A flexible smart skin for spacecraft structural health monitoring and its development method

Abstract

This invention discloses a flexible smart skin for spacecraft structural health monitoring and its fabrication method. It utilizes multiple sensor arrays, including strain, temperature, acceleration, and ultrasonic sensors, and fabricates the flexible skin through an integrated flexible packaging method, taking into account the characteristics of being lightweight, thin, flexible, small, and conformal to irregular curved surfaces or confined spaces. When in use, this invention can be attached to the corresponding spacecraft structural surface like a band-aid, enabling on-orbit status monitoring and space environment perception.

Description

Technical Field

[0001] This invention relates to a flexible smart skin for monitoring the structural health of spacecraft and its development method, belonging to the field of structural condition monitoring technology. Background Technology

[0002] Since the 1980s, intelligent structural systems, with their intelligent characteristics such as self-diagnosis, self-adaptation, and self-repair, have become one of the most challenging and strategically significant areas of innovative research. Undoubtedly, future research on multi-source sensing for spacecraft will be a key focus in the global aerospace field. Currently, structural health monitoring in the aerospace field has been gradually applied in practical engineering after more than 30 years of development. However, structural health monitoring in the space industry is still in its early stages. Therefore, intelligent skins for on-orbit condition monitoring and space environment perception of spacecraft are of great significance. Summary of the Invention

[0003] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose a flexible smart skin for spacecraft structural health monitoring and its development method. By designing an array of sensors and then flexibly packaging and integrating them, the smart skin can achieve health monitoring while taking into account the characteristics of being lightweight, thin, and flexible, and is easy to use.

[0004] The technical solution of this invention is:

[0005] A flexible smart skin for spacecraft structural health monitoring, the skin being a two-layer adhesive structure including an outer environmental protection layer and an inner flexible monitoring layer;

[0006] The environmental protection layer is used to protect the internal flexible sensor array layer and auxiliary modules from the force, heat and electromagnetic interference of the deep space environment;

[0007] The flexible monitoring layer includes a flexible substrate, a flexible sensor array, and an auxiliary module. The flexible sensor array and the auxiliary module are mounted on the flexible substrate, which is directly attached to the part of the device under test. The flexible sensor array converts physical quantities such as strain, temperature, acceleration, or acoustic parameters at multiple points on the part under test into electrical signals and transmits them. The auxiliary module is flexibly interconnected with the flexible sensor array layer, supplies power to the flexible sensor array layer, and modulates the electrical signals transmitted from the flexible sensor array layer into standard voltage signals for acquisition and digital processing.

[0008] Preferably, the flexible sensing array includes a plurality of strain sensors, a plurality of temperature sensors, a plurality of accelerometer sensors, and a plurality of ultrasonic sensors, wherein the above sensors are arrayed on the flexible substrate;

[0009] The strain sensor is a passive device, with three strain gauges forming a 45° strain rosette; the temperature sensor is a MEMS temperature sensor; the acceleration sensor is a MEMS accelerometer; and the ultrasonic sensor is a piezoelectric ceramic sensing unit.

[0010] The sensors are connected by serpentine wires, which can stretch, bend and deform with the flexible substrate.

[0011] Preferably, the environmental protection layer comprises, from the inside out, a dielectric layer, a heat insulation layer, and a high-energy particle shielding layer;

[0012] The dielectric layer uses epoxy resin as the base material and an anti-ozone aging agent as an auxiliary curing agent, which is uniformly dispersed in the epoxy resin.

[0013] The heat insulation layer is synthesized by chemical vapor deposition on the micron-sized cerium dioxide surface to form boron nitride;

[0014] The high-energy particle shielding layer is an electromagnetic shielding coating based on a thin film material with adhesiveness and conductivity. It is formed by inducing polypyrrole to form microspheres using polyvinyl alcohol, and then combining them with a dopamine-modified thin film material dispersion.

[0015] Preferably, the dielectric layer, the heat insulation layer, and the high-energy particle shielding layer are formed into an environmental protection layer by adhesive bonding.

[0016] A method for developing a flexible smart skin includes:

[0017] Based on the structure of the equipment under test and the testing requirements, determine the type, quantity, and location of the sensors to be mounted, determine the number of nodes, layout, and connection method of the flexible sensor array and auxiliary modules, and customize the flexible intelligent skin structure.

[0018] The silicon substrate of each chip in the auxiliary module is thinned to a thickness of less than 25μm to obtain the corresponding ultra-thin flexible chips.

[0019] Each designed node is pre-reserved on a flexible substrate, and serpentine wires between the nodes are formed by spraying using 3D printing.

