A method for automatically detecting electrode contact conditions

Abstract

A method for automatically detecting electrode contact status relates to the field of human body electrical impedance signal detection. Accurate detection of human body electrical impedance signals requires full contact between the human body surface and the electrodes. The proposed method for automatically detecting electrode contact status, based on human body electrical impedance theory, determines that the points corresponding to the real and imaginary parts of the human body electrical impedance measured under currents of different excitation frequencies lie on a circular arc. Utilizing this characteristic, for a set of discrete points corresponding to the real and imaginary parts of the detected resistance, the algebraic sum of the difference between the distance from the point to the center of the circle to be determined and the square of the radius of the circle is used as the loss function. The method of undetermined coefficients and partial derivative calculations are applied to determine the coordinates of the center and radius of the fitted circle. The minimum distance between the discrete points and the arc of the fitted circle is calculated to automatically determine the contact status between the human body surface and the electrodes.

Description

Technical Field

[0001] The present invention relates to the field of human physiological signal detection, in particular to human electrical impedance signal detection. Background Art

[0002] Bioelectrical impedance is an important parameter that reflects the physiological state of the human body. Bioelectrical impedance detection technology has the advantages of being fast, non-destructive, safe, and low-cost, and can be applied to human body composition analysis and health status assessment. Human body electrical impedance detection is to maintain good contact between the excitation electrode and the detection electrode and the human body surface. An excitation current is applied to both ends of the excitation electrode and the detection electrode, allowing the current to pass through the body. The voltage value at both ends is detected, and the amplitude and phase angle of the human body electrical impedance are calculated. If the electrode is not in good contact with the human body surface, it will lead to measurement deviations. Especially when using dry electrodes, it is very important to ensure sufficient contact between the electrode and the human body surface. If the contact is poor, it is necessary to readjust the contact angle, fit strength, or increase the contact area. Relying on manual observation and experience is both cumbersome and prone to misjudgment. Summary of the Invention

[0003] According to human body impedance theory, the real and imaginary parts of the human body's impedance correspond to the intracellular and extracellular fluids, respectively. Under the influence of currents of different excitation frequencies, the impedance of human tissue changes due to differences in current penetration. Ideally, in the complex plane formed by the real and imaginary parts of the human body's impedance, the points corresponding to the real and imaginary parts should lie on a circular arc. In actual measurements, if the body surface is in good contact with the electrodes, these points will be approximately distributed on a circular arc.

[0004] The present invention utilizes the distribution characteristics of the human body's electrical impedance to innovatively propose a method for automatically determining the contact status between electrodes and the human body surface. The technical solution provided by the present invention is: a method for automatically detecting electrode contact status, comprising:

[0005] 1) Determine the test site and place the excitation electrode and detection electrode of the impedance tester in contact with the surface of the body part to be tested;

[0006] 2) Impedance detection: generating currents of different excitation frequencies, applying them to both ends of the electrodes, and detecting the voltage between the excitation electrode and the detection electrode;

[0007] 3) Calculate the amplitude and phase of the human body electrical impedance based on the detected voltage value;

[0008] 4) Determine whether the electrical impedance amplitude exceeds the normal range of the human body's electrical impedance amplitude. If it is too large, it means that the electrode is not in contact with the human body surface or is not in sufficient contact;

[0009] 5) Calculate the real and imaginary parts of the electrical impedance at each frequency based on its amplitude and phase.

[0010] 6) The real and imaginary parts of the impedance are used to construct a complex plane. The measured real and imaginary impedance values ​​are discrete points in the complex plane.

[0011] 7) Fit the discrete points into a circle and obtain the center and radius;

[0012] 8) For each discrete point, calculate the minimum distance between that point and the points on the circumference, and find the average of the minimum distances;

[0013] 9) If the average value is less than a given threshold, it indicates that the electrode is in good contact with the human body surface; otherwise, it indicates poor contact.

[0014] In step 3), the amplitude and phase of the human body impedance are calculated, and the current source excitation signal is assumed to be , whose size is:

[0015]

[0016] in is the excitation signal amplitude, is the excitation signal angular frequency, t is the time, is the initial phase of the excitation signal. Assume that the bioelectrical impedance to be measured is The voltage detected at the measuring electrode is , then:

[0017] = / (2)

[0018] (3)

[0019] in is the impedance amplitude, is the impedance phase, which can be obtained from equations (2) and (3) respectively. .

[0020] The process of fitting the discrete points into a circle as described in step 6) is as follows:

[0021] a) Let the impedance data point be p i (x i , y i ), where i is the point number, x i , y i is its corresponding coordinate, a total of N data points; the coordinate of the center of the circle to be fitted is O(x c , y c ), with a radius of r;

[0022] b) Calculate the distance d from each point to the center of the fitted circle i = ;

[0023] c) Define the objective function , This function first calculates the absolute value of the difference between the square of the distance from each point to the center of the circle and the square of the radius, and then sums them;

[0024] d) Use the partial differential and undetermined coefficient method to solve the parameter x of the fitting circle. c , y c and r. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart of the present invention.

[0026] Figure 2 are the points and fitting circles in the complex impedance plane when the human body surface is in good contact with the electrode.

