“Equation Based Surface” for Conformal and Non-Planar Antenna Design

ANYSY HFSS provides many options for creating non-planar and conformal shapes. In MCAD you may use shapes such as cylinders or spheres, and with some steps, you can design you antennas on various surfaces. In some applications, it is necessary to study the effect of curvatures and shapes on the antenna performance. For example for wearable antennas it is important to study the effect of bending, crumpling and air-gap between antenna and human body.

Equation Based Surface

One of the tools that HFSS offers and can be used to do parametric sweep or optimization, is “Draw equation based surface”. This can be accessed under “Draw” “Equation Based Surface” or by using “Draw” tab and choosing it from the banner (Fig. 1)

Fig. 1. (a) Select Draw -> Equation Based Surface
Fig. 1. (b) click on the icon that is highlighted

Once this is selected the Equation Based Surface window that opens gives you options to enter the equation with the two variables (_u, _v_) to define a surface. Each point of the surface can be a function of (_u,_v). The range of (_u, _v) will also be determined in this window. The types of functions that are available can be seen in “Edit Equation” window, by clicking on “…” next to X, Y or Z (Fig. 2). Alternatively, the equation can be typed inside this window. Project or Design Variables can also be used or introduced here.

Fig. 2. (a) Equation Based Surface window
Fig. 2. (b) Clikc on the “…” next to X and see the “Edit Equation: window to build the equation for X

For example an elliptical cylinder along y axis can be represented by:

This equation can be entered as shown in Fig. 3.

Fig. 3. Elliptical surface equation

Variation of this equation can be obtained by changing variables R1, R2, L and beta. Two examples are shown in Fig. 4.

Fig. 4. Elliptical surface equation

Application of Equation Based Surface in Conformal and Non-Planar Antennas

To make use of this function to transfer a planar design to a non-planar design of interest, the following steps can be taken:

  • Start with a planar design. Keep in mind that changing the surface shape can change the characteristics of the antenna. It is a good idea to use a parameterized model, to be able to change and optimize the dimensions after transferring the design on a non-planar surface. As an example we started with a planar meandered line antenna that works around 700MHz, as shown in Fig. 5. The model is excited by a wave port. Since the cylindrical surface will be built around y-axis, the model is transferred to a height to allow the substrate surface to be made (Fig 5. b)
Fig. 5. Planar meandered antenna (a) on xy plane, (b) moved to a height of 5cm
  • Next, using equation based surface, create the desired shape and with the same length as the planar substrate. Make sure that the original deisgn is at a higher location. Select the non-planar surface. Use Modeler->Surface->Thicken Sheet … and thicken the surface with the substrate thickenss. Alternatively, by choosing “Draw” tab, one can expand the Sheet dropdown menu and choose Thicken Sheet. Now select the sheet, change the material to the substrate material.
Fig. 6. Thicken the equation based surface to generate the substrate
  • At this point you are ready to transfer the antenna design to the curved surface. Select both traces of the antenna and the curved substrate (as shown in Fig. 7). Then use Modeler->Surface->Project Sheet…, this will transfer the traces to the curved surface. Please note that the original substrate is still remaining. You need not delete it.
Fig. 7. Steps for transferring the design to the curved surface (a)

Fig. 7. Steps for transferring the design to the curved surface (b)

Fig. 7. Steps for transferring the design to the curved surface (c)
  • Next step is to generate the ground plane and move the wave port. In our example design we have a partial ground plane. For ground plane surface we use the same method to generate an equation based surface. Please keep in mind that the Z coordinate of this surface should be the same as substrate minus the thickness of the substrate. (If you thickened the substrate surface to both sides, this should be the height of substrate minus half of the substrate thickness). Once this sheet is generate assign a Perfect E or Finite Conductivity Boundary (by selecting the surface, right click and Assign Boundary). Delete the old planar ground plane.
Fig. 8. Non-planar meandered antenna with non-planar ground

Wave Port Placement using Equation Based Curve

A new wave port can be defined by the following steps:

  • Delete the old port.
  • Use Draw->Equation Based Curve. Mimicking the equation used for ground plane (Fig. 9).
Fig. 9. Use Equation Based Curve to start a new wave port (a) Equation Based Curve definition window (b) wave pot terminal created using equation based curve and sweep along vector
  • Select the line from the Model tree, select Draw->Sweep->Along Vector. Draw a vector in the direction of port height. Then by selecting the SweepAlongVector from Model tree and double clicking, the window allows you to set the correct size of port height and vector start point (Fig. 10).
  • Assign wave port to this new surface.
Fig. 10. Sweep along vector to create the new wave port location

Similar method can be used to generate (sin)^n or (cos)^n surfaces. Some examples are shown in Fig. 11. Fig. 11 (a) shows how the surface was defined.

Fig. 11. (a) Equation based surface definition using “cos” function, (b), (c), & (d) three different surfaces generated by this equation based surface.

