Flexible fluid sensing system based on inkjet printing and method of making the same

Abstract

The application relates to the technical field of sensors, and provides a flexible fluid sensing system based on inkjet printing and a preparation method thereof. The sensing system comprises a flexible substrate, an energy collection antenna, an energy management unit, a microfluidic sensor, a micropump and a signal modulation unit arranged on the flexible substrate. The energy collection antenna and the energy management unit are arranged, the system can autonomously collect radio frequency energy from the environment and convert the radio frequency energy into electric energy to supply power to the whole system, the collected dispersed energy can be stored, and instantaneous high-power output can be provided when needed, so that the system is free from the dependence on traditional batteries or external power sources.

Description

Technical Field

[0001] This application relates to the field of sensor technology, and in particular to a flexible fluid sensing system based on inkjet printing and its fabrication method. Background Technology

[0002] With the rapid development of IoT technology, the market demand for multifunctional, large-scale sensor networks continues to rise. Currently, sensors for gas, heat, and vibration have been implemented; however, fluid sensing technology remains a key technological weakness in large-scale IoT sensor networks. Existing solutions in flexible fluid drive technology, such as pneumatic actuators and electrohydraulic actuators, have been successfully implemented in applications such as soft robots. However, these technologies generally rely on external power supply equipment, making it difficult to achieve fully autonomous operation. Meanwhile, the rise of energy harvesting technology has provided a feasible path for building battery-free sensing systems, but a single energy source, limited by its own characteristics, still cannot simultaneously meet the dual requirements of continuous and stable power supply and instantaneous high-power output. Summary of the Invention

[0003] This application aims to improve at least one technical problem in the background art.

[0004] This application provides a flexible fluid sensing system based on inkjet printing, which includes a flexible substrate and a component disposed on the flexible substrate:

[0005] An energy harvesting antenna is used to harvest ambient radio frequency energy and transmit modulated backscattered signals.

[0006] An energy management unit, electrically connected to the energy harvesting antenna, is used to convert the ambient radio frequency energy harvested by the energy harvesting antenna into DC power and store and distribute it.

[0007] A microfluidic sensor for containing a fluid to be measured and sensing changes in the conductivity of the fluid to be measured, comprising a microchannel disposed on the flexible substrate and sensing electrodes disposed on both sides of the microchannel;

[0008] A micropump, one end of which is electrically connected to the energy management unit and the other end of which is connected to the microchannel, is used to drive the fluid to be measured into the microchannel when it obtains electrical energy;

[0009] A signal modulation unit, which is electrically connected to the sensing electrode and the energy harvesting antenna respectively, is used to convert the conductivity change into a sensing signal and modulate it into a backscattered signal that can be transmitted back through the energy harvesting antenna.

[0010] According to some technical solutions of this application, the energy harvesting antenna is an ultra-wideband antenna, and the ultra-wideband antenna is provided with a radiating patch, and the radiating patch is provided with at least one "C" shaped groove.

[0011] According to some technical solutions of this application, the ultra-wideband antenna is provided with three different sizes of "C" shaped slots, and the three "C" shaped slots are arranged with one of them as the reference position and the other two are arranged outward in sequence along the reference position to generate notch filters in different frequency bands.

[0012] According to some technical solutions of this application, the energy management unit includes:

[0013] A rectifier, the input terminal of which is electrically connected to the energy harvesting antenna, is used to convert AC radio frequency signals into DC power;

[0014] An energy storage capacitor, which is connected to the output terminal of the rectifier, is used to store electrical energy;

[0015] A power management chip, connected to the energy storage capacitor, is used to monitor the voltage of the energy storage capacitor and control the release of electrical energy to the micropump and the signal modulation unit according to the voltage change.

[0016] According to some technical solutions of this application, the signal modulation unit includes:

[0017] A timer chip, whose input terminal is connected to the sensing electrode, is used to generate an oscillation signal of a corresponding frequency based on the resistance value of the sensing electrode.

