Flexible LC sensor for skin humidity detection
By using a flexible sensor with Au@ZIF-67 composite material and LC resonant circuit, the problems of stability and response speed of traditional humidity sensors in high humidity environments have been solved, realizing non-contact, fast, and accurate skin humidity detection.
Patent Information
- Application Number
- CN202422774423.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-14
- Publication Date
- 2026-01-30
- Estimated Expiration
- 2034-11-14
AI Technical Summary
Existing flexible humidity sensors are difficult to operate stably for long periods in high humidity environments, have slow response speeds, low resolution, and are mostly contact-based, leading to inaccurate test results.
The composite humidity-sensitive material Au@ZIF-67 is used, combined with interdigitated electrodes and inductors to form an LC resonant circuit. The composite material of chloroauric acid and dimethylimidazolium cobalt is used to improve the water molecule adsorption capacity. The interdigitated electrodes and inductors are distributed on both sides of the flexible substrate to avoid water droplet condensation and achieve non-contact detection.
It achieves wireless, passive, fast-response, high-sensitivity, high-resolution, and wide-range skin humidity detection. The sensor has a compact structure, is suitable for complex environments, and avoids the shortcomings of contact measurement.
Smart Images
Figure CN223845654U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to the technical field of humidity sensing, especially a flexible LC sensor for skin humidity detection. BACKGROUND
[0002] Humidity is a physical quantity that measures the concentration of water vapor in the air. A humidity sensor converts the relative humidity in the environment into a detectable electrical signal and outputs corresponding information. Today, the requirements for humidity sensors are becoming increasingly high. The dynamic range of sensor detection is also required to be increasingly wide. At the same time, there are more stringent requirements for the response, response speed, and accuracy of sensor detection performance.
[0003] Skin humidity detection technology has developed significantly in recent years, especially in the field of wearable devices and health monitoring. With the emphasis on health management, the application of skin humidity sensors has gradually attracted attention. These sensors not only monitor the moisture status of the skin, but also reflect the individual's physiological condition and environmental changes. However, many flexible humidity sensors currently have difficulty in stable operation for a long time in a high-humidity environment. Water molecules in the device are difficult to desorb, which limits their long-term application. Generally, humidity sensors have slow response speed and low resolution, making it difficult to quickly analyze data changes in humidity. On the other hand, existing skin humidity detection sensors are basically contact type, with a small touch area between the skin, and the test results are not accurate. SUMMARY
[0004] The emission of skin moisture is very important for maintaining the physiological function and health status of the skin. It not only helps to regulate body temperature, but also helps to remove waste and toxins from the body. Since there is a difference in the spatial distribution of skin-emitted water vapor and air humidity, the sensor can be placed close to the skin surface for detection, reducing the interference of surrounding air humidity, and more accurately measuring the skin-emitted water vapor.
[0005] In order to realize the function of wireless and passive non-contact skin humidity detection, in view of the problems of short range, slow response, fast energy consumption, and insufficient water molecule desorption ability of existing skin humidity detection sensors, the physical effect of humidity-sensitive materials that can adsorb water molecules is utilized. The utility model provides a flexible LC sensor for skin humidity detection, which includes a composite humidity-sensitive film, an interdigital electrode, a through hole, a flexible substrate, and an inductor coil. The upper surface of the interdigital electrode is covered with a composite humidity-sensitive film, which together constitutes a humidity-sensitive unit. The interdigital electrode and the inductor coil are arranged on both sides of the flexible substrate and connected through the through hole to form an LC resonant circuit.
[0006] In order to improve the sensitivity of the sensor, preferably, chloroauric acid and dimethyl imidazole cobalt (Au@ZIF-67) are selected as the humidity-sensitive material. Dimethyl imidazole cobalt (ZIF-67) is a metal organic framework material with a dodecahedron structure and uniform particles. The surface of ZIF-67 has abundant -CH3, -NC=CN- groups that can form hydrogen bonds with water, providing a large number of active sites. When the relative humidity increases, water molecules begin to chemisorb and bind to the hydrophilic groups through hydrogen bonds, forming a water molecule layer on the surface of the humidity-sensitive unit. As the relative humidity continues to increase, water molecules begin to physisorb, forming a second layer of water molecules, which improves the response capability. ZIF-67 has a special detection capability for changes in relative humidity, but due to incomplete desorption of water molecules, the hygroscopic performance of ZIF-67 is poor.
