This post written by David Sherman originally appeared on Rogers PORON Cushioning Blog.

You’ve probably heard quite a bit about concussions in the news lately.  In recognition of Brain Injury Awareness month, which takes place in March, the Brain Injury Association of America (BIAA) is launching a nation-wide campaign to ensure coaches of school athletic teams and extracurricular athletic activities are trained to recognize the signs and symptoms of concussions.

All of us at Rogers are excited to see that proper attention is finally being brought to the causes and effects of brain and impact injuries.  Extreme impact protection is the very reason we developed our PORON XRD technology, which is not only used in helmets, but also in compression garments, elbow and knee pads, and protective footwear.

As we travel around to trade shows all over the world, we are consistently asked how PORON XRD Material works.  How can such soft, flexible and breathable foam protect against something like a baseball flying at 100mh?  It all has to do with a short lesson in physics 101 and strain rate dependant materials.

Strain rate dependent materials are used in a variety of protective applications mentioned above.  They are useful in these applications because of their unique ability to adapt to the applied impact.  At low strain rates the material feels soft and contours to the body.  While at high strain rates the material instantaneously stiffens to absorb the impact and then returns to its original ‘resting’ state.

For those who want more technical information….

PORON XRD Material gets its softness when at rest or simply being worn, by being above the glass transition temperature (Tg) of the urethane molecules.  (Glass transition temperatures are similar to a melting point – for those who are not the foam geeks that we are.)

When stressed at a high rate or impacted quickly, the glass transition temperature of the material goes up to the point where the urethane momentarily “freezes.”  (Think of water freezing into ice.)  Many materials have glass transition temperatures, which is why strain rates are always specified in material testing.

When impacted, it is the firming of the material that allows PORON XRD Material to instantly form a comfortable, protective shell around the wearer.  Unlike many other materials which often maintain their “frozen” state, PORON XRD Protection immediately returns to its soft, flexible and contouring state.

For a more visual example, think of diving into water at a low height versus a higher height.  At low heights, jumping into water feels very soft and helps cushion the dive.  But at high heights (i.e. jumping from a bridge) the water feels like frozen ice.  This is due to the speed at which the person is entering the water.

Another example is to envision removing a Band-Aid™.   If you remove a Band-Aid ™ slowly, the

adhesive sticks to the surface, but if you remove it quickly, the adhesive freezes and sticks less.

PORON XRD Material was engineered to react very quickly in various impact situations.  For example, PORON XRD Technology is effective at absorbing not only smaller, repeated impacts (such as nudging players during a basketball game) but it is also effective at absorbing larger impacts (such as in a ballistic vest applications).  Rogers’ ability to manipulate the PORON XRD chemistry makes this unique material soft and flexible at rest or when it’s wrapped around your body, but instantly absorbs energy upon impact.

If you would like more information on all the various testing methods that we have conducted on PORON XRD Materials, we have plenty to share!  Just give us a comment below.

Please come back and visit us!  We will be posting some interesting news over the next several weeks in collaboration with our PORON XRD partners in recognition of Brain Injury Awareness Month.   As always, we would love to hear your questions and comments/views you may have on our products as well as how brain injuries/concussions are treated among team sports.

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In a recent article on DesignNews.com, Boeing announced that it was shifting to plastic composites for its 787 Dreamliner floor beams.  It’s well-known that the airline has had trouble getting this aircraft to market starting with being three years late. But it hasn’t stopped them in finding new, innovative ways to reduce its carbon footprint and drive sustainability into their design decisions:

The Boeing 787 Dreamliner is a long-range airliner that seats 210 to 330 passengers. As a result of a fuselage and wings made primarily of carbon composites, the Dreamliner consumes 20 percent less fuel than the Boeing 767, which has similar seating capacity.

TAL Manufacturing Solutions of India reports that Boeing changed the design for floor beams in the Dreamliner 787 from titanium to a composite plastic structure….the floors will be made from materials that are similar to the materials used in the body of the Dreamliner… The beams will be used for flooring located between passenger and luggage compartments.

In talking with Ken Kozicki from our BISCO Silicones Division, he elaborated on the considerations that are made when choosing materials for aircraft flooring.  He also shared how silicone foam can act as a barrier in between the floor beams and help reduce the vibration and overall noise from engines.  And we all know any reduction in noise when flying is MOST appreciated!  Here’s what Ken said:

Dynamic flooring designs and structures have a few purposes – but can be concentrated into three general categories:

  • Minimize vibration and acoustic noise generation
  • Propagation or “modularize” the floor into segments that can be fabricated and layered prior to final assembly,
  • Shrink the thickness of the profile of the entire floor allowing for increased head room in a rail car or aircraft.

With each of these objectives, the selection of the viscoelastic materials used for the vibration isolation and damping pads is critical.  The performance of the floor is dependent on the material’s physical characteristics such as the stiffness to support maximum loads and the damping coefficient to balance the amount of vibration energy that is isolated versus dissipated.  In addition, especially in the aircraft and rail markets, the materials need to comply to the very stringent flame, smoke, and toxicity standards.