[0027] Figure 3 These are the points and fitting circles in the complex impedance plane when the human body surface is in poor contact with the electrode. DETAILED DESCRIPTION

[0028] The present invention will be further described below through figures and specific embodiments.

[0029] The process of the method for automatically detecting the electrode contact status of the present invention is as follows: Figure 1 Shown, including:

[0030] 1) Determine the test site and place the excitation electrode and detection electrode of the impedance tester in contact with the surfaces of the left and right thumbs respectively;

[0031] 2) Impedance detection: Start the impedance detection program. The detector generates 12 excitation currents in the range of 1kHz to 100kHz through the signal generator. Starting from the low frequency, the frequency is gradually increased. The voltage value across the electrode is detected at each excitation current frequency until the highest excitation current frequency is reached.

[0032] 3) Based on the voltage value detected at each frequency excitation current, refer to formulas (1) to (3) to calculate the impedance amplitude and phase;

[0033] 4) Determine whether the impedance amplitude under the 1kHz to 100kHz excitation current is within the normal range (400Ω to 1200Ω). If it exceeds 1200Ω, it means that the electrode is not in contact with the human body surface or is not in sufficient contact;

[0034] 5) Calculate the real and imaginary parts of the electrical impedance at each frequency based on its amplitude and phase.

[0035] 6) Construct a complex plane with the real and imaginary parts of the impedance, and correspond the measured real and imaginary impedance values ​​to a series of discrete points, such as Figure 2 As shown;

[0036] 7) Fit the discrete points into a circle and get the center and radius, as Figure 2 The coordinates of the center O of the fitted circle shown are (705.0, 142.2) and the radius is 186.7;

[0037] 8) For each discrete point, calculate the minimum distance between the point and the point on the circumference, and find the average of the minimum distances, such as Figure 2 The average value of the minimum distance is 3.2;

[0038] 9) Set the threshold T=10. Since 3.2<10, it means that the fitting error of the discrete impedance points is small, that is, they are approximately distributed on a circular arc, indicating that the electrode has good contact with the thumb surface.

[0039] Similar to the above steps, restart the impedance detection, and the measured set of impedance real and imaginary values ​​correspond to a series of discrete points such as Figure 3 As shown, the discrete points are fitted into a circle, as Figure 3 The coordinates of the center O of the fitted circle shown are (786.0, -171.7) and the radius is 180.9;

[0040] Calculate the minimum distance between each discrete point and the point on the circumference, and find the average value of each minimum distance, such as Figure 3 The average value of the minimum distance is 19.5, indicating that the fitting error of the impedance discrete points is large and the contact between the electrode and the thumb surface is poor, suggesting that the contact angle, fitting force or contact area needs to be readjusted.

Claims

1. A method for automatically detecting electrode contact conditions, characterized in that: include: 1) Determine the test site and place the excitation electrode and detection electrode of the impedance tester in contact with the surface of the body part to be tested; 2) Impedance detection: generating currents of different excitation frequencies, applying them to the excitation electrode ends, and detecting the voltage between the excitation electrode and the detection electrode; 3) Calculate the amplitude and phase of the human body electrical impedance based on the detected voltage value; 4) Determine whether the electrical impedance amplitude exceeds the normal range of the human body's electrical impedance amplitude. If it is too large, it means that the electrode is not in contact with the human body surface or is not in sufficient contact; 5) Calculate the real and imaginary parts of the electrical impedance at each frequency based on its amplitude and phase. 6) The real and imaginary parts of the impedance are used to construct a complex plane. The measured real and imaginary impedance values ​​are discrete points in the complex plane. 7) Fit the discrete points into a circle and obtain the center and radius; 8) For each discrete point, calculate the minimum distance between that point and the points on the circumference, and find the average of the minimum distances; 9) If the average value is less than a given threshold, it indicates that the electrode is in good contact with the human body surface; otherwise, it indicates poor contact.

2. The method for automatically detecting electrode contact conditions according to claim 1, characterized in that: The calculation of the human body electrical impedance amplitude and phase in step 3) is as follows: , its size is: in is the excitation signal amplitude, is the excitation signal angular frequency, t is the time, is the initial phase of the excitation signal; let the bioelectrical impedance to be measured be The voltage detected at the measuring electrode is , then: = / (2) (3) in is the impedance amplitude, is the impedance phase, which can be obtained from equations (2) and (3) respectively. .

3. The method for automatically detecting electrode contact conditions according to claim 1, characterized in that: The process of fitting the discrete points into a circle as described in step 6) is as follows: a) Let the impedance data point be p i (x i , y i ), where i is the point number, x i , y i is its corresponding coordinate, a total of N data points; the coordinate of the center of the circle to be fitted is O(x c , y c ), with a radius of r; b) First, calculate the distance d from each point to the center of the fitted circle i = ; c) Then, define the objective function , This function first calculates the absolute value of the difference between the square of the distance from each point to the center of the circle and the square of the radius, and then sums them; d) Finally, the partial differential and undetermined coefficient method is used to solve the parameter x of the fitting circle. c , y c and r.

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