Portable intelligent measuring instrument for soil natural moisture content based on multi-source sensing fusion

Abstract

The application relates to the technical field of in-situ measurement of soil physical parameters, and discloses a portable intelligent measuring instrument for natural water content of a soil layer based on multi-source sensing fusion, which comprises a composite probe assembly and an intelligent measurement and control host machine which are physically connected; the composite probe assembly is configured to be inserted into a to-be-measured soil layer to build a multi-physical-field test environment, and is internally integrated with an electrical transmitting and receiving unit and an acoustic transmitting and receiving unit. By building a cross-physical-field excitation and multi-phase parameter collaborative decoupling mechanism, a multi-dimensional dynamic correlation model is established by using the thermal sensitive drift characteristics of the sound velocity of a mixed medium during thermal disturbance and the transient step response of the dielectric constant under the acoustic radiation force field, the problem that a traditional method cannot distinguish the coupling influence of water content and bulk density and cannot separate the conductive characteristics of bound water and free water is effectively solved, four independent physical quantities, namely, the volume water content, the in-situ dry bulk density, the bound water content and the real conductivity of pore water, are simultaneously inverted by a single probe, and the decoupling precision of the equipment on the parameters of complex multi-phase soil media is improved.

Description

Technical Field

[0001] This invention relates to the field of in-situ measurement technology of soil physical parameters, specifically a portable intelligent measuring instrument for natural soil moisture content based on multi-source sensor fusion. Background Technology

[0002] Soil moisture content is a crucial basic physical parameter in fields such as geotechnical engineering investigation, precision agricultural irrigation, and geological disaster monitoring. Accurate acquisition of soil moisture data is essential for assessing soil shear strength, developing crop irrigation systems, and predicting landslide risks. In field operations, portable and easy-to-use contact measuring instruments are widely used to quickly and in real-time acquire soil moisture information over large areas, becoming a primary technical means to replace traditional drying methods for in-situ measurements.

[0003] In existing industry applications, portable soil moisture measurement technology mainly relies on electromagnetic methods based on dielectric principles, such as time-domain reflectometry, frequency-domain reflectometry, or standing wave ratio methods. These devices typically use a metal probe inserted into the soil as a waveguide or capacitor plate to obtain the apparent dielectric constant of the soil by detecting the propagation speed of electromagnetic waves in the soil medium, the reflection coefficient, or the impedance frequency response. Since the dielectric constant of liquid water is much higher than that of soil particles and air, existing technologies typically rely on this significant difference to establish a single mapping relationship between the apparent dielectric constant and the volumetric water content of the soil using pre-defined empirical formulas, thereby achieving rapid estimation of moisture content.

[0004] However, existing single-physical-principle measurement methods suffer from significant parameter coupling bottlenecks when facing complex natural soil environments, severely limiting measurement accuracy. Specifically, the electrical response measured by the sensor is actually a comprehensive result of the combined effects of multiple variables, such as volumetric water content, in-situ dry bulk density of the soil, pore water salinity, and the state of bound water. However, conventional measurement models are often forced to assume uniform soil density and ignore the dielectric difference between bound and free water. This makes it impossible for the instrument to independently resolve the contribution ratio of volumetric water content and dry bulk density in a single measurement, and it is also difficult to effectively separate the polarization effect and pore ion conductivity effect caused by bound water from the total signal. Consequently, under heterogeneous conditions where soil texture is heavy or compaction changes, the measurement results will exhibit large coupling errors. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a portable intelligent measuring instrument for natural soil moisture content based on multi-source sensor fusion, which solves the problem of inaccurate measurement caused by the inability to decouple multiphase parameters of soil using a single method.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a portable intelligent measuring instrument for natural soil moisture content based on multi-source sensor fusion, comprising a physically connected composite probe assembly and an intelligent measurement and control host;

[0007] The composite probe assembly is configured to be inserted into the soil layer to be tested to construct a multiphysics testing environment, and integrates the following:

[0008] An electrical transceiver unit is used to construct an alternating electric field and a thermal diffusion field in the soil layer to be tested, and to sense electrical parameters;

[0009] An acoustic transceiver unit is used to construct an ultrasonic propagation field and a mechanical vibration field in the soil layer to be tested, and to sense acoustic parameters.

