CN114984453A - An impedance detection device for multi-channel transcranial electrical stimulator - Google Patents

Abstract

The invention discloses an impedance detection device for a multi-channel transcranial electrical stimulator, comprising a multi-channel electrical stimulation output module, a DAC output module, an ADC acquisition module, an FFT processing module and an impedance detection calculation module; the FFT processing module is respectively connected with the The ADC acquisition module is connected with the impedance detection and calculation module, and the DAC output module is connected with the multi-channel electrical stimulation output module. The present invention does not require additional power sources or electrodes, and only uses the difference between the frequencies of the multi-channel stimulation signals to calculate the corresponding impedance of each electrode. The core principle of the present invention is to use the interference between the multi-channel current signal outputs in the common cathode circuit, and to judge the real-time impedance situation of the corresponding electrode according to the value of the mutual influence of the signals between the channels.

Description

An impedance detection device for multi-channel transcranial electrical stimulator

technical field

The invention relates to an impedance detection device for a multi-channel transcranial electrical stimulator.

Background technique

Impedance detection is an integral part of various transcranial electrical stimulation systems (tDCS, tACS, tRNS). For the voltage output system, the electrode impedance will divide the voltage. The larger the impedance, the smaller the actual stimulation power of the human body, and the less obvious the stimulation effect. For the current output system, firstly, because the current output is fixed, excess power will be generated when passing through the electrodes. If the device is powered by batteries, the overall use time will be reduced; secondly, in order to ensure that the output is a stable current, the output voltage needs to be based on the overall impedance (electrode and human body). ) changes at any time, in order to ensure safety, the output voltage needs to be controlled within a certain range. If the impedance is too large, the overall stimulation signal will be distorted and affect the stimulation effect; finally, if the electrode impedance is large, it means that the area of poor contact with the human body is small. The electric current may burn the skin in the corresponding area. To sum up, for the transcranial electrical stimulation system, in order to ensure a good stimulation effect, impedance monitoring is essential, and at the same time, it cannot interfere with the normal stimulation experiment.

The impedance in the transcranial electrical stimulation system generally consists of three parts: electrode impedance, contact impedance, and human body impedance. However, the general impedance detection mainly analyzes the electrode contact impedance, because the impedance of the electrode itself is determined by the material used, while the impedance of the human body itself is more complex There are differences between individuals. Although both of them are not easy to optimize, in general their actual impedance (tens to hundreds of ohms) is much smaller than the contact impedance between the electrode and the human body (hundreds to tens of thousands of ohms), so In the calculation, the other two are often ignored to simplify the calculation.

At present, the commonly used impedance detection methods are mainly divided into DC signal detection and AC signal detection according to different input waveforms. DC signal detection requires inputting a DC signal and then detecting the voltage and current values at both ends of the electrode, and using Ohm's law to calculate the overall impedance. In order not to interfere with the stimulation experiment as much as possible, the input signal is mainly a short-time pulse signal or a square wave signal, which has the advantages of simple structure and cost. Low, but usually can only be used for single-channel impedance detection. For multi-channel electrical stimulation output, the current between different channels will cause crosstalk, and simple impedance detection results will become unreliable. At present, the commonly used impedance detection waveform is AC signal, mainly because high-frequency AC signal has less influence on the brain than DC signal, and the output is not easily disturbed by the frequency of EEG signal (several Hz to hundreds of Hz).

US 9339642 B1 "System and method for conducting multi-electrodeelectrical stimulation" discloses a stimulation and monitoring method suitable for multi-electrode experiments. Its structure is shown in Figure 1. The controller is responsible for the parameter configuration of each module. The output source is divided into a first stimulus source and a second stimulus source. The first stimulus source is the main output and is responsible for generating the stimulus signals required for the experiment. The second stimulus source The output needs to be different from the first source for impedance detection, such as transcranial direct current stimulation (tDCS). The electrode impedance is calculated by measuring the AC signal while the DC stimulation experiment effect is performed, and the monitor is responsible for collecting the signal of each electrode to calculate the impedance. The patent application only proposes a multi-electrode stimulation method through two stimulation sources and a monitor, and specifically describes how to build the entire system by changing the electrode connection method, without discussing the specific impedance detection algorithm in depth.