Lastly, something that is often times overlooked is the change in performance of the material over time.  In reference to foams, it is important to consider compression set and stress relaxation.

Compression set is the amount of reduction in thickness the foam will permanently experience over time.  Stress relaxation is how much “springback force” does the material lose over time.  If a solid material is chosen for the pads, other factors such as brittleness and performance capabilities over the required temperature range will be key.

BISCO silicones are a great choice to accommodate all of these conditions.  Noise is generated from two major sources:

1.  The first is the transfer of structure-borne vibration to a propagating sound wave.  Reducing vibration ultimately reduces noise.

2.  The second noise source is propagating sound waves from outside or beneath the flooring structure, such as jet engine noise transferring into the fuselage or rail wheels moving along the tracks.  Sound barrier materials can be laminated to the dynamic flooring structure to block the waves from propagating.  Again, choosing silicone sound barriers is an imperative, especially if a standard such as FAR 25.856 is required.

Can you hear me now?

Images source: http://showpanmohsin.blogspot.com

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This post authored by John Coonrod originally appeared on the Rog-Blog hosted by Microwave Journal

Digital circuit design once had less demands. When clock speeds were 100 MHz or less, signal loss wasn’t an issue. Digital circuits, in fact, have long been designed to be more tolerant of signal level variations than analog circuits. But with digital circuits continuing to increase in speed, they are assuming more of the characteristics of analog microwave signals, and requiring more attention to design detail and even choice of PCB material as in the case of high-frequency analog circuits.

When 100 MHz was considered fast, the choice of a low-cost laminate like FR-4 was a sound decision. If anything, the performance provided by an epoxy-based circuit-board material like FR-4 was often better than necessary for most digital circuit designs. In early digital circuits operating at 100 MHz or less, it was important for a PCB material to provide a consistent relative dielectric constant across the material in order to maintain circuit traces with consistent impedance and maintain even timing of digital signals across the circuit. In an analog/microwave circuit, consistent impedance is also important, since impedance mismatches can cause unwanted signal reflections and shifts in signal phase and frequency.

But times have changed and now digital signals travel at microwave speeds. The same design guidelines and choices in PCB materials used for lower-speed digital circuits can’t be applied at higher operating speeds without penalties, such as timing problems, signal crosstalk, and even electromagnetic-interference (EMI) problems. High-speed signals more and more resemble the fast pulses of microwave radar systems, and designers of high-speed digital circuits must think more like microwave circuit engineers to create successful designs.

Digital circuit designers have come to learn what microwave circuit designers have known for years: the choice of PCB material can have a great impact on the performance of high-speed digital circuits as well as analog microwave circuits. Digital circuit designers once paid little attention to the loss of a PCB, since that material characteristic had little effect on digital functionality at lower speeds. But analog microwave systems, such as receivers, depend on signal strength, and any loss in a system or its components, including the PCB material, must be minimized. For that reason, microwave circuit designers have paid attention to a laminate’s dissipation factor, choosing materials with low values corresponding to low loss. As digital circuits move to multi-GHz speeds, loss can also be a concern, especially for its effect on digital signal integrity.

Losses in a high-speed or high-frequency PCB can stem from a number of sources, including dielectric losses (especially above about 3 GHz), conductor losses, ground-plane losses, and even losses attributed to the surface roughness of a PCB’s conductive metal used to form signal and power traces. The performance of a high-speed digital PCB can also be affected by crosstalk between signal traces on one layer of the PCB or between layers of a multilayer PCB, by noise from the power and ground planes due to inadequate decoupling, and by external radiated and conducted noise sources. High-speed digital circuit designers must also control levels of EMI to meet global regulatory requirements.

Microwave circuits may never match the complexity of high-speed digital circuits in terms of number of layers in a multilayer PCB assembly, but there are a number of parallels that can be drawn between the two circuit technologies. In fact, it is not unusual to find both types of circuit on one multilayer- circuit construction. Both benefit from PCB materials with typical low values of relative dielectric constant that are also consistent across a substrate and with frequency. Both circuit approaches can benefit from materials with low dissipation factor for low loss, which translates into good signal integrity in a high-speed digital circuit and low insertion loss in an analog microwave circuit.

Relative dielectric constant is only one of many different PCB material parameters, but it can be used as a starting point when considering laminate choices for a high-speed digital circuit design. Ideally, a PCB material for high-speed digital circuits would have isotropic dielectric constant characteristics—that is, with dielectric constant values that are about the same in the x, y, and z directions of the material. Another benefit would be to have the dielectric constant remain within a narrow range of values across a wide frequency range. Not only would this support broadband microwave use, but would ensure excellent signal integrity in high-speed digital circuits.

Unfortunately, most PCB materials are anisotropic in their relative dielectric constant values, with different values in each direction. And most exhibit dielectric constants that decrease with increasing frequency. For high-performance digital as well as microwave circuits, it can be helpful to select PCB materials that are as closely matched in relatively dielectric constant in all three axes, and with dielectric constant that is fairly consistent with frequency. For an increase in dielectric constant, the impedance of a circuit trace or transmission line will decrease and the speed of a wave through the trace or line will slow. In a digital circuit, a material with dielectric constant that significantly decreases with frequency can cause digital signal edges to reflect more at higher frequencies than at lower frequencies, causing timing problems. The problem can be minimized by selecting a PCB material with relative dielectric constant that is as flat as possible with frequency (low dispersion).  The chart in figure 1 displays dispersion when measured using a stripline transmission line.  Typically stripline transmission lines are considered a non-dispersive medium so what effect is shown with dielectric constant in relation to frequency is likely material dispersion.

