The linearity of the power response of yttrium iron garnet films to a microwave pulse having length shorter than the delay time characteristic of the specimen is investigated. In particular, a threshold is found above which output power increases with respect to standard linear trend. The above novel effect, analyzed in some detail on five epilayers of different thicknesses, cannot be explained in terms of usual nonlinear processes. An interpretation in terms of soliton excitation, accounting for the existence in the system of both intrinsic nonlinearity and dispersion, is proposed. PACS numbers: 75.30.Ds, 76.50.+g, 85.70.Ge Presently, solitons are an active field of interest in both fundamental and applied solid-state physics. The mathematical advances in finding out analytical solutions to a certain number of nonlinear dispersive wave functions 1 have given a powerful tool to their study and characterization.As is well established, a soliton results as a fairly delicate balance between the dispersion (which forces the signal to spread out) and the nonlinearity (which forces the signal to steepen) of the system under investigation. Apart from the interest in basic research, the remarkable applications of soliton propagation in optical fibers, 2 nonlinear transmission lines, 3 and Josephson junctions 4 (just to mention a few of them) seem to justify the search for solitons in media which are inherently both dispersive and nonlinear. Some systems in the field of acoustical 5 and radio-frequency signal transmission are in principle suitable to fit those requirements. Among them, the analysis of possible soliton excitation in a magnetostatic wave (MSW) device such as a dispersive delay line 6 operating at microwave frequency is particularly appealing. From a theoretical standpoint, a dipolar model dealing with the nonlinear properties of nonexchange MSW's propagating in a low-loss magnetic film of yttrium iron garnet (YIG) has been recently developed. 7 To account only for nonlinearities produced by self-action processes, a nonlinear Schrodinger equation describing the evolution of envelope solitons has been derived in the weak nonlinearity approximation. In this way, expected threshold powers for the onset of selfmodulation and self-channeling have been derived.Furthermore, through an analysis of the unique experimental data available in current literature, it turns out that attempts to detect purely magnetostatic solitons in YIG films have been so far unsuccessful. 8 In this framework, some nonlinear phenomena, interpreted in terms of multisoliton excitation as deduced by our analyzing the time envelope of an output pulsed signal, 8,9 have been reported. In order to get that result, the operational frequency had to fall within a few defined regions of the spectrum close to so-called repulsion gaps. 10 According to the theory and experimental findings, 11 resolvable gaps can be observed under specific conditions of spin pinning whenever the dipolar and exchange energy terms are comparable in magnitude. From an ...

This paper describes the development phases of a numerical-experimental integrated approach aimed at obtaining sufficiently accurate predictions of the noise field emitted by an external gear pump by means of some vibration measurements on its external casing. Harmonic response methods and vibroacoustic analyses were considered as the main tools of this methodology. FFT acceleration spectra were experimentally acquired only in some positions of a 8.5 cc/rev external gear pump casing for some working conditions and considered as external excitation boundary conditions for a FE quite simplified vibroacoustic model. The emitted noise field was computed considering the pump as a 'black box', without taking into account the complex dynamics of the gear tooth meshing process and the consequent fluid pressure and load distribution. Sound power tests, based on sound intensity measurements, as well as sound pressure measurements in some positions around the pump casing were performed for validation purposes. The comparisons between numerical and experimental results confirmed the potentiality of this approach in offering a good compromise between noise prediction accuracy and reduction of experimental and modelling requirements.

A first application of a new measurement technique to detect vibration transmitted to the human body in working conditions is presented. The technique is based on the use of a laser scanning vibrometer. It was previously developed, analysed and tested using laboratory test benches with electrodynamical exciters, and comparisons with traditional measurement techniques based on accelerometers were made. First, results of tests performed using a real machine generating vibration are illustrated. The machine used is a pedestrian-controlled tractor working in a fixed position. Reference measurements by using the accelerometer have been simultaneously performed while scanning the hand surface by the laser-based measurement system. Results achieved by means of both measurement techniques have been processed, analysed, compared and used to calculate transmissibility maps of the hands of three subjects.

The status of magnetostatic wave (MSW) straight-edge resonators (SERs) and their applications in tunable oscillator circuits are reviewed. The resonators are based on magnetostatic waves propagating in high-Q cavities fabricated in thin ferrimagnetic yttrium iron garnet (YIG) films. The resonance frequency of these resonators can be tuned using a bias magnetic field. The theory of operation and design criteria for the straight-edge resonators are described with emphasis on the effect of the resonator parameters on the tuning range, power handling, and phase noise performance. The use of the SER as the frequency-selective element in oscillator circuits is reported. Examples of tunable oscillators are included.

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