Flexible wireless humidity respiration sensor based on ultrahigh frequency and preparation method thereof

Abstract

The invention discloses a flexible wireless humidity respiration sensor based on ultrahigh frequency and a preparation method and application thereof. The preparation method comprises the following steps: providing a flexible tag antenna with an RFID chip; a first windowing mask plate is attached to the tag antenna, an aluminum layer at the windowing position of the first windowing mask plate is removed through mechanical scraping, and a second windowing mask plate is attached; a mixed solution of Ti < 3 > C < 2 > T < x > MXene and GO is dripped into the windowing holes of the second windowing mask plate and the first windowing mask plate, and after drying, the flexible wireless humidity respiration sensor based on the ultrahigh frequency is obtained. The MXene and GO mixed humidity-sensitive sensing material is adopted, the resistance change response capability is improved, and the sensitivity of the humidity respiration sensor is enhanced; meanwhile, the ultrahigh frequency tag antenna is adopted, and the purpose of long-distance wireless passive humidity-sensitive sensing is achieved.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, specifically to a flexible wireless humidity breathing sensor based on ultra-high frequency and its fabrication method. Background Technology

[0002] With the rapid advancement of modern technology, information collection, transmission, and processing technologies have become an indispensable part of social production and daily life. Flexible wireless sensors, with their excellent mechanical flexibility, extensibility, and lightweight characteristics, demonstrate unique advantages in wearable health monitoring projects, compensating for the shortcomings of traditional wired sensors in engineering applications. Flexible humidity sensors can sense ambient humidity and convert it into measurable electrical signals, enabling seamless and continuous monitoring of human health and environmental conditions.

[0003] Currently, many flexible sensing principles are used to detect humidity, including traditional inorganic materials such as metal oxides. These materials have good stability but poor flexibility, and usually need to be used in combination with flexible substrates. Graphene oxide (GO) also has excellent humidity sensitivity due to its abundant hydrophilic functional groups and is often used to make humidity sensors. However, GO suffers from structural instability and slow response speed. Once the functional groups on the GO surface bind to water molecules, they are difficult to separate quickly when humidity decreases. Furthermore, GO's chemical properties are not entirely stable; it undergoes slow chemical degradation in water-oxygen environments, resulting in poor long-term stability. Carbon nanomaterials, such as graphene and carbon nanotubes, offer significantly improved sensitivity and response speed due to their excellent conductivity and mechanical flexibility. However, their high cost and manufacturing difficulty are undeniable drawbacks.

[0004] The current mainstream research direction is towards molecular polymer materials and composite multifunctional materials. Combining different materials creates synergistic effects, simultaneously achieving characteristics such as high sensitivity, wide-range detection, and self-powered operation. For example, Ti3C2T... x MXene, as a sensing material for humidity sensors, has abundant functional groups (such as -OH, -O, and -F) on its surface. These functional groups interact with water molecules, causing changes in the conductivity of MXene. Moisture adsorption increases electron migration and transport on the material surface, thus altering the resistance of MXene. Humidity can be detected by measuring the resistance change of MXene under different humidity conditions. Existing reports disclose humidity sensors fabricated using MXene / silver nanowires that exhibit fast response speeds (5s) and good deformability, but their recovery time is as long as 80s, and their response rate is only 3%.

[0005] In the aforementioned humidity sensing technologies, sensor information is acquired via a wired method, meaning that sensor signal extraction requires wires to connect to a signal conditioning circuit and then send it to a host computer. However, in the field of wearable health monitoring, this wired method restricts the wearer's range of motion and cannot accurately reproduce relevant information about the user in their real-life environment. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a flexible wireless humidity breathing sensor based on ultra-high frequency and its fabrication method, using Ti3C2T. x The hybrid sensing material of MXene and GO improves the response to resistance changes and enhances the sensitivity of the humidity breathing sensor. The introduction of GO makes Ti3C2T... x The enhanced hydrogen bonding between MXene and water molecules further improves the material's conductivity. Simultaneously, based on an ultra-high frequency tag antenna, wireless passive humidity sensing is achieved, enhancing the sensor's reliability during use.

[0007] To address the aforementioned technical problems, the first aspect of this invention provides a method for fabricating a flexible wireless humidity breathing sensor based on ultra-high frequency, comprising the following steps:

[0008] S1. Provides a flexible tag antenna with an RFID chip;

[0009] S2. Attach the first windowed masking template to the tag antenna, and remove the aluminum layer below the window position of the first windowed masking template by mechanical scraping, attach the second windowed masking template, and make the window opening of the second windowed masking template face the window opening of the first windowed masking template.

