php $ FILES是空的

i try to insert a row to db with php and jquery

I have this code

$.post('/json/management/AddArtistAjax', 
    {
       "artistName": $("#nameSurnameID").val()
            ,
            "Country": $("#country").val()
            ,
            "bDate" :  $("#demo1").val()
            ,
            "dDate" :  $("#demo2").val()
            ,
            "bio" : $("#bioID").val()


    },
    function(response){
            alert(response);
        });

I can send php side all of above.However, i cannot send files to php side

print_r($_FILES) array is empty why ?

You cannot upload files like this via AJAX. If you do not need to support old browsers, you can use the form plugin which supports AJAX file uploads and can even fallback to a hidden iframe for older browsers.