CN114777968A - Preparation method of multi-layer flexible pressure sensor with lotus leaf microstructure - Google Patents
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- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/103—Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
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Abstract
The invention discloses a method for preparing a multi-layer flexible pressure sensor with a lotus leaf microstructure, which adopts the technical scheme that a lotus leaf papilla microstructure is taken as a bionic template, the bionic microstructure is transferred to a flexible substrate layer, four layers of lotus leaf microstructure PDMS conductive films are overlapped together by adopting an electrode layer-substrate layer multi-layer overlapping method, and lotus leaves are taken as templates and subjected to twice replication forming methods In the fields of electronic skin, artificial intelligence and the like, an effective new method is provided for the design and development of a flexible sensor.
Description
Technical Field
The invention relates to the field of sensor preparation, in particular to a preparation method of a multi-layer flexible pressure sensor with a lotus leaf microstructure.
Background
In recent decades, flexible pressure sensors have come into force as a new pressure and touch sensing method, and besides good dynamic and static stimulation response and light and thin flexible device structure, the flexible pressure sensors also have the advantages of high resolution, deformability, stretchability, light weight, good conformability and the like. With the development of artificial intelligence, the method can be widely applied to medical and industrial fields such as electronic skins, wearable medical equipment and flexible pressure sensors.
Among the various types of sensors, pressure sensors have shown great potential for use due to their simple structure, ease of manufacture, high sensitivity, and low cost. The pressure sensor is composed of a flexible substrate and an electrode layer, and a sensor device required for adapting to practical application is expected to have high sensitivity and a wide linear response range.
In previous research, researchers have improved the performance of sensors by changing the structure of the sensors. Currently, flexible pressure sensors have been used to monitor subtle movements, such as tactile sensing, non-invasive blood pressure measurements, and gross pressure movements, such as walking, running, and jumping. Different applications correspond to different pressure ranges: in vivo pressure and palpation cardiovascular activity is typically less than 10 kPa; the high pressure of the blood pressure monitoring equipment can reach more than 10kPa, and the pressure of the soles of the human bodies can reach more than 100 kPa. Wide linearityRange is an important characteristic of a sensor that maintains high pressure resolution over a wide pressure range and simplifies data processing and conversion. When the linear range is small, the applied pressure easily exceeds the measurement range of the sensor, resulting in failure of pressure measurement and loss of sensing function. In order to expand the linear range, Korea institute of science and technology, D Kwon et al, developed a wide linear range flexible wearable pressure sensor based on three-dimensional microporous dielectric elastomer, which was tested to have a sensitivity of only 0.601kPa when the pressure was less than 5kPa-1When the pressure is more than 30kPa, the sensitivity is lowered to 0.077kPa-1. Therefore, it is a great challenge to prepare a flexible sensor with both high sensitivity and wide linear range performance.
The sensitivity of conventional pressure sensors is limited by the low compressibility of the substrate, and therefore, designing microstructured substrates with higher compressibility has proven to be an effective way to increase sensitivity. The usual method is casting on a clever silicon mold or a laser etched mold, another common method is the templating method. By the method, the substrate with the micro-pillar array, the micro-pyramid array, the micro-dome array, the micro-cone and the conical truncated cone-shaped microstructure required by the high-sensitivity sensor can be prepared. In a low pressure range, the microstructures can effectively concentrate a load, so that the contact area with the load is rapidly increased, and the sensitivity is greatly improved. However, as pressure increases, incremental deformation and stress accumulation in the pre-existing contact area can cause sensitivity to drop, thereby deviating from linearity.
Disclosure of Invention
The invention provides a piezoresistive pressure sensor which is flexible, sensitive and wide in linear range and is designed and prepared by adopting a lotus leaf mastoid microstructure as a bionic template, transferring the bionic microstructure to a flexible substrate layer and adopting an electrode layer-substrate layer multilayer superposition method, and is used for solving the problems in the background technology.
