Multi-information flexible touch sensor of bionic cilium structure and preparation method thereof
Technical Field
The invention belongs to the field of bionic tactile sensing, and particularly relates to a multi-information flexible tactile sensor with a bionic cilium structure and a preparation method thereof.
Background
The sensor is the main component of environmental signal detection and is the basis of modern information acquisition systems. With the improvement and breakthrough of manufacturing technology and network information technology, sensors are rapidly developing in the direction of miniaturization, networking and intelligence. The traditional sensor has the defects of poor flexibility, inextensibility and the like, and the application range of the traditional sensor is limited. In recent years, flexible sensors have attracted much attention due to their promising applications in wearable electronics, artificial skin, robots, and healthcare. The breakthrough of the flexible sensor makes it possible to manufacture flexible electronic products with low cost and excellent performance on a large scale. Through structural design, the flexible sensor can realize the monitoring of various mechanical signals (such as pulling, pressing, shearing, bending, torsion, vibration and the like) and environmental stimulus signals (such as temperature, humidity, airflow and the like).
Robots generally require sensors to sense external environmental changes, thereby achieving precise motion control. However, the conventional rigid sensor cannot meet the requirement of the soft robot for large deformation measurement. In addition, the rigid sensor may interfere with the driving of the robot. In order to break through the limitations, a flexible sensor can be used for replacing a rigid sensor, so that the sensing of signals such as ambient temperature, humidity, mechanical stimulation and the like can be realized. For example, a flexible and stretchable tactile sensor is used for a manipulator or a surgical glove, so that the manipulator or the surgical glove can obtain touch, grasping and other feelings, and can distinguish human organs and operating instruments by sensing the shape and hardness of an object; under the condition of not influencing the movement, the flexible touch sensor capable of bearing large deformation is arranged at the joint of the robot, so that the robot can be accurately controlled, and the collision between the robot and other objects is avoided.
The bionic sensor is a novel sensor developed by simulating a biological structure or a sensing mechanism, and can realize functions and characteristics which cannot be realized by a conventional method, for example, the skin is the largest organ of a human body, and the body of people can be protected from external injury. Meanwhile, the skin is also a sensor organ for sensing external signals, and can detect various shapes, textures, temperature changes and contact pressure of different degrees. The flexible electronic skin prepared by simulating the structure of the human skin can be well attached to a non-planar surface, and further can be used for monitoring the human health, building the body and tracking the motion performance. In addition, the unique properties of certain organisms can be imparted to the sensor by engineering and modifying the process by studying biological structures and sensing mechanisms. In the evolution process, a plurality of animals sense external environmental signals through cilia structures, can monitor information such as airflow and displacement, and performs space mapping and touch sensing on nearby objects. Such as spider leg cilia, cricket tail cilia, seal beard, and rat beard are extremely sensitive biological receptors that capture ambient environmental information through the cilia structure and feed it back to the brain for subsequent behavioral actions. Researchers have now produced various biomimetic cilia sensors. However, these ciliary sensors are mostly rigid and not suitable as flexible wearable devices. Meanwhile, the existing bionic cilia sensor has a single function, can only detect a single signal to be detected mostly, seriously restricts the application range of the sensor, and cannot meet the requirement of the future complex environment on a high-performance sensor. Therefore, the development of new materials and manufacturing techniques has helped to improve the sensing ability and develop a biomimetic cilia sensor that is close to or better than the sensitivity of the natural system.
The flexible touch sensor with the bionic structure is developed by combining the bionic structure with the flexible sensor material, and is a research hotspot in the field of current touch, and the flexible touch sensor with multiple functions and high sensitivity is expected to be prepared by simulating the sensing mechanism of organisms through the design of the flexible material and the bionic structure.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide the multi-information flexible tactile sensor with the bionic cilia structure, which has high sensitivity, good stability and strong anti-interference capability, and the preparation method thereof.
