CN-121977664-A - Non-invasive micro thermal flowmeter based on laser-induced graphene and preparation method thereof

CN121977664ACN 121977664 ACN121977664 ACN 121977664ACN-121977664-A

Abstract

The invention provides a non-invasive micro thermal flowmeter based on laser-induced graphene and a preparation method thereof, wherein a polyimide film is used as a substrate of the flowmeter, a modified Ashby-EASTERLING model is used for optimizing laser parameters, and a three-dimensional porous graphene sensing array with stable negative temperature coefficient characteristic is generated through in-situ induction and is used as a central heating resistor and a temperature sensing resistor pair which are arranged in a circumferential orthogonal mode. The packaging layer adopts the aqueous modified polyurethane with the thickness, so that baseline drift caused by thermal mismatch is effectively reduced, and the packaging layer shows excellent mechanism stability in 100 bending cycle tests. The device forms a cooperative mechanism of 'active thermal field excitation' and 'precise differential detection' through a constant temperature difference method and a Wheatstone bridge, and the precise measurement and calculation of the flow scalar and the two-dimensional flow vector are realized in an ultralow flow velocity interval of 0-10 mm/s. The invention has the advantages of simplified preparation process (without photoetching), strong flexible fit, high sensitivity and the like, and is especially suitable for nondestructive monitoring scenes of microfluidic chips and biomedical infusion.

Inventors

XIE YU
HUANG MINGHONG
CHEN JIANXIONG
CHEN HUI

Assignees

福州大学

Dates

Publication Date: 20260505
Application Date: 20260213

Claims (10)

1. The noninvasive micro thermal flowmeter based on the laser-induced graphene is characterized by comprising a flexible sensing unit, a signal processing circuit and a controller, wherein the flexible sensing unit comprises a flexible substrate, a dielectric packaging layer, a laser-induced graphene sensing array and a metal wire network, wherein the laser-induced graphene sensing array and the metal wire network are positioned between the flexible substrate and the dielectric packaging layer; The laser-induced graphene sensing array is arranged on the flexible substrate and comprises a heating resistor positioned at the center and a temperature sensitive resistor group with a negative temperature coefficient characteristic, wherein the temperature sensitive resistor group is distributed on the periphery of the heating resistor; The metal wire network comprises two branches which are electrically isolated from each other, and the signal processing circuit comprises a power driving circuit and a bridge measuring circuit; the heating resistor is electrically connected with the controller through a first branch of the metal wire network and the power driving circuit, and the temperature sensitive resistor group is electrically connected with the controller through a second branch of the metal wire network and the bridge measuring circuit; The controller drives the heating resistor in a constant temperature difference mode and receives a differential voltage signal output by the bridge measurement circuit to calculate a fluid flow rate scalar and a two-dimensional plane flow vector.
2. The laser-induced graphene-based non-invasive micro thermal flowmeter of claim 1, wherein the flexible substrate is a polyimide film.
3. The non-invasive micro thermal flowmeter based on laser-induced graphene according to claim 1, wherein the dielectric encapsulation layer is aqueous modified TPU, and has a thickness of 。
4. The non-invasive micro thermal flowmeter based on laser-induced graphene of claim 1, wherein the set of temperature sensitive resistors comprises a first pair of temperature sensitive resistors and a second pair of temperature sensitive resistors; the first temperature sensing resistor pair consists of two temperature sensing resistors distributed on two opposite sides of the heating resistor along a first direction, the two temperature sensing resistors are respectively connected into two adjacent bridge arms of a first Wheatstone bridge topological structure, and the other two bridge arms of the first Wheatstone bridge topological structure are connected into fixed resistors; The second temperature sensing resistor pair consists of two temperature sensing resistors distributed on two opposite sides of the heating resistor along a second direction, the two temperature sensing resistors are respectively connected into two adjacent bridge arms of a second Wheatstone bridge topological structure, and the other two bridge arms of the second Wheatstone bridge topological structure are connected into fixed resistors; The first direction and the second direction are perpendicular to each other in the plane of the flexible substrate.
5. The non-invasive micro thermal flowmeter based on the laser-induced graphene according to claim 1, wherein the controller drives the heating resistor in a constant temperature difference mode, specifically comprising the controller monitoring the temperature of the heating resistor in real time and dynamically adjusting the heating power output to the heating resistor so that the difference between the temperature of the heating resistor and the temperature of the fluid to be measured is kept constant.
6. The non-invasive micro thermal flowmeter based on the laser-induced graphene of claim 1, wherein the controller is a single chip microcomputer.
7. The method for preparing the non-invasive micro thermal flowmeter based on the laser-induced graphene according to any one of claims 1 to 6, comprising the following steps: S1, placing a polyimide film in deionized water for cleaning, placing the polyimide film in an incubator for drying, and sticking a conductive copper foil on the surface of the dried polyimide film to realize prefabrication of a metal wire network; S2, adopt Scanning a preset region of the polyimide film by a far infrared laser, in-situ inducing the polyimide surface to be converted into laser-induced graphene, and synchronously forming a laser-induced graphene sensing array comprising a heating resistor and a temperature-sensitive resistor group; s3, coating conductive silver paste on a contact area of the laser-induced graphene sensing array and the conductive copper foil and curing the conductive silver paste to ensure circuit connectivity between the laser-induced graphene sensing array and a metal wire network; s4, covering a water-based modified TPU packaging layer on the surface of one side of the flexible substrate, which is provided with the laser-induced graphene sensing array and the metal wire network, so as to obtain a flexible sensing unit; And S5, connecting the flexible sensing unit with a controller through a signal processing circuit.
8. The method for preparing a non-invasive micro thermal flowmeter based on laser-induced graphene according to claim 7, wherein the laser-induced process parameters are optimized based on a modified Ashby-EASTERLING model: Wherein, the Is the highest temperature inside the PI substrate, As a result of the initial temperature being set, As the absorptivity of PI material with respect to wavelength, For the laser power to be high, 、、 Respectively the density, specific heat capacity and thermal diffusivity of the material, For the time of the laser irradiation, 、 In order to irradiate the planar spatial coordinate system, Is the radius of the light spot; and obtaining the technological parameter collocation of the laser power and the scanning speed by reversely solving the Ashby-EASTERLING model.
9. The method for preparing the non-invasive micro thermal flowmeter based on the laser-induced graphene according to claim 7, wherein the wavelength is adopted A kind of electronic device The prepared polyimide film is subjected to laser induction by far infrared laser, and the laser power is The scanning speed is 。
10. The method for preparing the non-invasive micro thermal flowmeter based on the laser-induced graphene according to claim 7, wherein the laser-induced graphene sheet resistance is Interval.

