Tree diameter at breast height real-time monitoring system based on high-performance flexible strain sensor

Abstract

The invention discloses a real-time monitoring system for the diameter at breast height of a tree based on a high-performance flexible strain sensor. The real-time monitoring system comprises the flexible strain sensor, a connecting piece, a signal acquisition circuit, a Bluetooth module, a power supply and an upper computer, wherein the flexible strain sensor sequentially comprises a substrate layer, a sensitive layer and a protective layer from bottom to top; the connecting piece is composed of a base, a cover plate and a PVC plastic sheet. The method can cover a range of several kilometers or even farther, and is suitable for being deployed in a wide forest environment.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible strain sensors, and particularly to a real-time monitoring system for tree diameter at breast height based on high-performance flexible strain sensors. Background Art

[0002] At present, in the forest resource inventory and measurement operations in China, two main methods are used for measuring the tree diameter at breast height. One is invasive measurement, which realizes continuous monitoring by wearing growth rings on the trees. However, this method will cause physical damage to the trees, affect the healthy growth of the trees, and the range of the growth ring is limited. As the trees grow continuously, the equipment needs to be replaced frequently, which not only increases the monitoring cost but also reduces the overall operation efficiency. The other is non-invasive measurement, which uses tools such as vernier calipers and tape measures for measurement. However, these methods are complex to operate and generally require the cooperation of two staff members. One is responsible for measurement and the other is responsible for recording data. The labor cost is high and the operation efficiency is low. Moreover, these measurement methods cannot carry out real-time and all-weather monitoring of the tree diameter at breast height, and the measurement accuracy is extremely vulnerable to human factors and environmental conditions, making it difficult to meet the actual needs of modern forestry resource monitoring. Therefore, designing a tree diameter at breast height measurement system with simple operation, accurate measurement, high operation efficiency, and capable of realizing remote all-weather monitoring is of great practical significance for improving the quality and efficiency of forest resource inventory work. Summary of the Invention

[0003] Object of the Invention: The present invention aims to provide a real-time monitoring system for tree diameter at breast height based on high-performance flexible strain sensors, as well as a preparation method for the sensors. This system endeavors to overcome the deficiencies of existing measurement technologies and achieve the following technical advantages: (1) Non-destructive monitoring: The system adopts a non-invasive design to avoid any physical damage to the trees, fully ensuring the natural growth of the trees and practically implementing the concept of green monitoring; (2) Remote real-time monitoring: By accessing the Internet of Things, this system can remotely telemeter the tree diameter at breast height, breaking through the time and space limitations and greatly improving the convenience of monitoring. After the device is installed, monitoring data can be obtained in real time without manual on-site operation, significantly reducing the labor cost; (3) Wide-range design: The sensors adopted by this system have a large measurement range, can meet the monitoring needs of trees at different growth stages, do not require equipment replacement due to tree growth, effectively reduce the monitoring cost, and significantly improve the monitoring efficiency.

[0004] Technical Solution: A real-time monitoring system for tree diameter at breast height based on high-performance flexible strain sensors according to the present invention includes: flexible strain sensors, connectors, signal acquisition circuits, Bluetooth modules, power supplies, and upper computers; among them, the flexible strain sensors are successively a substrate layer, a sensitive layer, and a protective layer from bottom to top; the connectors are composed of bases, covers, and PVC plastic sheets.

[0005] Further, conductive silver paste and copper foil conductive tape are coated on both ends of the sensitive layer; the substrate layer is flexible Ecoflex silicone rubber; the sensitive layer is a multi-walled carbon nanotube coating layer based on the percolation threshold theory.

[0006] Further, the electrode layer is composed of conductive silver paste and copper foil conductive tape, and is led out through the copper foil conductive tape; the overall shape is in the shape of a bone rod.

[0007] Further, the base is connected to the PVC plastic sheet to form an annular structure; the cover plate is used to fix the sensor; the base (201) and the cover plate are made of 3D printed PETG material and are fixed by M3 screws and nuts.

[0008] Further, the signal acquisition circuit is a voltage division circuit. Using the voltage division circuit design, the resistance change of the sensor is calculated by measuring the output voltage and converted into breast diameter data; the circuit adopts the flexible printed circuit board FPCB process and performs analog-to-digital conversion through the STM32F103C8T6 microcontroller.

