Surface Acoustic Wave Sensor Research Articles

Applications of Gas Sensing in Food Quality Detection: A Review.

Food products often face the risk of spoilage during processing, storage, and transportation, necessitating the use of rapid and effective technologies for quality assessment. In recent years, gas sensors have gained prominence for their ability to swiftly and sensitively detect gases, making them valuable tools for food quality evaluation. The various gas sensor types, such as metal oxide (MOX), metal oxide semiconductor (MOS) gas sensors, surface acoustic wave (SAW) sensors, colorimetric sensors, and electrochemical sensors, each offer distinct advantages. They hold significant potential for practical applications in food quality monitoring. This review comprehensively covers the progress in gas sensor technology for food quality assessment, outlining their advantages, features, and principles. It also summarizes their applications in detecting volatile gases during the deterioration of aquatic products, meat products, fruit, and vegetables over the past decade. Furthermore, the integration of data analytics and artificial intelligence into gas sensor arrays is discussed, enhancing their adaptability and reliability in diverse food environments and improving food quality assessment efficiency. In conclusion, this paper addresses the multifaceted challenges faced by rapid gas sensor-based food quality detection technologies and suggests potential interdisciplinary solutions and directions.

Detecting Airborne Pathogens: A Computational Approach Utilizing Surface Acoustic Wave Sensors for Microorganism Detection

The persistent threat posed by infectious pathogens remains a formidable challenge for humanity. Rapidly spreading infectious diseases caused by airborne microorganisms have far-reaching global consequences, imposing substantial costs on society. While various detection technologies have emerged, including biochemical, immunological, and molecular approaches, these methods still exhibit significant limitations such as time-intensive procedures, instability, and the need for specialized operators. This study presents an innovative solution that harnesses the potential of surface acoustic wave (SAW) sensors for the detection of airborne microorganisms. The research involves the establishment of a sensor model within the framework of COMSOL Multiphysics, utilizing a predefined piezoelectric multi-physics interface and employing a 2D modeling approach. Chitosan, selected as the sensing film for the model, interfaces with lithium niobate (LiNbO3), the chosen piezoelectric material responsible for detecting airborne pathogens. The analysis of microbe presence centers on solid displacement and electric potential frequencies, operating within the 850–900 MHz range. Notably, the first and second resonant frequencies are identified at 856 and 859 MHz, respectively. To enhance understanding, this study proposes a novel mathematical model grounded in Stokes’ Law and mass balance equations. This model serves to analyze microbe concentration, offering a fresh perspective on quantifying the presence of airborne pathogens. Through these endeavors, this research contributes to advancing the field of airborne microorganism detection, offering a promising avenue for addressing the challenges posed by infectious diseases.

Investigation of a Polymer-based SAW Sensor to Detect Volatile Organic Compound (VOC)

Two surface acoustic wave (SAW) sensors with polyethyleneimine (PEI) and polyisobutylene (PIB) layers respectively are modelled by using COMSOL Multiphysics software to detect acetone, benzene, and toluene. The main parameter of the SAW sensor is the thickness of the sensing layer, and the concentration of VOCs is varied to study their relationships with regard to the sensitivity of the SAW sensor. Both configurations portrayed the same pattern where the frequency shift and the sensitivity increase as the concentration of VOCs increases. In addition, the two layers have also produced promising results in sensing toluene even as low as 5 ppm which means that both layers are more selective towards toluene when the three VOCs are concurrently presented on the surface of the sensor. The data also shows that in detecting acetone and benzene, the PEI layer showed higher shifts in frequencies as compared to the PIB layer.

