Shear Horizontal Surface Acoustic Wave Sensor Research Articles

Methanol Sensor Using Shear Horizontal Surface Acoustic Wave Device for Direct Methanol Fuel Cell

A liquid-phase sensor is realized that uses a shear horizontal surface acoustic wave (SH-SAW) device. The advantage of using an SH-SAW sensor is the simultaneous detection of liquid properties, such as density, viscosity, permittivity, and conductivity. In this study, the SH-SAW sensor is applied as a methanol (MeOH) sensor for a direct methanol fuel cell (DMFC). As the generation efficiency of the DMFC depends on the methanol concentration, the monitoring of MeOH concentration is needed. The SH-SAW sensor is applied to the MeOH sensor to measure the electrical properties. The efficiency of the DMFC is also influenced by materials contained in the fluid. If a component of the SH-SAW sensor is eluted into the fuel, the SH-SAW sensor cannot be used in the DMFC. The SH-SAW sensor was dipped into the fuel at 80 °C and it was found that the concentration of eluted components from the SH-SAW sensor was low and that the efficiency was not influenced by such components. Then, the temperature characteristics of the SH-SAW sensor with various MeOH solutions were measured. The maximum operating temperature of the DMFC is 80 °C and the minimum temperature depends on the place of installation. In this work, the minimum temperature is assumed to be -5 °C. Thus, the SH-SAW sensor must measure the MeOH concentration from -5 to 80 °C without malfunction. The results indicate that the MeOH concentration can be measured when the temperature is lower than 60 °C. If the temperature is higher than 60 °C, bubbles are generated on the sensor surface and the sensor is influenced by them. A liquid flow system was demonstrated to reduce the influence of bubbles.

Methanol Sensor Using Shear Horizontal Surface Acoustic Wave Device for Direct Methanol Fuel Cell

A liquid-phase sensor is realized that uses a shear horizontal surface acoustic wave (SH-SAW) device. The advantage of using an SH-SAW sensor is the simultaneous detection of liquid properties, such as density, viscosity, permittivity, and conductivity. In this study, the SH-SAW sensor is applied as a methanol (MeOH) sensor for a direct methanol fuel cell (DMFC). As the generation efficiency of the DMFC depends on the methanol concentration, the monitoring of MeOH concentration is needed. The SH-SAW sensor is applied to the MeOH sensor to measure the electrical properties. The efficiency of the DMFC is also influenced by materials contained in the fluid. If a component of the SH-SAW sensor is eluted into the fuel, the SH-SAW sensor cannot be used in the DMFC. The SH-SAW sensor was dipped into the fuel at 80 °C and it was found that the concentration of eluted components from the SH-SAW sensor was low and that the efficiency was not influenced by such components. Then, the temperature characteristics of the SH-SAW sensor with various MeOH solutions were measured. The maximum operating temperature of the DMFC is 80 °C and the minimum temperature depends on the place of installation. In this work, the minimum temperature is assumed to be -5 °C. Thus, the SH-SAW sensor must measure the MeOH concentration from -5 to 80 °C without malfunction. The results indicate that the MeOH concentration can be measured when the temperature is lower than 60 °C. If the temperature is higher than 60 °C, bubbles are generated on the sensor surface and the sensor is influenced by them. A liquid flow system was demonstrated to reduce the influence of bubbles.

Measurement Characteristics of Flow-Type Shear-Horizontal Surface Acoustic Wave Sensor for Direct Methanol Fuel Cells

Direct methanol fuel cells (DMFCs) offer promising future power sources. Operating DMFCs at ideal conditions, fuel concentration management is required, and therefore, devices for methanol concentration measurement are considered important to DMFC systems. Shear-horizontal surface acoustic wave (SH-SAW)-based methanol concentration sensors can be used as DMFCs offering advantages such as miniature size, mass-production ability, and reliability. The objective of this study was to develop and evaluate an easy to install SH-SAW sensor in a wide variety of DMFC systems. In this paper, we describe the detailed structure and measurement characteristics of the developed sensor system. The evaluations were focused on the linearity and response to methanol concentration change. Through the evaluations, theoretically predicted response linearity to the methanol concentration change was confirmed on the developed sensor. It was found that the response speed of the sensor was so quick that even a transient phenomenon of methanol spreading into water could be detected. These measurement abilities will be useful for accurate fuel control of DMFC systems, and should be able to extend the application range of SH-SAW sensors.

