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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.

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.

The current work provides an extensive study of SH-SAW response to various surface loading conditions. A parametric study was conducted by varying crucial functional parameters of the devices such as (i) piezoelectric substrate, (ii) operating frequency, and (iii) presence of waveguide. Twelve device configurations emerged out of various combinations of the above parameters. In order to be evaluated, the devices were subjected to various kinds of surface perturbations, namely (i) Au deposition, representing pure mass loading, (ii) glycerol solutions of various concentrations, representing liquid loading of a broad viscosity range, spanning both Newtonian and Maxwellian regions, and (iii) adsorption of proteins. The sensitivity in all cases was evaluated, and appropriate comparisons were made in order to fully characterize the systems and identify the most favorable device for each application.

For a multimode-optical-fiber surface plasmon resonance (SPR) sensor with a gold film supporting surface plasmon waves (SPWs), we have investigated the effects of gold thickness on sensor performance experimentally to find the optimal thickness when a white-light source is used. It is found that the sensor with a thickness of around 65 nm enables most precise measurement of a resonance wavelength and gives relatively high sensitivity, which is 1557 nm/RIU in the refractive index range of 1.333–1.3469. Also, we have confirmed that a simulation model based on meridional rays cannot explain the minimum reflectance of SPR spectra for values below 0.5.

A way to improve the angular sensitivity of surface plasmon resonance (SPR) biosensor by tuning the resonance position to a higher incident angle region using a lower refractive index glass prism is described in this paper. A novel effective 3-layer (E3L) model is described to transform a multiple layer biosensor configuration in context of SPR condition. The E3L model supports the use of a low refractive index prism for biosensing. The performance of the sensor in immunosensing is checked for two glass prisms of different refractive index materials. The experimental results showed an enhancement in the amount of resonance angle shift of the immunosensor for the lower refractive index glass prism.

A methanol sensor for direct methanol fuel cell (DMFC) is required. A shear horizontal surface acoustic wave (SH-SAW) sensor for electrical property determination is applied for this purpose. The operating temperature of DMFC is above 50 °C. The wave propagation characteristics were calculated while considering temperature coefficient. The results indicate that the sensitivity increases with increasing temperature. Then, the concentrations of methanol solutions were measured using the SH-SAW sensor. Measured temperature ranged from 25 °C to 60 °C and concentration ranged from 0 to 50% by weight. Linear relationships between the sensor response and concentration were obtained. An increase in the sensitivity is experimentally confirmed. The limit of the detection was estimated from experimental results to be 0.1% by weight. Because formic acid is produced in the DMFC electrode reaction, its effect was discussed. The concentrations of mixture solutions of methanol and formic acid were measured. Using a chemometric method, we succeeded in determining the concentrations of both, simultaneously. Therefore, the SH-SAW sensor can be possibly used for DMFC.

The performance of a surface plasmon resonance (SPR) sensor depends on its design properties. In this paper, we described, both theoretically and experimentally, the role of the prism material in sensor design. The analyses were carried out by employing three prisms of different refractive indices and the reflection spectra were studied under the angular interrogation mode. The results proved that the choice of prism material can tailor the resonance condition and thus can effectively tune the working region of the sensor. Also, the experimental value of angular sensitivity increased from 94.46°/RIU to 204.41°/RIU on changing the refractive index of the prism from 1.597 to 1.456, without changing the other parameters. The variation of the angular sensitivity was in accordance with the analytical and numerical results. The dynamic range decreased and the full width at half maximum (FWHM) of the reflection spectra increased as the refractive index of the prism was lowered, thereby affecting the sensor's performance.

Surface plasmon resonance (SPR) has been widely utilized for immunoreaction measurements. In this paper, we describe a novel SPR sensor with an optical waveguide and dual light emitting diodes (LEDs). The advantage of the system is that the refractive index of the waveguide and the wavelength of the LED can easily be changed. Also, it is suitable for the immobilization of antibodies and adsorption of molecules, since the waveguide has a planar structure. High sensitivity was realized by using a combination of two monochromatic light sources and so the refractive index range of the measured samples could be considered. The developed system is applied for measuring an immunoreaction. The results indicate that the proposed SPR system with dual LEDs is effective for biosensor applications.

In this paper, we report on the development of a practical compact and stable sensing system with a shear horizontal surface acoustic wave (SH-SAW) sensor for liquid. First, the oscillation circuits for the liquid-phase sensor based on the SH-SAW device is discussed. Two sensor outputs, i.e., frequency and amplitude, are required for evaluating the liquid properties. To monitor the amplitude, an automatic gain control amplifier (AGC amp) is utilized in the oscillation circuit. The developed sensing system has a low standard deviation of noise that is less than the temperature coefficient of the frequency of the dual SH-SAW sensor and from which the detection limit is estimated. The dynamic range of the developed SH-SAW sensing system is also estimated. The system is applied for the measurement of Japanese tea. The results indicate that the slight differences among teas can be detected by the SH-SAW liquid sensing system.

A liquid-flow system with a shear horizontal surface acoustic wave (SH-SAW) sensor is developed to identify electrolytes in an aqueous solution without selective coatings. When the electrical properties of sample solution are the same, it is impossible to identify the differences by using steady-state values. The transient responses from the liquid-flow system, however, depend on the materials contained in a sample solution. Therefore, it is possible to determine the type of ion species in the solution from the transient responses. To identify and evaluate the sample solutions, the self-calibrating ratiometric method (SCRM) is proposed. Since the SCRM is based on the time differences between rise and fall responses, the influences of experimental conditions can be calibrated and thus ignored. The results indicate that the SCRM is an effective identification method based on the transient responses. Moreover, the mechanisms are discussed and it is found that the dispersion of an electrolyte based on the gravity effect and the evanescent piezoelectric potential are essential for the identification.

A shear horizontal mode surface acoustic wave (SH-SAW) device has many attractions for chemical-sensing applications in liquid media. The SH-SAW that propagates on 36° rotated Y-cute, X-propagating LiTaO3 is affected by a strong acoustoelectric interaction between the piezoelectric potential and electric properties of the adjacent liquid. This paper describes an enzyme-immobilized SH-SAW biosensor in which the detection principle is the acoustoelectric interaction due to the pH change in the enzyme reaction. Two kinds of enzymes, urease and cholinesterase, are immobilized on the sensor surface and highly sensitive detection of the enzyme reaction is obtained experimentally. The urease-immobilized SH-SAW biosensor is implemented in a liquid-flow system. By using the cholinesterase-immobilized SH-SAW sensor, we have succeeded in detecting an inhibition effect of a pesticide.

A shear horizontal surface acoustic were (SAW) that propagates on 36° rot. Y-cut X-propagating LiTaO3 immersed in a liquid is affected by an acoustoelectric interaction between the piezoelectric potential and the electrical properties of the materials in the liquid. Using the SAW device, pH changes in enzymatic reactions can be detected by the measurement of the SAW velocity change caused by a pH change associated with the reactions. In this paper, preliminary experiments on a urea—urease reaction and the inhibition effect of the butyrylcholine chloride-cholinesterase reaction due to a pesticide are reported.