[0010] S3, Ti3C2T x A mixed solution of MXene and GO is dripped into the openings of the second and first windowed templates, and after drying, it is used as a humidity-sensitive sensing material to obtain the ultra-high frequency-based flexible wireless humidity breathing sensor.

[0011] This invention uses Ti3C2T x The hybrid MXene and GO humidity-sensitive material improves the response to resistance changes and enhances the sensitivity of the humidity breathing sensor. The introduction of GO makes Ti3C2T... x The enhanced hydrogen bonding between MXene and water molecules further enhances the change in the material's electrical conductivity.

[0012] Furthermore, the Ti3C2T x The method for preparing a mixed solution of MXene and GO is as follows: Ti3C2T x The MXene solution and GO solution were mixed, ultrasonically dispersed, and then stirred using a vortex mixer.

[0013] Furthermore, the Ti3C2T x In a mixed solution of MXene and GO, Ti3C2T x The mass ratio of MXene to GO is (4-6):1. Insufficient GO results in weak synergistic effect; excessive GO will accumulate, hindering the penetration of water molecules and reducing sensor performance.

[0014] Furthermore, the tag antenna is selected from a dipole microstrip patch antenna or a circularly polarized microstrip patch antenna.

[0015] Furthermore, the sensing material is placed at the feed point of the low-frequency resonant ring of the tag antenna, located at the corner of the square resonant ring.

[0016] Furthermore, the central axes of the opening holes of the second window-opening masking template and the first window-opening masking template coincide, and the area of ​​the opening hole of the second window-opening masking template is larger than the area of ​​the opening hole of the first window-opening masking template.

[0017] A second aspect of the present invention provides a flexible wireless humidity respiration sensor based on ultra-high frequency (UHF) obtained by the preparation method described in the first aspect, comprising a flexible tag antenna, a sensing material attached to the tag antenna, and an RFID chip. Preferably, it further comprises a reference tag (reference sensor), which includes the same tag antenna and RFID chip as the UHF-based flexible wireless humidity respiration sensor.

[0018] Furthermore, the sensing material includes Ti3C2T x MXene and GO.

[0019] A third aspect of the present invention provides an RFID wireless sensing system, including an RFID reader, a reader antenna, the UHF-based flexible wireless humidity and respiration sensor described in the second aspect, and a host computer.

[0020] This invention employs an ultra-high frequency tag antenna to achieve long-distance wireless passive humidity sensing, thereby enhancing the reliability of the sensor during use.

[0021] The fourth aspect of this invention provides a method for operating the RFID wireless sensing system described in the third aspect. When the flexible wireless humidity breathing sensor enters the magnetic field generated by the reader antenna controlled by the RFID reader, the flexible wireless humidity breathing sensor receives the radio frequency signal emitted by the reader antenna. The flexible wireless humidity breathing sensor obtains energy by the induced current generated by the radio frequency signal and wakes up the RFID chip therein. The ambient humidity in the RFID chip is backscattered to regulate the resistance of the humidity-sensitive sensing material, thereby regulating the relevant information of the backscattering. Then, the RFID reader reads the relevant information and decodes it, and finally sends it to the host computer for data processing.

[0022] The beneficial effects of this invention are:

[0023] This invention employs an ultra-high frequency (915MHz) sensing system, by adjusting the Ti3C2T x The MXene to GO mass ratio and sensing material sites improve the sensitivity of wireless humidity sensors.

[0024] This patented flexible wireless humidity breathing sensor based on ultra-high frequency has a relative humidity measurement range of 19-96%RH, excellent reversibility and long-term stability, and a sensitivity as high as 0.13dBm / %RH, with a normalized sensitivity of 6.5*1e-3, which is an order of magnitude higher than that of ordinary wireless humidity sensors. Attached Figure Description

[0025] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the fabrication method of the flexible wireless humidity breathing sensor based on ultra-high frequency according to the present invention.

[0027] Figure 2 It is Ti3C2T x Schematic diagram of MXene humidity sensing mechanism;

[0028] Figure 3 In this diagram, a is a schematic diagram of the sensor structure of the present invention, b is a physical diagram of the sensor, and c is an equivalent circuit diagram of the sensor.

