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Integration of high-sensitivity sensors with multiple sensing performance for the environmental detection of permittivity (er), conductivity (σ), and the refractive index (n) is required to support Societies 5.0. However, there are still many sensors with low sensitivity that stand alone. A shear-horizontal surface acoustic wave (SH-SAW) sensor is usually used because of its high-sensitivity performance in detecting electrical properties. Moreover, localized surface plasmon resonance (LSPR) sensors show remarkable optical side capability. Here, we have successfully combined these advantages with an additional benefit of sensitivity enhancement. We propose a hybrid acoustoplasmonic sensor generated by integrating SH-SAW and LSPR devices to simultaneously detect er, σ, and n. The SH-SAW sensor was fabricated on a 36XY-LiTaO3 substrate using a developed interdigital transducer. Then, the LSPR sensor was implemented by the deposition of gold nanoparticles (AuNPs) on the propagation surfaces of the SH-SAW sensor. Fascinatingly, the AuNPs not only generate the LSPR effect but also enhance the SH-SAW sensor sensitivity. Comprehensive investigations were performed with atomic force microscopy imaging, CST software used for plasmonic E-field simulation, and hybrid sensing evaluation. Moreover, the SH-SAW sensitivity enhancement achieved using AuNPs was verified by frequency-domain and time-domain measurements. Thus, the SH-SAW sensor with AuNPs has a wide er detection range (25-85), sensing capabilities for ultrasmall σ (0.00528-0.02504 S/m), and high sensitivity for n detection (45.5-201.9 nm/RIU). The cross-sectional effects were also evaluated. The effect of the LSPR device on the SH-SAW device was examined by turning the light OFF or ON (hereafter OFF/ON). The impact of the SH-SAW device on the LSPR device was investigated by turning the sine signal OFF/ON. We found that the SH-SAW sensor was not impacted by light. Interestingly, the presence of the SH-SAW sensor affects the positions of the AuNPs, which consistently generates a small blueshift in the LSPR effect. However, insignificant variation was noted in independent performances. In general, the SH-SAW sensor with AuNPs shows multifunctional independent characteristics and high-sensitivity performance, making it suitable for a chemical environment, with the possibility of integration with a wireless network.

A disposable digital microfluidic system is realized using sensor plate/thin water layer/piezoelectric substrate. It is important to clarify the Lamb wave mode, which propagates in the sensor plate. In this paper, the phase velocity of the Lamb wave was experimentally estimated and compared with the Rayleigh-Lamb equation. Also, the acoustic streaming velocity was experimentally obtained. The results indicate that the high phase velocity is realized by decreasing plate thickness and increasing the operating frequency.

Shear horizontal surface acoustic waves (SH-SAW) are the surface wave generated by the piezoelectric material such as 36XY-LiTaO 3 after feed using electric signal via interdigital transducer (IDTs). SH-SAW was applied for many applications such as biosensors, physical and chemical sensors. Another interesting phenomenon is localized surface plasmon resonance (LSPR). LSPR effect refers to the collective oscillation of conduction electrons band at the metallic NPs structure while interacting with a specific wavelength of incident light. However, the interaction between SH-SAW vibration with LSPR is still rarely studied. Here, we propose investigating the interaction between SH-SA and LSPR by fabricating gold nanoparticles (AuNPs) at the middle part of the SH-SAW device. As a result, SH-SAW was assisted AuNPs vibration and produced a blue-shift effect with high capability tunable the LSPR spectrum. Finally, this research can make a bridge between SH-SAW and LSPR technology to create tunable LSPR spectrum and multifunctional sensors.

Integration of high-sensitivity sensors with multiple sensing performance for the environmental detection of permittivity (ε

In the paper, the results of production of Ag inkjet printed interdigital transducers to the acoustic delay line based on Y-cut X-propagation direction of lithium niobate plate for the frequency range from 1 to 14 MHz are presented. Additionally, morphological, structural, and electro-physical characteristics of the obtained electrodes were investigated. Mathematical modeling of the excitation of acoustic waves by these electrode structures was carried out. Comparison of the theoretical results with experimental ones showed their qualitative and quantitative coincidences. It was shown that conventional inkjet printing can replace the complex photolithographic method for production of interdigital transducers for acoustic delay lines working up to 14 MHz. The resulting electrode structures make it possible to efficiently excite acoustic waves with a high value of electromechanical coupling coefficient in piezoelectric plates.