A method for preparing a multi-layer flexible pressure sensor with lotus leaf microstructures adopts a lotus leaf papilla microstructure as a bionic template, the bionic microstructure is transferred to a flexible substrate layer, an electrode layer-substrate layer multi-layer superposition method is adopted, four layers of lotus leaf microstructure PDMS conductive films are superposed together, a lotus leaf is used as the template, a micropatterned PDMS flexible substrate with a high aspect ratio and a low-density papilla structure is prepared through two-time copying and forming, metal silver is sputtered on the flexible substrate to prepare a metal electrode layer, a conductive copper adhesive tape and a non-conductive common adhesive tape are respectively adhered to two ends of the flexible substrate, the rough surfaces of the four layers of microstructure PDMS flexible substrates with silver electrodes are arranged face to face, the surfaces are adhered to be flat, the substrates adhered with the conductive copper adhesive tapes are arranged at the same end, one end of the two layers of the middle layers of the substrates adhered with the conductive copper adhesive tapes is adhered by the conductive copper adhesive tapes again, and bonding copper wires on one sides of the upper layer and the lower layer which are bonded with the conductive copper adhesive tapes, and finally packaging the copper wires with polyethylene terephthalate to obtain the lotus leaf microstructure multilayer flexible pressure sensor.
A preparation method of a multi-layer flexible pressure sensor with a lotus leaf microstructure comprises the following specific technological processes:
1) preparing a lotus leaf microstructure PDMS conductive film:
a) cutting fresh folium Nelumbinis into 4 × 2.5cm pieces2Selecting large flat leaves to avoid coarse veins, washing with deionized water for 3 times, drying at room temperature, and fixing dried folium Nelumbinis on glass substrate with double-sided tape;
b) preparing a lotus leaf microstructure PDMS flexible film: mixing an epoxy resin base material and a curing agent according to the weight ratio of 3: 1, mixing, mechanically stirring for at least 10 minutes, degassing, pouring the mixture on treated lotus leaves, degassing again, curing for 20 hours at room temperature, obtaining an epoxy resin mold with a negative lotus leaf microstructure after the lotus leaves are stripped, preparing PDMS solution from Dow Corning DC184 organic silicon polymer and a cross-linking agent according to the weight ratio of 10:1, stirring for 15 minutes, degassing, pouring on the negative epoxy resin mold, degassing again to promote the infiltration of PDMS, and curing for 2 hours in a drying box at 80 ℃, wherein the PDMS film with the lotus leaf microstructure is very easy to strip from the epoxy resin mold;
c) performing magnetron sputtering on metal silver on the microstructure PDMS film by using a full-automatic high-performance ion sputtering coating instrument to prepare a metal flexible electrode, and controlling the thickness of a conductive metal silver layer by adjusting the spraying time to be 90s and the spraying current to be 30mA to obtain the lotus leaf-shaped microstructure PDMS conductive film;
2) preparing a flexible pressure sensor:
respectively sticking a conductive copper adhesive tape and a non-conductive common adhesive tape at two ends of the lotus leaf microstructure PDMS conductive film, stacking the patterned PDMS conductive films in a face-to-face manner, wherein, the film pasted with the conductive copper adhesive tape and the other film pasted with the common non-conductive adhesive tape are stacked on the same side, the flat surfaces of the stacked films are pasted together through glue, wherein, the films pasted with the conductive copper adhesive tapes are placed on the same side, and finally, the film ends pasted with the conductive adhesive tapes on the two middle layers are pasted again by the conductive copper adhesive tapes, so that the four stacked films have good conductivity, respectively sticking conductive copper wires on the ends of the upper and lower layers adhered with the conductive adhesive tapes, fixing the conductive copper wires with the conductive adhesive tapes again, and finally, and packaging the film by using polyethylene terephthalate to obtain the multilayer structure flexible pressure sensor with the lotus leaf pattern on the surface.
The invention has the beneficial effects that:
1) the design concept of the invention is that four layers of silver-PDMS films are stacked together, the high sensitivity is ensured, and simultaneously, the pressure linear range is greatly widened.
2) The invention relates to a preparation method of a multilayer flexible piezoresistive pressure sensor, which adopts a simple method to prepare the sensor with excellent performance and has the characteristics of good sensitivity, stability, wide linear range, low detection limit, low preparation cost, high robustness and the like. The flexible pressure sensor has been proven to be useful for detecting minute vibrations of wrist pulse, carotid pulse, sound wave, etc., and also for measuring plantar pressure in large sports such as walking, running, and jumping.
