This paper presents the design and testing of a new CO2 gas sensor that is based on a piezoelectric Langasite (La3Ga5SiO14) crystal resonator with temperature compensation. CO2 gas concentration change can be measured by monitoring frequency shift due to the adsorption of CO2 gas molecules. The sensor is designed and fabricated as a body acoustic wave (BAW) resonator, and coated with Zinc Oxide thin film for sensitivity improvement. Then it is experimentally tested in the laboratory with a self-designed, temperature controlled gas chamber at a wide CO2 concentration range. Moreover, temperature compensation is formulated and tested by applying the dual mode behavior of the Langasite BAW resonator. The sensor shows a good relationship between CO2 gas concentration and its resonant frequency shift. The proposed sensor can be applied at high temperatures particularly in combustion engines, power plant and other high temperature applications.
Development of indigenous CO<sub>2</sub> sensing element operated at an extreme operating temperature (≥ 350 °C) is highly desirable. Use of langasite based surface acoustic wave (SAW) gas sensors is extremely advantageous compared to other commercially available sensors as it can operate at a higher temperature (> 300 °C). Only a few literature reports exist which demonstrated a high-temperature CO<sub>2</sub> gas sensor. In the present study, we have demonstrated CO<sub>2 </sub>sensing properties using langasite based SAW sensors. The temperature-dependent gas sensing characteristics have been determined by observing frequency shift due to the adsorption of gas molecules.
In this paper, a novel torsional resonator is proposed to measure the viscosity of fluids. The proposed measurement system is based on the torsional mode vibration of a metallic cylindrical tube bonded with specially designed twisting-motion-d33-piezo actuators. Two piezoelectric patches are bonded nearer to the fixed end of the cylindrical tube. The one bonded on the upper semicircle of the cylindrical tube is used as a twisting actuator and the other on the bottom semicircle is used as a sensor. The entire system is maintained at its torsional mode resonance frequency by using simple closed loop resonator electronics connected between the two piezo patches. The free end of the resonating cylindrical tube is half immersed into a viscous medium of which the viscosity is intended to be measured in this proposed paper. The torsional resonator experiences an additional viscous drag force-Fd due to the viscosity of the fluid medium which alters its torsional mode resonance frequency (ωT). The value of drag force Fd acting on the torsional resonator will vary depending on the type of viscous fluids in use. The closed loop resonant circuit tracks the change in torsional resonance frequency due to Fd and vibrates the tube with the new resonance frequency whenever the force generated by the viscous fluid changes. The shift in torsional resonant frequency is related to the viscosity of the fluid medium. The analytical model of the vibrating cylindrical tube with viscous fluid is derived and the results are validated with numerical simulation and experimentation. The key enabling concept of this proposed paper is the benefit of torsional mode resonator over the flexural mode resonator i.e., the torsional mode resonator experiences much less viscous damping at its resonance frequency. For the real-time laboratory experimentation, the hollow cylindrical tube with 30cm length and 2.5cm diameter is used. For the actuation and sensing, the MFC M-8528-F1 type (450 fiber orientation) d33 twisting actuator is used. The torsional resonance frequency of the tube in air is 2.5KHz. The proposed fluid viscosity measurement concept is novel and it is found to have better sensitivity and linearity than the flexural mode viscosity measurement system.
CO2 concentration is considered as a very important index for the health of human respiratory system and industrial greenhouse gas emission so that CO2 sensing/monitoring becomes an interesting and challenging topic for both medical purpose as well as environmental engineering application. This paper proposes an innovative CO2 sensor by using the crystal resonators, including both Langasite and Quartz. The sensing principle is based on the frequency-mass effect, by which the adsorption of CO2 molecules on the crystal electrodes (typically Silver, Gold or Platinum) will cause the mass change and thereby determine the frequency shift according to the Sauerbrey equation. Lab experiments are carried out with both Langasite resonator and Quartz Crystal Microbalance. To evaluate their CO2 sensing performance, a mixed gas of CO2 and Nitrogen (reference gas) is applied to both Langasite CO2 sensor (with Platinum electrodes) and QCM CO2 sensor (with Gold electrodes), the concentration of CO2 is adjusted from 0% to 100% with a step of 25% by using a gas proportioner. Experiments results show that both Langasite resonator and QCM have a frequency shift with CO2 concentration change that is associate with the principles mentioned above. Moreover, Langasite resonator performs more accurately, stably and reliably, which is mainly due to the crystal and electrodes properties. The proposed CO2 sensor could be used as convenient breath monitoring for chronic respiratory disease, industrial greenhouse emission monitoring and chemical lab CO2 alarm.
This paper proposes an innovative sensing system for high temperature (up to 150°C) I-beam crack detection. The proposed system is based on the piezoelectric effect and laser sensing mechanisms, which is proved to be effective at high temperature environment (up to 150°C). Different from other high temperature SHM approaches, the proposed sensing system is employing a piezoelectric disk as an actuator and a laser vibrometer as a sensor for remote detection. Lab tests are carried out and the vibrational properties are studied to characterize the relationship between crack depth and sensor responses by analyzing the RMS of sensor responses. Instead of utilizing a pair of piezoelectric actuator and sensor, using the laser vibrometer will enable 1) a more flexible detection, which will not be limited to specific area or dimension, 2) wireless sensing, which lowers the risk of operating at high temperature/harsh environment. The proposed sensing system can be applied to engineering structures such as in nuclear power plant reactor vessel and heat pipe structures/systems.
In recent decades, the I-beam has become one of the most important engineering structural components being applied in areas such as mechanical, civil, and constructional engineering. To ensure safety and proper maintenance, an effective and accurate structural health monitoring method/system for I-beams is urgently needed. This paper proposes a smart sensing system for I-beam crack detection that is based on the energy diffusivity (attenuation) between two individual piezoelectric transducers (PZTs). Sensor (one of the PZTs) responses are analyzed and applied to characterize the health status of the I-beam. Lab experiments are carried out for effective evaluation of this approach in structural health monitoring. The characteristics of crack distribution are studied by calculating and analyzing the energy diffusivity variation of the sensor responses to artificially cuttings to the I-beam. Moreover, instead of utilizing an actuator and a sensor, the system employs a couple of PZTs sensors, which offer the potential for in-field, in situ sensing with the sensor arrays. This smart sensing system can be applied in railway, metro, and iron-steel structures for I-beam health monitoring applications.