Surface Transverse Wave Resonators Research Articles

Asynchronous STW resonators with the high quality factor and reduced sizes

Surface transverse waves (STW) on quartz have the high propagation velocity, which is higher by 60% than velocity of the Rayleigh surface acoustic waves (SAW), high temperature stability comparable with temperature stability of SAW on quartz. Those advantages allow successfully use STW in the high frequency resonators. However, a large number of the electrodes 400 in the reflectors is required to ensure the high quality factor of the resonators. This leads to increase the resonators sizes, especially on the frequencies < 1000 MHz. The 500-1000 MHz STW resonators with high quality factor on 36°YX90° cut quartz and reduced size were presented. Use of the asynchronous topology, constructional, topological and technological optimization with a computer simulation on the base of a equivalent circuit model allowed obtain in the frequency range of 500-1000 MHz the high quality factor of 8600-9500, reduced sizes of the topology in comparison with the known prototypes and place the resonators in the 3×3×1.2 mm and 5×5×1.8 mm SMD packages. The developed STW resonators with high quality factor and reduced sizes will be widely used in the miniature low noise oscillators.

USE OF THE SURFACE TRANSVERSE WAVES (STW) – 
 ONE OF EFFICIENT METHODS FOR ENHANCEMENT 
 OF THE SAW DEVICES OPERATING FREQUENCIES

This paper presents an efficient method for enhancement of the operating frequen-cies of the SAW devices - use of surface transverse waves (STW) with high propa-gation velocity V = 5000 m/s on a standard piezomaterial quartz. The approaches for a realization of the STW resonators with the high quality factor and STW filters with the low insertion loss were considered. The quantitative and qualitative char-acteristics of above 1 GHz STW devices for each approach were given.

Long-term capability of polymer-coated surface transverse wave sensors for distinguishing vapors of similar hydrocarbons

Arrays with polymer-coated sensors have successfully been introduced for the detection of volatile organic compounds (VOC). The VOCs are typically identified via the signal pattern delivered by the sensor array. Therefore, if the VOCs are to be monitored over a longer period, long-term stability of all polymer layers within the array is required. In this study, an array of eight surface transverse wave resonators coated with different polymers was used for semi-annual measurements within one year. The sensor array was used to distinguish between either two aromatic hydrocarbons, i.e., xylene and toluene, or two aliphatic hydrocarbons, i.e., octane and cyclohexane. The polymer coatings proved to be robust as no significant time-related changes of sensor signals and signal patterns were observed. The polymer-coated sensors enabled differentiation of similar aromatic and similar aliphatic hydrocarbons, respectively, as well as subsequent quantification of the VOCs during the complete one-year study.

Passive wireless measurement of tension for overhead transmission line based on surface transverse wave

This study presents a passive wireless surface transverse wave (STW) torsion sensor for an overhead transmission line (OHTL). Two key techniques, namely the design of STW sensing element and clamping structure, were investigated. The relationship between the tension and the frequency shift of the STW resonator was analysed. A numerical analysis on the tension sensitivity and temperature coefficient using different cut types was performed. Results showed that Y − 51° cut quartz, which has a close to zero temperature coefficient of frequency, is a suitable substrate of the STW tension sensors. Other parameters were optimised to obtain a resonator with a Q value of >11,000. Two STW resonators were adopted as sensing element to form a differential structure to reduce the temperature interference. An OHTL clamping and tension transfer mechanical structure was designed, which has an ability of adjusting the tension sensitivity and can be easily installed at any point of OHTL. Moreover, the OHTL tension measurement system was set up and evaluated. Experimental results indicated that the STW tension sensitivity was 24.31 kHz/kN, the non-linearity was 0.26%, and the repeatability error was 0.32%. The OHTL tension measurement method is feasible for practical application.

Long-Term Stability of Polymer-Coated Surface Transverse Wave Sensors for the Detection of Organic Solvent Vapors.

