Business development for new applications of ultrasonic transducers requires new designs, improved production process, or solving problems in production or improved performance with lower cost requires improved transducers. Depending on the requirements, design modification are required, such as lowering material or process cost, enhancing signal strength, widening bandwidth of signal spectrum, reducing noise for improving SN ratio, operation at high pressure or high temperature, etc.
Design key points predicted by use of simulation programs used for consulting services:
Piezoelectric material : Single plate PZT is featured by low cost but spurious resonances arising from planer waves modify response performance predicted by thickness mode analysis. Composites of diced piezo-material with kerfs filled with polymer are featured by pure thickness mode without degrading effect due to spurious planer modes, high sensitivity with wideband even by use of simple polymer film with quarter wave thickness as matching layer leading lower cost with regard to simple layer structure without backing absorber. The simulation programs predict all the effective piezo-parameters such as d33, electromechanical coupling constant dielectric constant and impedance etc. if kerf width and period of PZT is given
Transducer area and drive voltage: Large area makes stronger acoustic output and also increased drive cycle number of burst renders full buildup of resonance giving high acoustic output. However, for the large area devices, far field radiation pattern shows sharp directivity with high acoustic signal only at the center but near field radiation pattern show complicated distribution of acoustic signal without enhanced acoustic signal. Receiver sensitivity does not increase with increasing transducer area but angle dependence shows sharp directivity. All these effects are predicted and combined with transducer modelling for simulation.
Bandwidth : Heavily depends on design of matching layer for required bandwidth and sensitivity. Double stage matching layer makes more smooth bell shaped response curve. Single stage matching layer may be used to design broad bandwidth but reduced sensitivity at central region of response curve with double peaks at side of the response curve. Multilayer of polymer-metal matching layer (mass spring model) is featured by thinness of layer (~1/20 ~ 1/30 wavelength) and almost same performance as traditional quarter wave design. Backing absorber makes bandwidth broader but sensitivity is very much reduced (because waves goes to back absorber) and not preferable. Best design strategy is to use best front matching structure and no absorber or air backing. All feature can be predicted by the simulation programs.
External circuit : In MHz region, connected cable of a few meters does not only have effect of pure capacitance but it is transmission line with distributed inductance L, and therefore drive voltage is unexpectedly increased at transducer due to capacitance C of transducer forming series L-C resonance. It is possible to design the sensitivity and bandwidth modified by external network, which may be designed with different networks at driver side and receiver side and combined with TR switch, and these effects are combined with transducer modelling in simulation programs.
All the above effects are combined in MATLAB models and it is possible to predict the effects by use of simulation program for consulting service.
