Abstract: A driver system for an ultrasonic probe using a tunable inductor in series with the piezoelectric crystal excitation transducer in the probe. The bias current through this flux moduation coil is controlled by the system such that the inductance of the tunable inductor cancels out the capacitive reactance of the load impedance presented by the probe when the probe is being driven by a driving signal which matches the mechanical resonance frequency of the probe. The resulting overall load impedance is substantially purely resistive. The system also adjusts the frequency of the driving signal to track changing mechanical resonance conditions for the probe at different power levels. This method of operation insures substantially maximum power transfer efficiency and substantially linear power control over a range of power dissipation levels.

Abstract: Hydrogel polymeric material, suitable for preparing optical devices such as contact lenses. The material is of improved oxygen permeability and mechanical properties in comparison with conventional hydrogels. It comprises, in addition to the hydrogel material, from about 5% to about 60% by weight of a siloxane comonomer containing both an aromatic ring and vinyl functionality. Its cooperation and combination of performance characteristics with traditional hydrogel forming monomers provides a very useful polymeric material for making lenses of the soft hydrogel type.