[0029] Figure 4 This is a block diagram illustrating the principle of the RFID wireless sensing system of the present invention;

[0030] Figure 5 In Figure a, it is a schematic diagram of the dripping area of ​​the sensing material in Example 1, and in Figure b, it is the change in RSSI of the sensing material placed at different positions.

[0031] Figure 6 In Example 2, a represents the resistance variation characteristics of humidity-sensitive materials with different MXene / GO mass ratios between 19% and 96% RH, and b represents the locally magnified variation characteristics of a.

[0032] Figure 7 This is a graph showing the relationship between the relative resistance change of the sensor and the relative humidity in Example 3;

[0033] Figure 8In Example 3, a represents the resistance change of the sensor during humidification and dehumidification, and b represents the hysteresis characteristic curve of the sensor.

[0034] Figure 9 In Example 3, ac represents five cycles of testing the sensor at 19%RH, 43%RH, and 75%RH, respectively, and d represents the sensor's response / recovery time.

[0035] Figure 10 This is the long-term stability test curve of the sensor in Example 3;

[0036] Figure 11 This is the curve showing the relationship between ΔRSSI and humidity for the MXene / GO mass ratio in Example 4;

[0037] Figure 12 In Example 5, a is the relationship curve between relative humidity and RSSI1 of the sensing tag at different distances, and b is the relationship curve between relative humidity and RSSI2 of the reference tag at different distances.

[0038] Figure 13 The curves showing the relationship between the RSSI difference (RSSI1-RSSI2) between the sensing tag and the reference tag and the relative humidity at different distances in Example 5, along with their linear fitting results;

[0039] Figure 14 The RSSI signal output by the respiratory channel identification system in Example 6 under mouth breathing and nose breathing;

[0040] Figure 15 In Example 6, a represents the RSSI1 signal output by the sensor tag under different breathing modes; b represents the RSSI1-RSSI2 signals received by the monitoring system through the RFID reader; and c and d are magnified views of normal breathing and rapid breathing, respectively. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0042] refer to Figure 1 This embodiment relates to a method for fabricating a flexible wireless humidity breathing sensor based on ultra-high frequency, comprising the following steps:

[0043] S1. Provides a flexible tag antenna with an RFID chip;

[0044] S2. A first windowed mask template is attached to the tag antenna, and the aluminum layer below the window position of the first windowed mask template is removed by mechanical scraping. A second windowed mask template is then attached, with the window opening of the second windowed mask template aligned with the window opening of the first windowed mask template. The central axes of the window openings of the second and first windowed mask templates coincide, and the area of ​​the window opening of the second windowed mask template is larger than that of the window opening of the first windowed mask template.

[0045] S3, Ti3C2T x A mixed solution of MXene and GO is dripped into the openings of the second and first windowed templates, and after drying, it is used as a humidity-sensitive sensing material to obtain the ultra-high frequency-based flexible wireless humidity breathing sensor.

[0046] like Figure 2 As shown, Ti3C2T x MXene surfaces possess abundant functional groups (such as -OH, -O, and -F), which interact with water molecules. Specifically, when MXene is exposed to moisture, water molecules adsorb onto these functional groups, causing a change in the conductivity of MXene. Moisture adsorption increases electron migration and transport on the material surface, thus altering the resistance of MXene. Humidity can be detected by measuring the resistance change of MXene under different humidity conditions. However, the amplitude of the electrical signal change caused by humidity is relatively small, and it is easily oxidized to substances such as TiO2 in a water-oxygen environment, exhibiting poor stability. Graphene oxide (GO) retains the two-dimensional single-atom-layer structure of graphene, but introduces a large number of oxygen-containing functional groups on its surface and edges, forming a quasi-two-dimensional spatial structure. These oxygen-containing groups endow GO with good hydrophilicity. However, GO has a very low intrinsic conductivity, limiting the baseline signal and response amplitude of the sensor; moreover, GO has a strong binding ability to water molecules, and the desorption process is slow, resulting in a long sensor response recovery time when returning from a high-humidity environment to a low-humidity environment. This embodiment uses Ti3C2T. x The sensing material, a blend of MXene and GO, utilizes the high conductivity of MXene to provide a rapid electron transport channel for the entire composite material, while leveraging the high sensitivity of GO to enhance the material's responsiveness to changes in resistance. Because GO also possesses abundant oxidized functional groups, such as carboxyl groups (-COOH) and epoxy groups (-COC), these functional groups interact strongly with water molecules, further enhancing the sensitivity of moisture sensing. Furthermore, its O content is higher than that of MXene; therefore, the introduction of GO strengthens the hydrogen bonding between the material and water molecules, further enhancing the material's conductivity.

