New Electronic Fiber Sensors Said to “Smell” and “Hear”

October 13, 2020 by Luke James

The "invisible" 3D printed fiber sensors could be used to power electronic devices and sensors that are capable of sensing breath and sound.

A device that's able to sense smells, sound, and touch in the way humans do may be one step closer to becoming a reality thanks to the realization of 3D printed electronic fibers in recent research. 

Researchers from the University of Cambridge say they’ve used 3D printing techniques to create these “invisible” electronic fibers, each of which is 100 times thinner than a human hair.  Functioning as sensors, these fibers have capabilities beyond that of conventional film-based sensor devices.

This is according to research that was reported in the journal Science Advances.


Inexpensive and Extremely Sensitive E-Fibers

Small-diameter conducting fibers have unique properties that set them apart from other classes of film-based conducting micro and nanostructures. However, existing fabrication techniques such as chemical growth, wet spinning, and 2D/3D direct printing do not readily allow the assembly of fiber architectures.

This leads to device functions that exploit combinations of the fibers’ unique characteristics: directionality, conductivity, and high surface-area-to-volume ratio. 

To solve this challenge, the Cambridge researchers developed a new printing method that can be used to make non-contact, wearable, portable respiratory sensors that are highly sensitive and cheap to produce. They can also be attached to an electronic device such as a smartphone to concurrently collect breath pattern information, sound, and images. 


The portable trilayer fiber sensor

The portable trilayer fiber sensor can attach to the front camera of a smartphone, positioning the single-layer fiber sensor above the nose. Image (modified) used courtesy of Science Advances

According to the research paper, the fibers could be particularly useful for applications in health monitoring (respiration rate, for instance) and the Internet of Things.

Andy Wang, first author of the study and PhD student at Cambridge’s Department of Engineering, used the fiber sensor to measure the amount of breath moisture that leaked through his face covering during different simulated respiratory conditions like regular breathing, rapid breathing, and coughing.

According to Wang, the fiber sensors outperformed comparable commercial sensors that are currently available, especially when monitoring rapid breathing. 


Inflight Fiber Printing (IFP)

Wang and his colleagues 3D printed the composite fibers, which are made from silver and/or semiconducting polymers, using a method they developed known as inflight fiber printing (IFP).

This technique creates a core-shell fiber structure with a high-purity conducting fiber core wrapped in a thin polymer sheath that acts as a protective coating. It’s very similar to the structure of electrical wires but at a much smaller scale of only a few micrometers in diameter. 


3D printed invisible fibers

The research team’s IFP fiber sensor is attached to a face covering to detect human breath with high sensitivity. Image used courtesy of the University of Cambridge


IFP is carried out at sub-100°C, which creates in situ bonds of thin conducting fiber arrays. These can either be suspended or placed on a surface and require no postprocessing. By optimizing the size of the fibers, the researchers claim they’ve demonstrated a versatile technique for rapid on-circuit creation of small-diameter conducting fibers. 


Making Way for "Floating Electronic Architectures"

As a proof of concept, the researchers produced inorganic, metallic silver fibers from a solution-based reactive synthesis and organic conducting PEDOT:PSS fibers. 

With IFP able to fabricate fibers directly onto a circuit, the researchers say they were able to exploit the functional advantages of the fiber array to explore the novel circuitry architecture afforded by the IFP process. Namely, this process opens doors for the concept of 3D “floating electronic architectures” that merge organic and inorganic fiber materials in the same transparent conducting network. 


Architecture of 3D-layered floating circuit

Architecture of 3D-layered floating circuit. Image (modified) used courtesy of Science Advances

The team is currently looking to develop the IFP method for a number of multi-functional sensors.