Commercial Surface Acoustic Wave Research Articles

The Application of Commercial Surface Acoustic Wave Radio Communication Filters as Transducers for DMMP Sensors.

In the present study, we used two popular radio communication SAW resonators as a base for gas sensors and tested their performance. Taking into account issues related to sensor sensitivity, the possibility of applying a sensor layer, the availability of devices, and other related issues, we selected two popular single-port resonators with center frequencies of 315 and 433 MHz (models R315 and R433, respectively) for testing purposes. Both resonators were equipped with a sensitive film of hexafluoroisopropanol-substituted polydimethylsiloxane, a material that selectively absorbs molecules with a high ability to form basic hydrogen bonds. Fabricated sensors were used to detect trace amounts of dimethyl methylphosphonate (DMMP) vapor, which has often been used in similar studies as a nerve chemical warfare agent simulant. Sensors using both devices loaded with sensor layers of an optimal thickness rapidly reacted to a gas containing DMMP at a concentration of 3 mg/m3, generating a stable analytical signal ranging from several to several dozen kilohertz. In the case of R433, the frequency signal was 20.5 kHz at 1 min from the beginning of exposure to DMMP. The obtained results showed that the used transducers exhibited good performance as a base for gas sensors. Finally, their suitability for sensing applications was confirmed by a comparison with the results obtained in previous similar studies.

On the Performance Evaluation of Commercial SAW Resonators by Means of a Direct and Reliable Equivalent-Circuit Extraction

Nowadays, surface acoustic wave (SAW) resonators are attracting growing attention, owing to their widespread applications in various engineering fields, such as electronic, telecommunication, automotive, chemical, and biomedical engineering. A thorough assessment of SAW performance is a key task for bridging the gap between commercial SAW devices and practical applications. To contribute to the accomplishment of this crucial task, the present paper reports the findings of a new comparative study that is based on the performance evaluation of different commercial SAW resonators by using scattering (S-) parameter measurements coupled with a Lorentzian fitting and an accurate modelling technique for the straightforward extraction of a lumped-element equivalent-circuit representation. The developed investigation thus provides ease and reliability when choosing the appropriate commercial device, depending on the requirements and constraints of the given sensing application. This paper deals with the performance evaluation of commercial surface acoustic wave (SAW) resonators by means of scattering (S-) parameter measurements and an equivalent-circuit model extracted using a reliable modeling procedure. The studied devices are four TO-39 packaged two-port resonators with different nominal operating frequencies: 418.05, 423.22, 433.92, and 915 MHz. The S-parameter characterization was performed locally around the resonant frequencies of the tested SAW resonators by using an 8753ES Agilent vector network analyzer (VNA) and a home-made calibration kit. The reported measurement-based study has allowed for the development of a comprehensive and detailed comparative analysis of the performance of the investigated SAW devices. The characterization and modelling procedures are fully automated with a user-friendly graphical user interface (GUI) developed in the Python environment, thereby making the experimental analysis faster and more efficient.

Measuring Torque and Temperature in a Rotating Shaft Using Commercial SAW Sensors

Real-time monitoring of torque in a rotating shaft is not easy to implement with technologies such as optic fiber sensors or strain gages. Surface acoustic wave (SAW) sensors are wireless and passive and can be used to monitor strain in moving parts. Commercial solutions (sensors, antennas and interrogation unit) can easily be purchased from some companies; however, they are not customized and may not meet the specificity of the measurements. In order to evaluate the adequacy of commercial off-the-shelf (COTS) solutions, temperature and strain sensors fabricated by SENSeOR (Besançon, France) were mounted on a load cell. The sensors were calibrated using a thermal chamber and a universal testing machine. The load cell was then assembled together with a steel shaft that rotated at different speeds inside an oven. The commercial antennas were replaced with an RF (radio frequency) coupler and the sensors were interrogated with the commercial interrogation unit. The influence of rotation in the accuracy on the measurements, as well as the adequacy of the sensors structure, was evaluated. It can be concluded that SAW sensors can be used to measure temperature or torque in a rotating environment; however, some customization of the components is required in order to overcome the limitations posed by COTS sensing solutions.

