While-drilling frequency-adjustable full-polarization borehole radar detection device and working method

Abstract

The invention belongs to the technical field of highway construction, and particularly relates to a while-drilling frequency-adjustable fully-polarized drilling radar detection device and a working method, the device comprises a drill rod body, the drill rod body is a hollow cylinder, and the end part of the drill rod body is connected with a drilling tool through a metal joint; the at least two medium windows are annularly and uniformly distributed on the drill rod body; each dielectric window is internally provided with a radial fully-polarized antenna unit used for annular detection. The radial fully-polarized antenna unit is switched among a plurality of frequency bands through the frequency-adjustable circuit module and realizes impedance matching, and the signal processing and transmission module processes radar signals and uploads data to the ground; the barrel comprises a carbon fiber reinforced composite layer, a wear-resistant layer is arranged on the outer surface of the carbon fiber reinforced composite layer, a glass fiber transition layer is arranged between the area where the dielectric window is located and the inner wall face of the carbon fiber reinforced composite layer, the periphery of the dielectric window is sleeved with an outer lantern ring, and a wave absorbing layer is arranged on the inner wall face of the glass fiber transition layer. The carbon fiber composite material bearing cylinder is used for replacing a metal section, so that the problem of metal shielding is solved.

Description

Technical Field

[0001] This invention relates to the field of highway construction technology, specifically to a frequency-adjustable fully polarized borehole radar detection device and its working method. Background Technology

[0002] The statements in this section merely refer to the background art related to this invention and do not necessarily constitute prior art.

[0003] During the tunnel exploration and construction phase, drilling is the most direct means of obtaining accurate underground information. For ultra-deep buried tunnels exceeding 10 kilometers in length, traditional exploration-stage drilling is insufficient to conduct continuous and complete exploration of the main tunnel section, presenting a "missing point" problem. This results in numerous geological blind spots in the preliminary exploration results, leaving insufficient geological basis for tunnel design and decision-making.

[0004] Borehole radar technology is widely used in downhole geological exploration in tunnels, mines, and other fields due to its advantages of high resolution and sensitivity to adverse geological features such as water anomalies and fractures. However, most existing borehole radar technologies are drop-down logging methods implemented after drilling is completed, which cannot achieve real-time geological information acquisition during the drilling process, resulting in serious timeliness issues. To address the real-time problem, some technical solutions attempt to embed the radar antenna into a short metal section of the drill pipe to achieve detection while drilling.

[0005] In these schemes, because the antenna is enclosed inside the metal drill pipe, the metal shell has a strong shielding effect on electromagnetic waves, which compresses the effective bandwidth of the radar signal, distorts the radiation pattern, and introduces strong direct wave interference. It is difficult to obtain a stable and low-loss wave transmission effect, which seriously affects the detection accuracy and range.

[0006] At the same time, these schemes are mostly fixed frequency bands and single polarization, which cannot be adaptively adjusted according to the dielectric properties of complex surrounding rocks, and also lack axial forward-looking detection capabilities and the ability to identify anomalies in front is insufficient. Summary of the Invention

[0007] To address the technical problems mentioned above, this invention provides a frequency-adjustable, fully polarized borehole radar detection device and its operating method, solving the geological blind zone problem caused by "out-of-reach" conditions in ultra-deep buried tunnel exploration. By achieving real-time, fully polarized, and adaptive frequency geological detection of the 360° circumference around the drill barrel and the area 10-20 meters in front of the drill bit during drilling, it provides accurate advanced geological prediction for tunnel construction, enabling responses to extreme geological risks such as water inrush and collapse, and ensuring project safety.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: The first embodiment of the present invention discloses a drilling-while-drilling frequency-tunable fully polarized borehole radar detection device, comprising: The drill pipe body includes a hollow cylinder, the end of which is connected to the drill string via a metal connector; The medium window has at least two, which are evenly distributed circumferentially on the drill pipe body; each medium window is equipped with a radially fully polarized antenna unit for circumferential detection; the radially fully polarized antenna unit switches between multiple frequency bands and achieves impedance matching through a frequency-tunable circuit module, and processes radar signals and uploads data to the ground system through a signal processing and transmission module; The cylinder includes a carbon fiber reinforced composite layer, a wear-resistant layer on the outer surface of the carbon fiber reinforced composite layer, a glass fiber transition layer between the area where the medium window is located and the inner wall of the carbon fiber reinforced composite layer, an outer ring around the outer periphery of the medium window, and a wave-absorbing layer on the inner wall of the glass fiber transition layer. The inner wall of the cylinder is equipped with segmented electrodes or slit arrays, which are connected to the signal processing module via a coupling network to serve as a distributed sensing or radiation unit.

[0009] Furthermore, it also includes an axial forward-looking antenna unit, which is located at one end of the drill pipe body and covered with an end cap, for longitudinal forward detection in front of the drill bit.

[0010] Furthermore, the connection between the metal joint and the cylinder, as well as the connection between the end of the drill pipe body and the end cap, are all equipped with a double O-ring sealing structure, and the end cap has a set dielectric constant range.

[0011] Furthermore, the fiberglass transition layer has multiple layers of fiberglass cloth with a set angle range, and the overlap length between the fiberglass cloth and the carbon fiber reinforced composite layer and the dielectric window is not less than a set value; the outer ring is a thin-walled ring with a low dielectric constant.

[0012] Furthermore, the device is equipped with an electronic compartment that houses a frequency-tunable circuit module and a signal processing and transmission module. The electronic compartment is filled with low-loss epoxy resin to form a potting layer. The wear-resistant layer is a polyurea or ceramic filler coating sprayed onto the outer surface of the carbon fiber reinforced composite layer.

[0013] Furthermore, the radially fully polarized antenna element includes mutually orthogonally arranged dipole antennas or slot antennas, and the operating mode of the radially fully polarized antenna element is controlled by a switching matrix to switch different polarization states.

