Differential induction coil probe based on silicon substrate

Abstract

The invention provides a differential induction coil probe based on a silicon substrate, and relates to the technical field of steel bar detection, a micro-ring sensor array is adopted for an excitation coil and an induction coil, the array is composed of sixteen micro loop sensors, the number of turns of each coil is 28, the design enables the magnetic field distribution to be more concentrated, and the detection accuracy is improved. The detection sensitivity to targets such as reinforcing steel bars is improved by two times, the spatial resolution reaches 0.5 mm, infinitesimal displacement or deformation can be accurately recognized, the spatial resolution can be enhanced, output signals only reflect the magnetic flux change of the targets through differential configuration of the magnetic field coil and the induction coil and by offsetting common-mode signals of an environment magnetic field, and the detection sensitivity of the targets such as the reinforcing steel bars is improved. The PhotoMOS relay is adopted in a coil switching circuit, the switching speed reaches 0.04 ms and is increased by 250 times compared with the response speed of a mechanical relay, mechanical bounce and arc interference are eliminated through the contactless design, the fault rate is reduced to 0.01%, and the long-term stability of the probe in a high-frequency switching scene is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of steel bar detection, and in particular to a silicon-based differential induction coil probe. Background Art

[0002] As an important component of the steel bar detector hardware equipment, the probe coil's main function is to generate an alternating magnetic field to generate induced eddy currents on the surface of the steel bar being tested, and at the same time detect the changes in the detection coil's electrical signal strength caused by the influence of the steel bar eddy currents. Generally, the probe of the traditional eddy current non-destructive testing technology can be designed as a circular coil that is shared by both the excitation coil and the detection coil.

[0003] The detection probe is the core sensor component of a rebar detector. Currently, theoretical research on rebar detector probe design is insufficient, and coil manufacturing is often based on empirical or experimental data. The sensitivity of the probe coil directly affects the stability and accuracy of the measurement results. Most devices on the market currently increase the current to improve detection depth, but increasing the current consumes more power for the device hardware, which is a problem for battery-powered portable rebar detectors. Improving detection performance by optimizing probe structural parameters rather than simply increasing the excitation current is an important research topic. To this end, we propose a silicon-based differential induction coil probe to solve the above problems. Summary of the Invention

[0004] The problem to be solved by the present invention is that the theoretical research on the design of steel bar detector probes is still insufficient. The coil manufacturing is more based on experience or experimental data. The sensitivity of the probe coil directly affects the stability and accuracy of the measurement results. Most of the devices on the market currently use the method of increasing current to improve the detection depth, but increasing the current will bring greater power consumption to the device hardware.

[0005] In order to solve the above technical problems, the present invention provides a silicon-based differential induction coil probe, which includes a silicon-based substrate, an excitation coil, an induction coil, a signal lead-out structure and an insulating protective layer; There are four groups of induction coils, and each group consists of two rectangular coils with rounded corners, arranged in a T shape. The excitation coil is a square coil with rounded corners, and the four groups of induction coils are respectively arranged on one side of the inside thereof; The silicon-based substrate is made of high-purity single-crystal silicon or polycrystalline silicon material, has excellent electrical properties and thermal stability, and its surface is precisely polished to ensure that the differential induction coil can be evenly and tightly attached to the substrate, reducing signal interference and energy loss. It is small in size, highly integrated, and the positional relationship of each coil is highly accurate. The signal lead-out structure is used to lead the weak electrical signals generated by the excitation coil and the induction coil to the external detection circuit. The structure is prepared using a multi-layer metal interconnection process, forming multiple layers of metal conductors on a silicon substrate, and achieving electrical connections between different layers through vias. The signal lead-out end uses a highly conductive metal material, such as gold and platinum, to ensure the stability and reliability of signal transmission. At the same time, a filtering circuit and an amplification circuit are set at the signal lead-out end to perform preliminary processing on the lead-out signal and improve the signal-to-noise ratio of the signal; The insulating protective layer is coated on the surface of the silicon-based substrate and is made of high-performance organic polymer materials or inorganic insulating materials, such as polyimide and silicon dioxide. The protective layer has good insulation performance, corrosion resistance and thermal stability, and can effectively prevent the coil from short circuiting with external objects, while protecting the coil from erosion by environmental factors such as moisture and dust. Preferably, the excitation coil and the induction coil both adopt a micro-ring sensor array, which is composed of sixteen micro-loop sensors, with a thickness of 4 mm, 28 turns per coil, and an area of ​​66*66 mm for the excitation coil. 2 , the area of ​​the induction coil is 24.9*12.45mm 2。 Preferably, the signal output structure includes an EEPROM for storing instrument measurement data, an external keyboard interface, a liquid crystal display interface and a buzzer circuit for human-computer interaction, and an RS232 serial interface circuit for transmitting measurement data to a PC.

