A microwave flexible array sensor for ice detection

Abstract

The present invention discloses a microwave flexible array sensor for ice detection, belonging to the field of sensors. The sensor primarily comprises: a central flexible substrate layer 4; an upper flexible dielectric layer 3 and a lower flexible dielectric layer 6 tightly attached to either side of the flexible substrate layer 4; a sensitive array element 1 and a metal microstrip line 5 structure attached to the upper flexible dielectric layer 3; and a metal reference ground 2 attached to the lower flexible dielectric layer 6. In the present invention, an outer resonant ring 33 and an inner resonant ring 34 form a complementary split ring resonator (CSRR). The CSRR provides a narrow insertion loss bandwidth, making its capacitance highly sensitive to objects placed on the sensitive element 1. Specifically, the notch frequency is highly sensitive to changes in the dielectric constant of the ice layer, resulting in superior quality factor and accuracy to conventional planar resonator sensors. The addition of additional rings has minimal impact on sensor performance, and coupling with the outer ring 32 increases the resonator's equivalent capacitance, enhancing the fringe electric field and improving interaction with the test sample. The interdigitated structure at the center of the sensitive element 1 enhances the electric field density on the sensitive element 1, providing an expanded capacitive coupling gap, thereby achieving miniaturization and, importantly, greater sensitivity to changes in ice thickness.

Description

Technical Field

[0001] The present invention belongs to the field of sensors, and in particular to the field of a microwave flexible array sensor for ice detection. Background Art

[0002] Freezing is the process by which liquid water solidifies below 0°C. Freezing is a common occurrence in winter. Failure to promptly remove ice in many critical sectors can lead to significant economic losses, disrupt normal production and life, and endanger personal safety, particularly in the drone sector. Compared to manned aircraft, drones, with their smaller size and slower flight speeds, are more susceptible to icing, and icing has become a significant obstacle to the development of drones. Based on the above scenario, timely detection of icing on drones, and further, measuring ice thickness and identifying ice type, and transmitting this information to controllers or issuing warnings to personnel, will significantly minimize the losses and harm caused by icing on drones.

[0003] Research on ice sensors for manned aircraft has a long history. Various types of ice sensors have been developed both domestically and internationally, including the 87 series magnetostrictive ice sensor developed by Rosemount (USA), the capacitive ice sensor developed by Innovative Dynamics (USA), and the barrier-type ice sensor developed by LUCAS Aviation (UK). However, these sensors are often difficult to use directly on drones due to their cost, size, and slow detection speed. Furthermore, most ice sensors used on manned aircraft measure ice at a single point, which is difficult to meet the multi-point thickness measurement requirements of drones.

[0004] Microwave resonant sensors primarily use transmission lines to excite resonant elements such as split ring resonators (SRRs) and complementary split ring resonators (CSRRs), establishing a mapping relationship between the measured quantity and the resonant characteristics. These sensors enable non-contact, real-time, and high-precision detection. Their simple manufacturing process, low cost, high stability, and compact size have made them a hot topic of research in recent years. The paper "Modified Microwave Sensor with a Patterned Ground Heater for Detection and Prevention of Ice Accumulation" designs an SRR that effectively distinguishes water from ice by detecting changes in the dielectric properties of its surface or surroundings, enabling the study of real-time frost growth. However, split ring resonators are insensitive to changes in ice thickness and cannot accurately determine ice thickness. Furthermore, traditional sensors are generally rigid. For example, an ice sensor for wind turbine blades (patent CN 217002167U) cannot be bent, folded, or extended, and cannot conform to complex surfaces. Its high requirements for the measured surface limit its applicability.

[0005] Therefore, there is an urgent need in the art to propose a flexible microwave array sensor for detecting the shape of ice layers, which is suitable for surfaces of different areas and has a good fit with the surfaces being measured. Summary of the Invention

[0006] The present invention provides a microwave flexible array sensor for ice detection that can solve the above problems.

[0007] A microwave flexible array sensor for ice detection mainly includes: a central flexible base layer 4, an upper flexible dielectric layer 3 and a lower flexible dielectric layer 6 tightly attached to both sides of the flexible base layer 4, a sensitive array element 1 and a metal microstrip line 5 structure attached to the upper flexible dielectric layer 3, and a metal reference ground 2 attached to the lower flexible dielectric layer 6;

[0008] The sensitive array elements 1 and the metal microstrip lines 5 are array structures etched on the same metal layer. The sensitive array elements 1 are evenly arranged on the upper flexible dielectric layer 3 in a one-dimensional or two-dimensional form. The microwave signals are led out by the metal microstrip lines 5 extending outward on both sides of each sensitive array element 1.

