WO2022160953A1

WO2022160953A1 - Weak current amplifier circuit and sensor system

Info

Publication number: WO2022160953A1
Application number: PCT/CN2021/136231
Authority: WO
Inventors: 董瑛; 韩留洋; 王晓浩
Original assignee: 清华大学深圳国际研究生院
Priority date: 2021-01-29
Filing date: 2021-12-08
Publication date: 2022-08-04
Also published as: CN112968682A; CN112968682B

Abstract

A weak current amplifier circuit and a sensor system. The weak current amplifier circuit is provided with two stages of amplification structures and two stages of filtering structures, which are arranged in an intersecting manner and comprise a charge amplifier, a first-stage filter, a second-stage amplifier and a band-stop filter which are connected to one another. The charge amplifier converts a weak current into an amplified voltage and outputs same; the first-stage filter performs at least one of low-pass filtering, band-pass filtering and high-pass filtering on the voltage output by the charge amplifier; the second-stage amplifier executes a second-stage amplification process, and the second-stage amplifier is provided with a two-stage differential amplifier circuit, wherein a pre-stage amplifies a differential-mode input signal in an in-phase differential input manner, and serves the function of following a common-mode input signal, so as to increase the amplitude ratio of the differential-mode signal to the common-mode signal, which are sent to a post-stage; and the band-stop filter is used to filter out noise interference at the power frequency of 50 Hz. The weak current amplifier circuit overcomes the problems of a conventional amplifier circuit, such as strong noise, power frequency interference, output-end impedance mismatching, output saturation of an operational amplifier, etc.

Description

Weak current amplifier circuit and sensor system

technical field

The invention relates to a weak current amplifying circuit and a sensor system having the weak current amplifying circuit.

Background technique

In practical applications, it is often faced with the precise measurement of weak signals such as low light intensity, micro magnetic field, micro displacement, micro pressure, and micro temperature difference. The sensing of these physical quantities to be measured is often achieved using photoelectric sensors, magnetometers, displacement sensors, piezoelectric sensors, and pyroelectric sensors. Because the signal to be measured is very weak, the output current directly obtained by the sensor is often only in the order of pA-nA. Such a weak current signal is very difficult to handle, and is easily overwhelmed by noise in the process of line transmission, and often requires further amplification and filtering before it can be displayed on the meter head of the instrument. Therefore, it is of great practical significance to amplify the weak current of pA-nA level.

However, the conventional amplifier circuit has strong noise and is not suitable for the amplification of micro-current. For example, the offset voltage of a conventional operational amplifier is in the order of μV, and the bias current is in the order of nA, which is much larger than the pA-nA level weak current that needs to be amplified. Amplified output effect. In addition, it will be found that the power frequency interference of 50Hz is the largest noise source in practical applications. For example, using a flexible pressure sensor to measure the physiological signals of the human body, the sensor needs to directly contact the surface of the human body, and then enter into strong power frequency interference. In addition, in different applications, after the amplification and filtering of the circuit, the obtained output signal needs to be connected to different back-end devices such as meter, DAQ, and microprocessor. The input impedance of these back-end devices is very different. If the output signal does not undergo special processing, the output effect will be very different in these different applications.

It should be noted that the information disclosed in the above Background section is only for understanding of the background of the application, and therefore may include information that does not form the prior art known to a person of ordinary skill in the art.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to overcome the above-mentioned problems in the background art, and to provide a weak current amplifying circuit and a sensor system having the weak current amplifying circuit.

To achieve the above object, the present invention adopts the following technical solutions:

A weak current amplifying circuit has a cross-arranged two-stage amplification and two-stage filtering structure, including a charge amplifier, a first-stage filter, a second-stage amplifier and a band-stop filter connected in sequence, and the charge amplifier is used to The weak current is converted into an amplified voltage output, the first-stage filter is used to perform at least one of low-pass, band-pass, and high-pass filtering on the voltage output by the charge amplifier, and the second-stage amplifier is used to perform The second-stage amplification process, the second-stage amplifier has a two-stage differential amplifier circuit, wherein the front-stage amplifies the differential-mode input signal through the same-phase differential input method, and follows the common-mode input signal, so as to improve the signal sent to the rear The amplitude ratio of the differential mode signal to the common mode signal of the stage, and the band-stop filter is used to filter out the 50Hz power frequency noise interference.

further:

Also included is an output buffer connected to the output of the band-stop filter, the output buffer being used for impedance matching to accommodate different types of output back ends.

The band-stop filter is a notch filter.

It also includes a power management module for reversing the positive and negative polarities of the power supply and converting a single power supply to a positive and negative dual power supply.

A sensor system includes a sensor and the weak current amplifying circuit, an output end of the sensor is connected to an input end of the weak current amplifying circuit, and an output end of the weak current amplifying circuit is connected to a back-end device.

further:

The sensor is a flexible pressure sensor, including a first metal electrode layer, a first electret layer, a second electret layer and a second metal electrode layer stacked together in sequence, the first electret layer and the There is an air cavity between the second electret layers, and the positive and negative charges ionized by the air in the air cavity through the corona polarization are respectively charged by the first electret layer and the second electret layer. It is captured to form a charge dipole. In the initial state, the charge dipole and the induced charges on the first and second metal electrode layers form an electric field balance. When the sensor is deformed under pressure, the dipole moment changes. The induced charge is transferred to form a current on the external circuit. When the pressure is released, the sensor returns to its original state due to its own elasticity, and a reverse current is formed on the external circuit to restore the electric field balance.