Arrays with polymer-coated acoustic sensors, such as surface acoustic wave (SAW) and surface transverse wave (STW) sensors, have successfully been applied for a variety of gas sensing applications. However, the stability of the sensors’ polymer coatings over a longer period of use has hardly been investigated. We used an array of eight STW resonator sensors coated with different polymers. This sensor array was used at semi-annual intervals for a three-year period to detect organic solvent vapors of three different chemical classes: a halogenated hydrocarbon (chloroform), an aliphatic hydrocarbon (octane), and an aromatic hydrocarbon (xylene). The sensor signals were evaluated with regard to absolute signal shifts and normalized signal shifts leading to signal patterns characteristic of the respective solvent vapors. No significant time-related changes of sensor signals or signal patterns were observed, i.e., the polymer coatings kept their performance during the course of the study. Therefore, the polymer-coated STW sensors proved to be robust devices which can be used for detecting organic solvent vapors both qualitatively and quantitatively for several years.

Characterization of Protein Using Two-Port STW Resonators

A surface acoustic wave (SAW) is an acoustic, mechanical wave that propagates on the surface of a piezoelectric crystal. Coupling to any medium that interacts the surface strongly affects the velocity and amplitude of the wave. In a typical surface transversal wave (STW) resonator, an electrical signal is converted at interdigital transducers (IDT’s) into polarized transversal waves travelling parallel to the sensing surface, utilizing the piezoelectric properties of the substrate material. This approach is very sensitive to biological interactions on the sensor surface. Typically, the wave transmitted is confined to the surface of the substrate. Thus, the acoustic energy is concentrated within the guiding layer rather than in the bulk of the piezoelectric material. The sensitivity of the sensor for surface modifications is increased, by the choice of material, and the design of the guiding layer as well as by the structure of the sensor and the transducers. The output signals are transformed in terms of their frequency or phase with respect to the input signals, due to the interaction of the input signal with the fluid contacting the sensitive surface. Surface acoustic wave (SAW) devices hold a promise in providing ultra fast sensing platform. Research focus is on studying methods to characterize conductance, susceptance, viscosity, and other properties of protein samples, like albumin using Two-Port Surface Transverse Wave (STW) resonator devices quickly and inexpensively using nano-liter volume. When a mass is deposited on the electrode the resultant decrease in resonant frequency can detect mass changes at nanogram level. We propose to advance the sensitivity of the characterization by use of quartz Two-Port STW resonator since they can operate at much higher frequency than bulk wave oscillators.

Original coupled FEM/BIE numerical model for analyzing infinite periodic surface acoustic wave transducers

This paper proposes a new numerical coupled Finite Element Method/Boundary Integral Equations (FEM/BIE) technique which allows the 2D physical simulation of Surface Acoustic Waves (SAWs) transducers infinitely periodic in one direction. This new technique could be generalized to various periodic acoustic 2D simulations.This new method uses an original Variational Formulation (VF) which formally includes harmonic periodic boundary conditions, and, efficient boundary integral formulations allowing to account for the semi-infinite dielectric and piezoelectric spaces. In the case of the piezoelectric semi-space, the Green’s functions are efficiently computed using Fahmy–Adler’s method [8]. Only periodic boundary conditions are needed, which greatly simplifies the code implementation.This numerical model has been developed to analyze an Inter-Digital Transducer (IDT) with complex electrode shape (unburied, buried or raised electrodes). The use of buried electrodes in SAW transducer designs on quartz has important advantages when compared with unburied metal electrodes on the surface. One important property is the suppression of transverse waveguide modes in transducers. A second advantage is the ability to use thicker metal thereby reducing the resistive losses. Buried electrodes have also been shown to increase the quality factor of Surface Transverse Wave (STW) resonators [15]. This numerical model is a very useful tool for optimizing the electrode geometry. Analysis of raised electrodes is useful for predicting the effects of Reactive Ion Etch (RIE) on the SAW or STW electrical filter characteristics. RIE is commonly used as a frequency trimming technique for SAW or STW filters on Quartz.The first part of the paper presents the theory, and, the second part is devoted to numerical validations and numerical results.

