Electrical impedance positioning circuit and method

Abstract

The invention discloses an electrical impedance positioning circuit and method. The circuit is composed of an excitation current source, a medium inner positioned electrode, a medium outer reference electrode and a voltage measurement and analysis part. A positioning function is realized by adopting the circuit, firstly, a plurality of non-collinear and non-coplanar reference electrodes are fixed on the surface of a medium, known three-dimensional coordinates of the reference electrodes are acquired, secondly, the positioned electrodes are inserted into the medium and are connected with an excitation current source, current signals emitted by the excitation current source are modulated square wave signals with a certain frequency and capable of driving the electrodes, and the three-dimensional coordinates of the reference electrodes are acquired. According to the relation between the resistance difference and the distance and the relation between the signal transmission time and the distance, the distance between the electrodes in the medium and each electrode can be obtained, and then the electrodes in the medium are accurately positioned. The circuit and the method can be used for positioning an in-vivo intervention catheter in medical equipment, a drilling position in industrial equipment and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of object positioning, and in particular to an electrical impedance positioning circuit. Background Art

[0002] In many fields such as medicine and industry, accurately determining the position of an object inside a medium is a key requirement. In the medical field, accurate positioning of interventional catheters in the body is crucial for the diagnosis and treatment of diseases. Traditional positioning methods may have problems such as insufficient accuracy, complex operation, or greater trauma to patients. In the industrial field, such as drilling operations, accurately understanding the drilling location can effectively improve work efficiency and quality and avoid unnecessary losses.

[0003] However, existing positioning technologies often fail to meet the requirements of high precision, non-invasiveness, and ease of operation. For example, some methods may rely on complex imaging equipment, which is costly and inconvenient to use; others may cause certain interference or damage to the medium or the object being positioned. Existing electrical impedance measurement equipment has limitations in positioning accuracy and data processing speed, and it is difficult to meet the requirements of certain application scenarios. Therefore, there is an urgent need for an innovative, high-precision, and easy-to-operate positioning technology to meet the growing needs of fields such as medicine and industry. Summary of the invention

[0004] In order to overcome the deficiencies and defects in the prior art, the present invention provides a novel circuit and method based on electrical impedance positioning, which has the characteristics of accurate positioning, non-invasiveness, simple structure and low cost.

[0005] The technical solution adopted by the present invention is: 1. A positioning circuit based on electrical impedance The electrical impedance positioning circuit is composed of an excitation current source, a positioned electrode in a medium, a reference electrode outside the medium and a voltage measuring part.

[0006] The first is the excitation current source, which provides a stable current signal for the located electrode. The current source uses square wave modulation technology to generate a square wave signal of a specific frequency. The modulated constant current is injected into the medium through the located electrode to form a current path and a corresponding electric field. Square wave modulation has strong anti-interference ability and can effectively filter background noise to ensure the purity of the signal. In this way, the current source can provide the system with a high-quality excitation signal to ensure that reliable voltage data can still be obtained in a complex medium environment.

[0007] The excitation current source is connected to the positioned electrode through a metal wire with an insulating layer, and the positioned electrode is located inside the medium. Multiple reference electrodes are placed on the outer surface of the medium, and are distributed in a non-collinear and non-coplanar manner.

[0008] The reference electrode is connected to the signal acquisition module to collect and process the voltage signal of each reference electrode. Corresponding to multiple reference electrodes, they are connected to the measurement channel through a switch. The system is allowed to obtain the voltage signal of each reference electrode in turn through a dynamic switching mechanism. Dynamic switching not only improves the measurement efficiency, but also effectively reduces the electromagnetic interference between electrodes, ensuring the accuracy of the measurement data. The voltage signal of each reference electrode is transmitted to the signal processing module through a dedicated channel to ensure the real-time and integrity of signal acquisition.

[0009] The voltage signal is collected in real time by the signal acquisition circuit. Due to the square wave modulation characteristics of the current source, the collected voltage signal is usually a periodically changing waveform. In order to obtain effective measurement data, the signal acquisition module first performs peak detection on each voltage signal. By identifying the peak voltage value within each square wave cycle, the system can extract the key signal features that reflect the positional relationship between the electrode and the medium.

[0010] After the signal acquisition is completed, the signal processing module in the circuit normalizes the collected peak voltage signal. Normalization can eliminate signal deviations caused by system noise, equipment errors and other factors, making the data between different measurement channels more comparable. Then, the system calculates the difference between the normalized signal and the standard square wave signal, and analyzes the width and time characteristics of the difference. The key signal features related to the position of the electrode inside the medium are extracted to ensure the stability and reliability of the measurement results.

