Carbon-nanotube-based resonant-circuit sensor for ammonia

Abstract

We present the design and development of highly sensitive and fast-responsive microwave resonant sensors for monitoring the presence of ammonia gas. The sensor consists of a circular disk electromagnetic resonant circuit coated with either single- or multiwalled carbon nanotubes that are highly sensitive to adsorbed gas molecules. Upon exposure to ammonia, the electrical resonant frequency of the sensor exhibits a dramatic downshift of 4.375 MHz. The recovery and response times of these sensors are nominally 10 min. This technology is suitable for designing remote sensor systems to monitor gases inside sealed opaque packages and environmental conditions that do not allow physical wire connections.

Carbon nanotube‐sensor‐integrated microfluidic platform for real‐time chemical concentration detection

“…With the rapid progress and improvement of nanotechnology, sensors fabricated by using carbon nanotubes (CNTs) as the sensing element were reported to give electrical response to different chemicals, such as NO 2 , NH 3 , CO, H 2 , and O 3 for gas detection [4][5][6][7][8][9]. CNT sensors provide high sensitivity, low power, and portable tools for in situ chemical analysis.…”

Nanotechnology Enables Wireless Gas Sensing

“…Although the use of CNTs in practical applications was limited up to 2005 due to issues with fabrication and repeatability, lately they have been used in many domains, ranging from gas sensing and shielding to nanotube-based antennas and RF interconnects [2]- [13]. It has to be stressed that CNT mixtures/composites have been found to have electrical properties highly sensitive to extremely small quantities of gases, such as NH 3 , carbon dioxide (CO 2 ), nitrogen oxide (NO x ), etc., at room temperatures. CNTs have a very fast response time [2], which is a key feature for sensitive gas sensors.…”

“…NH 3 is primarily a concern in areas of high agricultural activity because it is a natural waste product of livestock whereas it can also be a product of industrial sources, including the manufacturing of basic chemicals, metals, and textile products as well as automotive emissions. High levels of NH 3 can result in irritation to the eyes and respiratory tracts of humans and can negatively impact wildlife, livestock, and agricultural health. NO 2 is also a potentially toxic gas that can lead to respiratory symptoms in humans and detrimentally influence the growth of agriculture.…”

“…One of the most important applications of such gas sensors involves the ability to monitor the leakage of nitrogen-based gases such as ammonia (NH 3 ) and nitrogen dioxide (NO 2 ) in the air because these chemicals adversely affect human and environmental health [5]. NH 3 is primarily a concern in areas of high agricultural activity because it is a natural waste product of livestock whereas it can also be a product of industrial sources, including the manufacturing of basic chemicals, metals, and textile products as well as automotive emissions.…”

Multifunctional meshed carbon nanotube thread patch antenna

“…Additionally, recent research has shown that the permittivity, ε r , and conductivity, σ, of a CNT is temporarily altered when it is subjected to certain gases, especially oxidizing/reducing gases such as NH 3 (ammonia) and O 2 (oxygen) [10]. This reaction has been exploited as a gas sensor by incorporating a thin layer of either randomly scattered SWNTs [11][12][13][14] or aligned multiwall nanotubes (MWNTs) [15] as part of a microwave resonator. The resonator center frequency shifts in direct response to the change in the permittivity of the CNT layer that occurs due to the presence of a reacting gas.…”