You can give your panel a itemId
Ext.define('AM.view.metadata.List' ,{
extend: 'Ext.grid.Panel',
alias: 'widget.metadatalist',
title: '<center>Results</center>',
store: 'Metadata',
itemId: 'targetPanel'
and use this ComponentQuery
search: function(btn)
Ext.ComponentQuery.query('#targetPanel');
...