[0011] After signal processing is completed, the system will enter the calculation stage of the three-dimensional positioning algorithm. By combining the information of the resistance voltage signal and the signal transmission time delay, the system uses a set of nonlinear equations to calculate the distance between the located electrode and each reference electrode. Specifically, the system measures the relationship between the voltage peak and the current, and combines the time delay data in the equation group to solve the three-dimensional coordinate position of the located electrode. This method makes full use of the complex relationship between the voltage signal and the time delay to achieve accurate positioning of the target electrode inside the medium.

[0012] 2. Electrical impedance positioning method using the above circuit The following steps are involved: 1. System initialization and electrode placement First, determine the medium type, evenly arrange multiple non-collinear and non-coplanar reference electrodes on the surface of the medium, measure and record their known three-dimensional coordinates, and insert the positioned electrode into the medium to the target position. Ensure that the electrode is in full contact with the medium and connected to the excitation current source.

[0013] 2. Generation and modulation of excitation signal The current source emits a current signal, and the square wave generation module generates a square wave signal, which is modulated at a certain frequency by the square wave modulation module to output a square wave emission signal that can drive the electrode. The modulated current is injected into the medium through the positioned electrode to form a current path and a corresponding electric field. This modulation method can effectively distinguish the target signal from the background noise and improve the accuracy of the measurement.

[0014] 3. Signal measurement and acquisition After the excitation current is injected into the medium, the signal needs to be measured and collected. The measurement channel is switched by switching the switch, and the measurement module is connected to each reference electrode in turn, collecting the voltage signal of each electrode one by one. This method can effectively reduce the mutual interference between electrodes and ensure the purity of the signal. Next, the peak voltage detection module is used to record the peak value of the voltage signal of each measurement channel to obtain the most effective signal data. In addition, in order to improve the stability and reliability of the signal, the above process is repeated to collect voltage signals of multiple square wave cycles for subsequent data analysis.

[0015] 4. Signal processing First, the peak voltage signal of each measurement channel is normalized to reduce measurement inconsistencies caused by system noise and errors. Next, the difference between the normalized signal and the standard square wave signal is calculated, and effective positioning information is extracted by analyzing the width and time difference of the signal difference. Finally, the difference calculation result is corrected according to the characteristics of the medium, such as conductivity and capacitance effect, to ensure the accuracy and reliability of the measurement data.

[0016] 5. Analysis and calculation Combining the relationship between voltage signal, signal transmission time, resistance and distance, the following set of equations is obtained: The left side of the equation calculates the position of the reference electrode to the electrode being located. , represents the coordinates of the reference electrode, and the signal transmission time is , Represents the signal transmission speed, is the material conductivity, is the contact area between the reference electrode and the medium, and The voltage and current values ​​measured by the reference electrode, and is the error; The system of equations is solved numerically to obtain the three-dimensional coordinates of the electrodes inside the dielectric .

[0017] Beneficial effects of the present invention: The present invention utilizes the signal peak value and the difference width to obtain the resistance difference and the signal transmission time difference between the electrode inside the medium and each external electrode. According to the relationship between the resistance difference and the distance and the relationship between the signal transmission time and the distance, the distance between the electrode inside the medium and each external reference electrode can be obtained, thereby accurately locating the electrode inside the medium. This is a new method for realizing electrical impedance positioning.

[0018] The present invention is a simpler and more accurate electrical impedance positioning circuit and method, which has great application value in the fields of medical imaging, material testing, and environmental monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the electrical impedance positioning circuit structure. Figure 1 Middle: Contains excitation current source, positioned electrode, reference electrode, and voltage measurement circuit; Figure 2 for Figure 1 The data flow diagram of the electrical impedance positioning method corresponding to the circuit in the figure. Figure 2 Middle: The current source and square wave signal modulate a square wave current to the located electrode, the reference electrode receives the signal, and the voltage measurement circuit performs signal acquisition, signal processing and analysis. DETAILED DESCRIPTION

[0020] The present invention will be further described and illustrated below in conjunction with the accompanying drawings and examples: This example is based on the technical solution of the present invention and provides a specific implementation method and operation process. The protection scope of the present invention includes but is not limited to the following examples.

[0021] The circuit structure diagram of the present invention is as follows Figure 1 As shown, the data flow diagram is as follows Figure 2 shown.

[0022] The excitation current source uses a constant current source circuit modulated by a square wave switch, which can provide an adjustable output current from 1μA to 10mA to adapt to the characteristics of different media. The current source supports square wave modulation frequency adjustment in the range of 1Hz to 1MHz, which can effectively avoid signal distortion caused by the capacitance effect of the medium. At the same time, the current source is a linear regulated power supply with low noise and high stability, ensuring accuracy at low current output. Figure 2 As shown, the power supply I provides power for the entire measurement system, ensuring the normal operation of all electronic components and circuits. It provides a stable current source for the square wave modulation circuit.