[0010] The intelligent monitoring and control host includes:

[0011] The contact state adaptive adjustment module is configured to coordinately control the acoustic transceiver unit to generate mechanical vibration and the electrical transceiver unit to monitor the contact impedance before measurement, until a physical contact interface between the probe and the soil layer that meets the preset convergence conditions is established.

[0012] The cross-physical field excitation module is configured to control the electrical transceiver unit to inject thermal disturbance energy into the soil layer to be tested according to a preset timing sequence, and to control the acoustic transceiver unit to emit an acoustic radiation force field into the soil layer to be tested.

[0013] The multidimensional dynamic response acquisition module is configured to synchronously acquire the dynamic response data of sound velocity during the thermal disturbance energy action and the transient response data of dielectric constant during the acoustic radiation force field action.

[0014] The multiphase parameter collaborative decoupling module is configured to jointly calculate and output the volumetric water content, in-situ dry unit weight, bound water content, and true electrical conductivity of pore water of the soil layer under test based on the sound velocity dynamic response data and the dielectric constant transient response data.

[0015] Preferably, the contact state adaptive adjustment module includes:

[0016] The acoustic transceiver unit is driven to operate in a preset high-frequency mode, and the thixotropic effect is used to induce soil particles around the probe to fill the interface voids.

[0017] The electrical transceiver unit monitors the contact impedance value and its rate of change between the electrodes in real time.

[0018] When the rate of change of the contact impedance value is lower than the preset convergence threshold, it is determined that the contact interface has been densified, and the vibration drive of the acoustic transceiver unit is immediately stopped.

[0019] Preferably, the composite probe assembly comprises multiple parallel-arranged corrosion-resistant alloy needles;

[0020] The electrical transceiver unit is composed of the alloy needle body itself, which serves as both a measuring electrode for conductivity and dielectric constant and a heating resistor for Joule heating.

[0021] The acoustic transceiver unit includes a piezoelectric transducer array conformally embedded inside or at the root of the alloy needle body, and the acoustic wave propagation path of the piezoelectric transducer array traverses the test area surrounded by the alloy needle body.

[0022] Preferably, the data collected by the multi-dimensional dynamic response acquisition module specifically includes:

[0023] Initial sound velocity, initial apparent dielectric constant, and initial apparent conductivity measured under initial steady state;

[0024] The maximum drift of the sound velocity in the mixed medium in the soil layer under test as the temperature increases after the injection of thermal disturbance energy.

[0025] The transient step change in the apparent dielectric constant of the soil layer under test due to the double electric layer disturbance at the instant the acoustic radiation force field is turned on and off.

[0026] Preferably, the multiphase parameter collaborative decoupling module includes a first-dimensional decoupling unit, which is configured as follows:

[0027] Based on the static mapping relationship between the sound velocity of the mixed medium and the volumetric water content and in-situ dry bulk density, a first relationship model is constructed.

[0028] A second relationship model is constructed based on the dynamic thermosensitive response relationship between the maximum drift of the sound velocity in the mixed medium and the injected thermal disturbance energy, volumetric water content and in-situ dry bulk density.

[0029] Solve the first relational model and the second relational model simultaneously to obtain the volumetric water content and in-situ dry unit weight of the soil layer to be tested.

[0030] Preferably, the multiphase parameter collaborative decoupling module further includes a second-dimensional decoupling unit, which is configured as follows:

[0031] The transient step change in the apparent dielectric constant is used to characterize the polarization response of bound water molecules and double-layer ions to the acoustic radiation force field.

[0032] An acoustic-electric coupling model was established to describe the relationship between transient step changes and acoustic radiation force field intensity, bound water content, and pore water ion concentration.

[0033] The volumetric water content and in-situ dry unit weight obtained from the first dimension decoupling unit are substituted into the acoustic-electric coupling model and the multiphase dielectric mixing model to separately calculate the bound water content and the true electrical conductivity of pore water in the soil layer to be tested.

