative dielectric constant is increased by about 3 times. Furthermore, the simultaneous action of high voltage and gas pressure during the fabrication process ensures smooth printing and promotes the formation of a large amount of polar phase (β phase) in the PVDF flexible matrix, which is also beneficial to improving the dielectric properties of the flexible composite film. Finally, by using the high-dielectric flexible composite film as the dielectric layer, the length and width dimensions of the rectangular patch antenna are significantly reduced.

[0029] (2) The surface-treated zirconia nanoparticles contain abundant -OH groups, which enhance the bonding force with the PVDF flexible matrix through hydrogen bonding and make it easier to disperse stably in the matrix, improving the uniformity and density of the material, reducing defects, and resulting in lower dielectric loss of the flexible composite film. The low-loss flexible composite film, as a dielectric layer, enhances the radiation efficiency of the sensor and forms a strong electromagnetic resonant cavity between the patch antenna and the metal substrate. When the sensor receives an external microwave frequency-modulated signal, the electromagnetic wave forms a stable oscillation in the resonant cavity and reflects the signal. The horn antenna obtains the return loss curve through a network vector analyzer. When a crack initiates in the metal substrate, the return loss curve will change significantly, and the sensitivity will be significantly improved, thereby realizing crack detection.

[0030] (3) The present invention, combined with the printing preparation method, breaks through the limitations of antenna sensors in terms of size or structure, and can accurately obtain devices with millimeter-level size or more fine structure; so that the length and width of a single patch antenna sensor does not exceed 10mm and the thickness does not exceed 1mm, and the sensitivity of detecting cracks on metal structural parts is close to 200MHz / mm. Attached Figure Description

[0031] Figure 1 The infrared spectra of the composite films prepared in Examples 1 and 2 are shown, where (a) is the PVDF / ZrO2 composite film and (b) is the PVDF / ZrO2-OH composite film.

[0032] Figure 2 The images show the surface morphology of the composite films prepared in Examples 1 and 2, where (a) is a PVDF / ZrO2 composite film and (b) is a PVDF / ZrO2-OH composite film.

[0033] Figure 3 The diagram shows the structure of the patch antenna sensor, where (a) is a top view and (b) is a side view.

[0034] Figure 4 This is a schematic diagram of a patch antenna sensor used for crack detection in an experimental example.

[0035] Figure 5 The PVDF / ZrO2 composite film prepared in Example 1 was used to fabricate a patch antenna sensor. The detection results were obtained for cracks with lengths of 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm in the metal plate. Among them, (a) shows the return loss curve of the antenna under each crack length; (b) shows the resonant frequency under each crack length.

[0036] Figure 6The PVDF / ZrO2-OH composite film prepared in Example 2 was used to fabricate a patch antenna sensor. The detection results of crack lengths of 1 mm, 2 mm, 3 mm, 4 mm and 5 mm in the metal plate were obtained. Among them, (a) is the return loss curve of the antenna under each crack length; (b) is the resonant frequency under each crack length.

[0037] Figure 7 The PVDF film prepared in Example 3 was used to fabricate a patch antenna sensor. The detection results were obtained for cracks with lengths of 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm in the metal plate. Among them, (a) shows the return loss curve of the antenna under each crack length; (b) shows the resonant frequency under each crack length. Detailed Implementation

[0038] The present invention will be further described in detail below through specific embodiments and with reference to the accompanying drawings, but it should not be construed as limiting the scope of the invention to the following examples. Various substitutions or modifications made based on ordinary technical knowledge and conventional methods in the art without departing from the above-described methodological spirit of the invention should be included within the scope of the invention.

[0039] Reagents: Zirconia nanoparticles (ZrO2) powder with an average particle size of 0.5–1 μm and a purity >99.0%; polyvinylidene fluoride (PVDF, Kynar 741), dimethylformamide (DMF, >99.9%), zirconia nanoparticles (ZrO2, >99.0%), acetone (C3H6O, >96.0%), and methanol (CH4O, >99.5%).