On site monitoring of engine oil is required. The features of a shear horizontal surface acoustic wave (SH-SAW) sensor include simultaneous detection of mechanical and electrical properties of liquids (such as viscosity, relative permittivity, and conductivity) and loaded mass on the sensor surface. In this paper, the used engine oil extracted from a motorbike was measured using the SH-SAW sensor. The degradation factors of the used engine oil were experimentally discussed. Especially, the influences of the particles in the engine oil, heating effect, and water contained in the engine oil were considered by comparing the differences between new and used engine oils. The results indicate that the influence of the water contained in the engine oil is the primary cause of the degradation of the used engine oil.

The aim of this study is to show the possibility to control structural and optical properties of Au nanoparticles (AuNPs) by changing their size and concentration and make comparison between methods of their formation. 1.4 nm thick Au films were formed on borosilicate glass substrates by the vacuum evaporation method. AuNPs were formed on the surface of the substrate by two methods. First is the irradiation by the Nd:YAG laser pulses with intensities from 75 to 180 MW/cm2. Second is thermal annealing, at temperature T=400 °C and the time of curing was varied from 24 to 72 hours. The irradiation of Au film by laser leads to formation of AuNPs. The increase of intensity of laser radiation causes the disappearing of small Au nanoparticles and growing of big nanoparticles from 113-180 nm due to the agglomeration of small particles into big ones and, correspondingly, concentration of particles decreases. In contrast, thermal annealing at T=400 °C from 48 to 72 hours leads to the island formation with the non-spherical shape and their dividing into several islands according to the spinodal dewetting model. As a result, the mean diameter of AuNPs is decreased from 161 to 85 nm but concentration increases.

Reconfigurable localized surface plasmon resonance (LSPR) is an essential characteristic for various applications to support Society 5.0. However, many LSPR spectrum have poor reconfigurability. As a novelty, we proposed a reconfigurable LSPR spectrum by acousto-dynamic coupling in arrays of gold nanoparticles (AuNPs) induced by shear-horizontal vibrations. The vibrations were produced by piezoelectric phenomena especially shear horizontal surface acoustic waves (SH-SAWs) on a 36XY-LiTaO3 substrate after applying an electric signal, the ON-condition. The experimental results demonstrated that the ON-condition produced a blueshift effect on the peak position (λP) with an adjustment quality factor compared to the OFF-condition. Moreover, in order to perform the finite-difference time-domain (FDTD) analysis, we reproduced the morphological structure of AuNPs base on scanning electron microscope (SEM) images. The different coupling distances and different arrays structures were utilized as ON-condition approaches for dimer AuNPs and arrays AuNPs, respectively. The FDTD simulation obtained a blueshift effect compared to the initial structure. Finally, the proposed structure successfully combines piezoelectric phenomena with plasmonic phenomena to produce reconfigurable LSPR. The LSPR spectrum can be switched comfortably and reverses easily. The proposed method can be applied for multifunctional sensors with the high possibility of integration into a wireless network.

The localized surface plasmon resonance phenomenon of gold (Au) nanostructured in thin film form has many attractiveness for optical based sensing applications. Plasmon resonance robustly influences optical properties the Au thin film. Therefore, the optical response of Au thin film determined by nanostructure of Au nanoparticles on the surface of substrate. However, the thermal annealing strongly affects to the nanostructure Au thin film. In this study, low-cost Au thin film has been developed by vacuum thermal evaporation technique and thermal annealing process. The thermal annealing was applied in certain temperature 400 °C with various annealing durations were applied to generate Au thin- films. The effect of thermal annealing on nanostructure and optical properties of Au thin films were measured. The statistical quantities of the average height value of grain particles was between 13 to 21 nm and the density was between 100 to 200 particles per square micrometer after annealing. The optical properties of gold thin-film in terms to be applied as sensor in optical-based biosensor reported. The best of RIS sensitivity obtained above 90 nm RIU-1. The results appearance a great promising for sensor applications.

Simultaneous measurements of several properties are important for a microfluidic system application. In this paper, electrochemical and localized surface plasmon (LSPR) sensors were integrated on an interdigital electrode (IDE) for simultaneous monitoring of impedance and refractive index of samples. First, the IDE was made and then gold nanoparticles were formed on the IDE electrodes by the thermal annealing method for the LSPR sensor. The measured results suggest that the electrical and optical properties of samples are measurable by the integrated IDE.