[0018] A switching element, connected to the output of the timer chip, is used to change the load impedance of the energy harvesting antenna according to the oscillation signal to achieve backscattering.

[0019] According to some technical solutions of this application, the capacitance of the energy storage capacitor is 47mF.

[0020] This application also provides a method for fabricating a flexible fluid sensing system based on inkjet printing, which includes the following steps:

[0021] An ultra-wideband antenna is formed on a flexible substrate by inkjet printing and sintering.

[0022] Microchannels are formed on a flexible substrate by photopolymerization 3D printing;

[0023] Sensing electrodes are obtained by inkjet printing on regions corresponding to microchannels on a flexible substrate.

[0024] The microchannels are integrated with and solidified on a flexible substrate that carries the sensing electrodes;

[0025] The power management unit, micropump, and signal modulation unit are mounted on a flexible substrate and electrically connected to an ultra-wideband antenna, microchannel, and sensing electrodes.

[0026] According to some technical solutions of this application, microchannels are formed on a flexible substrate by photopolymerization 3D printing, specifically including:

[0027] Flexible photosensitive resin is used as the printing material. The photopolymer 3D printer exposes and cures the resin layer by layer according to the preset three-dimensional model and the preset number of layers to form a microchannel structure with a semi-circular cross-section.

[0028] The printed microchannel structure was placed in isopropanol to clean the uncured resin.

[0029] After cleaning, the microchannel structure is post-cured and reinforced at a preset temperature, and the supporting material is removed to obtain the microchannel.

[0030] According to some technical solutions of this application, sensing electrodes are obtained by inkjet printing in areas corresponding to microchannels on a flexible substrate, specifically including:

[0031] In the region corresponding to the microchannel on the flexible substrate, multi-layer inkjet printing is performed using conductive ink with a set droplet spacing and printing platform temperature.

[0032] After printing, the conductive ink is cured by sintering to obtain the sensing electrode.

[0033] According to some technical solutions of this application, an ultra-wideband antenna is formed on a flexible substrate by inkjet printing and sintering, specifically including:

[0034] Using conductive ink, an antenna pattern with a radiating patch, a feed line, a ground plane, and a "C"-shaped groove structure formed on the radiating patch is printed on the flexible substrate according to a preset path; the printed antenna pattern is then sintered and cured to obtain an ultra-wideband antenna.

[0035] This application provides a flexible fluid sensing system based on inkjet printing, which has at least the following advantages: by setting up an energy harvesting antenna and an energy management unit, the system can autonomously harvest radio frequency energy from the environment and convert it into electrical energy to power the entire system. It can also store the harvested dispersed energy and provide instantaneous high-power output when needed, thus eliminating the dependence on traditional batteries or external power sources. At the same time, by integrating microfluidic sensors, wireless energy harvesting, and signal transmission functions on a single flexible substrate, a miniaturized battery-free fluid sensing system with good flexibility and wearability is realized. Attached Figure Description

[0036] Figure 1 A schematic diagram of the antenna fabrication process provided in the embodiments of this application;

[0037] Figure 2A device structure diagram of a flexible fluid sensing system based on inkjet printing provided in an embodiment of this application;

[0038] Figure 3 A schematic diagram of the connection structure of a flexible fluid sensing system based on inkjet printing provided in an embodiment of this application;

[0039] Figure 4 This is a schematic flowchart illustrating the fabrication method of the flexible fluid sensing system based on inkjet printing provided in the embodiments of this application.

[0040] In the attached figure: 100-flexible substrate; 110-microfluidic sensor; 130-micropump; 141-rectifier; 142-energy storage capacitor; 143-power management chip; 151-timer chip; 152-switching element; 131-micropump control chip. Detailed Implementation

[0041] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0042] In the description of this application, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation or be constructed or operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0043] In the description of this application, unless otherwise expressly defined, terms such as "setup," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this application in conjunction with the specific content of the technical solution.