[0047] As a preferred embodiment, the Ti3C2T x The method for preparing a mixed solution of MXene and GO is as follows: Ti3C2Tx MXene and GO solutions were mixed, ultrasonically dispersed, and then stirred using a vortex mixer. The Ti3C2T solution contained... x The mass ratio of MXene to GO is (4-6):1.

[0048] In a preferred embodiment, the tag antenna is selected from a dipole microstrip patch antenna or a circularly polarized microstrip patch antenna. The sensing material is placed at the feed point of the low-frequency resonant loop of the tag antenna, which is a key node in the L-type matching network and is located at the corner of the square resonant loop.

[0049] Another embodiment provides a flexible wireless humidity breathing sensor based on ultra-high frequency prepared by the preparation method described in the above embodiments, with reference to... Figure 3 The RFID tag includes a flexible tag antenna, a sensing material attached to the tag antenna, and an RFID chip, wherein the sensing material includes Ti3C2T. x MXene and GO.

[0050] Another embodiment provides an RFID wireless sensing system, see reference. Figure 4 As shown, the system includes an RFID reader, a reader antenna, the UHF-based flexible wireless humidity breathing sensor described in the above embodiment, and a host computer. The RFID wireless sensing system operates as follows: When the flexible wireless humidity breathing sensor enters the magnetic field generated by the reader antenna controlled by the RFID reader, the flexible wireless humidity breathing sensor receives the radio frequency signal emitted by the reader antenna. The flexible wireless humidity breathing sensor obtains energy through the induced current generated by the radio frequency signal and wakes up the RFID chip within it. The backscattering of the ambient humidity in the RFID chip regulates the resistance of the humidity-sensitive sensing material, thereby regulating the relevant backscattering information. Then, the RFID reader reads and decodes the relevant information and finally sends it to the host computer for data processing.

[0051] Example 1

[0052] This embodiment relates to a method for fabricating a flexible wireless humidity breathing sensor based on ultra-high frequency, comprising the following steps:

[0053] (1) Provide a 915MHz dipole microstrip patch antenna with an RFID chip.

[0054] (2) At different locations on different tag antennas (refer to) Figure 5 The first window opening mask (1.5mm×1mm rectangular window) is attached to the middle a (P1-P5) and the aluminum layer below the window opening position of the first window opening mask is removed by mechanical scraping. The second window opening mask (2.5mm×1.5mm rectangular window) is attached, and the window opening of the second window opening mask is directly opposite the window opening of the first window opening mask.

[0055] (3) In a centrifuge tube, add MXene solution (5 mg / ml, Ti3C2T) at a mass ratio of 5:1. x The Ti3C2T solution was mixed with GO solution (5 mg / ml), ultrasonically dispersed for 30 min, and then stirred with a vortex mixer for 10 min. x A mixed solution of MXene and GO was dripped (3.75 ml) into the openings of the second and first windowed templates and dried at 45°C for 2 hours to obtain the flexible wireless humidity breathing sensor based on ultra-high frequency.

[0056] The effect of sensing materials in different regions of the tag antenna on sensor performance was tested. For example... Figure 5 As shown in Figure a, P1 is the feed point of the low-frequency resonant loop, a key node in the L-shaped matching network, located at the corner of the square resonant loop; P2 is another feed point of the low-frequency resonant loop, located near the opening of the resonant loop, which is typically used to generate a lower resonant frequency; P3 is the feed point of the high-frequency radiating element, connected to a vertical metal line on one side, used to generate a higher resonant frequency; P4 is located on the right metal arm, which improves impedance matching in the RFID band through coupling; P5 is the connection point of the feed port, part of the adjustable matching loop. The sensitivity of the tag antenna at different nodes was tested using variable resistors. A 0603 packaged standard resistor (resistance range 0~2kΩ, tolerance 1%) was used as a variable load, and loading tests were performed at the key nodes (P1-P5) of the antenna structure. Figure 5 As shown in Figure b, the Received Signal Strength Indicator (RSSI) exhibits significant differences when the variable resistor is applied at different locations: the P1 region demonstrates the highest sensitivity. Within the 0-330Ω range, the RSSI gradient with resistance variation, calculated via linear fitting, yields ΔRSSI / ΔR of -0.053dBm / Ω. Between 330Ω and 2000Ω, the RSSI gradient, calculated via fitting, yields ΔRSSI / ΔR of -0.002dBm / Ω. In contrast, the RSSI gradients with resistance variation in other regions are smaller, and the total RSSI change is less than that in the P1 region. Therefore, it can be seen that the sensing performance of the P1 region is significantly better than that of other regions. This is because, from the perspective of current distribution, the P1 region is closest to the feed point.

