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Various types of interference signals are available in the working environment of passive wireless surface acoustic wave (SAW) sensors. Among these kinds of interference, co-channel interference is difficult to suppress. To solve this problem, a SAW sensor anti-interference technology was proposed to improve the reliability of the SAW sensor. Wavelet denoising method was used to denoise SAW resonator (SAWR) response, which can maintain the envelope characteristics of the SAW response. The entropy energy model of the SAW response signal was established, and the signal envelope was extracted from the proposed entropy energy function. The waveform envelope and the entropy energy curve were adopted as the signal characteristics to form two-dimensional points. The K-Means algorithm was used to classify the two-dimensional points to distinguish the SAW response from sinusoidal interference. Simulation results showed that the SAW response can be detected with a rate of more than 85% when the signal-to-noise ratio was greater than 4 dB, whereas the false detection rate of the sinusoidal interference signal was less than 8%. Finally, the proposed algorithm was used to detect the actual SAW response and sinusoidal interference signal. The experimental results showed that the proposed method can clearly distinguish the SAW response from the co-channel interference signal. Moreover, the proposed method can be used as the anti-interference technology to improve the stability of the SAW sensor.

Surface acoustic wave (SAW) gas sensors are simulated and discussed for the detection of the Dichloromethane (DCM) volatile organic gases (VOC) gas. The simulation was performed using Comsol Multip...

Surface acoustic wave (SAW) devices show promising applications for highly sensitive gas sensors for continuously monitoring of hazardous and flammable gases when integrating with specifically designed sensing materials. Improving the SAW sensor’s responses by using nanostructure sensing materialshas become a research hot topic in recent years. In this work, we presented a SAW room temperature NO2 gas sensor with high sensitivity using one-dimensional (1D) Bi2S3 Nanobelts as the sensing materials. SAW devices with thecentral frequency of ~200 MHz were fabricated on ST-cut quartz substrate as the sensing platform. The Bi2S3 Nanobelts were synthesized by solvothermal method and deposited onto SAW sensors using a spin-coating technology. The response of the prepared SAW gas sensors was 2 kHz when subjected to 10 ppm NO2 even at room temperature. Moreover, the sensor shows good selectivity, reversibility, and stability. The sensing mechanism of one-dimensional Bi2S3 nanobelts-based SAW sensors for NO2 detection was also be discussed.

Introduction Korean mugwort has been used as a traditional medicine. Specifically, air-dried Artemisia princeps Pamp. cv. ssajuari (ssajuari-ssuk; Korean mugwort) has been used as moxa in moxibustion therapy. Thus, the evaluation of high quality ssajuari-ssuk containing herbal volatiles is of great interest in clinical therapy and the food industry. Objective The aim of this study is to determine whether fast gas chromatography with uncoated surface acoustic wave (fast GC/SAW) sensor can be a useful technique for performing quality control using herbal volatiles of ssajuari-ssuk air-dried for different times. Methodology Fast GC/SAW sensor, called "Electronic zNose", is also a headspace sampling method and is an effective simple analytical method with a second unit analysis providing on-line measurements without the need for pretreatment of the sample. 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. Results Artemisia princeps Pamp. cv. ssajuari air-dried for 2 years and 4 months (the third year), containing the highest total amount of herbal volatiles, was superior to the others (the first year, the second year, the fourth year) in quality. Moreover, fast GC/SAW sensor shows a high repeatability (relative standard deviation 0.77% ∼ 6.23%), excellent sensitivity (limit of detection value of 0.47 pg/mL), and good linearity (correlation coefficient r2 = 0.997) over the range of nanogram for α-thujone. Conclusion Therefore, the fast GC/SAW sensor can be a useful analytical method for the discrimination and quality control of volatiles of herbal and medicinal plants according to air-drying time, as it provides a simple and second unit analysis.