A shear horizontal surface acoustic wave (SH-SAW) sensor can be applied for measuring liquid properties. Measurements of engine oils are one of the SH-SAW sensor applications. In our previous study, the possibility of the SH-SAW sensor for monitoring degradation of the engine oil was discussed. In this study, the SH-SAW sensors with three frequencies were applied to discuss the frequency dependence of the sensor sensitivity. The two primary subjects discussed in this paper are: first, a comparison between used engine oil extracted from a scooter traveling 6000 km and new engine oil, and second, heating effect of the new engine oil. In the comparison between used and new engine oils, although the sensor responses related to liquid viscosity can be explained by the decrease in viscosity, those related to liquid electrical characteristics cannot be explained using the electrical perturbation theory. An effective single layer and an apparent relative permittivity were introduced to explain the obtained results. The results indicated that the higher frequency SH-SAW sensor is suitable for engine oil monitoring. Moreover, an amplification of the SH-SAW was observed when the heated engine oil was measured. This phenomenon could only be explained using a negative conductivity.

To monitor the health of large-scale structures, a wireless measurement system, such as a bridge, is required. One of the methods of monitoring the health of large-scale structures involves the application of an impedance-loaded wireless surface acoustic wave (SAW) sensor. Additionally, a pressure-sensor-loaded SAW sensor can detect the vibration of a cantilever. In this study, a continuous wavelet transform (CWT) is adopted to analyze the sensor responses. The CWT results obtained were classified into two categories based on the attenuation at each frequency, which include the exponential or linear type. Furthermore, machine learning was applied to evaluate cantilever damage. The results indicate that a high accuracy evaluation of damage is feasible with the proposed method.

In the medical field, point-of-care testing (POCT) is garnering attention. An online inspection system can be realized by combining POCT and the Internet. Herein, we report the performances of a measurement system developed using online software for a shear horizontal surface acoustic wave (SH-SAW) sensor. The developed SH-SAW measurement system does not require a phase detection circuit. The developed system can be used when the system is connected to the Internet. This enables an online measurement system that can be used “by anyone, at anytime, and anywhere.” In this study, we used samples of glycerol and water mixtures and then measured the amplitude ratio and phase difference of the SH-SAW sensor. The validity of the developed system is confirmed by comparing the measured results with theoretical values.

An experimental method is demonstrated to enhance the refractive index sensitivity (RIS) of gold (Au) ultrathin films used in a localized surface plasmon resonance (LSPR) sensor as an optical transducer using sequential temperature treatment in fabrication processes. The Au ultrathin films were fabricated by the vacuum thermal evaporation technique to deposit Au nanoparticles on a glass substrate, followed by annealing. The ultrathin layer of Au had a thickness of 1.13 nm. Furthermore, two different annealing times were employed in two different treatment processes with annealing temperature of 400 °C. The first treatment involved longer annealing times (8 h, 12 h, 24 h, and 36 h) and a normal cooling process (cooling rate: 0.02 °C/s); the second treatment involved shorter annealing times (1 min, 5 min, 10 min, and 30 min) and a quenching process (cooling rate: 25 °C/s). The Au ultrathin films were spectroscopically evaluated based on their morphology and optical properties in the transmissive mode integrated in a self-assembled optofluidic. The highest RIS of the Au ultrathin films was obtained at 240.45 nm/RIU for the short annealing time-quenching treatment and 90.85 nm/RIU for the long annealing time-normal cooling treatment. This method demonstrates the great potential toward fabrication of Au ultrathin films based LSPR for liquids sensing.

There is a need for digital microfluidic systems that can integrate pretreatments and sensors on the same substrates in the medical and biotechnology fields. Surface acoustic waves (SAW) can be used to manipulate and mix droplets. Sensors integrated on the droplet-manipulating surfaces can measure droplet properties. The adhesion of liquids to the substrate surfaces necessitates the development of disposable devices. We therefore propose a three-layer structure of glass plate/water/128YX-LiNbO3. A disposable device can be realized by replacing the inexpensive glass. However, the details of the propagation mode in these structures have not yet been studied. In this paper, numerical analysis and experiments were carried out. For the numerical analysis, the Rayleigh-Lamb equations for the glass plate immersed in liquid were used. Comparisons between the numerical analysis and experimental results indicate that the symmetric mode of the Lamb wave propagates in the glass plate.

To realize a sensitive and low cost optofluidic biosensor, we propose a localized surface plasmon resonance (LSPR) sensor chip based on supported gold nanoparticles (AuNPs). The AuNPs were generated by vacuum thermal evaporation and annealing process. Sample liquids with different concentration were utilized to characterize the sensitivity of the self-assembled AuNPs film. Important issue, one of the advantages of optofluidics can be coupling with LSPR sensors. The LSPR sensor integrated self-assembled continuous flow optofluidics with the flow rate of 50 μl/m showed the sensitivity along with its potential application of simple and low-cost fabrication.

