Piezoresistive double-spherical flexible pressure sensor and preparation method thereof

Abstract

The invention provides a piezoresistive double-spherical flexible pressure sensor and a preparation method thereof, and relates to the technical field of flexible electronics. The flexible pressure sensor comprises at least two flexible substrate layers, a sensing material layer and a flexible electrode layer, the two flexible substrate layers are arranged in a spaced mode, each flexible substrate layer comprises a base plate and a protrusion, and the protrusions are arranged on one side of the base plate. When the flexible substrate layer is stressed, the resistance of the sensing material layer is increased, so that an electrical signal is output; due to the adoption of the structural design of the double-ball-shaped pressure sensor, two independent point position pulse wave signals can be synchronously output, the transmission time of pulse waves before and after the wrist radial artery is obtained through double-channel pulse wave collection, the propagation speed of the pulse waves can be calculated in combination with the monitoring distance, and therefore a reliable data set is provided for blood pressure detection; key technical support is provided for the wearable real-time human health monitoring system; meanwhile, the flexible substrate layer is made of the flexible material, so that the wearing comfort of the sensor is improved.

Description

Technical Field

[0001] The present invention relates to the field of flexible electronic technology, and in particular to a piezoresistive double-ball flexible pressure sensor and a preparation method thereof. Background Art

[0002] Currently, with the rapid development of the Internet of Things, smart medical and other fields, the demand for sensors is growing. Traditional rigid sensors have limitations in terms of comfort, adaptability and fit to complex surfaces. Therefore, flexible pressure sensors have become a hot topic of research. While maintaining sensing performance, they provide better user experience and a wider range of application scenarios.

[0003] Flexible sensors make wearable real-time human health monitoring a reality. Among human physiological parameters, pulse wave, as a key indicator of human health, is closely related to a series of cardiovascular parameters such as heart rate and blood pressure, and has attracted widespread attention from researchers in the field of flexible sensing. Therefore, it is a challenging task to design a flexible pressure sensor with high sensitivity, good durability and fast response time to achieve accurate non-invasive pulse wave detection. Summary of the invention

[0004] The invention provides a piezoresistive double-ball flexible pressure sensor, which is used to solve the problems of low detection accuracy, poor comfort and low sensitivity of the existing sensors.

[0005] The present invention provides a piezoresistive double-ball flexible pressure sensor, comprising: At least two flexible substrate layers, the two flexible substrate layers are arranged at intervals, the flexible substrate layer comprises a substrate and a protrusion, and the protrusion is arranged on one side of the substrate; A sensing material layer, the sensing material layer is disposed on the surfaces of the substrate and the protrusions; A flexible electrode layer, wherein the flexible electrode layer is arranged on one side of the substrate, and the flexible electrode layer is provided with two conductive solder paste layers arranged at intervals, the two conductive solder paste layers are located on both sides of the protrusion, and the two conductive solder paste layers are connected to the sensing material layers on both sides of the protrusion through conductive glue, and when the flexible substrate layer is subjected to pressure, the resistance of the sensing material layer increases.

[0006] According to a piezoresistive double-ball flexible pressure sensor provided by the present invention, the piezoresistive double-ball flexible pressure sensor further comprises: The packaging layer is arranged on a side of the sensing material layer away from the flexible substrate layer.

[0007] According to a piezoresistive double-spherical flexible pressure sensor provided by the present invention, the protrusion is a semi-ellipsoid.

[0008] According to a piezoresistive double-ball flexible pressure sensor provided by the present invention, the connection between the substrate and the protrusion is connected by a rounded corner.

[0009] According to a piezoresistive double-ball flexible pressure sensor provided by the present invention, the material of the flexible substrate layer and the material of the packaging layer are both Ecoflex, and the material of the sensing material layer is aqueous graphene slurry.

[0010] According to a piezoresistive double-ball flexible pressure sensor provided by the present invention, the flexible electrode layer is provided with two through holes, and the distance between the two through holes is equal to the distance between the two protrusions in the same group.

