The detection of ammonia vapor in the air is always challenging and in great demand, with the main issues are their low sensitivity. In this contribution, we developed a quartz crystal microbalance (QCM) gas sensor to detect ammonia vapor in the air using electrospun polyacrylonitrile (PAN) nanofiber mixed with citric acid (CA) as its sensing material. The nanostructured morphology of the as‐prepared nanofiber sensors was confirmed using scanning electron microscopy (SEM), while the existence of the CA in the PAN/CA nanofiber confirms using Fourier transform infrared (FTIR) spectroscopy. The average diameter of the PAN and PAN/CA nanofiber sample was found in the range of 260 nm to 307 nm. The highest sensor sensitivity was obtained by the PAN/CA4 nanofiber sensor with the value of 0.28 Hz/ppm, increasing almost 4 times compared to the unmodified PAN nanofiber sensor (0.075 Hz/ppm). Moreover, the sensor also shows good reversibility, fast response/recovery time, and excellent repeatability sensing performance. The addition of CA into the PAN nanofiber structures enhances the sensor sensitivity, probably due to the enrichment of carboxyl group at the sensor surface. This work could become a promising and alternative way to enhance the sensitivity of a QCM gas sensor modified with polymers doped with suitable compounds.
Determination of the specific toxic, harmful, or flammable gases concentration i.e. butane, cannot be done directly. It requires devices that can do this measurement without any direct contact between the gas and human (observer) i.e. gas sensors. These sensors are typically used in security systems or early warning system. This research is about design and development of a gas sensor based on acoustic resonance. The sensor that has been developed is acoustic resonator based sensor, with two speakers as the sources of acoustic vibrations. This sensor is made to work at its resonance frequency. Since the resonance frequency of acoustic resonator is influenced by the speed of sound in the acoustic resonator, and the speed of sound is influenced by the density and concentration of the gas in the acoustic resonator, the changing of gas concentrations will cause resonance frequency shifting of the acoustic resonator. So, by taking measurement of resonance frequency shifting of resonator, gas concentration can be determined. This research was conducted in four stages, the first stage is designing of acoustic resonator, the second stage is manufacturing and initial testing of the acoustic resonator, the third stage is conditioning stage to make acoustic resonator works at its resonance frequency automatically, and the final stage is the testing stage of acoustic resonator using butane. Based on the research conducted, it can be concluded that the acoustic resonator system can work accurately and precision to detect the changing of butane gas concentration. Absolute error and relative error are relatively small, the largest of absolute error is 7.69% and the largest relative error is 0.47%.
In preliminary research, a system for detecting the flow rate of the gas mixture (N2 and CO2) has been successfully built using acoustic measurements. This detector consists of a speaker as a transmitter of ultrasonic waves, and 3 microphones as a receiver of the ultrasonic waves. The quantity measured in this detection system test is the phase difference of the ultrasonic waves captured by the left and right microphones. The flow rate of the gas mixture will affect the phase difference value between the left and right microphones. With the increase of the flow rate of the gas mixture, the phase difference between the two microphones will increase. The flowrate range tested was between 0 and 0.8 l/min, with a concentration of 20% CO2 in the gas mixture of N2 and CO2. In testing this detection system, the absolute error is 2,4 10-2 l/min.
In this research, an acoustic sensor has been successfully built to measure the concentration of CO2 gas in a mixture of gases (N2 and CO2). The nitrogen and carbon dioxide gases used are ultra-high purity (UHP) gas. The measurement parameter used is the speed of sound by utilizing the phase shift between ultrasonic wave signals that are sent and received continuously. The acoustic method in this research is by using the speaker as an ultrasonic wave transmitter, and the microphone as an ultrasonic wave receiver emitted by the speaker on the gas medium. This acoustic phase shift method is very sensitive to be used to determine the speed of sound on a gas medium. From the sensor testing, the sensor has good linearity in detecting changes in CO2 concentration in the gas mixture. The sensor test results have been validated theoretically and obtained an RMS error of 3.36 (3.36% with a maximum concentration of 100%), this proves that the work of the sensor is in accordance with the theory. In addition to theoretical validation, the work of the sensor has also been validated by looking at the direct relationship between sensor input and output through the inverse function, and an RMS error of 3.51 (3.51% with a maximum concentration of 100%) is obtained. From the overall results obtained, the acoustic CO2 gas sensor that is built can detect changes in CO2 concentrations in the gas mixture accurately, fabrication of the sensor is easy to do, and the costs required in the manufacturing process are cheap.
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