[0014] Furthermore, the tunable circuit module includes a transmit chain and a receive chain; The transmit chain employs a π-type or T-type reconfiguration matching network switched by relays or PIN diodes. The reconfiguration matching network is configured to cover three frequency bands: 60-150 MHz, 150-400 MHz, and 400-900 MHz. The receiver chain is equipped with a MEMS or BST variable capacitor array, with a tuning range of 5pF to 50pF and a step of no more than 2pF.

[0015] Furthermore, the signal processing and transmission module includes a limiter, a low-noise amplifier, an anti-aliasing filter, and an analog-to-digital converter connected in sequence, supporting a frequency step of 1 MHz to 5 MHz for stepped continuous waves, with a dynamic range not less than the set value.

[0016] The second embodiment of the present invention discloses a method for operating a frequency-tunable fully polarized borehole radar detection device while drilling, comprising the following steps: The device is connected to the drill string via a metal connector and is lowered into the borehole along with the drill string to perform drilling. During drilling, the operating frequency band and polarization mode of the radar system are selected based on the acquired or preset operating parameters; among which, the operating parameters include at least one of well diameter, mud conductivity, or near-end echo amplitude. The polarization modes of the radially fully polarized antenna elements are switched sequentially according to a preset timing sequence. For each polarization mode, the frequency-tunable circuit module generates radar signals in the selected operating frequency band and transmits them through the corresponding antenna element, while simultaneously receiving reflected echo signals from the surrounding rock. The signal processing and transmission module performs amplitude limiting, low-noise amplification, filtering, and analog-to-digital conversion on the received echo signal. The processed radar data is then uploaded to the ground system via a drilling cable or electromagnetic wave inductive coupling. The ground system receives radar data and performs joint imaging and geological attribute inversion on data under different polarization modes and operating frequency bands to generate geological structure images and anomaly information in the borehole circumferential direction.

[0017] Furthermore, joint imaging and geological attribute inversion are performed on data from different polarization modes and operating frequency bands, including the following steps: Amplitude and phase calibration and direct wave template suppression are performed on multi-channel SFCW data; Angular beamforming and fk / Kirchhoff offset imaging are performed in cylindrical coordinates. Construct a voxel-level scattering matrix and perform polarization decomposition to output fracture strike / dip estimates; By employing multi-frequency joint constraints and TV-L2 regularization for attribute inversion, we obtained the water content indicator index and anomaly confidence map.

[0018] Compared with existing technologies, one or more of the above technical solutions have the following beneficial effects: 1. By using carbon fiber reinforced polymer (CFRP) as the body material of the drill pipe sub, replacing the traditional metal section, the excellent properties of CFRP—non-conductive and low dielectric loss—completely eliminate the shielding effect of the metal shell on radar electromagnetic waves. This allows radar signals to penetrate into the surrounding rock mass with low loss and low distortion, effectively avoiding signal bandwidth compression, radiation pattern distortion, and strong direct wave interference. This significantly improves the stability and quality of the detection signal, thus laying the physical foundation for improving detection accuracy and range.

[0019] 2. By arranging orthogonal dipole / slot antenna pairs within each medium window and combining them with switch matrix control, different polarization modes can be flexibly switched for measurement. The full polarization capability enables the system to effectively identify key geological properties such as fracture orientation, rock mass anisotropy, and fluid saturation, solving the problem of insufficient information dimensions in traditional single polarization modes.

[0020] 3. Through a tunable circuit combining segmented reconstruction (e.g., frequency band switching using π / T matching networks) and fine-grained tuning (e.g., micro-tuning using MEMS capacitor arrays), the system can adaptively adjust its operating frequency over a wide bandwidth (e.g., 60~900 MHz). This allows the system to optimize detection performance based on the dielectric properties of the surrounding rock (e.g., using low frequencies to increase penetration depth in low-loss rock masses, and using high frequencies for high-resolution applications), effectively balancing the conflicting requirements of "penetration depth" and "resolution," and enhancing its adaptability to complex geological conditions.

[0021] 4. By integrating radially fully polarized antenna units arranged around the drill pipe and axially forward-looking antenna units arranged at the drill pipe's front end, the system simultaneously possesses the capability for circumferential detection and longitudinal forward detection within a certain distance in front of the drill bit. This multi-view detection system combining radial and forward-looking capabilities can not only finely characterize the geological structure around the drill pipe but also effectively predict potential hazards such as water inrush and mudslides ahead, significantly enhancing construction safety and the comprehensiveness of geological understanding.

[0022] 5. To address the challenges of high pressure, high temperature, strong vibration, and mud erosion in the drilling environment, a multi-layered sealing and protection design was adopted. This includes double O-ring seals between the CFRP shell and metal joints, low-loss epoxy potting of the electronics compartment and antenna cavity, polyurea or ceramic wear-resistant coatings on the outer surface, and fiberglass transition layers and wave-absorbing layers, collectively forming a robust protection system. These measures effectively ensure the structural integrity, sealing, and circuit stability of the equipment under harsh drilling conditions, enabling long-term continuous and reliable operation.

[0023] 6. CFRP material itself has the characteristics of high specific strength and high specific modulus. Through optimized layup design, the short section can achieve lightweight components while possessing mechanical properties comparable to or even better than metals (withstanding high torque and complex loads), and perfectly meeting the functional requirements of electromagnetic wave transmission. This integrated structure-function design provides an ideal load-bearing and wave-transmitting platform for drilling radar. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 A schematic diagram of the structure of a drilling-while-drilling frequency-tunable fully polarized borehole radar detection device provided in one or more embodiments of the present invention; Figure 2 A cross-sectional schematic diagram of a frequency-tunable fully polarized borehole radar detection device provided in one or more embodiments of the present invention; Figure 3 A polarization and switching matrix architecture diagram of a frequency-tunable fully polarized borehole radar detection device provided in one or more embodiments of the present invention; Figure 4 This is a transmit reconfiguration + receive fine-tuning architecture diagram provided for one or more embodiments of the present invention.