[0009] Each sensitive array element 1 is formed by etching, from the outside to the inside, a coupling outer ring 32 concentric with the sensitive element structure, an outer resonant ring 33 and an inner resonant ring 34 with complementary openings, and a coupling interdigital structure 35 on a metal sheet 31. The metal sheet 31 can be circular, elliptical, or a regular polygonal structure. After etching, each sensitive array element 1 is a symmetrical structure with a hollowed-out portion.

[0010] The coupling outer ring 32 is etched on the outermost side of the sensitive oscillator and is part of a complete circular ring. The angle is generally 90°~270°. The outer resonant ring 33 and the inner resonant ring 34 are etched on the inner side of the coupling outer ring 32. Both are incomplete circular rings and their opening directions differ by 180°, so that the two form a complementary positional relationship. To increase the detection accuracy, a part of the inner part of the circular ring can be retained and only the edge can be etched to form a hollow complementary circular ring. The interdigital structure 35 is etched on the inner side of the small complementary hollow resonant ring 34 and its opening direction is the same as it.

[0011] Furthermore, to ensure that the pattern etched inside a single sensitive element is symmetrical about the metal microstrip line 5, the pattern size can be adjusted according to the size of the sensitive element, and the spacing between adjacent rings and the width of each ring are preferably kept within the radius of the sensitive element. .

[0012] Furthermore, the coupling interdigital structure 35 is a symmetrical structure composed of an outer incomplete circular ring and a long strip connected to the ring on the inner side. The long strip extends from the inside of the circular ring to the point closest to the center of the sensitive oscillator and is parallel to the metal microstrip line 5. The index, that is, the number of long strips, is 1 to 9.

[0013] More preferably, the thickness of the flexible dielectric layers 3 and 6 is between 0.01 mm and 1 mm, and the material is generally a light-weight, thin, freely bendable and foldable material such as polyester film (PET) or polyimide (PI).

[0014] More preferably, the thickness of the flexible substrate layer 4 is between 0.1 mm and 10 mm, and the material is generally polydimethylsiloxane (PDMS), liquid crystal polymer (LCP), aliphatic aromatic random copolyester (Ecoflex) and other flexible, corrosion-resistant, impact-resistant and chemically stable materials.

[0015] More preferably, the thickness of the metal reference ground 2 and the metal microstrip line 5 is between 0.01 mm and 1 mm, and the material is generally a metal material such as copper and gold. The basic size of the metal microstrip line 5 is determined by the impedance of the feeder, the material and thickness of the flexible dielectric layers 3 and 6, and the material and thickness of the flexible base layer 4 to achieve corresponding impedance matching.

[0016] The length and width of the metal reference ground 2, flexible dielectric layers 3 and 6, and flexible substrate layer 4 vary according to the size and arrangement of the array sensitive elements 1. Each sensitive element corresponds to a square area with a side length of 1 to 20 mm. The more sensitive elements of the same size there are, the larger the size of the sensitive element 1, and the larger the device size.

[0017] In general, the above technical solutions conceived by the present invention have the following technical advantages compared with the existing technology:

[0018] 1. Experimental verification shows that, under the same excitation, the circular ring has higher sensitivity and quality factor in characterizing the dielectric constant of the sample under test when compared to a square ring and a circular ring of the same area. The outer resonant ring 33 and the inner resonant ring 34 form a complementary split ring resonator (CSRR). The implementation of the CSRR provides a narrow insertion loss bandwidth, so its capacitance is very sensitive to the object placed on the sensitive resonator 1. That is, the notch frequency is very sensitive to changes in the dielectric constant of the ice layer, making it superior to traditional planar resonator sensors in terms of quality factor and accuracy. The further addition of additional rings has very little impact on the performance of the sensor, and the coupling of the outer ring 32 increases the equivalent capacitance of the resonator and the fringe electric field, thereby better interacting with the test sample. The interdigital structure at the center of the sensitive resonator 1 enhances the electric field density on the sensitive resonator 1, has an extended capacitive coupling gap, thereby achieving miniaturization, and importantly, is more sensitive to changes in ice thickness. Compared with the sensitive oscillators of existing structures, the structure adopted by the present invention is more sensitive to changes in ice thickness. The patterns in the sensitive oscillators are coupled with each other, increasing the equivalent capacitance. For every 0.1 mm increase in thickness, the resonant frequency and amplitude change significantly, making the detection results more accurate.

