Variable-frequency borehole radar antenna and method

Abstract

The invention discloses a variable-frequency drilling radar antenna and a method. The variable-frequency drilling radar antenna comprises a three-stage sleeve type telescopic radiator, a control system, a traction device, a displacement sensor, a limiting device, an impedance switcher, a pulse source circuit board and an acquisition circuit board. According to the invention, through a three-stage sleeve type telescopic structure, continuous variation of the physical length of the antenna is realized in a standard drill hole with the diameter of 76mm, so that a frequency adjustment range of 100-400MHz is obtained; the mechanical structure realizes large-range step switching of frequency, and the circuit switching performs frequency fine tuning and impedance optimization on each step point, so that the overall impedance matching efficiency is improved to more than 85%, and the radiation efficiency under each frequency point is ensured; a single antenna can replace a plurality of traditional fixed-frequency antennas, so that the equipment cost and the line changing time of single-hole operation are greatly reduced; according to the impedance self-adaptive matching link based on the dielectric electric constant, matching parameters can be dynamically optimized according to actual slurry in the drill hole or the stratum environment, and the signal quality under different depths and different stratum conditions is improved.

Description

Technical Field

[0001] This invention belongs to the field of borehole radar technology, and relates to a variable frequency antenna device suitable for borehole detection and its frequency control method. Background Technology

[0002] Borehole radar, as an important geophysical exploration tool, has been widely used in mineral resource exploration, engineering geological survey, geological disaster early warning, and underground space exploration. Its working principle involves emitting high-frequency electromagnetic pulses into the strata surrounding the borehole and receiving reflected echoes from interfaces with different dielectric constants, thereby inverting the underground structure and physical property distribution. The center frequency of the antenna is the core parameter determining the radar system's detection performance: the higher the frequency, the shorter the wavelength, and the finer the spatial resolution, but the more severe the attenuation of electromagnetic waves in conductive media, limiting the detection depth; conversely, the lower the frequency, the stronger the penetration capability and the greater the detection depth, but the resolution decreases accordingly.

[0003] Currently, commercial and research-grade borehole radar systems commonly employ dipole antenna designs with a fixed center frequency. Once the physical length of this antenna (typically about half the operating wavelength) and its packaging medium are determined, its key characteristics, such as resonant frequency, radiation pattern, and input impedance, are fixed. This traditional design paradigm exposes the following increasingly serious technical bottlenecks and limitations in practical engineering applications: 1. The contradiction between the demand for "multiple explorations in one borehole" and the reality of "one antenna, one frequency": Complex geological exploration tasks, such as deep mineral exploration, often require comprehensive multi-scale and multi-target detection within the same borehole. This necessitates both low-frequency signals (e.g., 50-100MHz) penetrating hundreds of meters of overburden to detect large deep structures, and mid-to-high-frequency signals (e.g., 200-400MHz) for high-resolution imaging of shallow mineralized zones, faults, or karst. However, fixed-frequency antennas cannot dynamically adjust their detection scale during a single borehole run. To resolve this contradiction, the current operating model is forced to adopt a "multiple antennas rotating downhole" approach. Engineering practice shows that in a borehole deeper than 500 meters, each antenna change, including the processes of pulling, disassembling, connecting, calibrating, and lowering, takes an average of more than 2 hours. For boreholes requiring detection across three frequency bands, the antenna change time alone extends the operation cycle by more than 40%, significantly reducing exploration efficiency. Meanwhile, the procurement and maintenance of multiple antennas and related equipment at different frequencies directly increased the project's equipment costs and logistical complexity.

[0004] 2. The inherent conflict between extreme space constraints in borehole drilling and antenna performance expansion: To adapt to various geological drilling standards, the outer diameter of borehole radar antennas is typically strictly limited to between 76mm and 100mm. Within this extremely confined cylindrical space, the radiator, shielding layer, transmitter, receiver, power supply, and control circuitry must be accommodated, making the design space extremely limited. Existing technical approaches attempting to achieve multi-band detection mainly include: Path 1: Multi-frequency antenna physical integration. This involves arranging or connecting multiple dipole elements of different lengths in parallel or in series within a single antenna tube. However, this not only causes strong mutual coupling between the elements, severely distorting the radiation pattern, but also the arrangement of multiple elements and their independent feed networks within a limited cross-section inevitably leads to the overall antenna diameter exceeding the limit, making it unsuitable for underground deployment.

[0005] Path Two: Electrically Tuned Antennas Based on Adjustable Components. This involves using varactor diodes or RF MEMS switches to adjust the antenna's resonant frequency. While this approach can achieve a certain degree of frequency variation, it suffers from two fundamental drawbacks: First, the tuning range is limited (usually no more than one octave), making it difficult to cover the wide frequency span required for deep surveys to shallow detailed surveys (several octaves). Second, the introduced adjustable components themselves introduce additional insertion loss, reducing radiation efficiency, and their reliability and stability face severe challenges in the harsh environment of high temperature, high pressure, and high humidity inside boreholes.

[0006] The aforementioned conflict can be attributed to the inherent "frequency-aperture-efficiency" relationship of drill-hole radar antennas, which makes it difficult to simultaneously achieve a wide frequency tuning range and high radiation efficiency with a given small aperture. Traditional fixed-frequency designs sacrifice frequency flexibility, while existing electronically tuned schemes often sacrifice efficiency and reliability for limited flexibility.

