Method and system for determining soil particle size and gradation based on ultrasonic sensors

Abstract

The application belongs to the field of soil classification and identification in engineering geology, and particularly relates to a method and system for measuring soil layer particle size and grading based on an ultrasonic sensor, aiming to solve the problem of accurate soil layer classification and naming. The application adopts high-frequency and low-frequency ultrasonic waves to alternately emit to the soil layer to be measured. After synchronously capturing two kinds of reflected signals, the scattering characteristics of the first diameter particles and the penetration characteristics of the second diameter particles are extracted respectively. The two kinds of characteristics are fused to generate a composite particle size distribution curve, which is compared with a pre-stored soil classification and identification model to infer the particle size and grading of the soil layer. The method is implemented by an ultrasonic acquisition device of an engineering geology in-situ test equipment, the ultrasonic emission interval is dynamically adjusted according to the penetration rate of the equipment, continuous acquisition and real-time measurement of the vertical stratum are realized, and the entire stratum profile scanning is completed. The application solves the technical problems of synchronous and accurate detection of coarse and fine particles and in-situ continuous measurement.

Description

Technical Field

[0001] This invention belongs to the field of soil classification and identification in engineering geology, and specifically relates to a method and system for determining the particle size and gradation of soil layers based on ultrasonic sensors. Background Technology

[0002] Ultrasonic sensors primarily work by utilizing the properties of ultrasound. Specifically, they detect objects by emitting ultrasonic signals and receiving the reflected signals. When an ultrasonic signal encounters an object being detected, it generates a reflected echo. After receiving the reflected signal, the sensor processes its intensity and timing to determine information such as the object's position, distance, and shape.

[0003] An ultrasonic sensor is a sensor that converts ultrasonic signals into other energy signals (usually electrical signals). Ultrasonic waves are mechanical waves with vibration frequencies higher than 20 kHz. Due to their unique physical properties, ultrasonic sensors have wide applications in the medical, industrial, environmental monitoring, and materials science fields. For example, ultrasonic sensors can be used for fingerprint recognition. The transmitter in the ultrasonic sensor emits ultrasonic pulses, which are reflected when they encounter the surface of the finger and are subsequently captured by the same sensor or another receiver.

[0004] In engineering geology, soil layers are named based on their physical, chemical, and mechanical properties, as well as their environment and engineering requirements. A soil layer is a layer of soil roughly parallel to the ground surface in a soil profile, possessing unique physical, chemical, and biological characteristics. Soil formation is influenced by various factors, including soil-forming processes, topography, climate, and human activities. Each soil layer differs in color, structure, and texture, reflecting variations in its characteristics and composition. In engineering geology, soil layers are named by taking samples from them for classification.

[0005] In engineering geology, soil is classified into categories such as silt, fine sand, medium sand, coarse sand, angular gravel, and rounded gravel based on its particle size and distribution. Based on different plasticity indices, soil can be classified into silt, silty clay, and clay. Different regions and industries may use different names for soil classification, but the plasticity index and particle size distribution are still the primary indicators.

[0006] The ultrasonic reflection properties of soil can comprehensively reflect the particle size structure of sandy soils. Different sandy soils exhibit different ultrasonic characteristics, making it possible to classify sandy soil layers using ultrasonic data. Ultrasonic analysis is a non-destructive testing method that does not require complex soil pretreatment and can be performed without altering the original state of the soil. This method is not only low-cost but also fast, providing a novel method for soil classification and naming in engineering geology.

[0007] Based on this, the present invention proposes a method and system for determining the particle size and gradation of soil particles based on ultrasonic sensors. Summary of the Invention

[0008] To address the aforementioned problems in the prior art, namely how to establish the correspondence between the ultrasonic reflection characteristics of different sands and their physical properties (such as particle size and structure) in order to achieve accurate soil layer classification and naming, this invention provides a method and system for determining the particle size and gradation of soil layers based on ultrasonic sensors.

[0009] In a first aspect, the present invention provides a method for determining the particle size and gradation of soil particles based on an ultrasonic sensor, the method comprising:

[0010] High-frequency and low-frequency ultrasonic waves are alternately emitted into the soil layer to be tested. High-frequency ultrasonic waves are used to excite the scattered echo of fine particles on the surface, while low-frequency ultrasonic waves are used to penetrate the coarse particle layer to obtain the deep reflected signal.

[0011] Synchronously capture reflected echo signals, including high-frequency and low-frequency reflected signals;

[0012] Scattering characteristics of particles with a first diameter are extracted from high-frequency reflected signals, and penetration characteristics of particles with a second diameter are extracted from low-frequency reflected signals; wherein, the first diameter is smaller than the second diameter.

[0013] The particle scattering characteristics and particle penetration characteristics are combined to generate a composite particle size distribution curve;

[0014] The composite particle size distribution curve is compared with the pre-existing soil classification and determination model to estimate the particle size and gradation of the soil layer until the continuous vertical strata are collected.

[0015] The method is implemented by an ultrasonic acquisition device mounted on an in-situ engineering geological testing equipment. The ultrasonic emission interval is dynamically adjusted according to the equipment penetration rate to achieve continuous vertical stratum acquisition and real-time measurement.

[0016] Furthermore, the scattering characteristics of particles with the first diameter are extracted from the high-frequency reflection signal, and the penetration characteristics of particles with the second diameter are extracted from the low-frequency reflection signal. The method is as follows:

[0017] The scattering characteristics of the first diameter particle are obtained by performing a short-time Fourier transform on the high-frequency reflected signal.

[0018] Envelope detection analysis is performed on the low-frequency reflected signal to obtain the penetration characteristics, which include the penetration depth of the second diameter particle and the reflection energy attenuation rate.

[0019] Furthermore, the composite particle size distribution curve is compared with the pre-existing soil classification and determination model to estimate the particle size and gradation of the soil layer until continuous vertical stratum sampling is completed. The method is as follows:

[0020] The composite particle size distribution curve is compared and analyzed with the pre-stored soil classification and determination model. Based on the pre-constructed frequency-particle size mapping relationship model, the error is corrected, and the particle size and particle size distribution of the soil layer are estimated.