Development of Surface Acoustic Wave Sensor Electronic Nose for the Identification of Volatile Compound Organic Using Artificial Neural Network

Development of Surface Acoustic Wave Sensor Electronic Nose for the Identification of Volatile Compound Organic Using Artificial Neural Network

Comparative Analysis of Sinusoidal Oscillators with Surface Acoustic Wave Sensor in the Feedback Loop

Surface acoustic wave sensors can be implemented within the feedback loop of sinusoidal oscillators for detecting pollutants. This detection process involves analyzing the variation of oscillator output voltage parameters, such as amplitude and oscillation frequency. However, each oscillator topology has a distinct operating range concerning frequency and component values. Therefore, a comparative analysis is necessary to determine the oscillator with optimal performance to use with the sensor. To obtain results, a surface acoustic wave sensor model was chosen based on a piezoelectric crystal with a resonant frequency of 117.6 MHz, and three sinusoidal oscillator topologies were used: Pierce, Colpitts, and Clapp. The oscillators were simulated with the sensor model in the feedback loop using the Montecarlo method. The simulation occurred in two steps: individually varying each component by +/- 20% with 250 iterations, and simultaneously varying all components by +/- 20% with 1000 iterations. The variables analyzed in the simulations were amplitude, oscillation frequency, and a new parameter indicating the percentage of time there is an oscillation, termed "robustness." As a result, it was determined that all three oscillators generated oscillations in the output voltage, making them viable for use with the sensor. Furthermore, it was discovered that the Clapp oscillator had a robustness of 84.5%, while the Colpitts and Pierce oscillators had a robustness of 56.3% and 49.9%, respectively. Therefore, based on the results presented in this study, the Clapp oscillator is the optimal choice for use with the surface acoustic wave sensor.

Temperature, pressure, and humidity SAW sensor based on coplanar integrated LGS

This paper presents a surface acoustic wave (SAW) sensor based on coplanar integrated Langasite (LGS) that is fabricated using wet etching, high-temperature bonding, and ion beam etching (IBE) processes. The miniaturized multiparameter temperature‒pressure-humidity (TPH) sensor used the MXene@MoS2@Go (MMG) composite to widen the humidity detection range and improve the humidity sensitivity, including a fast response time (3.18 s) and recovery time (0.94 s). The TPH sensor was shown to operate steadily between 25–700 °C, 0–700 kPa, and 10–98% RH. Coupling issues among multiple parameters in complex environments were addressed by decoupling the Δf-temperature coupling factor to improve the accuracy. Therefore, this work can be applied to simultaneous measurements of several environmental parameters in challenging conditions.

Comparative Study of Leak Detection in PVC Water Pipes Using Ceramic, Polymer, and Surface Acoustic Wave Sensors.

The detection and location of pipeline leakage can be deduced from the time arrival leak signals measured by acoustic sensors placed at the pipe. Ongoing research in this field is primarily focused on refining techniques for accurately estimating the time delays. This enhancement predominantly revolves around the application of advanced signal processing methods. Additionally, researchers are actively immersed in the utilization of machine learning approaches on vibro-acoustic data files, to determine the presence or absence of leaks. Less attention has been given to evaluating the sensitivity, performance, and overall effectiveness of these sensors in leak detection; although acoustic methods have been successfully used for leak detection in metallic pipes, they are less effective in plastic pipes due to the high attenuation of leak noise signals. The primary thrust of this research centers on identifying sensors that not only possess sensitivity but also exhibit high efficiency. To accomplish this goal, we conducted an exhaustive evaluation of the performance of three distinct categories of acoustic sensors employed for detecting water leaks in plastic pipes: specifically, lead zirconate titanate (PZT) sensors, polyvinylidene fluoride (PVDF) sensors, and surface acoustic wave (SAW) sensors. Our evaluation encompassed the performance of PVDF and SAW sensors in leak detection, comparing them to PZT sensors under a variety of conditions, including different leak sizes, flow rates, and distances from the leak. The results showed that all three sensors, when they were placed in the same position, were able to detect water leaks in plastic pipes with different sensitivities. For small leaks (1 mm, 2 mm), the PVDF sensor showed the greatest sensitivity (0.4 dB/L/h, 0.33 dB/L/h), followed by the SAW sensor (0.16 dB/L/h, 0.14 dB/L/h), and finally the PZT (0.13 dB/L/h, 0.12 dB/L/h). Similarly, for larger leaks (4 mm, 10 mm), the PVDF sensor continued to show superior sensitivity (0.2 dB/L/h, 0.17 dB/L/h), followed by the SAW sensor (0.13 dB/L/h, 0.11), and finally the PZT sensor (0.12 dB/L/h, 0.1 dB/L/h), outperforming the PZT sensor. This suggests that SAW and PVDF sensors, have the potential to serve as valuable, cost-effective alternatives to traditional commercial leak noise transducers. The outcomes of this comparative study involving three acoustic sensors hold the potential to advance the development of robust and dependable systems for the detection of water leaks in plastic pipelines.

