Heat shields are also known as burner shields, heat plates, heat tents, radiation shields, or heat angles. They serve the same purpose as a rock grate and rock, protecting the burner from corrosive meat drippings and dispersing heat. They are more common in newer grills. Heat shields are lighter, easier to replace and harbor less bacteria than rocks.
Like lava rock or ceramic briquettes, heat shields also vaporize the meat drippings and 'infuse' the meat with more flavor.