Pure shear horizontal SAW biosensor on langasite

The undetected introduction of pathogens into food or water supplies can produce grave consequences in terms of economic loss and human suffering. Sensitive and selective sensors capable of quickly detecting microbial pathogens are urgently needed to limit the effects of bioterrorist incidents, accidents, or pollution. Shear horizontal surface acoustic wave (SH SAW) devices provide an attractive platform for the design of microbial biosensors that function in liquid media, where Rayleigh-type modes are rapidly attenuated. This paper reports on an exploratory SH SAW delay line designed and fabricated on langasite, La3Ga5SiO14 (LGS), along the novel Euler propagation direction (0 degrees, 22 degrees, 90 degrees). A liquid chamber was fabricated and attached to the top surface, and the device was submitted to liquid and biochemical tests. Moderate (6 dB) additional attenuation of the transmission coefficient, /S21/, was consistently observed when the SH SAW delay line was assembled in the test fixture and submitted to the liquid tests, indicating that LGS is an attractive candidate for liquid sensing. Sensor selectivity can be achieved by integrating the LGS SH SAW delay line with a biochemical recognition layer. A test setup was implemented for the characterization of LGS SH SAW-based biosensors. The delay line response to biomolecule binding was shown by detection of sequential binding of proteins to the SH SAW device delay path. The biotinylated sensor was exposed sequentially to biotin-binding deglycosylated avidin, biotin-modified rabbit IgG, and goat anti-rabbit IgG antibody. As each protein was bound to the sensing surface, marked changes in the delay-line phase were recorded. The reported results demonstrate the capability of these devices to act as biochemical detectors in aqueous solutions, and this work represents the first effort using the novel material LGS in SAW-based biosensor technology.     

Gigahertz range resonant devices for oscillator applications using shear horizontal acoustic waves

It is shown that surface transverse wave (STW) resonant devices are not only very well suited for stable oscillator applications but have some unique features offering greater design flexibility than their surface acoustic wave (SAW) counterparts. Various designs for single- and multimode resonators and resonator filters are presented, and their properties in respect to applications in stable fundamental-mode fixed-frequency and voltage-controlled oscillators in the range of 750 MHz to 2 GHz are discussed. Characteristics of SAW and STW two-port metal strip resonators using identical designs are compared. Data from frequency trimming on STW resonators, using heavy ion bombardment, are presented.     

Analysis of viscosity sensitivity for liquid property detection applications based on SAW sensors

An investigation of viscosity sensitivity for liquid property detection applications based on the ZnO/SiO₂/Si layered structure Love mode surface acoustic wave (SAW) sensors is presented. One of our interests in this paper is to optimize the SAW viscosity sensor under the condition of temperature stability by considering the relations among electromechanical coupling coefficient, viscosity sensitivity and temperature coefficient of delay (TCD). Some important results have been obtained by solving the system of coupled electromechanical field equations and Navier–Stokes equation. It is found that the electromechanical coupling coefficient and viscosity sensitivity can be further improved by adjusting the thickness of SiO₂ thin film and a zero TCD device also can be obtained by introducing a SiO₂ thin film with proper thickness. We try to obtain a device which possesses the viscosity sensitivity as high as possible and has zero TCD. Another interest of this paper is to improve the traditional viscosity sensitivity expression by considering the coupling effect between the liquid viscosity and density. It is shown that the coupling effect cannot be neglected from the numerical results. This modification could make the obtained viscosity more accurate. This analysis is meaningful for the manufactures and applications of the ZnO/SiO₂/Si structure Love wave sensor for liquid property 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.     

SAW devices for consumer communication applications

An overview of surface acoustic wave (SAW) filter techniques available for different applications is given. Techniques for TV IF applications are outlined, and typical structures are presented. This is followed by a discussion of applications for SAW resonators. Low-loss devices for mobile communication systems and pager applications are examined. Tapped delay lines (matched filters) and convolvers for code-division multiaccess (CDMA) systems are also covered. Although simulation procedures are not considered, for many devices the theoretical frequency response is presented along with the measurement curve.     

High-temperature langasite SAW oxygen sensor

High-temperature langasite SAW oxygen sensors using sputtered ZnO as a resistive gas-sensing layer were fabricated and tested. Sensitivity to oxygen gas was observed between 500°C to 700°C, with a sensitivity peak at about 625°C, consistent with the theoretical predictions of the acoustoelectric effect.     

High-reliability SAW bandpass filters for space applications

High-reliability surface-acoustic-wave (SAW) bandpass filters have been developed for use in transponders for more than 25 earth-orbital and deep-space satellite programs. SAW filters have been incorporated in several NASA standard TTandC transponders and NASA standard tracking and data relay satellite system (TDRSS) user transponders. The author gives examples of the electrical performance, summarizes the manufacturing processes, and discusses qualification testing for these SAW devices. He identifies reliability problems encountered and their solutions.     

