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A study is made regarding the development of SAW correlators using orthogonal frequency coding (OFC) for use in ultra-wideband (UWB) spread spectrum communication systems. Result for the OFC device is shown and is compared to the ideal correlation which demonstrates the feasibility of using an OFC SAW correlator in UWB communication transceivers.

The article analyses the several new, man-made piezoelectric single crystal, Czozhralski-grown substrate materials that are used for surface acoustic wave (SAW) applications. The Y-cut langasite structured materials are perfect for these applications, as they are very dense and have higher coupling.

The concept of orthogonal frequency coding (OFC) for applications to surface acoustic wave (SAW) sensor technology is presented. The OFC approach is general and is applicable to several differing SAW sensors for temperature, pressure, liquid, gases, and others.

Generalized surface acoustic wave (GSAW), pseudo-SAW (PSAW), and high-velocity PSAW (HVPSAW) propagation for langatate (LGT) are presented and discussed.

Propagation characteristics for the three bulk acoustic wave (BAW) modes of langanite (LGN) are investigated. LGN is described as a promising candidate material for BAW applications requiring low temperature sensitivity with good bandwidth characteristics because of its values of coupling coefficient larger than quartz.

Measurements of the thermal coefficients of expansion and density of langasite (LGS), langanate (LGN), and langatate (LGT) are reported and discussed.

An approach is described, for 2-D numerical analysis of acoustic wave generation from finite-length leaky surface acoustic wave (LSAW) transducer structures. Mass loading of the electrodes is accomplished using the finite element method (FEM), and the substrate is modeled using analytical and numerical methods.

A differential phase shift keying (DPSK) single surface acoustic wave (SAW)-based correlator on GaAs was designed and constructed for direct spread spectrum applications. The DPSK modulation format permits noncoherent data demodulation and the SAW device correlator acts as the despreader. The system employs two in-line correlators unlike the usual method of utilizing parallel correlators and a one data bit delay element.

The null frequency bandwidth of a layered structure surface acoustic wave filter was determined using the delta function and the equivalent circuit models. The velocity was treated as a function of frequency for a given group of layer thicknesses while the effect of velocity dispersion was correlated in the theta function. Results showed that the deviation of the impedance was larger at the higher and lower frequency regions.

A new algorithm for finite impulse response (FIR) is proposed. It uses a summation of weighted, frequency shifted sampling functions as basis to construct the frequency response of a filter. The algorithm is simple, efficient and accurate for the design of arbitrary filter specifications and involves fewer computations compared to other FIR methods. It can be used to design filters with customized passband and stopband responses to produce a near-optimum time length.

Surface acoustic wave (SAW) FIR filters are used in quadrature binary modulation (QBM) systems as full response signalling modulators. New symbol shapes are obtained using precalculated binary emphasis as input to the filter and the symbol shape for each pulse as the modulated output. Time and frequency-domain measurements are made for any QBM system by designing the proper SAW modulator.

Surface acoustic wave (SAW) technology may be useful for symbol shaping in quadrature binary modulation systems due to its precise time response definition capability. A system to analyze its quadrature system modulation capability is built using a single radio frequency circuit, and is used to analyze various waveforms. The SAW system has developed many new symbol shapes and shows good measurement correlations with theoretical data.

A proposed charge injection model for acoustic charge transport (ACT) devices based on an earlier model simplifies computations required to simulate charge injection by using the Poisson equation alone. The comparison between the proposed model, an existing one and past experimental results confirm that the new model accurately predicts the frequency response abilities of an ACT device. Practical applications on a 25-MHz personal computer shows a reduced computation time of eight to 12 hours as compared to the previous 24 to 40 hours on a Hewlett-Packard 9000 minicomputer of the 500 series.

An analytical derivation of the transduction coupling parameters required by the coupling-of-modes (COM) method of modeling arbitrary transducers is given. It is a synthesis of the contrast between the solutions of the COM method and a quasi-static technique. Applicable to the characterization of periodic surface acoustic wave transducers, the procedure may also determine a transducer's transduction magnitude and phase.

A SAW device is utilized in a correlator receiver for a differential phase shift keying direct sequence spread spectrum system. Constructed out of lithium tantalate, the correlator supports a one wideband input transducer and a couple of coded in-line inter-digitated transducers. A programmable word generator was used to obtain the input test signal for the correlator. An autocorrelation peak of 63 to 1 was acquired using a 63 chip sequence input.

This paper will discuss a SAW passive, wireless multi-sensor system under development by our group for the past several years. The device focus is on orthogonal frequency coded (OFC) SAW sensors, which use both frequency diversity and pulse position reflectors to encode the device ID and will be briefly contrasted to other embodiments. A synchronous correlator transceiver is used for the hardware and post processing and correlation techniques of the received signal to extract the sensor information will be presented. Critical device and system parameters addressed include encoding, operational range, SAW device parameters, post-processing, and antenna-SAW device integration. A fully developed 915 MHz OFC SAW multi-sensor system is used to show experimental results. The system is based on a software radio approach that provides great flexibility for future enhancements and diverse sensor applications. Several different sensor types using the OFC SAW platform are shown. [ABSTRACT FROM AUTHOR]

La3Ga5.5Ta0.5O14 (LGT) is a new piezoelectric material with superior electromechanical properties and high Q·f product. Transverse-wave splitting behavior of LGT was observed in the acoustic velocity measurements. The velocities of the two shear waves propagating in Y-(010) direction are very close and they cannot be separated completely. This has a tremendous influence on determining the correct velocity of the shear modes. It is proposed that the singular value decomposition (SVD) technique can be used to determine the splitting time of two shear modes in Y-plane LGT crystal. Moreover, it also helps to correct the arrival time of the transverse waves. It is believed that the presented approach is efficient and accurate for determining the correct velocities of shear modes in anisotropic media. [ABSTRACT FROM AUTHOR]

Research has recently begun on the use of ultrathin films and nanoclusters as mechanisms for sensing of gases, liquids, etc., because the basic material parameters may change because of film morphology. As films of various materials are applied to the surface of SAW devices for sensors, the conductivity of the films may have a strong acoustoelectric effect, whether desired or not. The purpose of this paper is to reexamine the theory and predictions of the acoustoelectric effect for SAW interactions with thin conducting or semi-conducting films. The paper will summarize the theory and predict the effects of thin film conductivity on SAW velocity and propagation loss versus frequency and substrate material. The theory predicts regions of conductivity which result in extremely high propagation loss, and which also correspond to the mid-point between the open and short-circuit velocities. As an example of the verification and possible usefulness of the acoustoelectric effect, recent experimental results of palladium (Pd) thin films on a YZ LiNbO3 SAW delay line have shown large changes in propagation loss, depending on the Pd film thickness, exposure to hydrogen gas, or both. By proper design, a sensitive hydrogen leak detector SAW sensor can be designed. [ABSTRACT FROM AUTHOR]