How to use jquery validate with FormData Object

I have a form with 3 fields being one of type file. Validation works perfectly. When I try to send data using ajax, I get the error: "SyntaxError: JSON.parse: unexpected end of data at line 1 column 1 of the JSON data".

When checking with the browser debug it displays this in "params":

----------------------------- 147651797215788 Content-Disposition: form-data; name="archp"; filename="100_1369.JPG" Content-Type: image / jpeg

ÿØÿáBàExif (several characters of this type)

I tried in many other ways, searching the net, but it did not work out at all.

This is the script:

$("#formAgendaConsulta1").validate({
    // Define as regras
    unkeyup: false,
    rules:{
        arqup:{
            required: true
        },
        especialidade:{
            required: true
        },
        especialista:{
            required: true
        },
        dataConsulta:{  
            required:true, 
            dateBR:true 
        },
        horaConsulta:{ 
            required:true, 
            timeBR:true 
        }
    },
    submitHandler: function( form ){
        //var dados = $( form ).serialize();
        var dados = new FormData($(this)[0]);

        $.ajax({
            type: "POST",
            url: $( form ).attr('action'), // "saveAgendaConsulta1.php",  
            data: dados,
            processData: false,
            contentType: false,
            dataType: "json",
            success: function( data ){ 
                var msgFinal = data.msgFinal;
                $('#resultAgendaConsulta1').html( msgFinal );
                $('#resultAgendaConsulta1').show( 'slow' );
            },
            beforeSend: function(){ 
                $('#loadAgendaConsulta1').css({display:"block"});
            },
            complete: function(msg){ 
                $('#loadAgendaConsulta1').css({display:"none"});
            },
            error: function(){
                bootbox.alert("Falha de Conexão!<br />Não foi possível efetuar sua requisição.<br/>Aguarde alguns instantes e faça uma nova tentativa.");
            }
        });
        return false;
    }
});