A low frequency, waveguide array transducer, for operation in hostile environments, is studied and optimised for operation in fluids. The design consists of multiple stainless steel, rectangular cross-section strips which are used to support Lamb-like guided waves, which with appropriate delays allows the steering of the emitted beam. Wave propagation within the waveguide strips is discussed and the effect of the strip geometry on the supported wave modes is studied using comprehensive finite element modelling that is validated experimentally. Deviations from Lamb wave behaviour is observed due to coupling that occurs across the finite width of the strip, leading to dispersive behaviour that is slightly different to that of Lamb waves in a plate of the same thickness. As a result of this study, suggestions are made for modifications to the waveguide geometry that may favourably change this dispersive behaviour, over a desired frequency range. The effect of thermal gradients on the propagation of ultrasonic waves within the waveguide strips is also studied. Using Lamb waves as a basis for the analysis, general trends in the wave behaviour were identified before a series of experiments were conducted to demonstrate similar effects in the waveguide strips. Computational fl uid dynamics models were also used to study the heat distribution within the waveguide strips of the transducer to allow the in uence of these effects in a practical application to be assessed. Finally, the phased array capabilities of the strip waveguide array transducer were demonstrated. Initially, finite element modelling was conducted to allow the optimisation of the array geometry before the construction of a prototype. Using this prototype and a custom low frequency phased array controller, experimental steering of the beam emitted from the transducer was demonstrated up to angles of 45°.