One other material parameter that is worth noting in selecting substrates for high-speed digital circuits is the coefficient of thermal expansion (CTE) in the z-axis (through the thickness) of a laminate. This parameter is one indicator of the expected reliability of plated through holes (PTHs), which are plated vias used to make signal, power, and ground connections between the different layers in a multilayer PCB.

A low-dielectric-constant PCB material can support good performance in high-speed digital circuits, but it must also be a material that is compatible with the processing steps used to fabricate the multilayer circuits typical of digital designs. As an example, Theta™ circuit materials from Rogers Corporation are low-loss, low-dielectric-constant materials with excellent thermal and mechanical properties for high-layer-count circuit boards. They maintain dielectric constant within a fairly narrow window with frequency, with z-axis values of 3.90 at 1 GHz and 4.01 at 10 GHz. Theta materials also have a z-axis CTE (about 50 ppm/°C) that is approximately 30% lower than that of FR-4, and more closely matched to that of copper, for highly reliable PTHs in multilayer circuits. These materials are halogen free and compatible with lead-free soldering processes. They have the mechanical traits needed for multilayer digital designs, but also the excellent electrical characteristics suitable for both microwave and high-speed digital circuits or, in fact, both types of circuits within the same multilayer PCB.

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PORON® Urethane Gap Filling Design Tool

On March 8, 2011, in Design Tools, HPF, by juliann

Need the perfect gasketing material?  Look no further; Rogers Gap Filling Tool for PORON® Urethanes is designed to do just that!

When designing a hand-held device, appliance or enclosure, it’s important for design engineers to understand the tolerances and performance of PORON Urethane foam materials for gaps both large and small.

When filling a space within a device or trying to make a tight seal, it’s important to know the stress or “push back” force the material will exert at that specific percent compression or final gap thickness before selecting a material.  If a material’s push back force exceeds the design’s limitations, it can cause deformation in the device or enclosure.

Rogers engineers have created a unique tool to help the design community calculate the push back force of PORON Urethane foams at various gap thicknesses.  This important design information is obtained through Compression Force Deflection (CFD) curves of various PORON materials.  A guided YouTube tutorial is available for quick training!

The Rogers Gap Filling Tool is useful for design engineers who are responsible for designing products in the automotive, appliance, and consumer electronics markets, as well as industrial applications like enclosure units or any product that requires a gasket, spring or seal.

Below is a screen shot of the Rogers Gap Filling Tool with a link to access the tool. Good luck and let us know what you think. Your feedback is crucial for us to continue to make useful tools that help solve your design challenges.

PORON Eurethane Gap Filling Tool

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Ken Kozicki from our BISCO division recently led a discussion with one of our resellers, the Grogan Group (based in Australia), that highlighted some key design considerations for engineers when it comes to choosing seat cushion materials in rail cars. Ken highlighted the differences between Rogers MF-1 silicone foam for seat cushions vs. typical molded polyurethane cushions and their advantages for rail and transit authorities.  Fortunately the discussion was videotaped (thanks to the folks at Grogan Group!) and you can watch it at your leisure.   However we wanted to capture some of the key points Ken made during his talk.  He shared that while silicone foam is a bit more expensive than polyurethane materials, there are some intangibles that need to be considered:

About Molded Polyurethane Seating

Typical seating cushions in rail cars are a molded polyurethane that has a low performing compressibility rate when it comes to cushion comfort.  What this means is that a polyurethane seat wears out quicker over time, and it loses its “spring-back” force that helps make the seat comfortable.  Over time the foam actually shrinks and flattens out, the upholstered material covering the cushion stretches out, gets loose, and the seat’s comfort declines as more passengers sit on it.  This material also needs to be treated with fire retardant chemicals, which adds to the production cost.

About Silicone Foam

The production of silicone foam is a more sensitive process than polyurethane.  There are precise control factors that come into play when manufacturing silicone foam because it creates a chemical reaction, and if the recipe is slightly off or there is added humidity or temperature changes, it can change the nature of the end product and be out of spec ranges.  This complex process tends to keep the price higher than polyurethane when comparing the two materials side by side.

But on the flip side, silicone foam has many advantages that polyurethane does not.  It will not lose its “spring-back” force, and does not require fire retardant treatment.  And, the issues that happen with molded polyurethane don’t happen here:  the upholstery doesn’t loosen, the seat does not lose shape from long wear and the cushion does not shrink in height.  As a result, the life of a silicone foam seat cushion is much longer (getting back to those intangible benefits).  There is also less repair and refurbishment costs for a transit authority (and these are very tangible benefits).

To learn more about Rogers MF-1 Silicone Foam and how it provides better, long-lasting comfort in rail car seating, sit back and watch the video:

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