Foldable display stands with a vertical board for showing merchandise are provide with a self erecting base to provide stability to the stand when merchandise is placed or mounted on the stand. The catalyst is formed from a precursor, wherein the precursor includes aluminum in the form of hydrotalcite and aluminum separate from the hydrotalcite. The base has interior compartments containing vendor products such as frozen ices, a cold source such a dry ice to keep the interior compartments cold and thus keep the vendor products cold, and lids that open to provide access to the vendor products within the interior compartments and that close. As a result of the parallax effect, the invention will then provide the observer with an estimate of the distance between the observer and the designated object. An attenuation peak is generated at the lower-frequency side of the passband with the multipath slot and the three adjacent through holes, and an attenuation peak is generated at the higher-frequency side of the passband with the two through holes and the outer conductor within the step.