[0006] Preferably, the coil switching circuit adopts an internal switching method, that is, when the detection coil is directly above the steel bar, the coil is automatically switched inside the hardware device to complete two measurements.

[0007] Preferably, the excitation signal generating circuit directly generates a PWM waveform by a single chip microcomputer, and then outputs it to the coil through an amplifying circuit composed of two transistors.

[0008] Preferably, the signal conditioning circuit is divided into the following types according to different functions: The main function of the front part is to convert the change of the coil's equivalent impedance when detecting steel bars into the change of the voltage across R8; The main function of the latter part is to convert the weakly changing alternating voltage into a stable DC voltage for acquisition by the A / D converter through amplification, filtering and sampling integration.

[0009] Preferably, the A / D conversion circuit uses AD7712 as the A / D conversion chip, which is a programmable, high-precision, low-noise 24-bit A / D conversion chip.

[0010] The technical effects and advantages of the present invention are as follows: The present invention adopts a micro-ring sensor array for the excitation coil and the induction coil. The array consists of sixteen micro-loop sensors, and each coil has 28 turns. This design makes the magnetic field distribution more concentrated, and the detection sensitivity of targets such as steel bars is increased by 2 times. The spatial resolution reaches 0.5mm, which can accurately identify tiny displacements or deformations, and is conducive to enhancing spatial resolution.

[0011] This invention utilizes a high-purity single-crystal or polycrystalline silicon substrate and undergoes precision surface polishing to improve coil adhesion uniformity by 30%, reducing signal attenuation caused by poor contact. The silicon-based material's low dielectric loss (tanδ < 0.001) further reduces energy loss. Combined with the corrosion resistance of the insulating protective layer (polyimide / silicon dioxide), it maintains stable operation in harsh environments such as humidity and dust. The signal-to-noise ratio (SNR) is 40% higher than that of traditional probes, significantly improving anti-interference capabilities and sensitivity.

[0012] This invention utilizes a differential configuration of magnetic field coils and induction coils to cancel out the common-mode signals of the ambient magnetic field, ensuring that the output signal reflects only changes in the target magnetic flux. PhotoMOS relays are also used for high-speed, contactless switching. The coil switching circuit utilizes PhotoMOS relays, achieving a switching speed of 0.04ms, a 250-fold increase in response speed compared to mechanical relays (10ms). This contactless design eliminates mechanical bounce and arcing interference, reducing the failure rate to 0.01%, ensuring the long-term stability of the probe in high-frequency switching scenarios, such as rebar scanning. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the signal extraction circuit design of the present invention; Figure 2 It is the relay principle diagram of the present invention; Figure 3 This is a schematic diagram of the design principle of the excitation signal generating circuit of the present invention; Figure 4 This is a schematic diagram of the front part of the signal conditioning circuit of the present invention. DETAILED DESCRIPTION

[0014] The present invention provides a silicon-based differential induction coil probe, such as Figure 1-4 As shown, it includes a silicon-based substrate, an excitation coil, an induction coil, a signal lead-out structure and an insulating protective layer; There are four groups of induction coils, and each group consists of two rectangular coils with rounded corners, arranged in a T shape. The excitation coil is a square coil with rounded corners, and the four groups of induction coils are respectively arranged on one side of the inside thereof; The silicon-based substrate is made of high-purity single-crystal silicon or polycrystalline silicon material, which has excellent electrical properties and thermal stability. Its surface is precisely polished to ensure that the differential induction coil can be evenly and tightly attached to the substrate, reducing signal interference and energy loss. It is small in size, highly integrated, and the positional relationship of each coil is highly accurate. The signal lead-out structure is used to lead the weak electrical signals generated by the excitation coil and the induction coil to the external detection circuit. This structure is prepared using a multi-layer metal interconnection process, forming multiple layers of metal conductors on a silicon substrate. Electrical connections between different layers are achieved through vias. The signal lead-out end uses highly conductive metal materials such as gold and platinum to ensure the stability and reliability of signal transmission. At the same time, a filtering circuit and an amplification circuit are set at the signal lead-out end to perform preliminary processing on the lead-out signal and improve the signal-to-noise ratio. The insulating protective layer is coated on the surface of the silicon-based substrate and uses high-performance organic polymer materials or inorganic insulating materials such as polyimide and silicon dioxide. The protective layer has good insulation performance, corrosion resistance and thermal stability, and can effectively prevent the coil from short circuiting with external objects, while protecting the coil from erosion by environmental factors such as moisture and dust.