Analysis of CNT-based SAW sensor for the detection of volatile organic compounds

This paper presents a multi-layer one-port surface acoustic wave (SAW) sensing device and its response based on the adsorption of different volatile organic compounds (VOCs). The finite element method was used to model and simulate a multi-layered SAW device. A piezoelectric substrate 128ᵒ YX-cut Lithium Niobate (LiNbO3), polyisobutylene (PIB) polymer, and carbon nanotube (CNT) multilayer SAW resonating sensor was modeled and used for generating Rayleigh waves. Electromechanical coupling coefficient (K2), admittance (Y11), S-parameter (S11), and metallization ratio (MR) were computed for the proposed heterostructured device. The sensing properties of proposed SAW sensor was investigated for several organic compounds such as trichloroethylene (C2HCl3), trichloromethane (CHCl₃), acetone (C3H6O), acetonitrile (C2H3N), cyclohexane (C6H12), dichloromethane (CH2Cl2) and diethyl ether (C4H10O). Eigenfrequency analysis of the SAW sensor was evaluated from 100 ppm to 500 ppm gas concentration at room temperature. The observed results were compared with the existing research and found to be more effective in terms of sensitivity.

Finite Element Study for Mass Sensitivity of Love Surface Acoustic Wave Sensor with Si3N4-SiO2 Double-Covered Waveguiding Layer.

Love surface acoustic wave (L-SAW) sensors are miniaturized, easy to integrate, and suitable for detection in liquid environments. In this paper, an L-SAW sensor with a thin Si3N4-SiO2 double-covered layer was proposed for samples with small mass loads. The output response, phase velocity of the acoustic wave, and the mass sensitivity were analyzed using the finite element method (FEM). The simulation results show that the Si3N4 layer with high wave velocity greatly weakens the limitation of SiO2 on the phase velocity. The phase velocity can reach about 4300 m/s, which can increase the frequency shift when the same mass load is applied. Within a certain range, the mass sensitivity of the sensor is enhanced with the increase in the total thickness of the waveguiding layer and the thickness ratio of Si3N4 in the double-covered layer. When the thickness ratio is 1:2, the peak value of the mass sensitivity of the sensor is approximately 50% higher than that achieved with only the SiO2 waveguiding layer. The surface average stress of the delay line region follows the same trend as the mass sensitivity. The increase in mass sensitivity is the result of the heightened stress on the sensor surface. This L-SAW sensor, featuring a double-covered waveguiding layer, demonstrates high sensitivity and a simple structure. The simulation results lay a foundation for the design and manufacture of SAW sensors.

Phononic crystals for Love waves based on thin-film lithium niobate

This paper presents a type of surface acoustic wave (SAW) phononic crystals based on thin-film lithium niobate (LN). They are created by forming micro-pillar or micro-well structures on the LN, resulting in significant Rayleigh and Love SAW bandgaps. Especially for Love waves, they offer an irreplaceable advantage because they overcome the inability of conventional electrodes to reflect Love waves effectively. This enables the creation of high-quality, compact, high electromechanical coupling coefficient, stable and power-resistant acoustic resonators based on Love waves, potentially leading to a new generation of high-performance SAW filters and sensors. In this paper, we demonstrate the feasibility of such phononic crystals using xy-cut LN-on-SiC. However, it is worth noting that other piezoelectric materials such as lithium tantalate can also be used instead of LN, and high acoustic velocity substrates such as sapphire and diamond can be substituted for SiC.

