Your code is trying to store in fname the content of the field 'bin' of the struct 'Measurement_20190829_18_15_10', which propably doesnt exist.
fname needs to be a char array:
fname = 'Measurement_20190829_18_15_10.bin';
I have no idea about your folder structure, but Im guessing its 'Figures\t_20190829_18_15_10' ? If so, you would need to write
and the same as the argument for 'exist'