[0007] 3. Impedance Mismatch Challenges in Time-Varying Non-Uniform Media: Effective antenna radiation into the formation relies on impedance matching. Fixed-frequency antenna matching networks are designed and optimized for homogeneous media (typically air or water) with specific dielectric constants. However, actual borehole environments are extremely complex: boreholes may be filled with mud, water, or air, with dielectric constants varying drastically from 1 to over 80. Simultaneously, the conductivity and dielectric constant of the surrounding rock formations change non-linearly with increasing depth. As the antenna moves within the borehole, the surrounding equivalent medium constantly changes, causing the antenna's input impedance to drift. Fixed matching networks cannot adapt to this dynamic change, resulting in severe impedance mismatch. Consequently, most signal energy is reflected back to the transmitter, significantly reducing effective radiated power and detection depth, and generating multiple reflections that degrade the received signal quality. The lack of online, adaptive impedance matching capability in existing systems is one of the key factors limiting their detection performance in complex formations.

[0008] 4. The Urgent Need for Adaptive Detection Technology in Deep Exploration: As mineral resource exploration advances to deeper depths (above 1000 meters), the cost of acquiring stratigraphic information has risen sharply. Deep drilling itself is extremely costly, therefore maximizing the use of each borehole to obtain comprehensive, high-quality geophysical data has extremely high economic value. Fixed-frequency borehole radar antennas in deep holes can only provide single-scale data, which may be of poor quality due to impedance mismatch, undoubtedly wasting valuable borehole resources. The industry urgently needs an intelligent antenna system that can automatically adjust its operating frequency and impedance state during a single well run based on preset programs or real-time feedback, adapting to the optimal detection requirements at different depths.

[0009] In summary, existing borehole radar antenna technology, limited by fixed frequency design, narrow space constraints, and static impedance matching, can no longer meet the urgent needs of modern geological exploration for high-efficiency, low-cost, multi-scale, and adaptive detection. Developing a novel antenna device and method capable of achieving wide bandwidth, high precision, and adaptive tuning within a standard borehole diameter is crucial to overcoming current technological bottlenecks and unlocking the application potential of borehole radar. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention aims to provide a variable frequency drilling radar antenna and method, specifically a variable frequency drilling radar antenna and method with a compact structure, wide adjustment range, and good impedance matching, enabling multi-scale adaptive detection within a single borehole.

[0011] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A variable frequency drilling radar antenna includes a three-stage sleeve-type telescopic radiator, a control system, a traction device, a displacement sensor, a limiting device, an impedance switch, a pulse source circuit board, and a data acquisition circuit board. The three-stage telescopic radiator adopts a coaxial telescopic mechanical structure, consisting of three stages of tubes from the outside to the inside: a coaxial outer tube, a relay tube, and a core tube. Adjacent tubes slide axially through a sliding rail and keyway structure on the tube wall. In the fully extended state, each stage of the tubes is tightly pressed together by elastic metal contact pieces at the ends to form a continuous radiator with electrical conductivity. At this time, the effective electrical length of the antenna is the longest, corresponding to the lowest operating frequency. In the retracted state, relative axial displacement occurs between the tubes, the contact pieces separate, the electrical connection is broken, the effective electrical length of the antenna is shortened, and the corresponding operating frequency is increased. The traction device is located inside the three-stage telescopic radiator and is used to drive the telescopic movement of the three-stage telescopic radiator. It includes a micro stepper motor, a winch, a traction rope, a drive slider, spring I, and spring II. The control system is the control center of the antenna, and integrates a main controller, a power management module, a communication module and a displacement accuracy sensor; The displacement sensor is mounted on the drive slider and is used to measure the axial displacement of the drive slider relative to the core tube in real time and feed the data back to the main controller to form a closed-loop position control. The limiting device is used to achieve precise mechanical locking and indication of the telescopic position of the three-stage sleeve-type telescopic radiator, and includes a limiting block and a limiting key pin. The impedance switch is used to achieve fine frequency adjustment and impedance matching. It integrates a main control MCU, a matching network control unit, an impedance detection unit and a power management unit. The pulse source circuit board is connected to the input of the impedance switch via a coaxial cable to generate nanosecond-level electromagnetic pulses with high peak power; the acquisition circuit board receives the antenna echo signal preprocessed by the impedance switch via another coaxial cable, and amplifies, samples and digitizes it; the two circuit boards are synchronized and transmit data via optical fiber.

[0012] The present invention also includes the following technical features: Specifically, the outer tube is the outermost cylindrical metal conductive tube, serving as the main radiating arm and outer protective shell of the antenna; the repeater tube is a cylindrical metal conductive tube located inside the outer tube, with its outer diameter slightly smaller than the inner diameter of the outer tube, and capable of sliding axially along the inner wall of the outer tube; the core tube is a cylindrical metal conductive tube located inside the repeater tube, with its outer diameter slightly smaller than the inner diameter of the repeater tube, and capable of sliding axially along the inner wall of the repeater tube.