The purpose of the invention can be realized by the following technical scheme:
a multi-information flexible touch sensor with a bionic cilium structure comprises a cilium array sensing unit and a piezoelectric film sensing unit which are combined with each other, wherein the cilium array sensing unit comprises 12 cilium sensors which are arranged on a common matrix layer in a rectangular array mode, the cilium sensors comprise an inner electrode, a piezoelectric sensing layer, a shielding layer and a protective sheath protecting layer which are arranged layer by layer from inside to outside, the inner electrode is made of a conductive metal material, the piezoelectric sensing layer is made of a piezoelectric material, the protective sheath protecting layer is made of a polymer material and plays a role in protecting the whole cilium sensors, a signal wire is led out from the inner electrode of each cilium sensor, and a grounding lead is led out from the shielding layer;
the piezoelectric film sensing unit is divided into an upper electrode layer, a piezoelectric film layer, a bump layer, a lower electrode layer and a protective layer from top to bottom, wherein the piezoelectric film layer is a PVDF nanofiber film, the bump layer is a processed copper foil, a plurality of hemispherical bump structures are arranged on the surface of the copper foil in an array form, a signal electrode is led out from the upper electrode layer, and a grounding electrode is led out from the lower electrode layer;
the multichannel signal conditioning circuit is provided with signal input terminals in one-to-one correspondence with each cilium sensor and an additional signal input terminal connected with a lead-out wire of a signal electrode, a signal wire led out from an inner electrode of each cilium sensor is respectively connected with the corresponding signal input terminals of the multichannel signal conditioning circuit, the lead-out wire of the signal electrode is connected with the other signal input terminal of the multichannel signal conditioning circuit, and a grounding lead led out from the shielding layer and the lead-out wire of the grounding electrode are jointly connected with the grounding terminal of the multichannel signal conditioning circuit.
The further technical scheme comprises the following steps:
the material of the common matrix layer is polydimethylsiloxane.
The cilia sensor uses an inner electrode as a center, the inner electrode adopts a conductive silver column or a copper column, a piezoelectric sensing layer is coated on the outer surface of the inner electrode, a copper net covers the shielding layer, and a protective cover protective layer is prepared by polydimethylsiloxane outside the shielding layer.
The piezoelectric film layer is made of PVDF (polyvinylidene fluoride) nano fibers, and the thickness of the fiber layer of the PVDF nano fibers is 50-500 micrometers.
The copper foil of the bump layer is 50-200 microns thick, and the distribution mode of a plurality of bump structures on the copper foil adopts a rectangular array or a circular array.
The protective layer is made of polymer material, specifically polyethylene terephthalate or polydimethylsiloxane.
The invention also provides a preparation method of the multi-information flexible tactile sensor of the bionic cilium structure, which comprises the following specific steps:
(1) preparing a common matrix layer:
fully mixing the PDMS prepolymer and a curing agent in a ratio of 10:1 to prepare a PDMS solution, putting the PDMS solution into a vacuum drier, removing bubbles generated in the stirring process, spin-coating the PDMS solution on the surface of a silicon wafer, setting a forward rotation speed of 1000-; then placing the PDMS solution in an environment of 80-100 ℃ for heat curing for 50-80min, and obtaining a public matrix layer with the thickness of 100-500 microns after stripping;
(2) preparing a cilium sensor:
selecting a high-conductivity silver column with the radius of 0.5mm as an inner electrode, selecting a PVDF nano-fiber film with the thickness of 100-300 microns, uniformly coating the outer surface of the silver column, using a copper net woven by copper wires as a shielding layer to spirally wind and wrap the outer side of the PVDF nano-fiber film, preparing PDMS solution by PDMS prepolymer and a curing agent according to the proportion of 8:1, integrally seating the PVDF nano-fiber film wrapped by the copper net and the inner electrode in a mould with a designed cilium-shaped structure, adding the PDMS solution into the mould, curing for 3 hours at 60 ℃ to prepare a cilium sensor, leading out a signal wire at the inner electrode, leading out a grounding lead at the shielding layer, and repeating the process to prepare 12 cilium sensors;
(3) bonding:
picking up the 12 cilia sensors flatly using a water-soluble adhesive tape, adhering the bottoms of the 12 cilia sensors with the water-soluble adhesive tape completely, exposing the top of each cilia sensor, and depositing a layer of chromium and a layer of silicon dioxide on the exposed surface of each cilia sensor; the public matrix layer is placed in a plasma cleaning machine, surface oxidation treatment is carried out by oxygen to realize the cleaning effect, then the water-soluble adhesive tape adhered with 12 cilia sensors and the public matrix layer are quickly bonded into a whole in a hot-pressing mode and then placed in water to enable the water-soluble adhesive tape to be completely dissolved, and therefore the cilia array sensing unit is obtained.