[0057] Example 2

[0058] The difference between this embodiment and embodiment 1 is that the sensing material is fixedly placed in the P1 region, and MXene groups without GO are set up, as well as groups with MXene to GO mass ratios of 1:1, 5:1, 10:1, and 20:1 respectively. Figure 6In the figure, 'a' represents the resistance variation characteristics of humidity-sensitive materials with different MXene / GO mass ratios between 19% and 96% RH. Figure 6 b is Figure 6 The magnified variation characteristics of MXene in section a are shown. These characteristics reveal that the initial resistivity of pure MXene is 5.45Ω, and its humidity response range (ΔR) is only 3.46Ω. When the MXene:GO ratio is 1:1, the initial resistivity increases to 19.10Ω, but ΔR remains low at 2.92Ω. When the ratio is optimized to 5:1, the initial resistivity significantly increases to 84.43Ω, and ΔR reaches 257.82Ω, a 74-fold increase compared to pure MXene. When the ratio increases to 10:1, the initial resistivity drops back to 26.45Ω, and ΔR decreases to 23.79Ω. At MXene:GO = 20:1, the resistivity is the initial value of 7.70Ω, and ΔR = 6.51Ω, approaching the level of pure MXene without added GO. It can be seen that when the GO concentration is too low or too high, the rate of change in material resistivity is very low, which corresponds to the working principle of the humidity sensing unit described above. Therefore, this experiment ultimately selected a composite material with MXene:GO=5:1 for subsequent performance testing.

[0059] Example 3

[0060] This embodiment is similar to the method in Embodiment 1, but the sensing material is fixed in the P1 region to prepare a flexible wireless humidity breathing sensor based on ultra-high frequency.

[0061] To test the sensor's sensitivity, the sensor was first placed in a sealed environment of a 19%RH saturated salt solution and left to stand for 60 seconds until its resistance response stabilized. The initial resistance value was then recorded using a computer data acquisition system. Subsequently, it was quickly transferred to a 31%RH indoor environment, held for 60 seconds, and the resistance value was recorded again. The measurement process was then repeated three times at each point, with the same procedure applied to the previously prepared humidity-saturated salt solution. To avoid interference from ambient humidity fluctuations, the opening and closing time of the solution bottle was controlled within 1 second during the test to minimize humidity drift caused by air circulation. Resistance data was obtained through three independent experiments at each humidity gradient. The averaged values ​​were then used to calculate the sensitivity and linearity parameters to ensure the accuracy of the test results. To quantify the sensitivity of the humidity-sensitive material, the sensitivity S was defined as the ratio of the normalized relative resistance change rate (ΔR / R0) to the humidity change (ΔRH). In the formula, R0 is the initial resistance at a reference humidity of 19%RH, and R x The resistance value is measured under the specified humidity, and ΔRH is the difference between the test humidity and the reference humidity.

[0062] like Figure 7The figure shows the relationship between the relative resistance change of the sensor and relative humidity. Linear regression analysis revealed a high linear correlation between the resistance change of the humidity-sensitive material and humidity within the RH range of 19%–96%. The fitted equation is as follows: This indicates that the sensor sensitivity is 3.51 / %RH, and the correlation coefficient R of the equation is... 2 =0.97, indicating a clear linear relationship between the output signal and humidity, meeting the requirements for accurate detection over a wide humidity range.

[0063] Moisture hysteresis, a key performance indicator of flexible humidity sensors, is defined as the maximum deviation of the sensor's output characteristic value at the same humidity point during humidification and dehumidification cycles. The calculation formula is as follows: In the formula, R A With R D The values ​​represent the resistance values ​​of the sensor during humidification and dehumidification at specific humidity levels, respectively, with S representing the sensitivity (the rate of change of resistance per unit humidity). During the experimental evaluation, each humidity level was maintained for 60 seconds, and stable resistance values ​​were recorded. After responding to different humidity levels, the sensor was placed in an outdoor humidity environment (31%RH) for 60 seconds. Then, the sensor was placed in a saturated salt solution environment in ascending order (19%RH→34%RH→43%RH→58%RH→75%RH→84%RH→96%RH). The test procedure was then repeated in reverse descending order (96%RH→84%RH→75%RH→58%RH→43%RH→34%RH→19%RH), with the resistance values ​​of the humidity-sensitive material recorded in real time.