Custom PXIe-567X-Based SAW RFID Interrogation Signal Generator

This paper presents a fully reconfigurable and reliable PXIe-567X software-defined interrogation signal generator for surface acoustic wave (SAW)-based passive radio frequency identification (RFID). Contrary to most commercial SAW RFID readers that operate only at a unique predefined frequency, the proposed vector signal generator is aimed to operate at any frequency defined by the user, from 85 MHz to 6.6 GHz, including the 902–928 MHz and 2.45-GHz industrial scientific and medical bands. The PXIe-567X-based signal generator can accurately generate not only conventional ON–OFF keying (OOK)-modulated or pulsed binary phase shift keying (BPSK)-modulated SAW RFID interrogation signals, but also completely user-defined interrogation signals. A custom LabVIEW user interface that allows to control the carrier frequency, the power, and the waveform of the interrogation signal has been designed. The operator can switch between custom waveforms without resetting and reprogramming the whole system. The proposed RFID request signal generator has been validated using a complete measurement setup. Time-domain and frequency-domain validation tests of OOK modulated and wideband pulsed BPSK-modulated signal generation have been conducted at 170, 340, 915 MHz and 2.45 GHz. Very accurate results have been obtained. The PXIe-567X-based RFID interrogator has been tested with a fabricated 3-b SAW RFID tag. The operability of the entire SAW RFID system has been demonstrated.

Development of a hydrogen gas sensor using a double SAW resonator system at room temperature.

A double SAW resonator system was developed as a novel method for gas sensing applications. The proposed system was investigated for hydrogen sensing. Commercial Surface Acoustic Wave (SAW) resonators with resonance frequencies of 433.92 MHz and 433.42 MHz were employed in the double SAW resonator system configuration. The advantages of using this configuration include its ability for remote measurements, and insensitivity to vibrations and other external disturbances. The sensitive layer is composed of functionalized multiwalled carbon nanotubes and polyaniline nanofibers which were deposited on pre-patterned platinum metal electrodes fabricated on a piezoelectric substrate. This was mounted into the DSAWR circuit and connected in parallel. The sensor response was measured as the difference between the resonance frequencies of the SAW resonators, which is a measure of the gas concentration. The sensor showed good response towards hydrogen with a minimum detection limit of 1%.

Response mechanism for surface acoustic wave gas sensors based on surface-adsorption.

A theoretical model is established to describe the response mechanism of surface acoustic wave (SAW) gas sensors based on physical adsorption on the detector surface. Wohljent's method is utilized to describe the relationship of sensor output (frequency shift of SAW oscillator) and the mass loaded on the detector surface. The Brunauer-Emmett-Teller (BET) formula and its improved form are introduced to depict the adsorption behavior of gas on the detector surface. By combining the two methods, we obtain a theoretical model for the response mechanism of SAW gas sensors. By using a commercial SAW gas chromatography (GC) analyzer, an experiment is performed to measure the frequency shifts caused by different concentration of dimethyl methylphosphonate (DMMP). The parameters in the model are given by fitting the experimental results and the theoretical curve agrees well with the experimental data.

Isolation Circuits Based on Metamaterial Transmission Lines for Multiplexers(Invited Paper)

Multiplexers based on isolation circuits made of metamaterial lines are proposed and studied. The new approach provides unique advantageous features beneficial to system designer. For instance, there is no need to modify the filters used in multiplexers. Also, the design process is straightforward. In this paper, two types of multiplexers based on metamaterial isolation circuits are presented, and their operation concepts are explained. Also, theories and design process of isolation circuits are presented to help readers design and fabricate proposed multiplexers. For verifying the concepts, two types of triplexers and two types of quadruplexers are designed and fabricated. All filters used in the multiplexers are commercial surface acoustic wave filters. The measured results are well matched with the simulation results.

