Because collision-avoidance systems (CASs) must obviously be fail-safe, they rely on microwave absorbers or "noise-suppression sheets" (NSSs) to reduce electromagnetic interference (EMI). All electronics that operate at high frequencies can have problems with noise emissions. Inside the enclosure of CASs, however, the energy increases in phases at frequencies that will cause resonances that hinder the system's performance. In a new application note from Laird Technologies, the firm explains that this is especially true for CASs, as they employ sensors that have absorbers in back of them to function properly.

Specifically, this five-page application note, titled "Q-Zorb Microwave Absorbers for Collision Avoidance System Applications," reviews two of the company's magnetic-absorber product lines. In doing so, it discusses the advantages of a magnetic versus lossy foam-type absorber. Foam absorbers are more cost effective if they meet performance goals. Yet they can physically break down over time, causing resistive particles to drop onto the circuit traces. In addition, they fail to perform well in H-field-dominated current applications. Magnetic absorbers, in contrast, boast high H-field loss and attenuate those currents.

The document notes that surface-wave absorbers are used for high-angle-of-incidence applications and cavity-noise suppression. When faced with a cavity noise problem, many engineers want to use an absorber that is tuned specifically to that frequency. Although tuned frequency materials offer good performance at normal angles of incidence, they fail to perform well at higher angles of incidence. As noted, noise is generated at a number of angles of incidence inside the cavity.

While this document focuses on the Front Collision Avoidance System and Side-looking Collision Avoidance System, the firm notes that such systems are expected to be used beyond road vehicles. Examples of future applications include large earth-moving vehicles in open-pit mines.

Laird Technologies, Inc., 3481 Rider Trail S., Earth City, MO 63045; (636) 898-6000, FAX: (636) 898-6100, www.lairdtech.com.