3) The sensor prepared by the method can identify tiny human body signals such as vocal cord vibration, pulse vibration and the like, has a wider pressure linear range, can monitor larger plantar pressure in various motion modes, and has remarkable characteristics that the sensor has huge application potential in wearable electronic equipment, motion monitoring and health monitoring, particularly in application in a large pressure range, and an effective new method is provided for the design and development of flexible sensors in the fields of biomedicine, wearable equipment, electronic skin, artificial intelligence and the like.
Drawings
FIG. 1 is a schematic diagram of a multi-layer flexible pressure sensor with a lotus leaf microstructure according to the present invention;
FIG. 2 is a surface image of a multi-layer flexible pressure sensor with a lotus leaf microstructure under a scanning electron microscope;
FIG. 3 is a graph of the resistance change of four and two layer sensors;
FIG. 4 is a graph of current change over sensor response time;
FIG. 5 is a graph showing the resistance change in 1000 loading and unloading cycles;
FIG. 6 is a graph showing the variation of the real-time output current of carotid pulse monitoring at 1V;
FIG. 7 is a graph of the variation of the real-time output current of the radial artery pulse monitoring at 1V voltage;
FIG. 8 is a diagram of real-time output current variation of vocal cord vibration monitoring during "Hello" sound production;
fig. 9 is a graph of resistance change in detecting human gait.
Detailed Description
Referring to fig. 1 to 9, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
Example 1:
preparing a multilayer flexible piezoresistive pressure sensor;
cutting fresh folium Nelumbinis into 4 × 2.5cm pieces2Size, selecting large flat leaf to avoid coarse veins, washing with deionized water for 3 times, drying at room temperature, and fixing folium Nelumbinis belt on plate glass substrate with double-sided adhesive tape.
Preparing a microstructure PDMS flexible film: epoxy resin base material and curing agent are mixed according to the weight ratio of 3: 1, mixing, mechanically stirring for at least 10 minutes, degassing, pouring the mixture on treated lotus leaves, degassing again, curing for 20 hours at room temperature, obtaining a negative epoxy resin mold after the lotus leaves are stripped, preparing a PDMS solution from the Dow Corning DC184 organic silicon polymer and a cross-linking agent according to the weight ratio of 10:1, stirring for 15 minutes, pouring the mixture on the negative epoxy resin mold after degassing, degassing again to promote infiltration of PDMS, and placing the mold in an oven at 80 ℃ for curing for 2 hours, so that a microstructure PDMS film is stripped from the epoxy resin mold, wherein the epoxy resin mold is a thermosetting material, and has high strength, corrosion resistance and no deformation; therefore, the epoxy resin mold can be used for a long time, and the obtained polydimethylsiloxane base layer microstructure is stable in shape;
and preparing the flexible metal electrode on the microstructure PDMS film by using a full-automatic high-performance ion sputtering coating instrument and using a sputtering coating method to carry out metal silver. The thickness of the silver film is controlled by adjusting the spraying time to be 90s and the spraying current to be 30mA, and the lotus leaf microstructure PDMS conductive film is obtained.
Respectively sticking a conductive copper tape and a non-conductive common tape on two ends of the lotus leaf microstructure PDMS conductive film, stacking the lotus leaf microstructure PDMS conductive films with patterns in a face-to-face manner, wherein, the film pasted with the conductive adhesive tape and the other film pasted with the non-conductive adhesive tape are stacked on the same side, the flat surfaces of the stacked films are pasted together through glue, wherein, the films pasted with the conductive adhesive tapes are placed on the same side, and finally, the ends of the films pasted with the conductive adhesive tapes on the two middle layers are pasted again by the conductive adhesive tapes, so that the four stacked films have good conductivity, respectively sticking conductive copper wires on the ends of the upper and lower layers adhered with the conductive adhesive tapes, fixing the conductive copper wires with the conductive adhesive tapes again, and finally, and packaging the film by using polyethylene terephthalate to obtain the multilayer-structure flexible piezoresistive pressure sensor with the lotus leaf micro-pattern on the surface.
Example 2
And testing the sensing performance of the prepared sensor by using a universal testing machine.
In order to research the influence of the superposition of four layers of lotus leaf microstructure PDMS electrodes on the sensing performance, a traditional two-layer microstructure PDMS electrode sensor is manufactured for comparison, a universal testing machine is used for testing the sensing performance of the sensor, and conductive copper wires at two ends of the prepared sensor are connected to an interface of the universal testing machine.