Recently, efforts have been made to adapt surface acoustic waves (SAWs) for use in chemical sensors for detection of chemical warfare agents (CWAs). In this study, a four-channel real-time CWA detection system was constructed using four 250-MHz SAW sensors. Each system consists of three different chemical sensors and one reference sensor. The reference sensor compensates for frequency variations according to humidity and temperature conditions. Signals from the SAW sensors can be checked on a PC-based graphical user interface without additional measuring equipment. To measure dimethyl methylphosphonate (DMMP), a simulant of sarin gas, polyhedral oligomeric silsesquioxane (POSS) and thiourea (TU)-based synthetic polymers were used as sensing materials. The reference sensor was not coated, whereas the three different chemical sensors were coated with POSS, TU-1, and TU-2. The maximum frequencies of POSS, TU-1, and TU-2 were shifted 15.86, 13.85, and 0.944 kHz, showing significant values. We also found a relatively good linear relation between the frequency shift and the concentration of DMMP. The three sensing materials selected-POSS, TU-1, and TU-2-responded significantly to DMMP and triethylphosphate in the selectivity tests. This response is due to the chemical bonding of the sensing materials with the phosphonate in the nerve-agent simulants. These results indicate that the four-channel SAW monitoring system described in this paper shows potential as a portable real-time monitoring system to detect a variety of toxic vapors simultaneously, without using complex measuring equipment. In addition, this approach has demonstrated potential for developing excellent portable sensors to detect different types of CWAs.

The effects of a plasma treatment on the sensing performance of surface acoustic wave (SAW) sensors to detect chemical warfare agents (CWAs) were investigated. SAW sensors designed for an operating frequency of 250 MHz were fabricated using lift-off techniques followed by the deposition of a very thin thiourea (TU) layer as a sensing film on the sensing area of the SAW sensor. To achieve some advantages from the plasma treatment on the surface, such as cleaning, surface activation and modification, a post-plasma treatment was performed on the sensing layer and the sensing performance of the SAW sensor was measured by a comparison with the measured responses, providing different simulant gases through the gas feeding system. The sensitivity test revealed significant improvement in the sensing ability of the SAW sensor to detect DMMP, a simulant of a CWA, but with a relatively longer recovery time. The responses of other simulants at different concentrations and different simulant vapors were compared. The results showed that a plasma treatment on the sensing layer of a SAW device can improve the selectivity and sensitivity to a certain target gas or some volatile organic compounds. Therefore, a plasma treatment will be very useful for improving the selectivity and sensitivity of SAW sensors for the detection of CWAs.

Purpose The objectives of this study are to provide the detailed information of designing, fabrication process, and performance test results of a surface acoustic wave (SAW) sensor for evaluating chicken meat storage time (up to 15 days). Methods The aldehyde gas generated from chicken meat was selected as the reactive material, and Love wave was used among various SAWs due to its high sensitivity of the aldehyde gas particles. The SAW sensor was fabricated on the surface of LiNbO3 piezoelectric wafer with a cross-linked polydimethylsiloxane (PDMS)-sensitive layer using standard photolithographic techniques. To analyze the fabricated SAW sensor characteristics, the S21 parameters and base line noise were acquired by a vector network analyzer. Before measuring chicken meat gas samples, a reference gas (a mixture of 25, 50, 75, and 100 ppm acetaldehyde (a functional group with the structure –CHO, CH3CHO) and nitrogen (N2) gas) was measured to verify the reactive performance of the SAW sensor. Among the VOCs from chicken meat gas, CH3CHO was selected as an intrinsic biomarker due to its harmful effects on the human body. Then, aldehyde gas from chicken meat samples was measured and the phase changes of the response signals with increasing the chicken meat storage time were obtained by the SAW sensor. Results About − 4 dB insertion loss occurred due to the PDMS coating and the high electromechanical coupling factor of used substrate. The phases of the response signals decreased linearly with increase of both the reference gas concentration and the storage time of the chicken meat samples. The determination coefficients of the reference gas and the storage time were over 0.9. The results show that the developed SAW sensor can provide valuable information about evaluating the chicken meat storage time. Conclusion The newly developed SAW sensor clearly demonstrates that chicken meat storage could be evaluated by detecting aldehyde gas. This opens a promising research avenue to explore.