The inner surface of the first electret layer and/or the second electret layer has grooves.

The inner surface of the first electret layer has a plurality of first strip-shaped grooves that are parallel to each other, and the inner surface of the second electret layer has a plurality of second strip-shaped grooves that are parallel to each other, The first strip-shaped groove and the second strip-shaped groove are opposite to each other, preferably also perpendicular to each other.

The material of the first electret layer and/or the second electret layer is selected from fluorinated ethylene propylene copolymer (FEP), polypropylene (PP), polyvinylidene fluoride (PVDF); The material of a metal electrode layer and/or the second metal electrode layer is selected from gold (Au), silver (Ag), copper (Cu), aluminum (Al), and chromium (Cr).

A closed air cavity is jointly formed by the first electret layer and the second electret layer.

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

The invention proposes a weak current amplifying circuit with a cross-arranged two-stage amplification and two-stage filtering structure, wherein the charge amplifier performs the first-stage amplification to convert the weak current into an amplified voltage output, and the first-stage filter is used for all The voltage output by the charge amplifier is filtered in the first stage, and the second stage amplifier performs the second stage amplification process. It follows the common mode input signal to improve the amplitude ratio of the differential mode signal to the common mode signal sent to the rear stage, and achieves better common mode rejection capability. Power frequency noise interference. The invention can input pA～nA weak current from the sensor, and after cross-stage amplification and filtering processing, it can be output to different back-end equipment such as meter, DAQ, micro-processing, etc., which solves the problem of the strong noise of the previous weak current amplifying circuit. , There are problems such as power frequency interference, impedance mismatch at the output end, etc., and adapt to the application needs of different occasions. In the present invention, the step-by-step amplification and filtering effect of the cross can also avoid the output saturation of the operational amplifier caused by the continuous amplification process. In addition, the portability of each part of the circuit is good, which is convenient for the user's personalized design.

The weak current amplifying circuit of the present invention can be used for amplifying and filtering the pA-nA level weak current output by the sensing front-end of piezoelectric sensors, photoelectric sensors, pyroelectric sensors, etc. The designed circuit can easily amplify the gain multiple and filter cut-off frequency. So that the circuit can be widely used in the amplification and filtering of weak current signals of different strengths and different frequency bands. A processing module for 50Hz power frequency interference is designed in the circuit, which effectively eliminates the source of human noise. Preferably, output buffers for different back ends are provided, which increases the practicability of the designed circuit. In addition, the power management module reduces the dependence of the designed circuit on an external power supply, making it easier to transplant the circuit into portable measurement devices such as wearable devices.

The flexible pressure sensor of the preferred embodiment of the sensor system of the present invention has the ability to store charges stably for a long time, which enables the sensor to be used for a long time without performance degradation, that is, it has excellent stability and can measure stably for a long time. Weak pressure signals such as pulse. In addition, the sensor has high sensitivity and can measure the pulse in a small area, which is very beneficial for the measurement of fingertip pulse and venous pulse. The sensor of the present invention can be very light and thin, has good flexibility, can be in good contact with the skin surface to obtain a clearer pulse signal, and will not cause discomfort to the user when worn for a long time. It is convenient to make multiple sensors at the same time, and meet the needs of mass production and rapid production and prototyping in practical applications.

Description of drawings

FIG. 1 is a schematic diagram of a sensor system with a weak current amplifying circuit according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of functional modules of a weak current amplifying circuit according to an embodiment of the present invention.

FIG. 3 is a specific circuit structure diagram of a weak current amplifying circuit according to an embodiment of the present invention.

FIG. 4 is a flow chart of the fabrication of a sensor according to an embodiment of the present invention.

FIG. 5a is a schematic structural diagram of a sensor according to an embodiment of the present invention.

Fig. 5b is a cross-sectional view of the sensor shown in Fig. 5a along line I-I.

Fig. 5c is an exploded schematic view of the sensor shown in Fig. 5a.

FIG. 6 is a working principle of a sensor according to an embodiment of the present invention.

FIG. 7 is a schematic diagram of the overall structure of a sensor system according to an embodiment of the present invention.

FIG. 8 is a schematic structural diagram of a system with a fixed-point pressurizing device according to an embodiment of the present invention.

FIG. 9 is a diagram showing the effect of the fixed-point pressure on the wrist by the fixed-point pressure device according to the embodiment of the present invention.

10 is a schematic structural diagram of a multi-channel fixed-point pressure device according to an embodiment of the present invention.

Detailed ways

Embodiments of the present invention will be described in detail below. It should be emphasized that the following description is exemplary only, and is not intended to limit the scope of the invention and its application.

