Jquery :: JSON Submit - Decode Empty Array At Server Side

I am doing a password reset form using Jquery and PHP. If I try to submit an email id it should sent and email and report back the response text as success so that the user knows email has been sent. But I am stuck with JSON submit as I have an empty array to decode at the serverside. I am using minified version of json2.js from the official json.org website

Here is the code.
Code JavaScript:
var formdata = $("#log-box").serializeArray();
formdata = JSON.stringify(formdata);
var notifymsg;
alert(formdata);
$.ajax({
type: "POST",
url: "forgot-pass.php",
contentType: 'application/json',
data: formdata,
success: function(responsedata){
var some = responsedata.split("&");
$.each(some, function(index,value){
//alert("index="+index+"value="+value);
});
},
error: function(o, s, e){
alert("Form not posted
"+e);
}});
formdata alerted gives:
[{"name":"email","value":"ravi.k@gmail.com"},{"name":"acctype","value":"loginaccount"}]

PHP forgot-pass.php
Code PHP:
print_r($_POST);
Gives
Array(
)