The work reported here is aimed at the development of a non-contact method to excite a focused, low-frequency acoustic radiation field in the residual limb of a lower-limb amputee. In conjunction with the estimated acoustic radiation force, resultant tissue displacement can be used to estimate elasticity and could aid the prosthetist during limb assessment and socket fabrication. In this work a piezoceramic focusing bowl has been used to create a two-element, confocal array driven at f ± δf/2. The nonlinear nature of tissue as a propagation medium supports the creation of a parametric array, and waves at the sum (2f) and difference (δf) frequencies are generated in the bowl's focal zone. Higher frequencies are attenuated strongly and the low frequency of interest remains as an excitation source. Low frequency excitation is essential to this application to simulate the tissue loading that will occur as a result of gait.