[0013] Specifically, the micro stepper motor serves as the power source, with its body fixedly mounted on the fixed frame near the antenna end; the winch is coaxially and fixedly connected to the output shaft of the micro stepper motor; the traction rope is made of high-strength, low-tensile fiber rope, with one end wound and fixed to the winch, and the other end axially passing through the inside of the core tube; the drive slider is a cylindrical slider, slidably disposed in the inner cavity of the core tube, and fixedly connected to the end of the traction rope; springs I and II are both compression springs, with the two ends of spring I fixedly connected to the far end of the drive slider and the inner wall of the outer tube, respectively; the two ends of spring II are fixedly connected to the same end of the drive slider and the inner wall of the repeater tube, respectively.

[0014] Specifically, the main controller receives the operating frequency command sent by the ground control system via cable, calculates the corresponding target mechanical gear and target circuit parameters, and then generates a control signal to drive the micro stepper motor and impedance switch to work together; the displacement accuracy sensor is used to assist in monitoring the overall displacement.

[0015] Specifically, the displacement sensor is a high-precision linear displacement sensor.

[0016] Specifically, the limiting block is fixed to the outer periphery of the driving slider; there are multiple sets of limiting key pins, which are respectively fixedly installed on the inner walls of the outer tube and the relay tube to form a multi-level limiting groove; when the driving slider moves to the target position, the limiting block is engaged in the corresponding limiting key pin and sends a mechanical positioning signal.

[0017] Specifically, the main control MCU is used to receive impedance adjustment commands issued by the control system; The matching network control unit includes a π-type adjustable matching network, a multiplexer analog switch, and a balun converter. The π-type adjustable matching network includes two parallel digitally controlled variable capacitors C1 and C2 and an adjustable inductor L1. The capacitance value is adjusted by the main control MCU to achieve continuous and fine adjustment of the antenna input impedance. The multiple output channels of the multiplexer analog switch are respectively connected to three feed points located on the outer wall of the outer tube: feed point I, feed point II, and feed point III. By switching the switch channels, the physical position of the radar pulse signal fed into the antenna can be changed. The impedance detection unit and power management unit are used to monitor the matching status in real time and supply power to the internal circuits.

[0018] Specifically, the pulse source circuit board and the acquisition circuit board are installed side by side in the moisture-proof shielding chamber at the rear of the antenna.

[0019] A method for operating the variable frequency drilling radar antenna includes the following steps: Step S1: The ground operator sends the target center frequency command f to the downhole antenna through the ground control system according to the exploration requirements; Step S2: The main controller of the downhole antenna receives the instruction f, queries the built-in frequency-parameter mapping table, and determines the following required to achieve frequency f: the total contraction length of the three-stage sleeve corresponding to the target mechanical telescoping stage N, the target feed point number K, and the theoretical initial values ​​of the target matching network parameters C1, C2, and L1. Step S3: The main controller drives the micro stepper motor to rotate forward, which drives the winch to wind the traction rope; the traction rope pulls the slider to slide towards the near end, i.e. towards the motor; during this process, the displacement sensor reports the slider position in real time. Step S4: The sliding block first compresses spring I, and the spring force causes the outer tube and the repeater tube to slide relative to each other, completing the first stage of contraction. If a second stage of contraction is required, the sliding continues, further compressing spring II, causing the repeater tube and the core tube to slide relative to each other. When the slider displacement reaches the target value, the limit block on it engages with the limit key on the corresponding tube wall, the mechanical movement stops, and the effective length of the antenna is fixed. This step achieves coarse adjustment of the operating frequency, with an adjustment range of 100MHz to 400MHz. Step S5: The main controller sends the target matching network parameters to the main control MCU of the impedance switch; the main control MCU adjusts the values ​​of the digitally controlled capacitors C1 and C2 in the π-type matching network through the digital interface, selects the matching inductor L1, and sets the turns ratio of the balun transformer to achieve optimal matching between the antenna input impedance and the pulse source output impedance, maximizing energy transmission efficiency; the target impedance value is matched according to the transmission line theory formula. The estimation and optimization are performed, where D is the current equivalent inner diameter of the outer tube and d is the equivalent diameter of the inner conductor. The relative permittivity of the medium inside the borehole; Step S6: The main control MCU of the impedance switch controls the multi-channel analog switch to switch the pulse source output signal to the target feed point K determined in step S2; the three feed points are non-uniformly arranged along the axial direction of the outer wall of the outer tube, and their positions are optimized by simulation, corresponding to the optimal current distribution points under different mechanical lengths; switching the feed points can finely adjust the resonant characteristics of the antenna, realizing fine frequency calibration with an accuracy of ±10MHz; thus, through the dual synergistic mechanism of changing the electrical length by mechanical extension and switching to optimize the current distribution, the antenna is accurately tuned to the target frequency f, and the impedance matching is good; Step S7: The system is ready. The pulse source circuit board is triggered to generate an electromagnetic pulse that radiates to the surrounding strata through the matching network and the selected feed point. The echo signal is received by the antenna and sent to the acquisition circuit board for processing and storage via the impedance switch. Step S8: If it is necessary to switch from high frequency to low frequency, the main controller commands the micro stepper motor to reverse and release the traction rope; under the action of the elastic restoring force stored in spring I and spring II, the slider is driven to slide to the far end, causing each stage of the tube to extend and reset in sequence; at the same time, the impedance switch synchronously switches the matching network parameters and the feed point back to the corresponding state.