[0019] 2. The present invention uses a flexible dielectric substrate. Compared with traditional rigid dielectric substrates, this substrate can be attached to curved surfaces rather than being confined to flat surfaces. It also allows for better alignment of the interdigitated sensitive elements with the ice layer being measured, improving measurement accuracy. The present invention etches the sensitive element 1 structure onto a metal microstrip line 5 rather than onto a traditional metal reference ground 2, so that the measurement results only represent the thickness of the ice layer, avoiding the influence of the attached surface on the resonant electromagnetic field. Furthermore, this method has a low resonant frequency and is insensitive to changes in the environment outside the ice layer, thus isolating the device from the outside environment. In summary, the present invention provides more accurate measurement results and is applicable in practice.

[0020] 3. The present invention adopts the resonance method, which is highly favored for its advantages such as simple design, low manufacturing cost, easy miniaturization and real-time monitoring. During measurement, the ice layer to be measured can be directly placed on the sensitive element, without any processing of the material sample to be measured, thus achieving the purpose of non-destructive testing. In addition, the present invention adopts the design concept of array sensitive array elements. The density, size and number of the elements can be designed and adjusted according to the size of the measured area and the measurement accuracy. Unlike traditional fixed-size sensors, this greatly expands the application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a diagram of a usage scenario in which a microwave flexible array sensor for detecting ice layer shape provided by the present invention is installed on a wing.

[0022] Figure 2 This is a front structural schematic diagram of a microwave flexible array sensor for detecting ice layer shape provided by the present invention.

[0023] Figure 3 This is a schematic diagram of the back structure of a microwave flexible array sensor for detecting ice layer shape provided by the present invention.

[0024] Figure 4 The present invention provides a schematic structural diagram of a sensitive oscillator of a microwave flexible array sensor for detecting ice layer shape.

[0025] Figure 5 This is a comparison between the S parameter-frequency simulation diagram (b) of a microwave flexible array sensor for detecting ice layer shape provided by the present invention detecting ice layers of different thicknesses and the S parameter-frequency simulation diagram (a) of an existing ice sensor detecting ice layers of different thicknesses.

[0026] Figure 6 The present invention provides a microwave flexible array sensor for detecting ice layer shape and an operation flow chart for detecting ice layer thickness.

[0027] In the figure, 1-array sensitive element, 2-metal reference ground, 3-flexible dielectric layer, 4-flexible base layer, 5-metal microstrip line, 31-metal disc, 32-semicircular ring 32, 33-outer ring, 34-inner ring, 35-interdigital structure. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following describes the embodiments of the present invention through specific examples. It should be understood that the present invention can also be implemented or applied through other different specific embodiments, which are not intended to limit the present invention. In addition, the technical features involved in the following embodiments and the illustrations provided are only schematically illustrating the basic concept of the present invention. In the absence of conflict, the technical features involved can be combined with each other.

[0029] Figure 1 This diagram illustrates a scenario where a microwave flexible array sensor for detecting ice layer shape, provided by the present invention, is installed on a wing. The diagram shows an example of a microwave flexible array icing sensor 6 being installed in an icing-prone area of ​​a wing 7 of a drone, used to detect icing conditions.

[0030] like Figure 2 、 Figure 3 The figure shows a schematic diagram of the structure of a microwave flexible array ice sensor for detecting the shape of ice layers provided by the present invention, comprising an array sensitive element 1, a metal reference ground 2, a flexible dielectric layer 3, a flexible substrate layer 4, and a metal microstrip line 5. The metal microstrip lines 5 are connected to both sides of the array sensitive element 1, and the metal microstrip lines 5 extend to the edge of the sensor for access to the radio frequency detection circuit. From the top to the bottom, the sensor structure comprises the array sensitive element 1, the metal microstrip line 5 structure, the flexible substrate layer 3, the flexible dielectric layer 4, the flexible substrate layer 3, and the metal reference ground 2, with each part fitting tightly together. When microwaves pass through the area between the metal reference ground 2 and the metal microstrip line 5, resonance occurs in a certain frequency band, causing the microwaves to exist in the form of standing waves. At this time, the impedance is a pure real number, the power loss reaches its maximum, and it can be equivalent to an LC circuit. Based on the above analysis and calculations, the metal reference ground 2 provided by the present invention is 80mm long, 40mm wide, and 0.03mm thick; the flexible substrate layer 3 is 0.5mm thick; and the flexible dielectric layer 4 is 80mm long, 40mm wide, and 3mm thick, with a relative dielectric constant of 4.4 and a tangent loss of 0.22. The array sensitive elements 1 are arranged on the symmetric axis of the flexible substrate layer width. The distance between the center of the sensitive element and the adjacent wide side is 10mm, and the distance between the centers of adjacent sensitive elements is 20mm. The metal microstrip line extends symmetrically about the center of the sensitive element to the edge of the flexible substrate layer and has a width of 2.6mm. In the preferred embodiment of the present invention, the metal reference ground 2 and metal microstrip line 5 are made of copper, and the flexible substrate layer 3 and flexible dielectric layer 4 are made of PDMS.

