MAST Technologies’ silicone based RF absorbers are well suited for space applications. The industry standard test for measuring outgassing of RF absorbers and similar materials is ASTM E595. Developed by NASA to screen low outgassing materials for use in space, the test determines the volatile content of material samples placed in a heated vacuum chamber. If a material passes this NASA low outgassing test, it can be used in a multitude of applications including outer space, high vacuum, specialty optical and electro-optical applications, among others.

Want to read a copy of the test report?
Visit this report and others at: http://masttechnologies.com/technical-bulletins/

Marine Grade Materials
Corrosion Resistance for Extreme Environments

Did you know that MAST Technologies can produce many of its standard products in a corrosion resistant form?

MAST understands that there are some applications which require materials able to withstand the harshest of environments, which is why it has developed technologies for marine grade materials. By altering the formulation, MAST is able to achieve equivalent RF and electrical properties as standard grade materials, in weather/corrosion resistant form. MAST has provided materials which have passed ASTM G53, which is a 1,000 hour accelerated QUV weatherometer test, as well as 500 hour salt fog chamber exposure.

Whether you are seeking a Tuned Frequency, Cavity Resonance, or Surface Wave RF absorber, MAST can design a suitable corrosion resistant material for applications like shipboard radars, reducing unwanted reflections from radar view, weather radars, among others.

Contact your local MAST Technologies sales representative for more information!

Does the difficulty of getting your fingernail behind an adhesive liner sound all too familiar to you?  Well then you might be a perfect candidate to evaluate a kiss cut solution!

What’s the difference?

Die cutting is a process of using a punch press and steel ruled die to cut sheet or roll stock into a prescribed shape or size.

The sheet or roll stock is placed on a cutting board then compressed with a punch press.  The knife edge blades in the steel ruled die produce a clean and precise cut.  Die cut parts are completely cut through the material, adhesive and release liner.  Die cut parts are packed in a manner referred to as “bag and tag”, where many cut parts will be placed in a common bag for shipping and presentation to the end production line.

Kiss Cutting is a similar process which uses a punch press and steel ruled die.  However, rather than cutting all the way through the material, adhesive, and liner, kiss cutting is a form of cutting where controlled pressure is applied to make an impression in the “peel-off” portion of the material, but not through the adhesive liner.  This enables the die cutter to locate several parts on one common liner.  A good example of kiss cutting can be found in printer labels, where you have several labels on one sheet of paper.

When a part is kiss cut and presented on a common liner, it makes the removal from the liner much quicker than a die cut part. Rather than carefully inserting your fingernail between the liner and the material, the operator can simply flex the liner exposing a corner of the material to be removed.  Especially when working with small die cut parts, this can save a lot of production installation time.

MAST Technologies is one of the few manufacturers that can provide all sheet and roll products in kiss cut format.  Contact an Applications Engineer at sales@masttechnologies.com to discuss you how you might be able to save installation time with a kiss cut solution from MAST Technologies.with small die cut parts, this can save a lot of production installation time.

Within 77 GHz radar sensors, there are many active components generally driven by a silicon chipset. The automotive industry is pushing manufacturers of sensors towards smaller form factor designs, thus increasing the population density of active components and antenna elements. With the increased component density, traditional means for shielding for RF emissions and susceptibility become challenging. Traditional means for RF shielding include creating faraday cages (metal boxes) around active components, and installing conductive gaskets around the outboard rail of devices. Although these traditional shielding solutions are effective at providing a path to ground for incoming and emitted RF energy, the solutions have issues at 77 GHz.

The wavelength of a 77 GHz signal is 3.9mm, which means that any VERY small seam, mounting hole, or other aperture may act as an energy leakage point or radiator. Furthermore, while the intention of traditional shielding is to contain energy, this may not be the best performing solution at 77 GHz. As these smaller millimeter wavelengths are contained they are beginning to approach the physical dimensions of the cavity which is containing it, which can lead to cavity resonance effects. The resonant frequency is the frequency where the integer half-wavelength corresponds to the physical dimension of a cavity. A wave is set up inside the cavity whose nodes (i.e. zero amplitude) lie on the conductive walls of the enclosure. The danger of a cavity resonance is that if a noise source has a frequency component that corresponds to a resonant point, then a large field can be generated at this frequency due to the multiplication or amplification effect by the “Q factor”. One of the most effective ways to reduce the Q-factor is by introducing cavity losses via Cavity Resonance absorbers.