[0026] In the diagram: 1 CFRP short section body, 2 metal connector, 3 dielectric window, 4 fiberglass transition layer, 5 absorbing layer (inner wall of window), 6 orthogonal dipole / slot antenna, 7 axial forward-looking biconical antenna, 8 low dielectric end cap, 9 electronics / tuning bay, 10 double O-ring seal, 11 inner channel. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0028] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0029] As described in the background section, existing technologies embed radar antennas into short metal sections of drill pipes to achieve detection while drilling. However, due to the metal shielding problem, the effective bandwidth of the radar signal is compressed, the radiation pattern is distorted, and strong direct wave interference is introduced, making it difficult to obtain stable and low-loss wave transmission effects, which seriously affects the detection accuracy and range.

[0030] At the same time, these schemes are mostly fixed frequency bands and single polarization, which cannot be adaptively adjusted according to the dielectric properties of complex surrounding rocks, and also lack axial forward-looking detection capabilities and the ability to identify anomalies in front is insufficient.

[0031] Specifically: Single polarization mode: Existing systems mostly use fixed single polarization (such as vertical polarization VV) antennas, which cannot perform full polarization (VV, HH, VH, HV) measurements, making it difficult to effectively identify key geological information such as fracture orientation and rock mass anisotropy.

[0032] Fixed operating frequency band: The system typically operates in a fixed frequency band and cannot adaptively adjust according to the dielectric properties of the actual surrounding rock. Low-frequency signals are needed in low-loss rock masses to achieve deep exploration, while high-frequency signals are needed in high-resolution scenarios. Fixed frequency bands make it difficult to meet the conflicting requirements of "penetration depth" and "resolution".

[0033] Lack of forward-looking capability: Most existing devices can only achieve circumferential detection around the drill pipe radially, and do not have the ability to detect potential hazards within a certain distance (such as 10-20 meters) in front of the drill bit in the axial direction, and the ability to predict risks such as water inrush and mud inrush is insufficient.

[0034] Environmental durability challenges: Under drilling conditions, the equipment is subjected to high pressure, high temperature, strong vibration and mud erosion for a long time. Existing systems are often poorly designed in terms of sealing, protection and circuit reliability, making it difficult to guarantee long-term stable operation.

[0035] Therefore, this solution presents a frequency-tunable, fully polarized borehole radar detection device and its operating method, replacing the metal section with a carbon fiber reinforced polymer (CFRP) load-bearing cylinder to fundamentally solve the metal shielding problem. Based on this, a circumferentially fully polarized antenna and an axial forward-looking antenna are integrated to achieve multi-field detection; and through a segmented reconfiguration and fine-grained tuning frequency-tunable circuit, the system can adapt to complex geological conditions. Finally, multiple sealing protection technologies ensure its long-term stable operation in harsh drilling environments.

[0036] Example 1: This embodiment achieves a balance between mechanical load-bearing capacity and electromagnetic wave transmission by using a carbon fiber reinforced composite material cylinder and setting a low-loss dielectric window. A radially fully polarized antenna unit is arranged within the dielectric window, and an axial forward-looking antenna is configured at the front end to achieve 360° circumferential detection and longitudinal forward-looking detection. Combined with a segmented reconstruction and fine-grained tuning tunable circuit, it supports adaptive operation within the 60~900MHz range, thereby achieving integrated detection of full polarization, multiple frequency bands, forward-looking, and radial waves under drilling conditions. This simultaneously solves the coexistence problems of "metal shielding, fixed frequency bands, insufficient polarization, and lack of forward-looking capability," forming a multi-view, fully polarized adaptive detection system that can operate stably for a long time while drilling, improving the identification accuracy and forward prediction capability of adverse geological bodies in complex surrounding rock environments.

[0037] Carbon fiber reinforced polymer (CFRP) is an advanced structural material made by using high-strength, high-modulus carbon fibers as reinforcement and polymers such as epoxy resin as the matrix, formed through specific processes (such as winding layup and hot-pressing curing). This material provides structural strength comparable to or even higher than alloy steel, while its density is much lower than that of metals, enabling lightweight detection sub-sections while ensuring it can withstand high torque and complex loads during drilling. Furthermore, the non-conductive and low dielectric loss properties of CFRP allow it to replace metals as the carrier of radar antennas. Simultaneously, by adjusting the layup direction, sequence, and volume fraction of the carbon fibers, the mechanical properties of the sub-section in different directions can be precisely optimized, achieving a unified function of mechanical load-bearing and electromagnetic wave transmission.

[0038] like Figure 1 As shown, a frequency-tunable fully polarized borehole radar detection device includes a drill pipe body, which is a CFRP short section with a set outer diameter and wall thickness. Figure 1 CFRP short section body 1 in the middle.

[0039] One end of the CFRP sub-body 1 is connected to a metal connector 2, which is used to connect to a conventional drill pipe. The other end is connected to an end cap. In this embodiment, the end cap is a low-dielectric end cap 8. An axial forward-looking biconical antenna 7 is installed in the cavity between the low-dielectric end cap 8 and the CFRP sub-body 1. The low-dielectric end cap 8 is 6 to 8 mm thick, enabling longitudinal detection in the range of 10 to 20 m.

[0040] The CFRP short section body 1 is provided with seals at both ends for sealing between the CFRP short section body 1 and the metal connector 2, and for sealing between the CFRP short section body 1 and the end cap. In this embodiment, the seal is a double O-ring seal 10, and the outer surface is coated with a polyurea or ceramic filler coating with a thickness of about 0.6 mm, which has wear resistance and corrosion resistance.