Wireless and passive surface acoustic wave (SAW) devices with nanoporous metal-organic framework (MOF) sensing layers are attractive gas sensors for applications in many fields such as energy industries and air pollution control. Here, we report on enhancing the sensitivity and detection limit of zeolitic imidazolate framework-8 (ZIF-8) MOF-coated SAW reflective delay line mass sensors by increasing the operating frequency for sensitive detection of carbon dioxide (CO2) and methane (CH4) at ambient conditions. In particular, we show at least four times higher sensitivity of an 860 MHz (4-{\mu}m periodicity) SAW reflective delay line coated with a 240 nm thick ZIF-8 compared to the sensitivity of a 430 MHz (8-{\mu}m periodicity) otherwise identical sensor device to the targeted gases. The detection limits of the higher frequency wireless devices for CO2 and CH4 were estimated to be 0.91 vol-% and 7.01 vol-%, respectively. The enhanced sensitivity for higher frequency devices is explained in terms of the frequency dependent acoustic wave energy confinement., Comment: 8 pages, accepted to publish in IEEE Sensors Journal

For the first time, a 3less (batteryless, chipless, wireless) underground sensor system was developed for real time monitoring of variations in temperature, humidity, and hydrogen gas concentrations around underground utility burials. The completed sensor system consists of several magnetic core antennas, surface acoustic wave (SAW) sensors, and a measurement system. Each SAW sensor was activated by pure magnetic energy, and showed high sensor performances in sensitivity and linearity. A long readout distance was observed between the upper and underground antennas, and wireless magnetic communication was analyzed in terms of the interdistances, the angles between antennas, and the underground constituent mediums. A circulator was employed to discern magnetic signals emitting and receiving in between the upper and underground systems. A COMSOL simulation and coupling of mode (COM) modeling were also conducted to determine optimal design parameters for the sensor modules, and to predict the experimental results in advance.

Many petroleum products like oil and gas are transported from one place to another through pipelines, although they can undergo leakage due to pipeline leaks and cause risks to industries, the environment, and people. In this review work, we have presented a comprehensive overview of acoustic emission technology for gas pipeline leak detection. Essential gas leak detection system requirements, principles, terminologies, and risks due to failure of the natural gas pipeline system have been discussed while proposing a surface acoustic wave sensor with a combination of the Hilbert–Huang transforms (HHTs) as the best method for real-time leak detection system in the gas pipeline network. The variation of wave energy causes propagation of elastic waves that can be detected by sensors mounted on the pipeline. Natural gas pipeline networks require a continuous real-time monitoring system to ensure that the pipelines are delivering the products from one station to another at optimum conditions.

This minireview appraises the chemical sensors and biosensors with the bio/sensitive active films obtained by matrix assisted laser evaporation (MAPLE). An overall presentation and examples of the materials utilized thus far introduce the discussion of sensing applications, where the following categories of biosensors are critically appraised: optical sensors (surface plasmon resonance, fluorescence microscopy, long period grating fiber); surface acoustic wave sensors; and electrochemical sensors. The deposition of active layers of biomolecules, potentially useful as sensing interfaces, is discussed in relation to the experimental parameters of MAPLE deposition, with emphasis on the preservation of structure and activity of biomolecules. Additionally, chemoselective layers, temperature responsive and antifouling coatings are also reviewed, as these be can be combined with the active layers to obtain advanced sensing interfaces, showing the versatility of MAPLE. The review concludes with future developments and perspectives.

