Abstrnct-In surface-acoustic-wave (SAW) convolver4 used to process long-duration waveforms, the output plate electrode behaves like a lossy transmission line and the effects of electromagnetic delay and electrode resistivity must be taken into account in evaluating convnlver characteristics. These effects are characterized by a spatial uniformity or weighting function, which results in a device output that is a weighted, instead of a t rue, convolution. When a single tap is used to extract signal from a long cnnvolver, the amplitude and phase nonuniformities due to electromagnetic effects degrade the convolver performance. A common way of overcoming this spatial uniformity problem is to use many taps to extract the output signal. Although it reduces the effect of nonuniformities to acceptable levels, the multiple tapping solution can increase device insertion loss and decrease bandwidth unless special output-matching netwnrks are incorporated. These transmission line effects can be modeled by a simple equivalent circuit which makes it possible to calculate the spatial uniformity functions fnr both single and multiply tapped cnnvolver geometries. Using realistic values for parasitic elements introduced hy honding pads and wires, a multisection circuit for the multiply tapped structure is assembled and analyzed using ac circuit analysis programs. The characteristics of multiply tapped convolvers are presented with particular emphasis on spatial uniformity, system bandwidth, and insertion loss. Examples of the computer-aided design of appropriate output-matching networks which maximize handwidth and output level a r e given.
Avantages des dispositifs acoustoelectriques a ondes acoustiques de surface utilisant une couche piezoelectrique de ZnO deposee sur un substrat semiconducteur
A new blood Row imaging system is described that com- bines a conventional pulsed Doppler device and a newly developed au- tocorrelator. In the system blood flow within a given cross section of a live organ is displayed in real time. The direction of blood Row and its variance are expressed by means of a difference in color and its hue, respectively. Experiments were conducted with a mechanical and an electrical scanner using phantoms, and good agreement with the theory was obtained. Studies on clinical significance have also been carried out for normal and diseased hearts, and successful results have been found.
The fabrication and testing of a SAW phase modulator based on the d effect in magnetostrictive thin films is described. 4n Fe-Si-B film on lithium niobate was used and peak phase deviations of about 5 degrees at nodulating frequencies of 100 KHz were observed at a center frequency of 115 MHz. A simple t heory for the phase modulator has been developed w hich is in reasonable agreement with experiment. The need for a dc bias field, in addition to the ac modulating field, for linear phase modulation is discussed.
Abstmct-A modified ZnO film model to calculate the elastic and pi- ezoelectric constants and the SAW velocities of ZnO film (c-axis ori- ented) substrate layer structure is proposed. The influences of the ran- dom orientation and lattice distortion have been taken into account. Compared to the traditional single crystal model, the theoretical results of the modified model fit better with the experimental values of a laser- probe measuring system. minor effect on the SAW properties of the ZnO substrate layer structure when it is not larger than O. In the present case the mean is less than l; therefore, for simplicity it is assumed to be zero, and only the effect of U (o is equal to 3 from the X-ray diffraction pattern) is taken into ac- count. In our model, the ZnO film is treated as a collec- tion of many monocrystal columns. The orientation 7 of the c-axis of each crystal column has the value within ( -T/ 2, 7r/2) on both the y-z and x-z planes. The material pa- rameters of the monocrystal column with the c-axis ori- entation of 17 can be calculated by assuming that 17 follows the normal distribution Since all the monocrystal columns with c-axis orientations contribute to the material parameters, their mathematical expectation can be taken as the material parameters of ZnO film. The average can be obtained by integrating with respect to 7 twice, first in the x-z plane and then in the y- z plane. Since 7 is a two-dimensional variable, the first integration process in the x-y plane can be stated as fol- lows :
Bubbles artificially generated in blood are being used to provide contrast in ultrasonic echocardiography. Being able to measure their size could prove useful in estimating the pressure gradients at various points of the cardiovascular system. In this work bubbles are simultaneously illuminated by a relatively low 'pumping' frequency near their resonance, as well as a much higher 'imaging' frequency. It is shown theoretically and experimentally that the imaging frequency echo is modulated by the bubble pulsations and therefore contains sidebands whose spacing from the c enter (imaging) frequency equals t he bubble resonant frequency. This sideband spectrum is sharp enough to readily differentiate bubbles of different size and has h igh spatial resolution.
Leaky Rayleigh waves, generated by an acoustic lens, may give rise to image artifacts in the reflection acoustic microscope. A new acoustic lens:transducer to suppress the Rayleigh wave excitation is proposed and demonstrated in experiments at 4 MHz.
A spectrophotometric and a radioacti ve-1 abel The exposure system was a glass technique were used to assess acoustically induced iodine release. test tube insonated transversely with a 1 MHz ultrasound source. The medium used for the assays was 5.0 mM sodium iodide in the presence of carbon tetrachloride. In one assay 1311 was quantitated by liquid scintillation counting and in the other the optical density of the solution was monitored at 520 nm. For both techniques there was a dose dependent re1 ationship between the percentage of iodine released and the u ltrasound intensity (1