Detection of Cells Captured with Antigens on Shear Horizontal Surface-Acoustic-Wave Sensors

Techniques to separate cells are widely applied in immunology. The technique to separate a specific antigen on a microfluidic platform involves the use of a shear horizontal surface-acoustic-wave (SH-SAW) sensor. With specific antibodies conjugated onto the surface of the SH-SAW sensors, this technique can serve to identify specific cells in bodily fluids. Jurkat cells, used as a target in this work, provide a model of cells in small abundance (1:1000) for isolation and purification with the ultimate goal of targeting even more dilute cells. T cells were separated from a mixed-cell medium on a chip (Jurkat cells/K562 cells, 1/1000). A novel microchamber was developed to capture cells during the purification, which required a large biosample. Cell detection was demonstrated through the performance of genetic identification on the chip.

The estimations of ammonia concentration by using neural network SH-SAW sensors

This paper presents the estimations of ammonia concentration by using neural network (NN) models. The shear horizontal surface acoustic wave (SH-SAW) devices coated with L-glutamic acid hydrochloride and polyaniline (PANI) film, respectively, were applied as the ammonia sensors. The data sensed by SH-SAW sensors were implemented by using different NN models. A reliable and superior neural network SAW identifier is expected to be found for effectively overcoming the interference of humidity in ammonia detection.

Single-channel shear horizontal surface acoustic wave sensor for the identification of liquid-phase substances

The principal possibility of liquid-phase substances recognition with the aid of a single-channel sensor operating on a shear horizontal surface acoustic wave (SH-SAW) delay line has been experimentally demonstrated. The SH-SAW sensor was manufactured as a SAW delay line based on a layered structure on 36°YX LiTaO3 crystal substrate. The response signal is related to the analyt-induced change in a pulse characteristic obtained by the frequency-to-time domain transformation of one of the measured S-parameters.

Measurements of Standard-Viscosity Liquids Using Shear Horizontal Surface Acoustic Wave Sensors

A shear horizontal surface acoustic wave (SH-SAW) sensor can be used to detect the properties of liquids. We propose one application of the SH-SAW sensor as a viscosity sensor. The Japanese Industrial Standards Committee (JISC) has determined the standard liquids used to calibrate a viscometer. If the SH-SAW sensor is to be commercialized, it is necessary that the viscosities of these liquid can be measured. In this study, the standard-viscosity liquids are measured using the SH-SAW sensor operating at different frequencies. The sensor responses to the standard-viscosity liquids are less than those for a glycerol/water mixture. This is due to the viscoelasticity of the standard-viscosity liquids. A simple viscoelastic model is applied to explain the experimental results.

Propagation characteristics of shear horizontal surface acoustic waves in (11 2 0) ZnO film/silica glass substrate structures

This paper presents the propagation characteristics of the shear horizontal surface acoustic wave (SH-SAW) in ZnO (0deg, 90deg, psi) (11 2macr 0) textured ZnO films. ZnO (0deg, 90deg, 0deg) film/interdigital transducer (IDT) electrode/silica glass substrate structures were fabricated by RF magnetron sputtering. Experimental results demonstrate that SH-SAW was clearly excited in these structures. We also theoretically estimated the electromechanical coupling coefficient K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in the ZnO (0deg, 90deg, psi) film/silica glass substrate structure. The theoretical results show that the IDT electrode/ZnO (0deg, 90deg, 55deg) film/silica glass substrate structure had a relatively high K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> value of 3.4%. Moreover, the shear horizontal displacement component of the SH-SAW in this structure is much larger than the transverse and longitudinal displacement components. This structure could be used in SH-SAW sensors for evaluating the electrical properties of liquids.

Enhancing effects of microcavities on shear-horizontal surface acoustic wave sensors: A finite element simulation study

Shear-horizontal surface acoustic wave (SAW) sensors with microcavities in the delay paths of 36° YX-LiTaO3 substrate were studied using finite element methods. Microcavities of square cross sections of sizes λ∕4 and λ∕2 and of different depths were located in the middle of the delay path. Simulation results for nonfilled and polystyrene-filled microcavity devices were compared with standard delay line shear-horizontal SAW, optimized Love-wave, and etched grating sensors. We found that the best case microcavities studied reduce insertion loss by 19.25dB from 33.28dB and exhibit velocity sensitivity 4.83 times larger than that of the standard SAW sensor simulated.

Ammonia identification using shear horizontal surface acoustic wave sensor and quantum neural network model

The ammonia detection at room temperature employing a shear horizontal surface acoustic wave (SH-SAW) sensor coated with polyaniline (PANI) film and the recognition of ammonia concentrations in humid environments based on quantum neural network (QNN) have been investigated in this study. Studies were performed in the ranges of 0–67.5% relative humidity and 15–72 ppm ammonia. The frequency shift of SH-SAW was measured to detect the presence of ammonia. The SH-SAW sensor in this study responded to the ammonia gas and could be recovered using dry nitrogen. Detecting at an ammonia concentration of 40.91 ppm in dry environment, the frequency shift was 0.75 ppm and the noise level was 0.08 ppm. In humid environment, the frequency shift increased as the humidity increased. In order to recognize the ammonia in humid environment, the QNN was used as the identifier. From the performance results shown, the neural model we proposed can effectively perform the identification of ammonia in a common ambience and overcome the inference of humidity caused.