[0041] Multiple dielectric windows 3 are evenly distributed circumferentially along the CFRP short section body 1. A pair of orthogonal dipole / slot antennas 6 are installed in each dielectric window 3 to form a radially fully polarized antenna element. In this embodiment, four dielectric windows 3 are set, and the VV, HH, VH, and HV polarization modes are switched through a switching matrix. The four dielectric windows achieve 360° circumferential coverage.

[0042] The CFRP short section body 1 has an inner channel 11 in the middle of its cross-section, and the medium windows 3 are evenly distributed circumferentially around the inner channel 11 as the axis. A fiberglass transition layer 4 is provided between the dielectric window 3 and the wall of the CFRP short section body 1, and a wave-absorbing layer 5 is provided on the inner wall of the fiberglass transition layer 4.

[0043] The CFRP sub-section body 1 also houses an electronics / tuning compartment to accommodate the signal processing and transmission module. The electronics compartment is encapsulated with low-loss epoxy. The signal processing and transmission module includes a limiter, a low-noise amplifier, an anti-aliasing filter, and a 14-bit ADC. It supports stepped continuous wave (SFCW) mode with a frequency step of 1 to 5 MHz, a dynamic range of ≥90 dB, and is compatible with pulse mode. Data is transmitted to the surface system via a drilling cable or inductive coupling.

[0044] like Figure 1 As shown, the drill pipe body is a hollow short section of carbon fiber reinforced polymer (CFRP) with an outer diameter of Φ89 mm and a wall thickness of 18 mm, with a total length of approximately 1.35 m. The cylinder is made of T700 / T800 grade carbon fiber prepreg, wound and laid up and hot-pressed for curing. The outer layer is covered with a 0.5 mm polyurea wear-resistant layer, the middle layer is a [±45° / 0° / 90°]s laminated structure with a fiber volume fraction of 55-60%, and the inner wall is covered with a 0.2 mm epoxy isolation layer. The end of the cylinder is connected to the conventional drill pipe through a metal threaded joint. The metal joint is made of 40CrNiMo alloy steel with a nickel-plated surface for corrosion protection. Preferably, a PEEK insulating sleeve is installed between the CFRP and the metal joint, and high-strength epoxy resin is injected to form a reliable structural connection and electrostatic discharge path.

[0045] To balance multiple objectives such as "mechanical load-bearing capacity, electromagnetic wave transmission, sealing durability, and fluid disturbance suppression," this device adopts a three-layer composite structure consisting of a "CFRP cylinder / glass fiber transition layer / medium window." The specific mechanism and effects are as follows: 1) Mechanical-Electromagnetic Decoupling and Stress Transfer: The medium window differs from the CFRP cylinder in elastic modulus and coefficient of thermal expansion. By setting a ±45° fiberglass transition layer between the two, a "soft gradient" interface is formed, which significantly reduces stress concentration and interlayer delamination risk at the medium window boundary and maintains the geometric stability of the medium window area under drilling impact / torsional loads.

[0046] 2) Suppression of direct wave coupling with annular gap: An absorbing layer is set on the inner wall of the medium window and a low dielectric outer ring is added to the outer periphery, so that the boundary equivalent impedance of the window area is closer to the surrounding rock / well fluid environment; combined with the low loss characteristics of the CFRP cylinder, it can weaken the coupling echo caused by window diffraction and annular fluid, reduce the sensitivity to near-end direct / multipath components, and thus improve the amplitude and phase stability under the SFCW system.

[0047] 3) Improved sealing and media resistance: The transition layer and double O-rings together form a dual-path sealing system of "structural seal - material seal"; the fiberglass transition layer between the end cap and the cylinder can absorb the minor mismatch caused by thermal cycling / pressure pulsation, inhibit long-term leakage and micro-crack propagation, and improve durability in mud / groundwater environments.

[0048] 4) Electrochemical and electrostatic safety: Introducing insulating components (such as PEEK sleeves) and epoxy isolation layers between CFRP and metal joints can cut off the electrochemical corrosion path; at the same time, a controlled electrostatic discharge path is set up inside the cylinder to reduce the risk of electrostatic accumulation and transient coupling during SFCW / pulse emission, and to ensure that the front-end LNA and ADC are not damaged by overshoot.

[0049] 5) Imaging robustness under asymmetric loading: The three-layer structure can maintain the relative attitude and thickness stability of the medium window under uneven loads such as drilling pressure, torque and mud scour, keeping the phase center offset of the multi-window within the calibrable range and reducing the element drift error in the imaging / inversion process.

[0050] like Figure 2 As shown, four media windows are symmetrically positioned circumferentially in the middle of the drill pipe body. The preferred dimensions of the media windows are an axial length of 240 mm, a circumferential arc length of 80°, and a thickness of 10 mm. The material is quartz fiber reinforced epoxy composite material with a dielectric constant of 3.6–4.1 and a dielectric loss tangent of less than 0.01. A fiberglass transition layer is provided between the media windows and the CFRP cylinder. The transition layer consists of 2–3 layers of ±45° fiberglass cloth, with a single layer thickness of approximately 0.25 mm and an overlap length of not less than 30 mm, to ensure mechanical continuity and reduce stress concentration. Preferably, a 1.5 mm thick ferrite / carbon-based composite absorbing layer is adhered to the inner wall of the media window, and a 1 mm thick low-dielectric-constant outer ring is fitted around its outer periphery to reduce the fluid coupling effect in the annular gap.

[0051] Each dielectric window houses a pair of orthogonal dipole antennas, forming a radially fully polarized antenna element. The dipole antennas preferably employ a folded or bow-tie loading structure, with a single arm length of approximately 110 mm and a copper strip thickness of 0.2 mm and a width of 5 mm, to extend the operating bandwidth. The four pairs of antenna elements formed by the four dielectric windows are connected to a frequency-tunable circuit module via a switching matrix. Under MCU control, the switching matrix can switch between four polarization modes: VV, HH, VH, and HV, thereby achieving 360° circumferential fully polarized detection.

