Simultaneous Detection of CO and NH3 Gases at Room Temperature with an Array of ZnS Chemiresistive Sensors and the Superposition Principle.

Simultaneous detection of multiple toxic gases in the air using room temperature gas sensors is significant in low-power environmental monitoring applications. However, the low-temperature resistive gas sensors are sensitive to more than one gas, and thus, an array of gas sensors and high energy-consuming machine learning algorithms are required to predict the concentrations of the individual gases in mixed target gas. Here, we report a computationally less intensive method to predict the composition of the target gases using linear gas sensors. A sensor array consisting of two ZnS resistive gas sensors biased at different voltages in conjunction with the superposition principle is used to predict the concentration of individual gases in the binary mixture of NH3 and CO present in the air. Further, the effect of humidity on response is mitigated by formulating the sensitivity of the sensors as a function of relative humidity. The proposed algorithm predicted the concentration of the individual gases in mixed gas with a maximum absolute error of ∼15% irrespective of humidity levels, which is practically allowed in most gas sensing applications. As the superposition principle is a low-power consuming technique, the proposed approach can be used in applications where trace levels of gases in mixed targets need to be detected with energy-efficient methods.

Reduction of the Measurement Time of a Chemiresistive Gas Sensor Using Transient Analysis and the Cantor Pairing Function.

It is vital to measure the concentration of gas quickly in many gas sensing applications. Predicting the steady-state response from the earlier transient response is the economical and viable solution in this regard. However, existing transient analysis approaches either need huge data and computationally intensive algorithms or are inefficient. Here, we described a method to reduce the measurement time of the concentration of CH4 with a chemiresistive gas sensor at room temperature (27 °C). The presented method considers the sensor's response at two fixed time intervals after gas exposure and maps their pairing number to the gas concentration. The proposed method measures the gas concentration in just 30 s from the gas exposure time. As the proposed method can quickly measure gas concentrations, it can be employed in widespread applications where quick quantification of gas is necessary.

Eco-friendly all-carbon paper electronics fabricated by a solvent-free drawing method.

Here we report the fabrication of high-performance all-carbon temperature and infrared (IR) sensors with a solvent-free multiwalled carbon nanotube (MWCNT) trace as the sensing element and commercial graphite pencil trace as the electrical contact on recyclable and biodegradable cellulose filter paper without using any toxic materials or complex procedures. The temperature sensor shows a large negative temperature coefficient of resistance (TCR) in the range of -3100 ppm K(-1) to -4900 ppm K(-1), which is comparable to available commercial temperature sensors, and an activation energy of 34.85 meV. The IR sensor shows a high responsivity of 58.5 V W(-1), which is greater than reported IR sensors with similar dimensions. A detailed study of the conduction mechanism in MWCNTs with temperature and the photo response with IR illumination was done and it was found that the conduction is due to thermally assisted hopping in band tails and the photo response is bolometric in nature. The successful fabrication of these sensors on cellulose filter paper with a comparable performance to existing components indicates that it is possible to fabricate high-performance electronics using low-cost, eco-friendly materials without the need for expensive clean-room processing techniques or harmful chemicals.