Ultrasonic guided wave microvolt-level weak signal amplification method

Abstract

The invention relates to the technical field of ultrasonic guided waves, in particular to an ultrasonic guided wave microvolt-level weak signal amplification method. The method comprises the following steps: designing an impedance matching input stage for a sensor impedance model, receiving a weak signal of an ultrasonic guided wave, amplifying the weak signal by using an amplifying circuit, reducing noise introduction, and according to the change of signal strength, performing post-two-stage amplification of the amplifying circuit and digitally controlling a gain amplifier. And the amplification gains of the rear two stages are adaptively adjusted, and the weak signals of the ultrasonic guided waves are amplified to the optimal output range. The impedance matching input stage is designed through the sensor impedance model, the impedance matching input stage is designed according to the sensor impedance model, the accuracy of receiving the weak signals of the ultrasonic guided waves is improved, the weak signals of the ultrasonic guided waves are fixedly amplified through the first two stages of amplification of the amplification circuit, and the weak signals of the ultrasonic guided waves are amplified according to the signal intensity change. And the output signal is ensured to be within the optimal input range of the analog-to-digital converter.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic guided waves, in particular to a method for amplifying microvolt-level weak signals of ultrasonic guided waves. Background Art

[0002] Ultrasonic guided wave testing (Ultrasonic Guided Wave) is a nondestructive testing technology based on the theory of low-frequency stress wave propagation in bounded structures. It has the advantages of long detection distance, high speed, harmlessness to the human body, and low cost. It is widely used in the flaw detection of slender structures such as pipelines, rails, steel bars, and plate materials.

[0003] In actual inspections, especially when detecting small defects at long distances, ultrasonic guided wave signals attenuate during propagation, causing the defect echo signal to become extremely weak, potentially at the microvolt level. Furthermore, various noises in the inspection environment, such as those generated by the inspection instrument and interference from the surrounding electromagnetic environment, can further mask the weak ultrasonic guided wave signal, drowning it in the noise and creating the risk of missed or false detections. To fully leverage the advantages of ultrasonic guided wave inspection technology and improve its efficiency and accuracy in detecting small defects, it is necessary to effectively amplify the weak microvolt-level signal. Only by amplifying the weak signal to a sufficient amplitude can the subsequent signal processing and analysis circuits accurately identify and extract useful signal features, thereby achieving the detection objectives of defect location and quantification. Therefore, we propose a method for amplifying weak microvolt-level signals using ultrasonic guided waves. Summary of the Invention

[0004] The present invention aims to address the problem of ultrasonic guided wave testing, which attenuates during propagation, causing the defect echo signal to become very weak. Furthermore, various noises in the testing environment can further mask the weak ultrasonic guided wave signal, drowning it in the noise and creating the risk of missed or false detections. To fully leverage the advantages of ultrasonic guided wave testing technology and improve its efficiency and accuracy in detecting small defects, it is necessary to effectively amplify the weak microvolt-level signal. Only by amplifying the weak signal to a sufficient amplitude can the subsequent signal processing and analysis circuits accurately identify and extract useful signal features, thereby achieving the detection objectives of defect location and quantification.

[0005] To achieve the above objectives, the present invention provides a method for amplifying microvolt-level weak signals using ultrasonic guided waves, comprising the following steps:

[0006] S1. Design an impedance matching input stage based on the sensor impedance model to receive weak signals from ultrasonic guided waves.

[0007] S2, using the first two stages of the amplifier circuit to amplify the weak signal of the ultrasonic guided wave while reducing the introduction of noise;

[0008] S3. According to the change of signal strength, the amplification gain of the last two stages of the amplifier circuit and the digitally controlled gain amplifier are adaptively adjusted to amplify the weak signal of the ultrasonic guided wave to the optimal output range.

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] 1. This ultrasonic guided wave microvolt-level weak signal amplification method uses a charge-sensitive amplifier chip in the front stage of the piezoelectric sensor's amplifier circuit to input the weak piezoelectric vibration guided wave signal into the circuit. This not only obtains a highly sensitive piezoelectric charge signal, but also isolates the subsequent circuit, facilitating back-end signal conditioning. A low-impedance input front-stage chip is used in the front stage of the magnetostrictive sensor, and impedance matching is performed with the sensor to reduce signal reflection. The front-stage amplifier chips of the two sensors use a universal package, so that if the circuits are different, only the chip needs to be replaced without modifying the circuit. This allows the impedance-matched input stage to be designed according to the sensor impedance model, improving the accuracy of receiving weak ultrasonic guided wave signals.

