Method for local skin electrical impedance measurement with small distance electrodes

Abstract

The core of the application realizes accurate measurement through specific electrode arrangement and double-frequency signal excitation. First, the measured skin is cleaned and dried, and a 5mm-15mm diameter excitation electrode piece is attached, and a 0.5mm-2mm long shielding layer microneedle is uniformly arranged at the edge of 1mm-2mm as a detection electrode. By applying f1, f2 two frequency sine excitation signals through a constant current source, first confirm the microneedle to be inserted into the subcutaneous tissue by means of phase signal change, and then respectively acquire current and voltage data under corresponding frequency, and calculate two complex impedance modulus values. The specific algorithm is used to derive the total resistance Rc and total capacitance Cc of the skin, and then the complex impedance expression of the skin at any frequency is obtained. The method can accurately measure the skin impedance, and by removing the microneedle detection electrode, it can also combine the body composition detection electric signal to separate the human body impedance from the total impedance of the body composition, and has the functions of skin local impedance measurement and body composition related detection. The electrode arrangement is compact and the measurement process is efficient and accurate.

Description

Technical Field

[0001] This invention relates to the field of bioimpedance measurement technology, and in particular to a method for measuring local skin electrical impedance using small-pitch electrodes. Background Technology

[0002] The structure of skin includes the epidermis, dermis, and subcutaneous tissue. From the outside in, the epidermis consists of the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. Due to the presence of the stratum corneum, stratum spinosum, and stratum lucidum, the skin naturally possesses a certain degree of insulation. Furthermore, because the stratum corneum has openings for sweat excretion and other factors, the surface layer naturally has a resistivity, which increases as the skin becomes drier.

[0003] Body composition analyzers utilize alternating current emitted by excitation electrodes to pass through the human body. The decaying current parameters are then measured by detection electrodes to deduce the content of various bodily fluids. This allows for a comprehensive assessment of the individual's physical condition.

[0004] Existing body composition analyzers do not have an effective method for measuring skin resistance. Current methods include subtracting the estimated skin resistance based on experience, or directly adding the skin resistance value to the total body resistance by measuring the applied conductive gel. Neither method is accurate.

[0005] Therefore, the measurement of human skin resistance is very important in the field of body composition measurement. Summary of the Invention

[0006] This invention provides a method for measuring local skin electrical impedance using small-pitch electrodes, aiming to solve the problem of measuring skin resistance. To achieve the above objective, this invention adopts the following technical solution: The method for local skin electrical impedance measurement using small-pitch electrodes includes the following steps: S1. Cleanse and dry the skin in the test area; S2. Attach an excitation electrode sheet with a diameter of 5mm-15mm to the skin surface; with a shielding layer covering the outside of the detection electrode, arrange several microneedles with a length of 0.5mm-2mm at a spacing of 1mm-2mm along the outline edge of the excitation electrode sheet as detection electrodes. S3. Apply a constant current source signal to the excitation electrode plate, wherein the constant current source signal is a first frequency. The first sinusoidal excitation signal; S4. Slowly press the microneedles of the detection electrode into the skin from the epidermis, and record the phase electrical signal change of each microneedle individually until the phase signal of each microneedle decreases, then stop pressing. S5. Remove the phase detection circuit from step S4; obtain the first current of the excitation electrode when the first sinusoidal excitation signal is flowing. The first voltage of the detection electrode, which consists of the excitation electrode sheet and all the microneedles. ; S6. Apply a second frequency to the excitation electrode. The second sinusoidal excitation signal; S7. Obtain the second current of the excitation electrode when the second sinusoidal excitation signal is flowing. The second voltage of the detection electrode, which consists of the excitation electrode sheet and all the microneedles. ; S8. Calculate the first complex impedance magnitude under the first sinusoidal excitation signal. The second complex impedance magnitude under the second sinusoidal excitation signal was calculated. ; S9. This yields the total skin resistance. and total skin capacitance They are: ; ; S10. For any current frequency, the obtained skin impedance is: .

[0007] Furthermore, conductive gel is evenly applied to the excitation electrode sheet; insulating paste is applied between the edge of the excitation electrode sheet and the microneedles to form an insulating strip.

[0008] Further, in step S4, in order to record the voltage phase signal change of each microneedle individually, all microneedles of the detection electrode are sequentially connected to the MUX multiplexer, instrumentation amplifier a, the measurement terminal of the IQ demodulation module, the ADC module and the MCU module via the ADC Bus; the reference terminal of the IQ demodulation module is connected to a reference signal obtained from the constant current source controller and synchronized with the first sinusoidal excitation signal.