It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, the connection can be used for both the fixing function and the coupling or communication function.

It is to be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top" , "bottom", "inside", "outside", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that The device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined as "first", "second" may expressly or implicitly include one or more of that feature. In the description of the embodiments of the present invention, "plurality" means two or more, unless otherwise expressly and specifically defined.

Referring to FIGS. 1 to 3, in one embodiment, a weak current amplifying circuit has a cross-arranged two-stage amplification and two-stage filtering structure, including a connected charge amplifier, a first-stage filter, and a second-stage filter. an amplifier and a band-stop filter, the charge amplifier is used to convert the weak current into an amplified voltage output, and the first-stage filter is used to perform low-pass, band-pass, and high-pass filtering on the voltage output by the charge amplifier At least one, the second-stage amplifier is used to perform the second-stage amplification process, and the second-stage amplifier has a two-stage differential amplifier circuit, wherein the previous stage amplifies the differential mode input signal through the same-phase differential input method, and It follows the common-mode input signal to improve the amplitude ratio of the differential-mode signal to the common-mode signal sent to the rear stage, and achieves better common-mode rejection. The band-stop filter is used to filter out 50Hz power frequency noise interference .

In a preferred embodiment, the weak current amplifying circuit further includes an output buffer connected to the output end of the band-stop filter, and the output buffer is used for impedance matching to adapt to different types of output back ends.

In a preferred embodiment, the band-stop filter is a notch filter.

In a preferred embodiment, the weak current amplifying circuit further includes a power management module for reversing the positive and negative polarities of the power supply and converting the single power supply to positive and negative dual power supply.

In a preferred embodiment, the weak current that can be amplified by the weak current amplifying circuit is in the pA-nA level, and the bias current of the operational amplifier in the charge amplifier is ±150fA.

The embodiment of the present invention proposes a weak current amplifying circuit with a cross-arranged two-stage amplification and two-stage filtering structure, wherein the charge amplifier performs the first-stage amplification, converts the weak current into an amplified voltage output, and the first-stage filtering The first-stage filter is performed on the voltage output by the charge amplifier, and the second-stage amplifier performs the second-stage amplification process. The second-stage amplifier has a two-stage differential amplifier circuit. Amplify the signal and follow the common-mode input signal to improve the amplitude ratio of the differential-mode signal to the common-mode signal sent to the rear stage, so as to achieve better common-mode rejection capability. Filter out 50Hz power frequency interference. The embodiment of the present invention can input pA-nA weak current from various sensors, and after cross-stage amplification and filtering processing, it can be output to different back-end equipment such as meter, DAQ, and micro-processing, which solves the problem of weak current in the past. The amplifier circuit has problems such as strong noise, power frequency interference, and impedance mismatch at the output end, and adapts to the application requirements of different occasions. In the embodiment of the present invention, the step-by-step amplifying and filtering effect of the cross can also avoid the output saturation of the operational amplifier caused by the continuous amplifying process. In addition, the portability of each part of the circuit is good, which is convenient for the user's personalized design.

The weak current amplifying circuit of the embodiment of the present invention can be used to amplify and filter the pA-nA level weak current output by the sensing front-end of piezoelectric sensors, photoelectric sensors, pyroelectric sensors, etc. It can be easily adjusted, so that the circuit can be widely used in the amplification and filtering of weak current signals of different strengths and different frequency bands. A processing module for 50Hz power frequency interference is designed in the circuit, which effectively eliminates the source of power frequency noise. Preferably, output buffers for different back ends are provided, which increases the practicability of the designed circuit. In addition, the power management module reduces the dependence of the designed circuit on an external power supply, making it easier to transplant the circuit into portable measurement devices such as wearable devices.

Referring to FIG. 1 to FIG. 3, in another embodiment, a sensor system includes a sensor and the weak current amplifying circuit, the output end of the sensor is connected to the input end of the weak current amplifying circuit, the weak current amplifying circuit The output end of the current amplifying circuit is connected to the back-end equipment.

In some embodiments, the sensor collects a pulse or heart rate signal, and the first stage filter is a low pass filter.

In some embodiments, the sensor collects the heart sound signal, and the first-stage filter is a high-pass filter.

In different embodiments, the sensor may be a piezoelectric sensor, a photoelectric sensor, a pyroelectric sensor, or the like.

In a preferred embodiment, the sensor is a flexible pressure sensor.

4 to 6 , the flexible pressure sensor of the preferred embodiment includes a first metal electrode layer 101, a first electret layer 102, a second electret layer 103, and a second metal electrode layer 104 that are stacked together in sequence, There is an air cavity 105 between the first electret layer 102 and the second electret layer 103, and the positive and negative charges ionized by the air in the air cavity 105 by corona polarization are respectively charged by the second electret layer. An electret layer 102 and the second electret layer 103 are captured to form charge dipoles. In the initial state, the charge dipoles are connected to the first metal electrode layer 101 and the second metal electrode layer 104. The induced charge forms an electric field balance. When the sensor is deformed under pressure, the dipole moment changes, and the induced charge is transferred to form a current on the external circuit. When the pressure is released, the sensor returns to its original state due to its own elasticity. A reverse current is formed and the electric field is restored to equilibrium.