[0044] The following is combined with Figures 1 to 4 Embodiments of the present invention will be described.

[0045] With the rapid development of IoT technology, the demand for multifunctional large-scale sensor networks is growing. Although significant progress has been made in sensors for gases, heat, and vibration, fluid sensing technology remains a crucial missing link in large-scale IoT sensor networks. Existing fluid analysis technologies are mostly limited to laboratory environments, and their transition to everyday applications still faces challenges such as high manufacturing costs and long development cycles, short wireless reading distances, susceptibility to environmental interference, and excessive power consumption due to battery dependence.

[0046] While existing microfluidic technology, as a core means of achieving wearable fluid analysis, offers advantages such as micro-level liquid analysis and precise reaction control, current glass etching and injection molding manufacturing processes still suffer from low efficiency and high cost. Regarding data transmission, existing solutions mostly rely on vector network analyzers for resonant frequency detection; these devices are bulky and typically have a reading distance of less than 50 centimeters, limiting their effectiveness. As for driving methods, battery-powered solutions are insufficient to meet the requirements of flexible wearable devices for thinness and flexibility.

[0047] In addition, flexible fluid actuation technology has made some progress, such as the application of pneumatic actuators and electrohydraulic actuators in the field of soft robotics. However, such technologies still rely on external power supply equipment and cannot achieve fully autonomous operation. Although energy harvesting technology makes battery-free systems possible, a single energy source cannot meet the needs of continuous power supply and instantaneous high power output.

[0048] Based on the above, this application provides a flexible fluid sensing system based on inkjet printing, which includes a flexible substrate 100 and components disposed on the flexible substrate 100:

[0049] An energy harvesting antenna is used to harvest ambient radio frequency energy and transmit modulated backscattered signals.

[0050] An energy management unit, electrically connected to the energy harvesting antenna, is used to convert the ambient radio frequency energy harvested by the energy harvesting antenna into electrical energy and store and distribute it.

[0051] A microfluidic sensor for containing a fluid to be measured and sensing changes in the conductivity of the fluid to be measured, comprising a microchannel disposed on the flexible substrate 100 and sensing electrodes disposed on both sides of the microchannel.

[0052] A micropump 130, one end electrically connected to the energy management unit and the other end connected to the microchannel, is used to drive the fluid to be measured into the microchannel when it receives electrical energy. The micropump 130 can pressurize various liquids into the microfluidic sensor. Wireless data transmission is achieved using a low-power backscattering topology that consumes only a few hundred microwatts. Compared to traditional solutions that require bulky and expensive vector network analyzers to detect the sensor's resonant frequency, this system achieves wireless reading through a cheap and compact software-defined radio, and significantly extends the reading distance thanks to its excellent resistance to multipath interference and clutter.

[0053] A signal modulation unit, which is electrically connected to the sensing electrode and the energy harvesting antenna respectively, is used to convert the conductivity change into a sensing signal and modulate it into a backscattered signal that can be transmitted back through the energy harvesting antenna.

[0054] Therefore, by setting up an energy harvesting antenna and an energy management unit, the system can autonomously harvest radio frequency energy from the environment and convert it into DC power to power the entire system. It can also store the harvested dispersed energy and provide instantaneous high-power output when needed, eliminating the dependence on traditional batteries or external power sources. At the same time, by integrating microfluidic sensors with wireless energy harvesting and signal transmission functions on a single flexible substrate 100, a miniaturized, wearable, battery-free fluid sensing system is realized.

