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Surface acoustic wave (SAW) sensors have attracted great attention worldwide for a variety of applications in measuring physical, chemical and biological parameters. However, stability has been one of the key issues which have limited their effective commercial applications. To fully understand this challenge of operation stability, this paper aims to systematically review mechanisms, stability issues and future challenges of SAW sensors for various applications.

This review paper starts with different types of SAWs, advantages and disadvantages of different types of SAW sensors and then the stability issues of SAW sensors. Subsequently, recent efforts made by researchers for improving working stability of SAW sensors are reviewed. Finally, it discusses the existing challenges and future prospects of SAW sensors in the rapidly growing Internet of Things-enabled application market.

A large number of scientific articles related to SAW technologies were found, and a number of opportunities for future researchers were identified. Over the past 20 years, SAW-related research has gained a growing interest of researchers. SAW sensors have attracted more and more researchers worldwide over the years, but the research topics of SAW sensor stability only own an extremely poor percentage in the total researc topics of SAWs or SAW sensors.

Although SAW sensors have been attracting researchers worldwide for decades, researchers mainly focused on the new materials and design strategies for SAW sensors to achieve good sensitivity and selectivity, and little work can be found on the stability issues of SAW sensors, which are so important for SAW sensor industries and one of the key factors to be mature products. Therefore, this paper systematically reviewed the SAW sensors from their fundamental mechanisms to stability issues and indicated their future challenges for various applications.

When designing the electrode widths of the electrode-width-weighted (EWW) input interdigital transducers (IDTs) according to the envelope amplitudes of the wavelet function, the EWW wavelet transform processor (WTP) using surface acoustic wave (SAW) devices can be fabricated. The electrode widths have influence on the frequency characteristic of the EWW WTP using SAW devices. The purpose of this research is to solve the influence of the electrode width accuracy on the frequency characteristic of the EWW WTP using SAW devices.

In order to solve the influence of the electrode width accuracy on the frequency characteristics of the EWW WTP using SAW devices, the function between the electrode widths and the −3 dB bandwidth is derived. That the −3 dB bandwidth varies as the electrode widths is known according to this function so that the exposure time and the etching are presented as the two key problems.

Solutions to these problems are achieved in this study. As long as there is accurate exposure time, the precision IDTs (i.e. the precision electrode widths) will be obtained. The accuracy of the exposure time for the EWW WTP using SAW devices is ±1 per cent. Because the dry etching is a type of etching technology in gas medium, it can etch nanometer lines, even more fine lines, so that the dry etching is used in EWW WTP using SAW devices.

Research highlights solving the influence of the electrode width accuracy on the frequency characteristic for the EWW WTP using SAW devices; deriving the function between the electrode widths and the −3 dB bandwidth (it is known from this function that the −3 dB bandwidth varies as the electrode widths); and presenting the exposure time and the etching as two key problems.

This paper aims to investigate the response behavior of the surface acoustic wave (SAW) sensor under the loading of micro-particles and to evaluate the feasibility of using the SAW sensor to study the micro-contact of the particle–plane interface.

An analytical perturbation theory of the coupled system of particle and SAW is presented. It shows that in the weak-coupling regime, the SAW sensor detects the coupling stiffness rather than the additional mass of the particle at the interface. The frequency perturbation formula expressed in parameters of the geometry and mechanical properties of the contact is further derived. The frequency shift of a 262-MHz Rayleigh-type SAW in the oscillation configuration under the loading of multiple starch particles of different sizes has been measured.

The experiment results of a linear relationship between the frequency increase and the sum of the radius of particles to the power of 2/3 verified the validity of the theory of linking the SAW response to the geometry and mechanical properties of the contact.

The SAW sensor could serve as a new candidate for studying the details of mechanical properties of the micro-contact of the interface.

This paper aims to give an overview about the state of wireless passive surface acoustic wave (SAW) gas sensor used in the detection of chemical vapor. It also discusses a variety of different architectures including delay line and array sensor for gas detection, and it is considered that this technology has a good application prospect.

The authors state the most of the wireless passive SAW methods used in gas sensing, such as CO2, CO, CH4, C2H4, NH3, NO2, et al., the sensor principles, design procedures and technological issues are discussed in detail; their advantages and disadvantages are also summarized. In conclusion, it gives a prospect of wireless passive SAW sensor applications and proposes the future research field might lie in the studying of many kinds of harmful gases.

In this paper, the authors will try to cover most of the important methods used in gas sensing and their recent developments. Although wireless passive SAW sensors have been used successfully in harsh environments for the monitoring of temperature or pressure, the using in chemical gases are seldom reported. This review paper gives a survey of the present state of wireless passive SAW sensor in gas detection and suggests new and exciting perspectives of wireless passive SAW gas sensor technology.

The authors will review most of the methods used in wireless passive SAW sensor and discuss the current research status and development trend; the potential application in future is also forecasted.

The authors will review most of the methods used in wireless passive SAW sensor and discuss the current research status and development trend; the potential application in future is also forecasted.

The detection of H₂ concentrations in concentrations undetectable by the conventional detection method of surface acoustic wave (SAW) sensors based on frequency shift, by correlating analyte presence with Fourier spectra components.

Fast Fourier Transform (FFT) and autocorrelation analysis of phase noise in a SnO2-coated SAW sensor was performed. Fourier spectra were obtained by FFT from the SAW sensor resonance frequency instability, in the absence of analyte, and for H₂ concentrations between 0.08 and 0.4 per cent.