[0052] Furthermore, this scheme deploys mutually orthogonal antennas within multiple uniformly distributed dielectric windows in a circumferential pattern to acquire multi-channel (antenna direction) and multi-polarization (VV / HH / VH / HV) SFCW data, and performs the following processing flow in the ground system: S1. Amplitude and phase calibration and direct wave suppression: Perform integrated laboratory / downhole calibration for each channel; A "near-end reference-sliding window adaptive" direct wave template was constructed, and the transient switching artifacts and metal joint echoes were suppressed by combining projection elimination and sparsity constraint methods. Perform IFFT transformation from frequency domain to time domain, and complete time zero, group delay and cable dispersion correction.

[0053] S2. 360° circumferential synthesis and 3D cylindrical coordinate imaging: Beamforming and angular deconvolution are performed on each window channel in the cylindrical coordinate system (r, θ, z); The cylindrical shell domain is imaged using fk or Kirchhoff offsets to obtain a joint energy map E(r,θ,z) of amplitude, phase and consistency.

[0054] S3. Construction of the fully polarimetric scattering matrix and polarization decomposition: For each voxel, construct a 2×2 scattering matrix S; calculate the Stokes parameters and the dimensions of the Pauli / Cloude-Pottier decomposition; The probability distribution of fracture orientation and dip angle is derived from anisotropic indices (such as H / A / α or depolarization rate), and the polarization rose diagram and dip angle heat map are output.

[0055] S4. Attribute inversion of multi-frequency joint constraints: Using complex reflection coefficient and coherence as observables, a forward model is established for target parameters such as "moisture content / electrical conductivity / fracture aperture". By using TV-L2 regularized multi-frequency joint inversion, angular and axial noise fringes are suppressed, and the L-curve criterion is used to adaptively select regularization weights. The output includes three types of results: ① Circumferential structural strength diagram; ② Fracture orientation and dip angle estimation; ③ Water content indicator index (confidence level of water body / fracture zone).

[0056] S5. Confidence Assessment and Engineering Criteria: A confidence map is constructed based on pixel-level Fisher information and multi-channel consistency. The system outputs an "early warning suggestion table" based on the surrounding rock grade / risk level, providing excavation parameters and grouting reinforcement suggestions.

[0057] An axial forward-looking antenna unit is installed at the front end of the drill pipe body. This antenna is preferably a biconical structure with a cone angle of approximately 60° and an arm length of 45 mm. The antenna is covered with a PTFE end cap with a thickness of 6 to 8 mm and a dielectric constant of 2.0 to 2.3 to ensure low-loss wave transmission and mechanical protection.

[0058] The tunable circuit module includes a transmit chain and a receive chain. The transmit chain employs three sets of π / T matching units, corresponding to three frequency bands: 60~150 MHz, 150~400 MHz, and 400~900 MHz, respectively, and achieves segmented reconfiguration through relays or PIN diodes. The receive chain is configured with a MEMS variable capacitor array, with a tuning range of 5~50 pF and a step size of no more than 2 pF, to achieve fine-grained impedance matching. The signal processing and transmission module includes a limiter, a low-noise amplifier, a 14-bit ADC, and an anti-aliasing filter, supporting stepped continuous wave (SFCW) mode with frequency steps of 1~5 MHz and pulse mode compatibility, achieving fine-grained impedance matching.

[0059] Furthermore, the internal electronics compartment and antenna cavity are both filled with low-loss epoxy resin to form an epoxy potting layer. Double O-ring sealing grooves are installed at the metal joints and CFRP interfaces. The outer surface is coated with a 0.6 mm thick polyurea wear-resistant coating. Through these sealing and protective structures, the device can maintain structural integrity and signal stability under normal operating conditions.

[0060] During operation, the device is connected in series with the drill string via a drill pipe section. The radial antenna unit sequentially switches polarization modes under MCU commands. The MCU adaptively selects polarization and frequency band based on thresholds for wellbore diameter, mud conductivity, and near-end echo amplitude, acquiring four types of data: VV, HH, VH, and HV. The polarization switching sequence follows a four-step process of "silence – switching – calibration – sampling" to avoid introducing hypothetical reflections during switching transients. The forward-looking antenna unit synchronously acquires longitudinal signals. The transmit chain switches frequency bands according to MCU commands, while the receive chain achieves real-time tuning via a MEMS capacitor array. The received signal is amplified by limiting and LNA before being sampled by an ADC. The acquired data is processed by an FPGA or MCU and then uploaded to the surface via a drilling cable or inductive coupling. The surface system performs joint imaging and attribute inversion on data from different polarizations and frequency bands, enabling real-time identification and prediction of surrounding rock fractures, water bodies, and anomalies ahead.

[0061] To reliably obtain high-information data in complex well fluids and variable surrounding rocks, this scheme proposes the following adaptive switching strategy: C1. Operating condition perception and prior estimation: Online estimation of well diameter, mud conductivity σ_m, near-end echo amplitude A_0, and early attenuation slope k_0; Based on the threshold ranges of σ_m and k_0, the operating conditions are divided into three categories: "high loss / medium loss / low loss", providing a priori information for frequency band optimization.

[0062] C2. Frequency band selection principle: In high-loss operating conditions, low-frequency bands should be used first (penetration priority); when low loss and high resolution requirements are met, mid-to-high frequency bands should be used first. Under the same operating conditions, a "low → medium → high" sequence is used for detection. If the SNR or coherence γ is lower than the threshold, the frequency band is reverted to the previous band.

[0063] C3. Polarization Selection and Sequence Scheduling: Strong reflection and geometric information are obtained by using VV / HH as the main channel, and depolarization / anisotropy cues are captured by using VH / HV. Based on online evaluation of multipolarization information gain ΔI (measured by pixel variance reduction / mutual information approximation), the decision to insert cross-polarization measurement is dynamically made. The four steps of "silence-switching-calibration-sampling" are solidified (silence period ≥ several pulse repetition cycles) to avoid switching transient artifacts.

