Wearable product technology breakthrough: flexible capacitance sensor innovation process
recently, a highly sensitive flexible capacitance sensor was created by a research team from the Weiss bioinspired Engineering Institute of Harvard University and John Paulson engineering and application department, our school of technology excellence. It is composed of silica gel and fabric, which can accurately and freely monitor the movement of the human body with the movement and bending of the human body
nowadays, from heart rate monitors to virtual reality helmets, a variety of wearable technology products have shown explosive growth and popularity in the consumer electronics market and research field
however, in order to detect and transmit data, most of the electronic sensors used in these wearable devices are made of hard and inflexible materials, which not only limits the natural movement of the wearer, but also affects the accuracy of data collection
recently, a team of researchers from the Wyss Institute for biologically inspired engineering at Harvard University and the John Paulson School of engineering and Applied Sciences (SEAS) created a highly sensitive flexible capacitive sensor, which is composed of silica gel and fabric, and can accurately and freely detect human motion as the human body moves and bends
breakthrough in wearable products: innovative technology of flexible capacitive sensors
this research paper was published in the latest issue of advanced materials technology, and the protocol has become a part of the flexible robot toolkit of Harvard biological design laboratory
the capacitive sensor is formed by a layer of silica gel sheet (a material with poor conductivity) sandwiched between two layers of silver plated conductive fabric (a highly conductive material) like a sandwich
this sensor records human motion by measuring the change of capacitance. The so-called capacitance, that is, the ability to contain charges, also refers to the electric field between two electrodesDaniel Vogt, a research engineer at Weiss Institute and one of the co authors of the paper, said:
"when we pull the sensor at one end of the sensor and apply tension, the silicone layer will become thinner and the conductive fabric layer will be closer, so the capacitance of the sensor will be changed in a way proportional to the applied tension. Therefore, we can measure how much the shape of the sensor has changed."
the superior performance of this hybrid sensor comes from its new manufacturing process. Through this manufacturing process, the fabric is connected to both ends of the silicone core through another layer of liquid silicone. This method allows silica gel to fill the air gap in the fabric and mechanically lock it on silica gel, thereby increasing the surface area used to disperse tension and store capacitance
this mixture of silica gel and fabric improves the sensitivity to motion by making full use of the characteristics of these two materials. When it is lifted, such imports are decreasing; 2. The strong, tough and interlocking fabric fibers can help silica gel limit its deformation; When the tension is removed, silicone can help the fabric restore its original shape. Finally, the soft thin wire is always connected to this conductive fabric through heat sealing tape. The most common is optical or electromagnetic sensor material, so that the electrical information from the sensor can be transmitted to the circuit without a hard and cumbersome interface
the team evaluated the new sensor they designed through tension experiments. In the experiment, researchers made various measurements when the sensor was stretched by the electromechanical test device. Generally speaking, when an elastic material is stretched, its length increases and its thickness and width decreases, so the total area of the material remains unchanged, that is, its capacitance remains unchanged. Surprisingly, researchers found that when the sensor was stretched, the conductive area increased and the capacitance was larger than expected. Asli Atalay, the lead author of the paper and a postdoctoral researcher at Weiss Institute, said:
"the capacitive sensor based on silica gel has limited sensitivity due to the natural characteristics of the material. However, after embedding silica gel into conductive fabric, a matrix is created, which can prevent the silica gel from shrinking laterally, thus improving the sensitivity to the bare silica gel we tested."
this mixture sensor can measure the increase of capacitance within 30 milliseconds of tension application and the physical change is less than half a millimeter, and effectively capture human motion. In order to test this ability in the real world, the researchers integrated them into a glove to measure delicate hand and finger movements in real time. When the fingers move, the sensor can successfully detect the change of capacitance and indicate the change of their relative position with timeVanessa Sanchez, a graduate student of sea biological design laboratory and one of the co-authors of the paper, explained:
"the higher sensitivity of our sensor means that it has the ability to distinguish more subtle movements, such as moving fingers slightly from one end to the other, rather than simply opening the whole hand or clenching the fist."
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John EB, the author of the paper, the core teacher of Weiss Institute and associate professor of sea engineering and applied science, said:
"we are very excited about this sensor. Because it is made of textiles, it is naturally suitable for integration into fabrics to become 'intelligent' robot clothing."Ozgur Atalay, one of the coauthors of the paper and a postdoctoral researcher at Weiss Institute, said:
"in addition, we have designed a unified mass production process, so that we can create custom shaped sensors, share unified characteristics, and can quickly manufacture according to a given application."
although this research is still in the proof of concept stage, the team is full of confidence in the future development direction of this technology. Walsh said:
"This research represents that our interest in using fabric technology in robot systems is growing, and we see broad prospects for capturing movement 'in the outdoor environment', such as sportswear that can monitor physical activity, or flexible medical devices that monitor patients at home. In addition, these sensors, combined with fabric based flexible brakes, can enable new robot systems to truly imitate clothing."