Method for nondestructive testing of the film coating behavior of surface acoustic wave (SAW) sensors

This paper presents a practical non-destructive method for studying the film coating behavior of SAW devices by using a water soluble dielectric film (manitol) deposited on the SAW device surface by resistive evaporation. After measuring the electrical parameters of the film coated SAW device, the film can easily be removed from its surface by water rinsing without causing any damage to it. The SAW device can then be used over and over again in a large number of film depositions. The method was tested on a 1 GHz surface transverse wave (STW) resonator coated with manitol of varying thickness. After each coating and evaluation, the STW device was successfully recovered without significant performance degradation. Data is presented on the electrical changes of the STW device as a result of depositing manitol coatings of various thicknesses.

STW resonator with organo-functionalized metallic nanoparticle film for vapor sensing

A 1 GHz surface transverse wave resonator on 36 degrees Y-cut quartz plate coated with organothiol-functionalized gold nanoparticle film has been studied as a chemical gas sensor. Considerable sensitivity of the resonant frequency to vapors of ethanol, methanol, chloroform, and acetic acid has been found. Owing to the high short-term stability of the oscillator built, the detection limit is in the low ppm range. The results qualitatively confirm previous results on the same film type obtained by conductivity measurements. In the present case, the conductivity effect resulting from variable separation of nanoparticles is accompanied with surface-attached mass of the absorbed gas. The film matrix exhibits considerable capacity to absorb large amounts of molecules at high gas concentrations.

A mixed finite element/boundary element approach to simulate complex guided elastic wave periodic transducers

The development of new surface acoustic wave devices exhibiting complicated electrode patterns or layered excitation transducers has been favored by an intense innovative activity in this area. For instance, devices exhibiting interdigital transducers covered by piezoelectric or dielectric layers have been fabricated and tested, but the design of such structures requires simulation tools capable to accurately take into account the actual shape of the wave guide elements. A modeling approach able to address complicated surface acoustic wave periodic structures (defined in the saggital plane) exhibiting any geometry then has been developed and implemented. It is based on the combination of a finite element analysis and a boundary element method. A first validation of the computation is reported by comparison with standard surface wave devices. Surface transverse wave resonators covered by amorphous silica have been built and consequently used for theory/experiment assessment. Also the case of recessed electrodes has been considered. The proposed model offers large opportunities for modeling any two-dimensional periodic elastic wave guide.

STW two-port asynchronous resonator on BT-cut quartz

A surface transverse wave (STW) 2-port asynchronous resonator on BT-cut (-50.5 degrees YX90 degrees) quartz was fabricated, measured, and calculated. At a frequency of about 332.4 MHz, insertion loss, and loaded and unloaded quality factors of about 11 dB, 8,000, and 11,500, respectively, were achieved. A turnover temperature of about 20 degrees C and a quadratic frequency-temperature coefficient of approximately -15 ppb/degrees C(2) were obtained. Compared with STW resonators on AT-cut quartz (36 degrees YX90 degrees), this temperature coefficient is about 4 times smaller, and about 2 times smaller than that for SAW on an ST cut. STW resonators and filters on BT-cut quartz can be used in applications requiring improved temperature stability.

STW in-line acoustically coupled resonator filter on quartz

The scattering-matrix method was used for design of a surface transverse wave (STW) in-line acoustically coupled resonator filter on quartz. In this filter, two one-port STW resonators were coupled by means of a center reflector, grating phase shifters were placed between interdigital transducers and reflectors, and the pass band of the filter was located near the center frequency of the reflectors. At a frequency of about 509 MHz, insertion loss of about 5 dB and a 3 dB bandwidth of about 0.23 MHz was obtained. Differences between the measured and calculated amplitude responses are explained and design guidelines are presented. High STW velocity, low insertion loss, and very weak transverse mode make this filter attractive for high-frequency applications.

