SAW Interdigital Transducers Research Articles

High-frequency characterization for SAW interdigital transducers

High-frequency characterization for SAW interdigital transducers

An integrated passive impedance-loaded SAW sensor

An integrated passive impedance-loaded SAW H2S sensor working at room temperature has been presented in this paper. The sensor consists of a SAW transponder with delay line structure and a resistive H2S sensor as an impedance-loaded sensor. The SAW delay line was fabricated on a 128° LiNbO3 substrate and its center frequency is 233MHz. The resistive sensor composed of the nano-crystalline SnO2 film and aluminum electrodes was also fabricated on the same substrate. The gas sensing properties of the resistive H2S sensor have been tested separately. In order to maximize the sensitivity of the whole sensor, the resistance of the impedance-loaded sensor was adjusted to match the output impedance of the SAW interdigital transducer (IDT) by changing the resistivity of the Sb-doped SnO2 nano-crystalline films and optimizing the electrode structure. The variation in the return loss magnitude was increased to 2.51dB. Finally, the impedance-loaded SAW sensor was configured and measured wirelessly for various H2S concentrations at room temperature. The measurement results show that the proposed H2S sensor not only has good repeatability and high sensitivity but also is capable of passive wireless detection at room temperature.

3-D electrostatic hybrid element model for SAW interdigital transducers

In this work, the singular behavior of charges at corners and edges on the metallized areas in SAW transducers are investigated. In particular, it is demonstrated that a tensor product of the commonly used Tchebychev bases overestimates the singularities at corners, and, hence, it cannot be used in a proper boundary element method formulation. On the other hand, it is shown that a simple finite element method-like approach is impractical due to the enormous number of unknowns required to model the electrode's large length-to-width ratio. These considerations are then used for defining a hybrid element model, which combines Tchebychev and linear polynomials over differently meshed domains. Such an approach is shown to suitably account for charge singularities while greatly reducing the number of unknowns. Results are obtained for isotropic and anisotropic substrates for non-periodic configurations.

A new reduced-order model of SAW interdigital transducers

The Green's function method is generally agreed to be the most satisfactory technique for the rigorous analysis of surface-acoustic-wave interdigital transducers (IDTs). However, its direct application to response investigations or optimization-based design activities is limited by its computational complexity. In this paper, we present a new reduced-order model of IDTs based on a moment-matching technique and on the singular value decomposition. Several numerical and experimental examples demonstrate the accuracy and the efficiency of the method.

The electrostatic problem for the SAW interdigital transducers in an external electric field. II. Periodic structures

For pt.I see ibid., vol.43, no.6, pp.1150-9 (1996). An exact solution of the electrostatic problem for calculating the surface charge and electric field distributions in an arbitrary periodic interdigital transducer (IDT) is given using the results of our companion paper. An arbitrary external electric field may be specified along the electrode structure with the unit cell containing one electrode, or several electrodes, of different widths. The potentials of the electrodes that may be specified are also arbitrary. It is shown that in the case without an external field, the solution includes all the known results as special cases. The case of shorted electrodes in the external electric field is investigated in detail. The surface charge and electric field distributions are calculated for a spatially harmonic external field with an arbitrary wavenumber. The results of the calculations are represented graphically for various ratios between the period of the electrode structure and the wavelength of the external field for the case of a unit cell containing one or two electrodes of different widths.

The electrostatic problem for the SAW interdigital transducers in an external electric field. I. A general solution for a limited number of electrodes

An exact solution for finding the surface charge and electric field distributions in interdigital transducers (IDTs) with a limited number N of electrodes is given. It is based on the Keldysh-Sedov solution to the mixed boundary problem of the analytic function theory. The IDT electrodes are placed on the plane boundary between two anisotropic dielectric media. The external electric field may arbitrarily vary along the structure. The solution contains N constants which may be found from the electrodes' connection conditions. For determining these constants a linear set of algebraic equations is obtained. The coefficients of this system are written in explicit form. The capacitance coefficients for a system of electrodes of different widths are obtained. For illustration purposes systems with one and two electrodes are considered in greater detail. In these cases the external electric field is assumed to vary harmonically along the structure with an arbitrary wavenumber. For one electrode the Fourier transform of the charge distribution is obtained in terms of the Bessel functions. For two electrodes of different widths a simple expression for the capacitance is found. The charge and electric field distributions are represented graphically for several wavenumbers and geometrical sizes of the electrode system. Section I contains a survey, including Russian literature, which is not well known in the west.