"Methods for Specific Electrode Resistance Measurement During Transcranial Direct Current Stimulation" is a specific electrode impedance detection method in tDCS stimulation. This paper proposes a method to measure the impedance of stimulation electrodes by adding extra electrodes or an extra power source. Multi-channel direct current stimulation can calculate the impedance of cathode and anode electrodes by adding additional reference electrodes to measure the brain voltage increase equation, or output a high-frequency current signal with a direct current bias as an experimental signal through a current source, and separate the direct current and alternating current signals to convert the direct current. As the experimental main signal, the AC signal establishes multiple equations for the auxiliary signal to calculate the real-time impedance of each electrode. This method is limited to tDCS experiments and is not applicable to other transcranial electrical stimulation.

CN201810566020.3 "An Impedance Detection System in Transcranial Electrical Stimulation" provides an impedance detection method suitable for various types of transcranial electrical stimulation, which mainly includes a DA module, an MCU unit, an AD sampling module, and an AD sampling module. The MCU controls the output signal parameters to drive the DA to generate an analog impedance detection signal, and performs peak detection and related control after output. Finally, the AD collects the corresponding signal to calibrate the data through the least square method, and returns the data to the MCU to control the entire process in real time. The impedance detection system designed in this application only adds peak detection and AD calibration to the existing method of measuring impedance by outputting a detection signal. The purpose is to use a low-cost method to achieve relatively accurate impedance measurement, and does not innovate the specific algorithm. , and does not involve multi-channel impedance detection.

At present, the commonly used impedance detection method needs to provide additional signal input or independent reference electrode for monitoring impedance, and the whole system may generate a large amount of extra power. The impedance results obtained by direct current, square wave, and sine wave with different frequencies vary greatly, and in order not to interfere with the stimulation experiment, the test signal often differs greatly from the stimulation signal parameters, which cannot well reflect the impedance changes before or during the experiment.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the prior art, and to provide an impedance detection method for a multi-channel transcranial electrical stimulator that only uses the difference between the frequencies of the multi-channel stimulation signals to calculate the corresponding impedance of each electrode without additional power sources or electrodes. device.

The object of the present invention is achieved through the following technical solutions: an impedance detection device for a multi-channel transcranial electrical stimulator, comprising a multi-channel electrical stimulation output module, a DAC output module, an ADC acquisition module, an FFT processing module and an impedance a detection calculation module; the FFT processing module is respectively connected with the ADC acquisition module and the impedance detection calculation module, and the DAC output module is connected with the multi-channel electrical stimulation output module;

The multi-channel electrical stimulation output module is used to provide multi-channel digital signals of different frequencies required for transcranial electrical stimulation, and send it to the DAC output module;

The DAC processing module is used to convert the digital signal from the multi-channel electrical stimulation output module into a current signal to generate the experimental stimulation signal;

The ADC acquisition module is used to convert the continuous analog signal collected by the electrodes of each channel into digital signals and transmit them to the FFT processing module;

The FFT processing module converts the digital signal collected by the ADC acquisition module into a frequency domain signal, and separates the voltage components of different frequencies at each electrode point;

Impedance detection calculation module, the module receives the voltage value of each frequency after FFT processing, and calculates the impedance value of each electrode point according to the impedance detection formula.

Further, the specific calculation method of the impedance value of each electrode point is: let R ₁ and R ₃ represent the contact resistance of the two electrodes of the first stimulation channel, and R ₂ and R ₄ represent the two electrodes of the second stimulation channel. The contact resistance of the electrode, R _t represents the simplified impedance of the human body, and R _ef1 and R _ef2 are fixed-value reference resistances;

R ₁ , R ₃ , and _{Ref1 are} connected in series, R ₂ , R ₄ , and _{Ref2 are} connected in series, the input frequency voltage components of the two stimulation channels are S ₁ and S ₂ respectively, and the currents are I ₁ and I ₂ respectively; R _{t is} connected in parallel between the outputs _of R1 and R2 _;