[0011] The present invention also provides a method for preparing a piezoresistive double-ball flexible pressure sensor, the method being used to prepare the piezoresistive double-ball flexible pressure sensor described in any one of the above, comprising: Using a substrate mold and Ecoflex as a substrate material, a plurality of sequentially connected flexible substrate layers are prepared, wherein the outer peripheries of the plurality of flexible substrate layers are formed with side walls; Drop-coating a graphene-isopropyl alcohol dispersion solution on the surfaces of the substrate and the protrusions and drying the solution to form a sensing material layer on the surfaces of the substrate and the protrusions; Cutting a plurality of the flexible substrate layers connected in sequence into a group of two flexible substrate layers; The flexible electrode layer is arranged on one side of the substrate, and the conductive solder paste layer of the flexible electrode layer is connected to the flexible electrode layer on both sides of the protrusion by using conductive glue, and then dried and solidified.

[0012] According to a method for preparing a piezoresistive double-ball flexible pressure sensor provided by the present invention, after the step of connecting the conductive solder paste layer of the flexible electrode layer with the sensing material layer on both sides of the protrusion using conductive glue and drying and curing, the preparation method further comprises: Ecoflex is suspended and coated on the side of the sensing material layer facing away from the flexible substrate layer, and dried naturally to form a packaging layer.

[0013] According to a method for preparing a piezoresistive double-ball flexible pressure sensor provided by the present invention, the height of the side wall is greater than the height of the protrusion.

[0014] According to a method for preparing a piezoresistive double-ball flexible pressure sensor provided by the present invention, the mass ratio of the aqueous graphene slurry to the isopropanol solution in the graphene-isopropanol dispersion solution is 1:10.

[0015] The piezoresistive double-ball flexible pressure sensor provided by the present invention increases the resistance of the sensing material layer when the flexible substrate layer is subjected to pressure, thereby outputting an electrical signal; due to the structural design of the double-ball pressure sensor, two independent point pulse wave signals can be output synchronously, and the transmission time of the front and rear pulse waves of the radial artery of the wrist can be obtained through dual-channel pulse wave collection. The propagation speed of the pulse wave can be calculated in combination with the monitoring distance, thereby providing a reliable data set for blood pressure detection and providing key technical support for a wearable real-time human health monitoring system; at the same time, since the flexible substrate layer is made of flexible material, the comfort of the sensor when worn is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 It is a schematic flow chart of a method for preparing a piezoresistive double-ball flexible pressure sensor provided by the present invention.

[0018] Figure 2 It is a structural schematic diagram of the piezoresistive double-ball flexible pressure sensor provided by the present invention.

[0019] Figure 3 It is a structural schematic diagram of the substrate mold provided by the present invention.

[0020] Figure 4 It is a schematic structural diagram of a flexible electrode layer used for testing the performance of a single-ball flexible pressure sensor provided by the present invention.

[0021] Figure 5 It is a schematic structural diagram of the flexible electrode layer used for testing the performance of the double-ball flexible pressure sensor provided by the present invention.

[0022] Figure 6 It is a sensitivity curve diagram for performance analysis of a single-ball flexible pressure sensor provided by the present invention.

[0023] Figure 7 This is a 1000-cycle curve diagram for performance analysis of a single-ball flexible pressure sensor provided by the present invention.

[0024] Figure 8 This is a radial artery pulse detection chart using a single-ball flexible pressure sensor.

[0025] Fig. 9 It is an enlarged waveform of the radial artery pulse.

[0026] Fig.10 This is a graph of fingertip arterial pulse detection using a single-ball flexible pressure sensor.

[0027] Fig.11 This is a carotid artery pulse detection chart using a single-ball flexible pressure sensor.

[0028] Fig.12 It is a diagram of dual-path pulse electrical signals output by the piezoresistive double-ball flexible pressure sensor provided by the present invention.

[0029] Fig.13 It is a schematic diagram of the enlargement of the dual-path pulse electrical signal provided by the present invention.

