I want to add samples in downloadable product programmatically.

I am trying this

     $samplefiles[] = array(
						'file' => '/u/n/untitled_1.png',
						'name' => 'Untitled.png',
						'size' => 4672,
						'status' => 'new'
				);
     $sampleModel = Mage::getModel('downloadable/sample')->setData(array(
						'product_id' => $product->getId(),
						'sort_order' => 0,
						'sample_url' => '',
						'sample_file' => json_encode($samplefiles),
						'sample_type' => 'url',
				));
				$sampleModel->save();

But its not working..And how to save sample title