Guenter Martin

A discrete one component wave model and its application to SAW resonator filters

A one component acoustic bulk wave model is presented for the description of SAW devices using plane waves or waveguide modes. No equivalent circuit components are used, and the calculations always remain on the level of acoustic waves. As fundamental elements the transfer matrix and the source vector of one electrode region are derived. Using these elements, the particle displacements in an array consisting of striplike electrodes can be calculated as a function of all single capacitor voltages taking into account the boundary conditions including the amplitudes of foreign waves meeting the array. After determining the waveguide mode velocities and profiles the model is applied to transversely coupled waveguide resonator filters resulting in the admittance matrix which is needed to calculate the filter insertion loss. Two filter examples are investigated, and a sufficiently good agreement of the theoretical and experimental results is found. The resonance splitting due to cascading of two (or more) single resonator filters can be increased by a coupling inductor yielding a smaller insertion loss under matched conditions at a given bandwidth.<<ETX>>

A SAW resonator filter using longitudinal and transverse modes

A SAW resonator filter using not only transverse but also longitudinal modes is presented. The design principle permits to construct four-pole filters without cascading or parallel connection. The input and output transducers arranged side by side have equal construction characterized by unsymmetrical withdrawing weighting. Neighboring disturbing longitudinal modes are suppressed due to weighting determined by an iterative procedure. The successful application of the principle to a device is demonstrated by experimental measurements.

Ring waveguide resonator on surface acoustic waves

A simple regular electrode structure for surface acoustic wave (SAW) devices is proposed. The structure consists of an interdigital transducer in the form of a ring placed on the Z cut of a hexagonal piezoelectric crystal. Finite thickness electrodes produce the known slowing effect for a SAW in comparison with this SAW on a free surface. The closed “slow” electrode region with the “fast” surrounding region forms an open waveguide resonator structure with the acoustic field concentrated in the electrode region. If the radius of the structure is large enough for a given wavelength, an acceptable level of radiation losses can be reached. The electrical admittance of such resonator does not have sidelobes.

Two-finger (TF) SPUDT cells [Correspondence]

SPUDT cells including two fingers only are hitherto known for so-called NSPUDT directions. In this case, usual solid-finger cells are used. The purpose of the present paper is to find SPUDT cell types consisting of two fingers only for pure mode directions. Moreover, SPUDT cells composed of two fingers suited to complete imperfect NSPUDT behavior or to compensate that are to be found. TF cells for pure mode directions on substrates like 128degYX LiNbO3, YZ LiNbO3 and STX quartz were found by means of an optimization procedure. The forward direction of a TF-cell SPUDT on 128degYX LiNbO3 was determined experimentally. The properties of the new cells are compared with those of conventional SPUDT cells. The reflectivity of TF cells on 128degYX LiNbO3 turns out to be two up to three times larger than that of DART and Hanma-Hunsinger cells at the same metal layer thickness. Furthermore, properties of TF cells on STX and SST quartz are reported. Examples for completing and compensating imperfect NSPUDT behavior are given.

3F-1 Thrombelastography Using Acoustic Sensors

The purpose of the present paper is to show that thrombelastography can be carried out by means of a quartz crystal microbalance (QCM) also known as a thickness shear mode resonator (TSM). A 9 MHz AT cut quartz was taken for the characterization of whole blood samples from healthy donors. To initiate fibrinolysis effects a special agent was used. The coagulation process was measured by monitoring the resonant frequency of the TSM. This frequency is affected by viscosity changes taking place during the coagulation process. The experimental setup was improved by covers made of PMMA (polymethyl methacrylate) and PDMS (polydimethylsiloxane). These covers seal the electrode in the TSM which is in contact with the coagulating blood sample. The use of such covers allows deleterious environmental effects such as evaporation and drying of the sample to be avoided. The ability of TSM to produce thrombelastograms was successfully demonstrated. The use of such devices allows state of the art measurement setups to be greatly simplified. No complicated mechanical or moving parts must be produced nor is an optical detection unit needed. In addition, direct monitoring of the viscosity results in additional findings at the end of fibrinolysis curves