[0030] Reference numerals: 100, flexible substrate layer; 110, substrate; 120, protrusion; 200, sensing material layer; 300, flexible electrode layer; 310, conductive solder paste layer; 400, packaging layer; 500, conductive glue; 600, substrate mold; 700, side wall. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limitations on the embodiments of the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0033] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0034] In the embodiments of the present invention, unless otherwise clearly specified and limited, the first feature being "above" or "below" the second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "above" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0035] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0036] Combine the following Figure 1-Figure 5 A schematic structural diagram describing the piezoresistive double-ball flexible pressure sensor of the present invention.

[0037] like Figure 1 and Figure 2As shown, the piezoresistive double-ball flexible pressure sensor includes at least two flexible substrate layers 100, a sensing material layer 200 and a flexible electrode layer 300. The two flexible substrate layers 100 are arranged at intervals. The flexible substrate layer 100 includes a substrate 110 and a protrusion 120. The protrusion 120 is arranged on one side of the substrate 110. The sensing material layer 200 is arranged on the surface of the substrate 110 and the protrusion 120. The flexible electrode layer 300 is arranged on one side of the substrate 110. The flexible electrode layer 300 is provided with two conductive solder paste layers 310 arranged at intervals. The two conductive solder paste layers 310 are located on both sides of the protrusion 120. The two conductive solder paste layers 310 are connected to the sensing material layers 200 on both sides of the protrusion 120 through conductive glue 500. When the flexible substrate layer 100 is subjected to pressure, the resistance of the sensing material layer 200 increases.

[0038] The piezoresistive double-ball flexible pressure sensor provided by the present invention increases the resistance of the sensing material layer 200 when the flexible substrate layer 100 is subjected to pressure, thereby outputting an electrical signal; due to the structural design of the double-ball pressure sensor, two independent point pulse wave signals can be output synchronously, and the transmission time (PTT) of the front and rear pulse waves of the radial artery of the wrist can be obtained through dual-channel pulse wave collection, and the pulse wave propagation velocity (PWV) can be calculated in combination with the monitoring distance (D), thereby providing a reliable data set for blood pressure detection and providing key technical support for wearable real-time human health monitoring systems; at the same time, since the flexible substrate layer 100 is made of flexible material, the comfort of the sensor when worn is improved.

[0039] In one embodiment of the present invention, Figure 2 As shown, the piezoresistive double-ball flexible pressure sensor further includes a packaging layer 400, which is disposed on the side of the sensing material layer 200 away from the flexible substrate layer 100. The material of the flexible substrate layer 100 and the material of the packaging layer 400 are both Ecoflex. Since the material of the flexible substrate layer 100 and the material of the packaging layer 400 are of the same model, the Young's modulus of the material of the flexible substrate layer 100 and the material of the packaging layer 400 are the same, which can prevent modulus mismatch under pressure; at the same time, the use of Ecoflex flexible material with good elastic properties makes the sensor comfortable to wear and can be applied to wearable monitoring in different scenarios.

[0040] In one embodiment of the present invention, the protrusion 120 is a semi-ellipsoid, that is, the protrusion 120 is a part of the ellipsoid. The purpose of adopting the ellipsoid structure design is that compared with the hemispherical structure, the flexible substrate layer 100 deforms more obviously when subjected to pressure, which helps to improve the sensitivity. Of course, the shape of the protrusion 120 is not limited to this, and it can also be a hemisphere or other shapes. The two flexible protrusions 120 form a flexible double-ball structure substrate, and the flexible double-ball structure substrate is prepared by a template method. In this embodiment, the substrate 110 is a rectangular plate body, of course, it can also be a regular polygon or other shapes. The protrusion 120 is arranged on one side of the substrate 110 and is integrally formed with the substrate 110.

