Flexible omnidirectional accelerometer based on sebeck effect of all-pei laser-induced graphene and processing method thereof

Abstract

This invention discloses a flexible omnidirectional accelerometer based on the Seebeck effect using laser-induced graphene in PEI (polyethylene terephthalate) and its fabrication method, belonging to the field of inertial sensing technology. The accelerometer consists of a PEI substrate and a structural layer. The structural layer integrates a central graphene thermistor and a ring-shaped arrangement of dual-material graphene balancing resistors. A Seebeck thermoelectric junction is formed by generating graphene with differential physical properties using dual-energy laser induction, and is further isolated from heat source interference by a ring-shaped heat insulation groove. The carrier acceleration drives airflow, changing the temperature of the central heat source. This results in the superposition of dual signals: the temperature-dependent voltage of the graphene resistor and the Seebeck thermoelectric potential. These signals are then converted into an acceleration voltage output via a constant-temperature feedback bridge. This invention's flexible PEI structure allows for conformal attachment to curved surfaces. In-situ laser fabrication eliminates the need for precious metal coating processes, resulting in low production costs. The superposition of the dual signals significantly improves detection sensitivity, making it widely applicable to flexible inertial measurement scenarios such as smart wearable motion acquisition, logistics collision monitoring, and vehicle-mounted curved surface acceleration detection.

Description

Technical Field

[0001] This invention belongs to the field of inertial measurement sensor technology, and in particular relates to a flexible omnidirectional accelerometer based on Seebeck effect full PEI laser-induced graphene and its processing method. Background Technology

[0002] With the continuous advancement of IoT technology, the revolution and upgrading of smart wearable devices, and the rapid iteration of intelligent transportation systems, new intelligent micro-devices integrating multiple disciplines and technologies are experiencing rapid development. By integrating various miniaturized, high-precision sensing and processing modules into one unit, emerging scenarios place extremely high demands on the compliance and multi-dimensional sensing capabilities of accelerometers. In these emerging scenarios, the limitations of traditional silicon-based rigid accelerometers are becoming increasingly apparent, mainly manifested in: (1) Logistics package collision monitoring: The sensor needs to be closely attached to the irregular surface of the package and be able to withstand high-frequency vibration and impact during transportation. However, silicon-based rigid accelerometers are prone to breakage due to compression due to their rigid structure and the cost of a single unit is high, making it difficult to achieve large-scale, one-time low-cost application; (2) Wearable motion tracking: requires sensors to be thin, flexible and biocompatible. The rigid substrate of silicon-based rigid accelerometers not only causes a skin-gripping sensation, but also cannot bend freely with human joint movements, making them extremely easy to fall off or be damaged; (3) Intelligent driving and navigation assistance: The sensors are required to be able to conformally fit the complex curved surface of the car body and measure the instantaneous acceleration vector of the car in real time. The rigid substrate of the silicon-based rigid accelerometer disrupts the streamlined surface of the car body and cannot achieve a completely seamless fit with the curved surface.