[0034] Preferably, the intelligent measurement and control host further includes a signal multiplexing and switching circuit, which is connected between the composite probe assembly and the cross-physical field excitation module, and further includes:

[0035] The electrical transceiver unit is time-division multiplexed between the DC heating drive circuit and the high-frequency impedance measurement circuit.

[0036] The acoustic transceiver unit performs time-division multiplexing switching between the high-power oscillation drive circuit and the pulsed ultrasonic transceiver circuit.

[0037] Preferably, the intelligent measurement and control host is further configured to store the stable contact impedance value when the contact interface is determined to be dense as a system reference parameter, which is used to eliminate the error influence of contact resistance when calculating the true conductivity of pore water in the subsequent process.

[0038] Preferably, in the first relational model, the sound velocity of the mixed medium is defined as a function of the equivalent elastic modulus and equivalent density of the mixture composed of soil skeleton, pore water and pore air; in the second relational model, the change in the sound velocity of the mixed medium is defined as being mainly contributed by the thermal sensitivity of the sound velocity of pore water with temperature change, and this change is inversely proportional to the total heat capacity of the soil layer to be tested.

[0039] Preferably, the intelligent monitoring and control host also includes a human-machine interaction display unit, which is used to intuitively display multiple soil physical parameters calculated by the multi-phase parameter collaborative decoupling module, as well as display the current probe contact status indication information.

[0040] This invention provides a portable intelligent measuring instrument for the natural moisture content of soil layers based on multi-source sensor fusion. It has the following beneficial effects:

[0041] 1. This invention constructs a cross-physical field excitation and multiphase parameter collaborative decoupling mechanism, and establishes a multidimensional dynamic correlation model by utilizing the thermosensitive drift characteristics of the sound velocity of the mixed medium during thermal disturbance and the transient step response of the dielectric constant under the acoustic radiation force field. This effectively solves the problem that traditional methods cannot distinguish the coupling effect of water content and bulk density, and are difficult to separate the conductivity characteristics of bound water and free water. It realizes the simultaneous inversion of four independent physical quantities by a single probe: volumetric water content, in-situ dry bulk density, bound water content, and true conductivity of pore water, thereby significantly improving the decoupling accuracy of the equipment for complex multiphase soil medium parameters.

[0042] 2. This invention integrates contact state adaptive adjustment function, utilizes the acoustic unit to emit high-frequency vibration to excite the soil thixotropic effect and induce micro-particles to fill the interface voids, and cooperates with the electrical unit to monitor the contact impedance change rate in real time to control the vibration duration in a closed loop. This effectively overcomes the problems of thermal conduction failure and excessive electrode polarization impedance caused by poor physical contact in hard or heterogeneous soils by portable probes. It realizes the automatic establishment of a dense and standardized test interface without the need for external heavy auxiliary equipment and eliminates contact errors by using reference impedance, thereby reducing the interference of contact thermal resistance and contact resistance on measurement stability.

[0043] 3. This invention employs a probe hardware reuse architecture and an in-situ thermal efficiency correction algorithm. It utilizes a corrosion-resistant alloy needle body as an electrical measurement electrode, a Joule thermal excitation source, and an acoustic propagation carrier. It also dynamically calibrates the system's thermal efficiency factor by combining the transient temperature rise slope characteristics at the initial stage of thermal disturbance. This solves the problem of bulky size caused by hardware separation in traditional portable devices. At the same time, the in-situ thermal efficiency correction algorithm overcomes the measurement deviation caused by the inability of fixed calibration parameters to adapt to changes in field contact thermal resistance. It achieves both multi-physics field measurement and high integration under a minimalist four-needle topology, while ensuring the accuracy of energy injection calculation, thereby enhancing the robustness of the equipment in field operations. Attached Figure Description

[0044] Figure 1 This is a system block diagram of the present invention. Detailed Implementation

[0045] The technical solutions in 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.

[0046] Example:

[0047] Please see the appendix Figure 1 This invention provides a portable intelligent measuring instrument for the natural water content of soil layers based on multi-source sensor fusion, comprising two main parts: a composite probe assembly and an intelligent measurement and control host.