Development of a Shear Horizontal Surface Acoustic Wave Sensor System for Liquids with a Floating Electrode Unidirectional Transducer

The development of sensors using surface acoustic wave (SAW) devices has been attracting attention. A shear horizontal SAW (SH-SAW) sensor can detect the properties and chemical reactions in liquids. To realize practical applications of the SAW sensor, it is necessary to discuss its properties. In this paper, SH-SAW sensors with a floating electrode unidirectional transducer (FEUDT) or an interdigital transducer (IDT) are compared and the insertion loss and phase characteristics are measured. Also, the phase shift between sample and reference liquids is evaluated. The results indicate that the SH-SAW sensor with the FEUDT is suitable for liquid measurements. The SH-SAW sensor with the FEUDT is then mounted in a newly developed SH-SAW sensing system. The system configuration is the same as that of a vector voltmeter measurement system. However, circuits have been developed that reduce its size. Using this system, several liquids are measured. The obtained results agree well with the theoretical values.

Degradation of Liquid-Phase Shear Horizontal Surface Acoustic Wave Sensor Owing to Lack of Energy Concentration of Surface and a Compensation Method

In this paper we describe liquid-phase two-channel shear horizontal surface acoustic wave (SH-SAW) delay-line sensor devices on 36° Y–X LiTaO3 substrates. One delay line has a metallized propagation area and the other has an unmetallized propagation area. The permittivity and conductivity of the liquids can be calculated from the velocity changes and attenuation changes of the SH-SAWs in the two delay-lines. However, in the case of the low-permittivity liquids, the SH-SAWs in the delay line with an unmetallized propagation area can be degraded owing to the lack of SH-SAW energy concentration of the surface. Thus the obtained permittivity and conductivity of the liquids were slightly different from the exact values. In this paper, the drawback of the liquid-phase SH-SAW sensors is described, and in order to overcome this drawback, a compensation method is presented.

Insulin Surface Acoustic Wave Immunosensor Based on Immobilized C60/Anti‐Insulin Antibody

AbstractImmobilized fullerene C60/anti‐insulin antibody was prepared and applied in shear horizontal surface acoustic wave (SH‐SAW) immunosensors to detect insulin in aqueous solutions. The immobilizations of anti‐insulin onto fullerene were studied through a C60/PVC coated SH‐SAW sensor system in liquid. The partially irreversible frequency response for an anti‐insulin antibody was observed by the desorption study, which implied that fullerene could chemically react with anti‐insulin. C60/anti‐insulin coating materials were successfully prepared and identified with an FTIR spectrometer. The C60/anti‐insulin coated SH‐SAW immunosensors were developed and applied for detection of insulin in aqueous solutions. Within the range of normal human insulin concentration, the SH‐SAW immunosensors immobilized with C60/anti‐insulin exhibited linear frequency responses to the concentration of insulin with a sensitivity of 130 Hz/pM. The SH‐SAW immunosensor immobilized with C60/anti‐insulin showed a detection limit of 0.58 pM for insulin in aqueous solution. The interference of various common bio‐species in human blood, e.g. urea, ascorbic acid, tyrosine, and metal ions, to the SH‐SAW immunosensor immobilized with C60/anti‐insulin for insulin was investigated. These common bio‐species interferences showed nearly no interference to the SAW immunosensors coated with C60/anti‐insulin. The reproducibility of the SH‐SAW immunosensor immobilized with C60/anti‐insulin for insulin was also investigated and is discussed.

Digital phase detection approach and its application for AlN dual-mode differential surface acoustic wave sensing.

Performance of a conventional phase detector implemented using analog circuitry is affected by, among other factors, the parameter value drifting of the analog components with environment (e.g., temperature) and time (i.e., aging). It is also adversely impacted by electromagnetic interferences likely existing in the analog circuits when the detector operates in a high frequency range. More importantly, such a detector is inflexible to compensate various nonlinear characteristics of sensors and is very difficult to realize sophisticated signal processing strategies desired for practical applications. To address issues like these, we have developed a digital system approach that uses the zero-crossing algorithm for phase detection. The phase detection limit and dynamic phase response of the system were assessed using surface acoustic wave (SAW) sensors. Our preliminary evaluation involved AlN dual-mode differential sensors, which were fabricated on an AlN(0001)/Al2O3(11 0) thin film structure, with the SAW and shear horizontal SAW (SH-SAW) operating at approximately 243 MHz and 256 MHz, respectively. Due to the hardware constraints, the digital phase processing was carried out in an off-line fashion. Our baseline experiments without sensor indicate that the system can achieve a lower level of phase noise with the standard deviation being about 0.005°. Experiments with the differential sensors running in the SAW and SH-SAW modes exhibit that the system can reach a phase detection limit of 0.02°. The differential system showed small temperature coefficient at ppm level measured by varying the sensor temperature using a thermal control oven. Finally, our use of the system in measuring the response of the SH-SAW sensor to sodium chloride (NaCl) solution conductivity shows that the system is capable of performing microanalysis of liquid properties. We conclude that a real-time fully digital phase detection system can be practically achieved.