[0040] Example 1 (Comparative Example of Composite Thin Film):

[0041] First, 2g of PVDF powder was weighed using an electronic balance and dissolved in 5g of polar DMF solution. The mixture was magnetically stirred for 15min and then sonicated at room temperature for 30min to obtain a PVDF solution. Different masses of nano-zirconia (ZrO2) powder were added to the PVDF solution, with the amounts of nano-zirconia powder being 7wt.%, 14wt.%, 21wt.%, 28wt.%, and 35wt.% of the PVDF solution, respectively. Magnetic stirring (15min) and sonication (30min) were continued at room temperature until the powder was uniformly mixed, resulting in PVDF / ZrO2 solutions of different mass concentrations. Finally, 0.02g of acetone was added to each PVDF / ZrO2 solution to obtain PVDF printing solutions with different ZrO2 concentrations.

[0042] Printing device: The printing device includes a metal printing needle, a needle tube, a printing substrate, an XYZ three-axis moving mechanism, a high-voltage DC power supply, a pressure relief valve, and an air compressor; the XYZ three-axis moving mechanism realizes the fixing and moving functions; the metal printing needle is connected to the needle tube, and the positive terminal of the high-voltage DC power supply is connected to the metal printing needle, while the negative terminal of the high-voltage DC power supply is connected to the printing substrate; the gas generated by the air compressor enters the printing needle tube through the pressure relief valve to realize printing.

[0043] First, a model of the thin film was created using Solidworks, and the model was sliced ​​to generate a G-code file for printing. Then, printing fluid was added to the printing syringe, and the distance between the metal printing needle and the printing substrate (a metal plate was selected as the substrate) was adjusted to 2 mm. A 6 kV DC voltage was connected. Printing parameters were set as follows: total film thickness 0.8 mm, layer height 0.2 mm, filling speed 15 mm / s, linear filling method, and fill density 90%. The pressure relief valve was set to 0.2 MPa, the syringe was connected to the pressure relief valve, and the air compressor was started to begin printing. After printing, the printed substrate with the film was placed in a vacuum drying oven at 40°C for 2 hours to obtain PVDF composite films with different ZrO2 concentrations and a thickness of 0.8 mm (denoted as PVDF / ZrO2 composite films).

[0044] Example 2:

[0045] 5g of nano-zirconia powder was weighed and added to 500mL of deionized water. The mixture was magnetically stirred at 30℃ for 72h to ensure complete mixing of the zirconia nano-powder and deionized water. After stirring, the upper clear liquid was discarded, and the lower precipitate was washed with 1.5 times its volume of methanol solution and then centrifuged. After centrifugation, the centrifuged product was placed in a vacuum drying oven at 60℃ and dried for 60h to obtain hydroxylated nano-zirconia powder (ZrO2-OH).

[0046] 2g of PVDF powder was weighed using an electronic balance and dissolved in 5g of polar DMF solution. The mixture was magnetically stirred for 15 minutes and then sonicated at room temperature for 30 minutes to disperse the PVDF powder in the DMF, thus obtaining a PVDF solution. Different masses of ZrO2-OH powder were added to the PVDF solution, with ZrO2-OH powder amounts of 7wt.%, 14wt.%, 21wt.%, 28wt.%, and 35wt.% of the PVDF solution. Magnetic stirring (15 minutes) and sonication (30 minutes) were continued at room temperature until the powder was uniformly mixed, resulting in PVDF / ZrO2-OH printing solutions of different mass concentrations. Finally, 0.02g of acetone was added to each PVDF / ZrO2-OH solution to obtain PVDF printing solutions with different ZrO2-OH concentrations.

[0047] Printing device: The printing device includes a metal printing needle, a needle tube, a printing substrate, an XYZ three-axis moving mechanism, a high-voltage DC power supply, a pressure relief valve, and an air compressor; the XYZ three-axis moving mechanism realizes the fixing and moving functions; the metal printing needle is connected to the needle tube, and the positive terminal of the high-voltage DC power supply is connected to the metal printing needle, while the negative terminal of the high-voltage DC power supply is connected to the printing substrate; the gas generated by the air compressor enters the printing needle tube through the pressure relief valve to realize printing.