[0011] 2. The first two stages of the amplifier circuit are used to perform fixed amplification on the weak signal of the ultrasonic guided wave, while reducing the introduction of noise. According to the change of signal strength, the amplification gain of the last two stages of the amplifier circuit and the digitally controlled gain amplifier are used to adaptively adjust the amplification gain of the last two stages to amplify the weak signal of the ultrasonic guided wave to the optimal output range. A multi-stage amplifier circuit is used, and the gain of each stage of the first two stages is 10 times. A fixed gain amplifier is used to initially amplify the microvolt level signal to the millivolt level. The fixed gain design can simplify the circuit stability control and reduce the introduction of noise. The last two stages use VGA, and the gain of each stage is adjustable from 0 to 32 times. The gain is adjusted by an external control signal to ensure that the output signal is within the optimal input range of the analog-to-digital converter according to the change of signal strength.

[0012] As a further improvement of the present technical solution, the step S1 designs an impedance matching input stage based on the sensor impedance model, comprising the following steps:

[0013] S1.1.1. For piezoelectric sensors, the piezoelectric sensor circuit is presented as a high impedance capacitor. A charge amplifier is configured to receive weak signals and input the weak piezoelectric vibration guided wave signal into the circuit.

[0014] S1.1.2. For magnetostrictive sensors, the magnetostrictive sensor circuit is presented as low-impedance inductance, a non-inverting amplifier is configured, a low-impedance input front-stage chip is used, and impedance matching is performed with the sensor to reduce signal reflection.

[0015] The beneficial effect of this further improvement is that maximum power transfer is achieved when the input stage impedance matches the sensor's output impedance. According to the maximum power transfer theorem, when impedances are matched, the sensor's output signal power is transmitted to the subsequent circuitry at maximum capacity, minimizing power loss during transmission and thus improving the sensitivity of the entire detection system.

[0016] As a further improvement of the present technical solution, in S1.1.1, the voltage sensor circuit includes capacitors C5 and C6, and inductor L2;

[0017] One end of the capacitor C5 is connected to the resistor R17 and to one end of the inductor L2. The other end of the capacitor C5 is connected to the other end of the resistor R17 and to one end of the capacitor C6. The other end of the capacitor C6 is connected to one end of the resistor R18. The other end of the resistor R18 is connected to the other end of the inductor L2. Both ends of the capacitor C5 are connected to the input signal VIN.

[0018] As a further improvement of the present technical solution, the S1.1.1 uses a charge amplifier to convert the charge signal output by the piezoelectric sensor into a voltage signal to match the high impedance characteristics of the piezoelectric sensor.

[0019] The beneficial effect of this further improvement is that for piezoelectric sensors, capacitors C5 and R17 are connected in parallel, forming a parallel circuit consisting of inductor L2, resistor R18, and capacitor C6. C5 plays a major role, and R17 has a relatively large resistance, resulting in a high-impedance capacitance. Because the piezoelectric element outputs a charge signal, a charge-sensitive amplifier chip is required to convert the charge signal into a voltage signal. The charge amplifier has a high input impedance, which effectively matches the high impedance characteristics of the piezoelectric sensor, while isolating the subsequent circuit and reducing the loading effect.

[0020] As a further improvement of the technical solution, in S1.1.2, the magnetostrictive sensor circuit includes an inductor L3 and a capacitor C7;

[0021] One end of the inductor L3 is connected to the resistor R19 and one end of the capacitor C7 , the other end of the inductor L3 is connected to the other end of the resistor R19 and the other end of the capacitor C7 , and both ends of the inductor L3 are connected to the input signal VIN.

[0022] The beneficial effect of adopting the above further improvement is that the magnetostrictive sensor is composed of an inductor L3, a resistor R19 and a capacitor C7 in parallel, where the inductor L3 has a high inductance, the resistor R19 has a low resistance, and the capacitor C7 is in the picofarad level. The overall low impedance inductance is presented, and the signal reflection is reduced through the impedance matching network to ensure efficient signal transmission.

