Surface Acoustic Wave Impedance Research Articles

Single Interdigital Transducer as Surface Acoustic Wave Impedance Sensor

Surface acoustic wave (SAW) devices are well-known for gravimetric sensor applications. In biosensing applications, chemical- and biochemically evoked adsorption processes at surfaces are detected in liquid environments using delay-line or resonator sensor configurations, preferably in combination with appropriate microfluidic devices. In this paper, a novel SAW-based impedance sensor type is introduced which uses only one interdigital electrode transducer (IDT) simultaneously as SAW generator and sensor element. It is shown that the amplitude of the reflected S11 signal directly depends on the input impedance of the SAW device. The input impedance is strongly influenced by mass adsorption which causes a characteristic and measurable impedance mismatch.

Quantitative Determination of Escherichia Coli in Water Sources in the Environment Using a Surface Acoustic Wave Impedance System Modified with a Syringe Filter

A novel surface acoustic wave (SAW) sensor was developed in the study to measure the density of Escherichia coli in water sources in the environment. With a modified syringe filter sealed by a Teflon cover, the sensor system ensured that the CO2 gas produced by bacteria flowed upward and accumulated at the headspace of the syringe filter. The measurements were obtained by immersing a pair of electrodes into a sealed syringe filter which contained a culture solution containing lauryl sulfate trytose (LST). The changes in frequency of the two electrodes were caused by generation of small CO2 bubbles on the surface of the electrodes, which were connected in series to a SAW resonator. The signals obtained by the system were 10 times greater than those obtained by conventional SAW systems. The calibration curve of detection time versus density of E. coli showed a linear relationship with a correlation coefficient (R 2 ) of 0.9434 over the range of 102 to 107 cells/mL. Further integration of this sensing system with a suitable automated sampling device will enable this device to be used on-site for analysis and field studies.

A novel surface acoustic wave-impedance humidity sensor based on the composite of polyaniline and poly(vinyl alcohol) with a capability of detecting low humidity

This paper presents a novel humidity sensor composed of a 433MHz surface acoustic wave (SAW) resonator and an interdigitated gold electrode connected in series. The gold electrode was covered with a sensitive film of a composite of processable conductive polyaniline and polyvinyl alcohol. The frequency response of the novel SAW-impedance humidity sensor toward relative humidity (RH) was investigated at room temperature. The sensitivity of the SAW-impedance humidity sensors increased with the increase in the conductivity of the sensitive film. The sensor showed a sensitivity of ∼7.4kHz/%RH at 30%RH, which was increased to 60kHz/%RH at 47%RH. Moreover, such sensors exhibited short response and recovery times and good repeatability. It is worth noting that the sensor showed a linear frequency response to humidity over the range of 0.4–20%RH with a good sensitivity of ∼2kHz/%RH, which reveals its potentials for detecting low humidity.

A surface acoustic wave impedance loaded sensor for wireless humidity measurement

The control of humidity is required in various areas such as the smart living space, industry, agriculture, and medicine. To reduce cost and increase lifetime, a wireless humidity sensor without an additional power supply should be developed to fulfill their needs. Recently, there are more and more efforts on surface acoustic wave (SAW) based radio frequency identification (RFID) system. The RFID system primarily consists of a reader and transponders, composed of SAW tags and antennas. Due to the capabilities of passive operation and wireless connection, SAW tags are also suitable for remote sensing. Therefore, in this study, a wireless humidity sensor is accomplished by integrating a 433MHz 128°YX‐LiNbO3 SAW tag with a resistive humidity sensor. The SAW tag is designed as an impedance loaded sensor. Moreover, because nanostructure sensing materials possess high surface‐to‐volume ratio, large penetration depth, and fast charge diffusion rate, CSA‐doped polyaniline nanofibers are synthesized by the interfa...

Surface acoustic wave impedance element ISM duplexer: modeling and optical analysis.

Surface acoustic wave (SAW) impedance element antenna duplexers provide compact, high performance, front-end components apt for industrial fabrication. We describe investigations on the design and modeling of a compact ISM antenna duplexer fabricated on a 36 degrees YX-cut LiTaO3 substrate based on SAW impedance elements. In particular, we have performed 3-D modeling of the inductive and capacitive electromagnetic couplings caused by the package parasitics for the duplexer. The use of a 1:3 IDT structure for the reduction of the passband width is discussed. The frequency response of the duplexer is predicted with the help of circuit simulation; the modeling is refined by optimization of the model parameters to improve the fit between the measured and simulated responses. We also report scanning optical imaging of the acoustic field within the resonator structures with the help of laser interferometry; this provides insight into the loss mechanisms beyond that attainable in mere electric measurements.

