The Textile Silicone Hybrid Sensor is a capacitive sensor. When the electrode area and the dielectric thickness change in response to applied strain, a capacitance change occurs. Consequently, measuring the change in capacitance can be used to determine the magnitude of an applied strain. A further discussion of the working principle can be found in Step 5 of the Fabrication Section. 


The electrode layers are knit fabric made from silver coated nylon/spandex blend yarns giving the fabric conductive properties. The dielectric layer is a silicone elastomer that exhibits high stretchability (up to 900%) and low viscosity, allowing easy penetration into fabric micro structures. The soft sensor is also pliable for comfortable applications on the human body as well as strong enough and robust for repeated wear and tear.


Manufacturing Method

To create the most repeatable sensor this documentation set uses a scale-able batch manufacturing process, which can produce a more accurate, robust, sensitive, and repeatable sensor. By fabricating in bulk, the process allowed for almost identical sensors with consistent baseline capacitance values to be produced. For example five such sensors cut from the same larger mat had 174 pF ± 1.41 as values for their initial capacitance. This process produces large sensor mats that can then be cut into size as determined by the application; for example, a small linear sensor for a pinky finger and a large curved sensor at the hip. A more detailed process for producing this sensors is described in the Fabrication Section of this documentation set. 



Variations in Construction

The sensor created in this documentation set is made using Ecoflex 00-30 and a MedTex 130 silver conductive knit spandex, however these materials are not the only ones that can use to create hybrid sensors. Substituting the Ecoflex for a harder silicone will create a stiffer yet fully functional sensor while substituting for a more softer silicone will result in a more flexible sensor. This sensor described here has a reliable working range up to 100% strain but if your application requires larger strains a conductive knit fabric with higher stretch properties can be used. No matter your sensor construction you will have to calibrate your sensor to understand its specific force-strain relationship.

Additional layers can be added to make the sensor more robust in environments where it may be subject to increased electrical interference. Simply adding an extra layer of conductive fabric for shielding will reduce the amount of EM interference and fringe fields from anything conductive (including biological entities). 

The sensor may also be completely encapsulated within silicone elastomer to modify its mechanical properties and provide hermetic sealing for aquaus environment applications as seen in the figures below. 

encapsulation2.png encapsulation-03.png