[0021] Furthermore, the reflected echo signals, including high-frequency and low-frequency reflected signals, are captured simultaneously. The attenuation characteristics of signals at different frequencies are compared to identify heterogeneous inclusions in the soil layer, and secondary verification is performed in conjunction with geotechnical parameters.

[0022] Furthermore, the geotechnical parameters include at least one of organic matter content, void ratio, or moisture content.

[0023] In a second aspect, the present invention provides a system for determining soil particle size and gradation based on an ultrasonic sensor, and a method for determining soil particle size and gradation based on an ultrasonic sensor. The system includes:

[0024] An ultrasonic transmitting and receiving module is configured as a multi-frequency ultrasonic transmitting array and an ultrasonic receiving array. The multi-frequency ultrasonic transmitting array is used to alternately transmit high-frequency ultrasonic waves and low-frequency ultrasonic waves to the soil layer to be tested. The high-frequency ultrasonic waves are used to excite the scattered echoes of the surface fine particles, and the low-frequency ultrasonic waves are used to penetrate the coarse particle layer to obtain the deep reflection signals. The ultrasonic receiving array is used to synchronously capture the reflected echo signals, including high-frequency reflection signals and low-frequency reflection signals.

[0025] The data processing module is configured to extract scattering features of particles with a first diameter from high-frequency reflection signals and to extract penetration features of particles with a second diameter from low-frequency reflection signals; wherein the first diameter is smaller than the second diameter; and to fuse the particle scattering features and particle penetration features to generate a composite particle size distribution curve.

[0026] The data output module is configured to compare the composite particle size distribution curve with the pre-stored soil classification and determination model to estimate the particle size and gradation of the soil layer until the continuous vertical stratum data collection is completed.

[0027] The wireless communication module is configured to transmit high-frequency and low-frequency reflected signals from the ultrasonic transmitting and receiving module to the data processing module.

[0028] Furthermore, the ultrasonic transmitting and receiving module and the wireless communication module are mounted inside the data acquisition section. One end of the data acquisition section is connected to the static cone probe rod, and the other end of the data acquisition section is connected to the static cone probe.

[0029] Furthermore, the multi-frequency ultrasonic transmitting array and the ultrasonic receiving array are enclosed within a protective cover, which is installed within the data acquisition section.

[0030] Furthermore, the multi-frequency ultrasonic transmitting array and the ultrasonic receiving array are mounted at one end of the circuit board, and the other end of the circuit board is connected to the power supply and communication lines of the battery and the static penetration probe, and the power supply and communication lines are used for data transmission.

[0031] Furthermore, the gaps between the multi-frequency ultrasonic transmitting array and the ultrasonic receiving array and the protective cover are filled with an electronically waterproof adhesive that matches the acoustic impedance.

[0032] The beneficial effects of this invention are:

[0033] This invention achieves targeted detection of particles of different sizes (fine and coarse) by alternately emitting high-frequency and low-frequency ultrasonic waves to capture the scattering characteristics of fine surface particles and the penetration characteristics of coarse deep particles, respectively. High-frequency ultrasonic waves sensitively respond to the scattering signals of micron-sized fine particles, while low-frequency ultrasonic waves effectively penetrate centimeter-sized coarse particle layers and acquire deep reflection information, significantly expanding the detectable particle size range.

[0034] This invention employs ultrasonic reflection analysis technology, eliminating the need for soil sampling or chemical pretreatment. Measurements are performed directly on-site using an ultrasonic probe mounted on a penetration tester. This avoids the disturbance to the soil structure caused by traditional sieving and sedimentation methods, ensuring that particle size distribution data accurately reflects the in-situ state of the strata.

[0035] This invention dynamically adjusts the ultrasonic transmission interval based on the real-time rate of the penetration device, ensuring that the ultrasonic signal density matches the formation change rate during vertical penetration. For example, the transmission interval is shortened during high-speed penetration to obtain high-resolution data, while the interval is extended during low-speed penetration to reduce redundancy, achieving continuous and fault-free acquisition of vertical formation particle size distribution.

[0036] This invention generates a composite particle size distribution curve by fusing scattering and penetration features, comprehensively reflecting the multi-scale particle structure of the soil layer (such as fine particle content and coarse particle distribution morphology). Combined with a pre-stored soil classification model (based on parameters such as plasticity index and particle size distribution), the soil layer name (such as silt, coarse sand, gravel, etc.) can be accurately estimated, reducing the risk of misjudgment from single feature analysis.

[0037] Compared to laboratory analysis methods (which take hours to days), this invention enables ultrasonic data acquisition and processing to be completed in seconds, significantly improving detection efficiency. It also eliminates the costs of sample transportation and pretreatment, providing a real-time, low-cost particle size distribution monitoring solution for large-scale engineering surveys (such as railway subgrades and reservoir dams), supporting intelligent geological decision-making. Attached Figure Description

[0038] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0039] Figure 1 This is a schematic flowchart of a method for determining the particle size and gradation of soil particles based on an ultrasonic sensor according to the present invention.

[0040] Figure 2 This is a schematic diagram of an ultrasonic sensor-based system for determining soil particle size and gradation, which includes an ultrasonic transmitting and receiving module and a data communication module.

[0041] Figure 3 This is a schematic diagram of a protective cover in a soil particle size and gradation system based on ultrasonic sensors;

[0042] Figure 4 This is a schematic diagram of a multi-frequency ultrasonic transmitting array and ultrasonic receiving array in a system for determining soil particle size and gradation based on ultrasonic sensors. Detailed Implementation

[0043] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0044] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0045] This invention provides a method for determining the particle size and gradation of soil layers based on an ultrasonic sensor. The method includes:

[0046] Step S10: Alternately transmit high-frequency and low-frequency ultrasonic waves to the soil layer to be tested. The high-frequency ultrasonic waves are used to excite the scattered echo of the fine particles on the surface, and the low-frequency ultrasonic waves are used to penetrate the coarse particle layer to obtain the deep reflection signal.

[0047] Step S20: Synchronously capture the reflected echo signals, including high-frequency reflected signals and low-frequency reflected signals;

[0048] Step S30: Extract the scattering features of particles with a first diameter from the high-frequency reflection signal, and extract the penetration features of particles with a second diameter from the low-frequency reflection signal; wherein, the first diameter is smaller than the second diameter.