[0031] Figure 4 This diagram illustrates the structure of a sensitive element in a microwave flexible array sensor for detecting ice layer shape, as provided by the present invention. Sensitive element 1 is etched at the center of a metal microstrip line 5. A semicircular ring 32, a complementary split resonant ring (outer ring 33 and inner ring 34), and an interdigital structure 35 are etched sequentially from the outside inward on a metal disc 31. The radius of the metal disc 31 is 7mm. Semicircular ring 32 has an inner radius of 6.25mm and an outer radius of 6.75mm, with its center coinciding with the center of the metal disc 31. The outer split ring 33 has an inner radius of 5mm and an outer radius of 6mm, with an etched area extending 0.25mm inward from the edge. The inner split ring 34 has an inner radius of 3mm and an outer radius of 4mm, with an etched area extending 0.25mm inward from the edge. The interdigital structure 35 consists of a 0.5mm-wide semicircular ring with an inner radius of 3.25mm and a 0.5mm-wide finger connecting the center of the disc 31 and the semicircular ring along its axis of symmetry.

[0032] Figure 5 The following figure compares the S-parameter-frequency simulation diagram (b) of a microwave flexible array sensor for detecting ice shape, as provided by the present invention, with the S-parameter-frequency simulation diagram (a) of an existing ice sensor detecting ice shape at different thicknesses. Simulating the S-parameter changes of the two sensors when detecting ice thicknesses of 0mm, 1mm, 2mm, 3mm, 4mm, and 5mm, and capturing the frequency band with the minimum S-parameter, clearly shows that the frequency change of the present invention is more pronounced as the ice thickness changes, indicating that the present invention is more sensitive and accurate in detecting ice shape.

[0033] Figure 6This is an operational flow chart of ice thickness detection by a microwave flexible array sensor for detecting ice shape provided by the present invention. The present invention acquires ice thickness, ice rate, and ice shape based on an array, which is specifically divided into two steps. First, the sensor output signal is collected to obtain the S parameters of each array unit. After obtaining the S parameters of the microwave metamaterial sensor unit, the second step is to solve the ice thickness, ice rate, and ice shape information based on the S parameters. To obtain ice thickness information, it is first necessary to perform data fitting on the resonant frequency or amplitude of the sensor under different ice thicknesses to establish a corresponding database of ice thickness and resonant frequency / amplitude. Then, the current ice thickness can be obtained by comparing the obtained S parameters with the database. Because the sensor has the ability to detect in real time and compare the difference in ice thickness in different time periods with time, the corresponding ice rate can be obtained. The ice sensor of the present invention has multiple arrays, allowing it to measure ice thickness at multiple points. By fitting the data from the ice thickness measurements at multiple points along the normal direction at the same location on the wing surface, the ice shape of the wing ice can be determined. Finally, the obtained ice thickness and icing rate are fed into a host computer for comparison with set thresholds, providing a reference for de-icing, warning, and return-to-flight instructions. A classic table for determining aircraft icing severity based on ice thickness per minute is shown in Table 1. Due to its advantages in response time, detection range, detection accuracy, and cost, the present invention is particularly suitable for ice detection on unmanned aerial vehicles.

[0034] Table 1 Relationship between aircraft icing severity and ice thickness per minute

[0035]

[0036] The manufacturing method of the microwave flexible array sensor for detecting ice layer shape specifically comprises the following steps:

[0037] Step 1: Using the chemical etching method for circuit boards, the flexible dielectric layer is used as the material to directly etch the flexible dielectric layer with a metal layer. The first step is cutting the copper-clad board into boards; the second step is copper electroplating; the third step is cleaning; the fourth step is applying a dry film; the fifth step is exposure, development, and etching; the sixth step is cleaning; the seventh step is film removal; and the eighth step is lamination. Four bottom flexible dielectric layers with metal reference grounds and four top flexible dielectric layers with metal microstrip lines and sensitive array elements are obtained.

