Soil ion concentration sensor suitable for hypergravity environment

Abstract

The application discloses a soil ion concentration sensor suitable for a supergravity environment, which comprises, from top to bottom, a packaging layer, a pore water extraction filter membrane, a measuring layer and a substrate layer; the packaging layer is provided with a sampling window; the pore water extraction filter membrane is provided with a filter hole area completely overlapping with the sampling window; the top surface of the measuring layer is provided with a microfluidic channel in a groove type structure and a fluorescent optical fiber concentration sensor arranged in the microfluidic channel; and the main channel at the first end of the microfluidic channel overlaps with the filter hole area of the pore water extraction filter membrane. The application has the advantages of small volume, strong anti-electromagnetic interference ability, high g resistance and corrosion resistance, can be embedded in the soil pore environment for long-term stable work, and realizes in-situ detection of heavy metal ion concentration through the fluorescent optical fiber concentration sensor.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, specifically to a soil ion concentration sensor suitable for use in hypergravity environments. Background Technology

[0002] In recent years, heavy metal pollution caused by industrial accidents, mining development, and improper emissions has become increasingly prominent, drawing widespread global attention to the ecological environment and human health. Polluted water bodies and soils often contain various heavy metal ions, such as cadmium, lead, mercury, and arsenic. These ions are non-degradable, highly biotoxic, and exhibit significant migration and accumulation characteristics in the environment, posing a significant source of long-term environmental risks. Heavy metal ions can enter and harm the soil environment through direct sedimentation, infiltration, and migration with groundwater. Their migration and transformation processes in soil typically last for years or even decades, representing a typical long-term, slowly changing environmental process. Therefore, there is an urgent need for an experimental method that can simulate real environmental conditions and achieve long-term, continuous monitoring of ion concentration changes. The time-lapse effect under hypergravity can be utilized to accelerate the simulation of the migration and concentration evolution of heavy metal ions in soil and to accurately monitor them. This necessitates the development of sensors and testing methods suitable for heavy metal ion concentration testing in hypergravity environments. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a soil ion concentration sensor suitable for hypergravity environments, which has the advantages of small size, strong anti-electromagnetic interference ability, high g resistance and corrosion resistance, and can be embedded in the soil pore environment for a long time to work stably and realize in-situ detection of heavy metal ion concentration.

[0004] The technical solution of this invention is as follows:

[0005] A soil ion concentration sensor suitable for use in hypergravity environments includes an encapsulation layer, a pore water extraction filter membrane, a measuring layer, and a base layer stacked sequentially from top to bottom.

[0006] The encapsulation layer is provided with a sampling window, and the pore water extraction filter membrane is provided with a filter hole area that completely overlaps with the sampling window. Multiple vertically penetrating pore water extraction filter holes are provided in the filter hole area.

[0007] The top surface of the measurement layer has a groove-shaped microfluidic channel, which includes a main channel, a diversion zone, a detection chamber, a reference chamber, and a drainage chamber. The main channel overlaps with the filter pore area of ​​the pore water extraction membrane. The diversion zone has a Y-shaped branch structure. The inlet end of the diversion zone is connected to the main channel, and the two outlet ends of the diversion zone are connected to the detection chamber and the reference chamber, respectively. Both the detection chamber and the reference chamber are connected to the drainage chamber, which is connected to a row of drainage outlets located at the edge of the measurement layer. The detection chamber is equipped with a detection probe of a fluorescent fiber optic concentration sensor, and the reference chamber is equipped with detection probes of a fiber optic temperature sensor and a fiber optic pH sensor. The optical fibers of the fluorescent fiber optic concentration sensor, the fiber optic temperature sensor, and the fiber optic pH sensor are all led out to the outside of the measurement layer and connected to the photoelectric signal excitation and reception unit.

[0008] The encapsulation layer is made of polyimide film.

[0009] The pore water extraction filter membrane is made of PVDF membrane. The PVDF membrane has multiple pore water extraction filter holes arranged in a matrix in the filter pore area. The average pore diameter of the pore water extraction filter holes is 0.1~0.4μm.

[0010] The measurement layer is a polydimethylsiloxane film with an elastic modulus of 0.5~3 MPa. Microfluidic channels are laser-cut into the top surface of the polydimethylsiloxane film.