[0055] In some embodiments, the energy harvesting antenna is an ultra-wideband antenna operating in the 3.1-10.6 GHz ultra-wideband frequency band. This antenna has stable signal radiation capability within the target ultra-wideband frequency band, while maintaining excellent notch characteristics, and its human body specific absorption rate meets safety standards, making it an ideal choice for flexible and wearable communication transmission devices. The ultra-wideband antenna has a radiating patch with at least one "C"-shaped slot. Specifically, it is an ultra-wideband "C"-shaped slot structure antenna formed on a flexible PET substrate using inkjet printing. Further, the ultra-wideband antenna has three different sizes of "C"-shaped slots, each etched into a different area of ​​the radiating patch. Optionally, one of the three "C"-shaped slots is used as a reference position, with the other two arranged sequentially outwards from the reference position to generate notch signals in different frequency bands. In this way, by using a nested "C"-shaped groove structure design of three different sizes, miniaturized three-notch characteristics can be achieved on a flexible PET substrate, which can effectively shield interference from WiMAX (3.3-3.6 GHz), WLAN (5.150-5.825 GHz), and X-band uplink frequencies (7.9-8.4 GHz).

[0056] Optionally, the overall antenna dimensions are 17.6 × 16 × 0.12 mm³, representing an improved structure of a circular monopole antenna. It consists of a ground plane, a feed line, and a radiating patch with three differently sized "C"-shaped slots. Therefore, this antenna structure is simple, requiring no additional components and effectively reducing complexity; the compact shape of the radiating patch and the smooth transition of the feed line expand the bandwidth while reducing size; the trapezoidal coplanar waveguide feed structure enhances anti-interference capabilities, improves impedance matching, optimizes bandwidth, and is more conducive to inkjet printing; the triple-nested "C"-shaped slot design on the radiating patch combines miniaturization with printability.

[0057] In some embodiments, the energy management unit includes:

[0058] A rectifier 141, the input terminal of which is electrically connected to the energy harvesting antenna, is used to convert AC radio frequency signals into DC power.

[0059] Energy storage capacitor 142 is connected to the output terminal of rectifier 141 and is used to store electrical energy;

[0060] The power management chip 143 is connected to the energy storage capacitor 142 and is used to monitor the voltage of the energy storage capacitor 142 and control the release of electrical energy to the micro pump 130 and the signal modulation unit according to the voltage change.

[0061] In some embodiments, the signal modulation unit includes:

[0062] The timer chip 151 has its input terminal connected to the sensing electrode and is used to generate an oscillation signal of a corresponding frequency based on the resistance value of the sensing electrode.

[0063] A switching element 152, which is connected to the output terminal of the timer chip 151, is used to change the load impedance of the energy harvesting antenna according to the oscillation signal in order to achieve backscattering.

[0064] When working, refer to Figure 2 The energy flow path and sensing signal flow path in the sensor are driven by energy harvesting technology. Specifically, energy harvested by the ultra-wideband "C"-shaped slot antenna is converted into DC power by rectifier 141 and delivered to the energy management unit to charge the energy storage capacitor 142. After charging, the energy management unit switches to a discharge state, driving the micropump control chip 131 to start the micropump 130, injecting the harvested liquid into the microfluidic sensor. The micropump 130 is responsible for delivering the liquid to the microfluidic sensor. The microfluidic sensor modulates the biological data into different resistance values. These resistors are connected in parallel with the default resistor to prevent open circuits when the microchannel is idle. A timer driven by energy harvesting captures and converts these resistances into voltage signals with different oscillation frequencies. The voltage signals generate differentiated switching frequencies through a control switch. These frequencies are modulated onto a carrier wave, and the signal is transmitted back to the SDR by adjusting the antenna load impedance. The receiver converts the modulation frequency into resistance values, ultimately restoring the biological data.

[0065] In some embodiments, the capacitance of the energy storage capacitor 142 is 47mF. The system uses a 47mF supercapacitor for energy storage, and automatically switches to the discharge state when the voltage reaches a threshold, providing wearable devices with continuous and stable autonomous fluid control capabilities.

