How to make strpos case insensitive

How can I change the strpos to make it non case sensitive. The reason is if the product->name is MadBike and the search term is bike it will not echo me the link. My main concern is the speed of the code.

<?php
$xml  = simplexml_load_file('test.xml');
$searchterm = "bike";
foreach ($xml->product as $product) {
if (strpos($product->name, $searchterm) !== false ) {
echo $product->link;
} }
?>