[0049] Step S40: Fuse the particle scattering characteristics and particle penetration characteristics to generate a composite particle size distribution curve;

[0050] Step S50: Compare the composite particle size distribution curve with the pre-stored soil classification and determination model to estimate the particle size and gradation of the soil layer until the vertical strata are continuously collected.

[0051] The method is implemented by an ultrasonic acquisition device mounted on an in-situ engineering geological testing equipment. The ultrasonic emission interval is dynamically adjusted according to the equipment penetration rate to achieve continuous vertical stratum acquisition and real-time measurement.

[0052] To more clearly explain the present invention's method for determining soil particle size and gradation based on ultrasonic sensors, the following is a detailed explanation. Figure 1 The steps in the embodiments of the present invention will be described in detail below.

[0053] A method for determining soil particle size and gradation based on an ultrasonic sensor according to the first embodiment of the present invention includes steps S10-S50, each step of which is described in detail below:

[0054] Step S10: Alternately transmit high-frequency and low-frequency ultrasonic waves to the soil layer to be tested. The high-frequency ultrasonic waves are used to excite the scattered echo of the fine particles on the surface, and the low-frequency ultrasonic waves are used to penetrate the coarse particle layer to obtain the deep reflection signal.

[0055] In this embodiment, high-frequency and low-frequency ultrasonic waves are based on multi-frequency ultrasonic transmission control. Specifically, two types of ultrasonic waves are alternately transmitted to the soil layer to be tested through a programmable multi-frequency ultrasonic transmission array 16.

[0056] High-frequency ultrasound (frequency range: 1-5MHz): excites the scattered echoes of fine surface particles (such as silt and clay) and captures the reflection characteristics of the particle surface.

[0057] Low-frequency ultrasound (frequency range: 20-100kHz): penetrates coarse-grained layers (such as gravel and coarse sand) to obtain deep reflection signals and energy attenuation characteristics.

[0058] Its transmission logic is to dynamically switch frequencies according to preset timing or real-time commands (for example, first transmit a high-frequency pulse, and then transmit a low-frequency pulse after a 1ms interval) to ensure that dual-frequency signals cover soil layers with different particle sizes.

[0059] In this embodiment, the penetration rate of the ultrasonic transmitting and receiving module 3 is monitored in real time by the control circuit, and the transmission interval is dynamically adjusted based on the rate. For example, when the penetration rate increases, the transmission interval is shortened to ensure vertical continuous sampling density.

[0060] Step S20: Synchronously capture the reflected echo signals, including high-frequency reflected signals and low-frequency reflected signals;

[0061] In this embodiment, the ultrasonic receiving array 17 synchronously captures the high-frequency and low-frequency echo signals reflected from the soil layer under test. The ultrasonic receiving array 17 is made of piezoelectric ceramic material. After the transmitting array alternately transmits high-frequency and low-frequency ultrasonic waves to the soil layer, the receiving array receives the dual-frequency reflected signals reflected from the soil interface in real time. The high-frequency reflected signal mainly contains the scattering characteristics of the surface fine particles (such as silt and clay), while the low-frequency reflected signal carries the penetrating reflection and energy attenuation information of the coarse-grained layer (such as gravel and coarse sand).

[0062] The received signal undergoes preliminary processing by the control circuit, including signal amplification and noise filtering. The reception time of each set of reflected signals is precisely marked and dynamically correlated with the penetration rate of the ultrasonic transmitting and receiving module (3). The time-stamped dual-frequency echo signal is transmitted in real time to the ground data processing module, providing a synchronous data source for subsequent frequency domain feature fusion analysis.

[0063] In this embodiment, the differences in the characteristics of the captured dual-frequency signals imply information about the soil structure: the rapid attenuation of the high-frequency echo indicates a fine-particle-rich layer, the stable penetration of the low-frequency echo reflects the distribution of a coarse-particle layer, and the abnormal fluctuations of the dual-frequency signals may reveal the presence of heterogeneous inclusions (such as ginger stones or organic matter clumps).

[0064] Step S30: Extract the scattering features of particles with a first diameter from the high-frequency reflection signal, and extract the penetration features of particles with a second diameter from the low-frequency reflection signal; wherein, the first diameter is smaller than the second diameter.

[0065] In this embodiment, short-time Fourier transform (STFT) analysis is performed on the high-frequency reflected signal captured by the ultrasonic receiving array 17 to extract the scattering intensity characteristics of the surface fine particles. The scattering intensity of the high-frequency signal is directly related to the particle size distribution of the fine particles, and its signal attenuation slope reflects the enrichment degree of particles with a particle size less than 0.075 mm. By quantifying the scattering intensity peaks, a particle size distribution histogram of the fine particle layer is generated, and anomalous scattering regions, such as intensity abrupt change points, are marked. These regions may indicate local changes in organic matter or porosity.

[0066] Envelope detection algorithms were used to process low-frequency reflected signals to analyze the penetration depth and reflection energy attenuation rate of coarse particles (such as gravel and coarse sand). The penetrating characteristics of low-frequency signals enable them to penetrate deep coarse-particle layers, and their energy attenuation rate is negatively correlated with the content of particles larger than 2 mm. By calculating the slope of the time-domain envelope of the low-frequency echo, the density and gradation continuity of the coarse-particle layer were quantified. If irregular distortion of the envelope was detected, it was determined to be evidence of the presence of deep heterogeneous inclusions, such as calculi or cementitious materials.

[0067] Step S40: Fuse the particle scattering characteristics and particle penetration characteristics to generate a composite particle size distribution curve;

[0068] In this embodiment, the high-frequency scattering features extracted in step S30 are weighted and fused with the low-frequency penetration features. The scattering intensity features of the high-frequency signal are given a higher weight to characterize the distribution pattern of fine particles in the surface layer (0-5cm depth); the energy attenuation rate features of the low-frequency signal are given a second-highest weight to characterize the gradation continuity of coarse particles in the deeper layer (5-20cm). The weighting coefficients are dynamically adjusted based on a pre-stored frequency-particle size mapping model, which is established by calibrating the ultrasonic response characteristics of different types of soil in the laboratory.

