The present invention relates to a dual frequency antenna, which integrates a square ring antenna and a patch antenna in order to have a compact circuit area that receives both low and high frequencies, to be used as the antenna of wireless LAN, wherein the wireless LAN is one of the following: IEEE 802. The rise in liquid level in the annular space is delayed for applications where the filter element is otherwise changed prematurely and has a longer life than otherwise indicated by the rising liquid level in the annular space. The shielding hood includes a top member and two side members positioned at the two lateral sides of the top member respectively to form a hood body and to define a top closing wall, two side closing walls and a bottom opening for the display of the notebook computer disposing within the hood body. In one preferred design, a hinged guide cover has a first leg geometry to engage the structure and a second leg geometry to engage the curtain guide assembly to effectively seal gaps created by various amounts of curtain guide assembly setback. The type of the print receiving medium is generally identified. A particularly preferred graft is a bone-tendon-bone graft.