[0009] Further, the Bluetooth module adopts the HC-05 low-power module to upload data to the host computer.

[0010] Further, the power supply is powered by a solar panel; the host computer is used to receive and process data, and analyze the tree growth status and forest management effect.

[0011] Further, the preparation method of the flexible strain sensor includes the following steps: Step 1: Fix the PVC mold on the backing plate; Step 2: Mix Ecoflex silicone rubber A glue and B glue in a ratio of 1:1 and pour it into the mold to semi-cure to form the substrate layer (101); Step 3: Uniformly coat MWCNTs on the surface of the substrate layer to form the sensitive layer; Step 4: Coat conductive silver paste on both ends of the sensitive layer, dry it and then paste copper foil conductive tape; Step 5: Cover the Ecoflex protective layer and dry it; Step 6: Remove the mold and cut to obtain the finished sensor.

[0012] Further, the base and the cover plate of the connector fix the sensor through a slot structure; the PVC plastic sheet is connected to the bottom surface of the base by M3 screws and nuts, and the length is adjustable to adapt to different breast diameters; the sensor cooperates with the connector through its own elasticity to achieve non-destructive wearing.

[0013] Further, in the voltage division circuit of the signal acquisition circuit, the resistance R1 and the sensor resistance R2 satisfy the relationship: R2 is R1*V out / (3.3 - V out ); where V outThe voltage value collected by the ADC port of the STM32F103C8T6 microcontroller.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: It can measure all-weather for a long time and reduce manual repetitive labor. By using the HC-05 low-power Bluetooth and communicating through the serial port, data such as the tree diameter at breast height are transmitted to the upper computer software in real time, enabling scientific researchers to monitor the tree diameter at breast height all-weather and better analyze characteristics such as the growth status of trees, providing a scientific basis for ecological protection and sustainable development. The strain sensor based on the Ecoflex flexible substrate has a low Young's modulus and will not affect the growth of trees even when worn for a long time; in addition, compared with traditional diameter sensors, this flexible strain sensor has higher sensitivity and can measure extremely small changes in the diameter size (the measurement accuracy can be controlled within 0.01 - 0.1 mm). Multi-walled carbon nanotubes (MWCNTs) have a high aspect ratio, good electrical conductivity, and excellent mechanical properties, and are ideal materials for making flexible strain sensors. The sensitive layer is formed by depositing multi-walled carbon nanotubes (MWCNTs) on the semi-cured Ecoflex substrate. An intertwined conductive network is formed between the MWCNTs in the sensitive layer. When strained, the contact state between the intertwined MWCNTs changes, resulting in a significant change in resistance, thereby improving the sensitivity; the shape of the system and the connector design are reasonable, and it is generally annular and specially configured on the surface of the tree to be measured, meeting the requirements of tree diameter measurement. The cover plate and the base are made of 3D-printed PETG material, and the plastic sheet is made of PVC material. The overall quality is light, and the size of the PVC plastic sheet can be flexibly adjusted according to the range of the tree diameter to be measured. The stable wearing at the tree diameter position is achieved through the elasticity of the sensor, and it will not cause irreversible damage to the growth of trees. Description of the Drawings

[0015] Figure 1 It is the block diagram of the tree diameter monitoring system of the present invention; Figure 2 It is the structural cross-sectional view of step A2 of the preparation method of the flexible strain sensor of the present invention; Figure 3 It is the structural cross-sectional view of step A3 of the preparation method of the flexible strain sensor of the present invention; Figure 4 It is the structural cross-sectional view of step A4 of the preparation method of the flexible strain sensor of the present invention; Figure 5 It is the structural cross-sectional view of step A5 of the preparation method of the flexible strain sensor of the present invention; Figure 6 It is the structural diagram of the connector of the present invention; Figure 7 It is the front view of the connector of the present invention; Figure 8It is the side view of the connector of the present invention; Figure 9 It is the top view of the connector of the present invention; Figure 10 It is the schematic structural diagram of the signal acquisition circuit of the present invention. Specific embodiments

[0016] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0017] As Figure 1 shown, the embodiment of the present invention provides a real-time tree diameter monitoring system based on a high-performance flexible strain sensor, including a flexible strain sensor 1, a connector 2, a signal acquisition circuit 3, a Bluetooth 4, a power supply 5, and a host computer 6.