[0066] Taking a wearable sweat sensing system as an example, during operation, the ultra-wideband antenna simultaneously collects UHF RFID (Ultra-High Frequency Radio Frequency Identification) signals and walkie-talkie signals from the environment. Energy is used to charge a 47mF supercapacitor via rectifier 141. When the capacitor voltage reaches a threshold, the power management unit drives the micropump 130 to inject sweat into the microchannel. The fluid causes a change in the sensor's resistance, which is converted into different backscattered frequency signals. These signals are captured and decoded by an SDR receiver at a distance of, for example, 3 meters, and restored to biosensor data. Thus, a self-powered system consisting of an energy harvesting antenna, a two-stage charge pump rectifier circuit, and a power management unit achieves battery-free fluid drive by collecting ambient UHF RFID signals to drive the micropump 130. Simultaneously, it breaks through the traditional dielectric constant detection method by converting changes in fluid conductivity into resistance signals, which are then modulated into differentiated switching frequencies by a timer. This mechanism avoids open-circuit faults by using a parallel default resistor and utilizes load modulation to transmit the signal back to the software-defined radio (SDR), achieving wireless reading with resistance to multipath interference within a 3-meter range, significantly improving the stability and transmission distance of biosensor signals. It should be noted that UHF RFID signals specifically refer to radio frequency signals in the frequency range of 860 MHz to 960 MHz. This frequency band is widely present in industrial and commercial environments and is suitable as a source of low-power energy harvesting.

[0067] refer to Figure 4 This application also provides a method for fabricating a flexible fluid sensing system based on inkjet printing, which includes the following steps:

[0068] S100, an ultra-wideband antenna is formed on a flexible substrate by inkjet printing and sintering.

[0069] S200 forms microchannels on a flexible substrate through photopolymerization 3D printing;

[0070] S300: The sensing electrode is obtained by inkjet printing on the area corresponding to the microchannel on the flexible substrate.

[0071] S400 integrates and solidifies microchannels with a flexible substrate that carries sensing electrodes;

[0072] The S500 mounts the power management unit, micropump, and signal modulation unit onto a flexible substrate and electrically connects them to an ultra-wideband antenna, microchannels, and sensing electrodes.

[0073] Specifically, an ultra-wideband antenna is obtained by inkjet printing and sintering on a flexible substrate 100. The flexible substrate 100 is a flexible polyethylene terephthalate (PET) substrate, chosen for its excellent flexibility and bendability. The PET substrate has a relative permittivity (εr) of 4, a dielectric loss tangent (tanδ) of 0.01, and a thickness of 0.12 mm. The ink consists of monodisperse silver nanoparticles or carbon nanotubes and an alcohol solvent, which are plasma-sintered to form highly conductive pathways.

[0074] Antennas and circuits were fabricated on a flexible PET substrate using an inkjet printing mask and etching process. SU-8 polymer ink was printed using an inkjet printer as a mask, and the circuit pattern was formed after exposure, development, and etching. Specifically, the fabrication was carried out using an inkjet printing mask and etching process.

[0075] First, the PET substrate surface is cleaned with acetone to remove dust. Then, a polymer ink mixture of SU-8 2002 and SU-8 2005 is used to print the mask pattern.

[0076] After printing, the sample is softened on a 95°C hot plate for 5 minutes to remove the solvent, then crosslinked and cured by 365nm ultraviolet light at a dose of 600 mJ / cm², and finally hardened on a 95°C hot plate for 10 minutes.

[0077] After the mask is made, the sample is immersed in a 55°C ferric chloride solution to etch the copper layer. Then, the SU-8 mask is removed with acetone to expose the circuit pattern. Finally, other electronic components are soldered.

[0078] Microchannels were obtained using photopolymer 3D printing technology; for example, a semi-cylindrical channel was fabricated using a photopolymer 3D printer and flexible resin. The printed part was cleaned with isopropyl alcohol for 10 minutes, then cured and strengthened at 60°C for 15 minutes, and the support material was removed.