MAST Technologies is an industry leader in the design and deployment of microwave and millimeter wave absorber solutions. Because the millimeter wave design community is advancing very quickly, MAST Technologies has partnered with an industry leader in Millimeter Wave Products, Inc. to aid in the validation and test of these absorbers products at the 77 GHz band. Use cases for RF absorbers in 77 GHz sensors are for EMI shielding (susceptibility and emissions), cavity resonance reduction, side and back lobe reduction, and cross talk reduction.

Reducing Reflections Inside the Box

In an ideal world, everyone would build an RF test box that was the size of an anechoic chamber and have plenty of room to place 24” thick pyramidal foam on the walls, floor, and lid of the box. But that’s not realistic in most test box applications. So, it takes a little creativity to accomplish the goals. To start, there are a few questions to ask yourself:

1. What frequency am I trying to attenuate or shield against?
2. How much thickness can you tolerate?

Depending on the device that you are testing, you likely don’t need the material to be as broadband as 24” pyramidal foam, since your DUT may not be susceptible to interference across all bands. Here are three common material types that are used in test box applications, and some facts and figures regarding using them in a test box application.

MR1 Tuned Frequency

MR1 Tuned Frequency Absorbers

Frequencies: 1 – 40 GHz

Tuned Frequency absorbers are thin rubber based magnetic resonance materials. The biggest benefit of this material is the very thin form factor. Tuned Frequency absorbers are narrowband, and achieve the best reflection loss at +/- 10% of the design frequency. These materials are designed to be used in intimate contact with a reflective ground plane. If your current box design is wood, or another non-conductive surface, MAST can sell the sheet products with an integral groundplane. MAST Technologies carries a standard product which is tuned to each integer frequency from 1 to 18 GHz, but can also custom tailor a material to your specific frequency (ie. 5.8 GHz). The MR1 tuned frequency materials are typically applied with factory installed Pressure Sensitive Adhesive (PSA).

MF2 Lossy Foam

MF2 Lossy Foam Absorbers

Frequencies: 500 MHz – 20 GHz

Lossy Foam absorbers are carbon impregnated foam materials which offer electric loss. The base foam and carbon solution are quite similar to that of standard anechoic chamber style pyramidal foam, without the geometric shaping. Lossy Foam materials are actually designed for insertion loss rather than reflection loss. However, when used inside a shielded box, they can be just the low cost lossy medium to effectively knock down resonances or create isolation from the outside world. Typically lossy foam should be used in 0.5” to 2.0” thicknesses, depending on the frequency which you are trying to attenuate. The lower the frequency, the thicker the material should be. The MF2 Lossy Foam products are typically applied with factory installed PSA.

MF3 Convoluted Foam

MF3 Convoluted Foam Absorbers

Frequencies: 1 GHz to 20 GHz

Convoluted Foam absorbers are very similar to traditional pyramidal foam in that they are carbon impregnated foam materials which possess an “egg-crate” shaping, much like that of pyramids. This egg-crate shaping provides a tapered impedance for the incoming wave, and you are left with a very good broadband absorbing material.  MAST has standard products in 1.5”, 3.0”, and 4.0” available. The MF3 Convoluted Foam products are typically applied with factory installed PSA.

Reducing RF Leakage

In your RF Test Box design, you may also be concerned with RF leakage through and enclosure seams, connector apertures, or lid mating surfaces. This is where conductive EMI elastomer gaskets can come in very handy! MAST Technologies has a range of different conductive particle impregnated silicone rubber sheets which can easily be hand-cut to make lid or flange gaskets. Equally important are conductive O-rings around connector bodies which may leak RF energy. Contact a MAST representative for more information on the MAST-O-Shield™ line of products.

