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The past and present of flexible pressure sensing technology

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  • Time of issue:2021-06-01 17:16
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【Summary】:Through the response of artificial skin to external stimuli, flexible tactile sensing technology has developed rapidly in the past ten years.

The past and present of flexible pressure sensing technology

(Summary description)Through the response of artificial skin to external stimuli, flexible tactile sensing technology has developed rapidly in the past ten years.

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  • Time of issue:2021-06-01 17:16
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The past and present of flexible pressure sensing technology

from the electrical sensor technology, the sensor from the droplet to the artificial skin


    Through the response of artificial skin to external stimuli, flexible tactile sensing technology has developed rapidly in the past ten years. Among them, flexible pressure sensing, as the most important part of tactile sensing, has been extensively studied and has been applied in the fields of industry, medical and consumer electronics. Traditionally, flexible pressure sensing is mainly based on two mechanisms, optical and electrical. The latter has attracted more attention due to its advantages of higher device flexibility, easy integration and simple structure. From electricity (Iontronic) is a recent development of a new sensing mechanism, which changes by measuring the ion under pressure - ultracapacitor size of the electronic value of the electric double layer, thereby recording the pressure values. Compared with other sensing mechanisms such as piezoresistance, pressure capacitance, piezoelectricity, and triboelectricity, ionization sensing is considered to have extremely high pressure response sensitivity, signal-to-noise ratio, anti-interference, pressure resolution, etc., in addition to Such as unique high transparency, wide dynamic and static force response and other characteristics .


    The former city face only so-called flexible sensor comparison MEMS pressure sensor, not really flexible pressure sensor device . The invention of ionized sensing technology represents the birth of true flexible sensing technology. This year is the tenth year that the ionization tactile sensing technology has been proposed for the first time in the world. It is also the fourth type of true flexibility, true touch, ultra-thin, and highly sensitive ionization force transmission after piezoresistive, capacitive, and strain gauge type. The tenth anniversary of the birth of sensor technology .


    Recently, from the electric tactile sensing technology inventor, California University of Medical Engineering, Davis bio of Professor Pan Tingrui joint Chinese Academy of Sciences Associate Professor Chang-yu of the Shenzhen Institute of Advanced Technology, Dr. Wang Liu Southern University of Science and Technology, Guo Chuan fly Associate Professor , etc. in international journals top material published on materials Advanced " First Decade of Iontronic Sensing: Sensors to the From Droplet Flexible Electronics " invited review articles . This article summarizes the development of ionization tactile sensing technology, and conducts an in-depth analysis and introduction of ionization mechanism from four aspects: pressure response mechanism, ionization functional materials, pressure response structure, and application of ionization technology. The future development of the electric mechanism proposes a vision and direction .


    What is ionized tactile sensing technology? What new features does this technology have? What product innovations will it trigger? Which industries will it promote? Today, we will unveil the mystery of the voltage-force sensing technology .    




Exploring Ionization Technology  --  Technical Innovation Caused by a Drop of Water 



The birth of ionization sensing technology
    The invention of the ionization sensor technology started when Professor Pan Tingrui observed the water droplets on the lotus leaf that vibrated with the breeze. Out of academic sensitivity, Professor Pan immediately realized that this is a superhydrophobic surface. The liquid-solid interface has mechanical instability, and even small disturbances can bring great instability. If the magnitude of the force can be judged through this instability, a force sensor with ultra-high sensitivity can be obtained.
    After repeated experiments and attempts by Professor Pan and his team’s colleagues, they were pleasantly surprised to find that this flexible sensing interface not only exhibits the characteristics of a supercapacitor, but its capacitance is proportional to the pressure applied to this simple-structured droplet sensor. Major breakthrough. What's more exciting is that the capacitance value is much higher than that of traditional parallel plate capacitors. The capacitance noise of the general environment is generally tens of pF; the measurement range of the traditional parallel plate capacitor is only tens of pF, and it is extremely susceptible to parasitic capacitance and environmental noise. However, the capacitance value of this droplet sensor is as high as μF level (1 μF = 10 ^ 6 pF)!
    In the end, Professor Pan and his colleagues confirmed that this ultra-high capacitance value is due to the formation of a layer of ionic-electron interaction EDL electric double-layer capacitor between the electron-conducting electrode and the ion-conducting electrolyte. The new pressure sensing principle is named Iontronic Sensing. The ionization sensing technology was born .