In a preferred embodiment, grooves are provided on the inner surface of the first electret layer 102 and/or the second electret layer 103 . The groove pattern may be a periodic line groove pattern, a triangular pyramid groove pattern, a rectangular parallelepiped groove pattern, etc., or a non-periodic and irregular groove pattern.

In a particularly preferred embodiment, the inner surface of the first electret layer 102 has a plurality of first strip-shaped grooves that are parallel to each other, and the inner surface of the second electret layer 103 has mutual A plurality of parallel second strip-shaped grooves, the first strip-shaped groove and the second strip-shaped groove are opposite to each other, preferably also perpendicular to each other.

In different embodiments, the material of the first electret layer 102 and/or the second electret layer 103 may be selected from fluorinated ethylene propylene copolymer (FEP), polypropylene (PP), polyethylene Vinylidene fluoride (PVDF).

In different embodiments, the material of the first metal electrode layer 101 and/or the second metal electrode layer 104 may be selected from gold (Au), silver (Ag), copper (Cu), aluminum (Al) , Chromium (Cr).

In different embodiments, the first metal electrode layer 101 and/or the second metal electrode layer 104 may be formed by metal coating (eg, vapor-deposited metal film), screen printing, or metal tape bonding.

In a preferred embodiment, a closed air cavity 105 is formed by the first electret layer 102 and the second electret layer 103 together.

Referring to FIG. 4 to FIG. 6, in another embodiment, a method for manufacturing the high-sensitivity flexible pressure sensor includes the following steps:

The first electret layer 102 and the second electret layer 103 are fabricated, and the first electret layer 102 and the second electret layer 103 are relatively joined together, and an air cavity is formed between them 105;

A first metal electrode layer 101 is formed on the outer surface of the first electret layer 102, and a second metal electrode layer 104 is formed on the outer surface of the second electret layer 103;

The positive and negative charges ionized by the air in the air cavity 105 through corona polarization are captured by the first electret layer 102 and the second electret layer 103 respectively to form charge dipoles son.

In a preferred embodiment, the manufacturing of the first electret layer 102 and the second electret layer 103 includes: engraving the first electret layer 102 and/or the second electret layer by laser engraving Recesses are formed on opposing surfaces of layer 103 .

In different embodiments, the bonding method of the first electret layer 102 and the second electret layer 103 may be thermocompression bonding, chemical bonding or glue bonding.

The specific embodiments of the present invention are described below with further examples.

The embodiment of the present invention proposes a weak current amplifying circuit with cross-stage amplification and filtering. Figure 1 shows the location and role of the proposed current amplification circuit in the overall system. Its front end, the input signal, is a weak current from the sensor. After being processed by the weak current amplifying circuit of the embodiment, it can be output to different back-end devices such as meter, DAQ, and microprocessor, so as to meet the application requirements of different occasions.

FIG. 2 is a schematic diagram of functional modules of a micro-current amplifying circuit according to a specific embodiment, and the entire circuit is composed of six parts in total. Module I is a charge amplifier, whose essence is I–V amplification, converting the microcurrent into an amplified voltage output (V ₁ ). The low-pass filter of module II is used to filter out high-frequency noise. In fact, the filter type of this module can be replaced. For low-frequency signals such as pulse and heart rate, a low-pass filter is suitable; for high-frequency signals such as heart sounds, a high-pass filter is used. So for module II, the filter type can be low-pass, band-pass, high-pass, or a combination thereof. Module III is the second stage amplifier for performing the second stage amplification process. Module IV is a band-stop filter, preferably a notch filter, and the main filtering object is 50Hz power frequency interference. Modules Ⅰ～Ⅳ realize the effect of step-by-step amplification and filtering, which can avoid the output saturation of the operational amplifier caused by the continuous amplification process. Module V is an output buffer, which has the effect of impedance matching to adapt to different types of output back ends. Module VI is the power management module. Many operational amplifiers require dual positive and negative power supplies, which complicates the external power supply. Module VI can realize the reversal of the positive and negative polarity of the power supply. Only the positive and negative power supplies can be obtained at the same time, which reduces the dependence of the entire circuit system on the external power supply, and is more conducive to transplanting the circuit into portable equipment. . The whole circuit can adopt a modular design, which is more conducive to the portability of each part of the circuit, and is conducive to the user to design more circuit types to meet the application requirements of different occasions.

FIG. 3 shows a circuit structure of a micro-current amplifier circuit according to a specific embodiment, including six modules. The charge amplifier (module I) adopts capacitive feedback (C ₂ ); the parallel resistor R ₁ and capacitor C ₁ are used to stabilize the DC operating point and resonance point of the charge amplifier. The relationship between the output voltage V ₁ and the input current I _in is:

When C ₁ is much larger than C ₂ , the above formula can be simplified to:

Since the weak current to be amplified is in the pA-nA level, the selection of the operational amplifier in the charge amplifier is very critical. Preferably, the typical bias current of the operational amplifier is ±150fA, which ensures the amplification accuracy of pA-nA current.