[0064] C4. Loop Closure and Fault Tolerance: If the SNR or γ of N consecutive frames is lower than the threshold, the "degradation mode" (fixed low frequency + main polarization polling) is triggered. If the anisotropy index of the target region increases significantly, the cross-polarization sampling density is increased and the polarization polling cycle is shortened.

[0065] C5. Feasibility Description: The switching strategy is implemented at the MCU / FPGA layer, and the threshold and sequence can be configured through the parameter table; The control logic and the host computer's imaging module share statistical quantities such as SNR, γ, and ΔI, forming an "online information-driven" adaptive loop.

[0066] Addressing the issues of high strength but severe electromagnetic shielding in metal drill pipes, and good wave transmission but insufficient mechanical properties in non-metallic materials, this solution employs a carbon fiber reinforced polymer (CFRP) load-bearing cylinder, combining near-metallic high strength, high torque capacity, and excellent electromagnetic wave transparency. Combined with a low-loss dielectric window and transition layer design, a perfect balance between mechanical and electromagnetic properties is achieved, providing an ideal "working platform" for drilling radar.

[0067] To address the limitations of existing technologies, which rely on a single perspective (circumferential only), a single polarization mode, and limited information dimensions, this solution employs a multi-view integrated design combining "radial full polarization circumferential detection + axial forward-looking detection" to achieve 360° circumferential scanning and detection of the geological conditions around the drill pipe. Full polarization measurements (VV, HH, VH, HV) significantly enhance the ability to identify fracture orientation, rock anisotropy, and water content.

[0068] To address the issue of drilling instruments failing due to vibration, high pressure, wear, and corrosion, this solution employs multiple protective measures, including epoxy potting, double O-ring seals, and polyurea / ceramic wear-resistant coatings, as well as the selection of high-temperature and high-pressure resistant components. This complete sealing and protection system ensures that the equipment can withstand harsh drilling conditions and achieve long-term stable operation.

[0069] At the structural level, a multi-layer gradient design of "CFRP cylinder / glass fiber transition layer / dielectric window" is adopted to balance load-bearing strength, low wave transmission loss, interface sealing and annular gap coupling suppression. At the algorithm level, a "360° joint imaging + polarization decomposition + multi-frequency joint inversion" is proposed for multi-window full polarization, and polarization / frequency band adaptive switching control is realized with working condition perception and information gain as the core, forming an integrated technical system of "structure-algorithm-control-engineering criteria".

[0070] Example 2: like Figure 1 and Figure 2 As shown, the overall structure of the tunable frequency fully polarized borehole radar detection device in this embodiment is basically the same as that in Embodiment 1, except that: The drill pipe body is made of carbon fiber reinforced polymer (CFRP) cylinder with an outer diameter of Φ89mm and a wall thickness of 10mm, with a total length of approximately 1.35m. After reducing the wall thickness, the inner diameter of the cylinder increases to Φ69mm, significantly reducing the weight of the device and facilitating long-term operation in medium-to-low strength surrounding rock and shallow strata. The CFRP laminated structure still uses a [±45° / 0° / 90°]s layup, with an outer layer covered by a 0.5mm polyurea wear-resistant layer and a fiber volume fraction of 55-60%, and an inner wall covered with a 0.2mm epoxy isolation layer. The connection method of the metal joints at both ends of the cylinder is the same as that of the one-end joint in Example 1, using 40CrNiMo alloy steel and equipped with PEEK insulating sleeves, allowing it to be mounted behind the drill bit.

[0071] like Figure 2As shown, there are four media windows, symmetrically arranged circumferentially. To accommodate the lightweight design, each media window is reduced to a length of 220 mm, an arc length of 70°, and a thickness of 8 mm. The material remains quartz fiber reinforced epoxy composite material with a dielectric constant of 3.6 ~ 4.1 and a media loss tangent of less than 0.01. Two ±45° glass fiber transition layers are installed between the media window and the CFRP shell, with a single layer thickness of 0.25 mm and an overlap length of ≥30 mm to ensure mechanical continuity. A 1.0 mm thick ferrite / carbon-based microwave absorbing layer is adhered to the inner wall of the media window, and a 0.8 mm thick low dielectric constant outer ring is fitted around the outer perimeter to further reduce electromagnetic coupling caused by well fluid flow.

[0072] The radially fully polarized antenna elements arranged within the dielectric window are the same as in Embodiment 1, still being orthogonal dipole or slot antenna pairs, with a single arm length of 95-110 mm, and employing a folded loading structure to extend the bandwidth. The antenna feed point is connected to the coaxial feed line, and the antenna elements formed by the four dielectric windows achieve four polarization modes—VV, HH, VH, and HV—through switching matrix switching.

[0073] Unlike Embodiment 1, this embodiment omits the forward-looking antenna unit. The front end is connected to other drill pipes via a metal connector, relying primarily on a radial antenna for 360° circumferential geological exploration. This structure is suitable for construction scenarios with low surrounding rock strength and low requirements for early warning of anomalies ahead.

[0074] The configuration of the tunable circuit module and the signal processing and transmission module is the same as in Embodiment 1, supporting adaptive tuning and SFCW in the range of 60~900MHz. The transmit chain uses a relay-switched π / T matching network, and the receive chain uses a MEMS capacitor array for fine-grained tuning.

[0075] In terms of protection, the device still employs epoxy potting, double O-ring sealing, and polyurea coating protection to ensure stable operation under normal working conditions. Due to the thinner wall thickness, the weight of the device in this embodiment is reduced by approximately 30%, making it suitable for weight-sensitive, long-term drilling environments.

[0076] Example 3: like Figure 1 and Figure 2 As shown, the overall structure of the tunable frequency fully polarized borehole radar detection device in this embodiment is the same as that in Embodiment 1. The difference is that the drill pipe body adopts a thicker wall to enhance its pressure resistance and torsion resistance.