U ₁ , U ₂ , U ₃ , and U ₄ represent the voltages at the four electrodes, respectively, and subdivide the voltage components of the first stimulation channel and the second stimulation channel with two different frequencies. U ₁ is divided into U _1S1 and U _1S2 , respectively represent the S1 frequency voltage component and the S2 frequency component, and the other electrodes are the same _{; U t1 and} U _t2 represent the voltage values of the first stimulation channel and the second stimulation channel at the brain _{; for a single voltage U t1 is} equally fine It is divided into S1 frequency voltage component U _t1S1 and S ₂ frequency component U _t1S2 , U _t2 is divided into U _t2S1 and U _t2S2 in the same way; U _t1 and U _{t2 can} not be obtained directly, but according to the principle of current crosstalk, U ₁ and U ₂ are separated by The rising values U _1S2 and U _2S1 of the opponent's channel interference are respectively approximately regarded as the values U _t2S2 and U _t1S1 of S ₂ and S ₁ at the brain, and since then the estimated voltages at the two ends of R ₁ and R ₂ about their own channel frequencies are known. , the impedance value can be approximated; similarly, the voltages at both ends of R ₃ and R ₄ are known, and _Ref is used to estimate the return channel current value to estimate it; then according to the above description, the contact impedance estimation formula of each electrode is obtained as follows:

R ₁ =(U _1S1 -U _t2S1 )/I ₁

R ₂ =(U _2S2 -U _t1S2 )/I ₂

The beneficial effects of the present invention are as follows: the present invention provides an impedance detection device for multi-channel transcranial stimulation equipment. Its main feature is that there is no need for additional power sources or electrodes, and only the difference between the frequencies of the multi-channel stimulation signals is used to calculate the corresponding impedance of each electrode. The core principle of the present invention is to use the interference between the multi-channel current signal outputs in the common cathode circuit, and to judge the real-time impedance situation of the corresponding electrode according to the value of the mutual influence of the signals between the channels. In a common-cathode system, when multiple channels need to send a fixed current signal at the same time, the voltage across the load increases. In order to maintain the same current output for each channel, the voltage across the electrodes will rise to a certain extent. This interference is also the same Following Ohm's law, the value of the inter-channel interference change is linearly positively related to the electrode impedance. Using this principle, the electrode impedance can be calculated as long as the frequency between the stimulation channels is different and the frequency information of other channels on each electrode is separated.

Description of drawings

Figure 1 is a schematic diagram of the structure of the multi-electrode electrical stimulation conduction system in "System and method for conducting multi-electrode electricalstimulation";

2 is a schematic structural diagram of an impedance detection device of the present invention;

Figure 3 is a schematic diagram of single-channel impedance detection;

Figure 4 is a schematic diagram of two-channel three-electrode (single ground terminal);

Figure 5 is a schematic diagram of the connection of two-channel four-electrode;

FIG. 6 is a schematic diagram of the improved connection of two-channel four-electrode;

FIG. 7 is a schematic diagram of impedance calculation of the present invention.

Detailed ways

The technical solutions of the present invention are further described below with reference to the accompanying drawings.

As shown in Figure 2, an impedance detection device for a multi-channel transcranial electrical stimulator of the present invention includes a multi-channel electrical stimulation output module, a DAC output module, an ADC acquisition module, an FFT processing module and an impedance detection calculation module; The FFT processing module is respectively connected with the ADC acquisition module and the impedance detection calculation module, and the DAC output module is connected with the multi-channel electrical stimulation output module;

The multi-channel electrical stimulation output module is used to provide multi-channel digital signals of different frequencies required for transcranial electrical stimulation, and send it to the DAC output module; this module is flexible and can be implemented by any circuit. In order to maintain consistency with subsequent modules, this paper mainly focuses on It is realized by the same piece of digital processing unit. Before the experiment starts, each channel can send a short-term electrical signal to calculate the impedance, display the impedance data of each electrode, and help the experimenter to adjust the electrode with poor contact in time; in the experiment, it can continuously output multi-channel stimulation for a long time, and the stimulation is collected and used at the same time. In order to calculate the real-time impedance situation, if there is an electrode abnormality, it will be displayed on the interface in real time. At this time, the experiment needs to be interrupted to adjust the electrode.