Use the second-order voltage-controlled voltage source low-pass filter circuit (module II) to low-pass filter the pulse wave signal. _The relationship between the output voltage V2 and the input voltage V1 is _:

Therefore its low-pass cutoff frequency

quality factor

The filtered signal is re-amplified using a second stage amplifier (module III). _The relationship between the output voltage _V3 and the input voltage V2 is:

The second-stage amplifier has a two-stage differential amplifier circuit, in which the front-stage amplifies the differential-mode input signal through the same-phase differential input method, and follows the common-mode input signal to improve the differential-mode signal and common-mode signal sent to the subsequent stage. Amplitude ratio to achieve better common mode rejection.

Then use the 50Hz trap circuit (module IV) to filter out the 50Hz power frequency interference introduced by the human body. The designed trap circuit is a common T-shaped network structure, and the relationship between the output voltage V ₄ and the input voltage V ₃ is:

Wherein, R ₁₁ =R ₁₂ =2 R ₁₃ =2R,

Choose appropriate RC parameters so that the center frequency of the stopband

Finally, the output buffer (module V) is used to achieve the effect of impedance matching, so that the circuit can be adapted to different back-end devices. The relationship between the final output voltage V _out and the voltage V ₄ is:

V _out = V ₄ (5)

By combining formulas (2) to (5), the relationship equation between the final output voltage V _out and the input current I _in can be obtained.

According to the calculation method of cut-off frequency and magnification in the formula, users can design different amplification and filtering effects by using the values of resistors and capacitors of different sizes. Or replace one or more resistors and/or capacitors in the circuit with an adjustable potentiometer or an adjustable capacitor, so as to realize rapid self-adjustment of the filtering effect and the magnification.

The bottommost circuit in Figure 3 is the power management circuit (module VI), which converts positive voltages to negative voltages so that only a single supply can be used to power the op amp, reducing the circuit's dependence on external power supplies. Preferably, the power supply polarity reversal circuit has the characteristics of large output current, so that the module is suitable for applications with large current and high power consumption.

Flexible pressure sensor

The sensor system of one embodiment has a flexible pressure sensor that enables pulse measurement. 4 to 6 , in the flexible pressure sensor provided by the preferred embodiment of the present invention, there is an air cavity 105 between the first electret layer 102 and the second electret layer 103 , and the air cavity 105 has an air cavity 105 . The air is ionized by corona polarization to generate positive and negative charges, which are captured by the first electret layer 102 and the second electret layer 103 to form charge dipoles. In the initial state, the charge dipoles are It forms an electric field balance with the induced charges on the metal electrode layers 101 and 104. When the sensor is deformed under pressure, the dipole moment changes, and the induced charge is transferred to form a current on the external circuit. When the pressure is released, the sensor is due to Its elasticity returns to its original state, forming a reverse current on the external circuit and restoring the balance of the electric field, so that the flexible pressure sensor can sense the pulsation of the pulse, output the corresponding current, and realize the measurement of the pulse.

Due to the electret material's ability to store charges stably, the sensor can be used for a long time without performance degradation, that is, it has excellent stability and can measure pulses stably for a long time. In addition, the sensor has high sensitivity and can measure the pulse in a small area, which is very beneficial for the measurement of fingertip pulse and venous pulse. The sensor of the embodiment of the present invention can be very thin (50-100 μm), has good flexibility, can be in good contact with the skin surface to obtain a clearer pulse signal, and will not cause discomfort to the user when worn for a long time sense. Multiple sensors can be produced at the same time to meet the needs of practical applications for mass production and rapid production and prototyping. The flexible pressure sensor of the embodiment of the present invention has wide application prospects in the fields of pulse and other physiological signal measurement, electronic skin, human-computer interaction interface, and the like.

In a specific embodiment, the flexible piezoelectric electret sensor is fabricated based on laser engraving and thermocompression bonding processes. Line grooves were cut on two electret films (FEP films as an example) using a laser, the line grooves on the two FEP films were placed perpendicular to each other, and thermocompression bonded to form a closed air cavity. After the metal electrode is evaporated on one side of the sensor, the sensor is corona charged by a high-voltage power supply, and finally a metal tape is attached to the other side of the sensor as the electrode on the other side. In an alternative embodiment, the vapor-deposited metal electrodes can also be replaced with attached metal tapes, which can further reduce the cost, shorten the manufacturing cycle, and improve the robustness of the sensor in long-term use.

Figure 4 shows an example of a sensor fabrication flow. 101 denotes the first metal electrode layer; 102 denotes the first electret layer; 103 denotes the second electret layer; 104 denotes the second metal electrode layer. The material of the electret film used can be fluorinated ethylene propylene copolymer (FEP), polypropylene (PP), polyvinylidene fluoride (PVDF), etc., and it is preferably a FEP film here; the metal electrode used can be gold (Au). ), silver (Ag), copper (Cu), aluminum (Al), chromium (Cr) and other materials, preferably Cu electrodes here. In order to achieve the effect of flexibility, the thickness of the electret film can be 10-100 μm, preferably 25 μm here; the thickness of the metal electrode is 0.1 μm-10 μm, preferably 10 μm here.