[0003] While silicon-based rigid accelerometers perform well in traditional industrial applications, their inherent limitations have become a bottleneck hindering the technology's implementation in the aforementioned emerging flexible and dynamic application scenarios. (1) Poor form adaptability and stress mismatch: It is highly dependent on planar installation. When it is forcibly applied to non-planar carriers such as curved surfaces, fabrics or human skin, it will not only fail to fit, but will also cause serious signal drift (error ≥10%) due to the internal stress mismatch between rigid encapsulation and flexible carrier, and even cause permanent structural damage. (2) Insufficient dynamic reliability: Micromechanical movable structures are extremely prone to embrittlement. In dynamic impact scenarios such as car collisions, intelligent navigation, and violent movements, the fracture failure rate of sensitive structures is as high as 30% or more. (3) High manufacturing cost: The photolithography, thin film deposition and vacuum packaging processes are extremely complex. The manufacturing cost of a single set is usually 5-10 times that of flexible devices, which cannot meet the needs of flexible or large-area array arrangement. In traditional flow velocity measurement technology, hot-wire anemometers primarily sense the heat exchange process between a heating element and the fluid by placing a thermistor (hot wire) within the fluid boundary or channel. Utilizing the convective heat dissipation differences caused by changes in fluid velocity, a feedback circuit (such as a constant temperature difference control system) precisely converts this into an electrical signal output that has a clear correlation with the fluid velocity. Because hot-wire anemometers completely eliminate movable structures such as mechanical impellers or Pitot tubes, their sensing mechanism relies entirely on heat exchange at the solid-fluid interface. Besides possessing significant advantages such as simplified structure, rapid response, and low manufacturing cost, they are easily integrated with flexible materials, making them ideal for applications in flexible microfluidic systems, wearable devices, or curved surface flow field monitoring, demonstrating strong flexibility and adaptability potential. A patent application for a portable adjustable hot-wire anemometer (application number: 202220347477.7) uses a rigid mounting base, a protective shell, and a mechanical height adjustment component to support and protect the internal hot-wire probe. However, this macroscopically rigid mechanical structure lacks flexibility and cannot conform to curved surfaces, fabrics, or human skin for measurement. When applied to non-planar surfaces, it is not only bulky but also easily damaged, failing to leverage the conformal advantages of flexible polymer materials such as all-PEI. The device uses traditional thin metal wires as thermistors and employs machined parts for assembly and positioning, resulting in a cumbersome assembly process and high manufacturing costs, which cannot meet the demand for low-cost flexible tags in emerging scenarios. Furthermore, the device is limited to external wind speed measurement in open environments and cannot be used to measure acceleration. At the same time, traditional metal hot wires rely solely on a single resistance-temperature characteristic for measurement, failing to combine material properties with the Seebeck effect to further amplify the thermoelectric potential difference output, resulting in insufficient response capability to temperature field changes caused by weak acceleration.

[0004] To address the problems existing in the background technology and meet the application needs of flexible inertial sensors, the present invention aims to provide a flexible omnidirectional accelerometer based on the Seebeck effect using laser-induced graphene resistance technology. This invention utilizes laser-induced graphene resistance technology, based on the fundamental principle of hot-wire flowmeters for measuring flow velocity. It uses a flexible sensing element to sense acceleration, and extracts electrical signals through the Seebeck effect to obtain the relationship between the acceleration of the moving carrier and the electrical signal, thus constructing a flexible omnidirectional accelerometer using laser-induced graphene resistance technology. Firstly, the omnidirectional accelerometer proposed in this invention can reflect the magnitude and direction of acceleration at the same horizontal plane within the measurement range when a fluid with changing acceleration is input along the plane of the structural layer, or when the sensor itself moves with changing acceleration, causing gas flow on the surface of the sensing element. Secondly, the sensing element of this invention uses a flexible PEI material. Its thermistor is formed by laser ablation of the flexible PEI material at high temperatures, eliminating the need for platinum sputtering and reducing costs to almost zero. Thirdly, the use of fully flexible PEI material eliminates internal stress mismatch, minimizing the temperature and time drift caused by material mismatch. Third, this invention uses slender graphene resistors as thermistors. The thinness of the resistors results in low heat capacity, low thermal inertia, and a fast sensor response. The long resistance increases the surface area of ​​the thermistor, improving the contact area with the fluid and significantly increasing temperature changes, thereby enhancing the sensor's sensitivity. This avoids the drawbacks of existing technologies using spiral or wavy resistors, which increase manufacturing difficulty due to their complex shapes. Fourth, acceleration causes changes in the thermistor resistance and also induces a Seebeck effect between tightly connected graphene molecules with different physical properties produced by different laser-induced processes. This creates a thermoelectric potential difference, and the voltage superposition of these two effects improves sensitivity. Finally, this invention integrates the sensor's thermistors with synchronous laser induction onto the same PEI substrate, ensuring strong process consistency. Simultaneous thermistor fabrication improves the initial balance accuracy of the extraction circuit; avoids mechanical / thermal mismatch between external resistors and the sensor, reducing signal drift under flexible deformation; simplifies packaging and assembly processes, reduces costs, and is suitable for mass production.