Types of Absorbers and their Pros and Cons

Generally speaking there are two classes of RF absorbers: magnetic resonant frequency absorbers, and graded dielectric materials. (For a more detailed discussion on the materials and principal of operation, please see this blog post.)
Magnetic resonant absorbers, like MAST’s MR1, MR2, and MR3 materials can be effective solutions for antenna isolation concerns which require a narrowband performing material. For example, if an antenna requires increased isolation specifically at 5.8 GHz, but does not require isolation at 10 GHz, then an MR1 Tuned Frequency Absorber might be a suitable choice. The difference between MR1, MR2, and MR3 magnetic resonant materials is the shape of the performance curve; some curves being more shallow and broad and others being deep and narrow. A quick review of performance plots can lead the engineer to a suitable material. Another benefit of magnetic resonant materials is the form factor of these materials. Typically magnetic resonant materials range in thickness from 0.010 – 0.150” thick, and are easily installed onto virtually any surface using pressure sensitive adhesive (PSA) that is sold with it. Magnetic absorbers’ performance is reliant on being in intimate contact with a conductive groundplane. If the application does not allow for intimate contact with a groundplane, MAST can provide an Integral Grounplane which is bonded to the back of the material. It’s also important to note, that magnetic resonant absorbers are NOT electrically conductive so they can be bonded or placed in intimate contact with a PCB without fear of short circuit.
Magnetic resonant absorbers are also more environmentally robust than that of the graded dielectric materials. Magnetic resonant absorbers are iron alloy impregnated rubber sheets, and are generally environmentally tough. However, when exposed to harsh outdoor environments which include high levels of moisture and rain, upon special request MAST can provide the magnetic absorber with corrosion resistant iron alloy filler. Another low cost alternative is to coat the absorber material with an outdoor corrosion preventing paint coating.
Graded dielectric absorbers, like MAST’s MF1, MF2, and MF3 materials can also be effective solutions for antenna isolation concerns which require a broadband performing material. The material can be designed either to provide insertion loss or reflection loss. Dielectric absorbers which provide insertion loss, like MF2 Lossy Foam, can be effective at reducing side or back lobe energy when used in applications with polymer or composite based radomes or enclosures. Alternatively, dielectric absorbers intended for reflection loss performance, are intended to be used in conjunction with a conductive groundplane, so are more appropriately used on shields or shrouds. MAST can install an integral groundplane on dielectric absorbers also.
Graded dielectric absorbers are not as environmentally robust as their rubber based magnetic resonant absorber counterparts, however there are a few steps that can be taken to improve the environmental toughness of these materials. For environments which have moderate moisture exposure, MAST can apply an encapsulant overcoat to protect the material. Alternatively, all graded dielectric materials can be coated in a weatherproof fabric cover which will enclose the material, protecting it from moisture and harsh weather.

Questions and answers to ask yourself:

• Is my frequency of concern a single narrow band frequency or am I concerned with a broadband energy?
  • If you are only concerned with a specific frequency, and/or you really want to ONLY attenuate energy at a specific frequency, then most likely you will want to look at our MR1 Tuned Frequency absorbers. These materials have a performance bandwidth of +/-10% of the design frequency, where they will achieve -20dB of reflection loss; outside of the performance band, they will achieve around -5dB of reflection loss. If it is broadband performance that you are looking for, you should focus your search either on the MR3 surface wave materials or on MF1, MF2, or MF3 graded dielectric absorbers.
• Am I trying to accomplish Insertion Loss or Reflection Loss by using RF Absorbers?
  • If insertion loss is what you’re after, then MF2 Lossy Foam should do the trick. If reflection loss if the effect that you are after, then refer to question number 1 about a narrowband or broad band absorption effect.
• Will I be mounting the RF absorber inside a sealed radome? Or, will it be mounted directly to the back of the antenna or on an adjacent metal shroud?
  • If the material will be mounted outside and in direct exposure the environment, MAST highly recommends either a corrosion resistant magnetic material, a corrosion resistant paint coating, or a weatherproof cover.
• How do I envision attaching the absorber to the antenna, radome, or shroud?
  • MAST commonly provides all absorber products with a PSA backing. This adhesive typically offers great peel strength onto surfaces like aluminum, stainless steel, most plastics, and PCB materials. We also have several liquid and paste adhesives to recommend if our standard PSA won’t work for your application.

For those of you whom we have not yet met, MAST Technologies is a leading designer and manufacturer of rf absorbers (radio frequency), EMI shielding elastomers, and high temperature coatings.  MAST Technologies was founded in 2009, when the founders recognized a market need for a smaller, more innovative materials company which was UNAMBIGUOUSLY customer driven.  From the humble beginnings at MAST, we have been completely dedicated to servicing our *new* and existing customer base and we believe that the success of this organization will be based on  what we call “doing the right thing”.

With our customers in mind, we have designed a product offering of materials which are manufactured in our own facility in San Diego, CA.  We employ material scientists and engineers, quality engineers, and production professionals who ensure that the entirety of our operations are focused on producing relevant and high quality products.

We have started this blog to address the common questions and keep our fans up to date with advances in the technology of RF absorbers, microwave absorbers, and EMI shielding solutions.  Some of the upcoming topics which we will be addressing are:  how to choose the right microwave absorber?  how do you measure an rf absorber?  why would you choose a different type of elastomer from silicone?

Please stay tuned and we hope that this blog becomes a useful resource to you.

We wish you a prosperous 2012.

-Andrew Sundsmo