[0069] The fused dual-frequency data generates a composite particle size distribution curve. The horizontal axis of the curve represents the particle size (unit: mm), and the vertical axis represents the vertical depth (unit: m). By linearly superimposing the high-frequency scattering intensity and the low-frequency attenuation rate, the particle size distribution parameters of the continuous vertical profile are directly output. During the curve generation process, the test deviation caused by changes in soil moisture content or differences in acoustic impedance of electronic waterproof adhesive (14) is automatically corrected. The correction logic is executed based on the frequency-particle size mapping relationship in the pre-stored database.

[0070] The composite curve synchronously marks the location of heterogeneous inclusions. When a mismatch occurs between the high-frequency scattering intensity and the low-frequency attenuation rate at a specific depth (e.g., a sudden drop in high-frequency signal while the low-frequency signal remains stable), it indicates the presence of a coarse-grained interlayer (such as gravel). If both frequency signals exhibit irregular fluctuations, it is marked as a potential organic matter agglomerate or calcite, triggering a geotechnical parameter cross-validation process (e.g., calling laboratory organic matter content data for auxiliary determination). The final generated composite particle size distribution curve is displayed in real time through the data output module, allowing users to output soil particle size curves and inclusion distribution maps as needed.

[0071] Step S50: Compare the composite particle size distribution curve with the pre-stored soil classification and determination model to estimate the particle size and gradation of the soil layer until the vertical strata are continuously collected.

[0072] In this embodiment, the composite particle size distribution curve generated in step S40 is compared with a pre-stored soil classification model. This model is established through geotechnical laboratory calibration. The specific process is as follows: First, ultrasonic tests are performed on various standard soil samples (such as silt, fine sand, coarse sand, gravel, etc.) in the laboratory, and their physical indicators (including particle size distribution curve, void ratio, organic matter content, etc.) are recorded simultaneously. Second, a feature matching algorithm is used to fit the mapping relationship between ultrasonic features and geotechnical parameters, generating a frequency and particle size response database and classification thresholds. During the comparison process, the morphological features of the composite curve (such as the slope of the fine particle proportion and the peak value of coarse particle enrichment) are matched with the standard gradation curve in the model for similarity, and the best-fit soil layer classification result is output.

[0073] The presumption logic includes a dual verification mechanism: if the composite curve shows that the proportion of particles smaller than 0.075 mm is greater than 85%, it is determined to be silt or clay; if particles larger than 2 mm are continuously enriched and the decay rate is lower than the threshold, it is classified as gravel layer.

[0074] Meanwhile, the composite particle size distribution curve is compared and analyzed with the pre-stored soil classification and determination model. Based on the pre-constructed frequency and particle size mapping relationship model, the error is corrected, and the particle size and particle size distribution of the soil layer are estimated.

[0075] Specifically, the model automatically identifies anomalous marker regions (such as abrupt changes in dual-frequency signals) in the composite curve, calls a pre-stored library of heterogeneous inclusion features (such as the frequency response fingerprint of ginger stones) for secondary verification, and combines geotechnical parameters (such as organic content data) to correct the classification results.

[0076] The final inference results are displayed in real time through the data output module, including the soil layer name (e.g., "medium sand with gravel layer"), particle size distribution range, and inclusion warning information. For vertical continuous test data, the system outputs the stratigraphic section particle size curve according to user requirements, and uses the difference in gradation between adjacent layers to help divide the soil layer sequence (e.g., the coarse-fine particle transition interface marks the stratigraphic boundary).

[0077] The method is implemented by an ultrasonic acquisition device mounted on an in-situ engineering geological testing equipment. The ultrasonic emission interval is dynamically adjusted according to the equipment penetration rate to achieve continuous vertical stratum acquisition and real-time measurement.

[0078] Although the steps in the above embodiments are described in the above order, those skilled in the art will understand that in order to achieve the effect of this embodiment, different steps do not need to be executed in such an order. They can be executed simultaneously (in parallel) or in a reverse order. These simple variations are all within the protection scope of this invention.

[0079] The second embodiment of the present invention proposes a method for determining the particle size and gradation of soil layers based on ultrasonic sensors. Building upon the method in the first embodiment, this method dynamically adjusts the ultrasonic emission interval according to the equipment penetration rate to achieve continuous vertical stratum acquisition and real-time measurement. Specifically, it includes:

[0080] Real-time acquisition of penetration rate; switching processing mode based on preset first and second rate thresholds.

[0081] When the penetration rate is less than or equal to the first rate threshold, the scattering characteristics of the first diameter particle are extracted from the high-frequency reflection signal as the first feature, and the penetration characteristics of the second diameter particle are extracted from the low-frequency reflection signal as the second feature.

[0082] When the penetration rate is greater than the first rate threshold and less than or equal to the second rate threshold, the main frequency peak of the high-frequency reflection signal is extracted as the first feature, and the inflection point feature of the low-frequency reflection signal is extracted as the second feature.

[0083] When the penetration rate is greater than the second rate threshold, the point of sudden drop in scattering intensity is matched by the pre-stored frequency response feature template as the first feature, and the penetration energy inflection point is extracted as the second feature.

[0084] By combining the first feature and the second feature corresponding to the current penetration rate, a composite particle size distribution curve is generated;

[0085] The composite particle size distribution curve is compared with the pre-existing soil classification and determination model to estimate the particle size and gradation of the soil layer until the vertical strata are continuously collected.

[0086] In this embodiment, the first rate threshold is preferably ≤2cm / s, and the second rate threshold is preferably ≤10cm / s.

[0087] In this embodiment, when the penetration rate changes abruptly, the frequency of the high-frequency and low-frequency ultrasonic waves is increased by a preset multiple. Based on the historical particle size distribution similarity data of adjacent layers, linear interpolation is used to generate a transition curve when the particle size difference between adjacent layers does not exceed the tolerance threshold. When a drastic change in particle size is detected, the output is frozen and manual intervention is requested.