[0048] 1. Detailed hardware structure of the composite probe assembly

[0049] The composite probe assembly is the physical front end for the system to interact with the medium under test, and it adopts a highly integrated mechatronics design.

[0050] 1.1 Overall Mechanical Structure of the Probe: The composite probe assembly adopts a four-needle parallel topology structure. All four needles are made of high-strength, corrosion-resistant 316L stainless steel alloy to adapt to complex soil environments such as acidic, alkaline, and saline soils in the field. The needle length is set at 60 mm, the diameter at 3 mm, and the center-to-center distance between the needles is strictly controlled at 15 mm to ensure the effective sensitive volume for electrical and acoustic measurements. The components are highly overlapped in space, with four needles vertically fixed to an insulating base made of precision-machined PEEK (polyether ether ketone) material. The connection between the needle root and the base is vacuum-sealed with high-temperature resistant epoxy resin to ensure that the component reaches the IP68 protection level and prevent soil moisture from seeping in and causing short circuits in the internal circuitry.

[0051] 1.2 Multiplexing Structure of Electrical Transceiver Unit The electrical transceiver unit does not introduce additional sensor components, but directly reuses the four stainless steel needles mentioned above. The needles are connected to the back-end circuit through an independent shielded coaxial cable inside the base.

[0052] Electric field sensing mode configuration: Four needles form a four-terminal impedance measurement electrode array. The two outer needles are defined as current excitation electrodes, and the two inner needles are defined as voltage sensing electrodes. This Kelvin four-wire structure can effectively eliminate the influence of transmission cable impedance and electrode-soil contact resistance on the baseline drift of high-frequency conductivity measurement. The needle surface is electrochemically polished to reduce electrode polarization effect.

[0053] Thermal field excitation mode configuration: The stainless steel needle body is reused as a heating element by utilizing its fixed volume resistance and temperature coefficient of resistance. The two outer needle bodies serve as the heat source circuit. When a controlled current is applied, Joule heat is generated inside the needle body and diffuses radially to the surrounding soil layer. A miniature high-precision thermistor is pre-embedded inside the needle body. This thermistor is only used to monitor the background temperature of the soil layer to calibrate static parameters and does not participate in the calculation of dynamic thermal response.

[0054] 1.3. Conformal Integrated Structure of Acoustic Transceiver Unit The acoustic transceiver unit consists of a piezoelectric transceiver array conformally embedded inside the needle body.

[0055] Transducer selection and layout: PZT-5 piezoelectric ceramic is selected as the core component. The transmitting transducer is installed in the internal acoustic window position of the first needle body on the outside, and the receiving transducer is installed in the corresponding position of the fourth needle body on the outside. The center lines of the acoustic axes of the two are kept horizontally aligned to ensure that the main beam path passes laterally through the soil area to be measured surrounded by the metal needle body.

[0056] Multi-layer acoustic encapsulation: The transducer assembly is constructed in radial layers. A high-attenuation backing layer made of tungsten powder and epoxy resin is bonded to the back of the piezoelectric crystal to absorb back-radiated sound waves and suppress pulse tailing caused by crystal reverberation, thereby improving the time resolution of time-of-flight measurement. An acoustic matching layer is bonded to the front of the crystal, and its acoustic impedance is designed as the geometric mean of the acoustic impedance of the piezoelectric material and the acoustic impedance of the stainless steel shell to maximize the transmission efficiency of sound energy to the soil layer. The metal shell of the needle body is precisely thinned at the corresponding position of the transducer to form an acoustic transmission window. Specifically, in order to balance the acoustic transmission efficiency and the mechanical strength of the needle body, the acoustic transmission window is processed by micro-laser etching process. The standard wall thickness of the needle body sidewall is 0.5mm, and it is locally thinned to 0.15mm to 0.20mm in the acoustic window area.

[0057] To prevent the thin wall from cracking due to shear force when the needle is inserted into hard soil, a nano-alumina modified epoxy resin layer is filled between the piezoelectric transducer and the thinned metal inner wall. This filling layer not only serves as an acoustic matching layer, but also as a rigid support structure to bear the external radial pressure.