Surface acoustic wave gas monitor for ppm ammonia detection

A shear horizontal surface acoustic wave (SH-SAW) sensor coated with polyaniline (PANI) film was investigated in this study. The frequency shift of SH-SAW was measured to detect the presence of ammonia. In addition, an analysis of humidity interference with the ammonia was performed. The SH-SAW sensor in this study responded to the ammonia gas and could be recovered using dry nitrogen. Detecting at an ammonia concentration of 20.45 ppm, the frequency shift was 1.79 ppm and the signal-to-noise ratio was 25.06 dB. This sensor had a response time of less than 150 s. Also, the frequency shift increased as the humidity increased. The cross-sensitivity varied nonlinearly with the ammonia concentration.

Development of methanol sensor using a shear horizontal surface acoustic wave device for a direct methanol fuel cell

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.

Taste sensors utilizing high-frequency SH-SAW devices

Recent interest in the development of taste sensors has been motivated by their potential application in the food and beverage industries as well as environmental monitoring. This paper describes the development of novel high-frequency dual delay line and two-port resonator shear-horizontal surface acoustic wave (SH-SAW) microsensors for liquid analysis. The acoustic devices have been designed to function without the need for analyte-specific coatings and to operate at the wireless ISM frequency of 433 MHz; the sensors are small, robust and are built on a piezoelectric substrate (36° YX LiTaO 3). Liquid samples are introduced to the active sensing area via a microfluidic cell that has been fabricated using microstereolithography (MSL) and then attached to the SH-SAW sensor substrate. A low cost flow system has been developed and integrated with the sensor housing to create a fully automated measurement system. Tests have been performed on aqueous solutions with different tastants representing not only the four basic tastes of saltiness, sweetness, sourness, and bitterness but also of umami and metallic. Results show that good discrimination between the different taste samples is possible using both delay-line and resonator type piezoelectric devices.

Measurements of Particles in Liquid Using Shear-Horizontal Surface Acoustic Wave Sensor

In this paper, we present interaction between a shear horizontal surface acoustic wave (SH-SAW) and particles in liquid. As the SH-SAW sensor can detect mechanical and electrical perturbations, a three-channel SH-SAW sensor is used in the experiments. The three-channel SH-SAW sensor simultaneously detects the mechanical and electrical perturbations. The SH-SAW sensor for the electrical perturbation detection is influenced by the particles in liquid. Therefore, it has high potential for detecting particles in liquid. On the other hand, the SH-SAW sensor for mechanical perturbation detection does not detect the particles in liquid. To detect the particles based on the mechanical perturbation, influence of viscous penetration is discussed.

Measurements of Particles in Liquid Using Shear-Horizontal Surface Acoustic Wave Sensor

not Available.

ATR-FTIR spectroscopic analysis of sorption of aqueous analytes into polymer coatings used with guided SH-SAW sensors

Attenuated total internal reflectance Fourier transform infrared (ATR-FTIR) spectroscopy was used for the investigation of sorption of aqueous solutions of analytes into polymer coatings. A series of simple model polymers, such as poly(dimethylsiloxane), poly(epichlorhydrin), and poly(isobutylene), and films and analytes, such as aqueous solutions of ethylbenzene, xylenes, toluene, and nitrobenzene, were used to evaluate the use of ATR-FTIR spectroscopy as a screening tool for sensor development. The ratios of integrated infrared absorption bands provided a simple and efficient method for predicting trends in partition coefficients. Responses of polymer-coated guided shear horizontal surface acoustic wave (SH-SAW) sensor platforms to the series of analytes, using polymer coatings with similar viscoelastic properties, were consistent with ATR-FTIR predictions. Guided SH-SAW sensor responses were linear in all cases with respect to analyte concentration in the tested range. Comparison of ATR-FTIR data with guided SH-SAW sensor data identifies cases where mass loading is not the dominant contribution to the response of the acoustic wave sensor. ATR-FTIR spectra of nitrobenzene, coupled with computational chemistry, provided additional insight into analyte/polymer interactions.