All analyte concentrations are below the sensor limit of detection, which is 0.8 per cent for H₂. Although these analyte concentrations caused no significant change in the resonance frequency of the SAW resonator, the FFT spectra presented several modifications, namely, the appearance of a new peak and the decrease of randomness. The authors consider that the effect is because of the chaotic behavior of the temporal dependence of the SAW resonance frequency. This explanation is substantiated by the decrease observed in the SAW oscillator autocorrelation function, which is an indication for a chaotic behavior.

As chaotic systems are extremely sensitive to perturbation, measurement methods based on chaos diagnosis could potentially greatly improve the SAW detection.

Fourier spectra components were correlated with analyte presence in concentrations undetectable by the conventional SAW detection method based on frequency shift.

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This study aims to demonstrate how critical realism (CR) can be used in spirituality at work (SAW) research and to provide a practical example of CR in SAW research.

CR is a philosophical meta-theory that allows the stratification of spirituality into different levels of reality, advocates for research methods matching the ontology of the level investigated and provides complementary methods of exploring this phenomenon’s causal power in social contexts. The authors present a study where CR was used to explain how and why SAW influences ethics in organisational contexts.

The results demonstrate that CR provides a useful approach to bridging the positivist-interpretivist difference in SAW research. Moreover, a CR approach helped explain the underlying conditions and causal mechanisms that power SAW to influence ethical decision-making and behaviour in the workplace.

While CR has been applied in the management literature, negligible SAW research has used this approach. That which exists is either conceptual or does not discuss methods of data analysis, or describe how critical realist concepts resulted in their findings. This paper addresses that lacuna. CR also provides value, as an alternative approach to SAW research, in that it allows the use of both quantitative and qualitative methods as complementary, not confrontational methods while providing a more integrated and deeper view of SAW and its effects.

The purpose of this paper is to test a model linking physical therapy (PT) and occupational therapy (OT) practitioners’ perceptions of resonant leadership, structural empowerment and psychological empowerment to their experiences of spirit at work (SAW), job satisfaction and organizational commitment within the Canadian workplace.

The authors tested the model using LISREL 8.80 and survey data from 101 OTs and 169 PTs, randomly selected by the Alberta professional licensing associations. Content analysis of responses to the open-ended comments section provided additional depth and insight.

Analysis of results culminated in minor modifications to the original theoretical model, creating separate PT and OT models. Both models revealed a good fit with the observed data. Several SAW concepts accounted for moderate to large amounts of variance in both PT and OT models, indicating that SAW is a comprehensive workplace outcome.

Theory was derived from business and nursing research literature due to limited rehabilitation research literature. Discussion of OT results must consider the small sample size. This study is initial exploratory research.

Each discipline-specific model provides professionals, health care leaders and policy makers with a rich body of information upon which to base beneficial workplace decisions. SAW will guide leaders in the holistic development and enrichment of the work environment.

This research contributes to the substantive knowledge of the OT and PT disciplines, particularly in the areas of leadership, workplace structural organization and indicators of healthy work environments such as SAW, empowerment, job satisfaction and organizational commitment.

This paper aims to present an context evaluation and frequency measurement method for surface acoustic wave (SAW) resonant sensor.

This method is based on a signal subspace construction, which, along with assembling optional value set, provides the results.

The method can assess the application context and improve the resolution and accuracy of the passive wireless SAW resonator sensor system.

Passive wireless SAW resonators have been used as sensor elements for different physical parameters such as temperature, pressure and force in a number of industrial and medical applications. Various wireless channel environments introduce different application contexts.

The purpose of this paper is to model multilayer structure surface acoustic wave (SAW) sensors, incorporated in CMOS or micro‐electro‐mechanical system integrated circuits, and to derive the corresponding wave velocity as an analytic expression in terms of the layers‘ thickness and density, which is suitable for analysis and design.

The method is based on an electro‐mechanical equivalent model of multilayer structure SAW sensors. A multilayered SAW device is represented by a two‐port electrical equivalent circuit consisting of three parts: input transducer, output transducer, and between them the delay line, which is the sensing part. The sensing part is modelled as a mechanical two‐port network. The wave velocity is calculated using analogy between the mechanical and electrical quantities and the fact that the wave motion of the SAW extends below the surface to a depth of about one wavelength.

The presented model predicts very efficiently and accurately the velocity of SAW sensors with multilayer substrates in the case where the thicknesses of upper layers are much smaller than the signal wavelength. The velocity can be calculated from the formula, so that elaborate numerical computations involving partial differential equations are avoided.

The model and the velocity calculation can be applied only to acoustically thin upper and middle layers where acoustically thin means that a layer is sufficiently thin and rigid (large shear modulus). The presented results provide a starting‐point for further research in the analysis and design of sensors fabricated using AlGaN, GaN, AlN/diamond.

Since the majority of SAW sensors is designed with acoustically thin layers, the proposed model and calculation can be of interest for many practical material combinations. The presented model and calculation can be used in most cases of the optimal sensor design with respect to the sensor sensitivity or required area on the sensor chip.

The paper presents a new original model of multilayer structure SAW sensors and a new method of SAW velocity calculation. The method gives good results, with much simpler calculations than in the wave equation method, in cases where certain layers are acoustically thin.