The data was collected for characterisation and validation of focusing, steering and aberration correction of a 256 element pseudorandom hemi ellipsoidal array transducer operating at 555 kHz. Measurements were made both in free field and after propagation through ex vivo human skulls. Measurements were made with a custom Fabry-Perot fibre optic hydrophone in a custom water tank with automated scanning axes. The system was driven with an 80 cycle pulse with 8 V drive voltage amplitude in free field. Measurements made with skulls used drive voltages required to obtain a focal pressure of 775 kPa after propagation through each skull.The study data contains 10 standard format measurement data files and an additional two files containing corresponding simulation data. UCL-k-Stim-Validation-01 – line scans at [0, 0, 0], [60, 0, 0] mm – 27/06/23UCL-k-Stim-Validation-02 – line scans at [0, 0, 50] mm, [0, 50, 0] mm, [30, 30, 30] mm – 28/06/23UCL-k-Stim-Validation-03 – line scans at [0, -50, 0] mm, [-60, 0, 0] mm – 30/06/23UCL-k-Stim-Validation-04 – line scans at [0, 0, 20] mm, [0, 0, -20] mm, [0, 0, -50] mm, [0, 20, 0] mm, [0, -20, 0] mm, [20, 0, 0] mm, [20, 20, 0] mm, [20, 20, 20] mm, [20, 20, -20] mm, [30, 30, -30] mm, [-20, 0, 0] mm.Scans with ex vivo human skulls, testing planning pipeline – inverse planning with aberration correction perfomed using k-Plan to obtain drive amplitudes and phases for a target focal pressure of 775 kPa:UCL-k-Stil-Validation-05 – line scans at [0, 0, 0] mm, [20, 0, 0] mm, [0, 20, 10] mm, [0, 0, 20] mm with skull A 2157 mounted within the helmet.UCL-k-Stim-Validation-06 – line scans at [0, 0, 0] mm, [20, 0, 0] mm, [0, 20, 0] mm, [0, 0, 20] mm with skull B 2120 mounted within the helmet.UCL-k-Stim-Validation-07 – line scans at [0, 0, 0] mm, [20, 0, 0] mm, [0, 20, 0] mm, [0, 0, 20] mm with skull C 2147 mounted within the helmet.UCL-k-Stim-Validation-08 – line scans at [0, 0, 0] mm, [20, 0, 0] mm, [0, 20, 0] mm, [0, 0, 20] mm, with skull D 2117 mounted within the helmet.Scans with an ex vivo human skull, testing the online replanning pipeline – inverse planning with aberration correction performed in k-Plan with an additional geometrical phase shift to move the focal position, target pressure of 775 kPa:UCL-k-Stim-Validation-09 – line scans at [0, 0, 0] mm, [0, 20, 0] mm with planned phases only, then with geometric phase shift from [0, 0, 0] mm to [5, 0, 0] mm, [-5, 0, 0] mm, [0, 5, 0] mm, [0, -5, 0] mm, with skull C 2147 mounted in the helmet.UCL-k-Stim-Validation-10 – line scans at with k-Plan focus at [0, 0, 0] mm with geometric phase shift from [0, 0, 0] mm to [0, 0, 5] mm, [0, 0, -5] mm, and from [0, 20, 0] mm to [5, 20, 0] mm, [0, 25, 0] mm, [2, 18, -2] mm, with skull C 2147 mounted in the helmet.Additional files: free_field_sims_water_steering_props.mat contains simulated free field focal parameters including spatial peak pressure, dimensions of the focal region, and line profiles through the focus for 16 focal positions. Simulations were run using the acousticFieldPropagator function in k-Wave. skull_plan_metrics.mat contains simulated transcranial focal parameters for 4 focal positions within each of 4 skulls, including profiles through the focus, location of the spatial peak pressure, focal dimensions, and the difference between these parameters and the measurements. Simulations were run with aberration correction in k-Plan using CT scans of the skulls.