[0048] First, a model of the thin film was created using Solidworks, and the model was sliced ​​to generate a G-code file for printing. Then, printing fluid was added to the printing syringe, and the distance between the metal printing needle and the printing substrate (a metal plate was selected as the substrate) was adjusted to 2 mm. A 6 kV DC voltage was connected. Printing parameters were set as follows: total film thickness 0.8 mm, layer height 0.2 mm, filling speed 15 mm / s, linear filling method, and fill density 90%. The pressure relief valve was set to 0.2 MPa. The printing syringe was connected to the pressure relief valve, and the air compressor was started to begin printing. After printing, the printed substrate with the composite film was placed in a vacuum drying oven at 40°C for 2 hours to obtain a PVDF composite film with a thickness of 0.8 mm (denoted as PVDF / ZrO2-OH composite film).

[0049] Figure 1 The infrared spectra of the composite films prepared in Examples 1 and 2 are shown in Figure 1. In Figure 2, (a) is a PVDF / ZrO2 composite film; and (b) is a PVDF / ZrO2-OH composite film. Figure 1 763cm in Figures (a) and (b) -1 The peaks at 840 cm⁻¹ correspond to the α-phase absorption peaks of the PVDF composite film. -1 The peak at this point corresponds to the absorption peak of the β phase, at a wavelength of 1180 cm⁻¹. -1 The absorption peak at that point is attributed to the stretching vibration of -CF2. Comparing the two graphs, the absorption peak at that point is due to... Figure 1 (b) It can be seen that the composite film at 1180 cm⁻¹ -1 The absorption peak intensity at the point is significantly enhanced because the surface of the modified ZrO2 nanoparticles is rich in hydroxyl groups. As PVDF molecular chains accumulate and crystallize along the surface of ZrO2, these hydroxyl groups readily form hydrogen bonds with the CF bonds in the PVDF molecular chains, leading to a more favorable arrangement of fluorine (F) atoms in the PVDF chains. This arrangement promotes the formation of the β phase, and the high content of polar β phase is extremely beneficial to improving the dielectric properties of the composite film. Calculations and comparisons show that the β phase content of the PVDF / ZrO2-OH composite film is significantly increased. When the printing solution contains 28 wt.% ZrO2-OH, the β phase content of the PVDF composite film reaches 82.01%, which is more than twice that of the PVDF composite film with the same ZrO2 content. Figure 2The images show the surface morphology of the composite films prepared in Examples 1 and 2, where 2(a) shows the surface morphology of the PVDF / ZrO2 composite film. Figure 2 (b) shows the surface morphology of the PVDF / ZrO2-OH composite film. Comparing the two figures, it is evident that ZrO2-OH particles exhibit better dispersion in the PVDF matrix than ZrO2 particles. This is not only due to the effect of hydrogen bonding, which enhances the bonding force between zirconium oxide and the PVDF matrix, but also because the hydroxyl groups on the ZrO2-OH surface increase the steric hindrance between particles. When zirconium oxide particles are dispersed in the PVDF matrix, these hydroxyl groups prevent direct contact and aggregation between particles, allowing for more uniform dispersion in the matrix, resulting in a high-quality composite film with fewer internal defects. Compared to the PVDF / ZrO2 composite film, the dielectric loss of the PVDF / ZrO2-OH composite film is significantly reduced.

[0050] Example 3 (PVDF Comparative Example):

[0051] Weigh 2g of PVDF powder using an electronic balance and pour it into 5g of polar solution DMF. Stir magnetically for 15 minutes, then sonicate at room temperature for 30 minutes. Finally, add 0.02g of acetone to obtain PVDF printing solution.

[0052] Printing device: The printing device includes a metal printing needle, a needle tube, a printing substrate, an XYZ three-axis moving mechanism, a high-voltage DC power supply, a pressure relief valve, and an air compressor; the XYZ three-axis moving mechanism realizes the fixing and moving functions; the metal printing needle is connected to the needle tube, and the positive terminal of the high-voltage DC power supply is connected to the metal printing needle, while the negative terminal of the high-voltage DC power supply is connected to the printing substrate; the gas generated by the air compressor enters the printing needle tube through the pressure relief valve to realize printing.