[0005] The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a laser-induced graphene flow velocity sensor based on the Seebeck effect and its processing method. This overcomes the shortcomings of existing silicon-based flow velocity sensors, such as high rigidity, difficulty in bonding to curved surfaces, high cost of precious metal materials, zero-point drift caused by multi-material composites, weak output signal, and low sensitivity. The goal is to achieve a low-cost, high-sensitivity, low-drift sensor that can be bonded to any curved surface.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A flexible omnidirectional accelerometer based on the Seebeck effect using PEI laser-induced graphene includes a base plate and a structural layer, both of which are PEI flexible substrates. The base plate has embedded grooves formed by laser dot matrix, and the structural layer is embedded and fixed in the grooves. The structural layer is provided with an annular heat-insulating groove and a laser-induced graphene sensing unit. The graphene sensing unit includes a graphene thermistor located at the geometric center and multiple sets of graphene balancing resistors symmetrically arranged around the thermistor. The graphene balancing resistors are composed of two types of graphene induced by two different laser energies in close composite, with different temperature coefficients forming Seebeck thermoelectric junctions. The central graphene thermistor is paired with each set of graphene balancing resistors to form a detection branch, and each branch is externally connected to a Wheatstone bridge and a constant temperature feedback circuit. The annular heat-insulating groove is arranged around the graphene sensing unit.

[0008] Furthermore: The graphene thermistor serves as an energized heat source, generating heat under steady-state conditions to form a centrally symmetrical temperature field. The heat-insulating groove prevents heat from diffusing to the balancing resistor, which is used to collect the ambient reference temperature in real time.

[0009] Further: Multiple sets of graphene balancing resistors are evenly distributed symmetrically along a 120° circle. Based on the numerical ratio of the output voltage of the multi-bridge circuit, the magnitude and direction of the planar acceleration are calculated.

[0010] The fabrication method of a flexible omnidirectional accelerometer based on the Seebeck effect using laser-induced full PEI laser technology includes the following steps: S1. A square structural layer substrate is prepared by laser cutting PEI sheet material; S2. A graphene thermistor is prepared in the center of the structural layer using a laser-induced process, and a balanced resistor composed of two types of graphene is prepared by stepwise irradiation using a dual-energy laser. S3. Laser ablation process is used to create an annular heat insulation groove surrounding the sensitive unit; S4. Magnetron sputtering of metallic silver to prepare conductive leads at the ends of graphene; S5. Laser dot matrix processing is used to create mounting grooves on the PEI substrate. The structural layer is then embedded into the grooves and bonded for encapsulation, completing the device fabrication.

[0011] By adopting the above technical solution, the present invention has the following beneficial effects: 1. The fully PEI flexible integrated structure can be bent and conformed to irregular curved surfaces and human skin, eliminating temperature drift and time drift caused by stress mismatch between rigid and flexible carriers, and ensuring high measurement stability under bending conditions. 2. It adopts the dual signal superposition output of resistance temperature change voltage and Seebeck thermoelectric potential. Compared with the traditional single thermistor detection, even a slight temperature change can generate a significant electrical signal, greatly improving the sensor sensitivity. 3. Graphene is generated entirely by in-situ laser induction, without the need for precious metal platinum wire, photolithography and vacuum packaging. The preparation process is simple and the raw material cost is low, making it suitable for mass array production and disposable sensor tag applications. 4. Three sets of balanced resistors are arranged symmetrically in a 120° ring. Through multi-channel voltage calculation, omnidirectional acceleration vector detection in any direction in a two-dimensional plane can be achieved. 5. The annular heat insulation groove isolates the central heat source, and the balanced resistor accurately collects the ambient temperature, reducing the systematic error caused by ambient temperature fluctuations; compared with traditional silicon-based inertial devices, it reduces gravitational acceleration interference in principle and reduces measurement error. 6. The thermistor and the balancing resistor are fabricated simultaneously on the same substrate using laser technology, resulting in consistent thermal and mechanical parameters. There is no additional signal drift under flexible deformation, reducing the difficulty of circuit debugging. Attached Figure Description

