Stretchable Cable
Overview
We demonstrate how to arrange non-elastic elements (wires, fibers, etc.) in a geometry that can extend to several times its resting length. This can be achieved using existing braiding techniques and materials, eliminating the need for specialized materials or equipment.
Technical Innovation
The resistance of this cable remains constant when stretched, unlike other elastic conductors whose resistance is a bulk or surface property. Since the conducting fiber does not itself stretch, the basic properties of the wire do not change as the braid is stretched.
Technical Details
Multiple Conductor Configurations
We can use multiple distinct, adjacent conductors and alternating conductors to form transmission lines with predictable impedance
Twisted pairs can be incorporated to increase noise immunity
When a braid containing a balanced transmission line is stretched, the spacing between conductors decreases, and so does the characteristic impedance of the transmission line
Structure and Implementation
The structure can be a single conductor forming a helical wrap around the inner elastomer, without opposing elements
Conductors can be woven into the braid in parallel to form a stretchable ribbon cable
The braid permits definition of transmission line structures:
Twisted pair is formed in the same braid and stays positioned by nature of the braid
As the braid is stretched, the characteristic impedance changes predictably
By sensing the change in impedance, drive electronics can compensate and determine degree of extension
Applications
While braided conductors are already used in cable manufacturing, they haven't previously been employed as structures for extensible electrical interconnects. Traditional applications use individual strands as electrically parallel conductors:
In braided shielding: uninsulated conductors form an effective shield at uniform electrical potential
In Litz wire: insulated conductors form distinct but parallel paths for high-frequency, high-current signals
Advanced Features
An adaptive impedance matching network can be included at each end to provide proper termination and compensate for variation of transmission line impedance as the braid is stretched
Optical fibers may be incorporated into the braid
Credits
Project by Rehmi Post and Kit Waal