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The output characterization of medical high intensity therapeutic ultrasonic devices poses several challenges for the hydrophones to be used for pressure measurements. For measurements at clinical levels in the focal region, extreme robustness, broad bandwidth, large dynamic range, and small receiving element size are all needed. Conventional spot-poled membrane hydrophones, in principle, meet some of these features and were used to detect large amplitude ultrasonic fields to investigate their applicability. Cavitation in water was the limiting effect causing damage to the electrodes and membrane. A new hydrophone design comprising a steel foil front protection layer has been developed, manufactured, characterized, tested, and optimized. The latest prototypes additionally incorporate a low absorption and acoustic impedance matched backing, and could be used for maximum peak rarefactional and peak compressional pressure measurements of 15 and 75 MPa, respectively, at 1.06 MHz driving frequency. Axial and lateral beam profiles were measured also for a higher driving frequency of 3.32 MHz to demonstrate the applicability for output beam characterization at the focal region at clinical levels. The experimental results were compared with results of numerical nonlinear sound field simulations and good agreement was found if detection bandwidth and spatial averaging were taken into account.

The pressure-volume-temperature behavior of miscible blends of poly(ethylene oxide) (PEO) and poly(methyl acrylate) (PMA) was studied over extended ranges of temperature and pressure. From pressure-volume-temperature data, the reduction parameters for the Flory-Orwoll-Vrij equation-ofstate were determined. It was found that reduction parameters as well as density, thermal expansion coefficient, and isothermal compressibility vary with composition in a nonlinear manner. The surface tension of the blends in the molten state was measured over the whole composition range using the sessile drop method. The surface tension was found to display negative deviation from additivity pointing toward a remarkable sur-face excess of PMA. Moreover, surface tension displays a minimum in the range of low PEO content at weight fraction of $0.19. In addition, the temperature coefficient of surface tension shows negative deviation from linearity. It stays constant when PMA is in excess. Results are discussed in terms of equation-of-state thermodynamics. The minimum of surface tension can be well explained by weak self-association of PEO in the bulk.

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