At a voltage of 1V, the device was loaded vertically with increasing pressure while recording the real-time current, as shown in fig. 3, the change in relative current increased with increasing load pressure, and two linear regions of current rate of change with applied pressure were observed. For a four-layer sensor, when the applied pressure is less than 30kPa, the sensitivity of the device reaches 2.525kPa-1. In the pressure range of 30kPa to 312kPa, the sensitivity of the device is 0.172kPa-1In contrast, the sensitivity of the two-layer sensor in the pressure region below and above 34kPa was 0.525 and 0.006kPa, respectively-1. Therefore, the sensitivity of the four-layer sensor is 5 times greater than that of the traditional two-layer sensor, and the pressure linear range of the four-layer sensor is improved by one order of magnitude than that of the two-layer sensor. In the four-layer structure, four layers of lotus leaf microstructure PDMS electrode layers are superposed. The pressure measuring range of the four-layer structure is as high as 312kPa, the sensitivity is enough to meet the pressure measurement of various parts and various motion modes of the human body, and therefore the sensing performance of the four-layer sensor is enough. A four-layer sensor can saturate the interface at a greater pressure than a two-layer sensor, and therefore the pressure range is much greater. Meanwhile, under the same pressure, the larger the contact area of the four-layer sensor is, the larger the current increase is, and the higher the sensitivity is.
To study the response time of the sensor, the surface of the sensor was pressed with a finger. As shown in fig. 4, the current of the sensor rapidly rises within a fast response time of 50ms, which is equivalent to the response time of human skin (30-50ms), and then after the pressure is released by maintaining at a stable value, the current of the sensor rapidly falls within about 100ms along with the original recovery state within a short time, and then decays to the initial value.
In order to test the stability of the prepared multilayer flexible pressure sensor, 1000 loading and unloading cyclic experiments were performed under a pressure of 6 kPa. The experimental result is shown in fig. 5, which shows signals of three stages of the repeated test, the waveform is very stable, which indicates that no fatigue occurs in 1000 loading and unloading cycles, no obvious crack exists on the metal surface of the film, and the metal electrode on the surface is not easy to be pilling and falling off, which indicates that the prepared sensor has good stability and reliability.
Example 3
And detecting a micro signal by using the prepared sensor.
The prepared sensor can be used as wearing equipment, and leads at two ends of the sensor are connected to the interface of the digital precision multimeter. The sensor was fixed to the neck and the carotid pulse was monitored in real time, with about 8 peaks (80 times/min) in 6 seconds as shown in fig. 6. In the single pulse period enlargement, the pulse waveform characteristics of the shock wave (P1), the tidal wave (P2), and the dissimilarity wave (P3) can be clearly distinguished.
The sensor is fixed at the wrist, the pulse of the radial artery is monitored in real time, the detection result is shown in fig. 7, about four peak values (80 times/min) exist in 16 seconds, and the pulse wave characteristics of the shock wave (P1), the tidal wave (P2) and the dissimilarity wave (P3) can be clearly distinguished in the single-pulse period enlarged diagram.
In addition to the pulse signal, the sensor can also detect the vibration of the vocal cords.
The sensor is fixed at the neck and throat to monitor the vibration of the vocal cords in real time, and the real-time current output result when the English language "Hello" is shown in fig. 8, which shows that the pressure sensor can generate a high-repeatability and recognizable strong current signal. The waveform of the phrase shown in the right graph is slightly changed by amplifying the "Hello" peak signal. This observation indicates that the pressure sensor is capable of "recognizing" and "speaking".
The above embodiments show that the prepared pressure sensor can well monitor the micro-motion of the human body.
Example 4
And monitoring human gait by using the prepared sensor.
In addition, the sensor has good stability and sensitivity in a wide linear range, so the sensor is applied to human gait monitoring. The pressure on the sole of an adult male (75 kg, 8.5 yards) in a static standing state is about 35kPa on average, and the sensor can work under the continuous pressure of the sole. We first install a multi-layer flexible pressure sensor on the sole and heel of the foot (as shown in fig. 9a, b). The two sensors are respectively connected with the two digital multimeters and are used for detecting current changes caused by sole pressure when the user walks slowly. Fig. 9 is a real-time signal waveform diagram of current change of the sole and heel sensors, wherein fig. 9b is a periodic change diagram, a curve with a higher peak corresponds to a current change curve generated by the heel, and a curve with a lower peak corresponds to a current change curve generated by the sole, and it can be seen from the diagram that the sensor has good motion detection performance.