Figure 1 Four aspects of the pressure response mechanism of ionization sensing mechanism, ionization functional materials, pressure response structure and technical application and their main classifications


Explore the ionization sensing mechanism and pressure response mechanism
    The capacitance value of the traditional parallel plate capacitor is often affected by several common factors of the area, distance, and dielectric constant of the parallel plate. The electric double layer capacitance is different, and its capacitance value is most related to the contact area between the interface. The pressure is different, and the contact degree of the ionization interface is different, which affects the capacitance value of the electric double layer .
   In view of the mechanism of separation voltage and force response, Professor Pan and his team have developed different pressure response theoretical formulas, which provide an important theoretical basis for the optimization of sensor performance. Professor Pan and his team also started from theoretical formulas to study the influence of sensor structure design on sensor performance, especially sensitivity. For example, in the structural bending mode, how structural parameters such as the thickness of the electrode layer and the height and width of the cavity affect the pressure response of the sensor. By adjusting the engineering parameters in theoretical formulas of different principles, the sensor performance, such as sensitivity and range, can be controlled in a directional manner. The theoretical breakthrough has made it possible to realize the real commercialization of ionization sensing technology.


Ionic functional materials everywhere
    The ionization sensor is generally composed of electrodes with movable electrons and a layer of functional materials with movable ions. Ionic functional materials are mainly divided into three categories: liquid ionic materials, solid ionic materials and natural ionic materials. Among them, liquid ionic materials can be divided into two types: water-based electrolyte and organic electrolyte. Because it is in liquid form, ions move faster, so it has high sensitivity. But because it is liquid, there may be a risk of leakage and volatilization. The solid ionic material does not have the problem of liquid leakage and volatilization. Solid ionic materials can be divided into ionic gels, polyelectrolytes and ionic composite materials. Ionic composite materials mainly refer to non-ionic substrates such as cloth and paper, which can become ionic materials after simple modification. For example, ion fiber cloth, ion paper, etc. The existence of ion composite materials greatly expands the form and characteristics of ionizing tactile sensors. The third category of natural ionic materials refers to materials that are naturally ionic in nature and life without modification, such as skin. This material is the advantage of the principle of ionization. Using these natural ionic materials, the sensing structure can be directly incorporated into it, greatly simplifying the structure .
   It is worth noting that the ionization sensor technology invented by Professor Pan can be directly applied to various contact materials without being restricted by materials, especially in a large number of natural materials. Because the functional material layer is selected as ionic materials, and ionic materials exist widely in nature, the ionization sensor can be integrated into these materials with an extremely simple structure; at the same time, for some non-ionic materials, only simple ionization modification is required. , It can make a variety of objects in life obtain tactile sensing function. What is exciting is that this method of ionization transformation is universal. Choosing the right ionizing material can also make the sensor obtain extremely high transparency, which is also the great advantage of ionizing sensor compared with other principle sensors. Therefore, the ionization sensor technology has the physical characteristics of real flexibility, ultra-thin, high light transmission and wide application characteristics. The dream of electronic skin surpassing human skin will no longer only exist in science fiction feature films .




The future is here-Ion-electric tactile sensing technology leads product and application innovation