We have developed 920 MHz band long range wireless SAW passive tag system (WSPTS) using patch antenna for the purpose of structural health monitoring (SHM). Our WSPTS has achieved more than 6 m reading distance. Each reflective FMCW signal from the passive tag can be distinguished in the reader unit by realizing Tx-Rx antenna isolation of more than 50 dB by patch antennas.

In this paper, we describe a 920 MHz band long range wireless SAW passive tag system (WSPTS) for vibration monitoring, which achieves more than 15 m reading distance. For the purpose of structural health monitoring (SHM) of aging infrastructures (e.g. bridge, building, and so forth), passive wireless sensor systems are an attractive option because they are operated battery-less and almost maintenance free. The feature of our developed passive tag is the flexibility improved by separating the SAW device for wireless communication and the vibration sensor. The transmitter frequency modulated continuous wave (FMCW) signal with an antenna power of +13dBm, meets the spectrum mask of the ARIB STD-T108 by cosine taper (Tukey) window to reduce spectral leakage for the time domain FMCW waveform. Identification of the passive tag is realized by the different delay time of a multiplication interval of 1.25 μs.

The creating different kinds of the phononic crystals and acoustic metamaterials, which has advanced ultrasound properties, have generated considerable recent research interest. The new kind acoustic materials, allows to studying the new effects of the ultrasound interaction and developing different types of the surface acoustic wave (SAW) devices for electronic industry. We represented the possibilities to creating of the controlled SAW devices on the base 36° rotated Y-cut, X-propagating LiTaO 3 single crystal with the volume electroinduced periodical domain structure. We are focusing on the theoretical and experimental investigations of volume induced and controlled domain structures.

Oil has been used in many fields, such as transportation systems and machine tools. Performances of those depend on oil quality. However, quality is normally checked by visual inspection. Therefore, it is required to develop a sensor for monitoring oil quality to measure online and real time. A shear horizontal surface acoustic wave (SH-SAW) sensor can detect liquid properties. In this paper, particles in oil were measured using the SH-SAW sensor.

In this paper, we describe a shear horizontal surface acoustic wave (SH-SAW) immunosensor that utilizes induce agitation by a Rayleigh SAW (R-SAW) on an X-cut 148-Y LiTaO

A shear horizontal surface acoustic wave (SH-SAW) device is used as a sensor for the liquid environment. As a main particle displacement of the SH-SAW is parallel in the propagation surface and perpendicular in the propagation direction, the SH-SAW does not radiate its energy into the liquid. Therefore, SH-SAW is suitable for the liquid measurement. In this paper, particles in oil are measured by using the SH-SAW. The experimental results show that the velocity and attenuation changes increase with increasing the amount of the iron particles. Whereas the velocity change obtained is qualitatively explained by the perturbation theory for the mass loading, the attenuation change cannot be explained. Therefore, it is necessary to develop the new theory for particle loading in oil environment.

A surface acoustic wave (SAW) is perturbed due to physical and/or chemical changes in an adjacent medium. If a liquid-phase sensor is to be realized, a shear horizontal SAW (SH-SAW) must be used. SH-SAW sensors have been investigated since 1987. Objects measured using an SH-SAW sensor include not only immunoreactions but also liquid properties. The advantage of an SH-SAW sensor is the simultaneous detection of the mechanical and electrical properties of liquids. In this paper, first, the theory behind the SH-SAW sensor is described. Then experimental results using the SH-SAW sensor on 36YX-LiTaO3 are introduced. In addition, the sensor sensitivities of the SH-SAW sensors that have been fabricated on piezoelectric substrates are theoretically compared. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(2): 41–49, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10407

Measurement of liquid concentration is important application using a shear horizontal surface acoustic wave (SH-SAW) sensor. In this paper, methanol concentration of a direct methanol fuel cell is monitored using the SH-SAW sensor. To determine the liquid concentration, the perturbation theory for an electrical perturbation is used. Estimated results indicate that the SH-SAW sensor can apply to the continuous estimation of liquid concentration without a reference liquid.

Droplet manipulation is one of important applications for surface acoustic wave (SAW) devices. To optimum control of the droplet, detection method of the droplet position must be considered. In this paper, we discuss about the reflected wave from the droplet. When a short burst signal was applied to the SAW device, the reflected signal from a droplet on it. Experimental results show that the observed time depends on a droplet volume. This means that the wave does not reflect at the air/droplet interface. Propagation model of the longitudinal wave in the droplet was assumed and the equation was derived using it. The experimental results of the re-flex time agree with the calculated results using the equation. As the longitudinal wave velocity is involved in the equation, the velocity is obtained by measuring the arrival time.