Surface-acoustic-wave (SAW) flow sensor

The use of a surface-acoustic-wave (SAW) device to measure the rate of gas flow is described. A SAW oscillator heated to a suitable temperature above ambient is placed in the path of a flowing gas. Convective cooling caused by the gas flow results in a change in the oscillator frequency. A 73-MHz oscillator fabricated on 128 degrees rotated Y-cut lithium niobate substrate and heated to 55 degrees C above ambient shows a frequency variation greater than 142 kHz for flow-rate variation from 0 to 1000 cm(3)/min. The output of the sensor can be calibrated to provide a measurement of volume flow rate, pressure differential across channel ports, or mass flow rate. High sensitivity, wide dynamic range, and direct digital output are among the attractive features of this sensor. Theoretical expressions for the sensitivity and response time of the sensor are derived. It is shown that by using ultrasonic Lamb waves, propagating in thin membranes, a flow sensor with faster response than a SAW sensor can be realized.     

Investigation on recent quartz-like materials for SAW applications

Recent progress in growing and characterizing quartz-like materials of the trigonal system class 32 has been reported by several groups. The promising perspective for bulk acoustic wave frequency control applications indicates the potentiality of employing these materials for SAW applications as well. This paper reports results of investigations focused on SAW orientations of langasite (LGS), gallium phosphate (GaPO(4)), and langanite (LGN), both singly and doubly rotated cuts. Among the characteristics explored, major attention is paid to the temperature coefficient of delay (TCD), the electromechanical coupling coefficient (K(2)), and the power flow angle (PFA). Contour graphs are plotted based on our calculated results and show the regions in space in which low TCD and high K(2 ) can be obtained; they also exhibit the associated PFA and phase velocity characteristics. The influence of different sets of material constants is addressed. The spatial investigation performed shows that there are promising orientation regions in these materials at which zero or reduced TCD (<10 ppm/ degrees C) and PFA are obtained. Additional attractive characteristics for SAW applications have been observed: values of K(2) a few times higher than the K(2) of quartz ST-X, thus finding applications in larger bandwidth devices; variation of the TCD with respect to temperature, which is comparable to the variation found for quartz ST-X and less than that for zero TCD Li (2)B(4)O(7) cuts like 45 degrees X-Z and (0 degrees 78 degrees 90 degrees ); and phase velocity values circa 13 to 26% smaller than the phase velocity of quartz ST-X thus allowing a reduction in size for intermediate frequency device applications.     

Dual SAW sensor technique for determining mass and modulus changes

Surface acoustic wave (SAW) sensors, which are sensitive to a variety of surface changes, have been widely used for chemical and physical sensing. The ability to control or compensate for the many surface forces has been instrumental in collecting valid data. In cases in which it is not possible to neglect certain effects, such as frequency drift with temperature, methods such as the "dual sensor" technique have been utilized. This paper describes a novel use of a dual sensor technique, using two sensor materials (quartz and GaAs) to separate out the contributions of mass and modulus of the frequency change during gas adsorption experiments. The large modulus change in the film calculated using this technique and predicted by the Gassmann equation provide a greater understanding of the challenges of SAW sensing.     

Gas thermal conductivity sensor based on SAW

An uncoated surface acoustic wave (SAW) delay line integrated with a suitable film heater is used as a gas sensitive element based on thermal conductivity change. It detects concentrations from 0.1-100% of H₂, O₂, He, and Ar in N₂ in the temperature range from 20-150°C. The value and sign of the SAW gas response are controlled by substrate material and reference gas     

Comparison between BAW and SAW sensor principles

A comparison is given between piezoelectrically excited bulk acoustic wave (BAW) and surface acoustic wave (SAW) elements with respect to their primary sensitivity functions and principal capabilities for sensor applications. The importance of mode purity for high dynamic range sensors is emphasized. Characteristic sensor examples are reviewed, and the special demands on the electronics for BAW and SAW elements in the sensor field are described (e.g., cable problem, wireless SAW sensors). For a fair evaluation, a performance figure, SQ, defined as the product of reduced sensitivity S and resonator Q-value, is introduced. The potential of alternative piezoelectric materials for future sensor developments is discussed briefly.     

SAW quadrature binary modulation system applications

A surface acoustic wave (SAW) modulation system has been built, using a combination of a digital message sequence, an impulse driver, and different SAW modulator filters, for experimental testing of a wide variety of quadrature binary modulation schemes. The RF testbed is described and characterized for system distortion, dynamic range, and spurious responses, and system optimization is discussed. Nine different SAW modulator filters having different time- and frequency-domain responses were designed and fabricated for use in the system. Several of the designs are representative of new modulation schemes which offer better spectral confinement; and time-domain envelope uniformity than MSK. The results obtained with the designed SAW quadrature binary modulation system are presented. Excellent agreement between time- and frequency-domain measurements and theoretical predictions using the SAW modulation system are shown.     