[0020] Each ultra-thin flexible chip in each sensor and auxiliary module is installed in the reserved position on the flexible substrate, glued to the flexible substrate, and the sensor pins are firmly welded to the serpentine wires to obtain the prepared flexible smart skin;

[0021] The flexible smart skin was attached to the surface of the spacecraft, and its measurement performance was calibrated and in-situ verified.

[0022] Preferably, the silicon substrate of each chip in the auxiliary module is thinned using the following method:

[0023] 1) Apply a film to the front side of the chip wafer, use a grinding wheel to rough grind the wafer, and use deionized water circulation cooling to accelerate the heat diffusion of the wafer during the grinding process and reduce the initiation of cracks caused by thermal stress.

[0024] 2) Use a grinding wheel to fine grind the wafer after rough grinding to reduce residual grinding stress and prevent wafer warping;

[0025] 3) The finely ground wafer is further ground using a grinding wheel. During the grinding process, a grinding slurry composed of chemical etchant and abrasive particles is added to further eliminate residual stress caused by grinding and improve wafer flatness.

[0026] 4) After the wafer is flattened and thinned, the back film is applied and the front protective film is removed. The wafer is then laser-cut and diced to obtain an ultra-thin flexible single chip.

[0027] Preferably, the wafer is coarsely ground using a grinding wheel, specifically a 4000-grit diamond grinding wheel.

[0028] Preferably, the wafer after rough grinding is finely ground using a grinding wheel, and the grinding wheel is an 8000-grit diamond grinding wheel.

[0029] The advantages of this invention compared to the prior art are:

[0030] (1) The present invention is a portable system in which all components are integrated on a flexible substrate and can be attached to the surface of the corresponding spacecraft structure like a band-aid when in use.

[0031] (2) The present invention uses multiple sensor arrays such as strain, temperature, acceleration, and ultrasound to prepare flexible skin through an integrated flexible packaging method, taking into account the characteristics of being light, thin, flexible, small, and conformal to irregular curved surfaces or narrow spaces. Attached Figure Description

[0032] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0033] Figure 1 This is a schematic diagram of the flexible smart skin structure according to an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of the flexible sensor array design according to an embodiment of the present invention. Detailed Implementation

[0035] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0036] This invention proposes a flexible smart skin for spacecraft structural health monitoring, a universal flexible spacesuit for spacecraft, to achieve on-orbit status monitoring and space environment perception.

[0037] The flexible smart skin includes an outer environmental protection layer and an inner flexible monitoring layer. The flexible monitoring layer includes a flexible substrate, a sensor array, and auxiliary modules, such as... Figure 1 As shown:

[0038] (1) Environmental protection layer

[0039] The environmental protection layer is the outermost structure of the skin, including a dielectric layer, a thermal insulation layer, and a high-energy particle shielding layer. It is used to protect the internal flexible electronic devices from the complex mechanical-thermal-electromagnetic environment interference caused by space radiation, alternating high and low temperatures, high-energy particle collisions, and atomic oxygen in the deep space environment.

[0040] The preparation method of the environmental protection layer is as follows:

[0041] First, epoxy resin is used as the base material, and an ozone-resistant aging agent (N-isopropyl-N-phenyl-p-phenylenediamine) is used as an auxiliary curing agent to ensure that it is evenly dispersed in the resin matrix.

[0042] Secondly, boron nitride (tBN) is synthesized on the surface of cerium dioxide (CeO2) by chemical vapor deposition to prepare micron-sized tBN-coated CeO2. This method can greatly reduce the catalytic activity of CeO2 while ensuring its high heat resistance and ultraviolet absorption range, thus achieving an anti-ultraviolet effect.

[0043] Polyvinyl alcohol was used to induce the formation of polypyrrole microspheres, which were then composited with a dopamine-modified film material dispersion to form a thin-film material-based electromagnetic shielding coating with excellent adhesion and high conductivity. The polyimide insulating dielectric material, Kapton, has a thickness of 0.18 μm.

[0044] The above materials are bonded together to form an environmental protection layer.

[0045] (2) Flexible sensor array

[0046] The sensor array, located between the device under test and the environmental protection layer, includes a strain sensor 1, a temperature sensor 3, an accelerometer sensor 4, a miniaturized ultrasonic sensor 2 (including excitation and reception), and a flexible substrate. It converts the physical quantities of strain, temperature, acceleration, and acoustic parameters of the measured part into electrical signals and transmits them. The flexible substrate is a double-copper-coated polyimide film.