[0018] As Figure 2 shown, the flexible strain sensor 1 includes a substrate layer 101, a sensitive layer 102, a protective layer 105 arranged in sequence from bottom to top, and conductive silver paste layers 103 and copper foil conductive tape layers 104 at both ends of the sensitive layer 102; conductive silver paste 103 and copper foil conductive tape 104 are coated at both ends of the sensitive layer 102; the substrate layer 101 is a flexible Ecoflex silicone rubber; the sensitive layer 102 is a multi-walled carbon nanotube coating layer based on the percolation threshold theory. The electrode layer is composed of conductive silver paste 103 and copper foil conductive tape 104 and is led out through the copper foil conductive tape 104; the overall shape is bone-shaped The preparation method of the above flexible pressure sensor, as Figure 2-5 shown, includes the following steps: Step 1: Stick a PVC mold on a backing plate.

[0019] Step 2: Mix Group A glue and Group B glue in a ratio of 1:1 and pour them into the mold, and then put them in an oven until they become semi-cured to form the substrate layer 101.

[0020] Step 3: Uniformly apply a layer of MWCNTs on it to form the sensitive layer 102.

[0021] Step 4: Coat conductive silver paste layers 103 at both ends of the MWCNTs sensitive layer. The conductive silver paste penetrates into the MWCNTs to form a good ohmic contact, and then put it in an oven to dry. After the silver paste is cured, paste the copper foil conductive tape layer 104.

[0022] Step 5: Coat another layer of Ecoflex as the protective layer 105 and send it into the oven to dry.

[0023] Step 6: Finally, remove the mold from the backing plate, cut the mold open, and take out the finished product.

[0024] When the flexible sensor of the present invention is in use, through as Figure 6-9The designed connector is specifically configured on the surface of the cylinder to be measured. One end of the flexible strain sensor 1 is placed in the card slot of the base 201, and then the cover plate 202 is installed. Both ends of the sensitive layer 101 are wound with the metal conductive tape 2, and then the metal conductive tape 2 is connected to the signal acquisition circuit 3 through a wire, and the wire passes through the small hole on the right side of the base 201. M3 screws and nuts are used to lock the base and the cover plate 202 at the wider hole positions on one side of the base 201, and M3 screws and nuts are used to fix the cut strip-shaped PVC plastic sheet on the bottom surface of the entire connection device at the narrower hole positions on the other side, so as to flexibly cope with the different breast diameters of trees.

[0025] The signal acquisition circuit used in the breast diameter sensor of the present invention is as Figure 10 shown. The measurement circuit 3 of the present invention consists of a resistor R1 and a flexible strain sensor 1 to form a voltage division circuit. The other side of the resistor R1 is connected to a 3.3V voltage, and the other end of the flexible strain sensor is grounded. The middle node between the resistor R1 and the flexible strain sensor is connected to the A0 port of the STM32F103C8T6 microcontroller. Through ADC analog-to-digital conversion, the voltage value Vout(V) of this node is obtained. Then, the resistance value R2 of the flexible strain sensor is R1*Vout / (3.3 - Vout), so as to calculate the breast diameter length of the tree. Finally, the signal acquisition circuit 3 is printed using the FPCB process, so this part has a light weight.

[0026] The Bluetooth 4 of the present invention uses an HC-05 low-power Bluetooth module and operates with a serial communication protocol, which can transmit the key data such as the breast diameter of the tree collected in real time and accurately to the software of the upper computer 6. By using the software of the upper computer to process and analyze the collected data, scientific researchers can understand the growth status, site quality and forest management effect of the trees more deeply, providing a strong scientific basis for ecological protection and sustainable development. The power supply 5 is powered by a solar panel, enabling the entire system to work stably in the outdoor environment for a long time without the need to frequently replace the battery, thus greatly reducing the maintenance cost and environmental impact. The solar panel is not only environmentally friendly and energy-saving, but also lighter and more portable than traditional batteries, which is beneficial to the deployment and movement of the system in complex environments such as forests.

[0027] Some possible improvements to the present invention: First, the introduction of long-distance communication technology. In the future, low-power wide-area network technologies such as LoRa and NB-IoT can be adopted to achieve long-distance and low-power data transmission. These technologies can cover a range of several kilometers or even farther, and are suitable for deployment in vast forest environments to ensure that each sensor node can transmit data to the central server in real time. Second, a multi-sensor node network. By deploying multiple flexible strain sensors as sensing nodes, a distributed monitoring network can be constructed to cover a larger area of the forest. Each node can independently monitor the changes in the diameter at breast height of the trees and transmit the data to the server through long-distance communication technology to form a comprehensive forest growth data map, which helps to better evaluate the forest health status, growth trend, and the impact of environmental changes on the forest.