Laser deposition was used to obtain Pd/ZnO bilayers, which were used as sensing layers in surface acoustic wave (SAW) sensors. The effect of laser deposition parameters such as deposition pressure, laser energy per pulse, laser wavelength or pulse duration on the porosity of the Pd and ZnO films used in the sensors was studied. The effect of the morphology of the Pd and ZnO components on the sensor response to hydrogen was assessed. Deposition conditions producing more porous films lead to a larger sensor response. The morphology of the ZnO component of the bilayer is decisive and has an influence on the sensor properties in the same order of magnitude as the use of a bilayer instead of a single Pd or ZnO layer. The effect of the Pd film morphology is considerably smaller than that of ZnO, probably due to its smaller thickness. This has implications in other bilayer material combinations used in such sensors and for other types of analytes.

A Surface Acoustic Wave sensor including grooved-grating chirp reflectors are designed to exploit Ultra-Wide-Band Hyperbolically Frequency Modulated signals. The study results have been published in our previous works. The purpose of this work is to investigate features of SAW temperature sensors with implemented HFM technology using radio frequency impulse signals in a wide frequency band.

Surface acoustic wave (SAW) devices are widely used for physical, chemical, and biological sensing applications, and their sensing mechanisms are generally based on frequency changes due to mass-loading effects at the acoustic wave propagation area between two interdigitated transducers (IDTs). In this paper, a new sensing mechanism has been proposed based on a significantly enhanced mass-loading effect generated directly on Au IDT electrodes, which enables significantly enhanced sensitivity, compared with that of conventional SAW devices. The fabricated ultrahigh-frequency SAW devices show a significant mass-loading effect on the electrodes. When the Au-electrode thickness increased from 12 to 25 nm, the Rayleigh mode resonant frequency decreased from 7.77 to 5.93 GHz, while that of the higher longitudinal leaky SAW decreased from 11.87 to 9.83 GHz. The corresponding mass sensitivity of 7309 MHz·mm2·μg–1 (Rayleigh mode) is ∼8.9 × 1011 times larger than that of a conventional quartz crystal balance (with a frequency of 5 MHz) and ∼1000 times higher than that of conventional SAW devices (with a frequency of 978 MHz). Trinitrotoluene concentration as low as 4.4 × 10–9 M (mol·L–1) can be detected using the fabricated SAW sensor, proving its giant mass-loading effect and ultrahigh sensitivity.

The detection of malaria parasite (plasmodium falciparum) is investigated by using a novel photoacoustics (PA) excited surface acoustic wave (SAW) sensor. The SAW sensor is designed to resonant around 10 MHz and is fabricated by using standard two-step photolithography. The photoacoustic PA-SAW sensing system is composed of a SAW sensor, cooperating with a pulsed laser, a neutral density filter, a convex lens, two analog front ends (AFEs) and an oscilloscope. PA signals and their spectrums of different materials are obtained for calibration, and the PA signals of normal blood and infected blood are chaterized through the PA-SAW sensing system, subsequently. The infected blood with cultured ring-stage malaria parasites concentrations of 1% can be detected. The demonstration shows that the PA-SAW sensor has good potential in the diagnosis of malaria at early stage. Nanyang Technological University This work was supported by the NTUHealth-LKCMedince-NHG under Grant IDPOCT17002.

Purpose This study aims to use resonant surface acoustic wave (SAW) sensors, which have advantages in the harsh application environments, to measure different physical parameters such as temperature, pressure and force. For SAW sensors, the locality in measurement resolution by the effective time is poor, it cannot give the detailed results of SAW echoes. Design/methodology/approach To promote the application of SAW sensor, this paper proposes a convex program-based super-resolution measurement method to recover the missing spectral line and enhance frequency resolution. Findings The proposed method reduces the reliance on effective time and improves the measurement resolution of SAW sensors. The performance was validated by experiments. Originality/value The limited resolution capability restricts the benefit of SAW technology in harsh environments. The proposed method shed light on SAW measurement resolution increase, exploiting its full potential and leading to commercial applications.