A longitudinal wave is radiated from a surface acoustic wave (SAW) at the solid/liquid interface and non-linear phenomena are observed, such as acoustic streaming. When a short burst signal was applied to the SAW device, the reflected signal from a droplet on it. Experimental results show that the observed time depends on a droplet volume. This means that the wave does not reflect at the air/droplet interface. Propagation model of the longitudinal wave in the droplet was assumed and the equation was derived using it. The experimental results of the reflex time agree with the calculated results using the equation. As the longitudinal wave velocity is involved in the equation, the velocity is obtained by measuring the arrival time.

Structural health monitoring, such as bridge and building is important. The wireless and passive sensor is the best for the monitoring. An impedance-loaded surface acoustic wave (SAW) sensor is a combination of a SAW device and a classical sensor. If the impedance-loaded SAW sensor can apply to the structural health monitoring, wireless sensing system is realized. For the monitoring, damage of the structure is measured. In this paper, damaged cantilevers are measured by using the pressure sensor-loaded SAW sensor. The result indicates that the degrees of the damage can be evaluated from the attenuation coefficient of the envelop.

In this paper, we describe a shear horizontal surface acoustic wave (SH-SAW) immunosensor that utilizes induce agitation by a Rayleigh SAW (R-SAW) on an X-cut 148-Y LiTaO3 substrate. On this substrate, SH-SAWs and R-SAWs with different frequencies can be effectively generated at an interdigital transducer (IDT). First, to consider the power flow angles of SH-SAWs and R-SAWs on this substrate, the 360-MHz delay lines with six different tilt angles were designed and fabricated. From the experiments, an optimal power flow angle of 9° for the SH-SAW on this substrate is obtained. Second, in order to consider the immunoreactions of the SH-SAW immunosensors, a delay line with a tilt angle of 9° was designed and fabricated on this substrate. The delay line, which can generate two SAWs, namely, a 100-MHz SH-SAW and an 88.8-MHz R-SAW, has a propagation area covered with antigens of human serum albumin between transmitting and receiving IDTs. The immunoreactions caused by antigen–antibody binding events on the surface of the delay line were investigated on the basis of the velocity changes of the SH-SAWs for sensing with and without the assistance of an R-SAW. As a result, it was confirmed that the SH-SAW velocity changes due to antigen–antibody reactions can be markedly increased by the assistance of R-SAW agitation.

This paper describes a shear horizontal surface acoustic wave (SH-SAW) immunoassay biosensor on a quartz substrate. The SH-SAW biosensor is a 250MHz SH-SAW delay-line which has a gold surface covered with antibodies. It is important to discuss the detection mechanism of SH-SAW biosensors on quartz. In this paper, the detection mechanism of SH-SAW biosensors are investigated, using three methods of numerical analysis. The first method is a mass loading model analysis. The second method is a viscosity model analysis. The third method is a viscoelasticity model analyasis. A numerical calculation method for SH-SAW propagation characteristics, which is a modified Campbell and Jones method involving the effect of liquid viscosity is applied to quartz. In order to confirm the proposed numerical analysis models, 250MHz SH-SAW biosensors on quartz substrates were tested. The mass, viscosity, and viscoelastic behavior of fluids on SH-SAW biosensors were theoretically and experimentally discussed.

Realization of high-sensitivity biosensors is required. Acoustic wave-based biosensors are promising because of their ability to detect immunoreactions. In this paper, a shear horizontal (SH) acoustic wave in layered structures, namely, the Love wave, is discussed on the basis of numerical calculations. To generate the Love wave, a 36YX-LiTaO3 was chosen as a piezoelectric substrate. SiO2, polymer, and gold were chosen as guiding layer materials. First, the phase velocity and propagation loss were calculated as a function of the layer thickness. Then, an additional mass layer was loaded on the guiding layer to simulate bio-layer deposition. Simulation results indicate that a highly sensitive biosensor was realized by using a gold guiding layer. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(4): 27–;32, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10417

Realization of high sensitive biosensors is required. As an acoustic wave based biosensor can detect immunoreactions, it is expected for applying the biosensor. In this paper, a shear horizontal (SH) acoustic wave in layered structures, namely Love wave, is discussed on the basis of numerical calculations. For generating the Love wave, a 36YX-LiTaO3 is chosen as a piezoelectric substrate. Also, SiO2, polymer, and gold are chosen as guiding layer materials. First, phase velocity and propagation loss are calculated as a function of layer thickness. Then, an additional mass layer is loaded on the guiding layer for simulating bio-layer deposition. The simulated results indicate that high sensitive biosensor is realized by using gold guiding layer.