[0064] The results of the humidity sensor's hysteresis characteristics are as follows: Figure 8 As shown in Figure a, during the humidification stage (red curve), the material's resistance increases monotonically with increasing humidity due to the adsorption of water molecules; during the dehumidification stage (black curve), the resistance decreases due to the desorption of water molecules, indicating that the material's electrical properties exhibit good humidity measurement performance in response to humidity changes. Hysteresis characteristic curves were constructed by extracting the maximum resistance values ​​at various humidity points (19%~96%RH), as shown in Figure a. Figure 8 As shown in Figure b, the humidification curve is located below the dehumidification curve, with the maximum offset corresponding to a hysteresis H of 9.66%RH. This asymmetric hysteresis is due to the strong hydrogen bonding between hydroxyl groups and water molecules in the MXene / GO composite material, making it difficult for some water molecules to dissociate during dehumidification. Experimental results demonstrate that this material exhibits excellent humidity measurement performance and reversibility.

[0065] In the experiment, three saturated salt solutions—LiBr (19%RH), K2CO3 (43%RH), and NaCl (75%RH)—were selected, and five cycles of switching were performed between an indoor environment of 31%RH and the target humidity. Figure 9The results showed that the sensor resistance value exhibited a periodic variation with humidity. In the repeatability test at 19% RH, the resistance showed a slight drift with an error of approximately 2.2%. In the repeatability tests at 43% RH and 75% RH, the resistance change curves remained basically consistent, indicating that the hydrogen bond network formed by the layered structure of MXene and the oxygen-containing functional groups of GO can effectively suppress the material's structural degradation and ensure the material's cyclic stability.

[0066] Response / recovery time is a key parameter for evaluating the dynamic performance of humidity sensors; a shorter response / recovery time facilitates real-time synchronous monitoring of environmental humidity changes. Existing studies generally use transition data within the maximum humidity variation range (e.g., 19%RH to 75%RH) as a performance benchmark, analyzing... Figure 9 The step response curve of material c, due to the small deviation in response time during five-cycle testing, was calculated using a single-cycle response curve (not the average of five cycles), indicating that the material possesses stable dynamic characteristics. For example... Figure 9 As shown in Figure d, Tres is defined as the time required for the material's resistance to reach 90% of its steady-state value after a humidity jump from its initial state, and Trec is the time required for the resistance to recover to 10% of its steady-state value when returning from a high-humidity environment to a reference humidity. The measured response time (Tres) of the MXene / GO humidity-sensitive material is 25.4 s, and the recovery time (Trec) is 31.1 s. These results verify the reliability of the dynamic response performance of the humidity-sensitive material over a wide humidity range.

[0067] Long-term stability is a key factor in evaluating the practical application value of flexible humidity sensors. As the sensor is used over time, the sensing material may degrade due to aging and environmental factors, thus altering its response characteristics. Therefore, conducting long-term stability tests is crucial for determining the sensor's performance in real-world environments. The sensing material was placed in three different humidity environments (19%RH, 43%RH, and 75%RH), and its resistance was measured for seven consecutive days. The results are as follows: Figure 10 As shown in the figure, it can be seen that the resistance of the sensing material changes very little under the three selected humidity gradients, indicating that the sensing material can be used for a long time and has good stability.

[0068] Example 4

[0069] To quantify the sensitivity of the humidity sensor, the sensitivity S of the sensor is defined as: The sensor humidity calibration system measured the sensitivity of three groups of sensors with different MXene / GO mass ratios (1:1, 5:1, and 10:1) in Example 2. The humidity sensors were placed in saturated salt solutions of various humidity concentrations and allowed to stand for 120 seconds. Relevant data were recorded, and the RSSI values ​​measured by the RFID reader were converted into relative received signal indication values ​​(ΔRSSI). A curve showing the relationship between ΔRSSI and humidity was plotted. Figure 11 As shown in the figure, the curves reveal that the ΔRSSI of the wireless sensor with an MXene / GO mass ratio of 1:1 remains essentially unchanged with humidity variations. The outputs of the other two sensors decrease as humidity increases. Specifically, the sensor with an MXene / GO mass ratio of 10:1 shows a relative RSSI change that gradually decreases from 0 to -5.1 dBm within a humidity range of 19%RH to 96%RH. In contrast, the sensor with an MXene / GO mass ratio of 5:1 exhibits superior sensitivity performance, with its relative RSSI change gradually decreasing from 0 to -7.9 dBm within the same humidity range, meaning its sensitivity is -0.1 dBm / %RH.