[0041] In one embodiment of the present invention, the connection between the substrate 110 and the protrusion 120 is connected by a rounded corner. Figure 2 The bottom of the middle protrusion 120 is connected to the upper surface of the substrate 110 by a rounded corner. By connecting the substrate 110 and the protrusion 120 with a rounded corner, the stress concentration at the connection can be effectively reduced, thereby improving the mechanical strength and service life of the structure and preventing damage under long-term use or repeated pressure.

[0042] In one embodiment of the present invention, Figure 5 As shown, the flexible electrode layer 300 is an FPCB (flexible circuit board). Of course, the specific type of the flexible electrode layer 300 is not limited thereto, and may also be other types of flexible electrode layers 300. The FPCB is in a Y-shaped structure, and the two branches of the Y-shaped structure are square frame layers. The frame layer is provided with a conductive solder paste layer 310, and is led out to the tail of the flexible electrode layer 300 through the linear conductive solder paste layer 310. The FPCB can lead out a dual-path sensor electrical signal, and the lead-out part and the sensing layer connection part adopt a rounded corner design, the purpose of which is to reduce stress concentration during long-term use and improve mechanical strength. The flexible electrode layer 300 is provided with two through holes, and the two through holes are located on the two branches of the Y-shaped structure. The distance between the two through holes is equal to the distance between the two protrusions 120 in the same group, that is, the distance between the two through holes and the distance between the two protrusions 120 in the same group are both D.

[0043] In one embodiment of the present invention, the piezoresistive double-ball flexible pressure sensor of the present invention can stably monitor the radial artery, fingertip artery and carotid artery at the human wrist, among which the test of the radial artery at the human wrist is relatively stable, has the best waveform effect, and is highly comfortable to wear. Since the distance between the two protrusions 120 is known to be D, by measuring the transmission time (PTT) of the pulse wave before and after the radial artery at the wrist, combined with the monitoring distance D, the propagation velocity of the pulse wave PWV=D / PTT can be calculated, thereby providing reliable data support for the prediction of blood pressure values.

[0044] In one embodiment of the present invention, the material of the sensing material layer 200 is water-based graphene slurry. Of course, the material of the sensing material layer 200 is not limited thereto, and other materials may also be used. Graphene is a sheet-like stacked material structure. When the protrusion 120 coated with graphene is subjected to pressure, on the one hand, the sheet structure will be stacked and staggered; on the other hand, the pressure will also cause the protrusion 120 to deform, thereby causing cracks in the graphene material of the sensing material layer 200. Both of the above situations will cause the resistance of the piezoresistive double-ball flexible pressure sensor to increase.

[0045] The present invention also provides a method for preparing a piezoresistive double-ball flexible pressure sensor, the method for preparing the piezoresistive double-ball flexible pressure sensor described in any one of the above embodiments, comprising: In step S100 , a substrate mold 600 is used to prepare a plurality of sequentially connected flexible substrate layers 100 using Ecoflex as the substrate material, and a side wall 700 is formed on the periphery of the plurality of flexible substrate layers 100 .

[0046] It should be noted here that the substrate mold 600 is processed by 3D printing, and the double-spherical flexible substrate is obtained by the reverse molding method when preparing the flexible substrate layer. A plurality of sequentially connected flexible substrate layers 100 form a 1×n (n is an even number) ellipsoid structure array, and n / 2 groups of flexible substrate layers 100 can be prepared in one batch. A side wall 700 is provided around the ellipsoid array, and the height of the side wall 700 is greater than the height of the protrusion. When applying the sensing material solution, the height of the side wall 700 is greater than the height of the protrusion to ensure that the sensing material solution on the six ellipsoids reaches a uniform horizontal plane, thereby making the coating uniform.

[0047] It should also be noted here that Figure 3 As shown, the design layout of the substrate mold 600 in this embodiment is a 1×6 ellipsoidal groove structure array, wherein two ellipsoidal grooves form a group, and one batch can prepare three groups of flexible substrate layers 100. The distance D between the two ellipsoidal grooves is 20 mm, and the lengths of the ellipsoidal grooves on the three semi-axes x, y, and z are 3.65 mm, 3.65 mm, and 5.5 mm. The base of the substrate mold 600 is a rectangular box with a thickness of 2 mm. The substrate mold 600 is also specially designed with side walls 700 surrounding the six ellipsoids, and the height of the side walls 700 is 8 mm.