[0023] As a further improvement of the present technical solution, the first two stages of the amplifier circuit in S2 are used to perform fixed amplification on the weak signal of the ultrasonic guided wave, and the first two stages of the amplifier in the amplifier circuit constitute a fixed gain amplifier circuit, including an operational amplifier IOP1 and an operational amplifier IOP2;

[0024] The negative electrode of the operational amplifier IOP1 is connected to one end of the resistor R12 and to one end of the resistor R2 in parallel. The positive electrode of the operational amplifier IOP1 is connected to one end of the resistor R1 and to the input signal VIN in parallel. The other end of the resistor R12 is connected to a power supply. The output end of the operational amplifier IOP1 is connected to the other end of the resistor R2 and to one end of the capacitor C1 in parallel. The negative electrode of the operational amplifier IOP2 is connected to one end of the resistor R3 and to one end of the resistor R4 in parallel. The positive electrode of the operational amplifier IOP2 is connected to one end of the resistor R9 and to the other end of the capacitor C1 in parallel. The other end of the resistor R3 is connected to the power supply. The output end of the operational amplifier IOP2 is connected to the other end of the resistor R4.

[0025] As a further improvement of the present technical solution, in S2, the resistors R2 and R4 have the same resistance value, amplify the weak signal by the same multiple, and use the capacitor C1 and the resistor R9 to form a filter circuit to reduce noise.

[0026] The beneficial effect of adopting the above further improvement is that the gain of each of the first two stages is 10 times, and a fixed-gain amplifier is used to initially amplify the microvolt level signal to the millivolt level. The fixed-gain design can simplify the circuit stability control and reduce the introduction of noise.

[0027] As a further improvement of the present technical solution, the amplification gain of the two subsequent stages is adaptively adjusted in S3, and the two subsequent stages of amplification and the digitally controlled gain amplifier constitute a variable gain amplifier circuit, including an operational amplifier IOP3, an operational amplifier IOP4, and an operational amplifier IOP5, a transistor T1, and an inductor L1;

[0028] The negative electrode of the operational amplifier IOP3 is connected to one end of the resistor R5 and to one end of the resistor R6 in parallel. The positive electrode of the operational amplifier IOP3 is connected to one end of the resistor R110 and to the other end of the capacitor C2. The other end of the resistor R5 is connected to a power supply. The output terminal of the operational amplifier IOP3 is connected to the other end of the resistor R6, to one end of the capacitor C3, and to the negative electrode of the operational amplifier IOP5. The negative electrode of the operational amplifier IOP4 is connected to one end of the resistor R7 and to one end of the resistor R8 in parallel. The positive electrode of the operational amplifier IOP4 is connected to one end of the resistor R11 and to the other end of the capacitor C3 in parallel. The other end of the resistor R7 is connected to the power supply. The output terminal of the operational amplifier IOP4 is connected to the other end of the resistor R8 and to the collector of the transistor T1.

[0029] The emitter of the transistor T1 is connected to the positive electrode of the operational amplifier IOP5, the base of the transistor T1 is connected to one end of the resistor R15, the other end of the resistor R15 is grounded, the output end of the operational amplifier IOP5 is connected to one end of the inductor L1, and is connected in parallel to the resistor R14 and the resistor R16, the other end of the inductor L1 is connected to one end of the capacitor C4, the other end of the capacitor C4 is grounded, and the output end of the operational amplifier IOP4 is connected to the output signal VOUT.

[0030] As a further improvement of the present technical solution, in S3, the operational amplifier IOP3, the operational amplifier IOP4 and the operational amplifier IOP5 all adopt variable gain amplifiers, and the amplification gain is adjusted by a potentiometer network composed of resistors R14, R15 and R16.

[0031] As a further improvement of the present technical solution, in S3, the variable gain amplifier circuit adopts a hierarchical amplification strategy, further amplifies the weak signal through the operational amplifier IOP3, and the operational amplifier IOP4 precisely controls the amplified signal to amplify the weak signal of the ultrasonic guided wave to the optimal output range.

[0032] The beneficial effect of adopting the above further improvement is that the last two stages use VGA, and the gain of each stage can be adjusted from 0 to 32 times. The gain is adjusted by an external control signal. The role of the VGA is to adapt to the changes in signal strength in different detection scenarios and ensure that the output signal is within the optimal input range of the analog-to-digital converter.

[0033] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the method flow of the present invention;

[0035] Figure 2 This is a schematic diagram of the S1 process of the present invention;

[0036] Figure 3 This is a circuit diagram of a piezoelectric sensor according to the present invention;

[0037] Figure 4 This is a circuit diagram of a magnetostrictive sensor according to the present invention;

[0038] Figure 5 is the amplifying circuit diagram of the present invention;

[0039] Figure 6 is a bandwidth curve diagram of the amplifier circuit of the present invention;

[0040] Figure 7This is a diagram of the simulation results of 1kHz, 10uV signal amplification of the present invention;

[0041] Figure 8 This is a diagram of the simulation results of 1MHz, 10uV signal amplification of the present invention;