[0009] Furthermore, before removing the voltage phase detection circuit in step S5, a second frequency is applied to the excitation electrode plate. The second sinusoidal excitation signal is used to determine whether the microneedle tip has penetrated the subcutaneous tissue by measuring the phase deviation.

[0010] Furthermore, the first frequency of the first sinusoidal excitation signal The range is 1kHz-5kHz, the peak-to-peak voltage is 1Vpp-5Vpp, and the current amplitude is 10µA~500µA RMS; The second frequency of the second sinusoidal excitation signal The range is 50kHz-100kHz, the peak-to-peak voltage is 1Vpp-5Vpp, and the current amplitude is 10µA~500µA RMS.

[0011] Furthermore, a precision resistor is connected in series in the connection circuit between the excitation electrode and the detection electrode. ;Measure the precision resistance when the first sinusoidal excitation signal is flowing. Voltage on both sides ;Measure the precision resistance when the second sinusoidal excitation signal is flowing. Voltage on both sides ; Calculate the first current , ; Calculate the second current ; .

[0012] Furthermore, precision resistors The magnification factor is Instrument amplifier b; when the first sinusoidal excitation signal flows, the instrument amplifier b measures the precision resistance. The voltage between them is When the second sinusoidal excitation signal is flowing, the instrumentation amplifier C measures the precision resistance. The voltage between them is ; ; .

[0013] Furthermore, the excitation electrode and the detection electrode are respectively connected to the two voltage measurement terminals of the instrumentation amplifier c, wherein the amplification factor of the instrumentation amplifier c is... When the first sinusoidal excitation signal flows, the instrumentation amplifier c measures the voltage between the excitation electrode and the detection electrode. When the second sinusoidal excitation signal flows, the instrumentation amplifier c measures the voltage between the excitation electrode and the detection electrode. ;Calculation yields: ; 。

[0014] Furthermore, the skin cleansing process includes: first cleaning the skin with 75% medical alcohol, and then allowing the skin to air dry naturally.

[0015] Furthermore, the conductive gel is a low-permeability or non-permeable conductive gel.

[0016] Compared with the prior art, the present invention has the following advantages: the excitation electrode in this solution is always fixed on the human skin, and the microneedle is at a small distance from the excitation electrode, which can accurately measure the total impedance of the skin.

[0017] Meanwhile, the excitation electrode and the detection electrode composed of microneedles work together to determine whether the tip of the microneedle has pierced the subcutaneous tissue, based on the presence of a phase detection module.

[0018] When the phase detection module is removed and a precision resistor is added, two sets of data can be obtained after two sinusoidal electrical signals of different frequencies pass through. Then, through the algorithm, the resistance and capacitance of the stratum corneum to the subcutaneous tissue can be obtained, and finally the complex form of the impedance between the stratum corneum and the subcutaneous tissue can be derived.

[0019] While keeping the excitation electrode plate stationary, the microneedle detection electrode is removed; a high-frequency, high-voltage body composition detection electrical signal can then be directly introduced into the human body from the excitation electrode plate for body composition detection.

[0020] When body composition analysis is completed, a new skin impedance can be obtained corresponding to the new frequency. The body impedance is then subtracted from the total impedance of the body composition.

[0021] In the process of collecting and measuring skin impedance information and inputting / outputting excitation electrode signals for body components in this invention, the pressure on the excitation electrode remains constant and its position is always fixed. Therefore, it can be assumed that the impedance is constant for the same skin.

[0022] In body composition measurement, an input excitation electrode and an output detection electrode are required. According to this invention, subcutaneous tissue resistance is obtained, allowing devices to be installed on areas such as the fingers and toes to measure skin resistance. Simply removing the microneedles allows the excitation electrode to also function as a detection electrode, thus creating a complete current loop within the human body. Attached Figure Description

[0023] Figure 1 This is a flowchart of the present invention; Figure 2 This is another flowchart of the present invention. Detailed Implementation

[0024] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0025] Human skin tissue is extremely complex. The international standard IEC 60990 uses parallel resistors and capacitors to simulate the overall electrical structure of human skin tissue. The paper "Estimating the skin impedance model using experimental data and the proposed human skin impedance model" discloses the Montagu model as a hybrid circuit of multiple series-connected resistors and capacitors connected in parallel. Therefore, regardless of the specific structure, there will ultimately be a skin tissue model with a specific total resistance and total capacitance.