Description

Non-invasive micro thermal flowmeter based on laser-induced graphene and preparation method thereof Technical Field The invention belongs to the technical field of micro-nano sensing, flexible electronics and fluid precise measurement, and particularly relates to a non-invasive micro-thermal flowmeter based on laser-induced graphene and a preparation method thereof. Background Thermal flow sensors have become the mainstay of choice in the field of micro flow monitoring by virtue of their significant advantages of no moving parts, fast response speed, etc. However, most of the conventional hot wire or hot film sensors adopt an invasive structure, and the probe is directly placed in the flow field, so that not only is the local flow field disturbed and pressure loss easily caused, but also the serious challenge of corrosion or cross contamination of the probe exists when corrosive media or biological fluids with high cleanliness requirements are measured. In the prior art, researchers have made various attempts to achieve non-invasive and miniaturized devices. For example, patent document CN203798395U discloses a graphene micro flow sensor, and a suspended heat insulation structure is fabricated on a silicon substrate by using a MEMS process. However, silicon-based sensors exhibit physical rigidity, are difficult to achieve intimate thermal contact with curved tube walls that are widely available in practical engineering, and their fabrication involves complex high vacuum lithography and sputtering procedures, resulting in low manufacturing efficiency and high production costs over large areas. In recent years, flexible sensors based on Laser Induced Graphene (LIG) have become a research hotspot due to their low cost and high specific surface area. For example, patent document CN116358653a discloses a thermal flexible flow sensor, which uses PDMS (polydimethylsiloxane) to encapsulate LIG for flexible bonding. However, the prior art has the obvious defects that the common packaging material (such as PDMS) has a higher thermal expansion coefficient, the thermal mismatch between the substrate and the conductive layer can cause serious resistance temperature drift under the scene of larger temperature fluctuation, and the prior non-invasive scheme often ignores the difference of the heat conducting property of the tested pipeline (pipe wall material and thickness). Most of the existing flexible flowmeters can only detect the flow velocity in a single dimension, and can not judge the backflow or the two-dimensional disturbance in a complex pipeline. Therefore, developing a non-invasive micro-meter with both high flexibility and thermal mechanical stability, capable of solving thermal drift by using an improved packaging interface process (such as water-based modified TPU), and having two-dimensional flow direction identification capability is an urgent need in the field of microfluidic sensing. Disclosure of Invention The invention aims to provide a non-invasive micro thermal flowmeter based on laser-induced graphene and a preparation method thereof. The process is guided to be preferable by a modified Ashby-EASTERLING heat conduction model, and the water-based modified TPU packaging technology is adopted, so that the problems that the existing flexible sensor is easy to generate baseline drift under the excitation of an active heat field, is easy to generate interlayer stripping under the mechanical stress circulation, and cannot consider the flow direction identification and the sensitivity in a micro flow range are solved. In order to achieve the above purpose, the technical scheme of the invention is as follows: the noninvasive micro thermal flowmeter based on the laser-induced graphene comprises a flexible sensing unit, a signal processing circuit and a controller, wherein the flexible sensing unit comprises a flexible substrate, a dielectric packaging layer, a laser-induced graphene sensing array and a metal wire network, wherein the laser-induced graphene sensing array and the metal wire network are positioned between the flexible substrate and the dielectric packaging layer; The laser-induced graphene sensing array is arranged on the flexible substrate and comprises a heating resistor positioned at the center and a temperature sensitive resistor group with a negative temperature coefficient characteristic, wherein the temperature sensitive resistor group is distributed on the periphery of the heating resistor; The metal wire network comprises two branches which are electrically isolated from each other, and the signal processing circuit comprises a power driving circuit and a bridge measuring circuit; the heating resistor is electrically connected with the controller through a first branch of the metal wire network and the power driving circuit, and the temperature sensitive resistor group is electrically connected with the controller through a second branch of the metal wire network and the bridge measuri