[0011] The detection chamber and reference chamber of the microfluidic channel are respectively connected to the two outlet ends of the diversion zone through corresponding L-shaped inlet channels. The outlet ends of the detection chamber and reference chamber are respectively connected to the drainage chamber through corresponding capillary valve structures. The capillary valve structure is a V-shaped bend capillary structure. The V-bend divides the capillary valve structure into a front and a rear part. The front end of the capillary valve structure is connected to the detection chamber or reference chamber, and the rear end of the capillary valve structure is connected to the drainage chamber. The aperture of the front part of the capillary valve structure is smaller than that of the rear part. The aperture of the front part is 50~150μm, and the aperture of the rear part is 300~500μm. The included angle of the V-bend is 30~60 degrees.

[0012] The cross-sectional area of ​​the drainage chamber is smaller than that of the main channel.

[0013] The detection probe of the fluorescent fiber optic concentration sensor is coated with a fluorescent coating at the end of the optical fiber. The fluorescent coating is made by embedding a Rhodamine B derivative into a polyvinyl alcohol matrix.

[0014] The substrate layer is made of polycarbonate film. The portion of the measuring layer located directly below the detection cavity and the reference cavity, as well as the substrate layer, are provided with optical fiber perforations. The optical fibers of the fluorescent optical fiber concentration sensor, optical fiber temperature sensor, and optical fiber pH sensor pass through the corresponding optical fiber perforations and are then connected to the external photoelectric signal excitation and reception unit.

[0015] The photoelectric signal excitation and reception unit includes a light source, a filter, a photodetector, and an electrical signal output module. The optical fibers of the fluorescent fiber optic concentration sensor, fiber optic temperature sensor, and fiber optic pH sensor are all connected to the light source. Using the optical fiber as a transmission medium, the light signal emitted by the light source is transmitted to the detection probe of the optical fiber. The detection probe transmits the detected light signal back and filters it through the filter. The signal is then converted into an electrical signal by the photodetector and finally output to the host computer through the electrical signal output module.

[0016] Advantages of this invention:

[0017] (1) The present invention can work stably under the conditions of high speed rotation and high g multiple of centrifuge, realize real-time, continuous and in-situ monitoring of heavy metal ion concentration in soil, without stopping the machine for sampling, and can obtain heavy metal ion concentration data with high time resolution, reflecting the transient changes and evolution law in the ion migration process in real time, thereby overcoming the problems of discontinuous data and missing information in traditional intermittent sampling methods, while avoiding the disturbance of soil seepage field and ion distribution caused by centrifuge deceleration or shutdown, so that the test results more realistically reflect the actual process of ion migration.

[0018] (2) The present invention has a layered structure, which is compact and flexible in layout. It can be arranged in multiple points according to the size of the geotechnical model box, and is suitable for long-term online monitoring under limited space conditions in the centrifugal test of ultragravity.

[0019] (3) The present invention is equipped with a pore water extraction filter membrane. Through the setting of micropores, soil particles, colloids and fine minerals are blocked from entering the microfluidic channel. The capillary effect and super gravity acceleration of the microfluidic channel are used to promote the flow of pore water and draw the pore water in the soil into the microfluidic channel.

[0020] (4) The main channel of the microfluidic channel of this invention guides pore water stably, slowly and continuously to the detection chamber and the reference chamber, which can effectively reduce shear disturbance, ensure that laminar flow is maintained under high g conditions, avoid turbulence or stratification, and stabilize the flow rate; the detection chamber and the reference chamber are respectively connected to the two outlet ends of the splitting zone through corresponding L-shaped inlet channels, thereby reducing the flow velocity in the detection chamber and the reference chamber, prolonging the residence time of pore water in the detection chamber and the reference chamber, creating a quasi-static detection area, providing a stable liquid-film-optical interaction environment for the optical fiber detection probe, so that the changes in ion concentration and refractive index can fully act on the fluorescence detection probe; the reference chamber is used to measure the real-time temperature and pH value of pore water, realizing the measurement of optical detection concentration information. Temperature and pH compensation are provided; the cross-sectional area of ​​the drainage chamber is smaller than that of the main channel to increase flow resistance, and a capillary valve structure is set at the inlet end. From upstream to downstream, the channel cross-section suddenly expands at the V-bend, forming an acute expansion angle. This means that when pore water moves from the high curvature interface to the low curvature interface, it needs to overcome the capillary pressure difference. Under hypergravity, the driving force is enhanced and exceeds the capillary pressure difference; while under normal gravity, the driving force is less than the capillary pressure difference. The structure of the microfluidic channel of this invention only allows pore water to be discharged under hypergravity, preventing pore water from flowing back under normal gravity. This achieves unidirectional discharge and pressure regulation of pore water, preventing liquid from flowing back into the detection chamber when the centrifuge decelerates or stops, and avoiding the impact of liquid retention and backflow on the monitoring results.