[0026] In the literature "Various skin impedance models based on physiological stratification," the stratum corneum, due to its natural insulating function, acts as a natural "capacitor." The structures beneath the stratum corneum, containing more body fluid, exhibit more resistive properties, with reduced capacitive properties. Therefore, although the skin is a multi-layered structure, it conforms to the parallel resistance and capacitance model. Based on the CC model, the RC skin model can be written as a complex expression of parallel resistance and capacitance. Right now: ;in, .

[0027] However, skin containing the stratum corneum is not part of the body fluids within human tissues. To make body composition measurements more accurate, the impedance of the skin needs to be removed from the total resistance of the body composition measurement.

[0028] When the distance between the excitation electrode and the detection electrode of the microneedle structure is set in the range of 0.5 mm to 2 mm, the alternating current signal passes through the stratum corneum, stratum lucidum, and stratum spinosum in sequence, and finally enters the microneedle detection electrode.

[0029] More specifically, Before implementing this invention, the skin in the test area needs to be cleaned and then kept dry. The purpose of cleaning is mainly to remove oil, dirt, and other substances from the skin surface that may affect the conduction of the electric current. Cleaning can be done by gently wiping with 75% alcohol and then allowing it to air dry naturally.

[0030] When the excitation electrode needs to come into contact with human skin, a conductive gel is applied to the surface of the electrode to reduce contact resistance. The purpose of applying the gel is to increase the contact area between the electrode and the microscopic depressions in the skin, while simultaneously closing the air gap between the skin and the electrode to reduce connection resistance. This step minimizes the impact of contact resistance. To prevent the conductive gel from penetrating into the stratum corneum and affecting the measurement of stratum corneum resistance, low-permeability or non-permeable gels are preferred for the conductive wires. For example, GreenTech's GT10 medical conductive gel.

[0031] To measure the complex impedance of the skin, the excitation electrode emits two sinusoidal excitation signals of different frequencies. The first sinusoidal excitation signal has a first frequency of... The range is 1 kHz to 5 kHz, the peak-to-peak voltage is 1 Vpp to 5 Vpp, and the current amplitude is 10 µA to 500 µA RMS; the second frequency of the second sinusoidal excitation signal. The range is 50kHz-100kHz, the peak-to-peak voltage is 1Vpp-5Vpp, and the current amplitude is 10µA~500µA RMS.

[0032] Because the structural resistance of skin approximates a parallel resistor and capacitor model, sinusoidal excitation signals of different frequencies will produce different total resistances upon contact with the resistor and capacitor. Generally, low-frequency sinusoidal excitation signals pass through resistors more easily and through capacitors more difficultly. Conversely, high-frequency sinusoidal excitation signals pass through capacitors more easily.

[0033] This invention comprises two parts. The first part measures and verifies that the microneedles have penetrated the subcutaneous tissue, enabling the measurement of resistance and capacitance across the entire skin layer. The second part measures and calculates the resistance and capacitance of the skin at the point where the excitation electrode is attached, constructing a complete complex impedance formula for the skin, which facilitates direct calculation during body composition measurement.

[0034] At the same time, these two parts are not completely separate; there are also parts that coordinate with each other, such as using the first frequency. When testing whether the microneedle has pierced the subcutaneous tissue, a sudden change in the phase of the voltage or current, forming a large phase difference, is used for judgment. To further verify whether the microneedle tip is indeed in the subcutaneous tissue, a second frequency is used. We re-verified whether the phase difference was actually achieved. Double safeguards ensured the microneedle tip was positioned within the subcutaneous tissue.

[0035] Simply remove the phase detection module and connect a precision resistor in series in the circuit. Under these circumstances, the first frequency was measured. Second frequency Under these conditions, the total voltage and current of the circuit are used to calculate the total impedance modulus. This allows for the calculation of the resistance and capacitance values ​​of the skin beneath the excitation electrode. This lays the foundation for subsequent measurements of the entire body composition at higher frequencies or with voltages passing through the excitation electrode. The excitation electrode remains fixed in place on the skin throughout the entire process, whether it's detection at the microneedle tip, measurement and calculation of the skin resistance and capacitance under the excitation electrode, or subsequent flow of body composition current. This significantly avoids the potential for resistance instability caused by changes in skin position, providing an accurate basis for overall body composition measurement.