[0012] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0013] Figure 1 This is a three-dimensional structural schematic diagram of the omnidirectional accelerometer of this application; Figure 2 This is a schematic diagram of the structural layers of this application; Figure 3 This is a schematic diagram of the structure of the base plate of this application; Figure 4 This is a schematic diagram of the electrode wire structure of this application; Figure 5 This is a schematic diagram illustrating the working principle of the omnidirectional accelerometer in this application; Figure 6 This is the schematic diagram of the output circuit of the omnidirectional accelerometer in this application; Figure 7 This is a flowchart illustrating the manufacturing process of the accelerometer for this application.

[0014] Wherein: 1 is the base plate, 2 is the electrode wire, 3 is the graphene balancing resistor, 4 is the annular heat insulation groove, 5 is the graphene thermistor, and 6 is the structural layer. Detailed Implementation

[0015] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Combination Figure 1-4 As shown, this application provides a flexible omnidirectional accelerometer based on the Seebeck effect using laser-induced graphene in a PEI substrate. The accelerometer consists of a base plate 1 and a structural layer 6. The base plate 1 forms grooves of fixed depth on the PEI substrate using a laser dot-matrix process. The surface of the structural layer 6 contains laser-induced graphene sensing units and annular heat-insulating grooves 4 formed using the laser dot-matrix process. Within the sensing units of the structural layer 6, graphene thermistors 5 and graphene balancing resistors 3 are formed on the PEI substrate using a laser-induced process. The overall contour of the structural layer is processed using laser cutting technology, ensuring that the size and thickness of the structural layer are highly consistent with the geometric parameters of the grooves on the base plate. These are then tightly integrated through embedding. The graphene balancing resistor 3 is fabricated using dual-energy laser induction, employing two lasers of different energy levels to induce the PEI substrate, thereby generating graphene resistors with significantly different temperature coefficients. The two graphene types are parallel and tightly bonded in the horizontal dimension, thus generating a thermoelectric potential difference based on the Seebeck effect. The graphene thermistor located at the geometric center is constructed using the same process as the graphene balancing resistor, and the graphene thermistor is set as the heat source center of the sensitive element. It forms a paired structure with the graphene balancing resistors distributed around it, thus forming a complete flexible omnidirectional accelerometer sensitive element.