[0079] On the flexible substrate 100, the sensing electrode is obtained by inkjet printing in the corresponding area of ​​the microchannel; silver nanoparticle or carbon nanotube ink is used to print on the PET substrate, and a conductive path is formed by stacking five layers of ink, and then sintering is completed in a 180°C convection oven for 60 minutes.

[0080] The microchannels are integrated and cured with a substrate supporting the sensing electrodes. Specifically, a flexible resin is used as an adhesive to press the microchannels and electrode substrate together, followed by UV curing for 3 minutes to complete the integration. The electrode spacing can be set to 30 mm. This composite additive manufacturing technology, combining inkjet-printed electrodes with photopolymer-cured 3D-printed microchannels, achieves a three-layer integrated structure using a flexible resin adhesive. This significantly shortens the prototype development time for the microchannels and sensing electrodes and reduces costs, making it particularly suitable for the rapid prototyping needs of wearable devices for flexible sensors.

[0081] The power management unit, micropump, and signal modulation unit are mounted on the flexible substrate and connected to the ultra-wideband antenna, microchannel, and sensing electrodes.

[0082] Leveraging the high structural adaptability of additive manufacturing technology, the fabrication process can be simplified to three steps, significantly shortening prototype development time and reducing costs. The specific process includes: first, fabricating microchannels using 3D printing; second, fabricating electrodes using inkjet printing technology; and finally, integrating the electrodes with the microchannels. Thus, in some embodiments, microchannels are formed on a flexible substrate using photopolymerization 3D printing, specifically including:

[0083] Flexible photosensitive resin is used as the printing material. The photopolymer 3D printer exposes and cures the resin layer by layer according to the preset three-dimensional model and the preset number of layers to form a microchannel structure with a semi-circular cross-section.

[0084] The printed microchannel structure was placed in isopropanol to clean the uncured resin.

[0085] After cleaning, the microchannel structure is post-cured and reinforced at a preset temperature, and the supporting material is removed to obtain the microchannel.

[0086] Specifically, flexible photosensitive resin is used as the printing material. Based on a pre-defined 3D model, the flexible photosensitive resin is exposed and cured layer by layer to form a microchannel structure with a semi-circular cross-section. After printing, the microchannel structure is immersed in isopropyl alcohol to remove uncured resin. For example, a semi-cylindrical channel with a diameter of 0.5 mm is manufactured using a photopolymer 3D printer and flexible resin. The printed part is cleaned with isopropyl alcohol for 10 minutes and cured at 60°C for 15 minutes. After cleaning, post-curing reinforcement treatment is performed at 60°C, and the support material is removed to obtain the microchannels.

[0087] In some embodiments, the sensing electrode is obtained by inkjet printing in a region corresponding to the microchannel on a flexible substrate, specifically including:

[0088] In the region corresponding to the microchannel on the flexible substrate, multi-layer inkjet printing is performed using conductive ink with a set droplet spacing and printing platform temperature.

[0089] After printing, the conductive ink is cured by sintering to obtain the sensing electrode.

[0090] Conductive ink is used and loaded into an inkjet printer. Printing is performed on a flexible substrate corresponding to the two sides of the microchannel according to the printing parameters. The printing parameters include using a droplet spacing of 20 μm, printing at least five layers with a 10-minute interval between each layer, and maintaining the printing platform temperature at 60°C.

[0091] After all printing is complete, the sample is placed in a 180°C convection oven for 60 minutes to sinter, allowing the conductive ink to fully cure and form the sensing electrode. Specifically, five layers of silver nanotube or carbon nanotube nanoparticle ink are stacked and printed on a PET substrate, with a droplet spacing of 20 μm. The solvent is evaporated by heating at a 60°C platform, followed by curing in a 180°C convection oven for 60 minutes. This five-layer stacking printing strategy, combined with 60°C platform heating and 180°C convection sintering, creates a highly conductive pathway. By controlling the solvent evaporation and layered curing process, electrode cracking is avoided and adhesion is improved, ensuring stable electrical performance of the electrode under the bending conditions of the flexible substrate, meeting the mechanical flexibility requirements of wearable sensors.