[0020] Compared with the prior art, the present invention has the following technical effects: (1) This invention breaks through the limitation of drilling diameter on multi-frequency antennas: through the innovative three-stage sleeve telescopic structure, the physical length of the antenna can be continuously variable in a standard drill hole with a diameter of only 76mm, thereby obtaining a frequency adjustment range of 100-400MHz.

[0021] (2) This invention achieves high-precision frequency tuning through electromechanical coordination: it pioneers a dual tuning mechanism of "mechanical expansion and contraction coarse tuning + circuit switching fine tuning". The mechanical structure realizes a wide range of frequency step switching, while the circuit switching (feed point and matching network) is responsible for fine-tuning the frequency and optimizing the impedance at each step point, improving the overall impedance matching efficiency to more than 85% and ensuring the radiation performance at each frequency point.

[0022] (3) This invention significantly improves exploration efficiency and economy: a single antenna can replace multiple sets of traditional fixed-frequency antennas, greatly reducing equipment costs and line-changing time for single-hole operations. Actual measurements show that, compared with traditional methods, this device can reduce overall exploration costs by about 60% and increase operational efficiency by 3 times.

[0023] (4) This invention enhances adaptability to complex geological conditions: the method includes a method based on the dielectric constant ( The impedance adaptive matching stage can dynamically optimize the matching parameters according to the actual mud or formation environment in the borehole, thereby improving the signal quality under different depths and formation conditions. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the axial cross-sectional structure of the antenna of the present invention in its fully extended state (low-frequency mode).

[0025] Figure 2 This is a schematic diagram of the axial cross-sectional structure of the antenna of the present invention in the first-stage contraction state (intermediate frequency mode).

[0026] Figure 3 This is a schematic diagram of the axial cross-sectional structure of the antenna of the present invention in the second-stage contraction state (high-frequency mode).

[0027] Figure 4 This is a block diagram of the control system structure of the antenna device of the present invention.

[0028] Figure 5 This is a system electrical connection block diagram of the antenna device of the present invention.

[0029] Figure 6 This is a block diagram illustrating the internal principle of the impedance switch in this invention.

[0030] Figure 7 for Figure 6 Detailed block diagram of the matching network control unit.

[0031] Figure 8 This is the circuit schematic of a π-type adjustable matching network.

[0032] Figure 9 This is a flowchart illustrating the operation of the variable frequency antenna of this invention.

[0033] The meanings of the labels in the diagram are as follows: 1-Outer tube, 2-Relay tube, 3-Core tube, 4-Traction device, 5-Drive slider, 6-Displacement sensor, 7-Spring I, 8-Limit block, 9-Spring II, 10-Control system, 11-Traction rope, 12-Windlass, 13-Limit key, 14-Feeding point I, 15-Feeding point II, 16-Feeding point III. Detailed Implementation

[0034] The present invention provides a variable frequency drilling radar antenna, comprising a three-stage sleeve-type telescopic radiator, a control system 10, a traction device 4, a displacement sensor 6, a limiting device, an impedance switch, a pulse source circuit board, and a data acquisition circuit board.

[0035] The three-stage telescopic radiator is the core radiating element of the antenna. It adopts a coaxial telescopic mechanical structure and consists of three stages of tubes from the outside to the inside: an outer tube 1, a repeater tube 2, and a core tube 3. Adjacent tubes slide axially through a sliding rail and keyway structure on the tube wall. In the fully extended state, each stage of the tubes is tightly pressed together by elastic metal contact pieces at the ends to form a continuous radiator with electrical conductivity. At this time, the effective electrical length of the antenna is the longest, corresponding to the lowest operating frequency. In the retracted state, relative axial displacement occurs between the tubes, the contact pieces separate, the electrical connection is broken, the effective electrical length of the antenna is shortened, and the corresponding operating frequency is increased.

[0036] The traction device 4 is installed inside the three-stage sleeve-type telescopic radiator to drive the telescopic movement of the three-stage sleeve-type telescopic radiator. It includes a micro stepper motor, a winch 12, a traction rope 11, a drive slider 5, a spring I7, and a spring II9.

[0037] The control system 10 serves as the control center for the antenna and integrates a main controller, a power management module, a communication module, and a displacement accuracy sensor.

[0038] The displacement sensor 6 is installed on the drive slider 5 to measure the axial displacement of the drive slider 5 relative to the core tube 3 in real time and feed the data back to the main controller to form a closed-loop position control.

[0039] The limiting device is used to achieve precise mechanical locking and indication of the telescopic position of the three-stage sleeve-type telescopic radiator, including the limiting block 8 and the limiting key pin 13.

[0040] Impedance switchers are used to achieve fine frequency adjustment and impedance matching. They integrate a main control MCU, a matching network control unit, an impedance detection unit, and a power management unit.

[0041] The pulse source circuit board is connected to the input of the impedance switch via a coaxial cable to generate nanosecond-level electromagnetic pulses with high peak power; the acquisition circuit board receives the antenna echo signal preprocessed by the impedance switch via another coaxial cable, and amplifies, samples and digitizes it; the two circuit boards are synchronized and transmit data through optical fiber.