Since the electret film is very thin, the electret film is placed on a hard substrate in order to make the film flat and facilitate the next processing. The selected rigid substrate should be flat and smooth, with low surface energy, so that the electret film can be easily peeled off after subsequent processing. The material of the hard base may preferably be a 1 mm thick copper plate. Place the electret film flat on the hard substrate, and wipe it with a soft paper several times to remove the dust on the electret film and make the electret film adsorb on the hard substrate. A groove pattern is then carved into the electret film. The engraving method used can be manual engraving, laser engraving, chemical reagent etching based on a mask (such as a photolithography process, a silk screen mold, etc.), etc., and a laser engraving process is preferred here. The carved groove pattern can be a periodic line groove pattern, a triangular pyramid groove pattern, a rectangular parallelepiped groove pattern, etc., or a non-periodic and irregular groove pattern. A line groove pattern is preferred here. Preferably, the depth of the groove is as deep as possible without breaking through the electret film.

Such groove characterization is performed on the two

electret films

102, 103, respectively. Here, line grooves are preferred, and the line grooves on the two films are perpendicular to each other. The two such films are then placed against each other so that they are bonded together to form a closed air cavity. The bonding method used may be thermocompression bonding, chemical reagent bonding, glue bonding, etc., and thermocompression bonding is preferred here. For the preferred FEP electret material, the parameters for thermocompression bonding are 90s at a pressure of 1 MPa and a temperature of 250°C. After hot pressing, the two electret films form an inseparable whole, and the groove pattern forms a sealed air cavity.

A metal electrode layer 101 is then provided on one side of the electret thin film. The way of setting can be metal coating, screen printing, metal tape bonding and so on. Metal coating and screen printing can achieve thinner metal layers for better flexibility; however, they are more expensive and time consuming. Here, the method of bonding with a metal tape is preferable. Corona polarization is then performed using a DC high voltage power supply, a corona needle, and a ground electrode. A specific embodiment is to place the metal electrode layer 101 on the ground electrode and place the corona needle above the other side of the sensor (eg 3 cm). Apply negative high voltage (-18～-30kV) to the corona needle, and perform corona charging for 2～5min. Finally, a metal electrode layer 104 is provided on the other side of the electret film to complete the fabrication of the sensor. The way of setting can still be metal coating, screen printing, metal tape bonding, etc. The method of metal tape bonding is still preferred here.

Figures 5a and 5b respectively show a complete structural schematic diagram of the sensor and a cross-sectional view along the line I-I. Figure 5c shows an exploded schematic view of the sensor. Figure 6 shows the working principle of the sensor. In the process of high-voltage corona polarization, the air in the sealed cavity 105 will be broken down, and equal positive and negative charges will be ionized. Then, under the action of the electric field, the positive and negative charges move to the upper and lower sides respectively, and are finally captured by the inner walls of the

electret films

102 and 103 to form a large number of charge dipoles. In the initial state (① in Figure 6), the charge dipoles trapped on the trench wall of the electret film and the induced charges on the metal electrode form an electric field balance, and there is no electrical response. When the sensor feels the external pressure and compresses and deforms (② in Figure 6), the dipole moment changes, the electric field balance is destroyed, and the induced charge on the metal electrode is transferred to form a current on the external circuit. When the pressure is released, the sensor returns to its original state due to its own elasticity, forming an opposite current in the external circuit (③ in Figure 6). In this way, the flexible pressure sensor can sense the pulse of the pulse, output the corresponding current, and realize the measurement of the pulse.

Because of the electret material's ability to stably store charge, the sensor continued to work for years. In addition, the output nature of the sensor is similar to that of a piezoelectric sensor, and it also has the characteristics of self-driving. It does not require an external power supply during operation, and has the effect of low power consumption. In addition, in the proposed manufacturing process, laser cutting, thermocompression bonding, corona polarization, and metal tape sticking are all very simple and low-cost processes, which are convenient for rapid manufacturing and molding and reduce costs. In addition, in these processes, multiple sensors can be produced in the same batch at the same time, which is conducive to mass production of sensors; or sensors of different sizes can be produced in the same batch, which can be easily adjusted in size.

Sensor systems, air bags and point pressurization devices

Referring to FIG. 7, in one embodiment, a sensor system includes a micropump, a microvalve, an air bag, an air pressure sensor, a pulse sensor, and a processing device. The processing device may be a circuit device with a microprocessor as the core, including a weak current amplifying circuit for processing the measured pulse signal. The processing device is connected with the micro pump, the air pressure sensor and the pulse sensor, the micro pump, the micro valve and the air pressure sensor are all connected to the air bag, and the pulse sensor is fixed on the air bag The airbag is used to wear on the wrist, the air pressure sensor is used to detect the air pressure in the airbag, the microvalve is closed during operation, and the processing device controls the micropump to inflate the airbag, so The pulse sensor is pressed on the wrist by the inflated air bag. When the air pressure sensor detects that the air pressure in the air bag reaches a set value, the processing device controls the micro pump to stop inflation and pass the pulse sensor. The pulse is measured, and after the measurement, the microvalve can be opened to discharge the gas in the air bag. The opening and closing of the microvalve can be automatically controlled by the processing device, or manually controlled by the user. The air pressure sensor communicates with the airbag, which may be communicated with the airbag through a pipeline, or the air pressure sensor itself may be arranged in the airbag.