[0088] The penetration rate mutation is defined as the change in penetration velocity per unit time exceeding a set threshold. In this embodiment, the set threshold is set to 5 cm / s. 2 .

[0089] A drastic change in particle size is indicated when the weighted average particle size of the current sampling layer (or point) exceeds a preset multiple threshold compared to the corresponding value of the previous effective sampling layer (or point).

[0090] In this embodiment, based on the reconstruction data of historical grain size distribution similarity between adjacent layers, when the grain size difference between adjacent layers does not exceed the tolerance threshold, linear interpolation is used to generate a transition curve. The method is as follows:

[0091] When the penetration rate exceeds the second rate threshold, a real-time analysis window is established by dynamically calling pre-stored historical grain size distribution data from adjacent strata. A comprehensive similarity score is formed by weighted calculation of the relative change in median grain size, the absolute difference in gradation uniformity coefficient, and the cumulative distribution curve morphology differences. When the score does not exceed the preset tolerance threshold, linear interpolation transition of key grain size parameters is automatically performed within the depth range of adjacent measurement points, and a continuous gradation curve is reconstructed based on the Fuller distribution model. At the same time, the rate of change of high-frequency scattering intensity and the low-frequency penetration energy attenuation value are monitored in real time. When both are lower than the preset gradient constraint threshold and the prediction deviation from the reconstructed curve is less than the tolerance range, a smoothly transitioned vertical stratigraphic gradation map is output. If any monitored value exceeds the limit, an inhomogeneous inclusion alarm is triggered and the process is interrupted. This reconstruction process achieves millisecond-level response through hardware acceleration and stores feature parameters in a lightweight metadata format to reduce system load.

[0092] More specifically, it includes the following 5 stages:

[0093] In the dynamic data management phase, the system caches the complete dataset of the 10 most recent valid measurement points in real time (including ultrasonic signals, particle size distribution curves, key particle size parameters, and depth coordinates). When a penetration rate exceeding 10 cm / s is detected, the historical data comparison function is automatically activated. A depth analysis window (typically within ±3 measurement points / 6 cm) is constructed centered on the previous and subsequent measurement points to provide a benchmark framework for subsequent similarity determination.

[0094] Intelligent similarity decision-making stage: A weighted algorithm is used to comprehensively evaluate the stratigraphic continuity between adjacent measuring points: First, the median grain size D is calculated. 50 The relative change (60%), the absolute difference of the superimposed gradation uniformity coefficient (30%), and the overall morphological difference of the cumulative distribution curve (10%) are considered. When the comprehensive difference score is ≤0.15 tolerance threshold, it is determined to be a continuously gradually changing stratum and the interpolation process is initiated; if it exceeds the threshold, the freeze alarm mechanism is triggered and the case is transferred to manual processing.

[0095] Transition curve construction stage: Within the depth range of adjacent measurement points (e.g., 6cm interval), perform multi-level interpolation with a resolution of 1mm: First, for the key particle size parameter (D... 10 / D 30 / D 60 Linear transition calculations are performed on the discrete parameters (etc.), and then the discrete parameters are inverted into continuous gradation curves using the Fuller distribution model. Corresponding particle distribution data is generated for each millimeter of depth, forming a fault-free gradient stratigraphic map.

[0096] Real-time physical verification stage: The transition curve must simultaneously meet the gradual constraint that the rate of change of high-frequency scattering intensity is ≤5 dB / cm, and the deviation between the low-frequency penetration energy attenuation value and the curve prediction value is <20%. If any condition is exceeded, an "inhomogeneous interference" alarm will be triggered and the process will be interrupted, and the confidence level of the corresponding section will be downgraded to medium.

[0097] Hardware integration and optimization phase: The interpolation algorithm is hardware-accelerated using an FPGA chip, ensuring that the reconstruction of a 6cm depth range is completed within 1 millisecond. The output data adopts a lightweight storage strategy, retaining only the start and end point parameters and the average slope feature, reducing storage overhead by 90% and seamlessly integrating into the real-time data processing pipeline.

[0098] This embodiment dynamically adjusts the ultrasonic sampling frequency and intelligently determines the formation continuity. While ensuring uninterrupted high-speed penetration operations, it automatically generates smooth transition data for conventional gradually changing strata. Automatic output is paused and manual intervention is requested only when unpredictable extreme grain size abrupt changes (such as boulders, hard interlayers, or artificial fillers) are encountered. This achieves a precise balance between exploration efficiency and geological risk control. In this embodiment, confidence levels are marked in the vertical stratigraphic map. A high-confidence interval is marked when the attenuation characteristics of the dual-frequency signal match the pre-stored model better than the first matching threshold; a medium-confidence interval is marked when only a single-frequency signal is valid and there are no inhomogeneous inclusion alarms.

[0099] Specifically, in the vertical stratigraphic map, when the attenuation characteristics of the dual-frequency signal match the pre-stored model by more than 90%, it is marked as a high confidence interval; when only a single frequency is effective and there is no alarm for heterogeneous inclusions, it is marked as a medium confidence interval.

[0100] Specifically, when generating vertical stratigraphic maps, the system performs a dynamic confidence calibration process in real time. When the combined attenuation characteristic curve of the dual-frequency ultrasonic signals (high and low frequencies) matches the pre-stored physical model database by more than 90%, the system automatically marks the continuous depth interval as a high-confidence segment (indicated by a red dashed box). In this state, the system determines that the current stratigraphic particle distribution conforms to the acoustic propagation theory model and can be directly used for automated engineering decision-making.

[0101] For sections where only a single frequency signal is valid due to sensor obstruction or thin-layer impurity interference (e.g., high-frequency channels are blocked by cohesive soil, and only low-frequency penetration signals are valid), the system initiates heterogeneous inclusion screening: if real-time scanning does not trigger an inclusion alarm (the inclusion alarm rule is: local abrupt change in scattering intensity > 40% and duration < 3mm), then the section is marked as a medium confidence section (marked with a yellow wavy line). At this time, the gradation data can still be displayed but with a confidence prompt, requiring manual verification and confirmation.

[0102] All confidence level markers are overlaid on the digital stratigraphic map as vector layers, and can be filtered and displayed by confidence level. High confidence level data is directly synchronized to the engineering analysis module; medium confidence level data needs to be released after authorized personnel click "Confirm Unlock," otherwise it is only retained as reference background data.