[0007] Further, in order to reduce the hysteresis of ZIF-67, Au nanoparticles are doped in ZIF-67. Au nanoparticles in chloroauric acid have the advantages of good catalytic activity, good biocompatibility, and high stability. After reduction, the Au nanoparticles in chloroauric acid are loaded onto ZIF-67, thereby improving the electrical conductivity, reducing the material resistance, increasing the water molecule adsorption sites, and improving the desorption capability of the humidity-sensitive material for water molecules, significantly reducing the hysteresis.
[0008] Further, in order to maintain the water absorption and elastic capability of a flexible LC sensor for skin humidity detection, the thickness of the composite humidity-sensitive film is 0.1-0.2 mm, which has good bending resistance and can fully contact the skin. When the thickness is larger, it will affect the flexibility of the entire flexible LC sensor and limit its application; when the thickness is too small, it will also affect the protection of the composite humidity-sensitive film to the material.
[0009] Preferably, the materials of the interdigital electrode and the inductor are copper or silver, and the thickness is 0.1-0.2 mm. Copper and silver have excellent electrical conductivity and low resistivity, resulting in a small impedance of the LC resonance circuit, more obvious changes in the resonance frequency, and higher measurement accuracy of the humidity.
[0010] Preferably, the inductor adopts a planar spiral structure with a square shape and a side length of 20-30 mm. Compared with a wire-wound inductor, the planar spiral structure can be integrated on a planar film, optimizing the occupied area and adapting to different space limitations.
[0011] In order to make the electrode structure better and improve the sensitivity of the sensor, preferably, the interdigital electrode width ranges from 0.4 to 0.6 mm, and the interdigital electrode spacing ranges from 0.3 to 0.5 mm. The change of the interdigital electrode width and spacing will cause the change of the number of interdigital electrodes. Under the condition that the applied excitation voltage and other conditions remain unchanged, the change of the interdigital electrode width and spacing will cause the change of the electric field distribution. With the increase of the electrode width, the electric field strength also increases, and the high potential distribution is more smooth and uniform. With the increase of the interdigital spacing, the electric field strength also gradually increases, but the high potential distribution is sparse and changes dramatically. The resistance gradually decreases with the increase of the interdigital width, and first decreases and then increases with the increase of the interdigital spacing, and the minimum value appears when the spacing is 0.4 mm.
[0012] In order to increase the capacitance value of the sensor, preferably, the length of the interdigital electrode ranges from 10 to 30 mm, which can ensure that the interdigital electrode is uniformly attached to the flexible substrate.
[0013] In order to ensure the flexibility of a flexible LC sensor for skin humidity detection, preferably, the material of the flexible substrate is polyethylene terephthalate (PET), the thickness is 0.2 to 0.4 mm, and the side length is 20 to 40 mm. The PET flexible substrate not only has good tensile property, but also has stable chemical property, which provides good mechanical support for the whole flexible LC humidity sensor. The flexible film structure makes the attachment ability stronger.
[0014] The interdigital electrode and the inductor coil are arranged on the upper and lower sides of the flexible substrate to avoid the problem of inductive short circuit caused by water droplet condensation in high humidity environment, and an additional planar space can be left to increase the number of interdigital electrodes as needed. The tail of the interdigital electrode and the inductor coil coincides with the position of the through hole, and is connected correspondingly to form an LC resonance circuit.
[0015] In order to realize wireless and passive measurement of the flexible LC sensor, an LC resonance circuit composed of interdigital electrodes and inductor coils is used for humidity detection. The change of the concentration of water molecules in the air has no effect on the inductance value, and the resonance frequency is only determined by the variable capacitance. The capacitance of the flexible LC humidity sensor is affected by the relative dielectric constant ε of the humidity sensitive unit, so when the water molecules in the air contact the humidity sensitive unit, the change of the dielectric constant ε of the humidity sensitive unit leads to the change of the capacitance value of the humidity sensor.
[0016] When the external humidity changes, the relative dielectric constant ε changes, thereby causing the change of the variable capacitance in the equivalent circuit. The variable capacitance composed of n pairs of interdigital electrodes is as follows:
[0017]
[0018] The change of the variable capacitance causes the change of the resonance frequency of the humidity sensor, so the change of the environmental humidity can be detected by the shift of the resonance frequency, and the resonance frequency expression of the sensor is as follows:
[0019]
[0020] Wherein, n, omega, l, h are the logarithm, width, length and thickness of the interdigital electrode respectively, L and C are the inductance value and capacitance value of the LC resonance circuit respectively.