[0023] One electrode to be located is placed in the medium, and three reference electrodes are placed on the outer surface of the medium. In the impedance positioning circuit, the medium can be different types of substances such as biological tissue, oil or water, which are used to conduct current and transmit signals. Its conductivity will vary depending on the material characteristics.

[0024] The electrodes positioned in the medium are connected to the excitation current source and emit square wave signals. The electrodes positioned in the medium are made of platinum material, which has excellent biocompatibility and electrochemical stability and is suitable for in vivo measurement in medical devices. The electrode is designed as a slender needle structure with a diameter of 0.5 mm and a length of 50 mm, so that it can be inserted into the medium for precise positioning. The outer layer of the connection line between the electrode and the current source is coated with a 10-micron thick polyimide insulation layer, which can effectively prevent current leakage and accidental contact with the medium.

[0025] The reference electrode outside the medium is arranged on the surface of the medium, and three or more non-colinear and non-coplanar electrodes are distributed to ensure good resolution in three-dimensional positioning. Each reference electrode is a silver sheet structure with a size of 10mm×10mm, which can form a stable electrical contact with the surface of the medium and reduce the fluctuation of the contact resistance.

[0026] Each external reference electrode is connected to a measurement channel, and is switched to different measurement channels in turn by switching switches. Each switch measures the voltage signal of a reference electrode. This design can reduce interference between electrodes and improve measurement accuracy. The signals collected by each channel are transmitted to the subsequent signal processing module.

[0027] The voltage measurement circuit uses a high-precision instrumentation amplifier AD620, which can accurately capture and amplify weak signals. The signal is digitized through a 16-bit resolution AD converter (ADS1115), and the sampling rate is set to 10kSPS to ensure accurate capture of signals of different frequencies. At the same time, a low-pass filter with a cutoff frequency of 1MHz is designed at the front end of the circuit to reduce high-frequency noise and electromagnetic interference.

[0028] The peak voltage module is used to detect the peak value of the voltage signal collected by each measurement channel. The peak voltage represents the voltage signal strength of each reference electrode, which can be further analyzed to obtain the resistance difference between the located electrode and the reference electrode. The normalized difference module normalizes the peak voltage signal. Normalization can reduce the impact of system noise and other non-ideal factors on the measurement results, thereby improving the reliability and comparability of the data. This module obtains the difference signal by normalizing each signal and performing difference calculation with the standard square wave signal of the modulated excitation current source. The difference module is used to further analyze the normalized difference signal. This module calculates the data width of each difference signal (i.e., the time width of the signal), and this width information is used to calculate the relative distance between the located electrode and each reference electrode.

[0029] In actual operation, firstly, three reference electrodes need to be fixed on the surface of the medium and their known three-dimensional coordinate data need to be input. Then, the electrodes to be positioned are inserted into the medium and connected to the excitation current source. When the self-calibration function of the device is started, the system will automatically adjust the excitation current output and measure the baseline signal of each reference electrode to compensate for the error caused by contact resistance or electrode deviation.

[0030] Subsequently, the excitation current source outputs a constant current through square wave modulation, and the modulation frequency is set to 500Hz, taking into account both signal transmission efficiency and measurement accuracy. The voltage measurement circuit switches to each reference electrode one by one to collect voltage signals within multiple square wave cycles. The collected voltage signals are converted into digital data by an AD converter and transmitted to the data analysis module.

[0031] In the data analysis module, the collected voltage signal is first subjected to a fast Fourier transform (FFT) to extract the signal's spectral components and peak voltage. Subsequently, the signal is normalized to eliminate the influence of system noise and background signals. The normalized voltage signal is synchronously processed with the excitation source square wave signal to calculate the difference signal between the two. Based on the phase difference and amplitude difference of the signal, the resistance difference between the electrode and each reference electrode is obtained.

[0032] Combining the relationship between voltage signal, signal transmission time, resistance and distance, the position of the located electrode in the medium is calculated by the following equations: in, are the coordinates of the positioned electrode within the medium, are the known coordinates of the reference electrode; is the signal propagation time difference, is the signal transmission speed, is the conductivity of the medium, is the electrode area, is the peak voltage of the signal at each electrode, is the excitation current, and are systematic errors associated with time and voltage measurements.

[0033] Using these equations, the precise three-dimensional coordinates of the positioned electrodes within the medium are calculated by triangulation.