Accurate measurement of anhydride fluorhydric acid concentration in controlled gaseous flow with STW sensors

This paper presents theoretical and experimental developments for the implementation of surface acoustic waves (SAW) sensors able to detect small concentrations of anhydride fluorhydric (HF) acid in air. Solutions based on the use of surface transverse waves (STW) on quartz (YXlt)/36 degrees/90 degrees have been analyzed to evaluate their sensitivity to HF. Devices have been tested first in a NH4F solution to evaluate the kinetics of the reaction. Measurements then were performed under various gaseous conditions to characterize the sensors when they are submitted to different controlled dilutions of HF in air. STW resonators have been successfully tested in different conditions, with capabilities to detect HF concentration much smaller than 1 ppm.

A Low Phase-Noise Voltage-Controlled SAW Oscillator With Surface Transverse Wave Resonator for SONET Application

A surface transverse wave (STW) resonator-based oscillator was developed in response to SONET OC-48 application. To meet the low jitter objective, a high-Q STW resonator was designed and fabricated in this study. The residual phase-noise measurement techniques are used to evaluate the feedback oscillator components, such as the loop amplifier, STW resonator, and electronic phase shifter, which can play important roles in determining the oscillator's output phase-noise spectrum. The oscillator's white phase-noise floor is -170dBc/Hz for carrier-offset frequency greater than 1 MHz. The oscillator's phase-noise level is -67dBc/Hz at a 100-Hz carrier offset. Both low close-in phase-noise and low white phase-noise floor makes the oscillator meet low jitter requirement. The electronic frequency tuning range exceeds plusmn200ppm. The oscillator provides 13.5 dBm of output power and consumes 65 mA from +5-V power supply

Phase-noise reduction in surface wave oscillators by using nonlinear sustaining amplifiers

Nonlinear sustaining amplifier operation has been investigated and applied to high-power negative resistance oscillators (NRO), using single-port surface transverse wave (STW) resonators, and single-transistor sustaining amplifiers for feedback-loop STW oscillators (FLSO) stabilized with two-port STW devices. In all cases, self-limiting, silicon (Si)-bipolar sustaining amplifiers that operate in the highly nonlinear AB-, B-, or C-class modes are implemented. Phase-noise reduction is based on the assumption that a sustaining amplifier, operating in one of these modes, uses current limiting and remains cut off over a significant portion of the wave period. Therefore, it does not generate 1/f noise over the cut-off portion of the radio frequency (RF) cycle, and this reduces the close-in oscillator phase noise significantly. The proposed method has been found to provide phase-noise levels in the -111 to -119 dBc/Hz range at 1 KHz carrier offset in 915 MHz C-class power NRO and FLSO generating up to 23 dBm of RF-power at RF versus dc (RF/dc) efficiencies exceeding 40%. C-class amplifier design techniques are used for adequate matching and high RF/dc efficiency.

Softlithography in Chemical Sensing – Analytes from Molecules to Cells

Imprinting is a flexible and straightforward technique to generate selective sensormaterials e.g. for mass-sensitive detection. Inherently, the strategy suits both molecularanalytes and entire micro organisms or cells. Imprinted polyurethanes e.g. are capable ofdistinguishing the different xylene isomers with very appreciable selectivity factors.Combining imprinted titanates with surface transverse wave resonators (STW) leads to apowerful tool for detecting engine oil degradation, which is an excellent example foroxidative deterioration processes in a highly complex matrix. Surface imprints withgeometrically equal cavities exhibit clear chemical selectivity, as can e.g. be seen throughthe example of different human rhinovirus (HRV) serotypes. Another example is a bloodgroup-selective sensor prepared by templating with erythrocyte ghosts. Both the bloodgroupA and B imprinted material selectively distinguish between blood groups A, B and O,whereas no difference in sensor signal has been observed for AB, where both blood groupantigen types are present on the cell surface.