(4) Preparing a piezoelectric film sensing unit, selecting a PVDF nanofiber film with the thickness of 50-500 microns as a piezoelectric film layer, processing a copper foil with the thickness of 50-200 microns to enable the surface of the copper foil to be uniformly distributed with a hemispherical bump structure in a rectangular array or annular array mode so as to prepare a bump layer, vertically placing the bump layer on the lower surface of the piezoelectric film layer, covering an aluminum electrode layer with the thickness of 100nm on the upper surface of the piezoelectric film layer by a vacuum evaporation method so as to form an upper electrode layer, covering an aluminum electrode layer with the thickness of 100nm on the lower surface of the bump layer by a vacuum evaporation method so as to form a lower electrode layer, leading out a signal electrode from the upper electrode layer, leading out a grounding electrode from the lower electrode layer, and carrying out polymer packaging below the lower electrode;
(5) preparing a multi-channel signal conditioning circuit:
the multi-channel signal conditioning circuit comprises a charge conversion circuit, a voltage amplification circuit, a low-pass filter circuit and an analog-to-digital conversion circuit, wherein signal input terminals and grounding terminals are welded at the input end, signal wires led out from inner electrodes are connected to the corresponding signal input terminals in a one-to-one correspondence mode, a leading-out wire of a signal electrode is connected to one of the signal input terminals, a grounding lead wire is led out from a shielding layer, and the grounding lead wire led out from the shielding layer and the leading-out wire of the grounding electrode are connected to the grounding terminal of the multi.
Compared with the prior art, the invention has the following advantages:
(1) the cilium array sensing unit and the piezoelectric film sensing unit are combined, when the cilium sensor array is pressed, the cilium array sensing unit on the upper portion and the piezoelectric film sensing unit on the lower portion can generate electric signals, when the cilium sensor array is subjected to transverse shear stress, only the cilium array sensing unit on the upper portion can generate electric signals, and the function of separating positive pressure and transverse shear stress is achieved.
(2) When the cilia sensor array is under the action of touch pressure, the cilia array sensing unit at the upper part and the piezoelectric film sensing unit at the lower part generate electric signals; if the sliding sense effect is received, the cilia sensor arrays are bent towards the same side in the sliding process, when the bending reaches the maximum degree, the sliding process is further evaluated through the output signals of the piezoelectric film sensing units, preliminary data processing is carried out on the output electric signals of the upper cilia array sensing units and the output electric signals of the lower piezoelectric film sensing units, then depth analysis is carried out through a multi-sensor data fusion algorithm, and effective distinguishing between the touch sense and the sliding sense is achieved.
(3) The cilium array sensing unit simulates the cilium action mechanism of animals, the piezoelectric cable structure is used for reference, the piezoelectric sensing layer is coated on the outer surface of the inner electrode, the protective layer of the protective sleeve is designed on the outer layer, the reliability of the cilium sensor is further enhanced, and the sensitivity of the sensor is effectively improved.
(4) The piezoelectric film sensing unit is additionally provided with the bump layer structure on the basis of adopting a sandwich structure, so that the sensitivity and the measurable range of the sensor are further improved.
(5) The sensor has the advantages of high sensitivity, good stability, strong anti-interference capability, high flexibility, long service life and the like, and has application value in the fields of bionic touch sensing, biomedical treatment and mechanical touch sensing.
(6) By adopting polymer encapsulation, the touch sensor can keep good flexibility, is acid-resistant, corrosion-resistant and aging-resistant, and has good protection effect on the sensor.
Drawings
FIG. 1 is a schematic structural diagram of a multi-information flexible tactile sensor of a bionic cilium structure provided by the invention;
figure 2 is a schematic view of the structure of a ciliary sensor according to the present invention;
figure 3 is a schematic top view of a ciliary sensor according to the present invention;
FIG. 4 is a block diagram of a multi-channel signal conditioning circuit according to the present invention;
in the figure: 1. the sensor comprises a cilium sensor, 2 a common matrix layer, 3 an upper electrode layer, 4 a piezoelectric thin film layer, 5 a salient point layer, 6 a lower electrode layer, 7 a protective layer, 8 a signal electrode, 9 a grounding electrode, 10 a multi-channel signal conditioning circuit, 11 a signal input terminal, 12 an inner electrode, 13 a piezoelectric sensing layer, 14 a shielding layer and 15 a protective sleeve protective layer.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
As shown in figure 1, the invention provides a multi-information flexible tactile sensor of a bionic cilium structure, which consists of two parts which are longitudinally distributed, wherein the upper part is a cilium array sensing unit, the lower part is a piezoelectric film sensing unit, and the two parts interact with each other.