In this study, we report a gold nanoparticle (AuNP)-amplified surface acoustic wave (SAW) sensor for exosome detection with high sensitivity. The SAW chip was self-assembled with mercapto acetic acid to generate carboxylic groups via the Au-S bond. Anti-CD63 was then anchored onto the chip by pretreatment with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide,1-hydroxypyrrolidine-2,5-dione (NHS). Due to the existence of a membrane protein, CD63, on the exosome surface, exosomes could be bound onto the antibody-immobilized SAW chip. To amplify the detection signal, both the biotin-conjugated epithelial cell adhesion molecule (EpCAM) antibody as a secondary antibody and AuNP-labeled streptavidin were applied onto the exosome-bound SAW chip, resulting in AuNP assembly on the chip through biotin-avidin recognition. The sensor was capable of detecting 1.1 × 103 particles/mL exosomes, which was about 2 orders of magnitude higher than those detected by the strategy without using signal amplification. The sensor also achieved a satisfactory specificity and could detect the low-abundance exosomes directly in blood samples from cancer patients with minimal disturbance. This makes the SAW sensor useful for early diagnosis of cancer.

Surface acoustic wave sensors have wide variety of applications. The application of SAW sensors includes measurement of different physical parameters like temperature, torque, acceleration, pressure, humidity etc. SAW sensor can also be used as gas sensor with certain construction constrains. The performance of gas sensor can be increased by adding nanomaterial to the MEMS (Micro-Electro Mechanical Systems) based gas sensor. In this study a 2D Surface Acoustic Wave sensor is designed to sense hydrogen gas. The sensor is designed with zinc oxide (ZnO) as sensing layer to increase the sensitivity. The performance of sensor is evaluated with gas and without gas with respect to the displacement and operating frequency. The maximum displacement obtained by the sensor is 0.00857 µm at the operating frequency of 30 MHz in absences of gas and 0.00502 µm displacements in presences of gas at the same operating frequency. Analysis of sensor is done with Finite Element Modeling (FEM). The sensor is simulated with COMSOL Multi Physics.

2D and nanostructured metal sulfide materials are promising in the advancement of several gas sensing applications due to the abundant choice of materials with easily tunable electronic, optical, physical, and chemical properties. These applications are particularly attractive for gas sensing in environmental monitoring and breath analysis. This review gives a systematic description of various gas sensors based on 2D and nanostructured metal sulfide materials. Firstly, the crystal structures of metal sulfides are introduced. Secondly, the gas sensing mechanisms of different metal sulfides based on density functional theory analysis are summarised. Various gas-sensing concepts of metal sulfide-based devices, including chemiresistors, functionalized metal sulfides, Schottky junctions, heterojunctions, field-effect transistors, and optical and surface acoustic wave sensors, are compared and presented. It then discusses the extensive applications of metal sulfide-based sensors for different gas molecules, including volatile organic compounds (i.e., acetone, benzene, methane, formaldehyde, ethanol, and liquefied petroleum gas) and inorganic gas (i.e., CO2, O2, NH3, H2S, SO2, NOx, CH4, H2, and humidity). Finally, a strengths–weaknesses–opportunities–threats (SWOT) analysis is proposed for future development and commercialization in this field.

This study presents finite element time-domain simulation of a SiO 2 /36°-YX LiTaO 3 Love wave (LW) delay line to explore coupled resonance phenomenon with ZnO nanorods designed on the top surface of the device. The effect of variation in ZnO nanorods height on the propagation of LW, mode-transitions, area-averaged stress, insertion loss, and mass sensitivity of the device is studied. Simulation results show that at the critical height of ZnO nanorods, coupled resonance occurs that causes a sharp swing in the phase shift indicating a transition from inertial to elastic loading. Coupled resonance increases the acoustic impedance of the device and also the average stress between nanorod and substrate interface. Simulation of mass loading is performed by applying an incremental surface mass density on the active area of the device. A nanorod packing density of 1 μm -2 gives a high mass sensitivity of 728 m 2 kg -1 which is more than ten times the sensitivity of a plain LW device. At the coupled resonant height, the insertion loss of the sensor increases, and a swing of about 1 dB is observed with variation in the nanorod height.