[0048] Furthermore, before executing step S100, the mold surface needs to be sprayed with Smooth-on Release200 silicone aerosol release agent for preliminary demoulding treatment before the experiment. The material of the flexible substrate layer 100 is Smooth-On Ecoflex™00-30AF Anti Funga. The mass ratio of A glue and B glue is 1:1 during the configuration, and they are stirred evenly. Then, the substrate material is poured into the substrate mold 600, left to stand for 5 hours for curing and molding, and then demolding is performed.

[0049] Step S200, drop-coating a graphene-isopropyl alcohol dispersion solution on the surfaces of the substrate 110 and the protrusions 120 and drying the solution to form a sensing material layer 200 on the surfaces of the substrate 110 and the protrusions 120; It should be noted that the sensing material layer 200 uses 5% aqueous graphene slurry. To ensure uniform coating, the aqueous graphene slurry must be dissolved in an isopropanol solution and dispersed uniformly by shaking. The mass ratio of the aqueous graphene slurry to the isopropanol solution in the graphene-isopropanol dispersion solution is 1:10. After the graphene-isopropanol dispersion solution is prepared, the graphene-isopropanol dispersion solution is dripped onto the Ecoflex substrate material, immersed to the top of the 6 ellipsoids, and placed in an 80°C oven for 3h to completely evaporate the isopropanol and water.

[0050] Step S300, cutting a plurality of sequentially connected flexible substrate layers 100 into a group of two flexible substrate layers 100; It should be noted that in this embodiment, six sequentially connected flexible substrate layers 100 are cut into two flexible substrate layers 100 as a group, thereby obtaining three groups of flexible substrate layers 100. Of course, the number of flexible substrate layers 100 is not limited thereto, and is determined according to actual needs.

[0051] Step S400 , disposing the flexible electrode layer 300 on one side of the substrate 110 , connecting the conductive solder paste layer 310 of the flexible electrode layer 300 to the sensing material layer 200 on both sides of the protrusion 120 using the conductive glue 500 , and drying and curing.

[0052] It should be noted here that when the flexible electrode layer 300 is connected to the double-ball substrate, a flexible conductive silver glue is used to connect the conductive solder paste layer 310 of the flexible electrode layer 300 to the sensing material layer 200 on both sides of the protrusion 120. The mass ratio of the curing agent and the colloid in the conductive silver glue is 1:10, and it is stirred evenly. After stirring evenly, the conductive silver glue is applied to both sides of the protrusion 120, and then covered with the flexible electrode layer 300, and placed in a 60°C oven for 1 hour to completely cure the conductive silver glue.

[0053] In one embodiment of the present invention, after the conductive solder paste layer 310 of the flexible electrode layer 300 is connected to the sensing material layer 200 on both sides of the protrusion 120 by using the conductive glue 500 and drying and curing, the preparation method further includes: Step S500 , Ecoflex is suspended on the side of the sensing material layer 200 facing away from the flexible substrate layer 100 , and is naturally dried to form a packaging layer 400 .

[0054] It should be noted here that after the flexible electrode layer 300 is fixed, the connection between the two protrusions 120 is cut off to make the two protrusions 120 electrically insulated, and then Smooth-On Ecoflex™ 00-30AF AntiFunga is used. The mass ratio of A glue and B glue is 1:1 during configuration, and they are stirred evenly; then the double-ball sensor device is suspended and coated with Ecoflex for packaging, and dried at room temperature for 5 hours.

[0055] like Figure 4 As shown, when the single-ball device performance test is performed on the piezoresistive double-ball flexible pressure sensor of the present invention, an FPC 6PIN flexible cable adapter board is used to connect the lead-out electrodes and is connected to a Keithley DMM6500 6.5-digit digital multimeter for testing.