[0042] Figure 9 This is a simulation diagram of the weak signal amplifying circuit board of the present invention;

[0043] Figure 10 This is a set of 450kHz waveguide amplification signal diagrams of the present invention. DETAILED DESCRIPTION

[0044] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0045] Currently, ultrasonic guided wave testing (UGW) attenuates during propagation, causing the defect echo signal to become extremely weak. Furthermore, various noises in the testing environment can further mask the weak UGW signal, drowning it out and creating the risk of missed or false detections. To fully leverage the advantages of UGW testing technology and improve its efficiency and accuracy in detecting small defects, effective amplification of the weak microvolt-level signal is necessary. Only by amplifying the weak signal to a sufficient amplitude can subsequent signal processing and analysis circuits accurately identify and extract useful signal features, thereby achieving detection objectives such as defect location and quantification.

[0046] Therefore, the present invention proposes to design an impedance-matching input stage through a sensor impedance model, receive the weak signal of the ultrasonic guided wave, use the first two stages of the amplifier circuit to fixedly amplify the weak signal of the ultrasonic guided wave, and reduce the introduction of noise. According to the change of signal strength, the amplification gain of the last two stages of the amplifier circuit and the digitally controlled gain amplifier are used to adaptively adjust the amplification gain of the last two stages to amplify the weak signal of the ultrasonic guided wave to the optimal output range.

[0047] The details are as follows:

[0048] See also Figure 1 As shown, the present invention provides a method for amplifying microvolt-level weak signals using ultrasonic guided waves, comprising the following steps:

[0049] S1. Design an impedance matching input stage based on the sensor impedance model to receive weak signals from ultrasonic guided waves.

[0050] S2, using the first two stages of the amplifier circuit to amplify the weak signal of the ultrasonic guided wave while reducing the introduction of noise;

[0051] S3. According to the change of signal strength, the amplification gain of the last two stages of the amplifier circuit and the digitally controlled gain amplifier are adaptively adjusted to amplify the weak signal of the ultrasonic guided wave to the optimal output range.

[0052] like Figure 2 As shown, S1 designs an impedance matching input stage for the sensor impedance model, including the following steps:

[0053] S1.1.1. For piezoelectric sensors, the piezoelectric sensor circuit is presented as a high impedance capacitor, and a charge amplifier is configured to receive weak signals and input the weak piezoelectric vibration guided wave signal into the circuit;

[0054] S1.1.2. For magnetostrictive sensors, the magnetostrictive sensor circuit is characterized by low impedance inductance, a non-inverting amplifier is configured, a low impedance input front-end chip is used, and impedance matching with the sensor is performed to reduce signal reflection;

[0055] First, a sensor signal model is constructed, and an impedance-matched input stage is designed based on its impedance model. A charge-sensitive amplifier chip is used in the piezoelectric sensor's preamplifier circuit to input the weak piezoelectric vibration waveguide signal. This not only captures a highly sensitive piezoelectric charge signal, but also isolates the downstream circuitry for easier signal conditioning. A low-impedance input preamplifier chip is used in the magnetostrictive sensor's preamplifier circuit, and impedance matching is performed with the sensor to minimize signal reflections. The preamplifier chips for both sensors share a common package, allowing for simple chip replacement without circuit modifications if the circuits differ.

[0056] like Figure 3 As shown, in S1.1.1, the voltage sensor circuit includes capacitors C5 and C6, and inductor L2;

[0057] One end of capacitor C5 is connected to resistor R17 and to one end of inductor L2. The other end of capacitor C5 is connected to the other end of resistor R17 and to one end of capacitor C6. The other end of capacitor C6 is connected to one end of resistor R18. The other end of resistor R18 is connected to the other end of inductor L2. Both ends of capacitor C5 are connected to input signal VIN.

[0058] In this circuit, capacitors C5 and R17 are connected in parallel, forming a series circuit consisting of inductor L2, resistor R18 and capacitor C6. C5 plays a major role, and R17 has a large resistance, presenting a high impedance capacitance as a whole. Capacitor C5 and resistor R17 are used to implement the feedback network of the charge amplifier (such as charge-voltage conversion) to match the high capacitive reactance characteristics of the sensor.