[0103] In this embodiment, based on the difference in matching accuracy between dual-frequency ultrasonic signals and pre-stored physical models, the reliability intensity of key sections is dynamically marked in the stratigraphic map. Continuous strata with high matching accuracy between dual-frequency signals (matching degree > 90%) are automatically marked as high-confidence intervals to support automated decision-making, while transitional strata with only single-frequency validity (and no signs of heterogeneous interference) are assigned medium confidence as risk buffer markers. This forms a visualized heat map of exploration data quality, providing accurate risk priority ranking for engineering design and manual review.

[0104] In this embodiment, during the device penetration process, when the confidence level of multiple consecutive depth acquisition points is continuously lower than the preset reliability threshold, the penetration rate forced adjustment mechanism is automatically triggered. The electro-hydraulic servo control unit reduces the penetration rate to below the low-speed processing mode threshold and switches to the dual-frequency signal feature extraction mode. When the processor's real-time load exceeds the critical load threshold in this state, the feature frequency band compression coding algorithm based on wavelet analysis is activated. That is, the main frequency band component of the ultrasonic reflection signal is selectively retained and the high-frequency noise component is removed to maintain the preset compression rate, ensuring that the real-time data processing delay is controlled within the set time limit.

[0105] After the penetration is terminated, data quality analysis is automatically performed based on the operational characteristics of the high-speed penetration section, and core parameters including the compression ratio, the grain size error compensation amount driven by confidence level, and the vertical formation continuity index are calculated. Finally, a quality assessment report is generated, which includes a spatial distribution map of integrated depth markers, a zoned quantized error heat map, and a continuity analysis log containing reconstruction operation records.

[0106] Specifically, when the confidence level of three consecutive depth acquisition points (default 1 point / 2cm) is lower than the preset reliability threshold (threshold setting range: high confidence interval ratio <55%-65%), the electro-hydraulic servo control unit receives the PLC instruction and reduces the penetration rate to ≤2cm / s (adjustable) through the proportional valve oil pressure adjustment. At the same time, it switches to low-speed processing mode and starts dual-channel independent analysis: the high-frequency sensor (500kHz) extracts the main frequency peak of the scattering signal of 1-3mm particle size, and the low-frequency sensor (50kHz) analyzes the penetration energy attenuation slope of 5-20mm particle size.

[0107] When the processor core temperature exceeds 85℃ or the real-time task backlog exceeds 150ms under this condition, feature compression based on the Daubechies wavelet basis is activated: the original 16-bit ultrasound signal is decomposed into 5 layers, retaining the low-frequency coefficients of 0-250kHz (accounting for 80% of the energy) and discarding the high-frequency detail coefficients >250kHz (compression ratio fixed at 5:1). The compressed data stream is processed through the PCIe through-DSP chip, with an end-to-end latency guaranteed to be <50ms.

[0108] Activate the wavelet analysis-based feature band compression coding algorithm, specifically:

[0109] Compression ratio calculation: The percentage of depth range compressed by features in the high-speed segment (>10cm / s), output result = Σ(compressed segment length) / total length of high-speed segment × 100%;

[0110] Error compensation modeling: The compensation value for the confidence downgraded section (including medium / low confidence markers) = section length × (1 - confidence level) × baseline error coefficient (0.02mm for clay / 0.08mm for sand), generating a heat map of compensation in 0.1m zones (red high compensation zone > 0.05mm).

[0111] Continuity index calculation: Continuity index = [1-(number of manual interventions / total number of interpolations)] × effective interpolation depth ratio, where the effective interpolation depth is the cumulative depth of successful linear reconstruction (judgment criterion: the transition curve dual-frequency verification passes).

[0112] like Figures 2-4 As shown, the third embodiment of the present invention provides a system for determining soil particle size and gradation based on an ultrasonic sensor, and is based on the first embodiment of a method for determining soil particle size and gradation based on an ultrasonic sensor. The system includes:

[0113] The ultrasonic transmitting and receiving module 3 is configured as a multi-frequency ultrasonic transmitting array 16 and an ultrasonic receiving array 17. The multi-frequency ultrasonic transmitting array 16 is used to alternately transmit high-frequency ultrasonic waves and low-frequency ultrasonic waves to the soil layer to be tested. The high-frequency ultrasonic waves are used to excite the scattered echo of the surface fine particles, and the low-frequency ultrasonic waves are used to penetrate the coarse particle layer to obtain the deep reflection signal. The ultrasonic receiving array 17 is used to synchronously capture the reflected echo signal, including the high-frequency reflection signal and the low-frequency reflection signal.

[0114] The data processing module is configured to extract scattering features of particles with a first diameter from high-frequency reflection signals and to extract penetration features of particles with a second diameter from low-frequency reflection signals; wherein the first diameter is smaller than the second diameter; and to fuse the particle scattering features and particle penetration features to generate a composite particle size distribution curve.

[0115] The data output module is configured to compare the composite particle size distribution curve with the pre-stored soil classification and determination model to estimate the particle size and gradation of the soil layer until the continuous vertical stratum data collection is completed.

[0116] The wireless communication module 5 is configured to transmit high-frequency reflected signals and low-frequency reflected signals from the ultrasonic transmitting and receiving module 3 to the data processing module.

[0117] The ultrasonic transmitting and receiving module 3 and the wireless communication module 5 are mounted in the data acquisition section 1. One end of the data acquisition section 1 is connected to the static cone probe 6, and the other end of the data acquisition section 1 is connected to the static cone probe 2.

[0118] Specifically, see Figure 2 The ultrasonic transmitting and receiving module 3 and the wireless communication module 5 are integrated inside the cylindrical data acquisition section 1. The data acquisition section 1 uses a high-strength alloy steel shell, and its outer diameter is consistent with that of the static cone penetrometer probe 2 and the probe rod, ensuring that there are no structural protrusions during penetration. One end of the data acquisition section 1 is screwed to the static cone penetrometer probe rod 6 through a threaded interface, and the other end is rigidly connected to the static cone penetrometer probe 2 through a thread of the same specification.

