Electrical response using nanotubes on a fibrous substrate
Inventors
Han, Jin-Woo • Meyyappan, Meyya
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-10031097-B1
Publication Date
2018-07-24
Expiration Date
2034-03-03
Interested in licensing this patent?
MTEC can help explore whether this patent might be available for licensing for your application.
Abstract
A device produces an electrical signal in response to a stimulus. The device is formed of a flexible substrate including a layer of fibers, for example, paper, and a solution of dispersed carbon nanotubes coated onto and within the fibers, the solution evaporated to leave carbon nanotubes intertwined within the layer of fibers. The carbon nanotubes are functionalized to be optimized for producing an electrical signal for a particular stimulus, where the stimulus includes exposure of the device to a particular gas or vapor. A number of such devices, some or all of which can be different, are housed together, for producing a complex electronic signal, or for sensing any of a wide variety of stimulus.
Core Innovation
The invention provides a device and method for sensing gases or vapors using carbon nanostructures on a flexible fibrous substrate, such as cellulose paper. The device comprises a layer of fibers coated with a solution of functionalized carbon nanotubes that remain intertwined within the fibers after solvent evaporation. These sensors produce electrical signals in response to stimuli, including specific gases or vapors, by exploiting changes in electrical parameters like resistance or conductance.
The problem addressed is that traditional sensors are fabricated on hard substrates like silicon or glass, which are often costly, rigid, and not environmentally friendly. Existing carbon nanotube sensors require sophisticated fabrication processes including heat or vacuum treatments, limiting their flexibility, disposability, and cost-effectiveness. There is a need for low-cost, flexible, foldable, and biodegradable sensors capable of detecting a wide range of gases and vapors with good sensitivity and ease of fabrication.
This invention solves these problems by employing a fibrous paper substrate that is porous and flexible, enabling the carbon nanotubes to form closely entangled networks with the cellulose fibers. Functionalization, for example with carboxylic acid, improves adhesion and sensing characteristics. The paper substrate provides increased contact area and charge transport pathways, resulting in enhanced sensitivity compared to glass substrates. The sensors can be manufactured without heat or vacuum processes, are low cost, disposable, and can be used singly or in arrays to form electronic noses.
Claims Coverage
The patent includes three independent claims covering a system and methods for estimating humidity and gas concentration using a functionalized fibrous substrate with carbon nanostructures. The main inventive features are outlined below.
Functionalized fibrous substrate with intertwined carbon nanostructures
The system or method uses a fibrous substrate having a layer of fibers functionalized with a selected functionalizing substance, with carbon nanostructures intertwined within the fiber layer. These carbon nanostructures include single wall and multi-wall nanotubes. The intertwining is achieved by dispersing nanostructures in volatile solutions and coating the substrate followed by evaporation to solidify the network.
Electrical parameter measurement for sensing
An electrical parameter value (EPV) measurement mechanism is electrically connected to the substrate at spaced apart locations, enabling measurement of an electrical path characterized by parameters such as current, voltage difference, conductance, resistance, impedance, capacitance, or inductance. This mechanism allows detecting changes associated with exposure of the substrate to gases or vapors.
System and method for estimating humidity or NH3 concentration
The system and methods expose the functionalized substrate with intertwined carbon nanostructures to a gas or vapor with unknown relative humidity or unknown NH3 concentration. A processor receives the measured EPV and estimates the humidity or concentration corresponding to the EPV, optionally compensating for relative humidity variations.
Together, these inventive features disclose a flexible sensing system and method employing functionalized nanotube networks on paper-like fibrous substrates, with electrical measurement enabling estimation of humidity or gas/vapor concentration, representing low-cost, foldable, and sensitive sensor technology.
Stated Advantages
Lower fabrication cost compared to prior sensors due to simple solution processing without heat or vacuum treatments.
Enhanced sensitivity due to the porous and rough paper substrate that promotes adhesion and increase in contact area with ambient gases or vapors.
Flexibility and foldability of the sensor substrate while maintaining full functionality.
Use of biodegradable materials enabling rapid degradation in landfill conditions, allowing economical disposable sensors.
Capability to detect a wide variety of gases and vapors, permitting construction of complex electronic noses with multiple sensors.
Lower power operation due to Ohmic characteristics permitting low voltage bias without sensitivity loss.
Faster response and recovery times in comparison to some similar CNT-based sensors on other substrates.
Reduced weight and versatility for disposable, flexible, and biosensor applications.
Documented Applications
Sensing relative humidity (humidity sensor).
Detection and estimation of ammonia (NH3) concentration in gases or vapors.
Sensing other gases and vapors including NO2, with potential for extension to many chemical sensing applications.
Use in electronic nose devices comprising a plurality of sensors for industrial, mining, security, biomedical, food processing, agricultural, and other applications.
Applications requiring low weight, flexible, foldable, disposable, and biodegradable sensor devices.
Interested in licensing this patent?