Micromechanical precision pressure sensor incorporating SAW delay lines

Summary We have developed a wireless surface acoustic wave (SAW) pressure sensor operating in the pressure range of 0 Pa to 250 kPa. In order to minimize the temperature sensitivity the pressure sensor is made of on an all-quartz package (AQP), which has been designed with the Finite Element Method. The package of the pressure sensor consists of a diaphragm and a cover, both made of conventional Y-cut quartz. A blind-hole was structured into the sensor cover. By attaching the cover and the diaphragm with an epoxy-adhesive, this blind-hole forms a closed cavity. The SAW element is a reflective delay line (RDL), working at 434 MHz. The RDL consists of ten reflectors and extends over the whole diaphragm. The pressure is determined by evaluating the change of the carrier phase shifts of the reflected impulses at the reflectors. We show that it is possible to minimize the temperature sensitivity and to achieve good linearity by proper positioning of the SAW reflectors. The measurements of the SAW pressure sensor show a deviation from linearity of less than ±0,7%. The temperature dependence is almost negligible in the range from-20°C to 100°C.The objective of this paper is to provide a deeper insight into the behaviour of SAW propagation on pre-stressed substrates. To do so, we start with investigating the behavior of SAWs on stress-free substrates followed by an analysis of SAW propagation on pre-stressed substrates. Further, the requirements on suitable substrate materials for the AQP are specified. Finally, we take advantage of the method of differences to compensate for the temperature dependence of our pressure sensor.     

Nanostructural palladium films for sensor applications

The composite films composed of palladium (Pd) nanocrystals and Pd-fullerenes nanocrystals obtained by physical vapor deposition (PVD) method were studied. These types of films can be applied as active material for sensor application.The films were prepared by PVD technique. They were deposited on different substrates and contained Pd in various concentrations. The structure and composition of the Pd films were studied by X-ray diffraction, scanning probe microanalysis, transmission and scanning electron microscopy. It was found that these films were composed of Pd nanocrystals placed in Pd-C₆₀ matrix.Changes of some electric properties of the film upon an influence of a toxic liquid have been characterized by DC electrical measurements. They were performed for different volatile organic compounds (VOCs). At 22 °C the electrical resistance was studied for VOC such as benzene and toluene.     

Pseudo-orthogonal frequency coded wireless SAW RFID temperature sensor tags

SAW sensors are ideal for various wireless, passive multi-sensor applications because they are small, rugged, radiation hard, and offer a wide range of material choices for operation over broad temperature ranges. The readable distance of a tag in a multi-sensor environment is dependent on the insertion loss of the device and the processing gain of the system. Single-frequency code division multiple access (CDMA) tags that are used in high-volume commercial applications must have universal coding schemes and large numbers of codes. The use of a large number of bits at the common center frequency to achieve sufficient code diversity in CDMA tags necessitates reflector banks with >30 dB loss. Orthogonal frequency coding is a spread-spectrum approach that employs frequency and time diversity to achieve enhanced tag properties. The use of orthogonal frequency coded (OFC) SAW tags reduces adjacent reflector interactions for low insertion loss, increased range, complex coding, and system processing gain. This work describes a SAW tag-sensor platform that reduces device loss by implementing long reflector banks with optimized spectral coding. This new pseudo-OFC (POFC) coding is defined and contrasted with the previously defined OFC coding scheme. Auto- and cross-correlation properties of the chips and their relation to reflectivity per strip and reflector length are discussed. Results at 250 MHz of 8-chip OFC and POFC SAW tags will be compared. The key parameters of insertion loss, cross-correlation, and autocorrelation of the two types of frequency-coded tags will be analyzed, contrasted, and discussed. It is shown that coded reflector banks can be achieved with near-zero loss and still maintain good coding properties. Experimental results and results predicted by the coupling of modes model are presented for varying reflector designs and codes. A prototype 915-MHz POFC sensor tag is used as a wireless temperature sensor and the results are shown.     

Piezoelectric composites for sensor and actuator applications

In the last 25 years, piezoelectric ceramic-polymer composites have been conceptualized, prototyped, fabricated, and implemented in an array of applications encompassing medical imaging and military missions, among others. A detailed snapshot of the materials used, and a detailed account of the major innovative methods developed in making various piezoelectric ceramic-polymer composites are presented. The salient aspects of processing of such composites are summarized, and structure-processing-property relations are described using connectivity as the unifying central concept. Computer-aided design (CAD)-based fabrication methods, which result in composites whose structural complexity surpass that of composites obtained with traditional methods, are described to introduce the reader to novel concepts in processing of piezocomposites. A brief survey of some recent advances made in modeling of (0-3), (1-3), and (2-2) composites also is provided.     

A novel sensor for X-ray imaging applications

In this study, a novel direct X-ray conversion electronic sensor for X-ray imaging, aimed at the enhancement of the signal characteristics of a cadmium zinc telluride (CdZnTe) detector substrate, is proposed. CdZnTe substrates are promising candidates in detector technology since they have a high stopping power. The novelty of the sensor lies in the material of use as well as in the signal collector design, which exhibits “Frisch-grid” capabilities. As a result, the proposed technology provides an effective mode to shield the electron-collecting electrode from the charge induced on it from moving positive ions and trapped charge. Overall, this technology would allow for a decreased sensor thickness, accompanied with a high collector efficiency, and consequently improved signal characteristics. Therefore, the signal quality of an imaging sensor as applied to medical detector technology, radio astronomy, aviation security, surveillance and nondestructive inspection, and other industrial areas will be significantly improved