[0053] First, a model of the thin film was created using Solidworks, and the model was sliced ​​to generate a G-code file for printing. Then, printing fluid was added to the printing syringe, and the distance between the metal printing needle and the printing substrate (a metal plate was selected as the substrate) was adjusted to 2mm. A 6kV DC voltage was connected. Printing parameters were set as follows: total film thickness 0.8mm, layer height 0.2mm, filling speed 15mm / s, linear filling method, and fill density 90%. The pressure relief valve was set to 0.2MPa. The printing syringe was connected to the pressure relief valve, and the air compressor was started to begin printing. After printing, the printed substrate with the composite film was placed in a vacuum drying oven at 40℃ for 2 hours to obtain a PVDF composite film with a thickness of 0.8mm.

[0054] Experimental example:

[0055] The relative β-phase content of the PVDF composite film was determined using a Fourier transform infrared spectrometer (Nicolet 6700, Nicolet, USA). The test method was ATR, and the infrared wavelength measurement range was set to 4000–650 cm⁻¹. -1 According to the Lambert-Beer law, the formula is shown in (1):

[0056] F(β)=A β / ((k β / (k α A α +A β )) (1)

[0057] Among them, A α A β These are wavelengths of 763 cm⁻¹ in the infrared spectrum. -1 840cm -1 The intensity of the absorption peak corresponding to the location; k α k β It is α crystal form (763 cm⁻¹) -1 ) and β crystal form (840cm) -1 The absorption coefficients are 6.1 × 10⁻⁶. 4 cm 2 / mol, 7.7×10 4 cm 2 / mol.

[0058] The capacitance (Cp) and dielectric loss (tanδ) of the composite thin film in the range of 20 Hz to 20 kHz were tested using an Agilent Technologies 4294A impedance analyzer (TH2816A, China). The formula for calculating the relative permittivity (ε') is as follows (2):

[0059] ε=(C P d) / (ε0A) (2)

[0060] Among them, C p The capacitance value measured by the experimental instrument is given by d, where d represents the dielectric thickness, which in this experiment represents the thickness of the prepared composite film. ε0 is the vacuum permittivity (8.85 × 10⁻⁶). -12 F / m), where A is the effective area of ​​the composite thin film surface electrode. Since the dielectric properties of the dielectric material are affected by temperature, the test is conducted at room temperature of around 24°C.

[0061] The composite films prepared in Examples 1 and 2 were subjected to the above tests. The β phase content and dielectric properties of each composite film are shown in the table below:

[0062]

[0063] As can be seen from the above, the polar β phase content and relative dielectric constant of the composite film in Example 2 are significantly higher than those in Example 1, while the dielectric loss is significantly reduced. This verifies that the polyvinylidene fluoride composite film containing hydroxylated zirconium oxide significantly improves the polar phase content and dielectric properties. Moreover, when the ZrO2-OH addition amount is 28wt.%, the overall effect is excellent and the dielectric properties are optimal.

[0064] The rectangular flexible patch antenna sensor structure is as follows: Figure 3 As shown, it includes a patch antenna on the upper surface, a flexible dielectric layer in the middle, and a metal plate (metal ground plane) at the bottom. The composite film prepared in the above embodiment is used as the dielectric layer, the conductive copper strip is used as the patch antenna (radiating patch), and the metal ground plane is made of copper foil material (thickness negligible). The length L and width W of the rectangular patch antenna in the coaxial feeding mode can be calculated by equations (3) and (4).

[0065]

[0066] W=(c / 2f)((ε r +1) / 2) -1 / 2 (4)

[0067] Where c is the speed of light, f is the operating frequency, h is the thickness of the dielectric layer, and ε r It is the relative permittivity of the dielectric layer material. Effective permittivity ε e The elongation ΔL can be obtained from equations (5) and (6).

