Mitigation Techniques for the Concealment of a New Fire Suppression Network and HVAC System within a Pre-Existing Large Anechoic Chamber

The traditional way to build an anechoic chamber with a fire suppression network and HVAC system is to use the “box within a box approach”. Meaning that the pipes comprising the fire suppression network and ducts of the HVAC system are located in a space external and separate from the actual anechoic chamber and only intrude minimally. In some cases, like the one discussed here, this is not possible. Therefore, it was necessary to place large metal pipes and ducts within the anechoic chamber. Obviously, large metal features are highly unwanted, and without taking special steps to hide them would defeat the purpose of an anechoic chamber. In this paper, the process to understand and minimize the negative effects of these intrusive structures is discussed. Descriptions of the mitigation techniques employed are included along with simulated and measured results of the reflectivity performance of the chamber. The data and the lessons learned from this exercise provide useful insights into the challenges of refurbishing older anechoic chambers with nonideal interior features and prove that they can still exhibit excellent performance afterwards.

I. Introduction

Anechoic chamber performance is largely dependent on the chamber layout and effectiveness of the electromagnetic absorbing material. Over time, absorbers begin to degrade and need to be replaced. Also, new health and safety standards, combined with more modern building fire code regulations, can necessitate updates to a chamber's absorber layout. These factors led to the complete restoration of the Canadian Space Agency's largest anechoic chamber, which is located at the David Florida Laboratory in Ottawa, Canada. Ideally, the internal walls and ceiling of an anechoic chamber should be free of intrusions to facilitate the installation of RF absorbers. Unfortunately, because of the chamber's coupled structure to the building, this was not possible and an extensive sprinkler system and large air circulation vents were installed within the chamber. A portion of the chamber is shown in Figure 1, with the internal sprinkler network and HVAC visible.