[0070] Example 5

[0071] A dual-tag humidity sensing system (comprising two parts: a sensing tag, a UHF humidity sensor coated with MXene / GO humidity-sensitive material on P1 as described in Example 1; and a reference tag, an antenna of the same model without the humidity-sensitive material coating) was constructed to reduce the impact of changes in communication distance. First, the sensing system was placed on a sensor humidity calibration system and left to stand for 120 seconds. Once the data received by the reader stabilized, the RSSI values ​​of the sensing tag and the reference tag were recorded using two channels.

[0072] Figure 12 In Figure 'a', the curves show the relationship between relative humidity and RSSI1 of the sensor tag at different distances. It can be seen that, under a certain humidity, the farther the communication distance, the smaller the RSSI1 value received by the reader. Figure 12 Figure b shows the relationship between relative humidity and RSSI2 of the reference tag at different distances. It can be seen that when the communication distance remains constant, changes in humidity do not affect the value of RSSI2. Therefore, it can be considered that the reference tag can indirectly represent the distance between the sensing system and the RFID reader.

[0073] Figure 13The relationship between the RSSI difference (RSSI1 - RSSI2) between the sensing tag and the reference tag and relative humidity at different distances is shown in the curves, along with the linear fitting results. It can be seen that at different communication distances, the difference in RSSI between the two tags almost coincides with the humidity curve of the sensing tag's location. A linear fitting of this data yields the following equation: The correlation coefficient R of this equation 2 The value of 0.95 indicates that the relationship curves between the RSSI difference (RSSI1 - RSSI2) between the sensor tag and the reference tag at these four different distances and the relative humidity can be fitted into a linear equation with good linearity. Therefore, in practical applications, the impact of changes in communication distance is reduced, and the relative humidity of the sensing system can be directly measured through the difference in RSSI between the two tags.

[0074] Example 6

[0075] (1) Sensor-based identification of the oral and nasal breathing channels

[0076] When a person exhales through the nose or mouth, the exhaled air contains a large amount of water vapor, which leads to a significant increase in local humidity. Nasal breathing airflow is typically concentrated near the philtrum and has a stable flow rate, while mouth breathing airflow diffuses more widely and does not reach the philtrum area. Therefore, sensors can distinguish breathing patterns by capturing these humidity changes in real time. To avoid interference from direct contact between the tag antenna and the human body, the back of the ultra-high frequency humidity sensor (refer to Example 1, with the sensing material placed on P1) is adhered to a 1mm thick Ecoflex substrate using double-sided tape. Then, a layer of double-sided tape is applied to the back of the Ecoflex substrate. The sensor is then attached directly below the nostril, and a reader is placed 10cm above the sensor, receiving data via a computer. Figure 14 The RSSI signals output by the respiratory channel identification system under mouth and nose breathing conditions demonstrate that the system can effectively distinguish between different respiratory channels using the RSSI signal from an ultra-high frequency flexible humidity sensor. When volunteers breathe through their nose, airflow is typically concentrated near the moisture-sensitive material of the attached humidity sensor, allowing the sensor to detect periodic humidity changes with breathing frequency. When volunteers breathe through their mouth, airflow is less likely to reach the moisture-sensitive material, making it impossible for the sensor to detect changes in respiratory humidity. Simultaneously, due to the reduced humidity around the sensor, the RSSI value measured by the sensor drops to approximately 24 dBm. The test results indicate that this respiratory channel identification system can effectively distinguish between mouth and nose breathing, enabling it to identify potential health risks and providing a scientific basis for clinical diagnosis and intervention.

[0077] (2) Respiratory humidity monitoring system of ultra-high frequency humidity sensing system

[0078] This monitoring scheme employs a non-contact measurement method, integrating an ultra-high frequency humidity sensor into the mask's interlayer to eliminate interference that might occur from skin contact. During the experiment, volunteers properly wore the modified mask, then fixed an RFID reader approximately 10cm above the sensor in a vertical plane and received data via a computer.