Smart Materials for Green(er) Cities, a Short Review

The transition to sustainable or green(er) cities requires the development and implementation of many innovative technologies. It is vital to ensure that these technologies are themselves as sustainable and green as possible. In this context, smart materials offer excellent prospects for application. They are capable of performing a number of tasks (e.g., repair, opening/closing, temperature measurement, storage and release of thermal energy) without embedded electronics or power supplies. In this short review paper, we present some of the most promising smart material-based technologies for sustainable or green(er) cities. We will briefly present the state-of-the-art in smart concrete for the structural health monitoring and self-healing of civil engineering structures, phase-change materials (PCM) for passive air-conditioning, shape-memory materials (SMA) for various green applications, and meta-surfaces for green acoustics. To better illustrate the potential of some of the solutions discussed in the paper, we present, where appropriate, our most recent experimental results (e.g., embedded SAW sensors for the Structural Health Monitoring of concrete structures). The main aim of this paper is to promote green solutions based on smart materials to engineers and scientists involved in R&D projects for green(er) cities.

UV light activated g-C3N4 nanoribbons coated surface acoustic wave sensor for high performance sub-ppb level NO2 detection at room temperature

The demand for efficient gas sensors in detecting low ppb-level NO2 gas is increasing rapidly for the human life and environmental protection. In this regard, surface acoustic wave (SAW) based gas sensor with selectively coated one dimensional (1D) graphitic carbon nitride (g-C3N4/GCN) nanostructure interface layer is a viable strategy for the sub-ppb level NO2 gas detection at room temperature (RT∼30 °C). Here, we explore SAW gas sensor employed with 1D GCN nanoribbons (NRs) for NO2 detection under UV-irradiation at RT. Intriguingly, the GCN NRs SAW sensor achieves an ultrahigh frequency response (Δf∼28.13 kHz), short response/recovery times (131 s/116 s), excellent selectivity to NO2 (10 ppm) gas and also records a lowest detection limit (∼42 ppb) under UV activation at RT. The enhanced sensing performances were attributed to the high mass loading effect induced by the enhanced charge transfer between the 1D GCN NRs surface and NO2 gas molecules, boosted by the photoexcited charge carriers, numerous surface sites, and improved specific surface area of 1D GCN NRs. The proposed GCN NRs SAW sensor demonstrates exceptional repeatability, good long-term stability with a minimal loss in its Δf, and exhibited robust sensitivity towards NO2 (10 ppm) under diverse relative humidity conditions (0–80%) at RT. The peculiar sensing results of GCN NRs SAW sensor was elucidates using energy band theory sensing mechanism assisted with resistive type gas sensor. Overall, this study offers significant insights into the development of cost-effective real-time RT based NO2 sensor, paving the way for practical air quality monitoring.

Aluminum based high temperature thin film electrode system for wireless sensors

Self-sustained, wireless high-temperature stable sensors are developed, which are based on an aluminum alloy as the electrode metallization. Due to its cost-effectiveness accompanied by a high-temperature stability, this alloy substitutes and outperforms the commonly applied expensive Pt- and Ir-based metals. For the first time, a comprehensive structural, electrical and high-frequency characterization of these surface acoustic wave (SAW) sensors is shown. They are based on Catangasite (Ca3TaGa3Si2O14, CTGS) in combination with properly structured cover and barrier layers for the metallization. The frequency characteristics is determined up to 700 °C by ex situ and in situ methods. In addition, the morphology of the AlRu electrodes is analyzed after the thermal loadings and the temperature dependent sheet resistance is measured. The results reveal a reproducible and linear correlation between the applied temperature and the sheet resistance as well as the resonant frequency. In addition, hardly any degradation of the electrodes is detected after the thermal loadings. The observed high-temperature stability of the devices up to at least 700 °C demonstrates the large potential of the AlRu based SAW sensors as a cost-efficient alternative to expensive noble metal based sensors in industrial applications for the support of energy efficient operation.