SAW filters including one-focus slanted finger interdigital transducers

The present paper describes a new filter type, slanted finger interdigital transducer (SFIT) that allows fast analysis as a precondition for fast optimization. Therefore, filter structure and analysis are especially suitable for optimizing unidirectional SFIT (USFIT) filters. For analysis, a SFIT filter is usually divided into many narrow channels. Every channel is considered to be a subfilter and is analyzed separately. Therefore, the total filter analysis is very time consuming. For reducing computing time, we suggest a one-focus structure. In contrast to conventional SFIT filters, not only the finger and gap widths but also the spaces between transducers of different channels differ by one and the same scaling factor. As a consequence, all prolonged finger edges of both transducers intersect in one point called focus. As a result, the parameters of all subfilters can be calculated from the parameters of only one subfilter by simple frequency scaling. Consequently, the total time for analysis is essentially reduced. However, one-focus SFIT filters with continuous finger edges show a deep minimum within the passband. This problem can be overcome by using stepped one-focus structures.

A four-pole SAW resonator filter combining transverse and symmetrical longitudinal modes

As a continuation of the activities concerning longitudinal and transverse modes, the present paper describes the combination of transverse and neighboring longitudinal modes with the same symmetry for designing a four-pole resonator filter. The construction of both interdigital transducers arranged side by side agrees and is characterized by a symmetrical withdrawing weighting. The present solution offers the advantage to achieve a wider bandwidth for the same layout dimensions compared with the principle using neighboring longitudinal modes of different symmetry. The applicability of the principle to the filter design is demonstrated by experimental measurements.

An alternative method for suppressing undesired transverse modes in longitudinally coupled SAW resonator filters

As known, perturbing transverse modes arising from the waveguide properties of the interdigital transducers and reflectors can appear in SAW resonator filters. Usually, these undesired modes are suppressed by transducer apodization. This method has the disadvantage of increasing the transducer impedance. We propose a longitudinally coupled resonator filter, the basic elements of which are able to guide the two slowest waveguide modes alone, but to excite and receive the first mode only. The basic elements are arranged side by side forming the complete filter permitting coupling with each other weak enough to fulfill the filter specification. The suppression of undesired modes by the construction is demonstrated by transmission measurements.

10E-0 Improved Temperature Stability of One-Port SAW Resonators Achieved without Coils

The temperature stability of surface acoustic wave (SAW) resonators on ST-like quartz cuts can be increased by using double resonators. For this the turnover temperatures of the two single resonators are chosen above and below the reference (i.e. room) temperature, respectively. In the past, coils were necessary for improving temperature stability. In the present paper, solutions of temperature stable one-port double resonators without coils are described. The improvement of temperature stability is discussed in connection with the resonance type (resonance or antiresonance), the connection type of the single resonators, the use of capacitances and inductances and with the considered resonance (or antiresonance) component occurred by splitting due to resonator coupling. The parallel connection of two single resonators with different propagation directions is treated in more detail. It is shown that the temperature coefficient of frequency of 1st order (TCF1) as well as that of 2nd order (TCF2) can be compensated by such a circuit. For this a capacitance connected in parallel to the double resonator is not required to compensate the TCF2 but it proved to be suitable for correcting the TCF1. Finally a double one-port resonator structure on 35.5degrotY quartz is investigated experimentally.

Design of SPUDT filters on quartz considering waveguide modes

This paper presents an innovative method to achieve maximum performance in SPUDT filters on quartz under particular consideration of waveguide modes. Waveguide modes are known to have a possible strong impact on pass band and transition band performances of SPUDT filters if more than one waveguide mode exists. Consequently, a standard approach is to create a single mode design to prevent it. In some cases, however, it may be advantageous to design a SPUDT filter using several waveguide modes. A patch for the COM theory to analyse the waveguide modes is presented. This method is then used to evaluate possible filter performance degradations caused by parasitic waveguide modes. By means of simulated and experimental results of some filter examples, filter performance is shown which may be achieved by considering or using waveguide modes.