[0079] Tests were conducted on four breathing patterns (rapid breathing, normal breathing, deep breathing, and sleep apnea), such as... Figure 15 Figure a shows the RSSI1 signals output by the sensor tag under different breathing modes. Figure 15 In the image, b represents the RSSI1-RSSI2 signals received by the monitoring system via the RFID reader. Figure 15 Images c and d show magnified views of normal and rapid breathing, respectively. It can be seen that the system effectively distinguishes different breathing states; the amplitude and frequency of RSSI1-RSSI2 differ significantly during rapid, normal, and deep breathing. In a 20-second breath-hold test simulating apnea, the RSSI value increased from 2.4 dBm to 5.2 dBm, because the humidity inside the mask decreases continuously during breath-holding. Further analysis of the measured data yields detailed respiratory rate and intensity parameters. By calculating the number of peak values ​​in the RSSI waveform, the volunteer's normal breathing rate was found to be 12.9 breaths / min, decreasing to 6.7 breaths / min during deep breathing, while rapid breathing reached a high of 25.3 breaths / min. The RSSI1-RSSI2 variation was largest during deep breathing, followed by normal breathing, while the amplitude variation was the weakest during rapid breathing. Therefore, the experimental data demonstrates that this sensor also has good detection capabilities in respiratory behavior monitoring.

[0080] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for fabricating a flexible wireless humidity breathing sensor based on ultra-high frequency, characterized in that, Includes the following steps: S1. Provide a flexible tag antenna with an RFID chip; S2. Attach the first windowed masking template to the tag antenna, and remove the aluminum layer below the window position of the first windowed masking template by mechanical scraping, attach the second windowed masking template, and make the window opening of the second windowed masking template face the window opening of the first windowed masking template. S3, Ti3C2T x A mixed solution of MXene and GO is dripped into the openings of the second and first windowed templates, and after drying, it is used as a humidity-sensitive sensing material to obtain the ultra-high frequency-based flexible wireless humidity breathing sensor.

2. The method for fabricating a flexible wireless humidity breathing sensor based on ultra-high frequency as described in claim 1, characterized in that, The Ti3C2T x The method for preparing a mixed solution of MXene and GO is as follows: Ti3C2T x The MXene solution and GO solution were mixed, ultrasonically dispersed, and then stirred using a vortex mixer.

3. The method for fabricating a flexible wireless humidity breathing sensor based on ultra-high frequency as described in claim 1, characterized in that, The Ti3C2T x In a mixed solution of MXene and GO, Ti3C2T x The mass ratio of MXene to GO is (4-6):

1.

4. The method for fabricating a flexible wireless humidity breathing sensor based on ultra-high frequency as described in claim 1, characterized in that, The tag antenna is selected from dipole microstrip patch antenna or circularly polarized microstrip patch antenna.

5. The method for fabricating a flexible wireless humidity breathing sensor based on ultra-high frequency as described in claim 4, characterized in that, The sensing material is placed at the feed point of the low-frequency resonant ring of the tag antenna, located at the corner of the square resonant ring.

6. The method for fabricating a flexible wireless humidity breathing sensor based on ultra-high frequency as described in claim 1, characterized in that, The central axis of the opening hole of the second window opening masking template coincides with the central axis of the opening hole of the first window opening masking template, and the area of ​​the opening hole of the second window opening masking template is larger than the area of ​​the opening hole of the first window opening masking template.

7. A flexible wireless humidity breathing sensor based on ultra-high frequency, prepared by the method according to any one of claims 1-6, characterized in that, This includes flexible tag antennas, sensing materials attached to the tag antennas, and RFID chips.

8. The flexible wireless humidity breathing sensor based on ultra-high frequency as described in claim 7, characterized in that, The sensing material includes Ti3C2T x MXene and GO.

9. An RFID wireless sensing system, characterized in that, It includes an RFID reader, a reader antenna, a flexible wireless humidity and breathing sensor based on ultra-high frequency as described in any one of claims 7-8, and a host computer.

10. A method for operating the RFID wireless sensing system according to claim 9, characterized in that, When the flexible wireless humidity breathing sensor enters the magnetic field generated by the reader antenna controlled by the RFID reader, the flexible wireless humidity breathing sensor receives the radio frequency signal emitted by the reader antenna. The flexible wireless humidity breathing sensor obtains energy by the induced current generated by the radio frequency signal and wakes up the RFID chip inside. It backscatters the relevant information in the RFID chip, and then the RFID reader reads the relevant information and decodes it. Finally, it sends the data to the host computer for data processing.

Images