[0059] In order to better perform signal conversion, S1.1.1 uses a charge amplifier to convert the charge signal output by the piezoelectric sensor into a voltage signal to match the high impedance characteristics of the piezoelectric sensor;

[0060] The core of a charge amplifier is a high-gain operational amplifier (OPA). Its input is connected to a piezoelectric sensor, and its feedback loop includes a capacitor Cf. When an external force acts on the piezoelectric sensor, a charge Q is generated. This charge accumulates at the amplifier's input. Due to the operational amplifier's virtual short circuit characteristic, the potentials at its non-inverting and inverting inputs are approximately equal. Since the non-inverting input is grounded, its potential is zero, so the inverting input is also approximately zero potential, i.e., virtual ground. At this point, the charge Q flows through the feedback capacitor Cf, forming a current I. Due to the principle of capacitor charging, the output voltage is proportional to the input charge, achieving charge-to-voltage conversion.

[0061] like Figure 4 As shown, in S1.1.2, the magnetostrictive sensor circuit includes an inductor L3 and a capacitor C7;

[0062] One end of the inductor L3 is connected to the resistor R19 and to one end of the capacitor C7. The other end of the inductor L3 is connected to the other end of the resistor R19 and to the other end of the capacitor C7. Both ends of the inductor L3 are connected to the input signal VIN.

[0063] In this circuit, the magnetostrictive sensor consists of an inductor L3, a resistor R19, and a capacitor C7 connected in parallel. The inductor L3 has a high inductance, the resistor R19 has a low resistance, and the capacitor C7 is in the picofarad level. The overall impedance is low, and the impedance matching network reduces signal reflection to ensure efficient signal transmission.

[0064] like Figure 5 As shown, in S2, the first two amplifier stages in the amplifier circuit form a fixed gain amplifier circuit, including an operational amplifier IOP1 and an operational amplifier IOP2;

[0065] The negative electrode of the operational amplifier IOP1 is connected to one end of the resistor R12 and to one end of the resistor R2 in parallel. The positive electrode of the operational amplifier IOP1 is connected to one end of the resistor R1 and to the input signal VIN. The other end of the resistor R12 is connected to the power supply. The output terminal of the operational amplifier IOP1 is connected to the other end of the resistor R2 and to one end of the capacitor C1. The negative electrode of the operational amplifier IOP2 is connected to one end of the resistor R3 and to one end of the resistor R4 in parallel. The positive electrode of the operational amplifier IOP2 is connected to one end of the resistor R9 and to the other end of the capacitor C1. The other end of the resistor R3 is connected to the power supply. The output terminal of the operational amplifier IOP2 is connected to the other end of the resistor R4.

[0066] In this circuit, operational amplifiers IOP1 and IOP2 use the same resistance values of resistors R2 and R4 to ensure that the gains of the first two stages are the same. Capacitors C1 and C2 are used for high-frequency compensation or decoupling to ensure that the bandwidth covers the ultrasonic guided wave frequency band. The gain of each of the first two stages is 10 times. Fixed-gain amplifiers are used to initially amplify microvolt-level signals to the millivolt level. The fixed-gain design simplifies circuit stability control and reduces noise introduction.

[0067] In order to better reduce noise, the first two stages of the amplifier circuit in S2 are used to amplify the weak signal of the ultrasonic guided wave. Resistors R2 and R4 use the same resistance value to amplify the weak signal by the same multiple. Capacitor C1 and resistor R9 form a filter circuit to reduce noise.

[0068] The first two stages use moderate gain (10x per stage) to avoid premature amplification of noise. If the gain is too high, the noise will be significantly amplified, leading to the risk of saturation in the subsequent stages. The sensor output signal is usually accompanied by a certain amount of noise. If too high a gain is used in the front end, the noise will also be amplified in the same proportion. However, moderate gain can make the noise growth relatively controllable during the gradual amplification of the signal, preventing the noise from prematurely drowning out the useful signal, which is beneficial to improving the signal-to-noise ratio.

[0069] Subsequent circuits, such as analog-to-digital converters (ADCs), have limited input ranges. If the gain of the preceding stage is too high, the signal may exceed the dynamic range of the subsequent circuit before reaching it, resulting in signal distortion or saturation. A moderate gain of 10x per stage gradually amplifies the signal to an appropriate amplitude, reducing the risk of saturation in the subsequent stage and ensuring accurate signal processing and conversion.