    In summary, due to its own technical principles, ionized sensing has technical advantages that other tactile and pressure sensing technologies cannot match. The flexible characteristics of the ionization sensor technology can subvert the rigid physical form of traditional information devices and systems, and realize the efficient integration of information with people, objects, and the environment. Realize the flexibility of information acquisition, processing, transmission, display and energy, and better realize the interconnection of everything. Ionization sensing technology has the characteristics of true flexibility, ultra-thin, high light transmission, high signal-to-noise ratio, and high environmental immunity. Due to its unique and natural technical characteristics, the principle of ionization sensing has quickly taken a place in the field of flexible pressure sensing, and has led product innovation in application fields such as environmental interaction, health monitoring, and motion recognition. For example, from a flexible electrically mass sensor can be attached to the whole flexible fabric having ultra-low power, to support a variety of wearing styles (shoes, wrist, socks), and therefore can be used for pulse wave, heart rate, respiration and blood pressure continuously Trends Therefore, it can be used for 7/24 physical sign monitoring of the human body; wearable gloves based on ionization sensing fabric can accurately obtain the pressure distribution of the grasping action; the flexible sensor integrated into the tongue can directly measure the number of steps and steps Frequency and other exercise data, pulse wave, respiratory wave and other physiological data, and calculate blood pressure, cardiovascular health, etc. through algorithms; safety helmets equipped with flexible sensors can not only detect the actual wearing of the helmet, but also monitor the wearer’s Vital signs, especially in special industries such as official business or mines, ensure the safe operation of workers; multi-point sensor arrays based on skin ion functional materials can measure muscle movements brought about by different gestures to complete sign language recognition. Technological innovation has led to the diversified innovation of products and applications, and solved the pain points of more industry applications, thereby contributing to the rapid development of the industry.




Always on the road-Ion-electric sensing technology empowers tactile sensing technology to help the industry develop rapidly



    With various industries gradually increased demand for multi-dimensional perception, related to the human sense of touch to be overcome flexible / noise / sensitivity encounter a problem, from the electrical sensing technology truly enabling touch sensing technology, promote industry, health, consumer costs Breakthrough and rapid development in electronics and other industries.


     Take the medical and health industries as an example, touch is a precise way to accurately know the vital signs of the human body. The disconnected flexible sensor greatly improves the pulse diagnosis accuracy of the pulse diagnosis instrument, allowing the wisdom of traditional Chinese medicine to benefit the common people. From electrical flexible sensor can be energized to healthy equipment, such as gait and plantar pressure wisdom trails, pedestrian detection distribution, learn suspected of having a neurodegenerative disease or recovery from illness, etc., from the health insurance industry Health evaluation and rehabilitation evaluation are more objective. The current medical robots or medical devices do not have the ability of tactile detection and tactile feedback, which puts forward higher requirements for the detection of many diseases and the manipulation of medical devices. Ion-electric tactile sensor arrays can give various medical devices the power of tactile perception, so that they can more accurately analyze the tissues and lesions in the human body and achieve better collaboration with doctors, which has a wide range of clinical application scenarios.


    Disconnected flexible sensor can make any material surface energized to be tactile controllable, and its array-type sensor layout can provide a more natural input method, so it can be widely used in simple weighing, gesture input and other programs, so that people and objects The interface between objects and objects has a sense of touch.



    Taking the production and manufacturing industries as examples, ensuring accurate pressure values ​​is crucial. Because the accurate pressure value can not only increase the life of the equipment, but also increase the production yield and improve the safety of the production line. Therefore , obtaining pressure value and pressure distribution data has become a key factor in optimizing and improving industrial efficiency. However, traditional pressure-sensitive paper is not only expensive, but can only give qualitative results, that is, the pressure distribution is uniform or uneven. A series of problems such as the inability to carry out quantitative analysis, the inability to rely on imports, independent intellectual property rights, and the inability to guarantee full inspection due to high prices, have resulted in traditional pressure detection methods that cannot meet the requirements of the rapid development of China's production and manufacturing industries. The pressure distribution measurement system based on ionization sensor technology can not only fully understand the size and distribution of the force, but also record the dynamic trajectory of the force change in real time. Therefore, the application of ionization technology can realize real-time monitoring of industrial manufacturing processes, reduce quality inspection costs, improve quality inspection coverage and efficiency, improve manufacturing, increase industrial yield, and improve production line operation safety. Ionization technology can also be integrated into industrial equipment such as manufacturing, empowering industrial equipment to become intelligent.


    In terms of technology, high signal-to-noise ratio ionization sensor signal processing, ionization sensor temperature and humidity stability research, research and development of implantable ionization sensor devices, etc. will also be the future power point of ionization sensor technology. . The continuous improvement and improvement of technology will enhance the competitiveness of the ionization technology itself, ultimately benefiting and assisting industry development and product innovation.


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