[0021] (5) The fluorescent coating of the fluorescent fiber optic concentration sensor of the present invention is prepared by embedding a Rhodamine B derivative into a polyvinyl alcohol matrix. The Rhodamine B derivative has significant selective fluorescence quenching characteristics for mercury ions, etc., and the polyvinyl alcohol as the matrix ensures the mechanical stability of the fluorescent coating.

[0022] (6) The measuring layer and the base layer of the present invention are provided with optical fiber through holes for optical fiber positioning to prevent the optical fiber from shifting in a high g environment, provide mechanical protection for the optical fiber, and improve the stability and durability of the soil ion concentration sensor under high g values. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the layered structure of the present invention.

[0024] Figure 2 This is a plan view of the pore water extraction filter membrane of the present invention.

[0025] Figure 3 This is a plan view of the microfluidic channel of the present invention.

[0026] Figure 4 This is a block diagram illustrating the principle of the photoelectric signal excitation and reception unit of the present invention.

[0027] Figure 5This is a schematic diagram of the layout structure for collecting soil ion concentration under hypergravity conditions according to the present invention.

[0028] Reference numerals: 1-Encapsulation layer, 11-Sampling window, 2-Pore water extraction filter membrane, 3-Measurement layer, 4-Base layer, 41-Fiber optic perforation, 5-Microfluidic channel, 51-Main channel, 52-Branch zone, 53-Detection chamber, 54-Reference chamber, 55-Drainage chamber, 56-L-shaped inlet channel, 57-Capillary valve structure, 58-Drainage port, 6-Photoelectric signal excitation and reception unit, 61-Light source, 62-Filter, 63-Photodetector, 65-Fiber optic cable, 7-Host computer, 01-Soil ion concentration sensor, 02-Model box, 03-Soil. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0030] See Figure 1 A soil ion concentration sensor suitable for hypergravity environments includes an encapsulation layer 1, a pore water extraction filter membrane 2, a measuring layer 3, and a base layer 4 stacked sequentially from top to bottom.

[0031] The encapsulation layer 1 is made of polyimide film, and a sampling window 11 is provided on the encapsulation layer 1.

[0032] See Figure 2 The pore water extraction filter membrane 2 is made of PVDF film. The pore water extraction filter membrane 2 is provided with a filter pore area 21 that completely overlaps with the sampling window 11. Multiple pore water extraction filter holes 22 are opened in the filter pore area 21 in a matrix distribution. The average pore diameter of the pore water extraction filter holes is 0.1~0.4μm.

[0033] See Figure 3The measuring layer 3 is a polydimethylsiloxane film with an elastic modulus of 0.5~3 MPa. A grooved microfluidic channel 5 is laser-cut into the top surface of the polydimethylsiloxane film. The microfluidic channel 5 includes a main channel 51, a diversion zone 52, a detection chamber 53, a reference chamber 54, and a drain chamber 55. The main channel 51 overlaps with the filter pore area 21 of the pore water extraction filter membrane 2. The diversion zone 52 has a Y-shaped branch structure, with its inlet end connected to the main channel 51. The detection chamber 53 and the reference chamber 54 are connected to the two outlet ends of the diversion zone 52 through corresponding L-shaped inlet channels 56. The outlet ends of the detection chamber 53 and the reference chamber 54 are connected to the drain chamber 55 through corresponding capillary valve structures 57. The capillary valve structure 57 is a V-shaped bend in the capillary tube structure, with the V-shaped bend dividing the capillary valve structure 57 into a front and a... At the rear, the front end of the capillary valve structure 57 is connected to the detection chamber 53 or the reference chamber 54, and the rear end of the capillary valve structure 57 is connected to the drain chamber 55. The aperture of the front part of the capillary valve structure 57 is smaller than that of the rear part. The aperture of the front part is 50~150μm, and the aperture of the rear part is 300~500μm. The included angle of the V-bend is 30~60 degrees. The cross-sectional area of ​​the drain chamber 55 is smaller than that of the main channel 51. The drain chamber 55 is connected to a row of drain ports 58 located at the edge of the measuring layer 3. The detection probe of the fluorescent fiber optic concentration sensor is installed in the detection chamber 53. The detection probe of the fluorescent fiber optic concentration sensor is coated with a fluorescent coating on the detection probe at the tail of the fiber optic 65. The fluorescent coating is made by embedding a Rhodamine B derivative into a polyvinyl alcohol matrix. The detection probes of the fiber optic temperature sensor and the fiber optic pH sensor are installed in the reference chamber 54.