Claims

1. An electrical impedance positioning circuit, characterized in that: The circuit uses the resistance difference and distance difference caused by the electrode position for positioning. The circuit and working environment include: An excitation current source, the excitation current source comprising a current source, a square wave generator and a square wave modulation module, the current source is used to provide an input current signal capable of driving the electrode, and the square wave modulation module modulates the current signal of the current source and the square wave signal of the square wave generator into a square wave current signal; medium; An electrode is positioned in a dielectric and connected to an excitation current source through a metal wire with an insulating outer layer; A voltage measurement circuit, the voltage measurement circuit comprising a signal acquisition module, an operational amplifier circuit, an A / D sampling module and a data analysis module, the signal acquisition module acquires the surface current signal of the medium and converts it into a voltage signal through the operational amplifier circuit, and obtains voltage data through the A / D sampling circuit, and the data analysis module performs further calculation and analysis; Multiple dielectric external reference electrodes transmit current signals to the voltage measurement circuit through metal wires.

2. An electrical impedance positioning circuit according to claim 1, characterized in that: The excitation current source is a constant current source circuit structure that can perform square wave modulation. The current source provides current to drive the square wave modulation module. The square wave generator generates a basic square wave signal. The square wave modulation module simultaneously receives the square wave signal and the current, modulates the current to form a square wave current. The square wave modulation is used to eliminate background noise and interference and improve the signal-to-noise ratio of the signal.

3. An electrical impedance positioning circuit according to claim 1, characterized in that: The electrode positioned in the medium is a metal structure, connected to an excitation current source through a metal wire with an insulating outer layer, and in contact with the medium; the outer layer of the connecting wire between the electrode and the current source is covered with an insulating layer.

4. An electrical impedance positioning circuit according to claim 1, characterized in that: The external reference electrode of the medium is a metal sheet structure closely attached to the surface of the medium. The external reference electrode of the medium is distributed non-collinearly and non-coplanarly on the surface of the medium. The external reference electrode of the medium is connected to the voltage measurement circuit structure through a metal wire to receive the signal sent by the positioned electrode in the medium.

5. The electrical impedance positioning circuit according to claim 1, characterized in that: Different measurement channels are dynamically switched by switching switches to achieve multi-channel voltage measurement and obtain the voltage signals of the reference electrodes one by one.

6. The electrical impedance positioning circuit according to claim 1, characterized in that: The voltage measurement circuit collects the current signal on the surface of the medium, amplifies the current signal and converts it into a voltage signal through an operational amplifier circuit, and then obtains voltage data through an A / D sampling circuit; the voltage measurement circuit normalizes the peak voltage signal to eliminate the system error caused by changes in the measuring equipment and the environment; the voltage measurement circuit performs difference calculation with the standard square wave signal to improve the accuracy of the signal; the voltage measurement circuit improves the reliability of the electrical impedance measurement through a dual signal processing method, and is used to provide a high-quality signal basis for positioning calculations.

7. An electrical impedance positioning method using the electrical impedance positioning circuit according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1: System initialization and electrode placement Determine the medium type, evenly arrange multiple non-collinear and non-coplanar reference electrodes on the surface of the medium, measure and record their known three-dimensional coordinates, insert the positioned electrode into the medium to the target position; ensure that the electrode is in full contact with the medium and connect it to the excitation current source; S2: Generation and modulation of excitation signal The current source sends out a current signal, the square wave generation module generates a square wave signal, which is modulated at a certain frequency by the square wave modulation module to output a square wave emission signal that can drive the electrode; the modulated current is injected into the medium through the positioned electrode to form a current path and a corresponding electric field; S3: Signal measurement and acquisition Switch the measurement channel, collect the voltage signal of each electrode one by one, use the peak voltage detection module to record the peak value of the voltage signal of each measurement channel, and obtain valid signal data; S4: Signal Processing Normalize the peak voltage signal of each measurement channel to reduce measurement inconsistency caused by system noise and error; calculate the difference between the normalized signal and the standard square wave signal, extract effective positioning information by analyzing the width and time difference of the signal difference, and correct the difference calculation result according to the characteristics of the medium to ensure the accuracy and reliability of the measurement data; S5: Analytical calculations Combining the relationship between voltage signal, signal transmission time, resistance and distance, the following set of equations is obtained: The left side of the equation calculates the position of the reference electrode to the electrode being located. , represents the coordinates of the reference electrode, and the signal transmission time is , Represents the signal transmission speed, is the material conductivity, is the contact area between the reference electrode and the medium, and The voltage and current values ​​measured by the reference electrode, and is the error; The system of equations is solved numerically to obtain the three-dimensional coordinates of the electrodes inside the dielectric .

8. The electrical impedance positioning method according to claim 7, characterized in that: Through the electrodes with known coordinate information outside the medium, the square wave signals emitted by the positioned electrodes inside the medium are received, and the differentiated information of the signals received by multiple external electrodes is obtained. By adopting multiple reference electrodes and signal processing technology, high-precision positioning effects can be maintained under multiple scattering and heterogeneous media conditions.

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