[0021] The utility model discloses a composite humidity-sensitive material that is fast in response and high in sensitivity, and the dielectric constant increases after the humidity-sensitive unit absorbs water molecules, the capacitance increases, and the resonance frequency of the LC resonance circuit decreases. The water molecules in the skin evaporate into the air and are adsorbed on the active sites of the humidity-sensitive unit, so that non-contact skin humidity detection can be performed.
[0022] The flexible LC sensor for skin humidity detection has the following advantages:
[0023] 1. The sensor is wireless and passive, and has good humidity sensitivity. The flexible LC sensor for skin humidity detection of the utility model adopts Au@ZIF-67 composite humidity-sensitive material, has the advantages of fast response recovery speed, good humidity performance, excellent repeatability, high resolution, wide range and strong desorption capacity. The LC resonance circuit realizes wireless and passive coupling to read out data, has low energy consumption, and can realize non-contact skin humidity detection.
[0024] 2. The sensor has small volume and low cost. The flexible LC humidity sensor has compact structure, and the composite humidity-sensitive material and the flexible substrate have small thickness, so it is easy to be attached to narrow spaces or complex structures, has excellent detection capacity, and has lower cost, thereby providing a development direction for intelligent integrated systems.
[0025] 3. The sensor has good mechanical properties and wide application range. The flexible LC humidity sensor is made of various materials that have good flexibility and excellent elastic capacity, and can be attached to curved surfaces such as skin. Since the inductor coil and the interdigital electrode are not in the same plane, the inductor short circuit phenomenon caused by water droplet condensation in a high-humidity environment can be avoided. BRIEF DESCRIPTION OF DRAWINGS
[0026] The utility model will be further described in connection with the drawings and examples:
[0027] Figure 1 It is a structure schematic view of a flexible LC sensor for skin humidity detection;
[0028] Figure 2 It is a system block diagram of the readout circuit of the flexible LC sensor;
[0029] Figure 3It is a response recovery time test diagram of a flexible LC sensor for skin humidity detection;
[0030] Wherein 11 is a composite humidity sensitive film, 12 is an interdigital electrode, 13 is a through hole, 14 is a flexible substrate, 15 is an inductor coil, 21 is a readout coil, 22 is a bridge detection module, 23 is an MCU module, 24 is a DDS module, and 25 is an upper computer module. DETAILED DESCRIPTION
[0031] To further illustrate the technical means adopted by the utility model to achieve the predetermined utility model purposes, the following will be combined with the drawings and the preferred embodiments, which are described in detail as follows:
[0032] Figure 1 It is a structural schematic diagram of a flexible LC sensor for skin humidity detection. The sensor comprises a composite humidity sensitive film 11, an interdigital electrode 12, a through hole 13, a flexible substrate 14, and an inductor coil 15. The interdigital electrode 12 is covered with the composite humidity sensitive film 11 on the upper surface, constituting a humidity sensitive unit; the interdigital electrode 12 and the inductor coil 15 are arranged on both sides of the flexible substrate 14 and connected through the through hole 13, constituting an LC resonant circuit. The composite humidity sensitive film 11 is composed of chloroauric acid and dimethyl imidazole cobalt composite material (Au@ZIF-67).
[0033] To improve the sensitivity of the humidity sensitive unit, the material of the composite humidity sensitive film 11 adopts Au@ZIF-67. After the chloroauric acid and dimethyl imidazole cobalt are compounded, a large number of water molecule adsorption sites are provided, and the desorption capacity is greatly improved.
[0034] To ensure the flexibility of the utility model, the thickness of the composite humidity sensitive film 11 is 0.15 mm, which can fully contact with the interdigital electrode 13 and improve the sensitivity.
[0035] To make the interdigital electrode 12 and the inductor coil 15 have better conductivity, copper or silver is selected as the material, and the thickness is 0.15 mm. Copper or silver has good conductivity, which ensures fast and stable signal transmission and further improves the moisture sensing performance. The inductor coil 15 adopts a planar spiral structure and is square in shape with a side length of 25 mm.
[0036] To make the performance of the interdigital electrode 12 better, the interdigital width of the interdigital electrode 12 is selected to be 0.6 mm, and the interdigital spacing is 0.4 mm. At this time, the resistance value of the interdigital electrode 12 appears a minimum value, and the potential distribution is more uniform.
[0037] To connect the interdigital electrode 12 and the inductor coil 15 in the upper and lower planes of the flexible substrate 14, the through hole 13 is filled with copper or silver after the corresponding position of the flexible substrate 14 is punched. If the tail of the interdigital electrode 12 and the inductor coil 15 is directly connected, a cavity gap is easily generated in the through hole 13, which causes water droplets to penetrate in a high humidity environment.