[0038] Step 2: Use CNC cutting to obtain an acrylic mold with a length of 110 mm, a width of 20 mm, and a depth of 1 mm;

[0039] Step 3: Mix Ecoflex00-30 glue A and glue B in a ratio of 1:1, use a vacuum centrifugal mixer to fully stir the mixed colloid until it is uniform, and then pour it into the acrylic base mold. Then, place the flexible base layer material together with the mold in a constant temperature and humidity chamber for curing. Set the constant temperature chamber to 50°, the humidity to 80%, and the curing time to 60 minutes to obtain the flexible base layer;

[0040] Step 4: Fit the blank surfaces of the four top flexible dielectric layers to the flexible base layer at intervals of 20 mm; fit the blank surfaces of the four bottom flexible dielectric layers to the other side of the flexible base layer at intervals of 20 mm to obtain 1 4. Microwave flexible array ice sensor for detecting ice layer shape and UAV ice detection. Note that the top flexible dielectric layer and the bottom flexible dielectric layer need to correspond one to one.

[0041] The above embodiments are only used to illustrate the technical solutions of the present invention. Those skilled in the art will easily understand that the above are only preferred embodiments of the present invention and are not limitations of the present invention. The present invention is not limited to the above examples. Modifications or equivalent replacements within the principles of the technical solutions of the present invention shall be included in the scope of protection of the present invention as long as they meet the requirements of the method of the present invention.

Claims

1. A microwave flexible array sensor for ice detection, characterized in that: It mainly includes: a central flexible base layer (4), an upper flexible dielectric layer (3) and a lower flexible dielectric layer (6) closely attached to both sides of the flexible base layer (4), a sensitive array element (1) and a metal microstrip line (5) structure attached to the upper flexible dielectric layer (3), and a metal reference ground (2) attached to the lower flexible dielectric layer (6); The sensitive array elements (1) and the metal microstrip lines (5) are array structures etched on the same metal layer. The sensitive array elements (1) are evenly arranged on the upper flexible dielectric layer (3) in a one-dimensional or two-dimensional form. The microwave signals are led out by metal microstrip lines (5) extending outward on both sides of each sensitive array element (1). Each of the sensitive array elements (1) is formed on a metal sheet (31), and a coupling outer ring (32) concentric with the sensitive oscillator structure, an outer resonant ring (33) and an inner resonant ring (34) with complementary openings, and a coupling interdigital structure (35) are sequentially etched from the outside to the inside; the metal sheet (31) is in the shape of a circle, an ellipse, or a regular polygonal structure, and each of the sensitive array elements (1) obtained after etching is a symmetrical structure with a hollowed-out portion; The coupling outer ring (32) is etched on the outermost side of the sensitive oscillator and is a part of a complete circular ring with an angle of 90° to 270°. The outer resonant ring (33) and the inner resonant ring (34) are etched on the inner side of the coupling outer ring (32). Both are incomplete circular rings and their opening directions differ by 180°, so that the two form a complementary position relationship. In order to increase the detection accuracy, a part of the inner part of the circular ring is retained and only the edge is etched to form a hollow complementary circular ring. The coupling interdigital structure (35) is etched on the inner side of the small complementary hollow resonant ring (34) and its opening direction is the same as that of the small complementary hollow resonant ring (34). The pattern etched inside a single sensitive array element (1) is symmetrical about the metal microstrip line (5), and the spacing between adjacent rings and the width of each ring are kept within the radius of the sensitive array element. ; The coupling interdigital structure (35) is a symmetrical structure composed of an outer incomplete circular ring and a long strip connected to the ring on the inner side. The long strip extends from the inside of the circular ring to the point closest to the center of the sensitive oscillator and is parallel to the metal microstrip line (5). The number of the long strips is 1 to 9.

2. A microwave flexible array sensor for ice detection as claimed in claim 1, characterized in that: The thickness of the upper flexible dielectric layer (3) and the lower flexible dielectric layer (6) is between 0.01 mm and 1 mm, and the material is polyester film or polyimide.

3. A microwave flexible array sensor for ice detection according to claim 1, characterized in that: The thickness of the flexible base layer (4) is between 0.1 mm and 10 mm, and the material is polydimethylsiloxane, liquid crystal polymer or aliphatic aromatic random copolyester.

4. A microwave flexible array sensor for ice detection as claimed in claim 1, characterized in that: The thickness of the metal reference ground (2) and the metal microstrip line (5) is between 0.01 mm and 1 mm.

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