Claims

1. A real-time monitoring system for tree diameter at breast height based on a high-performance flexible strain sensor, characterized in that, Including: A flexible strain sensor (1), a connecting piece (2), a signal acquisition circuit (3), a Bluetooth module (4), a power supply (5), and a host computer (6). Among them, the flexible strain sensor (1) includes a substrate layer (101), a sensitive layer (102), and a protective layer (105) from bottom to top; the connecting piece (2) consists of a base (201), a cover plate (202), and a PVC plastic sheet (203).

2. The real-time tree diameter monitoring system based on a high-performance flexible strain sensor according to claim 1, wherein Conductive silver paste (103) and copper foil conductive tape (104) are coated at both ends of the sensitive layer (102); the substrate layer (101) is flexible Ecoflex silicone rubber; the sensitive layer (102) is a multi-walled carbon nanotube coating layer based on the percolation threshold theory.

3. The real-time tree diameter monitoring system based on a high-performance flexible strain sensor according to claim 1, wherein The electrode layer consists of conductive silver paste (103) and copper foil conductive tape (104), and is led out through the copper foil conductive tape (104); the overall shape is in the shape of a bone rod.

4. The real-time tree diameter monitoring system based on a high-performance flexible strain sensor according to claim 1, characterized in that The base (201) and the PVC plastic sheet (203) are connected to form an annular structure; the cover plate (202) is used to fix the sensor; the base (201) and the cover plate (202) are made of 3D printed PETG material and are fixed by M3 screws and nuts.

5. The real-time tree diameter at breast height monitoring system based on a high-performance flexible strain sensor according to claim 1, wherein The signal acquisition circuit (3) is a voltage division circuit, designed with a voltage division circuit, calculates the resistance change of the sensor by measuring the output voltage, and converts it into breast diameter data; the circuit adopts the flexible printed circuit board FPCB process and performs analog-to-digital conversion through the STM32F103C8T6 microcontroller.

6. The real-time tree diameter monitoring system based on a high-performance flexible strain sensor according to claim 1, characterized in that The Bluetooth module (4) uses an HC-05 low-power module to upload data to the host computer (6).

7. The real-time tree diameter monitoring system based on a high-performance flexible strain sensor according to claim 1, characterized in that The power supply (5) is powered by a solar panel; the host computer (6) is used to receive and process data, and analyze the tree growth status and forest management effect.

8. The real-time tree diameter monitoring system based on a high-performance flexible strain sensor according to claim 1, characterized in that, The preparation method of the flexible strain sensor (1) includes the following steps: Step 1: Fix the PVC mold on the backing plate; Step 2: Mix Ecoflex silicone rubber A glue and B glue in a ratio of 1:1 and pour it into the mold to semi-cure to form the substrate layer (101); Step 3: Uniformly coat MWCNTs on the surface of the substrate layer (101) to form the sensitive layer (102); Step 4: Coat conductive silver paste (103) at both ends of the sensitive layer (102), and paste copper foil conductive tape (104) after drying; Step 5: Cover the Ecoflex protective layer (105) and dry it; Step 6: Remove the mold and cut to obtain the finished sensor.

9. The real-time tree diameter monitoring system based on a high-performance flexible strain sensor according to claim 1, characterized in that, The base (201) and the cover plate (202) of the connecting piece (2) fix the sensor (1) through a slot structure; the PVC plastic sheet (203) is connected to the bottom surface of the base (201) by M3 screws and nuts, and the length is adjustable to fit different breast diameters; the sensor (1) cooperates with the connecting piece (2) through its own elasticity to achieve non-destructive wearing.

10. A real-time tree diameter at breast height monitoring system based on a high-performance flexible strain sensor according to claim 1, characterized in that, In the voltage division circuit of the signal acquisition circuit (3), the resistor R1 and the sensor resistance R2 satisfy the relationship: R2 is R1*V out / (3.3 - V out ); Among them, V out is the voltage value collected by the ADC port of the STM32F103C8T6 microcontroller.

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