Claims (2)
1. A preparation method of a multi-layer flexible pressure sensor with a lotus leaf microstructure is characterized by comprising the following steps: the technical scheme is that lotus leaf papilla microstructures are used as a bionic template, the bionic microstructures are transferred to a flexible substrate layer, an electrode layer-substrate layer multilayer overlapping method is adopted, four layers of lotus leaf microstructure PDMS conductive films are overlapped together, lotus leaves are used as the template, a micropatterned PDMS flexible substrate with a papilla-shaped structure with a high aspect ratio and low density is prepared through two copying and forming methods, metal silver is sputtered onto a flexible substrate to prepare a metal electrode layer, a conductive copper adhesive tape and a non-conductive common adhesive tape are respectively adhered to two ends of the flexible substrate, the rough surfaces of the four layers of microstructure PDMS flexible substrates with silver electrodes are arranged face to bond flat surfaces, the substrate adhered with the conductive copper adhesive tape is arranged at the same end, one end of the middle two layers adhered with the conductive copper adhesive tape is adhered with the conductive copper adhesive tape again by the conductive copper adhesive tape, copper wires are adhered to one side of the upper layer and the lower layer adhered with the copper adhesive tapes, and finally, packaging the sensor by using polyethylene terephthalate to obtain the lotus leaf microstructure multilayer flexible pressure sensor.
2. The method for preparing the multi-layer flexible pressure sensor with the lotus leaf microstructure according to claim 1, wherein the method comprises the following steps: the specific process comprises the following steps:
1) preparing a lotus leaf microstructure PDMS conductive film:
a) cutting fresh folium Nelumbinis into 4 × 2.5cm pieces2Selecting large flat leaves to avoid coarse veins, washing with deionized water for 3 times, drying at room temperature, and fixing dried folium Nelumbinis on glass substrate with double-sided tape;
b) preparing a lotus leaf microstructure PDMS flexible film: mixing an epoxy resin base material and a curing agent according to the weight ratio of 3: 1, mixing, mechanically stirring for at least 10 minutes, degassing, pouring the mixture on treated lotus leaves, degassing again, curing for 20 hours at room temperature, obtaining an epoxy resin mold with a negative lotus leaf microstructure after the lotus leaves are stripped, preparing a PDMS solution by using Dow Corning DC184 organic silicon polymer and a cross-linking agent according to the weight ratio of 10:1, stirring for 15 minutes, degassing, pouring on the negative epoxy resin mold, degassing again to promote the infiltration of PDMS, and curing for 2 hours in a drying box at 80 ℃, wherein the PDMS film with the lotus leaf microstructure is easy to strip from the epoxy resin mold;
c) performing magnetron sputtering on metal silver on the microstructure PDMS film by using a full-automatic high-performance ion sputtering coating instrument to prepare a metal flexible electrode, and controlling the thickness of a conductive metal silver layer by adjusting the spraying time to be 90s and the spraying current to be 30mA to obtain the lotus leaf-shaped microstructure PDMS conductive film;
2) preparing a flexible pressure sensor:
respectively sticking a conductive copper tape and a non-conductive common tape at two ends of the lotus leaf microstructure PDMS conductive film, stacking the patterned PDMS conductive film in a face-to-face manner, wherein, the film pasted with the conductive copper adhesive tape and the other film pasted with the common non-conductive adhesive tape are stacked on the same side, the flat surfaces of the stacked films are pasted together through glue, wherein, the films pasted with the conductive copper adhesive tapes are arranged on the same side, and finally, the film ends pasted with the conductive adhesive tapes on the two middle layers are pasted again by the conductive copper adhesive tapes, so that the four stacked layers of films have good conductivity, respectively sticking conductive copper wires on the ends of the upper and lower layers adhered with the conductive adhesive tapes, fixing the conductive copper wires with the conductive adhesive tapes again, and finally, and packaging the film by using polyethylene terephthalate to obtain the multilayer structure flexible pressure sensor with the lotus leaf pattern on the surface.
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