[0042] The outer tube 1 is the outermost cylindrical metal conductive tube, serving as the main radiating arm and outer protective shell of the antenna; the repeater tube 2 is a cylindrical metal conductive tube located inside the outer tube 1, with an outer diameter slightly smaller than the inner diameter of the outer tube 1, and can slide axially along the inner wall of the outer tube 1; the core tube 3 is a cylindrical metal conductive tube located inside the repeater tube 2, with an outer diameter slightly smaller than the inner diameter of the repeater tube 2, and can slide axially along the inner wall of the repeater tube 2.

[0043] More specifically, the adjacent tubes of the outer tube 1, relay tube 2, and core tube 3 are connected by a slide rail and keyway structure on the tube wall to ensure smooth sliding and prevent radial rotation. In the fully extended state (e.g.) Figure 1 As shown), each tube is tightly pressed together by elastic metal contact pieces designed at its ends, forming a continuous radiator with electrical conductivity. At this point, the antenna's effective electrical length is at its longest, corresponding to the lowest operating frequency. In the retracted state (as shown...), Figure 2 , Figure 3 As shown, relative axial displacement occurs between the tubes, the contact pieces separate, the electrical connection is broken, the effective electrical length of the antenna is shortened, and the corresponding operating frequency increases.

[0044] The miniature stepper motor serves as the power source, and its body is fixedly mounted on the fixed frame near the antenna end (i.e., the end closest to the underground cable connector). The winch 12 is coaxially and fixedly connected to the output shaft of the miniature stepper motor. The traction rope 11 is made of high-strength, low-tensile fiber rope, with one end wound and fixed to the winch 12, and the other end axially passing through the inside of the core tube 3. The drive slider 5 is a cylindrical slider that is slidably disposed in the inner cavity of the core tube 3 and fixedly connected to the end of the traction rope 11. Springs I7 and II9 are both compression springs. The two ends of spring I7 are fixedly connected to the far end of the drive slider 5 (away from the motor end) and the inner wall of the outer tube 1, respectively. The two ends of spring II9 are fixedly connected to the same end of the drive slider 5 and the inner wall of the relay tube 2, respectively.

[0045] The main controller receives the operating frequency command sent by the ground control system 10 through the cable, and calculates the corresponding target mechanical gear (extension level) and target circuit parameters (feed point and matching network value) according to the preset algorithm, and then generates control signals to drive the micro stepper motor and impedance switch to work together; the displacement accuracy sensor is used to assist in monitoring the overall displacement.

[0046] Displacement sensor 6 is a high-precision linear displacement sensor.

[0047] The limiting block 8 is fixed to the outer periphery of the driving slider 5; there are multiple sets of limiting key pins 13, which are respectively fixedly installed at specific positions on the inner walls of the outer tube 1 and the relay tube 2 to form multi-level limiting grooves; when the driving slider 5 moves to the target position, the limiting block 8 is precisely engaged in the corresponding limiting key pin 13, and a clear mechanical positioning signal is emitted.

[0048] The impedance switcher is a key circuit module for achieving fine frequency adjustment and impedance matching. The main control MCU is used to receive impedance adjustment commands issued by the control system 10. The matching network control unit includes a π-type adjustable matching network, a multiplexer analog switch, and a balun converter. The π-type adjustable matching network includes two parallel digitally controlled variable capacitors (C1, C2) and an adjustable inductor (L1). The capacitance and inductance values ​​are adjusted by the main control MCU to achieve continuous and fine adjustment of the antenna input impedance. The multiple output channels of the multiplexer analog switch are respectively connected to three feed points (feed point I14, feed point II15, and feed point III16) located on the outer wall of the outer tube 1. By switching the switch channels, the physical position of the radar pulse signal fed into the antenna can be changed. The impedance detection unit and power management unit are used to monitor the matching status in real time and supply power to the internal circuitry.

[0049] The pulse source circuit board and the acquisition circuit board are installed side by side in the moisture-proof shielded chamber at the rear of the antenna.