[0119] See Figure 3 The multi-frequency ultrasonic transmitting array 16 and the ultrasonic receiving array 17 are enclosed in a protective cover 15, which is installed in the data acquisition section 1. The gaps between the multi-frequency ultrasonic transmitting array 16 and the ultrasonic receiving array 17 and the protective cover 15 are filled with acoustic impedance matching electronic waterproof adhesive 14.

[0120] The protective cover 15 is a metal protective cover.

[0121] The outer surface of the protective cover 15 of the ultrasonic transmitting and receiving module 3 is precisely flush with the outer shell of the data acquisition section 1, allowing the transmitting / receiving array to directly contact the soil layer to be tested. Specifically, the multi-frequency ultrasonic transmitting array 16 and the ultrasonic receiving array 17 are entirely enclosed within the high-strength steel protective cover 15. The protective cover 15 is rigidly fixed to the outer shell of the data acquisition section 1 by threads at both ends, and its outer surface is precisely flush with the outer shell of the section, avoiding structural protrusions or gaps during penetration. The aperture design of the protective cover 15 has been acoustically optimized.

[0122] High-frequency signal protection: The aperture size is less than 1mm, which reduces the energy leakage of high-frequency ultrasound and ensures the accuracy of the acquisition of signals reflected from fine particles on the surface.

[0123] Low-frequency penetration enhancement: The pore distribution density is adapted to the low-frequency ultrasonic wavelength to maximize the penetration efficiency of the coarse particle layer.

[0124] In this embodiment, the wireless communication module 5 is fixed inside the data acquisition sub-section 1, adjacent to the battery 4. Its antenna is encapsulated within the sub-section wall thickness, transmitting signals through a high-frequency dielectric window to avoid the shielding effect of the metal casing on the wireless signal. During the insertion process, the electronic waterproof adhesive 14 inside the sub-section fills all component gaps, providing an IP68-level waterproof seal while maintaining acoustic impedance matching characteristics.

[0125] See Figure 3 and Figure 4 The multi-frequency ultrasonic transmitting array 16 and the ultrasonic receiving array 17 are mounted on one end of the circuit board 12, and the other end of the circuit board 12 is connected to the power supply and communication line 11 of the battery 4 and the static probe 2. The power supply and communication line 11 is used for data transmission.

[0126] Specifically, the multi-frequency ultrasonic transmitting array 16 and ultrasonic receiving array 17 are integrated and mounted on the front end plane of the circuit board 12. The array units are connected to the circuit board via gold wire bonding, and the bonding points are sealed with epoxy resin to prevent moisture corrosion. A 32-pin metal connector is provided on the rear end plane of the circuit board 12, which is rigidly inserted into the cable connectors of the power supply and communication lines, forming the following connection path:

[0127] Power transmission: The positive and negative terminals of the line are directly connected to battery 4 to provide pulse drive power for the transmitting array;

[0128] Data Channel: The line data bus is bidirectionally connected to the data port of static cone penetration probe 2, synchronously transmitting two signals:

[0129] Uplink direction: Raw ultrasonic echo data captured by the receiving array;

[0130] Downward direction: Geotechnical parameters such as cone tip resistance and side friction resistance collected by static cone penetration probe 2.

[0131] The circuit board 12 is designed to separate high-frequency and low-frequency signal loops:

[0132] High-frequency circuit: In this embodiment, a serpentine trace can be used to control impedance and reduce signal reflection;

[0133] Low-frequency circuit: In this embodiment, twisted pair cables can be used to suppress electromagnetic interference.

[0134] A copper foil heat dissipation layer is laid on the back of the substrate to conduct the heat generated by the emission array to the protective cover 15 for dissipation.

[0135] The power supply and communication lines use shielded cables that run through the inner cavity of data acquisition section 1. The cables branch off at their ends into two paths:

[0136] One path connects to the four terminals of the battery via a waterproof plug;

[0137] Another connection is made to the multi-functional data interface of the static cone penetrometer 2 (supporting RS485 protocol), enabling real-time data fusion between the ultrasonic module and the static penetrometer system. The cable armor and the short section shell are electrically grounded to eliminate electrostatic interference.

[0138] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working process and related descriptions of the system described above can be found in the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0139] It should be noted that the above embodiment of the system for determining soil particle size and gradation based on ultrasonic sensors is only an example of the division of the functional modules described above. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the modules or steps in the embodiments of the present invention can be further decomposed or combined. For example, the modules in the above embodiments can be merged into one module, or further divided into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present invention are only for distinguishing the various modules or steps and are not considered as an improper limitation of the present invention.

[0140] An electronic device according to a fourth embodiment of the present invention includes:

[0141] At least one processor; and

[0142] A memory communicatively connected to at least one of the processors; wherein,

[0143] The memory stores instructions that can be executed by the processor to implement the above-described method for determining soil particle size and gradation based on an ultrasonic sensor.

[0144] A computer-readable storage medium according to a fifth embodiment of the present invention stores computer instructions, which are executed by the computer to implement the above-described method for determining the particle size and gradation of soil particles based on an ultrasonic sensor.

[0145] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working process and related descriptions of the storage device and processing device described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0146] Those skilled in the art will recognize that the modules and method steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. The programs corresponding to the software modules and method steps can be placed in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disks, removable disks, CD-ROMs, or any other form of storage medium known in the art. To clearly illustrate the interchangeability of electronic hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the invention.

[0147] The terms “first”, “second”, etc., are used to distinguish similar objects, not to describe or indicate a specific order or sequence.

[0148] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent in such process, method, article, or apparatus / device.