[0036] Regarding the first part, the solution of the present invention is as follows: Figure 1 As shown, it includes the following parts: Example 1: S1. Cleanse and dry the skin area to be tested. First, clean the skin with 75% medical alcohol, then allow the skin to air dry naturally. S2. Attach an excitation electrode pad with a diameter of 5mm-15mm to the skin surface. With the detection electrode covered by a shielding layer, evenly arrange several microneedles with a length of 0.5mm-2mm at 1mm-2mm intervals along the outline of the excitation electrode pad as detection electrodes, such as 4, 6, or 8 microneedles. Applying conductive gel evenly to the excitation electrode pad ensures a tighter fit between the skin and the electrode pad, minimizing contact resistance. Simultaneously, to prevent the current from flowing laterally from the skin surface to the microneedles, insulating paste is applied between the edge of the excitation electrode pad and the microneedles to form an insulating strip; this insulating strip adheres completely to the skin, thoroughly blocking current flow. Since the excitation electrode pad generates an alternating electrical signal, an alternating magnetic field will be generated at a distance of only 1mm-2mm, further affecting the data from the microneedles. Therefore, one or more shielding layers to block electromagnetic signals are required on the outer surface of the excitation electrode pad. Through these measures, a complete pathway can be established between the excitation electrode pad and the detection electrode composed of microneedles, while minimizing interference from noise signals.

[0037] S3. Apply a constant current source signal to the excitation electrode plate, wherein the constant current source signal is a first frequency. The first sinusoidal excitation signal; the first frequency of the first sinusoidal excitation signal The range is 1kHz-5kHz, the peak-to-peak voltage is 1Vpp-5Vpp, and the current amplitude is 10µA~500µA RMS.

[0038] S4. Slowly press the microneedles of the detection electrode into the skin, recording the phase electrical signal change of each microneedle individually, until the phase signal of each microneedle decreases, then stop pressing. Specifically, to record the voltage phase signal change of each microneedle individually, all microneedles of the detection electrode are sequentially connected to the MUX multiplexer, instrumentation amplifier a, the measurement terminal of the IQ demodulation module, the ADC module, and the MCU module via the ADC Bus; the reference terminal of the IQ demodulation module is connected to a reference signal obtained from the constant current source controller and synchronized with the first sinusoidal excitation signal.

[0039] The MUX multiplexer connects to multiple microneedles and cycles through a hold scan to activate one microneedle's path. This cycle continues, activating each microneedle in turn. The acquired microneedle electrical signal data is then transmitted via a bus to instrumentation amplifier a. The amplified signal enters the measurement terminal of the IQ demodulation module. The reference terminal of the IQ demodulation module is connected to a reference signal obtained from the constant current source controller and synchronized with the first sinusoidal excitation signal. This generates two electrical signal curves within the IQ demodulation module. The ADC module converts the values ​​of these two electrical signals before sending them to the MCU module for final calculation. The MCU module determines whether all microneedle channels have completely penetrated the subcutaneous tissue and displays to the operator which numbered microneedles have been inserted. The MCU then transmits the data to a display screen for the operator to view.

[0040] Based on this, after the microneedles are slowly inserted into the skin, the data of each microneedle is continuously scanned in a loop until a significant change in phase occurs, which can be considered as the microneedles having entered the subcutaneous tissue.

[0041] For example: The inner forearm skin of a healthy adult subject was selected as the test area. After cleaning and drying, electrode attachment, and insulation tape placement were completed according to the steps, the first frequency was applied. A sinusoidal excitation signal of 3kHz (3Vpp peak-to-peak voltage, 200µA RMS current amplitude) was applied. During slow pressure application of the microneedles, the phase signals of the eight microneedles were cyclically scanned using a MUX multiplexer. Initially, the phase deviation of all microneedles from the reference signal remained stable within ±2°. When the pressure depth reached 0.8mm, the phase of the first microneedle suddenly dropped to -15°. With continued pressure, the phases of the remaining seven microneedles successively showed significant decreases of 12°-18°, indicating that the microneedles had initially contacted the subcutaneous tissue.