High sensitivity anhydride hexafluorhydric acid sensor

This work demonstrates the relevance of a Love-wave device dedicated to the detection of low concentrations of anhydride hexafluorhydric (HF) ( C HF < 3 ppm). Improvements are demonstrated compared to previous versions of the detection system for which surface transverse wave (STW) devices were used. We also have tested a coating, specifically sensitive to HF, deposited atop a STW resonator, operating along the same Love-wave principle and exhibiting improved sensitivity compared to STW sensors. Time-life and sensitivity of each device are reported and discussed. Finally, a surface analysis has been performed to try and explain the actual effect of HF on the sensor surface.

Low voltage surface transverse wave oscillators for the next generation CMOS technology

The design and performance of voltage controlled surface transverse wave oscillators (VCSTWO) in the lower gigahertz frequency range, operating on supply and tuning voltages in the 1.2 to 3.3 V range, and suitable for direct interfacing with the next generation CMOS circuits are presented. By applying the "boost" principle, as used in direct current (DC)-DC converters, to the design of the sustaining amplifier, the VCSTWO outputs are switched between 0 V and a positive peak value, exceeding the supply voltage Us, to provide safe CMOS-circuit switching while keeping the radio frequency (RF)/DC efficiency to a maximum for low DC power consumption. The investigated 1.0 and 2.5 GHz VCSTWO are varactor tuned feedback-loop oscillators stabilized with two-port surface transverse wave (STW) resonators. Each VCSTWO has a DC-coupled, high-impedance switched output to drive the CMOS circuit directly, and an additional sinusoidal 50 ohmz high-power reference output available for other low-noise system applications. Phase noise levels in the -103 to -115 dBc/Hz range at 1 kHz carrier offset are achieved with 1.0 GHz VCSTWO at a RF/DC efficiency in the 21 to 29% range. The 2.5 GHz prototypes demonstrate phase noise levels in the -97 to -102 dBc/Hz range at 1 kHz carrier offset, and efficiencies range between 8 and 15%.

PECVD a-C:H films for STW resonant devices

Plasma polymeric hydrogenated amorphous carbon (a-C:H) coatings have been found to be a promising material for use in surface transverse acoustic wave (STW) resonator employed as humidity sensor. The tailoring of coating properties has been easily obtained by variation of CH 4 percentage in CH 4–Ar mixture that enables to tune the response of polymer-coated STW resonator. Specifically, the optimum sensing characteristics of the STW resonator has been exhibited by coating obtained at 50% of CH 4 percentage. The correlation between the device sensitivity and the material properties, as determined by small angle X-ray scattering (SAXS), X-ray reflectivity (XRR), ellipsometry and Fourier infrared spectroscopy (FTIR) measurements, permits us to highlight the sensing mechanism of the active a-C:H coatings. The porosity has been considered the main effect on the enhancement of the sensor response.

High relative humidity range sensor based on polymer-coated STW resonant device

A polymer-coated surface transverse acoustic wave (STW) resonator is used in high sensitivity relative humidity (RH) sensors ranging from 60 to 100%. The STW device is designed to resonate at 316 MHz and is realized on AT-cut quartz substrate to minimize thermal dependencies. Two kinds of polymeric films, HMDSO and a-C:H, produced by plasma enhanced chemical vapor deposition at room temperature, are tested. The resonant frequency shift of the coated device due to the sorbed water vapor mass is measured at controlled relative humidity and temperature. The most stable and sensitive a-C:H coating is obtained at 50% CH 4 of feeding CH 4Ar mixture. Average sensitivities for HMDSO and a-C:H coated device are found to be about 15 and 7.5 ppm/% RH, respectively. The response time to a step of 90% RH for both coatings is less than 30 s.