Dielectrophoretic responses of DNA and fluorophore in physiological solution by impedimetric characterization

Characterization of the DNA's dielectrophoretic (DEP) behavior is the foundation of DNA manipulation by electric fields. This paper presents a label-free DNA differentiation technique by a combination of DEP response and impedimetric measurement on the microchip.In contrast to most of the recent studies on DEP manipulation of DNA that use deionized water or diluted DNA buffer where living biomolecules cannot survive, we used physiological solutions (PBS with 154mM Na+) that are highly practical for pursuing DNA-based physical applications. The microchip, a commercial surface acoustic wave resonator, contains an array of interdigitated aluminum electrodes (1.4μm width, 1.1μm gap) on quartz substrate for DEP trap. Measurements were taken with a high precision impedance analyzer, which also acted as the excitation source to induce DEP response at 20kHz, 50kHz, 100kHz, 300kHz, 500kHz, 1MHz, 2MHz and 5MHz (N=3). To verify DEP response, fluorescence microscope images were captured before and after the electric excitation. Test results from the DEP experimentation after comparing with fluorescent images of pUC18 DNA show that a large change in impedance corresponds to positive DEP while little change corresponds to negative DEP. The strongest p-DEP and the maximum collection efficiency were observed around 300kHz for supercoiled pUC18 and 100kHz for linear λDNA. This work yields real-time impedimetric DEP response of DNA of different molecular conformations in practical settings. The technique can serve as the basis for submicron particle separation, disease diagnosis, cell life-circle research, and other applications in physiological surroundings.

HUMIDITY SENSOR USING NIPAAm NANOGEL AS SENSING MEDIUM IN SAW DEVICES

In this paper we report poly N-isopropylacrylamide (NIPAAm) nanogel used as sensing medium in Rayleigh wave type surface acoustic wave (SAW) devices to measure relative humidity. NIPAAm is synthesized by single-step surfactant-free emulsion polymerization reaction method. The prepared nanogel particles have dimensions less than 180 nm. Dynamic light scattering (DLS) analysis of these particles shows increase in size of the particles up to 100% when dispersed in water at room temperature. In this work we have developed two types of relative humidity (RH) sensors. In the first type commercial SAW resonators with resonance frequency at 315 MHz from EPCOSTM were used in our experiment. The casings of two resonators were removed carefully and one of them was left as such to serve as the reference device. The other was coated with the NIPAAm nanogel and used as the sensor. In the second type of SAW-based humidity sensor aluminum interdigital transducers (IDT) are fabricated over YZ lithium niobate piezoelectric substrate using metallization and lithography techniques. The fabricated IDTs have the pitch length of 34 μm and a resonance frequency of 51.6 MHz. Response of sensor to RH is measured by measuring the scattering parameters of both the types of sensors and reference devices recorded using the network analyzer.

Fabrication methods for creating flexible polymer substrate sensor tags

The authors describe the design, fabrication, and testing of a passive wireless sensor platform utilizing low-cost commercial surface acoustic wave (SAW) filters and sensors. Polyimide and polyethylene terephthalate sheets are used as substrates to create a flexible sensor tag that can be applied to curved surfaces. A microfabricated antenna is integrated on the substrate in order to create a compact form factor. The sensor tags are fabricated using 315MHz SAW filters and photodiodes and tested with the aid of a fiber-coupled tungsten lamp. Microwave energy transmitted from a network analyzer is used to interrogate the sensor tag. Due to an electrical impedance mismatch at the SAW filter and sensor, energy is reflected at the sensor load and reradiated from the integrated antenna. By selecting sensors that change electrical impedance based on environmental conditions, the sensor state can be inferred through measurement of the reflected energy profile. Testing has shown that a calibrated system utilizing this type of sensor tag can detect distinct light levels wireless and passively. The authors also demonstrate simultaneous operation of two tags with different center passbands that detects light. Ranging tests show that the sensor tags can operate at a distance of at least 3.6m.