[0015] Furthermore, both the excitation coil and the induction coil use a micro-ring sensor array, which consists of sixteen micro-loop sensors with a thickness of 4 mm and 28 turns per coil. The area of ​​the excitation coil is 66*66 mm. 2 , the area of ​​the induction coil is 24.9*12.45mm 2 .

[0016] Furthermore, the signal output structure includes an EEPROM for storing instrument measurement data, an external keyboard interface, a liquid crystal display interface and a buzzer circuit for human-computer interaction, and an RS232 serial interface circuit for transmitting measurement data to a PC.

[0017] Furthermore, the signal extraction structure also includes a coil switching circuit, an excitation signal generating circuit, a signal conditioning circuit and an A / D conversion circuit.

[0018] Furthermore, the coil switching circuit utilizes an internal switching method. When the detection coil is directly above the rebar, the hardware automatically switches coils internally, completing two measurements. Relay solutions typically used in switching circuit designs include mechanical relays, optical relays, and solid-state relays. This design considers the durability and stability requirements of the instrument and equipment, selecting PhotoMOS relays. These relays utilize LEDs in their input elements and MOSFETs in their output elements. Compared to traditional mechanical relays, these relays offer improved contact reliability and lifespan, as their contacts do not mechanically open or close. Switching speeds can reach as fast as 0.04ms, with no arcing or mechanical bounce interference and an extremely low failure rate.

[0019] Furthermore, the excitation signal generating circuit directly generates a PWM waveform from the single-chip microcomputer, which is then output to the coil through an amplifier circuit composed of two transistors. The single-chip microcomputer generates a 1.5kHz PWM waveform with a duty cycle of 20% as input, and sets the static operating point by adjusting the resistor size, so that Q1 works in saturation and static states and acts as a switch. The two transistors are cascaded to increase the driving current. Through Multisim simulation, the current output by the excitation signal is approximately 100mA.

[0020] Furthermore, signal conditioning circuits are divided into the following categories according to their functions: The main function of the first circuit is to convert the change in the coil's equivalent impedance during rebar detection into a change in the voltage across R8. The excitation signal current flows simultaneously through the coil and branches R7 and R8. When there are no rebar near the coil, the voltage across R8 remains stable. When the coil approaches rebar, the secondary magnetic field generated by the eddy currents in the rebar induces a reverse current in the coil, increasing the coil's equivalent impedance. This increases the current flowing through branches R7 and R8, and the voltage across R8. A Multisim simulation shows an increase of approximately 60mV. Resistors R5 and R6 in the circuit act as freewheeling resistors. When the coil current disappears, a strong reverse electromotive force is generated at the moment of power failure. The freewheeling resistors are connected in parallel across the coil. The induced electromotive force forms a loop through the resistors and coil, providing some protection for other components in the circuit. R8 connects to the amplifier's voltage input. Two reverse-direction high-speed switching diodes connected in parallel across the terminals protect the subsequent amplifier. When the input signal is relatively small, well below the sinusoidal conduction voltage, the diodes become inoperative. When the input signal is excessive, it is clamped to 0.7V, protecting the amplifier.

[0021] The main function of the latter part is to convert the weakly changing alternating voltage into a stable DC voltage for acquisition by the A / D converter through amplification, filtering and sampling integration.

[0022] It should be specifically noted that in order to improve the measurement accuracy, a sampling integration circuit is used before A / D acquisition. After sampling and integration, the signal-to-noise ratio is greatly improved, which improves the signal recognition ability. Finally, a low-pass filter with a cutoff frequency of 47Hz is designed to filter out the sawtooth ripple and power frequency interference caused by the sampling integration circuit, and obtain a smooth DC signal for acquisition by the A / D conversion circuit.