The cilia array sensing unit comprises 12 cilia sensors 1, which are arranged on a common matrix layer 2 in a rectangular array, the common matrix layer 2 is made of polydimethylsiloxane, and as shown in fig. 2, the cilia sensors 1 comprise an inner electrode 12, a piezoelectric sensing layer 13, a shielding layer 14 and a sheath protection layer 15, which are arranged layer by layer from inside to outside. The inner electrode 12 is made of a conductive metal material, the piezoelectric sensing layer 13 is a PVDF nanofiber film and is uniformly coated on the outer surface of the inner electrode 12, meanwhile, the piezoelectric sensing layer 13 is woven and wrapped by a shielding layer 14 made of a conductive material (copper or aluminum), and the outermost layer is made of a polymer material to form a sheath protection layer 15. The piezoelectric film sensing unit comprises five parts, namely an upper electrode layer 3, a piezoelectric film layer 4, a bump layer 5, a lower electrode layer 6 and a protective layer 7 from top to bottom, wherein the piezoelectric film layer 4 is a PVDF nanofiber film, the bump layer 5 is a processed copper foil, the surface of the copper foil is in an array arrangement hemispherical bump structure, a signal electrode 8 is led out from the upper electrode layer 3, and a grounding electrode 9 is led out from the lower electrode layer 6. The multi-channel signal conditioning circuit 10 is provided with signal input terminals 11 corresponding to each cilium sensor 1 one by one, signal lines led out from inner electrodes 12 of each cilium sensor 1 are respectively connected to the corresponding signal input terminals 11 of the multi-channel signal conditioning circuit 10, a leading-out wire of a signal electrode 8 is connected to one of the signal input terminals 11 of the multi-channel signal conditioning circuit 10, and a grounding lead led out from a shielding layer 14 and a leading-out wire of a grounding electrode 9 are commonly connected to a grounding terminal of the multi-channel signal conditioning circuit 10.
When the cilia sensor array is subjected to positive pressure, the cilia array sensing unit at the upper part and the piezoelectric film sensing unit at the lower part both generate electric signals, and when the cilia sensor array is subjected to transverse shear stress, only the cilia array sensing unit at the upper part generates the electric signals, so that the function of separating the positive pressure from the transverse shear stress is realized; when the cilia sensor array is under the action of touch pressure, the cilia array sensing unit on the upper portion and the piezoelectric film sensing unit on the lower portion can generate electric signals, if the cilia sensor array is under the action of sliding, the cilia sensor array can be bent towards the same side in the sliding process, when the cilia array sensing unit is bent to the maximum degree, the cilia array sensing unit outputs the electric signals, the electric signals cannot be changed, the sliding process needs to be further evaluated through the change of the piezoelectric film sensing unit output electric signals, the cilia array sensing unit output electric signals and the piezoelectric film sensing unit output electric signals are subjected to signal preprocessing through the multi-channel signal conditioning circuit 10, then the digital signals after analog-to-digital conversion are subjected to depth analysis through a multi-sensor data fusion algorithm, and effective distinguishing of the sensor between touch and sliding is achieved.
Figure 3 is a schematic top view of a cilia sensor, with the structures of the layers centered on the inner electrodes, the layers being wrapped and connected without gaps.
The multi-information flexible tactile sensor with the bionic cilia structure has the remarkable advantages of high sensitivity, good stability, strong anti-interference capability, high flexibility, long service life and the like, and can be applied to emerging fields of embedded and transplantable biosensors, medical health detection equipment, robot tactile sensors, robot electronic skins and the like.
The following describes a method for preparing a multi-information flexible tactile sensor of a bionic cilium structure, which is provided by the invention:
(1) preparation of the common matrix layer 2
Fully mixing the PDMS prepolymer with a curing agent in a ratio of 10:1 to prepare a PDMS solution, putting the PDMS solution into a vacuum drier, and removing bubbles generated in the stirring process; then, the PDMS solution is coated on the surface of the silicon chip in a spinning mode, the front rotating speed is controlled to be 1000r/min, the duration time is 50s, the rear rotating speed is 5000r/min, and the duration time is 60 s; and then placing the PDMS solution in an environment of 100 ℃ for heat curing for 50 minutes, peeling to obtain a PDMS film with the thickness of 200 micrometers, and cutting the PDMS film into the sizes of 2cm in length and 2cm in width to obtain the public matrix layer 2.