The DAC processing module is used to convert the digital signal from the multi-channel electrical stimulation output module into a current signal to generate the experimental stimulation signal;

The ADC acquisition module is used to convert the continuous analog signal collected by the electrodes of each channel into digital signals, and transmit them to the FFT processing module; this module is a necessary analog-to-digital conversion module, and the present invention adopts a digital device as the core processing module, It can only process digital signals, so the continuous analog signal collected at each set point needs to be converted into a digital signal by the ADC and sent to the device for subsequent processing.

The FFT processing module converts the digital signal collected by the ADC acquisition module into a frequency domain signal, and separates the voltage components of different frequencies at each electrode point; in the present invention, the same digital computing unit is also used to implement, first collect each The time domain signal data at the electrode is passed into the device and the digital signal collected by the ADC acquisition module is converted into a frequency domain signal using FFT; then the peak value of the output frequency value point in the frequency domain signal of each point is extracted, because FFT processing will exist Problems such as spectrum leakage will cause the output value to be unstable, but the time domain amplitude change of the signal at the same frequency is proportional to the frequency domain amplitude. Using this relationship, the amplitude signal of the same output frequency under 1KΩ impedance data is collected in advance. , normalize the collected data to obtain the voltage amplitude components at different frequencies at each electrode point, and finally calculate the impedance value of each electrode point according to the impedance detection formula.

Impedance detection calculation module, the module receives the voltage value of each frequency after FFT processing, and calculates the impedance value of each electrode point according to the impedance detection formula.

The impedance calculation principle of the present invention is as follows: the impedance detection principle adopted in this paper is to add another distinguishable variable to the original stimulation system for auxiliary detection, the original stimulation is called the first stimulation source, and the auxiliary stimulation is called the second stimulation source , except that a monitor is required for the acquisition and processing of the corresponding points, the scheme is the same as that of "System and method for conducting multi-electrode electrical stimulation", as shown in Figure 1. The visualized impedance detection is shown in Figure 3. Taking single-channel DC stimulation as an example, R ₁ , R ₂ , R ₃ , and R ₄ represent the electrode impedance, and R _t represents the simplified human body impedance (the actual situation is far more complicated than this). , in order to explain the principle, the simplified diagram is used), I ₁ and I ₂ are the set current values, the left DC signal is used as the main stimulation signal as the first stimulation source, and the DC signal below 2mA is output; the right signal is the auxiliary calculation signal As a second stimulus, it is necessary to distinguish two signal sources from the overall stimulus without affecting the effect of DC stimulation, so low-amplitude and high-frequency AC current stimulation can be used (1. The human body is not sensitive to lower-amplitude and low-frequency stimulation 2. The AC output can be effectively distinguished from the DC signal of the first current source for subsequent impedance calculation); the source monitor is replaced by a voltmeter, which mainly collects the output voltage across the first stimulus source. The known information in the figure is the set outputs I ₁ and I ₂ of the first and second current sources, and the collected voltage U across the first current source, which includes two kinds of voltage information: the DC bias of the first current source. configuration information, and frequency and amplitude information of the AC signal corresponding to the second current source. The specific calculation is:

Knowing that the output is a fixed current I ₁ , if there is no AC signal I ₂ , the voltage obtained by the voltage monitor is:

U=I ₁ ×(R ₁ +R ₂ +R _t ) (1)

At this time, if I ₂ is added, the current flowing through R _t is I ₁ +I ₂ , then the voltage across R _t is:

(U ₁ -U ₂ )=(I ₁ +I ₂ )×R _t (2)

_U2 is easily obtained as:

U ₂ =I ₁ R ₂ +I ₂ R ₄ (3)

Therefore, the value of U ₁ can be calculated by formula (2) and formula (3):

U ₁ =(I ₁ R ₂ +I ₂ R ₄ )+(I ₁ +I ₂ )R _t (4)

_The voltage at the right end _of R1 is known, and the current flowing through R1 is known, so the overall output voltage at the left end can be inferred. Let U' represent the voltage obtained after the first and second current sources are simultaneously activated, which is equal to the voltage at the left end _of R1. , so U' can be expressed as:

U'=(I ₁ R ₂ +I ₂ R ₄ )+(I ₁ +I ₂ )R _t +I ₁ R ₁ (5)

After simplification we get:

U′=I ₁ (R ₁ +R ₂ +R _t )+I ₂ (R ₄ +R _t ) (6)

Comparing the collected voltage equation (1) before the second signal source is started and the voltage expression (6) after startup, it can be seen that the first output source needs an additional voltage input to maintain the output current when the second output source is started, and this The voltage input is determined by the contact impedance between the output current of the second current source and one of them. This phenomenon not only shows that when multiple channels are turned on at the same time, different channels will affect each other and cause interference. At the same time, this phenomenon can be used to calculate the parameter. The core of the above impedance detection is to identify the voltage contribution of different channel currents to certain devices in the overall circuit, and then establish an equation to calculate the impedance based on these data. The current signal can be identified by FFT as long as the frequency is different. For this paper, as long as the multi-channel stimulation frequency is different, the impedance detection can be carried out, which perfectly meets the requirements of this calculation method. So the following is the application in the specific experimental circuit.

Figure 4 shows the situation of two channels and three electrodes (the actual situation should be two channels and four electrodes, but the FPGA chip used is a common equipotential point or a common cathode, and the electrodes connected to the equality point cannot be distinguished without using other methods. Impedance situation, temporarily turn it into the same resistance for discussion), the basic parameter settings are basically the same as in Figure 3, considering the fact that the impedance between electrodes is different in the actual situation, R ₁ , R ₂ , R ₃ represent the electrode impedance of The parameters to be determined, R _t1 , R _t2 , R _t3 , and R _t4 represent the simplified human body impedance between the electrodes. The specific calculation process is as follows:

First, the voltage representation of the current source S ₁ can be obtained from the figure:

This equation can be simplified, because the contact resistance of the electrode is as high as several thousand Ω, which is much larger than the impedance of the human body by several hundred ohms, so equation (7) can be approximated by removing the human body resistance:

U ₁ =I ₁ (R ₁ +R ₃ )+I ₂ R ₃ (8)

In the same way, only consider the voltage value at _both ends of S2:

U ₂ =I ₂ (R ₂ +R ₃ )+I ₁ R ₃ (9)

U ₁ and U ₂ are the overall output voltage of the current source, and the voltages between channels will affect each other, so each channel output should have two voltage components with different frequencies according to the current frequency. For example, U ₁ can be divided into its own voltage and frequency components U1 _S1 and the voltages U1 _S2 and U1 _S2 that are changed by the influence of U1 S2 and U1 _S2 are the same values collected and calculated in U ₁ and U _t1 (because the meaning is that S ₁ will increase the voltage value across U _t1 in order to match the output current), and the same is true _U2 can be divided into U2 _S1 and U2 _S2 .

According to the previous discussion, after the current source S ₂ is turned on, the voltage across S ₁ will be affected by it. If the value of U ₁ that is changed by the influence of S ₂ can be extracted, an additional calculation formula can be listed, because the current source S ₁ and S ₂ The output frequencies are different, so this paper uses the fast Fourier transform to extract the relevant voltage changes. When only S ₂ is considered, S ₁ is equivalent to an open circuit, and U ₁ can collect the voltage about S ₂ at U _t1 through electrodes:

The contact resistance _R3 is much larger than the body impedance, so the formula can also be simplified:

U2 _S1 = I ₂ R ₃ (11)

U1 _S2 represents the amplitude of the frequency voltage component of S ₂ extracted by the time domain voltage collected by U ₁ through FFT transformation. Similarly, U ₂ can obtain the voltage about the frequency of S ₁ :

U1 _S2 = I ₁ R ₃ (12)

Therefore, in the case of only considering the single frequency of S ₁ or S ₂ , the actual output voltage of an electrode, that is, the brain voltage U _t1 or U _t2 (approximately equal) can be approximately obtained by separating the corresponding frequencies of U ₁ and U ₂ , which can be calculated Equipotential electrode resistance R ₃ , and the output electrode resistance can be calculated according to formula (8) as:

R ₁ =(U1 _S2 -U2 _S1 )/I ₁ (13)

Similarly, R ₂ can be calculated:

R ₂ =(v2 _S2 -U1 _S2 )/I ₁ (14)

Figure 5 is a schematic diagram of a two-channel four-electrode connection in an actual situation, and the parameter settings are the same as before. Let R ₁ and R ₃ represent the contact resistance of the two electrodes of the first stimulation channel, R ₂ and R ₄ represent the contact resistance of the two electrodes of the second stimulation channel, R _t represent the simplified impedance of the human body, _Ref1 and _Ref2 R ₁ , R ₃ , and _{Ref1 are} connected in series, R ₂ , R ₄ , and _{Ref2 are} connected in series, the input frequency voltage components of the two stimulation channels are S ₁ and S ₂ respectively, and the currents are I ₁ , I , respectively ₂ ; R _{t is} connected in parallel between the output terminals of R ₁ and R ₂ ; this connection method is the same as the case of the expansion of the equipotential terminal in Fig. 4. This connection method cannot separate R ₃ and R ₄ by calculation, so it is necessary to introduce other methods to assist the calculation, improve The schematic diagram of the latter connection is shown in Figure 6. After R ₃ and R ₄ , the fixed-value reference resistors Re _ef1 and _{Ref2 are added} , and the current values I ₃ and I ₄ passing through the channel are calculated by collecting the voltage across the fixed-value reference resistor. Enter the subsequent calculation to separate the two resistance values (Figure 6 simplifies the human body impedance for the convenience of subsequent calculations, because the human body impedance is originally smaller than the click contact impedance, the human body impedance in series in the figure is ignored or understood as the calculated value of the integrated contact impedance).

U ₁ , U ₂ , U ₃ , and U ₄ represent the voltages at the four electrodes, respectively, and subdivide the voltage components of the first stimulation channel and the second stimulation channel with two different frequencies. U ₁ is divided into U _1S1 and U _1S2 , respectively represent the S1 frequency voltage component and the S2 frequency component, and the other electrodes are the same, as shown in Figure 7 _{; U t1 and} U _t2 represent the voltage _values of the first stimulation channel and the second stimulation channel at the brain; for A single voltage U _t1 is also subdivided into S ₁ frequency voltage components U _t1S1 and S ₂ frequency components U _t1S2 , and U _t2 is similarly divided into U _t2S1 and U _t2S2 ; U _t1 and U _t2 cannot be directly obtained, but according to the principle of current crosstalk, U t1 The values U _1S2 and U _2S1 at ₁ and U ₂ that are disturbed by the other channel are approximately regarded as the values U _t2S2 and U _t1S1 at the brain of S ₂ and S ₁ respectively. Since then, both ends of R ₁ and R ₂ are related to their own channels The estimated voltage of the frequency is known, and its impedance value can be approximately calculated; similarly, the voltages at both ends of R ₃ and R ₄ are known, and the current value of the return channel is estimated by _Ref to estimate it; the basic calculation method is the same as before, the difference is that the introduction The constant value impedance calculation obtains the estimated value of impedance through the current of R ₃ and R ₄ and the estimated voltage across the terminals.

The specific calculation method of impedance under actual conditions is obtained:

R ₁ =(U _1S1 -U _t2S1 )/I ₁

R ₂ =(U _2S2 -U _t1S2 )/I ₂

The multi-channel algorithm decomposes the multi-channel into multiple dual-channels. As long as any channel is jointly calculated with other channels with different output frequencies, the impedance of each electrode of the channel can be obtained through the dual-channel calculation method.

So far, the input and output electrodes of dual-channel electrical stimulation can estimate the impedance value, and the error is mainly determined by the human body impedance that is ignored in the calculation. Negligible; when the contact impedance is low, the error is larger, but the overall impedance does not affect the experimental stimulation signal output at this time. The purpose of impedance detection in the transcranial electrical stimulation system is to ensure the correct output of the stimulation waveform instead of accurately measuring the impedance value. The impedance detection algorithm proposed by the invention fully meets various experimental needs.