[0070] Among them, S3 adaptively adjusts the amplification gain of the latter two stages, and the latter two stages of amplification and the digitally controlled gain amplifier constitute a variable gain amplifier circuit, including operational amplifiers IOP3, IOP4, and IOP5, transistor T1, and inductor L1;

[0071] The negative electrode of the operational amplifier IOP3 is connected to one end of the resistor R5 and to one end of the resistor R6 in parallel. The positive electrode of the operational amplifier IOP3 is connected to one end of the resistor R110 and to the other end of the capacitor C2. The other end of the resistor R5 is connected to a power supply. The output terminal of the operational amplifier IOP3 is connected to the other end of the resistor R6 and to one end of the capacitor C3 and to the negative electrode of the operational amplifier IOP5. The negative electrode of the operational amplifier IOP4 is connected to one end of the resistor R7 and to one end of the resistor R8 in parallel. The positive electrode of the operational amplifier IOP4 is connected to one end of the resistor R11 and to the other end of the capacitor C3. The other end of the resistor R7 is connected to the power supply. The output terminal of the operational amplifier IOP4 is connected to the other end of the resistor R8 and to the collector of the transistor T1.

[0072] The emitter of the transistor T1 is connected to the positive electrode of the operational amplifier IOP5, the base of the transistor T1 is connected to one end of the resistor R15, the other end of the resistor R15 is grounded, the output end of the operational amplifier IOP5 is connected to one end of the inductor L1, and is connected in parallel to the resistor R14 and the resistor R16, the other end of the inductor L1 is connected to one end of the capacitor C4, the other end of the capacitor C4 is grounded, and the output end of the operational amplifier IOP4 is connected to the output signal VOUT;

[0073] In this circuit, operational amplifier IOP3 uses a voltage-controlled gain amplifier (VGA). The gain is adjusted by an external voltage (such as the potentiometer network composed of R15 and R16) within a range of 0-32 times. Operational amplifier IOP4 is further amplified by the VGA, and the total gain can reach more than 1,000 times, adapting to the dynamic range requirements of different signal strengths. Transistor T1 is used to switch the gain control signal and acts as a buffer to isolate the control circuit from the amplifier circuit to prevent load influence. Inductor L1, capacitors C3 and C4 form a π-type filter network to suppress power supply ripple and high-frequency noise.

[0074] The last two stages use VGA, and the gain of each stage can be adjusted from 0 to 32 times. The gain is adjusted by an external control signal. The function of VGA is to adapt to the changes in signal strength in different detection scenarios and ensure that the output signal is within the optimal input range of the analog-to-digital converter.

[0075] The bandwidth curve of the amplifier circuit is as follows Figure 6 As shown in the figure, it can be seen that as the frequency gradually increases, the bandwidth of the amplifier circuit gradually tends to be stable.

[0076] In order to better control the amplification gain, in S3, the operational amplifier IOP3, the operational amplifier IOP4 and the operational amplifier IOP5 all adopt variable gain amplifiers, and the amplification gain is controlled by a potentiometer network composed of resistors R14, R15 and R16;

[0077] Resistors R14, R15, and R16 in the potentiometer network change the feedback loop resistor ratio of the operational amplifier by adjusting their resistance values. For a variable-gain amplifier, its gain is typically determined by the ratio of the feedback resistor to the input resistor. By changing the resistance values of the resistors in the potentiometer network, the ratio of the feedback resistor to the input resistor can be changed, thereby adjusting the amplifier gain.

[0078] The potentiometer can achieve continuous adjustment of the gain within a certain range. Compared with some fixed-gain amplifiers, it can adjust the amplification factor more finely and better meet the precise requirements of signal amplification in various experiments or application scenarios.

[0079] like Figure 7As shown in the figure, it is the simulation result of 1kHz, 10uV signal amplification. It can be seen from the figure that the waveform of the input signal VIN and the waveform of the output signal VOUT are basically the same, indicating that the noise has little effect on them during the amplification process and can achieve accurate amplification results.

[0080] Similarly, if Figure 8 As shown in the figure, it is the simulation result of 1MHz, 10uV signal amplification. It can be seen from the figure that the waveform of the input signal VIN and the waveform of the output signal VOUT are basically the same, indicating that the amplifier circuit has the same amplification effect on the 1MHz signal.

[0081] In order to amplify the weak signal of the ultrasonic guided wave to the optimal output range, the variable gain amplifier circuit in S3 adopts a hierarchical amplification strategy. The weak signal is further amplified by the operational amplifier IOP3, and the operational amplifier IOP4 accurately controls the amplified signal to amplify the weak signal of the ultrasonic guided wave to the optimal output range.

[0082] The ultrasonic guided wave signal output by a piezoelectric sensor is typically very weak. After initial processing in the front-end, it still requires further amplification to meet the processing requirements of subsequent circuits. The operational amplifier IOP3 takes on this task, effectively amplifying the weak signal and increasing its amplitude. This ensures that the signal has sufficient strength for subsequent processing, facilitating precise control and analysis.

