Marc Solal

High performance SAW dispersive delay lines for low time bandwidth using periodically sampled transducers

It is shown that it is possible to construct dispersive devices with only periodic transducers. This structure allows better design accuracy and easier device manufacture. Gating or Frensel sidelobes can be rejected by approximately 12 dB by adding frequency extensions to the expander. These two techniques have been used to design a 10- mu s dispersion and 7.35-MHz-bandwidth nonlinear FM system. A 46 dB sidelobe level was achieved experimentally for an analyzed 50 dB level.<<ETX>>

State of the art SAW resonators in France

During the last three years Thomson has concentrated on producing reliable, low-noise, and high-stability SAW (surface acoustic wave) resonators. A complete resonator analysis was required, one which modeled effects such as transverse modes and intratransducer coupling. Research has yielded typically less than 1 p.p.m./yr aging and unloaded Q-factors higher than 18000 with resonators close to 500 MHz. The first oscillators realized at 320 MHz show a good phase noise spectrum. Standard production techniques coupled with a newly developed multichip all-quartz packaging technique were used in the resonator manufacture. In addition, with use of a finite element analysis, the mechanical structure of the resonator can now be optimized to minimize the accelerometric sensitivity, which is required in military environments. Details on the design, manufacture, and performance of resonators in the 300- and 500-MHz ranges are presented.<<ETX>>

A new method to decrease grating sidelobes level in medical acoustic arrays

The design of a medical acoustic array for a given echographic system is often a compromise between the lateral resolution and the grating sidelobe level. For a fixed number of active channels, the only way to decrease the grating sidelobe level is to decrease the array pitch. This can be done by working with an acoustical pitch smaller than the electrical pitch, which is possible by using an electrical passive interpolation circuit between the electrical channels and the transducers. This method takes advantage of the fact that in echographic systems the sampling of the array is generally limited by the maximum number of electronic channels and not by the minimum technically achievable pitch on the transducer. The theoretical analysis and design of such arrays are described. This technique was used to construct a 3.75-MHz curved array. The result is a 10-dB improvement of the sidelobe level.<<ETX>>