[0050] The present invention also provides a method for operating the above-mentioned variable frequency drilling radar antenna, comprising the following steps: Step S1 (Command Reception): The ground operator sends the target center frequency command f to the downhole antenna through the ground control system according to the exploration requirements; Step S2 (Command Parsing): The main controller of the downhole antenna receives command f, queries the built-in frequency-parameter mapping table, and determines the following required to achieve frequency f: target mechanical expansion stage N (corresponding to the total contraction length of the three-stage sleeve), target feed point number K, and target matching network parameters (theoretical initial values ​​of C1, C2, L1). Step S3 (Mechanical coarse adjustment - telescopic drive): The main controller drives the micro stepper motor to rotate forward, which drives the winch to wind the traction rope; the traction rope pulls the slider to slide towards the near end (i.e. towards the motor); during this process, the displacement sensor reports the slider position in real time. Step S4 (Mechanical coarse adjustment - positioning and locking): The drive slider slides first compresses spring I, and the spring force causes the outer tube and the relay tube to slide relative to each other, completing the first stage of contraction. Figure 2 (State); if a second stage of contraction is required, the sliding continues, further compressing spring II, causing the relay tube and the core tube to slide relative to each other ( Figure 3 (Status); when the slider displacement reaches the target value, the limit block on it engages with the limit key on the corresponding tube wall, the mechanical movement stops, and the effective length of the antenna is fixed; this step achieves coarse adjustment of the working frequency, with an adjustment range of 100MHz to 400MHz; Step S5 (Circuit Fine-tuning - Impedance Matching): The main controller sends the target matching network parameters to the main control MCU of the impedance switch; the main control MCU adjusts the values ​​of the digitally controlled capacitors C1 and C2 in the π-type matching network through a digital interface (such as SPI), selects the matching inductor L1, and sets the turns ratio of the balun converter to achieve optimal matching between the antenna input impedance and the pulse source output impedance, maximizing energy transmission efficiency; the target impedance value is matched according to the transmission line theory formula. The estimation and optimization are performed, where D is the current equivalent inner diameter of the outer tube and d is the equivalent diameter of the inner conductor. The relative permittivity of the medium inside the borehole; Step S6 (Circuit Fine-tuning - Feed Point Switching): The main control MCU of the impedance switch controls the multi-channel analog switch to switch the pulse source output signal to the target feed point K determined in step S2; the three feed points are non-uniformly arranged along the axial direction of the outer wall of the outer tube, and their positions are optimized by simulation, corresponding to the optimal current distribution points under different mechanical lengths; switching the feed points can fine-tune the resonant characteristics of the antenna, realizing fine frequency calibration with an accuracy of ±10MHz; thus, through the dual synergistic mechanism of changing the electrical length by mechanical extension and circuit switching to optimize the current distribution, the antenna is precisely tuned to the target frequency f, and the impedance matching is good; Step S7 (Detection Execution): The system is ready, the pulse source circuit board is triggered, and an electromagnetic pulse is generated and radiated to the surrounding strata through the matching network and the selected feed point; the echo signal is received by the antenna and sent to the acquisition circuit board for processing and storage through the impedance switch. Step S8 / S9 (Frequency Recall): If it is necessary to switch from high frequency to low frequency, the main controller commands the micro stepper motor to reverse and release the traction rope; under the action of the elastic restoring force stored in spring I and spring II, the slider is driven to slide to the far end, causing each stage of the tube to extend and reset in sequence; at the same time, the impedance switch synchronously switches the matching network parameters and the feed point back to the corresponding state.

[0051] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0052] Example 1: This embodiment provides a variable frequency drilling radar antenna, see [link to documentation]. Figures 1 to 3 This embodiment demonstrates three typical operating states of the antenna.

[0053] Initial state ( Figure 1): This corresponds to the lowest operating frequency (e.g., 100MHz). The micro stepper motor is in the initial position, and the traction rope is slack. Under the natural extension force of springs I and II, the drive slider is located at the farthest end of the core tube's inner cavity, and the three-stage sleeves (outer tube, relay tube, and core tube) are fully extended, reaching their maximum total length L_max. The elastic contact pieces at the ends of each stage of the tube body are in close contact under axial pressure, ensuring low-loss conduction of the RF signal.

[0054] First-order contraction state ( Figure 2 ): This corresponds to the intermediate operating frequency (e.g., 200MHz). The control system drives the micro stepper motor to rotate forward, tightening the traction rope via a winch. The traction rope pulls the drive slider to slide a distance ΔL1 towards the near end. During this process, spring I is compressed, and its reaction force pulls the outer tube relative to the repeater tube to slide a distance ΔL1 towards the near end, while no relative movement has occurred between the repeater tube and the core tube. At this time, the electrical connection between the outer tube and the repeater tube is broken, and the effective length of the antenna is shortened to L_max - ΔL1. The limiting block on the drive slider engages with the first-stage limiting key pin on the inner wall of the outer tube 1, achieving locking.

[0055] Second-order contraction state ( Figure 3 ): This corresponds to the highest operating frequency (e.g., 400MHz). The miniature stepper motor continues to rotate forward, driving the slider to slide a further distance ΔL2 towards the near end. During this process, spring II is compressed, and its reaction force pulls the repeater tube relative to the core tube to slide a further distance ΔL2 towards the near end. At this time, the electrical connection between the repeater tube and the core tube is also broken. The total effective length of the antenna is further shortened to L_max - ΔL1 - ΔL2. The limiting block engages with the second-level limiting key pin on the inner wall of the repeater tube.

[0056] Example 2: This embodiment provides a method for implementing electrical control and tuning of a variable frequency drilling radar antenna. (See also...) Figures 4 to 9 This embodiment details the electrical process of frequency conversion.

[0057] When ground operators need to switch the antenna from 100MHz to 400MHz for finer detection: 1. The ground control system sends the command "f=400MHz" through the communication cable.

[0058] 2. The main controller of the downhole control system receives the instruction, parses it to determine that it needs to enter the "second-level contraction" state, and calls the corresponding target feed point (e.g., feed point III) and a set of preset matching network parameters (C1', C2', L1').

[0059] 3. The main controller initiates the forward rotation program of the micro stepper motor and reads the feedback from the displacement sensor in real time. At the same time, the displacement accuracy sensor monitors the overall structural deformation.

[0060] 4. For example Figure 4 The process involves the motor driving the mechanical structure through the first stage of contraction and finally reaching the second stage of contraction, where the limit block engages.

[0061] 5. The mechanical positioning signal triggers the main controller to send an adjustment command to the main control MCU of the impedance switch.

[0062] 6. For example Figure 6 and Figure 7 As shown, the impedance switcher starts working. The main control MCU first controls the π-type matching network in the matching network control unit to adjust capacitors C1 and C2 to C1' and C2', and switch inductor L1 to the L1' position to perform preliminary impedance matching.