[0017] Combination Figure 5-6 As shown, the sensing element of this invention mainly consists of two parts: an outer graphene balancing resistor and a central graphene thermistor. The outer graphene balancing resistor functions as a temperature sensor, continuously monitoring the ambient temperature around the sensor. The central graphene thermistor acts as a heat source, generating heat. In equilibrium, a constant heating power is applied to the central graphene thermistor. When energized, the thermistor generates Joule heating, releasing heat to the surroundings through thermal diffusion, forming a stable temperature field around it. To maintain this stable temperature, even without fluid flow, a temperature difference must always exist between the thermistor and the ambient temperature (i.e., the temperature of the graphene balancing resistor). Furthermore, the heat dissipated by the thermistor is blocked by a heat-insulating groove, preventing the graphene balancing resistor from being affected by the temperature field generated by the heat source. This temperature field is centrally symmetrically distributed. The main purpose of this is to eliminate the influence of the ambient temperature difference on the final output result. Figure 5As shown on the left. When a fluid with linear acceleration is input along the positive x-axis, the acceleration causes an asymmetrical temperature distribution in the heat field generated by the heat source. Some of the heat generated by the three graphene thermistors in the center will be carried away by the fluid. At this time, the temperature of the graphene thermistors decreases, while the temperature of the graphene balancing resistor remains unchanged. The temperature difference between the graphene thermistors and the graphene balancing resistor at this point is different from the temperature difference in the initial steady state. The dynamic change in the value between the two is the change that needs to be monitored. Figure 6 The diagram shows a single extraction circuit for an omnidirectional accelerometer. Due to the negative temperature coefficient of the laser-induced graphene resistor, the resistance increases as the temperature decreases, causing a change in the voltage across the resistor. Simultaneously, as the temperature decreases, the Seebeck effect occurs between tightly connected graphene molecules with different physical properties produced by different laser-induced processes, generating a thermoelectric potential difference. The superposition of these two factors forms the input voltage of the feedback circuit. Therefore, the circuit input voltage can be adjusted based on the feedback circuit input voltage; that is, increasing the voltage through the feedback circuit increases the power (i.e., the heat generated by the resistor), allowing the bridge circuit to re-enter a stable state, maintaining a constant temperature difference. At this point, the input voltage of the bridge circuit is the sensor output. As acceleration increases, heat dissipation increases; the higher the voltage, the stronger the correlation between acceleration and voltage. Furthermore, for the entire circuit, the average output voltage of the three pairs of extraction circuits is also positively correlated with acceleration. The resistors in the circuit primarily adjust the temperature difference between the graphene balancing resistor and the graphene thermistor, which can be directly obtained from the circuit parameters under stable conditions. The unlabeled resistors in the diagram serve as the balancing bridge.

[0018] like Figure 5 As shown in the diagram on the right, when a linear acceleration along the x-axis is input, some of the heat generated by the three independent graphene balancing resistors in the central part is carried away. Due to the differences in the spatial position and orientation of the three independent resistors, different degrees of resistance changes occur after the linear acceleration is input, resulting in different output voltage signals. However, the changes in the three independent graphene balancing resistors are all positively correlated with their respective output voltages. The three independent graphene balancing resistors are centrally symmetrically distributed, and under different acceleration directions, their output voltage signal combinations have a specific correspondence with the direction of acceleration. Based on this correspondence, the direction of acceleration can be determined. This is the working principle of the fully PEI laser-induced graphene flexible omnidirectional accelerometer based on the Seebeck effect of this invention.

[0019] The advantages of the Seebeck effect-based flexible omnidirectional accelerometer using PEI laser-induced graphene proposed in this invention are as follows: By extracting the relationship between the voltage output from three pairs of independent resistor extraction circuits and the acceleration of the input fluid, the accelerometer can perform omnidirectional acceleration detection for movement on the same plane. Its detection principle mainly relies on the influence of fluid flowing across the surface at different accelerations on the heat source, generating a temperature field. Changes in the temperature field lead to changes in the thermistor. Traditional rigid silicon-based accelerometers respond not only to dynamic motion acceleration but also to gravitational acceleration. Compared to traditional inertial sensors, this principle eliminates some of the error caused by various factors, improving sensitivity. In terms of manufacturing, two lasers of different energy levels are used to induce PEI substrates, resulting in graphene resistors with significantly different temperature coefficients. The two graphene layers are then parallel and tightly bonded in the horizontal dimension, generating a thermoelectric potential difference based on the Seebeck effect. Not only does the voltage across the thermistor itself change with temperature, but the breakthrough in manufacturing also enables the application of the Seebeck effect to achieve thermoelectric potential difference output. This is why the flexible, high-sensitivity, omnidirectional heat flow accelerometer of this invention can perform high-sensitivity, omnidirectional angle, and acceleration detection.

[0020] Combination Figure 7 As shown, the fabrication process of the sensitive element of the all-PEI laser-induced graphene flexible omnidirectional accelerometer based on the Seebeck effect of this invention is as follows: 1. A square structural layer substrate is formed on the flexible material PEI by laser engraving, such as... Figure 7 As shown in (a).

[0021] 2. Graphene thermistors and central heat source resistors are induced to form on the PEI structural layer using a laser engraving machine, such as... Figure 7 As shown in (b).