[0077] The drill pipe body is constructed from a carbon fiber reinforced composite material cylinder with an outer diameter of Φ89 mm and a wall thickness of 20 mm, with a total length of approximately 1.2 m and an inner diameter of approximately Φ49 mm. The cylinder is made of high-strength T800 grade carbon fiber prepreg, cured through multi-layer winding layup. Two additional layups are added in the 0° and 90° directions to significantly improve bending and torsional resistance. The outer layer is coated with a 0.6 mm thick polyurea coating, exhibiting abrasion resistance ≥150 mg / 1000 revolutions.

[0078] like Figure 2 As shown, there are still four dielectric windows, arranged symmetrically in a circumferential direction, with dimensions consistent with Embodiment 1 (240 mm in length, 80° in arc, and 10 mm in thickness). A 1.5 mm absorbing layer is adhered to the inner wall, and a 1 mm low-dielectric-constant outer ring is fitted around the outer perimeter. A three-layer ±45° fiberglass transition layer with an overlap length of 35 mm is used between the dielectric windows and the CFRP cylinder to avoid stress concentration caused by the thick-walled structure.

[0079] The radially fully polarized antenna element structure within the dielectric window remains unchanged; it is still an orthogonal dipole / slot antenna with a single arm length of 110~120 mm, and a bow-tie loading structure is used to broaden the bandwidth. The four antennas are switched via a switch array to achieve VV / HH / VH / HV polarization modes.

[0080] The front end is still equipped with a biconical forward-looking antenna unit with a cone angle of 60°, an arm length of 45 mm, and a 6 mm thick PTFE end cap. This forward-looking unit works in conjunction with the radial antenna for detecting anomalous objects within a range of 10 to 20 m in front.

[0081] The tunable circuit module is the same as in Example 1, but to adapt to high-voltage and high-temperature conditions, the LNA in the receiver chain uses high-temperature resistant components, extending the operating temperature range to -20 ~ +120 ℃. The power supply module adopts a sealed design with a withstand pressure of 15 MPa to ensure long-term operation under high-voltage environments.

[0082] The entire machine adopts an epoxy potting and double O-ring sealing structure, with a PEEK insulating sleeve installed between the CFRP and the metal joint. Calculations show that this embodiment can withstand ≥15 MPa hydrostatic pressure and ≥1000 N·m torque, with S11 < -10 dB and polarization isolation >15 dB, making it suitable for drilling and exploration under hard rock and deep-buried high-stress tunnel conditions.

[0083] Example 4: A method for operating a frequency-tunable, fully polarized borehole radar detection device while drilling includes the following steps: The device is connected to the drill string via a metal connector and is lowered into the borehole along with the drill string to perform drilling. During drilling, the operating frequency band and polarization mode of the radar system are selected based on the acquired or preset operating parameters; among which, the operating parameters include at least one of well diameter, mud conductivity, or near-end echo amplitude. The polarization modes of the radially fully polarized antenna elements are switched sequentially according to a preset timing sequence. For each polarization mode, the frequency-tunable circuit module generates radar signals in the selected operating frequency band and transmits them through the corresponding antenna element, while simultaneously receiving reflected echo signals from the surrounding rock. The signal processing and transmission module performs amplitude limiting, low-noise amplification, filtering, and analog-to-digital conversion on the received echo signal. The processed radar data is then uploaded to the ground system via a drilling cable or electromagnetic wave inductive coupling. The ground system receives radar data and performs joint imaging and geological attribute inversion on data under different polarization modes and operating frequency bands to generate geological structure images and anomaly information in the borehole circumferential direction.

[0084] Joint imaging and geological attribute inversion of data from different polarization modes and operating frequency bands includes the following steps: Amplitude and phase calibration and direct wave template suppression are performed on multi-channel SFCW data; Angular beamforming and fk / Kirchhoff offset imaging are performed in cylindrical coordinates. Construct a voxel-level scattering matrix and perform polarization decomposition to output fracture strike / dip estimates; By employing multi-frequency joint constraints and TV-L2 regularization for attribute inversion, we obtained the water content indicator index and anomaly confidence map.

[0085] The adaptive switching control also includes: Operating conditions are classified based on well diameter, mud conductivity, and near-end echo characteristics, and selected according to the priority of low → medium → high frequency bands. Cross-polarization measurements are adaptively inserted between VV / HH and VH / HV based on information gain or coherence. Polarization and frequency band switching are performed in the sequence of "silent-switching-calibration-sampling", and degraded mode is entered when the threshold is triggered.

[0086] At the structural level, a multi-layer gradient design of "CFRP cylinder / glass fiber transition layer / dielectric window" is adopted to balance load-bearing strength, low wave transmission loss, interface sealing and annular gap coupling suppression. At the algorithm level, a "360° joint imaging + polarization decomposition + multi-frequency joint inversion" is proposed for multi-window full polarization, and polarization / frequency band adaptive switching control is realized with working condition perception and information gain as the core, forming an integrated technical system of "structure-algorithm-control-engineering criteria".

[0087] Example 5: Without altering the load-bearing and wave-transmitting functions of the CFRP cylinder, local areas can be constructed as distributed sensing or radiation units to enhance the integration of the device.

[0088] 1) Segmented Electrode / Slit Array: Several insulating isolation strips are pre-embedded in the inner wall or interlayer of CFRP, and circumferential segmented electrodes or slits are deposited on them; after being connected to the front-end circuit through a capacitive / inductive coupling network, it can be used as an axial "traveling wave leakage" radiation / sensing unit to assist the radial antenna in realizing angular sidelobe suppression or near-field environmental monitoring.