[0042] To verify accuracy, switch to the second frequency. A sinusoidal excitation signal of 80kHz (3Vpp peak-to-peak voltage, 200µARMS current amplitude) was applied, and all microneedles were scanned again. The results showed that the phase deviation of all eight microneedles from the reference signal was stable within the -10° to -20° range without significant fluctuations, confirming that all microneedle tips had reliably penetrated the subcutaneous tissue. Pressure was then stopped, and the subsequent impedance measurement step was initiated. If, upon rescanning all microneedles, any microneedle still exhibits a phase deviation outside the -10° to -20° range, pressure on the microneedles can be continued until a phase deviation occurs.

[0043] Measuring the first frequency After each microneedle enters the subcutaneous tissue, an alternating current signal is applied to the excitation electrode after step S4, followed by a second frequency. The second sinusoidal excitation signal can also be a second frequency. Continue monitoring to see if the phase changes by the same magnitude. This is to determine if the microneedle has indeed penetrated the subcutaneous tissue. Figure 2 As shown, if the second frequency If there is no phase deviation after testing, continue pressing the microneedle until a phase deviation occurs.

[0044] To obtain the resistance, capacitance, and total impedance in complex form of the skin under the excitation electrode, the following steps are required based on Example 1: S5. Remove the phase detection circuit from step S4; obtain the first current flowing through the excitation electrode when the first sinusoidal excitation signal is flowing. The first voltage of the detection electrode, which consists of the excitation electrode sheet and all the microneedles. ; S6. Apply a second frequency to the excitation electrode. The second sinusoidal excitation signal; S7. Obtain the second current of the excitation electrode when the second sinusoidal excitation signal is flowing. The second voltage of the detection electrode, which consists of the excitation electrode sheet and all the microneedles. Specifically, a precision resistor is connected in series in the connection circuit between the excitation electrode and the detection electrode. ;Measure the precision resistance when the first sinusoidal excitation signal is flowing. Voltage on both sides ;Measure the precision resistance when the second sinusoidal excitation signal is flowing. Voltage on both sides In order to make precision resistors The voltage measurement is more accurate, using precision resistors. The magnification factor is Instrument amplifier b; when the first sinusoidal excitation signal flows, the instrument amplifier b measures the precision resistance. The voltage between them is When the second sinusoidal excitation signal is flowing, the instrumentation amplifier C measures the precision resistance. The voltage between them is ; ; .

[0045] Calculate the first current , ; Calculate the second current ; .

[0046] To obtain the voltage between the excitation electrode and the detection electrode, the excitation electrode and the detection electrode are respectively connected to the two voltage measurement terminals of the instrumentation amplifier c, wherein the amplification factor of the instrumentation amplifier c is _____. When the first sinusoidal excitation signal flows, the instrumentation amplifier c measures the voltage between the excitation electrode and the detection electrode. When the second sinusoidal excitation signal flows, the instrumentation amplifier c measures the voltage between the excitation electrode and the detection electrode. ;Calculation yields: ; 。

[0047] S8. Calculate the first complex impedance magnitude under the first sinusoidal excitation signal. The second complex impedance magnitude under the second sinusoidal excitation signal was calculated. Furthermore, the magnitude of the first complex impedance is obtained. Second complex impedance modulus .

[0048] S9. This yields the total skin resistance. and total skin capacitance They are: ; ; S10. For any current frequency, the obtained skin impedance is: .

[0049] If using The resistance of the skin is expressed by... Let Z represent the complex form of the resistance of the skin, which is the capacitance of the skin. Therefore, the complex form of the skin resistance is: The modulus of skin impedance is: .

[0050] The following is the solution for resistance. and capacitor The derivation process: First frequency Impedance magnitude at time: —(1) Second frequency Impedance magnitude at time: —(2) Taking the reciprocal of both sides of formula (1): Squaring both sides: Further details: —(11) Similarly, formula (2) is processed to obtain: --(twenty one) Cancel the numerator and denominator on the left After rearranging formulas (11) and (12), we obtain the following formula: ——(111) ——(211) Combining formulas (111) and (211) into one, we get: Cross-multiplication: After splitting and organizing: = Taking the reciprocals of both sides and then taking the square root, we get the solution. .