[0149] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for determining the grain size and gradation of a soil layer based on an ultrasonic sensor, characterized by, The method comprises: Alternately emitting high-frequency ultrasonic waves and low-frequency ultrasonic waves to the soil layer to be tested, wherein the high-frequency ultrasonic waves are used to excite scattering echoes of surface fine particles, and the low-frequency ultrasonic waves are used to penetrate coarse particle layers to obtain deep reflection signals; Synchronously capturing reflection echo signals, including high-frequency reflection signals and low-frequency reflection signals; Extracting scattering characteristics of first-diameter particles from the high-frequency reflection signals and extracting penetration characteristics of second-diameter particles from the low-frequency reflection signals; wherein the first diameter is smaller than the second diameter; Fusing the particle scattering characteristics and the particle penetration characteristics to generate a composite particle size distribution curve; Comparing the composite particle size distribution curve with a pre-stored soil classification determination model to infer particle sizes and gradations of the soil layer, until continuous vertical stratum collection is completed; The method is implemented by an ultrasonic collection device carried on an engineering geology in-situ test equipment, dynamically adjusts ultrasonic emission intervals according to equipment penetration rates, and realizes continuous vertical stratum collection and real-time determination: Real-time collection of a penetration rate, switching processing modes according to preset first and second rate thresholds; When the penetration rate is less than or equal to the first rate threshold, extracting scattering characteristics of first-diameter particles from the high-frequency reflection signals as first characteristics, and extracting penetration characteristics of second-diameter particles from the low-frequency reflection signals as second characteristics; When the penetration rate is greater than the first rate threshold and less than or equal to the second rate threshold, extracting a main frequency peak value of the high-frequency reflection signals as the first characteristics, and extracting an inflection point characteristic of the low-frequency reflection signals as the second characteristics; When the penetration rate is greater than the second rate threshold, matching a scattering intensity drop point through a pre-stored frequency response characteristic template as the first characteristics, and extracting a penetration energy inflection point as the second characteristics; Fusing the first characteristics and the second characteristics corresponding to the current penetration rate to generate a composite particle size distribution curve; Comparing the composite particle size distribution curve with a pre-stored soil classification determination model to infer particle sizes and gradations of the soil layer, until continuous vertical stratum collection is completed.

2. The method according to claim 1, wherein the soil layer particle size and grading are determined based on the ultrasonic sensor. The method for extracting scattering characteristics of first-diameter particles from the high-frequency reflection signals and extracting penetration characteristics of second-diameter particles from the low-frequency reflection signals comprises: Performing short-time Fourier transform on the high-frequency reflection signals to obtain the scattering characteristics of the first-diameter particles; Performing envelope detection analysis on the low-frequency reflection signals to obtain the penetration characteristics, which include a penetration depth of the second-diameter particles and a reflection energy attenuation rate.

3. The method according to claim 1, wherein the soil particle size and gradation are determined based on the ultrasonic sensor. The method for comparing the composite particle size distribution curve with a pre-stored soil classification determination model to infer particle sizes and gradations of the soil layer, until continuous vertical stratum collection is completed, comprises: Comparing the composite particle size distribution curve with a pre-stored soil classification determination model, correcting errors based on a pre-constructed frequency and particle size mapping relationship model, and inferring particle sizes and gradations of the soil layer.

4. The method according to claim 1, wherein the soil particle size and gradation are determined based on the ultrasonic sensor. Synchronously capturing reflection echo signals, including high-frequency reflection signals and low-frequency reflection signals, wherein the attenuation characteristics of different frequency signals are compared to identify inhomogeneous inclusions in the soil layer, and the inhomogeneous inclusions are verified again in combination with soil parameters.

5. The method according to claim 4, wherein the soil layer is divided into a plurality of layers, and the soil layer is measured by the ultrasonic sensor for each layer. The soil parameters include at least one of organic matter content, void ratio, or water content.

6. A system for determining the grain size and gradation of a soil layer based on an ultrasonic sensor, based on the method for determining the grain size and gradation of a soil layer based on an ultrasonic sensor according to any one of claims 1 to 5, characterized in that The system comprises: An ultrasonic emission and reception module (3) is configured as a multi-frequency ultrasonic emission array (16) and an ultrasonic reception array (17), the multi-frequency ultrasonic emission array (16) is used for alternately emitting high-frequency ultrasonic waves and low-frequency ultrasonic waves to the soil layer to be measured, wherein the high-frequency ultrasonic waves are used to excite the scattering echo of the surface layer fine particles, and the low-frequency ultrasonic waves are used to penetrate the coarse particle layer to obtain deep layer reflection signals; the ultrasonic reception array (17) is used to synchronously capture reflection echo signals, including high-frequency reflection signals and low-frequency reflection signals; A data processing module is configured to extract scattering characteristics of first diameter particles from the high-frequency reflection signals and to extract penetration characteristics of second diameter particles from the low-frequency reflection signals; wherein the first diameter is smaller than the second diameter; and to fuse the particle scattering characteristics and the particle penetration characteristics to generate a composite particle size distribution curve; A data output module is configured to compare the composite particle size distribution curve with a pre-stored soil classification determination model, to infer the particle size and grading of the soil layer, and to continuously collect the vertical stratum until the collection is completed. A wireless communication module (5) is configured to transmit the high-frequency reflection signals and the low-frequency reflection signals from the ultrasonic emission and reception module (3) to the data processing module.

7. The system for measuring soil particle size and gradation based on ultrasonic sensors according to claim 6, wherein, The ultrasonic emission and reception module (3) and the wireless communication module (5) are carried in the data acquisition short section (1), one end of the data acquisition short section (1) is connected with the static sounding probe rod (6), and the other end of the data acquisition short section (1) is connected with the static sounding probe head (2).

8. The system for measuring soil particle size and gradation based on ultrasonic sensors according to claim 7, wherein, The multi-frequency ultrasonic emission array (16) and the ultrasonic reception array (17) are covered in the protective cover (15), and the protective cover (15) is installed in the data acquisition short section (1).

9. The system for measuring soil particle size and gradation based on ultrasonic sensors according to claim 8, wherein, The multi-frequency ultrasonic emission array (16) and the ultrasonic reception array (17) are installed at one end of the circuit substrate (12), the other end of the circuit substrate (12) is connected with the power supply and communication line (11) of the storage battery (4) and the static sounding probe head (2), and the power supply and communication line (11) is used for data transmission.

10. The system for measuring soil particle size and gradation based on ultrasonic sensors according to claim 8, wherein, The multi-frequency ultrasonic emission array (16) and the ultrasonic reception array (17) are filled with electronic waterproof glue (14) with acoustic impedance matching in the gap in the protective cover (15).

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