[0063] 7. Next, the main control MCU controls the multi-channel analog switch to switch the signal path to the channel connected to "Power Feed Point III".

[0064] 8. Finally, the signal is balanced by a balun converter and then fed into the antenna radiator. The impedance detection unit monitors the VSWR in real time and feeds the data back to the main control MCU. The main control MCU can perform small-range closed-loop fine-tuning of C1 and C2 based on the feedback until the impedance matching is optimal (e.g., VSWR < 1.5).

[0065] 9. Tuning complete, the system enters the ready state and can trigger the pulse source for high-resolution detection at 400MHz.

[0066] Example 3: This embodiment provides a multi-scale exploration application of a variable frequency borehole radar antenna, combined with... Figure 9 The flowchart, in a complete borehole exploration: Phase 1 (Survey): The antenna is fully extended into the well in 100MHz low-frequency mode to conduct a rapid and deep survey scan to delineate anomaly areas.

[0067] Phase Two (Detailed Investigation): In the discovered anomaly area, without going down into the well, the antenna is switched to 200MHz intermediate frequency mode (first-stage contraction) directly via ground command. The antenna performs high-resolution detection at this depth to preliminarily determine the nature of the anomaly.

[0068] Phase 3 (Detailed Investigation): If a more refined structure is required, the antenna is further switched to a 400MHz high-frequency mode (second-stage contraction) to obtain centimeter-level resolution data and accurately characterize the morphology of the anomalous body.

[0069] Throughout the process, the antenna did not need to be removed from the drilling, achieving a seamless transition from general survey to detailed survey, which greatly improved operational efficiency and data quality.

[0070] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0071] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0072] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A variable frequency drilling radar antenna, characterized in that, It includes a three-stage sleeve-type telescopic radiator, a control system (10), a traction device (4), a displacement sensor (6), a limit device, an impedance switch, a pulse source circuit board, and a data acquisition circuit board. The three-stage telescopic radiator adopts a coaxial telescopic mechanical structure, which includes three stages of tubes from the outside to the inside: a coaxial outer tube (1), a relay tube (2), and a core tube (3). Adjacent tubes slide axially through a sliding rail and keyway structure on the tube wall. In the fully extended state, each tube is tightly pressed together by elastic metal contact pieces at the ends to form a continuous radiator with electrical conductivity. At this time, the effective electrical length of the antenna is the longest, corresponding to the lowest operating frequency. In the retracted state, relative axial displacement occurs between the tubes, the contact pieces separate, the electrical connection is broken, the effective electrical length of the antenna is shortened, and the corresponding operating frequency is increased. The traction device (4) is installed in the three-stage sleeve telescopic radiator to drive the telescopic movement of the three-stage sleeve telescopic radiator, including a micro stepper motor, a winch (12), a traction rope (11), a drive slider (5), spring I (7) and spring II (9). The control system (10) is the control center of the antenna, and integrates a main controller, a power management module, a communication module and a displacement accuracy sensor; The displacement sensor (6) is mounted on the drive slider (5) and is used to measure the axial displacement of the drive slider (5) relative to the core tube (3) in real time and feed the data back to the main controller to form a closed-loop position control. The limiting device is used to achieve precise mechanical locking and indication of the telescopic position of the three-stage sleeve telescopic radiator, including a limiting block (8) and a limiting key (13). The impedance switch is used to achieve fine frequency adjustment and impedance matching. It integrates a main control MCU, a matching network control unit, an impedance detection unit and a power management unit. The pulse source circuit board is connected to the input of the impedance switch via a coaxial cable to generate nanosecond-level electromagnetic pulses with high peak power; the acquisition circuit board receives the antenna echo signal preprocessed by the impedance switch via another coaxial cable, and amplifies, samples and digitizes it; the two circuit boards are synchronized and transmit data via optical fiber.

2. The variable frequency drilling radar antenna as described in claim 1, characterized in that, The outer tube (1) is the outermost cylindrical metal conductive tube, serving as the main radiating arm and outer protective shell of the antenna; the relay tube (2) is a cylindrical metal conductive tube located inside the outer tube (1), with an outer diameter slightly smaller than the inner diameter of the outer tube (1), and can slide axially along the inner wall of the outer tube (1); the core tube (3) is a cylindrical metal conductive tube located inside the relay tube (2), with an outer diameter slightly smaller than the inner diameter of the relay tube (2), and can slide axially along the inner wall of the relay tube (2).

3. The variable frequency drilling radar antenna as described in claim 1, characterized in that, The micro stepper motor serves as the power source, and its body is fixedly mounted on the fixed frame near the antenna. The winch (12) is coaxially fixedly connected to the output shaft of the micro stepper motor. The traction rope (11) is made of high-strength, low-tension fiber rope, with one end wound and fixed on the winch (12), and the other end axially passing through the inside of the core tube (3). The drive slider (5) is a cylindrical slider that is slidably set in the inner cavity of the core tube (3) and fixedly connected to the end of the traction rope (11). Spring I (7) and spring II (9) are both compression springs. The two ends of spring I (7) are fixedly connected to the far end of the drive slider (5) and the inner wall of the outer tube (1), respectively. The two ends of spring II (9) are fixedly connected to the same end of the drive slider (5) and the inner wall of the relay tube (2), respectively.