[0034] The substrate layer 4 is made of polycarbonate film. The portion of the measuring layer 3 located directly below the detection cavity 53 and the reference cavity 54, as well as the substrate layer 4, are provided with optical fiber perforations 41. The optical fibers 65 (diameter 200 μm) of the fluorescent optical fiber concentration sensor, optical fiber temperature sensor, and optical fiber pH sensor pass through the corresponding optical fiber perforations 41 and are connected to the external photoelectric signal excitation and reception unit 6. The optical fibers 65 are in sealed contact with the measuring layer 3 and the substrate layer 4 to prevent pore water from flowing out from the optical fiber perforations 41.

[0035] See Figure 4 The photoelectric signal excitation and reception unit 6 includes a light source 61, a filter 62, a photodetector 63, and an electrical signal output module 64. The optical fibers 65 of the fluorescent fiber optic concentration sensor, fiber optic temperature sensor, and fiber optic pH sensor are all connected to the light source 61. Using the optical fiber 65 as a transmission medium, the light signal emitted by the light source 61 is transmitted to the detection probe of the optical fiber 65. The detection probe transmits the detected light signal back and filters it through the filter 62. The light signal is then converted into an electrical signal by the photodetector 63 and finally output to the host computer 7 through the electrical signal output module 64.

[0036] Working principle of the invention:

[0037] (1) Before the start of the hypergravity test, the soil ion concentration sensor 01 was routinely calibrated and its functions were verified, and deionized water was injected into the microfluidic channel 5 to confirm that it was free from blockage and leakage.

[0038] (2) See Figure 5 The soil ion concentration sensor 01 is placed inside the model box 02 at a predetermined depth in the soil 03. The encapsulation layer 1 of the soil ion concentration sensor 01 faces the seepage direction. The soil ion concentration sensor 01 is tightly attached to the soil 03 without air gaps. The optical fibers 65 of the fluorescent optical fiber concentration sensor, optical fiber temperature sensor and optical fiber pH sensor of the soil ion concentration sensor 01 extend to the outside of the model box 02 and are connected to the host computer 7 through the photoelectric signal excitation and reception unit 6.

[0039] (3) Place the model box 02 in the basket of the centrifuge, start the centrifuge, load it step by step to the target g value, start the hypergravity test, use hypergravity to accelerate the migration rate of ions in soil 03, and increase the driving force for pore water to flow into the microfluidic channel 5.

[0040] (4) When the target g value is stable, the light source 61 inputs the light signal to the optical fiber 65 to excite the fluorescent coating on the optical fiber probe to generate a fluorescent signal. The fluorescent signal returns along the optical fiber 65, is filtered by the filter 62, and is converted into an electrical signal by the photodetector 63. Finally, it is output to the host computer 7 through the electrical signal output module 64. The optical fiber temperature sensor and the optical fiber pH sensor synchronously collect the real-time temperature and pH value and send them to the host computer 7 through the photoelectric signal excitation and reception unit 6. The host computer 7 then performs temperature compensation and pH compensation adjustment to obtain the net fluorescence response signal. Finally, the fluorescence intensity corresponding to the net fluorescence response signal is converted into the target ion concentration according to the following formula (1).

[0041] The relationship between ion concentration and fluorescence intensity is shown in equation (1):

[0042] (1):

[0043] In equation (1), I represents the fluorescence intensity of the aqueous solution without the target ion, while I represents the fluorescence intensity of the aqueous solution in the presence of the target ion. denoted as the quenching constant of the target ion, and C is the concentration of the target ion.

[0044] Among them, the flow rate of the liquid (pore water) flowing in the microfluidic channel Satisfy the following equation (2):

[0045] (2);

[0046] In equation (2), The equivalent radius of microfluidic channel 5 is represented by the volume of microfluidic channel 5 and the axial distance between the inlet and outlet of microfluidic channel 5. The area is obtained after converting the cross-sectional area to a circle. Represents liquid viscosity; This represents the axial distance between the inlet and outlet of microfluidic channel 5; Represents the driving force of supergravity on the flow of liquids; This represents the capillary pressure in microfluidic channel 5; The coefficient representing the relationship with hypergravity reflects the enhancing effect of hypergravity on the driving force of flow. It is calibrated through experiments and has a value range of 1.2 to 1.8. The density of the liquid; For the target g value and gravitational acceleration Multiples of; The equivalent radial difference between the inlet and outlet of microfluidic channel 5; Represents the surface tension of a liquid; is the contact angle, and is a constant.

[0047] As can be seen from equation (2), by introducing a coefficient related to hypergravity... This study quantitatively describes the enhancing effect of hypergravity on the driving force of pore water flow within microfluidic channel 5, thereby increasing the driving force of hypergravity on pore water flow. Greater than capillary pressure This enables the detection of normal flow of pore water within the microfluidic channel 5.