[0058] In addition, a diamond-like carbon hard film with a thickness of 2-3 μm is coated on the outer surface of the needle, including the acoustic window area, by physical vapor deposition to improve the wear resistance of the acoustic window area and prevent acoustic window erosion caused by long-term insertion and removal.

[0059] 2. Circuit Implementation Principle of Intelligent Measurement and Control Host

[0060] The intelligent measurement and control host contains a highly integrated hardware circuit layer, which is responsible for performing microsecond-level timing control and high signal-to-noise ratio signal processing.

[0061] 2.1 Signal Multiplexing Switching Circuit This circuit is located at the interface between the host and the probe and is the key to realizing hardware multiplexing.

[0062] Electrical channel switching: A low-on-resistance, high-isolation solid-state relay matrix is ​​used. According to timing logic, this matrix switches the connection state of the probe between the precision constant current source drive circuit and the RF impedance measurement front-end circuit. Transient voltage suppression diodes (TVS) are set at the switching nodes to prevent the back electromotive force generated by the inductive load during thermal excitation cutoff from damaging the high-sensitivity measurement front end.

[0063] Acoustic channel switching: A high-voltage analog switch is used. According to timing logic, the switch switches the connection state of the transducer between the power ultrasonic drive circuit and the low-noise preamplifier circuit.

[0064] 2.2 Driving and Acquisition Circuit

[0065] Electrical drive: A constant current source circuit with closed-loop feedback control is used to monitor the output current and load voltage in real time to ensure constant thermal power of the injection probe. The built-in high-precision analog-to-digital converter synchronously acquires voltage and current waveforms to calculate the total energy injected. .

[0066] Electrical Acquisition: The radio frequency impedance measurement front end is based on the principle of automatic balancing bridge. A 100MHz sinusoidal excitation signal is generated by a direct digital frequency synthesizer. The real and imaginary parts of the current and voltage signals are extracted by an orthogonal demodulator to calculate the complex impedance. The circuit has an automatic gain control function to adapt to the impedance changes of soil with different moisture contents. In order to extract the weak dielectric constant step signal under strong sound field interference, the electrical acquisition circuit in this embodiment introduces a phase-locked amplification mechanism.

[0067] Specifically, the cross-physical field excitation module adopts a timing strategy that alternates between burst pulses and detection windows. Although the acoustic radiation force field is macroscopically continuous, on a microsecond scale, the acoustic driving signal is modulated into a high-frequency pulse train with a duty cycle of 90%. Electrical measurements are only sampled for a very short time within the zero-crossing window of the acoustic driving signal.

[0068] Meanwhile, the electrical receiving front end is equipped with a differential cancellation circuit. This circuit utilizes a reference capacitor unaffected by the sound field disturbance—that is, the capacitor formed by the two needles when the sound radiation force is not activated—or an internal standard capacitor and the capacitor under test forming a differential pair. Common-mode suppression filters out electromagnetic background noise introduced by the coupling of the high-voltage acoustic drive circuit, thus ensuring that only the differential-mode signal caused by changes in the polarization state of the soil medium is output. .

[0069] Acoustic drive: The programmable high-voltage pulse generator uses an FPGA to control a high-voltage MOSFET push-pull drive stage, which boosts the voltage through a pulse transformer and outputs an excitation signal with a peak-to-peak value of 100V to the transmitting transducer. The drive waveforms include single pulses for velocity measurement, continuous waves for vibration regulation, and long pulse trains for acoustic radiation force excitation. The ultrasonic center frequency is in the range of 100kHz to 500kHz, which ensures both the penetration depth in moist soil and provides sufficient time resolution.

[0070] Acoustic acquisition: The receiving front end includes a low-noise preamplifier and a variable gain amplifier, a bandpass filter to filter out low-frequency mechanical noise and high-frequency electromagnetic interference, and a high-speed ADC to acquire the full waveform of the acoustic signal at a sampling rate of 50MSPS.

[0071] 3. Logic control and calculation implementation process

[0072] The logic control program running inside the main control unit coordinates the timing of each physical field and executes a multi-phase parameter collaborative decoupling algorithm.