[0092] In related technical solutions, ultra-wideband antennas are mostly implemented using subtractive etching processes, such as etching copper-clad laminates, which suffers from problems such as significant material waste, numerous process steps, and severe pollution. Although some studies have achieved notch filtering functionality through grooving, loading parasitic units, or defect grounding structures, most antennas are typically larger than 30 mm in size, making them difficult to integrate into micro-devices, and their notch filtering performance is limited. Inkjet printing technology, as an additive process, has advantages such as no need for masks, high material utilization, and significant environmental benefits, but its application in the field of flexible ultra-wideband antennas is still rare. Therefore, in some embodiments, the process of inkjet printing and sintering curing on a flexible substrate to obtain an ultra-wideband antenna specifically includes:

[0093] In some embodiments, an ultra-wideband antenna is formed on a flexible substrate by inkjet printing and sintering. Specifically, this includes:

[0094] Using conductive ink, an antenna pattern with a radiating patch, a feed line, a ground plane, and a "C"-shaped groove structure formed on the radiating patch is printed on the flexible substrate according to a preset path; the printed antenna pattern is then sintered and cured to obtain an ultra-wideband antenna.

[0095] Specifically, on a flexible substrate, a pattern of an ultra-wideband antenna is formed using conductive ink containing silver nanoparticles and inkjet printing. This pattern includes a radiating patch, a feed line, and a ground plane, with a C-shaped groove structure printed on the radiating patch. For example, a 21×16×0.12mm³ coplanar waveguide-fed circular monopole ultra-wideband antenna is first designed; then miniaturization is achieved by trimming the top, side circular portions, and the ground plane; next, a C-shaped groove is introduced into the radiating patch to shield against WiMAX band interference; finally, two C-shaped grooves are superimposed to filter WLAN and X uplink band interference, forming the final structure. A trapezoidal coplanar waveguide feed structure is designed to address the characteristics of inkjet printing. By smoothing the feed line transition and optimizing the radiating patch morphology, antenna miniaturization is achieved while expanding bandwidth, enhancing anti-interference capabilities, and improving impedance matching. This structure is particularly suitable for printing on flexible substrates, solving the compatibility issue between the high-frequency performance of wearable antennas and manufacturing processes.

[0096] The printed pattern is then sintered and cured to obtain an ultra-wideband antenna. Thus, by combining inkjet printing and plasma sintering processes, the antenna maintains stable radiation performance in the 2.9-10.61 GHz frequency band, and its human absorptivity meets the safety standards for wearable devices, resolving the compatibility issues between multi-band interference and human safety in flexible devices.

[0097] The preferred embodiments of the present invention have been described in detail above, but the present disclosure is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of the present disclosure.

Claims

1. A flexible fluid sensing system based on inkjet printing, characterized in that: Includes a flexible substrate (100) and a surface disposed on the flexible substrate (100): An energy harvesting antenna is used to harvest ambient radio frequency energy and transmit modulated backscattered signals. An energy management unit, electrically connected to the energy harvesting antenna, is used to convert the ambient radio frequency energy harvested by the energy harvesting antenna into electrical energy and store and distribute it. A microfluidic sensor for containing a fluid to be measured and sensing changes in the conductivity of the fluid to be measured, comprising a microchannel disposed on the flexible substrate (100) and sensing electrodes disposed on both sides of the microchannel; A micropump (130), one end of which is electrically connected to the energy management unit and the other end of which is connected to the microchannel, is used to drive the fluid to be measured into the microchannel when it obtains electrical energy; A signal modulation unit, which is electrically connected to the sensing electrode and the energy harvesting antenna respectively, is used to convert the conductivity change into a sensing signal and modulate it into a backscattered signal that can be transmitted back through the energy harvesting antenna. The energy harvesting antenna is an ultra-wideband antenna, and the ultra-wideband antenna is provided with a radiating patch, and the radiating patch is provided with at least one "C" shaped groove; The ultra-wideband antenna is provided with three different sizes of "C" shaped slots, and the three "C" shaped slots are arranged with one of them as the reference position and the other two are arranged outwards in sequence along the reference position to generate notch filters in different frequency bands.