[0047] Strain sensor 1 is a passive device, consisting of three strain gauges arranged in a 45° strain rosette. A strain gauge is the unit in the sensor used to measure the physical quantity of strain. Plane strain involves deformation in two directions and in-plane shear deformation, thus requiring three strain gauges for measurement. The three strain gauges are arranged in a configuration where directions 1 and 2 are perpendicular to each other, and the third strain gauge is positioned at a 45° angle between directions 1 and 2, forming a strain rosette.

[0048] Temperature sensor 3 is a miniaturized MEMS temperature sensor; accelerometer 4 is a miniaturized MEMS accelerometer; ultrasonic sensor 2 is a miniaturized piezoelectric ceramic sensing unit. For example... Figure 1 As shown, the sensor units are arranged in an array, and the sensor units are connected by serpentine wires, which can be stretched, bent and deformed with the flexible substrate material.

[0049] (3) Auxiliary Module

[0050] The auxiliary modules include a signal conditioning module, an acquisition module, a power supply component, and a communication component.

[0051] The signal conditioning module conditions the electrical signals converted from different sensors into a standard voltage signal (-5 to 5V), and the acquisition module performs standardized acquisition and digitization. Both modules are flexible and can be conformally mounted to the equipment.

[0052] The power supply components mainly include flexible batteries or wireless power modules, which convert electromagnetic or ultrasonic energy into stable electrical energy required by each sensor, while also flexibly interconnecting with the sensors. The power supply components include an energy conversion module, a voltage regulator module, and an energy storage unit, incorporating wireless design to ensure continuous and stable energy output for the flexible sensor array layer.

[0053] The communication components include radio frequency power amplifiers, antenna switches, filters, adjustable phase shifters, and low-noise amplifiers, which amplify and filter digital signals before outputting them to an external processing computer.

[0054] The method for developing flexible intelligent skin is as follows:

[0055] Step 1: Based on the test object and test requirements, determine the type, quantity, and location of the sensors to be mounted; determine the number of nodes and layout scheme of the sensor network; simultaneously determine the power supply and communication scheme; and formulate the connection scheme for the sensor network portion of the flexible smart skin.

[0056] Step 2: Customize the flexible smart skin based on the testing requirements of the spacecraft structure under test. Taking a satellite antenna as an example, the heat generated by the power consumption of a high-power phased array antenna causes thermal deformation of the carbon fiber composite substrate, severely affecting the antenna flatness. Real-time in-situ monitoring of the deformation and temperature distribution of the satellite antenna substrate is required. Therefore, the sensing layer of the flexible smart skin mainly uses a network of strain sensors and temperature sensors. Furthermore, based on the accuracy requirements of the strain and temperature fields, the sensor spacing and specific models are determined. Simultaneously, considering that the serpentine wires possess stretchable and deformable capabilities, they contribute to the conformal local structure of the flexible smart skin to the antenna substrate, such as... Figure 2 As shown, (a) is the initial morphology, and (b) is the morphology after stretching deformation.

[0057] Step 3: Flexible data acquisition, communication, and power amplification chips require silicon substrates to be thinned to below 25μm to achieve sensor and chip flexibility. This involves three steps: rough grinding, fine grinding, and chemical mechanical polishing (CMP). 1) In the rough grinding stage, a protective film is first applied to the front side of the wafer to protect the front circuitry. Then, a smaller mesh wheel is used with a higher feed rate for rough grinding. Deionized water circulation cooling accelerates heat diffusion during the grinding process, reducing thermal stress-induced crack initiation. 2) In the fine grinding stage, a larger mesh wheel is used with a lower feed rate to reduce residual grinding stress and prevent wafer warping. 3) CMP uses a high-flatness grinding wheel. During grinding, a slurry composed of chemical etchants and abrasive particles is added to further eliminate residual grinding stress, improve wafer flatness, and reduce wafer warping. After flattening and thinning, the wafer undergoes back-side film application and front-side protective film removal processes. Laser cutting and scribing then yields an ultra-thin flexible single-chip.

[0058] Step 4: The sensing layer pre-reserves the sensing network nodes designed in Step 1, and the serpentine wires between the nodes are sprayed onto the flexible substrate using 3D printing.

[0059] Step 5: Transfer the various types of sensors and flexible data acquisition, communication and power amplification chips to the reserved positions on the flexible substrate, glue them to the flexible substrate, and firmly solder the sensor pins to the serpentine wires.

[0060] Step 6: The flexible skin is attached to the spacecraft structure operation status test platform, and the measurement performance of the flexible sensing system is calibrated and in-situ verified using auxiliary testing systems such as optical measurement.