In a preferred embodiment, a housing is further included, and the processing device is arranged in the housing. The case may be in the form of, but not limited to, the watch case 4 .

In a preferred embodiment, an airway tube is also included, the micropump, the microvalve and the air pressure sensor are arranged in the watch case 4 and are connected to the airbag through the airway tube.

In a preferred embodiment, the airbag is an airbag cuff in the form of a cuff.

The overall structure of the embodiment is shown in FIG. 7 . The main functional components are integrated in the watch case 4 , which can be divided into a circuit part 1 and a gas circuit part 2 . The circuit part 1 takes the microprocessor as the core, samples the pulse signal from the amplifying and filtering circuit, and performs further data storage, display or wireless transmission.

The microprocessor and the pump-valve control circuit also realize the working control of the micro-pump and micro-valve of the gas circuit part 2 . The micropump and the microvalve are communicated with the airbag cuff 5 through the airway 3, and the air pressure in the airbag is fed back to the microprocessor through the air pressure sensor. During normal measurement, the micro-valve is closed and the micro-pump works to inflate the air bag. Once the air pressure reaches the set value, the microprocessor controls the micropump to stop working. At this time, the air pressure in the air bag remains stable, and the pulse is measured by the pulse sensor fixed on the cuff, and transmitted to the microprocessor through the amplification and filtering circuit. When the work is over, the microprocessor will close the micro-pump, open the micro-valve, and quickly discharge the gas in the airbag.

Referring to FIGS. 8 to 10 , in an embodiment, a wearable real-time pulse detection device preferably adopts an airbag for fixed-point pressure, including an airbag cuff 5 and a plurality of sub-airbags 51 . There are air ports on the 5 for inflation and exhaust, the plurality of sub-airbags 51 are connected to the airbag cuff 5 through their respective air tubes 32, and the air tubes 32 of the plurality of sub-airbags 51 are located in the airbag cuffs according to their respective positions. The position on the belt 5 has corresponding dimensions, and the size of at least a part of the airway is different from the size of the rest of the airway, so that the sub-balloons 51 corresponding to the at least part of the airway and the airway within the same inflation time The sub-airbags 51 corresponding to the remaining airways are inflated and pressurized differently, so that when the airbag cuff 5 is worn on the human body, especially the wrist, the corresponding parts of the human body can be pressurized at a fixed point.

In a preferred embodiment, the plurality of sub-airbags 51 are distributed along the length direction of the airbag cuff 5 , and the size of the airway of at least one sub-airbag 51 in the middle position is larger than the size of the rest of the airway tubes.

In a more preferred embodiment, the air tube of the at least one sub-balloon 51 in the middle position includes a plurality of air tubes, wherein the size of the air tube in the middle is the largest, and the sizes of the air tubes on both sides are symmetrical. level becomes smaller.

In a preferred embodiment, the air tubes of the plurality of sub-airbags 51 have corresponding material properties according to their respective positions on the airbag cuff 5 . Preferably, at least one sub-airbag 51 in the middle position adopts Softer, more deformable material than the rest of the airway.

Referring to FIG. 10 , in a preferred embodiment, the airbag includes multiple layers of the plurality of sub-airbags 51 independently juxtaposed in the width direction of the airbag cuff 5 , preferably three layers of the plurality of sub-airbags 51 , The three-layer sub-airbags respectively form the inch airbag cuff 5a, the closing airbag cuff 5b, and the inch airbag cuff 5c.

The embodiments of the present invention provide a fixed-point pressure device with fixed-point distribution and adjustable pressure. The gas-driven pressure method is adopted. The positions on the airbag cuff have corresponding sizes, and the size of at least a part of the airway is different from the size of the rest of the airway, so that the molecular airbag and the remaining sub-airbags are inflated and pressurized differently at the same inflation time. , so that when the airbag cuff is worn on the human body, especially on the wrist, the corresponding parts of the human body can be pressurized at a fixed point, so that more pressure can be applied to a specific part, and the effect of fixed point pressure can be achieved. During use, by adjusting the wearing position of the airbag cuff, the position of the fixed-point pressure can also be flexibly adjusted. The fixed-point pressure device has good application prospects in the fields of digital traditional Chinese medicine pulse diagnosis, wearable electronic sphygmomanometer and the like.

In a preferred embodiment, the present invention achieves a multi-channel adjustable fixed-point pressurization effect through multiple layers of the plurality of sub-airbags that are independently and juxtaposed. The pressure of each channel can be adjusted independently, and the size of the pressure can also be adjusted according to the preset threshold value, which can well meet the needs of multi-channel fixed-point compression during pulse or blood pressure measurement.