[0056] In order to understand the performance of the piezoresistive double-ball flexible pressure sensor, the sensitivity of the piezoresistive double-ball flexible pressure sensor needs to be tested first, such as Figure 6 As shown in the figure, the resistance change rate ΔR / R0 of the piezoresistive double-spherical flexible pressure sensor changes with the change curve of the pressure. With the increase of pressure, the relative resistance change rate (ΔR / R0) of the piezoresistive double-spherical flexible pressure sensor increases significantly in the range of 0-50kPa, and the sensitivity reaches 18.8 KPa-1. Then, the growth rate gradually slows down in the pressure range of 50-120kPa, but the sensitivity can still reach 4.3 KPa-1.

[0057] The cyclic stability of the piezoresistive double-ball flexible pressure sensor was tested. Figure 7 As shown in the figure, during the test, the tensile machine provides a comparable pressure (~1 kPa) and cycle frequency (1 second / cycle) for simulating the pulse wave test, and the change curve of the resistance change rate Δ R / R0 during the 1000 cycle test can be seen. From the results, it can be concluded that the piezoresistive double-ball flexible pressure sensor of the present invention has good cycle stability, fatigue resistance and durability.

[0058] The piezoresistive double-ball flexible pressure sensor of the present invention can be applied to different scenarios and can simulate pulse wave tests on different parts of the human body. Several application scenarios of the piezoresistive double-ball flexible pressure sensor are described below.

[0059] Scenario 1: Place the flexible double-ball flexible pressure sensor on the human wrist to test the relative resistance change of the human radial artery. The test results are as follows: Figure 8 As shown in the figure, it can be seen that the resistance change rate shows a stable periodic change with the pulse frequency. The enlarged waveform of the radial artery is as follows Fig. 9 As shown, the output electrical data is a typical pulse waveform, with obvious ascending and descending branches, main wave (P), tidal wave (T), and heavy and thin wave (D).

[0060] In scenario 2, the piezoresistive double-ball flexible pressure sensor of the present invention is placed at the fingertips of a human body to test the relative resistance change of the fingertip arteries of the human body. Here, only the electrical signal output of a single ball of the device is detected. The test results are as follows: Fig.10 As shown, it can be seen that the resistance change rate presents a stable periodic change with the pulse frequency. When the piezoresistive double-ball flexible pressure sensor of the present invention is applied to test the fingertip artery of the human body, since the fingertip artery is relatively weak, a large pre-pressure needs to be applied.

[0061] In scenario three, the piezoresistive double-ball flexible pressure sensor of the present invention is placed on the human neck to test the relative resistance change of the human carotid artery. Here, only the electrical signal output of a single ball of the device is detected. The test results are as follows: Fig.11 As shown, it can be seen that the resistance change rate shows a stable periodic change with the pulse frequency.

[0062] As a preferred embodiment, the piezoresistive double-ball flexible pressure sensor is relatively stable and has the best waveform effect when testing the radial artery of the human wrist.

[0063] In scenario four, the piezoresistive double-ball flexible pressure sensor of the present invention is placed before and after the radial artery of the human wrist, combined with a collection circuit board, to collect dual-channel pulses at the same time, with a sampling frequency of 1kHz, and output dual-channel electrical signals.

[0064] The piezoresistive double-ball flexible pressure sensor of the present invention can stably collect dual-path pulse signals. The test results are as follows: Fig.12 As shown, it can be seen that the dual-channel output electrical signals show stable periodic changes with the pulsation frequency.