Equivalent networks for SAW interdigital transducers

An equivalent network approach is described for the analysis of surface-acoustic-wave interdigital transducers. Circuit parameters can he theoretically determined by applying the finite-element method to an infinite array. In this approach, all the effects of piezoelectric perturbation, mechanical perturbation, and energy storage are taken into account, To show the validity and usefulness of this approach, examples are computed for both single- and double-electrode interdigital transducers and one-port resonators. For single- and double-electrode interdigital transducers on 128/spl deg/Y-X LiNbO/sub 3/, X-112/spl deg/Y LiTaO/sub 3/,/sub 45//spl deg/X-Z Li/sub 2/B/sub 4/O/sub 7/, and ST-X quartz substrates, the dependence of excitation characteristics on electrode thickness and metallization ratio is investigated in detail. For a 128/spl deg/Y-XLiNbO/sub 3/ substrate, frequency responses of various one-port resonators are also investigated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Accurate computation of the electrostatic charge distribution on shielding plates of SAW-transducers

We compute the electrostatic charge distribution on the shielding plates of a packaged SAW-interdigital transducer (IDT) by the method-of-moments (MoM) and compare it to exact results; the shielding plates, which are used to suppress electric feedthrough, are placed on the substrate at the sides of the IDT. Correct modeling of their edge singularities is shown to be crucial for the accuracy of the MoM computations. The minimal length of the plates necessary for adequate shielding behavior is analyzed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance of SAW transducers on submicrometre n-GaAs epitaxial layers

Performance of the SAW interdigital transducer with doubled Al electrodes placed on GaAs structures with submicrometre n-GaAs epitaxial layers was investigated. A novel mode of operation on even overtone frequencies of this tranducer was observed and the possibility of electronic controllable SAW phase shift of up to 180 degrees was demonstrated.

Investigation of Impulse Response for an Interdigital Surface-Acoustic-Wave Transducer

The improved equivalent circuit model for a SAW interdigital transducer which we proposed in a previous paper contains an energy storage effect in addition to usual second order effects, and appropriately expresses the metallization effect. Using this model, this paper describes the relations between the impulse responses and the various second order effects for an IDT with an arbitrary metallization ratio on LiNbO3. To investigate in detail the influence of the second order effects on the performance of an IDT, figures of the characteristic responses are contrasted in both the frequency and time domains.

GHz‐range surface acoustic wave interdigital transducers and applications

AbstractGHz‐range SAW interdigital transducers, unidirectional transducers and SAW filters are described. Also, new fabrication technologies which can achieve higher operating frequencies are presented.

SAW Interdigital Transducers with Harmonic Responses Insensitive to Variations in Finger Widths

SAW Interdigital Transducers with Harmonic Responses Insensitive to Variations in Finger Widths

New technique for wavefront distortion compensation of apodised interdigital transducers

It is shown that in an apodised SAW interdigital transducer the inactive areas, where periodic electrodes do not overlap, can be replaced by a continuous metallisation. In the case of YZ LiNbO3, wavefront distortion compensation is achieved when the ratio of the metallisation length to the inactive area length is equal to about 0.8.

A General Approach to the Electrostatic Problem of the SAW Interdigital Transducer

The electrostatic problem of an arbitrary set of parallel strip electrodes on a dielectric substrate is examined, and a general analytic solution obtained. The general solution requires numerical computation to determine some parameten, but a particular class of problems has been solved completely. The solution for the important practical case of an infinite periodic array of electrodes is determined in the limit of the particular solution as the number of electrodes tends to infinity. W

Performance of 0.4-μm Linewidth SAW Interdigital Transducers Fabricated by Scanning-Electron-Beam Lithography

Performance of 0.4-μm Linewidth SAW Interdigital Transducers Fabricated by Scanning-Electron-Beam Lithography

Aluminum Evaporation Conditions for SAW Interdigital Transducers

Aluminum Evaporation Conditions for SAW Interdigital Transducers

Investigations on radiation and reflection characteristics of SAW interdigital transducers by equivalent circuit model.

Investigations on radiation and reflection characteristics of SAW interdigital transducers by equivalent circuit model.

The evaluation of the input admittance of SAW interdigital transducers

Using the moment-method technique, the exact charge distribution on a finite interdigital array is obtained. Full account is taken of the coupling to bulk and surface modes. The moment-method technique greatly simplifies the evaluation of the transducer input admittance. The frequency dependence of the input admittance is computed for a different number of electrode pairs, different metallization ratio, and different sequences. The electrostatic capacitance is proved to be 28% higher than the zero-coupling capacitance for Y-Z lithium niobate.