What’s The Difference Between Metallic And Non-Metallic Enclosures For Wireless Applications?

Research indicates that the use of wireless applications will increase exponentially over the next five years as a result of their association with lower costs and increased reliability. To optimize their wireless products, designers need a thorough understanding of wireless basics and the ability to readily identify open products that adhere to set standards.

Understanding Wireless Signals

Wireless transmission is useful where interconnecting wires are inconvenient, hazardous, or impossible. Reliable enclosures for sensitive controls and monitoring systems in the field are a pressing need for many industries where effective transmission is a must. With wireless data transmission such as radio, the proportion of energy received becomes critical if it is too low for the signal to be distinguished from the background noise.

Radio receivers retrieve all signals on the frequency at which the receiver is set. In the case of Wi-Fi, it’s 2.4 GHz. For data transmission to occur, the Wi-Fi signal must be at least 20 dBm greater than the signal level of the noise or spurious transmissions. If a signal is shielded, the signal-to-noise ratio (SNR) diminishes and the signal level drops below the 20-dbm threshold. Data transmission errors occur as a result. Laptop users would experience slow browsing or the inability to browse at all.

Material Selection For Wireless

Designers with the opportunity to select their material should investigate and determine that it’s appropriate for the intended environment. Every application has its unique demands. In fact, many of the capabilities are considered inherent in certain material choices.

An errant or over-estimated material choice, however, can have many repercussions in the life cycle of a product. It makes good sense to select a product that is sufficient across the board.

Metallic Enclosures

Premium metals such as stainless steel can be used where long life, corrosion resistance, and weatherability are critical, usually in control protection. However, many OEMs are unwilling to pass their higher cost and excessive weight along to their customers. Another key factor to consider is the environment in which stainless steel enclosures are to be placed. Steels often have high strength but exhibit low toughness, meaning they dent easily, yet are difficult to drill or penetrate.

Designers must also keep in mind the most critical issue in wireless application enclosure selection—metal enclosures block RF signals. To address this issue, users sometimes will install an internal cable assembly, linking the wireless module to a bulkhead connector. This is intended to bridge the gap, allowing an external antenna to screw directly onto the bulkhead connector. In practice, a metallic enclosure with this configuration of an external antenna generally performs better than one featuring an internal antenna.

For most applications, metallic enclosures for Wi-Fi components have proven ineffective unless there is an external antenna. Unfortunately, external antennas have many downsides including vulnerability to environmental elements such as corrosion, ferrous-oxide deterioration, and natural ambient interference coming from environmental forces. This is why many designers are making the switch to non-metallic materials because they allow for free transmission of electronic signals.

Composite Enclosures

Composite materials such as fiberglass enable electronic signals to transmit freely. Although many non-metallic enclosure materials offer a degree of corrosion resistance in less harsh environments, some wireless controls designers have discovered that fiberglass NEMA 4X enclosures are specifically fabricated and rated for resistance to the harshest corrosive agents. Fiberglass enclosures exhibit average strength but high toughness, allowing them to withstand sudden impacts while maintaining their shape.

The biggest advantage of non-metallic materials is that they enable electronic signals to transmit as freely as information systems require without the need for an external antenna. Fiberglass for wireless applications has several advantages. It does not block wireless signals, it’s easy of modify (simple to drill cutouts for audio/video connections), it properly protects controls in harsh environments, it’s non-conductive, and it withstands extreme cold and heat.

Polycarbonate Enclosures

Key benefits of polycarbonate enclosures include temperature and impact resistance. Polycarbonates are a particular type of engineered thermoplastic polymers. Components fabricated with polycarbonates are usually created by injection molding, thermoforming, or simple machining, and they are easily worked, molded, and thermoformed. Because of these properties, polycarbonates are useful for many applications, including wireless.

Polycarbonate enclosures are made with the injection molding process, allowing for integrated features not available on metallic or composite enclosures. Integrated bosses allow for equipment to be attached to the enclosures without using a back plate. Integrated slot channels provide numerous methods for mounting to the sidewall without having to penetrate the exterior. Integrated hinges and latches provide secure and reliable closure and security.

Polycarbonates also provide a feature-rich product that is engineered for the harshest environments. They are rated UL508A, UL50E, NEMA 4X, and IP68. In addition, polycarbonate enclosures allow for mounting options without a metal plate and integrated slot channels that provide additional space without penetrating walls. Also, the lack of metal latches and hinges means less chance for corrosion.