In addition to the above-mentioned dual-channel stimulation experiments, the present invention can expand the number of stimulation channels without making too many changes to the algorithm. As long as there are output signals of different frequencies during multi-channel stimulation, the dual-channel impedance detection algorithm can be used to calculate each channel one by one. The input and output electrode impedance.

Those of ordinary skill in the art will appreciate that the embodiments described herein are intended to assist readers in understanding the principles of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations without departing from the essence of the present invention according to the technical teaching disclosed in the present invention, and these modifications and combinations still fall within the protection scope of the present invention.

Claims (2)

1. an impedance detection device for multi-channel transcranial electrical stimulator, is characterized in that, comprises multi-channel electrical stimulation output module, DAC output module, ADC acquisition module, FFT processing module and impedance detection calculation module; FFT processing module It is respectively connected with the ADC acquisition module and the impedance detection calculation module, and the DAC output module is connected with the multi-channel electrical stimulation output module; The multi-channel electrical stimulation output module is used to provide multi-channel digital signals of different frequencies required for transcranial electrical stimulation, and send it to the DAC output module; The DAC processing module is used to convert the digital signal from the multi-channel electrical stimulation output module into a current signal to generate the experimental stimulation signal; The ADC acquisition module is used to convert the continuous analog signal collected by the electrodes of each channel into digital signals and transmit them to the FFT processing module; FFT processing module, used to separate the voltage components of different frequencies at each electrode point; Impedance detection calculation module, the module receives the voltage value of each frequency after FFT processing, and calculates the impedance value of each electrode point according to the impedance detection formula. 2. The impedance detection device for a multi-channel transcranial electrical stimulator according to claim 1, wherein the specific calculation method of the impedance value of each electrode point is: let R ₁ and R ₃ represent The contact resistance of the two electrodes of the first stimulation channel, R ₂ and R ₄ represent the contact resistance of the two electrodes of the second stimulation channel, R _t represents the simplified impedance of the human body, and _Ref1 and _Ref2 are fixed-value reference resistances; R ₁ , R ₃ , and _{Ref1 are} connected in series, R ₂ , R ₄ , and _{Ref2 are} connected in series, the input frequency voltage components of the two stimulation channels are S ₁ and S ₂ respectively, and the currents are I ₁ and I ₂ respectively; R _{t is} connected in parallel between the outputs _of R1 and R2 _; U ₁ , U ₂ , U ₃ , and U ₄ represent the voltages at the four electrodes, respectively, and subdivide the voltage components of the first stimulation channel and the second stimulation channel with two different frequencies. U ₁ is divided into U _1S1 and U _1S2 , respectively represent the S1 frequency voltage component and the S2 frequency component, and the other electrodes are the same _{; U t1 and} U _t2 represent the voltage values of the first stimulation channel and the second stimulation channel at the brain _{; for a single voltage U t1 is} equally fine It is divided into S1 frequency voltage component U _t1S1 and S ₂ frequency component U _t1S2 , U _t2 is divided into U _t2S1 and U _t2S2 in the same way; U _t1 and U _{t2 can} not be obtained directly, but according to the principle of current crosstalk, U ₁ and U ₂ are separated by The rising values U _1S2 and U _2S1 of the opponent's channel interference are respectively approximately regarded as the values U _t2S2 and U _t1S1 of S ₂ and S ₁ at the brain, and since then the estimated voltages at the two ends of R ₁ and R ₂ about their own channel frequencies are known. , the impedance value can be approximated; similarly, the voltages at both ends of R ₃ and R ₄ are known, and _Ref is used to estimate the return channel current value to estimate it; then according to the above description, the contact impedance estimation formula of each electrode is obtained as follows: R ₁ =(U _1S1 -U _t2S1 )/I ₁ R ₂ =(U _2S2 -U _t1S2 )/I ₂

The multi-channel algorithm decomposes the multi-channel into multiple dual-channels. As long as any channel is jointly calculated with other channels with different output frequencies, the impedance of each electrode of the channel can be obtained through the dual-channel calculation method.

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