[0048] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A soil ion concentration sensor suitable for use in hypergravity environments, characterized in that: It includes a packaging layer, a pore water extraction filter membrane, a measuring layer and a base layer stacked sequentially from top to bottom; The encapsulation layer is provided with a sampling window, and the pore water extraction filter membrane is provided with a filter hole area that completely overlaps with the sampling window. Multiple vertically penetrating pore water extraction filter holes are provided in the filter hole area. The top surface of the measurement layer has a groove-shaped microfluidic channel. The microfluidic channel includes a main channel, a diversion zone, a detection chamber, a reference chamber, and a drainage chamber. The main channel overlaps with the filter pore area of ​​the pore water extraction membrane. The diversion zone has a Y-shaped branch structure. The inlet end of the diversion zone is connected to the main channel, and the two outlet ends of the diversion zone are connected to the detection chamber and the reference chamber, respectively. Both the detection chamber and the reference chamber are connected to the drainage chamber. The drainage chamber is connected to a row of drainage ports located at the edge of the measurement layer. The detection chamber is equipped with a detection probe of a fluorescent fiber optic concentration sensor, and the reference chamber is equipped with detection probes of a fiber optic temperature sensor and a fiber optic pH sensor. The optical fibers of the fluorescent fiber optic concentration sensor, the fiber optic temperature sensor, and the fiber optic pH sensor are all led out to the outside of the measurement layer and connected to the photoelectric signal excitation and reception unit. The detection chamber and reference chamber of the microfluidic channel are respectively connected to the two outlet ends of the diversion zone through corresponding L-shaped inlet channels. The outlet ends of the detection chamber and reference chamber are respectively connected to the drainage chamber through corresponding capillary valve structures. The capillary valve structure is a V-shaped bend capillary structure. The V-bend divides the capillary valve structure into a front and a rear part. The front end of the capillary valve structure is connected to the detection chamber or reference chamber, and the rear end of the capillary valve structure is connected to the drainage chamber. The aperture of the front part of the capillary valve structure is smaller than that of the rear part. The aperture of the front part is 50~150μm, and the aperture of the rear part is 300~500μm. The included angle of the V-bend is 30~60 degrees.

2. The soil ion concentration sensor suitable for use in a high gravity environment according to claim 1, characterized in that: The encapsulation layer is made of polyimide film.

3. A soil ion concentration sensor suitable for use in hypergravity environments according to claim 1, characterized in that: The pore water extraction filter membrane is made of PVDF membrane. The PVDF membrane has multiple pore water extraction filter holes arranged in a matrix in the filter pore area. The average pore diameter of the pore water extraction filter holes is 0.1~0.4μm.

4. A soil ion concentration sensor suitable for use in hypergravity environments according to claim 1, characterized in that: The measurement layer is a polydimethylsiloxane film with an elastic modulus of 0.5~3 MPa. Microfluidic channels are laser-cut into the top surface of the polydimethylsiloxane film.

5. A soil ion concentration sensor suitable for use in hypergravity environments according to claim 1, characterized in that: The cross-sectional area of ​​the drainage chamber is smaller than that of the main channel.

6. A soil ion concentration sensor suitable for use in hypergravity environments according to claim 1, characterized in that: The detection probe of the fluorescent fiber optic concentration sensor is coated with a fluorescent coating at the end of the optical fiber. The fluorescent coating is made by embedding a Rhodamine B derivative into a polyvinyl alcohol matrix.

7. A soil ion concentration sensor suitable for use in hypergravity environments according to claim 1, characterized in that: The substrate layer is made of polycarbonate film. The portion of the measuring layer located directly below the detection cavity and the reference cavity, as well as the substrate layer, are provided with optical fiber perforations. The optical fibers of the fluorescent optical fiber concentration sensor, optical fiber temperature sensor, and optical fiber pH sensor pass through the corresponding optical fiber perforations and are connected to the external photoelectric signal excitation and reception unit. The optical fibers are in sealed contact with the measuring layer and the substrate layer, respectively.

8. A soil ion concentration sensor suitable for use in hypergravity environments according to claim 1, characterized in that: The photoelectric signal excitation and reception unit includes a light source, a filter, a photodetector, and an electrical signal output module. The optical fibers of the fluorescent fiber optic concentration sensor, fiber optic temperature sensor, and fiber optic pH sensor are all connected to the light source. Using the optical fiber as a transmission medium, the light signal emitted by the light source is transmitted to the detection probe of the optical fiber. The detection probe transmits the detected light signal back and filters it through the filter. The signal is then converted into an electrical signal by the photodetector and finally output to the host computer through the electrical signal output module.

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