2. The flexible fluid sensing system based on inkjet printing according to claim 1, characterized in that: The energy management unit includes: A rectifier (141) is electrically connected to the energy harvesting antenna and is used to convert AC radio frequency signals into DC power. An energy storage capacitor (142) is connected to the output terminal of the rectifier (141) and is used to store electrical energy; A power management chip (143) is connected to the energy storage capacitor (142) and is used to monitor the voltage of the energy storage capacitor (142) and control the release of electrical energy to the micro pump (130) and the signal modulation unit according to the voltage change.

3. The flexible fluid sensing system based on inkjet printing according to claim 1, characterized in that: The signal modulation unit includes: A timer chip (151) has its input terminal connected to the sensing electrode and is used to generate an oscillation signal of a corresponding frequency according to the resistance value of the sensing electrode. A switching element (152), which is connected to the output of the timer chip (151), is used to change the load impedance of the energy harvesting antenna according to the oscillation signal to achieve backscattering.

4. The flexible fluid sensing system based on inkjet printing according to claim 3, characterized in that: The capacitance of the energy storage capacitor (142) is 47mF.

5. A method for fabricating a flexible fluid sensing system based on inkjet printing, applied to the flexible fluid sensing system based on inkjet printing as described in any one of claims 1-4, characterized in that: Includes the following steps: An ultra-wideband antenna is formed on a flexible substrate by inkjet printing and sintering. Microchannels are formed on a flexible substrate by photopolymerization 3D printing; Sensing electrodes are obtained by inkjet printing on regions corresponding to microchannels on a flexible substrate. The microchannels are integrated with and solidified on a flexible substrate that carries the sensing electrodes; The power management unit, micropump, and signal modulation unit are mounted on a flexible substrate and electrically connected to an ultra-wideband antenna, microchannel, and sensing electrodes.

6. The method for fabricating a flexible fluid sensing system based on inkjet printing according to claim 5, characterized in that: Microchannels are formed on a flexible substrate using photopolymerization 3D printing, specifically including: Flexible photosensitive resin is used as the printing material. The photopolymer 3D printer exposes and cures the resin layer by layer according to the preset three-dimensional model and the preset number of layers to form a microchannel structure with a semi-circular cross-section. The printed microchannel structure was placed in isopropanol to clean the uncured resin. After cleaning, the microchannel structure is post-cured and reinforced at a preset temperature, and the supporting material is removed to obtain the microchannel.

7. The method for fabricating a flexible fluid sensing system based on inkjet printing according to claim 6, characterized in that: Sensing electrodes are obtained by inkjet printing on regions corresponding to microchannels on a flexible substrate, specifically including: In the region corresponding to the microchannel on the flexible substrate, multi-layer inkjet printing is performed using conductive ink with a set droplet spacing and printing platform temperature. After printing, the conductive ink is cured by sintering to obtain the sensing electrode.

8. The method for fabricating a flexible fluid sensing system based on inkjet printing according to claim 6, characterized in that: An ultra-wideband antenna is formed on a flexible substrate by inkjet printing and sintering. Specifically, this includes: Using conductive ink, an antenna pattern with a radiating patch, a feed line, a ground plane, and a "C"-shaped slot structure formed on the radiating patch is printed on a flexible substrate according to a preset path. The printed antenna pattern is then sintered and cured to obtain an ultra-wideband antenna.

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