Temperature and strain SAW/BAW sensors on metallic substrates with RFID capability

Surface acoustic wave (SAW) strain sensors require an adhesive—typically a glue—for the mounting on the part under measurement. This comes with strain-transfer, reproducibility and aging issues. In this paper, we propose a novel glue-less solution where the SAW sensor is directly fabricated onto the surface of interest, here a metallic substrate. Here, we study the layered structure ZnO/Ti numerically and experimentally, with ZnO as the piezoelectric layer and titanium as the substrate. In this structure, both bulk acoustic waves and SAW can propagate, and we used both of them to monitor temperature variations up to 300 °C and strain levels up to 1800 μϵ. Moreover, reflective delay line (R-DL) designs were used, to provide the future users with radio frequency identification functionalities. In order to overcome the limitations due to the relatively low electromechanical coupling coefficient of ZnO/Ti, a specific R-DL layout with connected inter-digital transducers was used. The obtained experimental results confirm that the proposed glue-less R-DL structure is a promising solution for the independent evaluation of temperature and strain, with identification.

P-CuO/n-TiO2 heterojunction nanostructure-based surface acoustic wave sensor with strong electric loading effect for highly sensitive H2S gas sensing

A surface acoustic wave (SAW) H2S gas sensor based on CuO-TiO2 p-n heterojunction film was designed and fabricated. The sensor exhibits high sensitivity to H2S due to the significant current response of CuO-TiO2 film to H2S gas and the appropriate work point of SAW sensor based on CuO-TiO2 composite film. The linearity change for sensor frequency shift is strongly associated with the location of work point when the H2S concentration increases from 1 to 300 ppm. In addition, the porosity of CuO-TiO2 film is beneficial to the efficient adsorption for H2S, leading to the higher frequency shift of the sensor. The SAW sensor also shows good selectivity and stability to H2S with stable frequency shift under different humidity levels.

SAW Sensor with Langmuir-Blodgett Layer for Detection of Benzene and its Derivatives

Vapors of benzene and its derivatives are harmful and toxic for human beings and natural environment. Their detection has fundamental importance. For this purpose authors propose surface acoustic wave (SAW) sensor with skeletonized layer deposited by Langmuir-Blodgett (L-B) method. This layer was obtained by depositing a binary equimolar mixture of 5-[[1,3-dioxo-3-[4-(1-oxooctadecyl) phenyl]propyl]amino]–1,3–benzenedicarboxylic acid with cetylamine. The skeletonized sensor layer has been obtained by removing cetylamine. Response of this sensor depends mainly of the electrical dipole momentum of molecule. Among the tested compounds, benzene has a zero dipole moment and gives the smallest sensor response, and nitrobenzene has the largest dipole moment and the sensor reacts most strongly to its vapor.

Review of Surface Acoustic Wave Sensors for the Detectionand Identification of Toxic Environmental Gases/Vapours

Detection and identification of toxic environmental gases have assumed paramount importance precisely in the defense, industrial and civilian security sector. Numerous methods have been developed for the sensing of toxic gases in the environment ever since surface acoustic wave (SAW) technology came into existence. Such SAW sensors called electronic nose (E-Nose) sensor use the frequency response of a delay line/resonator. SAW device is focused and given importance. The selective coating between input and output interdigital transducers (IDTs) in the SAW device is responsible for corresponding changes in operating frequency of the device for a specific gas/vapour absorbed from the environment. A suitable combination of well-designed SAW delay lines with selective coatings not only help to improve sensor sensitivity and selectivity but also leads to the minimization of false frequency alarms in the E-Nose sensor. This article presents a comprehensive review of design, development, simulation and modelling of a SAW sensor for potential sensing of toxic environmental gases.