[0065] The dual-path pulse signal collected by the piezoresistive dual-ball flexible pressure sensor of the present invention has a transmission time (PTT), such as Fig.13 As shown, the two-way pulse wave waveform transmission time (PTT) is about 5ms. Combined with the monitoring distance D=20mm, it can be calculated that the pulse wave propagation velocity PWV is about 4m / s. Combined with a large number of collected data sets, it provides reliable data support for the prediction of blood pressure values.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A piezoresistive double-ball flexible pressure sensor, characterized in that: include: At least two flexible substrate layers (100), the two flexible substrate layers (100) being arranged at intervals, the flexible substrate layer (100) comprising a substrate (110) and a protrusion (120), the protrusion (120) being arranged on one side of the substrate (110); A sensing material layer (200), the sensing material layer (200) being arranged on the surfaces of the substrate (110) and the protrusion (120); A flexible electrode layer (300), the flexible electrode layer (300) being arranged on one side of the substrate (110), the flexible electrode layer (300) being provided with two conductive solder paste layers (310) arranged at intervals, the two conductive solder paste layers (310) being located on both sides of the protrusion (120), the two conductive solder paste layers (310) being connected to the sensing material layers (200) on both sides of the protrusion (120) via conductive glue (500), and when the flexible substrate layer (100) is subjected to pressure, the resistance of the sensing material layer (200) increases.

2. The piezoresistive double-ball flexible pressure sensor according to claim 1, characterized in that: The piezoresistive double-ball flexible pressure sensor also includes: A packaging layer (400), the packaging layer (400) being arranged on a side of the sensing material layer (200) facing away from the flexible substrate layer (100).

3. The piezoresistive double-ball flexible pressure sensor according to claim 2, characterized in that: The protrusion (120) is a semi-ellipsoid.

4. The piezoresistive double-ball flexible pressure sensor according to claim 2, characterized in that: The connection between the substrate (110) and the protrusion (120) is connected via a rounded corner.

5. The piezoresistive double-ball flexible pressure sensor according to any one of claims 2 to 4, characterized in that: The material of the flexible substrate layer (100) and the material of the packaging layer (400) are both Ecoflex, and the material of the sensing material layer (200) is water-based graphene slurry.

6. The piezoresistive double-ball flexible pressure sensor according to any one of claims 1 to 4, characterized in that: The flexible electrode layer (300) is provided with two through holes, and the distance between the two through holes is equal to the distance between the two protrusions (120) in the same group.

7. A method for preparing a piezoresistive double-ball flexible pressure sensor, the method being used to prepare the piezoresistive double-ball flexible pressure sensor according to any one of claims 1 to 6, characterized in that: include: Using a substrate mold (600) and Ecoflex as a substrate material, a plurality of sequentially connected flexible substrate layers (100) are prepared, wherein the outer peripheries of the plurality of flexible substrate layers (100) are formed with side walls (700); Drop-coating a graphene-isopropyl alcohol dispersion solution on the surfaces of the substrate (110) and the protrusion (120) and drying the solution, so as to form a sensing material layer (200) on the surfaces of the substrate (110) and the protrusion (120); Cutting a plurality of the flexible substrate layers (100) connected in sequence into a group of two flexible substrate layers (100); A flexible electrode layer (300) is arranged on one side of the substrate (110), and a conductive solder paste layer (310) of the flexible electrode layer (300) is connected to the sensing material layer (200) on both sides of the protrusion (120) using conductive glue (500), and then dried and solidified.

8. The method for preparing the piezoresistive double-ball flexible pressure sensor according to claim 7, characterized in that: After the step of connecting the conductive solder paste layer (310) of the flexible electrode layer (300) to the flexible electrode layer (300) on both sides of the protrusion (120) using the conductive glue (500), and drying and curing, the preparation method further comprises: Ecoflex is suspended and coated on the side of the sensing material layer (200) facing away from the flexible substrate layer (100), and is naturally dried to form a packaging layer (400).

9. The method for preparing the piezoresistive double-ball flexible pressure sensor according to claim 8, characterized in that: The height of the side wall (700) is greater than the height of the protrusion (120).

10. The method for preparing the piezoresistive double-ball flexible pressure sensor according to claim 8, characterized in that: The mass ratio of the aqueous graphene slurry to the isopropanol solution in the graphene-isopropanol dispersion solution is 1:10.

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