[0083] Although the signal amplified by IOP3 has increased in amplitude, it may still be unstable or not meet requirements. The role of the operational amplifier IOP4 is to precisely control the amplified signal. Using a potentiometer network and other methods, it fine-tunes the signal gain according to actual needs, amplifying the weak ultrasonic guided wave signal to the optimal output range. This helps improve signal quality and stability, ensuring that the signal can be accurately processed by subsequent circuits such as the analog-to-digital converter (ADC), thereby enhancing the accuracy and reliability of the entire measurement system.

[0084] like Figure 9 As shown in the figure, it is a simulation diagram of a weak signal amplification circuit board. As can be seen from the figure, the actual area of the amplifier circuit is small and has a wide range of applications.

[0085] like Figure 10 As shown in the figure, it is a set of 450kHz waveguide amplified signals. It can be clearly seen from the figure that the waveguide signal is amplified.

[0086] In summary, the working principle of this solution is as follows:

[0087] This ultrasonic guided wave microvolt-level weak signal amplification method uses a charge-sensitive amplifier chip in the front stage of the piezoelectric sensor's amplifier circuit to input the weak piezoelectric vibration guided wave signal into the circuit. On the one hand, it obtains a highly sensitive piezoelectric charge signal, and on the other hand, it isolates the back-end circuit to facilitate back-end signal conditioning. For the front stage of the magnetostrictive sensor, a low-impedance input front-end chip is used, and impedance matching is performed with the sensor to reduce signal reflection. The front-end amplifier chips of the two sensors use a universal package. When the circuits are different, only the chip needs to be replaced without modifying the circuit. This implements the design of the impedance matching input stage according to the sensor impedance model, thereby improving the accuracy of receiving the ultrasonic guided wave weak signal.

[0088] The first two stages of the amplifier circuit are used to perform fixed amplification on the weak signal of the ultrasonic guided wave, while reducing the introduction of noise. According to the change of signal strength, the amplification gain of the last two stages of the amplifier circuit and the digitally controlled gain amplifier are used to adaptively adjust the amplification gain of the last two stages to amplify the weak signal of the ultrasonic guided wave to the optimal output range. A multi-stage amplifier circuit is used, and the gain of each stage of the first two stages is 10 times. A fixed gain amplifier is used to initially amplify the microvolt level signal to the millivolt level. The fixed gain design can simplify the circuit stability control and reduce the introduction of noise. The last two stages use VGA, and the gain of each stage is adjustable in the range of 0-32 times. The gain is adjusted by an external control signal to ensure that the output signal is within the optimal input range of the analog-to-digital converter according to the change of signal strength.

[0089] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and improvements fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. Ultrasonic guided wave microvolt-level weak signal amplification method, characterized in that: The method steps are as follows: S1. Design an impedance matching input stage based on the sensor impedance model to receive weak signals from ultrasonic guided waves. S2, using the first two stages of the amplifier circuit to amplify the weak signal of the ultrasonic guided wave while reducing the introduction of noise; S3. According to the change of signal strength, the amplification gain of the last two stages of the amplifier circuit and the digitally controlled gain amplifier are adaptively adjusted to amplify the weak signal of the ultrasonic guided wave to the optimal output range.

2. The method for amplifying microvolt-level weak signals using ultrasonic guided waves according to claim 1, wherein: The S1 designs an impedance matching input stage based on the sensor impedance model, including the following steps: S1.1.

1. For piezoelectric sensors, the piezoelectric sensor circuit is presented as a high impedance capacitor, and a charge amplifier is configured to receive weak signals and input the weak piezoelectric vibration guided wave signal into the circuit; S1.1.

2. For magnetostrictive sensors, the magnetostrictive sensor circuit is presented as low-impedance inductance, a non-inverting amplifier is configured, a low-impedance input front-stage chip is used, and impedance matching is performed with the sensor to reduce signal reflection.

3. The method for amplifying microvolt-level weak signals using ultrasonic guided waves according to claim 2, wherein: In S1.1.1, the voltage sensor circuit includes capacitors C5 and C6, and inductor L2; One end of the capacitor C5 is connected to the resistor R17 and to one end of the inductor L2. The other end of the capacitor C5 is connected to the other end of the resistor R17 and to one end of the capacitor C6. The other end of the capacitor C6 is connected to one end of the resistor R18. The other end of the resistor R18 is connected to the other end of the inductor L2. Both ends of the capacitor C5 are connected to the input signal VIN.

4. The method for amplifying microvolt-level weak signals using ultrasonic guided waves according to claim 2, wherein: The S1.1.1 uses a charge amplifier to convert the charge signal output by the piezoelectric sensor into a voltage signal to match the high impedance characteristics of the piezoelectric sensor.