[0068] ε e =(ε r +1) / 2+(ε r -1) / 2(1+12h / w)( -1 / 2 (5)

[0069] ΔL=0.412h(ε e +0.3)(W / h+0.264) / (ε e -0.258)(W / h+0.8) (6)

[0070] The origin of the coordinate system is taken as the center of the patch antenna. The antenna length is along the x-axis and the width is along the y-axis. The distance (L0) between the feed point and the center of the patch will affect the impedance matching of the antenna. The position of the feed point (L0, 0) can be calculated by equation (7).

[0071]

[0072] An antenna sensor was fabricated according to the calculated dimensions, with an operating frequency set to 6 GHz. An SMA standard connector was soldered onto the antenna sensor. The SMA standard connector was then connected to a vector network analyzer via a feed line to perform crack detection testing on the antenna sensor. To avoid potential measurement errors and ensure more accurate test data, short-circuit, open-circuit, and load calibrations were performed before using the vector network analyzer.

[0073] The least squares method is used to perform linear fitting on the wave loss data, and the slope K of the fitted curve can be calculated by formula (8).

[0074]

[0075] Among them, L c f is the actual length of the crack, and L is the average length of the crack; r Let f be the resonant frequency of the antenna, and let f be the average resonant frequency of the antenna. The resonant frequency of the antenna is negatively linearly related to the crack length, as shown in formula (9).

[0076] f r =f0-KL c (9)

[0077] Where f0 is the resonant frequency of the antenna when there is no crack, and K is the slope of the fitted curve, which can be used as the sensitivity of the antenna sensor for crack detection, with the unit being MHz / mm.

[0078] A schematic diagram of a patch antenna sensor used for crack detection is shown below. Figure 4 As shown; the patch antenna sensor prepared using the composite thin film prepared in Examples 1, 2, and 3 as the dielectric layer was used for the above-mentioned detection. The antenna size and device sensitivity are shown in the table below:

[0079]

[0080] in, Figure 5-7 The PVDF / ZrO2 composite film (28 wt.%) prepared in Example 1, the PVDF / ZrO2-OH composite film (28 wt.%) prepared in Example 2, and the PVDF film prepared in Example 3 were used to fabricate patch antenna sensors. The detection results of crack lengths of 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm in the metal plate were obtained. Among them, (a) shows the return loss curve of the antenna under each crack length, and (b) shows the resonant frequency under each crack length.

[0081] Combination Figure 5-7As shown in the table above, the patch antenna sensor prepared by the composite thin film obtained in Example 2 has a length and width of no more than 10 mm and a thickness of no more than 1 mm. Compared with Example 3, its area ratio is reduced by 67%, but the sensor's sensitivity to crack detection is more than twice that of the previous sensor, approaching 200 MHz / mm, achieving substantial technical results.

[0082] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a high-dielectric flexible composite film suitable for small-size patch antenna sensors, characterized in that, (1) Hydroxylation treatment of zirconium oxide powder: Weigh out nano zirconium oxide powder and add it to deionized water. Stir the nano zirconium oxide powder to completely disperse it in the water. After stirring, collect the lower precipitate, wash it with methanol and centrifuge it. After centrifugation, collect the centrifuged product and dry it under vacuum to obtain hydroxylated nano zirconium oxide powder. (2) Preparation of printing solution: Weigh polyvinylidene fluoride powder and mix it with a polar solvent. After stirring and ultrasonic treatment, a PVDF solution is obtained. Then, the hydroxylated nano-zirconia powder prepared in step (1) is added. Stirring and ultrasonic treatment are continued to obtain a PVDF / ZrO2-OH solution. Finally, acetone is added to obtain the printing solution. (3) Printing device: The printing device includes a printing needle, a needle tube, a printing substrate, an XYZ three-axis moving mechanism, a high-voltage DC power supply, a pressure relief valve and an air compressor; the positive terminal of the high-voltage DC power supply is connected to the printing needle, and the negative terminal of the high-voltage DC power supply is connected to the printing substrate. The gas generated by the air compressor enters the needle tube through the pressure relief valve to realize printing. (4) Thin film preparation: First, use Soildworks to model the three-dimensional dimensions of the composite thin film; then add the printing liquid prepared in step (2) into the syringe, adjust the distance between the printing needle and the printing substrate, connect the high voltage DC voltage, and set the printing parameters and pressure relief valve pressure. Then connect the syringe to the pressure relief valve, start the air compressor, and the gas generated by the air compressor enters the syringe through the pressure relief valve for printing. The printed film is received by the printing substrate. After printing, the printed substrate with the film is vacuum dried to obtain the printed film, which is a high-dielectric flexible composite film.