Similar to fiberglass, polycarbonates don’t block wireless signals. They’re easy to modify. They protect controls in harsh environments. They’re non-conductive. And, they sport an attractive finish and appearance to meet demands for aesthetics at the installed location

Ultimately, the choice of enclosure material depends on the concentration of various corrosives present in the application environment and other physical properties necessary to meet design specifications (see the table).

Composite Solutions For Wireless Controls

According to remote monitoring, alarm, and control solutions provider AMCi, fiberglass NEMA 4X enclosures are specifically fabricated and rated for resistance to the harshest corrosive agents (Fig. 1). The company determined that metal enclosures and radio frequency signals specific to wireless controls weren’t adequately compatible. As a result, it selected fiberglass composite enclosures for use in its housing and protection wireless controls.

1. For wireless applications, AMCi uses fiberglass NEMA 4X enclosures that are both fabricated and rated for resistance to the harshest corrosive agents.

Enviro Tech Instruments chose fiberglass for its AutoLAB 4 product line for harsh environments. Deployed in areas where it is exposed to continuous UV rays, humidity, and rainfall, the AutoLAB 4 provides high-frequency nutrient data with minimal operator overhead due to its wireless transmission ability (Fig. 2). The system’s data telemetry, via low-cost radio or cellular modems, provides complete real-time visibility of field conditions for monitoring and early warning.

2. AutoLAB systems installed in a nursery in central Florida are exposed to continuous UV rays, humidity, and heavy rainfall. They’re also in a remote location that requires a wireless application for optimum use.

Because AutoLAB’s applications are always deployed in extreme environments, the critical controls and instrumentation must be properly protected to ensure optimum performance and reliability. To safeguard these essential instruments, Enviro Tech Instruments relies on non-metallic enclosures.

RACO’s rugged Cellularm System employs a fiberglass enclosure to allow for ease of wireless data transfers (Fig. 3). Designed for temporary or permanent field use, RACO’s system needs to be rugged and housed in a heavy duty, weather-resistant enclosure. The housing also needs to incorporate a cellular phone transceiver, an antenna, and one of the company’s many versions of alarm auto dialers packaged in a single, integrated unit while still allowing for easy data transfer. The fiberglass enclosure the company selected met all of these requirements.

3. RACO’s Cellularm System employs a fiberglass enclosure to enable easy wireless data transfers.

The Metis Secure Solutions MS-6100 Emergency Help Station is designed to be on constant response to requests for help from people in need (Fig. 4). With the press of a button, people are connected to police dispatch in seconds. The company felt that fiberglass would be a prime choice of materials for two reasons.

4. A non-metallic enclosure protects the Metis Secure Solutions MS-6100 Emergency Help Station controls.

First, fiberglass allowed the transmission of wireless signals. Typically an exposed metal enclosure would require an external antenna to ensure signals could be sent and received. Second, systems are placed in extreme urban environments, which means Metis anticipated damage to antennas. In turn, the lowered functionality would pose a safety risk and create an ongoing maintenance and service issue. A custom, yellow, molded non-metallic enclosure was the final choice.

Key factors among all of these companies for their product needs were wireless compatibility, rugged durability, and resistance to harsh environments. Fiberglass enclosures meet all of these requirements.

Uses Of Polycarbonate For Wireless Controls

To remain competitive, many music and sporting events offer attendees free wireless Internet access. Due to their light weight, ease of use, competitive costs, and ability to withstand environment elements such as heat, cold, wind, rain, and dust, cost-competitive polycarbonate enclosures often are the first choice for housing wireless controls.

Conclusions

After reviewing the many available options, more and more companies requiring protection for wireless control systems are choosing non-metallic enclosures. In summation, the reasons are clear:

Metal is not as accommodating as non-metallic materials in terms of enabling electronic signals to transmit with the speed their information systems require.
Control systems are often placed in extreme and remote environments. Users do not want to risk exposing an external antenna, which makes remote solutions more vulnerable to failure.
Non-metallic enclosures, such as polycarbonate and fiberglass, ultimately provide proven durability.
Non-metallic enclosures do not present the problem of rust or corrosion in harsh elements.
Non-metallic enclosures are suitable for preventing unauthorized access with dual latching/lockable lids.
Non-metallic enclosures are also more resilient to impact. They “give” rather than dent.

One major negative consequence to metal enclosures can be the compromise of the gasket seal. This seal is extremely important because it prevents moisture, dust, and other environmental factors from damaging internal controls.