[0022] 3. Insulating grooves are formed by ablation using a laser engraving machine, such as... Figure 7 As shown in (c).

[0023] 4. Ag is sputtered using a magnetron sputtering instrument to form electrode wire 2, which is then electrically connected to a graphene thermistor and a graphene balancing resistor, such as... Figure 7 As shown in (d).

[0024] 5. Using a laser engraving machine, the PEI material of the base plate is cut, and grooves with the same parameters as the structural layer are formed on its surface through a dot matrix process. The structural layer is then embedded and bonded to the grooves of the base plate to complete the encapsulation of the flexible accelerometer sensing element. Figure 7 As shown in (e).

[0025] This invention relates to a fully PEI laser-induced graphene flexible omnidirectional accelerometer based on the Seebeck effect. It is manufactured using laser-induced technology on a PEI substrate. The core of the sensing element consists of a ring-shaped graphene balancing resistor and a graphene thermistor. Its working principle is as follows: the central graphene thermistor acts as a heat source, generating heat. In equilibrium, a constant heating power is applied to the central graphene thermistor, causing it to generate Joule heat and release heat to the surrounding area, creating a stable temperature field. When a fluid with varying acceleration is applied along the plane of the structural layers, or when the sensor itself undergoes acceleration changes, this stable temperature field is disrupted. This causes a change in the central thermistor, and the potential difference caused by the Seebeck effect of graphene with different physical properties breaks the stable state of the Wheatstone bridge. This converts the acceleration into a corresponding voltage signal, while maintaining stable detection capability even under bending conditions, enabling acceleration measurement in flexible environments.

[0026] 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 foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flexible omnidirectional accelerometer based on the Seebeck effect using full PEI laser-induced graphene, characterized in that: It includes a base plate and a structural layer, both of which are PEI flexible substrates; the base plate has embedded grooves formed by laser dot matrix, and the structural layer is embedded and fixed in the grooves; the structural layer is provided with an annular heat insulation groove and laser-induced graphene sensitive units; The graphene sensing unit includes a graphene thermistor located at the geometric center and multiple sets of graphene balancing resistors symmetrically arranged around the thermistor. The graphene balancing resistors are composed of two types of graphene induced by two different laser energies in close composite, with different temperature coefficients forming Seebeck thermoelectric junctions. The central graphene thermistor is paired with each set of graphene balancing resistors to form a detection branch, and each branch is externally connected to a Wheatstone bridge and a constant temperature feedback circuit. The annular heat-insulating groove is arranged around the graphene sensing unit.

2. The Seebeck effect-based full PEI laser-induced graphene flexible omnidirectional accelerometer according to claim 1, characterized in that: The graphene thermistor serves as an energized heat source. Under steady-state conditions, it generates heat to form a centrally symmetrical temperature field. The heat-insulating groove prevents heat from diffusing to the balancing resistor, which is used to collect the ambient reference temperature in real time.

3. The Seebeck effect-based full PEI laser-induced graphene flexible omnidirectional accelerometer according to claim 1, characterized in that: Multiple sets of graphene balancing resistors are symmetrically arranged evenly along a 120° circle. Based on the numerical ratio of the output voltages of the multi-bridge circuit, the magnitude and direction of the planar acceleration are calculated.

4. The processing method of the all-PEI laser-induced graphene flexible omnidirectional accelerometer according to any one of claims 1 to 3, characterized in that, It includes the following steps: S1. A square structural layer substrate is prepared by laser cutting PEI sheet material; S2. A graphene thermistor is prepared in the center of the structural layer using a laser-induced process, and a balanced resistor composed of two types of graphene is prepared by stepwise irradiation using a dual-energy laser. S3. Laser ablation process is used to create an annular heat insulation groove surrounding the sensitive unit; S4. Magnetron sputtering of metallic silver to prepare conductive leads at the ends of graphene; S5. Laser dot matrix processing is used to create mounting grooves on the PEI substrate. The structural layer is then embedded into the grooves and bonded for encapsulation, completing the device fabrication.

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