INVISI-SHIELD® Electrically Transparent Ice Shield

The ERI INVISI-SHIELD® provides protection for FM antennas without impacting the antenna pattern. This specially designed electrically transparent ice shield can be mounted immediately above the array and at intermediate locations within the array for FM antenna that are 8-bays of more without impacting the FM antenna’s electrical performance.

Radial icing occurs when water droplets are large enough to fall from the atmosphere and freeze on objects near the ground. The frozen deposits form a clear ice shell on antennas and tower components. Radial ice conditions are typically very short in duration. The thaw that follows releases segments of ice that fall or sail, causing significant damage to antenna elements mounted below the top of the tower.

The antenna elements are particularly susceptible to falling ice. Radial ice has a unit weight of 56 pounds per cubic foot (897 kg/m³) and can cause significant damage to unprotected tower appurtenances. Steel ice shields can offer some degree of protection. But due to pattern distortion inherent to their construction, the steel shields are placed at distances which diminishes their ability to protect the FM antennas adequately.

Some applications of a steel ice shield are prohibited due to the detracting effects it could have on neighboring antennas. The ERI INVISI-SHIELD® is an electrically transparent ice shield. Utilizing custom-fabricated materials and careful placement of connection components has resulted in a structure that has no perceptible effect on the antenna’s pattern. The INVISI-SHIELD® can be mounted directly over an antenna element. This close proximity allows the INVISI-SHIELD® to be significantly smaller while increasing protection when compared to a steel shield. The smaller size also results in less load on the tower. The electrical transparency of the INVISI-SHIELD® will permit installation between antenna bays in extreme icing conditions. The top edge of the INVISI-SHIELD® is permeated with a silicone grit. This material helps trap potential freezing rain on the shield reducing the potential of radial ice accumulation and detuning of the antenna element.

The INVISI-SHIELD is constructed of a high-strength one in thick pultruded bar grating made exclusively in the U.S.A. that can be used like traditional metal grates or fiberglass molded grating but offers the inherent benefits of pultrusion.

Pultruded fiberglass grating is made up of continuous glass strands, which are enclosed in resin and wrapped in a surfacing veil to safeguard the fibers whilst allowing the resin to saturate the outermost section of the bar and penetrate between glass fibers. This process means that a smooth and corrosion-resistant surface can be achieved with a favorable glass/resin ratio. Individual bars are assembled with cross bars and epoxy to fuse the load bars mechanically. Pultruded fiberglass grating possesses unidirectional strength and has a much higher glass content than molded fiberglass grating. This means that it has a higher span capability and is often used for applications that need heavier loading or larger spans.

Specifications

  • Load Rating:
    300 PSF (1465 kg/m²) uniform distribution 7,200 lbs. (3265.8 kg) total capacity, High Impact Resistance
  • Size:
    6 ft x 4 ft | 1.83 m x 1.22 m
  • Weight:
    No Ice 225-lbm | 102.1-kg
  • 1/2-inch (13 mm) Ice 500-lbm | 226.8-kg
  • Effective Project Area:
  • Normal Exposure
    No Ice 8.8-ft² | 0.82-m²
  • 1/2-inch (13 mm) Ice 10.0-ft² | 0.93-m²
  • Transverse Exposure
    No Ice 8.4-ft² | 0.78-m²
  • 1/2-inch (13 mm) Ice 9.7-ft² | 0.90-m²

Features and Benefits

  • Protection from falling ice
  • No perceptible pattern distortion
  • Can be mounted directly over each element
  • Reduces potential accumulation of radial ice
  • Convenient work platform

INVISI-SHIELD® Product Brochure