[0073] 3.1 Contact State Adaptive Adjustment Stage

[0074] After measurement is initiated, the system first performs contact state conditioning, controlling the acoustic transducer to operate in a high-frequency mechanical vibration mode. Utilizing the thixotropic effect of the soil, it induces the rearrangement of soil particles around the probe, filling the microscopic contact gaps. Simultaneously, the electrical unit monitors the real part of the contact impedance between the electrodes in real time. The logic module runs a sliding window differential algorithm to calculate the rate of change of the contact impedance over time. When the absolute value of the rate of change is lower than a preset convergence threshold for five consecutive sampling periods, it is determined that a dense physical contact has been formed between the probe and the soil. The system immediately stops vibrating and locks the current stable impedance value as the system reference impedance. This is used for contact resistance compensation in subsequent conductivity measurements.

[0075] 3.2 Cross-physics field excitation and dynamic response acquisition

[0076] The system executes two sets of cross measurements sequentially according to a preset time sequence:

[0077] Thermo-acoustic coupling measurement: The system control electrical unit injects a constant current thermal pulse with a duration of 500 milliseconds into the soil layer, and the total energy is calculated by integration. After the thermal pulse ends, the acoustic unit is immediately switched to velocity measurement mode to continuously acquire the dynamic change curve of ultrasonic flight time as a function of temperature diffusion, and the maximum sound velocity drift caused by temperature rise is extracted. .

[0078] Acoustic-electric coupling measurement: After the dielectric thermal equilibrium is restored, the system controls the acoustic unit to emit a high-power ultrasonic standing wave train with a duration of 20 milliseconds to construct an acoustic radiation force field. At the start and end of the standing wave train emission, the high-speed acquisition function of the electrical unit is synchronously triggered to capture the transient step response of the real part of the dielectric constant and extract the change in dielectric constant induced by the acoustic field. .

[0079] 3.3 Multiphase parameter cooperative decoupling calculation

[0080] The decoupling module has a built-in physical model group that performs two-level inversion calculations.

[0081] First-stage decoupling (water content and bulk density):

[0082] The input is the initial speed of sound. Sound speed drift and injecting energy .

[0083] The algorithm combines the following two physical equations:

[0084] (1) Static sound speed model (corrected form of Wood's equations): correlation With volumetric water content In-situ dry density .

[0085]

[0086] When constructing the first relational model, an effective saturation parameter is introduced, or the equivalent elastic modulus model at high frequency is adopted to reduce the influence of the gas phase, taking advantage of the characteristic that high-frequency ultrasound mainly propagates in the liquid phase and skeleton.

[0087] As is known to those skilled in the art, the equivalent bulk modulus coefficient of soil is related to its texture. The equivalent bulk modulus coefficient of the soil skeleton depends on the soil texture type and can be obtained by consulting a geological handbook or a pre-set empirical value. Soil particle density, also known as soil particle specific gravity, is usually taken as a standard empirical value. Let be the pore water density, and take it as a constant. .

[0088] (2) Dynamic thermoacoustic response model: correlation Similar to the heat capacity properties of the medium, this heat capacity property is also determined by... and Decide.

[0089]

[0090] in The sound velocity temperature sensitivity coefficient of water, The system thermal efficiency factor is obtained through factory calibration using standard samples with known heat capacities, such as agarose gels, and stored in the main unit. , Let be the specific heat capacity parameter, where The preset average specific heat capacity constant of the soil is used, for example, a typical value of 0.8-0.9 kJ / (kg·K), or an empirical value can be retrieved from the database after selecting the soil type through the user interface.

[0091] The Newton-Raphson iterative method was used to solve the system of equations to obtain the accurate volumetric water content. and in-situ dry bulk density .

[0092] Considering the difference between the actual thermal resistance of the soil and the probe and that of the agar gel used for calibration, this embodiment introduces a contact thermal resistance correction factor. Regarding the system thermal efficiency factor Perform in-situ correction.

[0093] The specific correction method is as follows: In the first 100 milliseconds after the thermal disturbance is injected, when the heat has not yet diffused into the deep soil, the temperature rise is mainly controlled by the thermal resistance of the contact interface. The system collects the slope of the transient temperature rise curve of the thermistor inside the needle body. .

