Microwave absorber materials can be "design savers" when electromagnetic interference (EMI) threatens to disrupt the proper operation of an RF/microwave circuit or system. In the case of the Q-Zorb family of microwave absorbers from Laird Technologies, one of the high-frequency systems that benefits from these thin materials is the 77-GHz front-directed millimeter-wave collision-avoidance system now included on many high-end consumer automobiles.

Proper application of these absorbing materials can minimize the effects of EMI on vehicular collision-avoidance-system (CAS) and other critical applications. In a CAS application, for example, sensors are protected from extraneous electromagnetic (EM) radiation by the signal attenuation provided by the absorbing material, which allows the CAS to adjust the cruise control without interference from high-frequency noise. In vehicular collision-avoidance systems, the front collision avoidance system (FCAS), which is also known as adaptive cruise control system, uses 77-GHz transmitters to detect slower vehicles and adjust the cruise control system accordingly. The side-looking collision avoidance system (SCAS) operates at 24 GHzalso known as a lane-change collision-avoidance system.

The Q-Zorb microwave absorbers are designed to ensure the proper operation of both FCAS and SCAS installations. To help designers appreciate the impact of these EM absorbing materials, the company offers a free application note, "Q-Zorb Microwave Absorbers for Collision Avoidance System Applications." This document details the various high-frequency functions provided by collision-avoidance-system electronics and the importance of microwave absorbing materials to the proper operation of these systems.

The firm offers two different types of Q-Zorb magnetic absorbing materials for CAS applications: Q-Zorb HP (tailored for high permeability) and Q-Zorb HF (designed for high frequency use). The former employs novel magnetic fillers to achieve high permeability values at low frequencies, so that very thin sheets of the material can provide substantial reduction of EMI at frequencies below 2 GHz. This material is supplied in sheet thicknesses of 0.15 and 0.50 mm.

Q-Zorb HF is targeted at cavity resonance problems spanning 2 to 18 GHz and higher in frequency. This latter material is available in sheet thicknesses from 0.5 to 3.2 mm or in die-cut forms. Q-Zorb material in 0.020 in. (0.5 mm) thickness, for example, is well suited for applications at 10 GHz and above. These EMI-shielding materials feature a UL-V0 fire retardant rating and can be used at temperatures as high as +350F for reliable application in engine compartments.

Q-Zorb materials can be supplied in standard sheet sizes of 24 x 24 in., 12 x 12 in., and 4 x 6 in. They are essentially thin polymeric materials filled with magnetic particles. They exhibit both high permeability (for high magnetic loss of EM field strength) and high permittivity (for high dielectric losses) in order to suppress unwanted EM fields and signals. The EM energy along the side walls of a cavity are dominated by current flow and the magnetic (H) field, requiring the use of materials with high H-field loss that can suppress or cancel the magnetic field (and the currents causing it). In such a case, the electric (E) field is at a minimum along the cavity walls, and materialssuch as resistive foamsthat only exhibit dielectric loss will not provide adequate attenuation of the magnetic field.

The Q-Zorb materials can be bonded to a surface using contact adhesives or supplied with a pressure-sensitive acrylic adhesive (PSA) for ease of attachment. Both sets of materials are also RoHS compliant. MWRF

Laird Technologies, 3481 Rider Trail S., Earth City, MO 63045; (866) 928-8181, (636) 898-6000, FAX: (636) 898-6100, e-mail: EMI-AmericasSales@lairdtech.com, www.lairdtech.com.