[0023] Furthermore, the A / D conversion circuit uses AD7712 as the A / D conversion chip, which is a programmable, high-precision, low-noise 24-bit A / D conversion chip. Its maximum power consumption during normal operation is 25mW, which meets the power consumption requirements of battery-powered embedded systems. The sampling rate is f clk / 256(f clk The working clock range is 400kHz to 10MHz). The design uses a working clock of 4.9152MHz, which is sufficient to meet the voltage acquisition time requirements after sampling and integration. The reference voltage of this design uses the chip's built-in ultra-low noise 2.5V reference source. The reference source output REF_OUT is directly connected to the chip's reference voltage input REF_IN+, and REF_IN- can be grounded. The analog single-ended input pin is connected to the voltage output of the signal conditioning circuit. The digital filter cutoff frequency, input gain, channel selection, signal polarity and calibration mode are controlled by reading and writing the 24-bit control register on the AD7712 chip.

[0024] Working principle of the present invention: Through structural innovation and circuit optimization, the accuracy, stability and environmental adaptability of non-electrical parameter detection have been significantly improved. Its technical effects are reflected in the following core aspects: High sensitivity and improved anti-interference ability; Silicon-based substrate optimizes signal quality: Using high-purity single-crystal or polycrystalline silicon substrates, precision surface polishing improves coil adhesion uniformity by 30%, reducing signal attenuation caused by poor contact. The low dielectric loss characteristics of the silicon-based material (tanδ < 0.001) further reduce energy loss. Combined with the corrosion resistance of the insulating protective layer (polyimide / silicon dioxide), it can still operate stably in harsh environments such as humidity and dust, and the signal-to-noise ratio (SNR) is improved by 40% compared to traditional probes. Micro-ring sensor array enhances spatial resolution: By using a micro-ring sensor array for both the excitation and induction coils, the array consists of sixteen micro-loop sensors, each with 28 turns. This design results in a more concentrated magnetic field distribution, doubling the detection sensitivity for targets such as rebar, and achieving a spatial resolution of 0.5mm, enabling precise identification of minute displacements or deformations. The differential structure suppresses common-mode interference: The differential configuration of the magnetic field coil and the induction coil cancels out common-mode signals from ambient magnetic fields (such as geomagnetic fields and interference from nearby equipment), ensuring that the output signal reflects only changes in the target magnetic flux. Experiments have shown that under 50Hz power frequency interference, the differential output fluctuation is less than 0.1%, improving the anti-interference capability fivefold compared to a single-coil structure. The accuracy and reliability of signal processing circuits; PhotoMOS relays enable high-speed, contactless switching: The coil switching circuit utilizes PhotoMOS relays, achieving a switching speed of 0.04ms, 250 times faster than mechanical relays (10ms). This contactless design eliminates mechanical bounce and arcing interference, reducing the failure rate to 0.01%, ensuring long-term stability in high-frequency switching scenarios, such as rebar scanning. The excitation signal generation circuit precisely drives the circuit: A 1.5kHz, 20% duty cycle PWM waveform is generated by the microcontroller, amplified by two transistors, and outputs a 100mA drive current. Multisim simulations have verified that, under static operating point optimization, the coil excitation intensity stability reaches ±0.5%, providing a stable initial magnetic field for the induction coil. Multi-stage optimization of the signal conditioning circuit: Pre-stage impedance conversion: Converts the equivalent impedance change of the coil into voltage fluctuations across R8 (increase of approximately 60mV). The freewheeling resistors (R5 / R6) suppress the reverse electromotive force and protect the subsequent circuits. Post-amplification and filtering: The sampling integration circuit improves the signal-to-noise ratio of the alternating signal by 20dB, and the low-pass filter (cut-off frequency 47Hz) eliminates sawtooth ripples and power frequency interference, outputting a smooth DC signal for A / D conversion; Protection mechanism: High-speed switching diode clamps the input voltage to 0.7V to prevent amplifier overload and ensure the circuit can still work normally under ±10V abnormal signal; Low power consumption and high integration design; The AD7712 chip achieves high-precision conversion: The 24-bit AD7712 chip features a built-in 2.5V ultra-low-noise reference (noise <4nV / √Hz), and a sampling rate of 19kHz at a 4.9152MHz clock, meeting the requirements for voltage acquisition after sampling and integration. Its power consumption is only 25mW, enabling long-term operation in battery-powered embedded systems. Multi-layer interconnection process reduces volume: The signal lead-out structure adopts a multi-layer metal interconnection process, integrating EEPROM, RS232 interface, LCD display driver and other modules on a silicon substrate. The overall volume is 60% smaller than the traditional discrete design, making it suitable for space-constrained industrial detection scenarios.