[0061] The embodiments described above are merely preferred embodiments of the present invention. Ordinary variations and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included within the protection scope of the present invention.

Claims

1. A flexible smart skin for spacecraft structural health monitoring, characterized in that, The skin is a two-layer adhesive structure, including an outer environmental protection layer and an inner flexible monitoring layer; The environmental protection layer is used to protect the internal flexible sensor array layer and auxiliary modules from the force, heat and electromagnetic interference of the deep space environment; The flexible monitoring layer includes a flexible substrate, a flexible sensor array, and an auxiliary module. The flexible sensor array and the auxiliary module are mounted on the flexible substrate, which is directly attached to the part of the device under test. The flexible sensor array layer converts physical quantities such as strain, temperature, acceleration, or acoustic parameters at multiple points on the part under test into electrical signals and transmits them. The auxiliary module is flexibly interconnected with the flexible sensor array layer, supplies power to the flexible sensor array layer, and modulates the electrical signals transmitted from the flexible sensor array layer into standard voltage signals for acquisition and digital processing. The flexible sensing array includes several strain sensors, several temperature sensors, several accelerometer sensors, and several ultrasonic sensors, all of which are arrayed on a flexible substrate. The strain sensors are passive devices, with three strain gauges forming a 45° strain rosette. The temperature sensors are MEMS temperature sensors; the accelerometer sensors are MEMS accelerometers; and the ultrasonic sensors are piezoelectric ceramic sensing units. The sensors are connected by serpentine wires that can stretch, bend, and deform with the flexible substrate. The environmental protection layer comprises, from the inside out, a dielectric layer, a heat insulation layer, and a high-energy particle shielding layer. The dielectric layer uses epoxy resin as the base material and an anti-ozone aging agent as an auxiliary curing agent, which is uniformly dispersed in the epoxy resin. The heat insulation layer is synthesized by chemical vapor deposition on the micron-sized cerium dioxide surface. The high-energy particle shielding layer is an electromagnetic shielding coating based on a thin film material with adhesiveness and conductivity. It is formed by using polyvinyl alcohol to induce polypyrrole to form microspheres, which are then combined with a dopamine-modified thin film material dispersion.

2. The flexible smart skin according to claim 1, characterized in that, The dielectric layer, heat insulation layer, and high-energy particle shielding layer are bonded together to form an environmental protection layer.

3. A method for developing a flexible intelligent skin as described in claim 1, characterized in that, include: Based on the structure of the equipment under test and the testing requirements, determine the type, quantity, and location of the sensors to be mounted, determine the number of nodes, layout, and connection method of the flexible sensor array and auxiliary modules, and customize the flexible intelligent skin structure. The silicon substrate of each chip in the auxiliary module is thinned to a thickness of less than 25μm to obtain the corresponding ultra-thin flexible chips. Each designed node is pre-reserved on a flexible substrate, and serpentine wires between the nodes are formed by spraying using 3D printing. Each ultra-thin flexible chip in each sensor and auxiliary module is installed in the reserved position on the flexible substrate, glued to the flexible substrate, and the sensor pins are firmly welded to the serpentine wires to obtain the prepared flexible smart skin; The flexible smart skin was attached to the surface of the spacecraft, and its measurement performance was calibrated and in-situ verified.

4. The method for developing flexible intelligent skin according to claim 3, characterized in that, The silicon substrate of each chip in the auxiliary module is thinned using the following method: 1) Apply a film to the front side of the chip wafer, use a grinding wheel to rough grind the wafer, and use deionized water circulation cooling to accelerate the heat diffusion of the wafer during the grinding process and reduce the initiation of cracks caused by thermal stress. 2) Use a grinding wheel to fine grind the wafer after rough grinding to reduce residual grinding stress and prevent wafer warping; 3) The finely ground wafer is further ground using a grinding wheel. During the grinding process, a grinding slurry composed of chemical etchant and abrasive particles is added to further eliminate residual stress caused by grinding and improve wafer flatness. 4) After the wafer is flattened and thinned, the back film is applied and the front protective film is removed. The wafer is then laser-cut and diced to obtain an ultra-thin flexible single chip.

5. The method for developing flexible intelligent skin according to claim 4, characterized in that, The wafer is rough-ground using a grinding wheel; a 4000-grit diamond grinding wheel is selected.

6. The method for developing flexible intelligent skin according to claim 4, characterized in that, The wafers that have undergone rough grinding are then finely ground using an 8000-grit diamond grinding wheel.

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