[0089] 2) Impedance / resistance network sensing: Utilizing the anisotropy of conductive fibers within the CFRP layer, it is used as a variable resistance-impedance medium to monitor the subtle changes in equivalent impedance caused by temperature, stress, and the water-bearing environment; this information can be combined with radar echoes as a multi-mode prior to improve the stability of attribute inversion.

[0090] 3) Electromagnetic compatibility and wave transmission guarantee: The distributed electrodes / slits adopt a thin-layer, intermittent and directional design, and through resonant frequency band avoidance and isolation band impedance matching, the influence on the main radar frequency band is controlled within the calibrable range; if necessary, the channel is independently calibrated and decoupled.

[0091] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A frequency-tunable, fully polarized borehole radar detection device for drilling, characterized in that, The application relates to a downhole radar system, which comprises the following parts: a drill pipe body, which comprises a hollow barrel, the barrel is connected with a drilling tool through a metal joint; a medium window, which is arranged on the drill pipe body in a ring shape and has at least two, each medium window is provided with a radial full polarization antenna unit, which is used for realizing ring direction detection; the radial full polarization antenna unit is switched among multiple frequency bands through an adjustable frequency circuit module and realizes impedance matching, radar signals are processed through a signal processing and transmission module and data is uploaded to a ground system; wherein the barrel comprises a carbon fiber reinforced composite layer, an outer surface of the carbon fiber reinforced composite layer is provided with a wear-resistant layer, a glass fiber transition layer is arranged between a region where the medium window is located and an inner wall surface of the carbon fiber reinforced composite layer, an outer periphery of the medium window is sleeved with a sleeve ring, and an inner wall surface of the glass fiber transition layer is provided with an absorbing layer; wherein an inner wall of the barrel is provided with a segmented electrode or a slit array and is connected with a signal processing module through a coupling network to serve as a distributed sensing or radiation unit.

2. The adjustable frequency, full polarimetric borehole radar system while drilling of claim 1, wherein, an axial forward-looking antenna unit is arranged at one end of the drill pipe body and is covered with an end cap outside, which is used for realizing longitudinal advanced detection in front of a drill bit.

3. The adjustable frequency, full polarimetric borehole radar system while drilling of claim 1, wherein, double O-shaped ring sealing structures are arranged at the connection between the metal joint and the barrel and at the connection between the end of the drill pipe body and the end cap, and the end cap has a set dielectric constant range.

4. The adjustable frequency, full polarimetric borehole radar system while drilling of claim 1, wherein, the glass fiber transition layer has multiple layers of glass fiber cloth with a set angle range, the overlapping length of the glass fiber cloth with the carbon fiber reinforced composite layer and the medium window is not less than a set value; and the sleeve ring is a low dielectric constant thin-wall ring.

5. The adjustable frequency, full polarimetric, borehole radar, while-drilling, apparatus of claim 1, wherein, an electronic cabin is arranged inside the drill pipe body and contains the adjustable frequency circuit module and the signal processing and transmission module, the electronic cabin is filled with low-loss epoxy resin to form a filling layer; and the wear-resistant layer is a polyurea or ceramic filler coating sprayed on the outer surface of the carbon fiber reinforced composite layer.

6. The adjustable frequency, full polarimetric borehole radar system while drilling of claim 1, wherein, the radial full polarization antenna unit comprises mutually orthogonal dipole antennas or slot antennas, the working mode of the radial full polarization antenna unit is controlled through a switch matrix to switch different polarization states.

7. The adjustable frequency, full polarimetric borehole radar system while drilling of claim 1, wherein, the adjustable frequency circuit module comprises a transmitting chain and a receiving chain; the transmitting chain adopts a relay or PIN diode switched pi-type or T-type reconfiguration matching network, and the reconfiguration matching network covers different working frequency bands; the receiving chain is provided with a MEMS or BST variable capacitance array, the variable capacitance array has a set tuning range, and the step is not greater than a set value.

8. The adjustable frequency, full polarimetric borehole radar system while drilling of claim 1, wherein, the signal processing and transmission module comprises an amplitude limiter, a low-noise amplifier, an anti-aliasing filter and an analog-to-digital converter which are sequentially connected in communication, the frequency step of the supported step continuous wave is 1 MHz to 5 MHz, and the dynamic range is not less than a set value.

9. A method of operating a drillable frequency-tunable full-polarimetric borehole radar probe according to any one of claims 1-8, characterized by, the following steps are included: the device is connected to a drilling tool string through a metal joint, is lowered into a borehole together with the drilling tool and performs drilling; during drilling, the working frequency band and polarization mode of the radar system are selected according to acquired or preset working condition parameters; wherein the working condition parameters include at least one of a well diameter, mud conductivity or near-end echo amplitude; The polarization mode of the radial full-polarization antenna unit is switched in turn according to a preset timing; for each polarization mode, the adjustable frequency circuit module generates a radar signal in the selected working frequency band and transmits the radar signal through the corresponding antenna unit, while receiving the reflected echo signal from the surrounding rock; The signal processing and transmission module performs amplitude limiting, low-noise amplification, filtering and analog-to-digital conversion processing on the received echo signal, and the processed radar data is uploaded to the ground system through the drill cable or electromagnetic wave inductive coupling mode; The ground system receives the radar data, performs joint imaging and geological attribute inversion on the data under different polarization modes and working frequency bands, and generates a geological structure image and abnormal body information around the borehole.

10. The method of operating a steerable, tunable, full-polarimetric ground-penetrating radar probe according to claim 9, wherein, The joint imaging and geological attribute inversion on the data under different polarization modes and working frequency bands include the following steps: Performing amplitude and phase calibration and direct wave template suppression on the multi-channel SFCW data; Performing angular beam synthesis and f-k / Kirchhoff migration imaging in the cylindrical coordinate system; Constructing a voxel-level scattering matrix and performing polarization decomposition to output a fracture strike / dip estimation; Using multi-frequency joint constraint and TV-L2 regular attribute inversion to obtain a water content indicator and an abnormal confidence map.

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