[0094] The measured slope The theoretical slope under ideal contact conditions stored in the host database Perform comparisons and construct correction functions:

[0095]

[0096] in The empirical index, determined by the probe geometry, is used in subsequent calculations, with the modified index applied. Replace the original This eliminates the error in estimating injected energy caused by loose soil texture or poor contact.

[0097] Second-stage decoupling (bound water and conductivity):

[0098] Input quantity is Initial apparent conductivity and the first-level decoupling obtained and .

[0099] The algorithm is based on the acoustic-electric coupling model:

[0100]

[0101] In the formula: The acoustic-electric coupling coefficient represents the dielectric increment generated by the polarization of bound water under unit sound intensity, and is related to the Zeta potential on the surface of soil particles.

[0102] The intensity of the acoustic radiation force field is calculated from the driving voltage power of the acoustic transmitter and the electroacoustic conversion efficiency of the transducer.

[0103] By combining the multiphase dielectric mixing model with the extended Archie's law model, the bound water content was separated. Furthermore, the initial apparent conductivity is subtracted from the conductivity obtained by... The surface conductivity contribution caused by the pore water is used to invert the true conductivity of the pore water. .

[0104] in The pore water conductivity correction factor is approximated using an empirical formula in this embodiment:

[0105]

[0106] in These are the experimental fit coefficients;

[0107] Furthermore, the multiphase dielectric hybrid model specifically adopts the complex refractive index model, with the following expression:

[0108]

[0109] In the formula:

[0110] The measured complex permittivity of the mixed medium; Soil porosity is calculated from the parameters obtained from the first-stage decoupling, i.e. ; , , $\epsilon_{air}$ are the dielectric constants of the soil solid framework, free water, bound water, and air, respectively. Take 80, Take 1, and Take an empirical constant or obtain it through calibration.

[0111] Ultimately, the system displays the result through a human-computer interaction interface. , , , With four independent parameters and automatic storage of measurement logs containing raw waveform data, the above implementation method enables decoupled measurement of complex soil physical parameters on a portable device.

[0112] 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 portable intelligent measuring instrument for natural soil moisture content based on multi-source sensor fusion, characterized in that, Includes a composite probe assembly with physical connections and an intelligent measurement and control host; The composite probe assembly is configured to be inserted into the soil layer to be tested to construct a multiphysics testing environment, and integrates the following: An electrical transceiver unit is used to construct an alternating electric field and a thermal diffusion field in the soil layer to be tested, and to sense electrical parameters; An acoustic transceiver unit is used to construct an ultrasonic propagation field and a mechanical vibration field in the soil layer to be tested, and to sense acoustic parameters. The intelligent monitoring and control host includes: The contact state adaptive adjustment module is configured to coordinately control the acoustic transceiver unit to generate mechanical vibration and the electrical transceiver unit to monitor the contact impedance before measurement, until a physical contact interface between the probe and the soil layer that meets the preset convergence conditions is established. The cross-physical field excitation module is configured to control the electrical transceiver unit to inject thermal disturbance energy into the soil layer to be tested according to a preset timing sequence, and to control the acoustic transceiver unit to emit acoustic radiation force field into the soil layer to be tested. The multidimensional dynamic response acquisition module is configured to simultaneously acquire dynamic response data of sound velocity during thermal disturbance energy action and transient response data of dielectric constant during acoustic radiation force field action. The multiphase parameter collaborative decoupling module is configured to jointly calculate and output the volumetric water content, in-situ dry unit weight, bound water content and pore water true conductivity of the soil layer under test based on the dynamic response data of sound velocity and the transient response data of dielectric constant. The contact state adaptive adjustment module includes: The acoustic transceiver unit is driven to operate in a preset high-frequency mode, and the thixotropic effect is used to induce soil particles around the probe to fill the interface voids. The electrical transceiver unit monitors the contact impedance value and its rate of change between the electrodes in real time. When the rate of change of the contact impedance value is lower than the preset convergence threshold, it is determined that the contact interface has been densified, and the vibration drive of the acoustic transceiver unit is immediately stopped. The data collected by the multi-dimensional dynamic response acquisition module specifically includes: Initial sound velocity, initial apparent dielectric constant, and initial apparent conductivity measured under initial steady state; The maximum drift of the sound velocity in the mixed medium in the soil layer under test as the temperature increases after the injection of thermal disturbance energy. The transient step change in the apparent dielectric constant of the soil layer under test due to the double electric layer disturbance at the instant the acoustic radiation force field is turned on and off. The multiphase parameter collaborative decoupling module includes a first-dimensional decoupling unit, which is configured as follows: Based on the static mapping relationship between the sound velocity of the mixed medium and the volumetric water content and in-situ dry bulk density, a first relationship model is constructed. A second relationship model is constructed based on the dynamic thermosensitive response relationship between the maximum drift of the sound velocity in the mixed medium and the injected thermal disturbance energy, volumetric water content and in-situ dry bulk density. Solve the first relational model and the second relational model simultaneously to obtain the volumetric water content and in-situ dry unit weight of the soil layer to be tested.