A technique to measure hydrogen absorption in isolated nanometer structures

We describe an apparatus assembled to measure hydrogen absorption on a monolayer of isolated nanometer scale entities. Utilizing inexpensive and readily available high frequency surface acoustic wave (SAW) sensors we achieve a sensitivity of 4 pg, sufficient to detect hydrogen uptake at less than 1% in nanogram level samples of such entities at room temperature. Results of hydriding rare earth metal nanoparticles and a transition metal-carbon complex measured with 315 MHz SAW resonators are presented. However, the design of our apparatus is general and can be used with a wide variety of commercial SAW sensors.

A surface acoustic wave sensor modified from a wireless transmitter for the monitoring of the growth of bacteria

This work presents a novel surface acoustic wave (SAW) sensor for the measurement of the microbial count in a biological culture. The signal translation interface of the sensor was modified using a common commercial wireless SAW transmitter design. A pair of conductive electrodes was inserted in a 314.5 MHz SAW stabilized oscillator of the transmitter. Measurements were made by placing the electrodes within the culture solution of interest and measured the time required to identify readily detectable frequency changes (detection time, DT). The change of frequency was caused by the impedance change of the microbial metabolism. The calibration curve of detection times against density of Escherichia coli shows a linear correlation coefficient ( R 2 = 0.924) over the range of 10 2 to 10 7 cells/mL. A sample that contains 10 2 cells/mL of E. coli required a detection times (DT) of 7 h, shorter than was required using instruments based on conventional conductance methods. The proposed ultra high frequency SAW sensor (314.5 MHz) shows a large total frequency change and gives a sharp inflexion at the DT but possesses the same stability compared with that of low frequency serial piezoelectric quartz crystal (PQC) sensor for the measurement of bacteria concentration. This sensor platform enabled real time monitoring of bacterial growth within a sealed opaque container. This sensor is potentially applicable to a remote query wireless measurement in hazardous environments when a suitable antenna device is adapted.

A New Configuration of Surface Acoustic Wave Intermediate-Frequency Filter with Compact Size and Improved Insertion Loss

Size reduction is always a major challenge to surface acoustic wave (SAW) manufacturers. For some years, commercial SAW filter designers have been developing various configurations of SAW filters just to fit into a smaller package. In this work, a new single-phase unidirectional transducer (SPUDT) based intermediate-frequency (IF) filter with improved insertion loss and compact size is proposed. This filter has an architecture that combines electrode-width controlled single-phase unidirectional transducer (EWC-SPUDT) and comb-type SPUDT. As a result of this improvement, a filter for IF-filtering of Digital European Cordless Telephone (DECT) system can be squeezed into a surface-mount device (SMD) 7.0×5.0 mm2 package. The performance of this filter even excels most commercial available IF filters in the same application.

Accurate measurements of the acoustical physical constants of LiNbO/sub 3/ and LiTaO/sub 3/ single crystals

The acoustical physical constants (elastic constant, piezoelectric constant, dielectric constant, and density) of commercial surface acoustic wave (SAW)-grade LiNbO(3) and LiTaO(3) single crystals were determined by measuring the bulk acoustic wave velocities, dielectric constants, and densities of many plate specimens prepared from the ingots. The maximum probable error in each constant was examined by considering the dependence of each constant on the measured acoustic velocities. By comparing the measured values of longitudinal velocities that were not used to determine the constants with the calculated values using the previously mentioned constants, we found that the differences between the measured and calculated values were 1 m/s or less for both LiNbO(3) and LiTaO(3) crystals. These results suggest that the acoustical physical constants determined in this paper can give the values of bulk acoustic wave velocities with four significant digits.