2. The method for preparing a high-dielectric flexible composite film suitable for small-size patch antenna sensors according to claim 1, characterized in that, The zirconium oxide powder mentioned in step (1) has an average particle size of 0.5 to 1 μm and a purity of not less than 99.0%; the ratio of zirconium oxide powder to deionized water is 1 g: 100 to 600 ml.

3. The method for preparing a high-dielectric flexible composite film suitable for small-size patch antenna sensors according to claim 1, characterized in that, The stirring operation in step (1) is as follows: zirconium oxide powder and deionized water are magnetically stirred at a temperature of 20-30°C for 72-80 hours; the volume ratio of the precipitate to methanol is 1:1-1.5; the vacuum drying temperature is 60°C and the time is 60-100 hours.

4. The method for preparing a high-dielectric flexible composite film suitable for small-size patch antenna sensors according to claim 1, characterized in that, The polar solvent in step (2) is dimethylformamide, and the amount of polyvinylidene fluoride powder is 20 wt.% to 40 wt.% of the polar solvent; the amount of hydroxylated nano-zirconia powder is 7 wt.% to 35 wt.% of the PVDF solution; the amount of acetone is 1 wt.% to 10 wt.% of the PVDF / ZrO2-OH solution; stirring and sonication are both carried out at room temperature, wherein the stirring method is magnetic stirring, the stirring time is 15-20 min, and the sonication time is 30-45 min.

5. The method for preparing a high-dielectric flexible composite film suitable for small-size patch antenna sensors according to claim 1, characterized in that, In step (4), the high voltage DC power supply voltage is set to 4-10kV, the pressure of the gas relief valve is 0.2-2MPa, the distance from the printing needle to the printing substrate is 2-5mm, and the printing parameters are set as follows: the total thickness of the printed film is 0.8-1mm, the printing layer height is 0.2mm, the filling speed is 15mm / s, the filling method is linear, and the filling density is 90%.

6. The method for preparing a high-dielectric flexible composite film suitable for small-size patch antenna sensors according to claim 1, characterized in that, The vacuum drying temperature in step (4) is 30-50°C and the time is 2-6 hours; the thickness of the printed film is 0.8-1 mm.

7. The high-dielectric flexible composite film prepared by the method according to any one of claims 1-6, characterized in that, The high-dielectric flexible composite film has a thickness of 0.8–1.0 mm, a β phase content greater than 65%, and a relative permittivity greater than 12.

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8. The use of the high-dielectric flexible composite film according to claim 7 in the fabrication of patch antenna sensors, characterized in that, The steps are as follows: The patch antenna sensor consists of three parts, including an antenna on the upper surface, a dielectric layer in the middle, and a metal plate at the bottom. A high-dielectric flexible composite film is used as the middle dielectric layer, and a gold film is sprayed on the surface of the dielectric layer as the antenna. Then, the film with the antenna is attached to the metal plate to be detected, and a feed point is added to form the patch antenna sensor.

9. The use of the high-dielectric flexible composite film according to claim 8 in the fabrication of patch antenna sensors, characterized in that, The thickness of the gold film sprayed on the surface of the dielectric layer is 15-30 μm, and the area of ​​the gold film sprayed is 60-90% of the area of ​​the dielectric layer; the length and width of the patch antenna sensor are both 5-10 mm, and the thickness is 0.8-1 mm.

10. The use of the patch antenna sensor according to claim 8 or 9 for detecting cracks in metal components, characterized in that, The metal components include precision metal components.

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