Immittance

Abstract: A method is described with which immittance data can be tested for Kronig‐Kramers compliance. In contrast with other procedures, this method is linear in nature and is based on a predetermined set of relaxation times. The model contains as many parameters (or less) as there are data sets. Three modes of operation are described, the first two are based on a linear fit of the model function to the imaginary part or to the real part of the data set. With the fit parameters the corresponding real or imaginary dispersion can be calculated and compared with the actual measurement. In the third mode a complex model function is fitted to the complete data set. As the model function does comply with (a relaxed set of) the Kronig‐Kramers (K‐K) rules, it will not be able to reproduce the data set satisfactory in the case of nonK‐K behavior, as can be observed from the residuals plot. Due to its linear nature, no starting values are needed for the data validation. The main limitation of this procedure is the size of the matrix and the accuracy of the matrix inversion.

Abstract: Immittance, transfer, and scattering characteristics are studied for acoustic surface wave transducers of the interdigital electrode form. Linear network models are used to represent the transducer as a chain of identical three-ports which are acoustically in cascade but electrically in parallel. Transducer operation at acoustic synchronism is described theoretically and compared to current experimental data for transducers operating at 100 MHz and fabricated on lithium niobate. Favorable lithium niobate configurations for efficient, broad-band transducer operation are given. Scattering characteristics as a function of electric load are discussed. Low values of acoustic reflection loss are predicted theoretically and observed experimentally when the electric load and transducer capacitance are in resonance. The frequency dependence of transducer radiation immittance is studied, and the response is found to be analogous to the response of an endfire antenna array.

Abstract: A method for analyzing characterisitcs of open microstrip disk structures is presented. The method is based on the spectral domain immittance matrix approach, and all the wave phenomena associated with the structures are incorporated. The method provides a number of unique and convenient features both in analytical and numerical phases. A numerical example illustrating the usefulness of the method is included. Some numerical results are compared with experimental data.

Abstract: The equivalent-circuit-modelling technique is useful for designing printed frequency-selective surfaces. A correction term is derived which enables transmission responses to be modelled at oblique angles of incidence. Models derived for arrays of gridded-square and double-square elements are compared with experimental results for plane waves at normal incidence and at oblique angles for TE- and TM-incidence. Good agreement is obtained for angles of incidence up to 45° in the principle planes. The importance of using the immittance correction terms in the models is also discussed.