5. The method for amplifying microvolt-level weak signals using ultrasonic guided waves according to claim 2, wherein: In S1.1.2, the magnetostrictive sensor circuit includes an inductor L3 and a capacitor C7; One end of the inductor L3 is connected to the resistor R19 and one end of the capacitor C7 , the other end of the inductor L3 is connected to the other end of the resistor R19 and the other end of the capacitor C7 , and both ends of the inductor L3 are connected to the input signal VIN.

6. The method for amplifying microvolt-level weak signals using ultrasonic guided waves according to claim 1, wherein: In the S2, the weak signal of the ultrasonic guided wave is fixedly amplified by the first two stages of the amplifier circuit, and the first two stages of the amplifier in the amplifier circuit constitute a fixed gain amplifier circuit, including an operational amplifier IOP1 and an operational amplifier IOP2; The negative electrode of the operational amplifier IOP1 is connected to one end of the resistor R12 and to one end of the resistor R2 in parallel. The positive electrode of the operational amplifier IOP1 is connected to one end of the resistor R1 and to the input signal VIN in parallel. The other end of the resistor R12 is connected to a power supply. The output end of the operational amplifier IOP1 is connected to the other end of the resistor R2 and to one end of the capacitor C1 in parallel. The negative electrode of the operational amplifier IOP2 is connected to one end of the resistor R3 and to one end of the resistor R4 in parallel. The positive electrode of the operational amplifier IOP2 is connected to one end of the resistor R9 and to the other end of the capacitor C1 in parallel. The other end of the resistor R3 is connected to the power supply. The output end of the operational amplifier IOP2 is connected to the other end of the resistor R4.

7. The method for amplifying microvolt-level weak signals using ultrasonic guided waves according to claim 6, wherein: In S2, the resistors R2 and R4 have the same resistance value and amplify the weak signal by the same multiple. The capacitor C1 and the resistor R9 form a filter circuit to reduce noise.

8. The method for amplifying microvolt-level weak signals using ultrasonic guided waves according to claim 1, wherein: The adaptive adjustment of the amplification gain of the latter two stages in S3, the latter two stages of amplification and the digitally controlled gain amplifier constitute a variable gain amplifier circuit, including an operational amplifier IOP3, an operational amplifier IOP4 and an operational amplifier IOP5, a transistor T1, and an inductor L1; The negative electrode of the operational amplifier IOP3 is connected to one end of the resistor R5 and to one end of the resistor R6 in parallel. The positive electrode of the operational amplifier IOP3 is connected to one end of the resistor R110 and to the other end of the capacitor C2. The other end of the resistor R5 is connected to a power supply. The output terminal of the operational amplifier IOP3 is connected to the other end of the resistor R6, to one end of the capacitor C3, and to the negative electrode of the operational amplifier IOP5. The negative electrode of the operational amplifier IOP4 is connected to one end of the resistor R7 and to one end of the resistor R8 in parallel. The positive electrode of the operational amplifier IOP4 is connected to one end of the resistor R11 and to the other end of the capacitor C3 in parallel. The other end of the resistor R7 is connected to the power supply. The output terminal of the operational amplifier IOP4 is connected to the other end of the resistor R8 and to the collector of the transistor T1. The emitter of the transistor T1 is connected to the positive electrode of the operational amplifier IOP5, the base of the transistor T1 is connected to one end of the resistor R15, the other end of the resistor R15 is grounded, the output end of the operational amplifier IOP5 is connected to one end of the inductor L1, and is connected in parallel to the resistor R14 and the resistor R16, the other end of the inductor L1 is connected to one end of the capacitor C4, the other end of the capacitor C4 is grounded, and the output end of the operational amplifier IOP4 is connected to the output signal VOUT.

9. The method for amplifying microvolt-level weak signals using ultrasonic guided waves according to claim 8, characterized in that: In the above S3 , the operational amplifier IOP3 , the operational amplifier IOP4 , and the operational amplifier IOP5 are all variable gain amplifiers, and the amplification gain is adjusted by a potentiometer network composed of a resistor R14 , a resistor R15 , and a resistor R16 .

10. The method for amplifying microvolt-level weak signals using ultrasonic guided waves according to claim 8, wherein: In S3, the variable gain amplifier circuit adopts a hierarchical amplification strategy, further amplifies the weak signal through the operational amplifier IOP3, and the operational amplifier IOP4 accurately controls the amplified signal to amplify the weak signal of the ultrasonic guided wave to the optimal output range.

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