MySQL — автозаполнение JQuery Ui PHP PDO

я пытаюсь сделать автозаполнение с помощью jquery ui и pdo connection на php, но не могу получить результат и ничего не вижу.

Здесь коды

HTML:

        <?php
require_once "../elements/header.php";
require_once "pemilihadd.php";
?>
<!-- page content -->
<div class="right_col" role="main">
<div class="row">
<div class="col-md-12 col-xs-12">
<div class="x_panel">
<div class="x_title">
<h2>SISWA <small> Tambah Pemilih</small></h2>
<div class="clearfix"></div>
</div>
<div class="x_content">
<br />
<form class="form-horizontal form-label-left input_mask">
<div class="form-group">
<div class="col-md-1" style="margin-right:5%"></div>
<label class="control-label col-md-2 col-sm-2 col-xs-12" for="date-picker_1">NIS</label>
<div class="col-md-6 col-sm-6 col-xs-12 form-group has-feedback">
<input type="text" name="StudentId" class="form-control has-feedback-left" id="StudentId" placeholder="type here ...">
<span class="fa fa-user form-control-feedback left" aria-hidden="true"></span>
</div>
</div>
<div class="ln_solid"></div>
<div class="form-group">
<div class="col-md-3" style="margin-right:4%"></div>
<div class="col-md-4 col-sm-4 col-xs-12 col-md-offset-4">
<button type="submit" class="btn btn-info">Cancel</button>
<button type="submit" class="btn btn-info">Submit</button>
</div>
</div>
</form>
</div>
</div>
</div>
</div>
</div>
<script>
$(function() {
$( "#StudentId" ).autocomplete({
source: "pemilihadd.php"});
});
</script>
<!-- /page content -->
<?php require_once "../elements/footer.php"; ?>

Java Script:

$(function() {
$( "#StudentId" ).autocomplete({
source: "pemilihadd.php"});
});

И код PHP:

error_reporting(E_ALL*(E_NOTICE | E_WARNING));

require_once '../../config/database.php';

if (isset($_GET['term'])){
$return_arr = array();
try {
$ac_term = "%".$_GET['term']."%";
$stmt = $db->prepare('SELECT StudentId FROM students WHERE StudentId LIKE :term');
$stmt->bindValue(":term", $ac_term);
$stmt->execute();

while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
$row_array[] = $row['StudentId'];

array_push($return_arr, $row_array);
}
} catch(PDOException $e) {
echo 'ERROR: ' . $e->getMessage();
}

echo json_encode($return_arr);
}

База данных подключений:

error_reporting(E_ALL*(E_NOTICE | E_WARNING));
$dsn= 'mysql:host=localhost; dbname=simvosmp; charset=utf8';
$db_user = 'root';
$db_pass = '';
$db = new PDO($dsn, $db_user, $db_pass, $opt);
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);

Кто-нибудь может помочь?