[0038] To provide mechanical support for the entire flexible LC humidity sensor, the flexible substrate 14 is made of polyethylene terephthalate (PET) with a thickness of 0.3 mm and a side length of 35 mm. PET has good environmental adaptability and compatibility.
[0039] To further improve the waterproofness and service life of the sensor, the tail of the interdigital electrode 12 and the inductor coil 15 is connected to form an LC resonance circuit. The LC resonance circuit can work stably for a long time and is very suitable for some complex environments such as narrow and closed spaces and mechanical rotating structures. The interdigital electrode 12 and the inductor coil 15 are distributed on both sides of the flexible substrate 14, which can avoid the inductive short circuit phenomenon caused by water droplet condensation in a high humidity environment.
[0040] To facilitate reading the real part of the impedance of a flexible LC sensor for skin humidity detection, a readout circuit is adopted, as shown in Figure 2 which includes a readout coil 21, a bridge detection module 22, an MCU module 23, a DDS module 24, and an upper computer module 25. The LC resonance circuit is coupled with the readout coil 21. The MCU module 23 controls the DDS module 24 to generate a certain frequency signal. After filtering and amplification, the signal enters the bridge detection module 22. The bridge detection module 22 outputs four scalar voltages using diode broadband detection. The MCU module 23 calculates the real part of the impedance of the LC humidity sensor according to the four voltage values. Subsequently, the system enters the next sampling frequency point, and the above process is repeated until the full-band measurement is completed.
[0041] In the above process, the MCU module 23 mainly completes three functions: one is to control the DDS module 24, the second is to sample the four voltages output by the bridge detection module 22 using the built-in AD conversion, and the third is to complete the communication with the upper computer module 25.
[0042] To study the humidity response performance of the composite humidity-sensitive material, the dynamic resistance response data of the sensor is collected. Figure 3 The response recovery time test diagram of a flexible LC sensor for skin humidity detection is shown in FIG. 6. The response recovery curve of the Au@ZIF-67 flexible LC humidity sensor between 11% RH and 95% RH relative humidity is shown in FIG. 6. The response time is 5 s.
[0043] The utility model discloses a flexible LC sensor for skin humidity detection wireless passive, compact structure, small thickness has good flexibility, can be attached to the curved surface, can long time stable operation under high humidity environment, and the ability of water molecule desorption is strong, response speed is fast, resolution is high, and the range is wide, can make data analysis to the humidity change fast.
[0044] The above is a specific description of the preferred embodiment of the utility model, but the utility model is not limited to the above-mentioned implementation, and those skilled in the art can make various equivalent modifications or replacements without departing from the spirit of the utility model, and these equivalent modifications or replacements are all included in the range defined by the claims of the present application.
Claims
1. A flexible LC sensor for skin moisture detection, characterized by, It comprises composite humidity-sensitive film, interdigital electrode, through hole, flexible substrate and inductive coil; the interdigital electrode is covered with composite humidity-sensitive film to form humidity-sensitive unit; the interdigital electrode and the inductive coil are arranged on two sides of the flexible substrate and connected through the through hole to form LC resonant circuit.
2. A flexible LC sensor for skin moisture detection as claimed in claim 1, wherein: The composite humidity-sensitive film is Au@ZIF-67 material.
3. A flexible LC sensor for skin moisture detection as claimed in claim 1, wherein: The thickness of the composite humidity-sensitive film is 0.1-0.2 mm.
4. A flexible LC sensor for skin moisture detection as claimed in claim 1, wherein: The material of the interdigital electrode and the inductive coil is copper or silver.
5. A flexible LC sensor for skin moisture detection as claimed in claim 1, wherein: The thickness of the interdigital electrode and the inductive coil is 0.1-0.2 mm.
6. A flexible LC sensor for skin moisture detection as claimed in claim 1, wherein: The inductive coil adopts planar spiral structure and is square in shape with side length of 20-30 mm.
7. A flexible LC sensor for skin moisture detection as claimed in claim 1, wherein: The interdigital electrode is 0.4-0.6 mm in width, 0.3-0.5 mm in interval and 10-30 mm in length.
8. A flexible LC sensor for skin moisture detection as claimed in claim 1, wherein: The flexible substrate is polyethylene terephthalate (PET) and is square in shape with side length of 20-40 mm.
9. A flexible LC sensor for skin moisture detection as claimed in claim 1, wherein: The thickness of the flexible substrate is 0.2-0.4 mm.