2. The portable intelligent measuring instrument for natural soil moisture content based on multi-source sensor fusion according to claim 1, characterized in that, The composite probe assembly includes multiple parallel-arranged corrosion-resistant alloy needles; The electrical transceiver unit is composed of the alloy needle body itself, which serves as both a measuring electrode for conductivity and dielectric constant and a heating resistor for Joule heating. The acoustic transceiver unit includes a piezoelectric transducer array conformally embedded inside or at the root of the alloy needle body, and the acoustic wave propagation path of the piezoelectric transducer array traverses the test area surrounded by the alloy needle body.

3. The portable intelligent measuring instrument for natural soil moisture content based on multi-source sensor fusion according to claim 2, characterized in that, The multiphase parameter collaborative decoupling module further includes a second-dimensional decoupling unit, which is configured as follows: The transient step change in the apparent dielectric constant is used to characterize the polarization response of bound water molecules and double-layer ions to the acoustic radiation force field. An acoustic-electric coupling model was established to describe the relationship between transient step changes and acoustic radiation force field intensity, bound water content, and pore water ion concentration. The volumetric water content and in-situ dry unit weight obtained from the first dimension decoupling unit are substituted into the acoustic-electric coupling model and the multiphase dielectric mixing model to separately calculate the bound water content and the true electrical conductivity of pore water in the soil layer to be tested.

4. The portable intelligent measuring instrument for natural soil moisture content based on multi-source sensor fusion according to claim 3, characterized in that, The intelligent measurement and control host also includes a signal multiplexing and switching circuit, which is connected between the composite probe assembly and the cross-physical field excitation module. It further includes: The electrical transceiver unit is time-division multiplexed between the DC heating drive circuit and the high-frequency impedance measurement circuit. The acoustic transceiver unit performs time-division multiplexing switching between the high-power oscillation drive circuit and the pulsed ultrasonic transceiver circuit.

5. The portable intelligent measuring instrument for natural soil moisture content based on multi-source sensor fusion according to claim 4, characterized in that, The intelligent measurement and control host is also configured to store the stable contact impedance value when the contact interface is densified as a system reference parameter, which is used to eliminate the error influence of contact resistance when calculating the true conductivity of pore water in the future.

6. The portable intelligent measuring instrument for natural soil moisture content based on multi-source sensor fusion according to claim 5, characterized in that, In the first relational model, the sound velocity of the mixed medium is defined as a function of the equivalent elastic modulus and equivalent density of the mixture composed of soil skeleton, pore water and pore air; in the second relational model, the change in the sound velocity of the mixed medium is defined as the contribution of the thermal sensitivity of the sound velocity of pore water with temperature change, and this change is inversely proportional to the total heat capacity of the soil layer to be tested.

7. The portable intelligent measuring instrument for natural soil moisture content based on multi-source sensor fusion according to claim 6, characterized in that, The intelligent monitoring and control host also includes a human-machine interaction display unit, which is used to intuitively display multiple soil physical parameters calculated by the multi-phase parameter collaborative decoupling module, as well as display the current probe contact status indication information.

Images