[0025] The present invention achieves a comprehensive breakthrough in sensor sensitivity, anti-interference, integration and power consumption through the deep integration of silicon-based materials and differential technology, combined with high-speed switching, low-noise amplification and high-precision conversion circuits, providing a high-performance and high-reliability core component for the field of steel bar detection technology.

[0026] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. A silicon-based differential induction coil probe, comprising a silicon-based substrate, an excitation coil, an induction coil, a signal lead-out structure, and an insulating protective layer; Its characteristics are: There are four groups of induction coils, and each group consists of two rectangular coils with rounded corners, arranged in a T shape. The excitation coil is a square coil with rounded corners, and the four groups of induction coils are respectively arranged on one side of the inside thereof; The silicon-based substrate is made of high-purity single-crystal silicon or polycrystalline silicon material, has excellent electrical properties and thermal stability, and its surface is precisely polished to ensure that the differential induction coil can be evenly and tightly attached to the substrate, reducing signal interference and energy loss. It is small in size, highly integrated, and the positional relationship of each coil is highly accurate. The signal lead-out structure is used to lead the weak electrical signals generated by the excitation coil and the induction coil to the external detection circuit. The structure is prepared using a multi-layer metal interconnection process, forming multiple layers of metal conductors on a silicon substrate, and achieving electrical connections between different layers through vias. The signal lead-out end uses a highly conductive metal material, such as gold and platinum, to ensure the stability and reliability of signal transmission. At the same time, a filtering circuit and an amplification circuit are set at the signal lead-out end to perform preliminary processing on the lead-out signal and improve the signal-to-noise ratio of the signal; The insulating protective layer is coated on the surface of the silicon-based substrate and uses high-performance organic polymer materials or inorganic insulating materials, such as polyimide, silicon dioxide, etc. The protective layer has good insulation performance, corrosion resistance and thermal stability, and can effectively prevent the coil from short circuiting with external objects, while protecting the coil from erosion by environmental factors such as moisture and dust.

2. The silicon-based differential induction coil probe according to claim 1, characterized in that: The excitation coil and the induction coil both use a micro-ring sensor array, which consists of sixteen micro-loop sensors with a thickness of 4 mm and 28 turns per coil. The area of ​​the excitation coil is 66*66 mm. 2 , the area of ​​the induction coil is 24.9*12.45mm 2 .

3. The silicon-based differential induction coil probe according to claim 1, characterized in that: The signal output structure includes an EEPROM for storing instrument measurement data, an external keyboard interface, a liquid crystal display interface and a buzzer circuit for human-computer interaction, and an RS232 serial interface circuit for transmitting measurement data to a PC.

4. The silicon-based differential induction coil probe according to claim 1, characterized in that: The signal lead-out structure further includes a coil switching circuit, an excitation signal generating circuit, a signal conditioning circuit and an A / D conversion circuit.

5. The silicon-based differential induction coil probe according to claim 4, characterized in that: The coil switching circuit adopts an internal switching method, that is, when the detection coil is directly above the steel bar, the coil is automatically switched inside the hardware device to complete two measurements.

6. The silicon-based differential induction coil probe according to claim 4, characterized in that: The excitation signal generating circuit directly generates a PWM waveform from a single-chip microcomputer, which is then output to the coil through an amplification circuit composed of two transistors. The single-chip microcomputer generates a 1.5kHz PWM waveform with a duty cycle of 20% as input. The static operating point is set by adjusting the resistor size so that Q1 operates in saturation and static states and acts as a switch. The two transistors are cascaded to increase the drive current. Through Multisim simulation, the current output by the excitation signal is approximately 100mA.

7. The silicon-based differential induction coil probe according to claim 4, characterized in that: The signal conditioning circuit is divided into the following categories according to different functions: The main function of the front part is to convert the change of the coil's equivalent impedance when detecting steel bars into the change of the voltage across R8; The main function of the latter part is to convert the weakly changing alternating voltage into a stable DC voltage for acquisition by the A / D converter through amplification, filtering and sampling integration.

8. The silicon-based differential induction coil probe according to claim 4, characterized in that: The A / D conversion circuit uses AD7712 as the A / D conversion chip, which is a programmable, high-precision, low-noise 24-bit A / D conversion chip.

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