(2) Preparation of the cilium sensor 1
Selecting a high-conductivity silver column as an inner electrode, selecting a PVDF nanofiber film with the radius of 0.5mm and a right circular cross section, uniformly coating the outer surface of the silver column with a PVDF nanofiber film with the thickness of 200 microns, using a copper mesh woven by copper wires as a shielding layer 14, spirally winding and wrapping the outer side of the PVDF nanofiber film, preparing a PDMS solution from the PDMS prepolymer and a curing agent according to the proportion of 8:1, integrally positioning the PVDF nanofiber film wrapped by the copper mesh and the inner electrode in a designed cilium structure mold, adding the PDMS solution into the mold, curing for 3 hours at 60 ℃ to prepare the cilium sensor 1, leading out a signal wire at the inner electrode, leading out a grounding lead at the shielding layer 14, and repeating the processes to prepare 12 cilium sensors 1.
(3) Bonding of
Picking up the 12 cilia sensors 1 flatly using a water-soluble adhesive tape, adhering the bottoms of the 12 cilia sensors 1 to the water-soluble adhesive tape completely, exposing the top of each cilia sensor 1, and depositing a layer of chromium and a layer of silicon dioxide on the exposed surface of each cilia sensor 1; the public matrix layer 2 is placed in a plasma cleaning machine, surface oxidation treatment is firstly carried out by oxygen to realize the cleaning effect, then the water-soluble adhesive tape adhered with 12 cilia sensors 1 and the public matrix layer 2 are quickly bonded into a whole in a hot-pressing mode and then placed in water to enable the water-soluble adhesive tape to be completely dissolved, and therefore the cilia array sensing unit is obtained.
(4) Preparation of piezoelectric thin film sensing unit
Selecting a PVDF nanofiber thin layer with the thickness of 500 microns, and cutting the PVDF nanofiber thin layer into sizes of 2cm in length and 2cm in width; processing a copper foil with the thickness of 100 microns through a specific die, arranging hemispherical bump structures on the surface of the copper foil in a rectangular array mode, wherein the distance between every two bumps is 1mm, and the cutting size is 2cm in length and 2cm in width to obtain a bump layer 5; covering an aluminum electrode layer with the thickness of 100nm on the upper surface of the piezoelectric thin film layer 4 by a vacuum evaporation method to form an upper electrode layer 3, and covering an aluminum electrode layer with the thickness of 100nm on the lower surface of the salient point layer 5 by a vacuum evaporation method to form a lower electrode layer 6; leading out a signal electrode 8 at the upper electrode layer 3 and leading out a grounding electrode 9 at the lower electrode layer 6 in a conductive silver adhesive bonding mode; and finally, packaging and solidifying the lower part of the lower electrode layer 6 by using a polyethylene glycol terephthalate material to form a protective layer 7, so as to manufacture the piezoelectric film sensing unit.
(5) Preparation of multichannel signal conditioning circuit
The multichannel signal conditioning circuit 10 includes a charge conversion circuit, a voltage amplification circuit, a low-pass filter circuit and an analog-to-digital conversion circuit, and from front to back, the functions of charge/voltage signal conversion, amplification filtering and analog-to-digital conversion are respectively realized, and 13 signal input terminals 11 and 1 ground terminal are welded at the same time, so that the multichannel signal conditioning circuit 10 is obtained.
The signal lines led out from the inner electrodes 12 of the 12 ciliary sensors 1 and the lead-out lines of the signal electrodes 8 of the piezoelectric thin film sensing units at the lower part are respectively connected to the signal input terminals 11 corresponding to the multi-channel signal conditioning circuit 10, and the ground lead-out lines led out from the shielding layer 14 and the lead-out lines of the ground electrodes 9 are commonly connected to the ground terminal of the multi-channel signal conditioning circuit 10. The original charge signal is conditioned into a voltage signal in a certain range through a charge conversion circuit, a voltage amplification circuit and a low-pass filter circuit, then an analog signal is converted into a digital quantity through an analog-to-digital conversion circuit to be output, the converted digital signal is sent to an upper computer, and a multi-sensor data fusion algorithm is adopted for depth analysis, so that the functions of distinguishing positive pressure/transverse shear stress and touch/slip are realized.
The multi-information flexible tactile sensor with the bionic cilia structure, which is prepared by the method provided by the invention, can effectively distinguish positive pressure from transverse shear stress and can further distinguish the tactile and sliding movement information of an object. Has good application prospect in the fields of medical health detection, robot touch perception, bionic electronic skin and the like.