Circumferential SH wave in piezo-reinforced composite structure with imperfect interface bonding

The present study fundamentally focuses on analyzing the limitations and transference of circumferential shear horizontal (CSH) waves in a four-layered compounded cylinder. The geometrical structure consists of cylinders of infinite length composed of self-reinforced (SR), fibre-reinforced (FR), piezo-magnetic (PM), and piezo-electric(PE) materials. In order to make the structure sensitive to the application pertaining to sensors and actuators, the PM and PE cylinders have been categorically placed in the outer part of the geometry. Whereas in order to provide stiffness and stability to the structure, the inner part consists of SR and FR materials. The common boundary between each of the cylinders has been essentially considered as imperfectly bounded. At the interface of PE and PM media, mechanical, electrical, magnetic, and inter-coupled types of imperfections have been exhibited. The closed-form of dispersion relation has been deduced for two contrast cases i.e. electrically open magnetically short (EOMS) and electrically short and magnetically open (ESMO) circuit conditions. Dispersion curves have been plotted to illustrate the salient features of parameters like normalized imperfect interface parameters, initial stresses, and radii of the concentric cylinders. The comparative effect of each one of these parameters on the phase velocity of the wave has been enlisted and marked individually. Every graph has been presented with two successive modes for a comprehensive understanding. This theoretical study may be implemented to improvise the performance of surface acoustic wave (SAW) sensors, actuators, and Piezo-cables in the form of Piezo-polymer sensors consisting of piezo-electric quartz, piezo-composite concentric cylinders, and coaxial piezo-cables.

Analysis of higher modes of Rayleigh-type waves in fiber-piezo thermoelastic composite structure

The study presents a theoretical modeling and analysis for the purpose of designing of acoustic devices and sensors with high performance. The propagation of Rayleigh-type waves in a piezoelectric substrate guided with fiber-reinforced layer is studied. Lord-Shulman (L-S) theory is used for thermoelasticity for both layer and substrate. Direct Sturm-Liouville method is employed to obtain the dispersion relation using traction free, thermally insulated, electrically open and short boundary conditions. The effect of different material parameters (e.g., reinforce, thickness ratio, and amplitude of thermal displacement) on the velocity (phase and group) of the considered wave are shown graphically by taking suitable numerical examples. The effect of specific loss factor is presented through graph. The present study may be utilized for better optimization of surface acoustic wave devices and sensors.

A useful species identification and quality control using volatile patterns of ssajuari-ssuk and sajabal-ssuk (Artemisia princeps Pamp. cv. ssajuari and Artemisia princeps Pamp. cv. sajabal; Korean mugwort) according to air-drying term by fast gas chromatography with uncoated surface acoustic wave sensor.

Ssajuari-ssuk and sajabal-ssuk have many clinical benefits. It is difficult to discriminate between these two species based on general characteristics aside from the shapes of the leaves. Thus, species identification and quality control between ssajuari-ssuk and sajabal-ssuk are of great concern in plant science and clinical therapy. The aim of this study is to determine whether fast gas chromatography with uncoated surface acoustic wave sensor (GC-SAW) can be a useful technique for performing species identification and quality control using volatile patterns of ssajuari-ssuk and sajabal-ssuk air-dried for 4months and 2years and 4months. Fast GC-SAW sensor provides second unit analysis, simple, on-line measurements that do not require pretreatment of the sample and rapid sensory information. Headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) was employed to confirm the identification of the volatiles and compared to fast GC-SAW sensor. In air-dried sajabal-ssuk, the concentration of 1,8-cineole was higher than that in air-dried ssajuari-ssuk, while the level of α-thujone was considerably lower than that of air-dried ssajuari-ssuk. Each of ssajuari-ssuk and sajabal-ssuk air-dried for 4months and 2years and 4months has its own characteristic volatile pattern owing to its individual chemotypes or chemical compositions. Consequently, the fast GC-SAW sensor can be a useful technique for species identification and quality control using volatile patterns of ssajuari-ssuk and sajabal-ssuk air-dried for 4months and 2years and 4months. This method can be used for the standardisation of quality control using volatile patterns of herbal medicines.