4. The variable frequency drilling radar antenna as described in claim 1, characterized in that, The main controller receives the working frequency command sent by the ground control system (10) through the cable, calculates the corresponding target mechanical gear and target circuit parameters, and then generates a control signal to drive the micro stepper motor and impedance switch to work together; the displacement accuracy sensor is used to assist in monitoring the overall displacement.

5. The variable frequency drilling radar antenna as described in claim 1, characterized in that, The displacement sensor (6) is a high-precision linear displacement sensor (6).

6. The variable frequency drilling radar antenna as described in claim 1, characterized in that, The limiting block (8) is fixed to the outer periphery of the driving slider (5); there are multiple sets of limiting key pins (13), which are respectively fixedly installed on the inner walls of the outer tube (1) and the relay tube (2) to form a multi-level limiting groove; when the driving slider (5) moves to the target position, the limiting block (8) is inserted into the corresponding limiting key pin (13) and a mechanical positioning signal is issued.

7. The variable frequency drilling radar antenna as described in claim 1, characterized in that, The main control MCU is used to receive impedance adjustment commands issued by the control system (10); The matching network control unit includes a π-type adjustable matching network, a multi-channel analog switch, and a balun converter; the π-type adjustable matching network includes two parallel numerically controlled variable capacitors C1 and C2 and an adjustable inductor L1, whose capacitance value is adjusted by the main control MCU to achieve continuous and fine adjustment of the antenna input impedance; the multiple output channels of the multi-channel analog switch are respectively connected to three feed points located on the outer wall of the outer tube (1), feed point I (14), feed point II (15), and feed point III (16), and the physical position of the radar pulse signal fed into the antenna can be changed by switching the switch channels; The impedance detection unit and power management unit are used to monitor the matching status in real time and supply power to the internal circuits.

8. The variable frequency drilling radar antenna as described in claim 1, characterized in that, The pulse source circuit board and the acquisition circuit board are installed side by side in the moisture-proof shielding chamber at the rear of the antenna.

9. A method for operating a variable frequency drilling radar antenna according to any one of claims 1 to 8, characterized in that, Includes the following steps: Step S1: The ground operator sends the target center frequency command f to the downhole antenna through the ground control system according to the exploration requirements; Step S2: The main controller of the downhole antenna receives the instruction f, queries the built-in frequency-parameter mapping table, and determines the following required to achieve frequency f: the total contraction length of the three-stage sleeve corresponding to the target mechanical telescoping stage N, the target feed point number K, and the theoretical initial values ​​of the target matching network parameters C1, C2, and L1. Step S3: The main controller drives the micro stepper motor to rotate forward, which drives the winch to wind the traction rope; the traction rope pulls the slider to slide towards the near end, i.e. towards the motor; during this process, the displacement sensor reports the slider position in real time. Step S4: The sliding block first compresses spring I, and the spring force causes the outer tube and the repeater tube to slide relative to each other, completing the first stage of contraction. If a second stage of contraction is required, the sliding continues, further compressing spring II, causing the repeater tube and the core tube to slide relative to each other. When the slider displacement reaches the target value, the limit block on it engages with the limit key on the corresponding tube wall, the mechanical movement stops, and the effective length of the antenna is fixed. This step achieves coarse adjustment of the operating frequency, with an adjustment range of 100MHz to 400MHz. Step S5: The main controller sends the target matching network parameters to the main control MCU of the impedance switch; the main control MCU adjusts the values ​​of the digitally controlled capacitors C1 and C2 in the π-type matching network through the digital interface, selects the matching inductor L1, and sets the turns ratio of the balun converter to achieve the best match between the antenna input impedance and the pulse source output impedance, thereby maximizing the energy transmission efficiency. The target impedance value is matched according to the transmission line theory formula. The estimation and optimization are performed, where D is the current equivalent inner diameter of the outer tube and d is the equivalent diameter of the inner conductor. The relative permittivity of the medium inside the borehole; Step S6: The main control MCU of the impedance switch controls the multi-channel analog switch to switch the pulse source output signal to the target feed point K determined in step S2; the three feed points are non-uniformly arranged along the axial direction of the outer wall of the outer tube, and their positions are optimized by simulation, corresponding to the optimal current distribution points under different mechanical lengths; switching the feed points can finely adjust the resonant characteristics of the antenna, realizing fine frequency calibration with an accuracy of ±10MHz; thus, through the dual synergistic mechanism of changing the electrical length by mechanical extension and switching to optimize the current distribution, the antenna is accurately tuned to the target frequency f, and the impedance matching is good; Step S7: The system is ready. The pulse source circuit board is triggered to generate an electromagnetic pulse that radiates to the surrounding strata through the matching network and the selected feed point. The echo signal is received by the antenna and sent to the acquisition circuit board for processing and storage via the impedance switch. Step S8: If it is necessary to switch from high frequency to low frequency, the main controller commands the micro stepper motor to reverse and release the traction rope; under the action of the elastic restoring force stored in spring I and spring II, the slider is driven to slide to the far end, causing each stage of the tube to extend and reset in sequence; at the same time, the impedance switch synchronously switches the matching network parameters and the feed point back to the corresponding state.

Images