Enzymatic Determination of Organo-Phosphorus Pesticides with a Surface Acoustic Wave Impedance Sensor

A novel and sensitive method, based on the inhibition of the lipase-catalyzed hydrolysis by combining hydroxyle groups of lipase with organophosphorous pesticide, is proposed for the enzymatic determination of organophosphorous pesticide. The inhibited enzymatic reaction is monitored with an SAW/impedance enzyme transducer, which is composed of an SAW resonator, oscillating at 61 MHz, and a pair of parallel electrodes. Employing the method described, the frequency response of the transducer is proportional to organophosphorus pesticide concentration over the range of 227ng/mL - 2.27μg/mL; the detection limit is 76ng/mL. The effects of temperature, pH, incubation, and solvent are also investigated. The method was successfully applied to the determination of dichlovors residues in the root, stem, and blade of Chinese cabbage.

Measurement of Serum Alkaline Phosphatase with a Surface Acoustic Wave Impedance Sensor Device

Measurement of Serum Alkaline Phosphatase with a Surface Acoustic Wave Impedance Sensor Device

A nonlinear regression model applied to kinetic multi‐component analysis of esters with a SAW‐impedance sensor

AbstractA kinetic nonlinear regression model for multi‐component assay of esters was proposed based on their different alkaline‐catalysed hydrolysis rate. The reaction rate was determined by monitoring the conductance change in solution with a liquid‐purpose surface acoustic wave impedance sensor(SAW). The model was tested theoretically and experimentally with the mixture of methyl acetate and n‐propyl acetate. The experimental detection limit of methyl acetate and n‐propyl acetate (within 10 min) was 0.5 μmol/L and 1.0 μmol/L respectively and the recovery of the sensor system ranged from 93% to 106% (n=6).

Assay of NAD+-Isocitrate Dehydrogenase in Extracts of Bread Yeast with a Surface Acoustic Wave Impedance Sensor.

The regulatory property of NAD+-isocitrate dehydrogenase (NADMCDH) was studied by means of a new device, a surface acoustic wave (SAW) impedance sensor, which comprises a 61 MHz SAW resonator and a pair of parallel platinum electrodes. The NAD+-ICDH is an allosterically regulated enzyme which shows sigmoidal kinetic for DL-isocitrate. The Hill coefficient was estimated to be 2.93. A linear relationship between the frequency response and the enzyme concentration was obtained, and the experimental detection limit was evaluated to be 45 mlU/ml. A comparison between the SAW impedance sensor and the conductometric method was carried out. The effects of AMP, ADP and ATP on the kinetic property of NAD+-ICDH were investigated; some other factors, such as the temperature and pH value, are also discussed.

Enzymic analysis of L-lactate dehydrogenase (LDH) with a surface acoustic wave impedance sensor and its application in the determination of LDH activity in human serum

A new method is described for the determination of L-lactate dehydrogenase (LDH) using a surface acoustic wave impedance sensor. The assay of this enzyme is based on the change in conductance of the solution caused by enzymic reaction between lactate, NAD+ and LDH. A linear relationship between frequency response and enzyme concentration was obtained and the detection limit was 4.8 U ml–1. The Michaelis constant for lactate and the corresponding maximum initial rate were 0.03 mol l–1 and 13 kHz min–1, respectively. Influences such as temperature, pH value and interferents were also investigated. The method was successfully applied in the clinical assay of LDH activity in human serum. The results compared well with the reported values and support the clinical diagnosis.

Rapid Determination of Acid Phosphatase by a Surface Acoustic Wave Impedance Sensor

Abstract A new type of surface acoustic wave impedance sensor based on a conductance-surface acoustic wave frequency reponse was applied to assay the activity of acid phosphatase. Using cytidine-5′-monophosphate (5′-CMP) as a substrate, the Michaelis constant and the corresponding maximum initial rate were estimated to be 4.13×10−3 and 9827 Hz/min, respectively. A linear relationship between frequency response and enzyme concentration was obtained in the range up to 250 μg/ml of acid phosphatase, at 25°C and pH 4.5. The experimental detection limit of acid phosphatase (within 1 min) was 0.9 min/ml and the recovery of the sensor system ranged from 94% to 106% (n = 6). Some other factors such as temperature, pH value and the effects of some metal ions were also discussed.

Circuit network analysis method applied to surface acoustic wave impedance system in liquids

The circuit network theory was applied to analyse a surface acoustic wave (SAW) impedance system constructed from a 61-MHz SAW resonator and a pair of conductive electrodes in series. Two oscillation equations were derived and used to explain the effects of solution capacitance and cell constant on the frequency characteristics. The effects of the solution density and the viscosity on the frequency response of the SAW impedance system were also investigated. The SAW impedance system can be applied to conductivity measurements in solution with a high concentration background of foreign electrolytes.