[0051] when The modulus of skin impedance is: ; From the above equation, we can deduce that: —(3) For the first frequency Second frequency Substituting into (3), the results are as follows: —(31) —(32) Subtract equation (32) from equation (31): —(33) —(34) The process of this invention is as follows: First, a circuit consisting of excitation electrode pads and multiple microneedles is constructed as detection electrodes. Phase changes are used to determine whether the microneedles have penetrated the subcutaneous tissue. Because the stratum corneum has high resistance and low capacitance, when it penetrates the subcutaneous tissue, the resistance of the subcutaneous tissue becomes very low while the capacitance becomes very high. Therefore, after the microneedles enter the subcutaneous tissue from the stratum corneum, both the voltage and current phases undergo significant changes. This is used to determine whether the microneedles are embedded in the subcutaneous tissue.

[0052] Without moving the excitation electrode, the phase detection module is removed, and voltage and current at two frequencies are measured by connecting a precision resistor in series. The total resistance and total capacitance of the skin from the stratum corneum to the subcutaneous tissue beneath the excitation electrode are obtained using the calculation method disclosed in this scheme. The complex impedance of the skin is then derived.

[0053] After removing the microneedles, the current for body composition detection can be directly introduced into the body from the excitation electrode.

[0054] When this solution is applied to the fingers, palms, heels, or toes of the human body, multiple forms of impedance can be obtained from the local skin.

[0055] If you remove the skin's impedance from the total impedance of the entire human body, what remains is the impedance within the body itself.

[0056] This completes the precise measurement of the internal impedance of the human body.

Claims

1. A device for measuring local skin electrical impedance using small-pitch electrodes, characterized in that, include: Excitation electrode pads are attached to the skin surface of the area to be tested; The microneedle detection electrode array is disposed at a spacing of 1mm-2mm from the edge of the excitation electrode sheet contour, and the length of the microneedles in the microneedle detection electrode array is 0.5mm-2mm. A constant current source module is connected to the excitation electrode plate and applies a first sinusoidal excitation signal of a first frequency and a second sinusoidal excitation signal of a second frequency to the excitation electrode plate. A phase detection module is removably connected to the microneedle detection electrode array. The phase detection module includes a MUX multiplexer, an instrumentation amplifier a, an IQ demodulation module, an ADC module, and an MCU module connected in sequence. The phase detection module acquires the phase electrical signal changes corresponding to each microneedle. Precision resistors, instrumentation amplifier b, and instrumentation amplifier c; Wherein, after the phase detection module is removed from the microneedle detection electrode array, the precision resistor is connected in series in the connection circuit between the excitation electrode and the detection electrode formed by the microneedle detection electrode array; the instrumentation amplifier b measures the voltage across the precision resistor, and the instrumentation amplifier c measures the voltage between the excitation electrode and the detection electrode; The MCU module determines whether the microneedle has penetrated the subcutaneous tissue based on the change in the phase electrical signal, and calculates the skin impedance based on the current and voltage measured at the first and second frequencies.

2. The apparatus according to claim 1, characterized in that, The diameter of the excitation electrode sheet is 5mm-15mm; The surface of the excitation electrode is uniformly coated with conductive gel, and insulating paste is applied between the edge of the excitation electrode and the microneedle detection electrode array to form an insulating strip.

3. The apparatus according to claim 1, characterized in that, All microneedles of the microneedle detection electrode array are sequentially connected to the MUX multiplexer, the instrumentation amplifier a, the measurement terminal of the IQ demodulation module, the ADC module, and the MCU module via the ADC Bus. The reference terminal of the IQ demodulation module is connected to a reference signal that is synchronized with the first sinusoidal excitation signal.

4. The apparatus according to claim 1, characterized in that, The first frequency is 1kHz-5kHz, the peak-to-peak voltage of the first sinusoidal excitation signal is 1Vpp-5Vpp, and the current amplitude is 10µA-500µA RMS. The second frequency is 50kHz-100kHz, the peak-to-peak voltage of the second sinusoidal excitation signal is 1Vpp-5Vpp, and the current amplitude is 10µA-500µA RMS.

5. The apparatus according to claim 1, characterized in that, The microneedle detection electrode array is covered with a shielding layer. The MCU module determines that the microneedle has penetrated the subcutaneous tissue when the phase electrical signal change meets the preset conditions. The preset condition is that the phase signal decreases relative to the initial state or the phase deviation reaches a preset threshold.

6. The apparatus according to claim 1, characterized in that, The precision resistor is connected to instrumentation amplifier b, which measures the voltage across the precision resistor. The excitation electrode and the detection electrode are respectively connected to the two voltage measurement terminals of the instrumentation amplifier c, and the instrumentation amplifier c measures the voltage between the excitation electrode and the detection electrode.

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