Stretchable Cable
Overview
We show how to arrange non-elastic elements (wires, fibers, etc.) in a geometry that can extend to several times its resting length. Furthermore, this can be done with existing braiding techniques and materials, obviating the need for specialized materials or equipment.
Technical Innovation
Electrical Properties
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
Multiple distinct, adjacent conductors and alternating conductors can form transmission lines with predictable impedance
Twisted pairs increase noise immunity
Technical Details
Construction Methods
Single conductor forming a helical wrap around the inner elastomer
Multiple conductors woven into the braid in parallel to form a stretchable ribbon cable
Optical fibers may be incorporated into the braid
Media
Cable assembly process showing the braiding technique.
Microscope image of the braided structure.
3D visualization of the braiding pattern.
Technical Diagrams
Impedance characteristics during stretching.
Cross-sectional view of the braid structure.
Twisted pair conductor geometry.
Technical Innovation
Novel Aspects
Braided conductors, while known in cable manufacture, have not appeared in prior art as structures intended to provide extensible electrical interconnects
Traditional braided conductors are used as electrically parallel conductors:
In braided shielding: uninsulated to form an effective shield at uniform potential
In Litz wire: insulated to form distinct but parallel paths for high-frequency, high-current signals
Impedance Characteristics
When a braid containing a balanced transmission line is stretched, the spacing between conductors decreases
The characteristic impedance of the transmission line changes predictably
An adaptive impedance matching network may be included at each end to:
Provide proper termination
Compensate for variation of transmission line impedance as the braid is stretched
Applications
Wearable electronics
E-textile systems
Medical devices
Flexible electronics
Transmission line systems
Stretchable interconnects
Sensing Capabilities
By sensing the change in impedance, drive electronics can:
Compensate for stretching effects
Determine degree of extension of the braid
Maintain signal integrity