Figure 8 is a schematic diagram of a system with a fixed-point pressurization device. One side of the airbag cuff is connected with a micropump, a microvalve and an air pressure sensor through an airway tube 31, so as to realize gas input, output and air pressure feedback. The other side is connected to each sub-airbag through an air tube 32, and for different sub-airbags, the corresponding air tube 32 has different thicknesses. The thicker the airway tube 32, the greater the degree of pressurization of the corresponding sub-balloon in the same time. In order to further enhance the effect of spot pressure, the materials of the sub-airbags are different. The sub-airbags on both sides can be made of harder and less deformable materials, while the sub-airbags in the middle can be made of softer and more deformable materials; under the same air pressure, the middle sub-airbags will deform more and exert more pressure on the wrist. Large pressure, which will help to apply more pressure on specific parts, and play the effect of fixed-point pressure. Figure 9 shows the effect of fixed-point compression on the wrist by the compression device based on the layered airbag design. In order to achieve the effect of multi-channel independent pressure, a plurality of such designed structures can be connected in parallel, such as the three-way independent pneumatic fixed-point pressure structure shown in Figure 10.

The Background of the Invention section may contain background information about the problem or environment of the invention and is not necessarily a description of the prior art. Therefore, what is contained in the Background section is not an admission of prior art by the applicant.

The above content is a further detailed description of the present invention in conjunction with specific/preferred embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art to which the present invention pertains, without departing from the concept of the present invention, they can also make several substitutions or modifications to the described embodiments, and these substitutions or modifications should be regarded as It belongs to the protection scope of the present invention. In the description of this specification, reference to the terms "one embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples" or the like is meant to be used in conjunction with the description. A particular feature, structure, material, or characteristic described by an example or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Those skilled in the art may combine and combine the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples, without conflicting each other. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope of the patent application.

Claims

A weak current amplifying circuit is characterized in that it has a cross-arranged two-stage amplifying and two-stage filtering structure, including a connected charge amplifier, a first-stage filter, a second-stage amplifier and a band-stop filter. The amplifier is used to convert the weak current into an amplified voltage output, the first-stage filter is used to perform at least one of low-pass, band-pass, and high-pass filtering on the voltage output by the charge amplifier, and the second-stage filter is used for The amplifier is used to perform the second-stage amplifying process, and the second-stage amplifier has a two-stage differential amplifier circuit, wherein the front stage amplifies the differential mode input signal through the same-phase differential input mode, and follows the common mode input signal, so as to The amplitude ratio of the differential mode signal to the common mode signal sent to the rear stage is improved, and the band-stop filter is used to filter out 50Hz power frequency noise interference.
The weak current amplifying circuit of claim 1, further comprising an output buffer connected to the output end of the band-stop filter, the output buffer being used for impedance matching to adapt to different types of output back ends.
The weak current amplifying circuit according to claim 1 or 2, wherein the band-stop filter is a notch filter.
The weak current amplifying circuit according to any one of claims 1 to 3, further comprising a power management module for reversing the positive and negative polarities of the power supply and converting a single power supply to a positive and negative dual power supply.
A sensor system, characterized in that it comprises a sensor and the weak current amplifying circuit according to any one of claims 1 to 5, the output end of the sensor is connected to the input end of the weak current amplifying circuit, and the weak current The output end of the amplifying circuit is connected to the back-end equipment.
The sensor system according to claim 5, wherein the sensor is a flexible pressure sensor, comprising a first metal electrode layer, a first electret layer, a second electret layer, and a second electret layer stacked together in sequence Metal electrode layer, there is an air cavity between the first electret layer and the second electret layer, and the positive and negative charges ionized by the air in the air cavity through corona polarization are respectively charged by the second electret layer. An electret layer and the second electret layer are captured to form charge dipoles, and in the initial state, the charge dipoles and the induced charges on the first and second metal electrode layers form an electric field balance, When the sensor is deformed under pressure, the dipole moment changes, and the induced charge is transferred to form a current on the external circuit. When the pressure is released, the sensor returns to its original state due to its own elasticity, and a reverse current is formed on the external circuit and recovers. The electric field is balanced.
6. The sensor system of claim 6, wherein the first electret layer and/or the second electret layer has grooves on the inner surface.
The sensor system of claim 7, wherein the inner surface of the first electret layer has a plurality of first strip-shaped grooves parallel to each other, and the inner surface of the second electret layer has a plurality of first strip-shaped grooves. There are a plurality of second strip-shaped grooves parallel to each other, the first strip-shaped groove and the second strip-shaped groove are opposite to each other, and preferably are also perpendicular to each other.
The sensor system according to any one of claims 6 to 8, wherein the material of the first electret layer and/or the second electret layer is selected from fluorinated ethylene propylene copolymer (FEP) ), polypropylene (PP), polyvinylidene fluoride (PVDF); the material of the first metal electrode layer and/or the second metal electrode layer is selected from gold (Au), silver (Ag), copper (Cu) ), aluminum (Al), chromium (Cr).
The sensor system according to any one of claims 6 to 9, wherein a closed air cavity is jointly formed by the first electret layer and the second electret layer.