A generalized dynamic model to depict the wave propagation properties in surface acoustic wave nano-devices is established based on the Hamilton's principle and variational approach. The surface effect, equivalent to additional thin films, is included with the aid of the surface elasticity, surface piezoelectricity and surface permittivity. It is demonstrated that this generalized dynamic model can be reduced into some classical cases, suitable for macro-scale and nano-scale, if some specific assumptions are utilized. In numerical simulations, Love wave propagation in a typical surface acoustic wave device composed of a piezoelectric ceramic transducer film and an aluminum substrate, as well as the shear-horizontal vibration of a piezoelectric plate, is investigated consequently to qualitatively and quantitatively analyze the surface effect. Correspondingly, a critical thickness that distinguishes surface effect from macro-mechanical behaviors is proposed, below which the size-dependent properties must be considered. Not limited as Love waves, the theoretical model will provide us a useful mathematical tool to analyze surface effect in nano-devices, which can be easily extended to other type of waves, such as Bleustein-Gulyaev waves and general Rayleigh waves.

Gaseous formaldehyde (HCHO) sensing is indispensable because HCHO is hazardous to health and widely exists in newly decorated house and newly painted furniture. Multitudinous HCHO sensors based on various platforms, such as semiconductor sensor, electrochemical sensor, surface acoustic wave sensor (SAW), fluorescent sensor, have been fabricated over the last few years. Except these sensors, quartz crystal microbalance (QCM) sensors have received increasing attention because of their high sensitivity, convenient operation, low energy consumption, and excellent modifiable property. Recently, based on QCM, many efforts have been made to design chemical sensing materials to detect HCHO gas sensitively and selectively. In this review, we summary the scientific researches of gaseous HCHO detection based on QCM platform, and introduce the related works of sensing HCHO carried out by our group as well as the exploration of sensing mechanism.

A highly sensitive ambient light sensor based on surface acoustic waves (SAWs) was investigated. The ambient light SAW sensor is fabricated by depositing sensitive film and its resonant frequency shift was calculated in response to a change in light intensities. The resonant frequency is generated between the piezoelectric substrate and a specifically designed transducer, which is usually called interdigitated transducer (IDT). The IDT design was determined to exhibit the resonant frequency at 244.5 MHz by considering the sensor size and fabrication process. We fabricated our ambient light SAW sensor by using a cadmium sulfide (CdS) thin film as a sensing material. Absorbance spectra of CdS thin film in visible light region were investigated. Then the lithium niobate (LiNbO3) substrate is adopted as a substrate due to its high coupling coefficient. Fabrication of CdS thin films was conducted by thermal evaporator and common lithography process including lift-off. To increase the sensitivity of the sensor, we focused on increasing the thickness and area of the sensitive film. As a result, the sensitivity increased by approximately three times when the area doubled.

International audience; This paper presents a study of an equivalent circuit for surface acoustic wave (SAW) devices in the context of SPICE simulations, but valid for any other circuit simulation tool. We expand on previous derivations of the Foster Theorem approximation of impedances, providing normalized tables that evaluate LC pairs for different orders of approximation, also comparing their relative error. We propose a simple circuit block that can be used to represent external perturbations in a SAW delay line, while also including a parallel capacitance to model the electromagnetic coupling between input and output IDTs, an important effect when working with liquid media. Our results show close agreement with the measurements, along with interesting time-domain behavior not discussed by other works.

Laser-deposited gold immobilization layers having different porosities were incorporated into love wave surface acoustic wave sensors (LW-SAWs). Variation of pulsed laser deposition parameters allows good control of the gold film morphology. Biosensors with various gold film porosities were tested using the biotin–avidin reaction. Control of the Au layer morphology is important since the biotin and avidin layer morphologies closely follow that of the gold. The response of the sensors to biotin/avidin, which is a good indicator of biosensor performance, is improved when the gold layer has increased porosity. Given the sizes of the proteins, the laser-deposited porous gold interfaces have optimal pore dimensions to ensure protein stability.