You can right click on "Results" -> "create "field report" -> "data table".
Then you choose the quantity you want to save within the data table (as it was for a "2D or 3D rectangular plot"). A new report is created at the bottom of the list. You can right click on it and export as a *.csv, which is a very convenient format to import in Matlab (but also in other softwares such as MS Excel if you need). Then you can save it as *.mat file in Matlab for futur re-import.
Hello, maybe i'm late for you, but somebody searching could find this usefull. To extract data from 3D space, you have to chose your desired quantity. This should unlock the third dimension.