Effect of Curvature on Antenna Matching

Bending a substrate can change the transmission line and antenna impedance. By using equation based port the change in transmission line impedance effect is removed. However, the overall radiation surface is also changed that will have effects on S11. The results of S11 for the planar design, cylindrical design (Fig. 8), cos (Fig. 11 b), and cos^3 (Fig. 11 c) designs are shown in Fig. 12. If it is of interest to include the change in the transmission line impedance, the port should be kept in a rectangular shape.

Fig. 12. Effect of curvature on the resonance frequency.

Equation based curves and surfaces can take a bit of time to get used to but with a little practice these methods can really open the door to some sophisticated geometry. It is also interesting to see how much the geometry can impact a simple antenna design, especially with today’s growing popularity in flex circuitry. Be sure to check out this related webinar  that touches on the impact of packaging antennas as well. If you would like more information on how these tools may be able to help you and your design, please let us know at info@padtinc.com.

You can also click here to download a copy of this example.

Presentation: Metal 3D Printing is Changing Design, Here is how Design Engineers can Adapt

Legacy Presentation Series:

The experts at PADT are often asked to speak at conferences around the country, even around the world. This is a great opportunity for us to present what we do and share what we know. The downside is that we only reach the people in the room. The solve this, we are going back and presenting past live seminars at our desks and recording them on BrightTalk. This is the first of those recordings. To find others go to our BrightTalk Channel

Metal 3D Printing systems, especially Powder Bed Fusion Additive Manufacturing machines, have made the free-form creation of metal parts directly from CAD a reality. This has freed geometry from the constraints of traditional manufacturing and reducing the product development process. 

This presentation goes over what Design Engineers need to know to adapt to the possibility and constraints of 3D Printing in metal.

View the recording here: https://www.brighttalk.com/webcast/15747/359359

Discovery Updates in ANSYS 2019 R1 – Webinar

The ANSYS 3D Design family of products enables CAD modeling and simulation for all design engineers. Since the demands on today’s design engineer to build optimized, lighter and smarter products are greater than ever, using the appropriate design tools is more important than ever.

Two key tools helping design engineers meet such demands are ANSYS Discovery AIM and ANSYS Discovery Live. ANSYS Discovery AIM seamlessly integrates design and simulation for all engineers, helping them to explore ideas and concepts in greater depth, while Discovery Live operates as an environment providing instantaneous simulation, tightly coupled with direct geometry modeling, to enable interactive design exploration.

Both tools help to accelerate product development and bring innovations to market faster and more affordably.

Join PADT’s Simulation Support Manager, Ted Harris for a look at what exciting new features are available for design engineers in both Discovery Live and AIM, in ANSYS 2019 R1. This webinar will include discussions on updates regarding: 

  • Suppression of loads, constraints, & contacts
  • Topology Optimization
  • Improving simulation speed
  • Transferring data from AIM to Discovery Live

Register Here

If this is your first time registering for one of our Bright Talk webinars, simply click the link and fill out the attached form. We promise that the information you provide will only be shared with those promoting the event (PADT).

You will only have to do this once! For all future webinars, you can simply click the link, add the reminder to your calendar and you’re good to go!

Introducing ANSYS Cloud Compute – Webinar

Engineering simulation has long been constrained by fixed computing resources available on a desktop or cluster. Today, however, cloud computing can deliver the on-demand, high performance computing (HPC) capacity required for faster high-fidelity results offering greater performance insight.

ANSYS Cloud delivers the speed, power and compute capacity of cloud computing directly to your desktop — when and where you need it. You can run larger, more complex and more accurate simulations to gain more insight into your product — or you can evaluate more design variations to find the optimal design without long hardware/software procurement and deployment delays.

Join PADT’s Application & Simulation Support Engineer Sina Ghods for a look at how ANSYS is working to drive adoption by providing users a ready to use cloud service that offers: 

  • Reduced Turnaround Time
  • More Accurate Results
  • Access to More Complex/Larger Models
  • Secure Workflows
  • And Much More
Register Here

If this is your first time registering for one of our Bright Talk webinars, simply click the link and fill out the attached form. We promise that the information you provide will only be shared with those promoting the event (PADT).

You will only have to do this once! For all future webinars, you can simply click the link, add the reminder to your calendar and you’re good to go!

Introducing ANSYS 2019 R1

PADT is excited to announce the release of ANSYS 2019 R1, the first group of updates for the suite of ANSYS simulation software this year. The release features updates for a wide variety of applications, including simulation for fluids, structures, electronics, 3D design, and much more.

We will be hosting a series of live webinars over the course of 2019 that will allow you to learn about what’s new in this release, from PADT’s team of expert support engineers.

Take a look at the following upcoming product update webinars for 2019 R1 and register by clicking the links below.

There is more to come, so stay tuned


Fluent Updates in ANSYS 2019 R1
Wednesday, February 13th – 11:00 am – 12:00 pm MST AZ

Computational Fluid Dynamics (CFD) is a tool with amazing flexibility, accuracy and breadth of application. Serious CFD, the kind that provides insights to help you optimize your designs, could be out of reach unless you choose your software carefully. Experienced engineers need to go further and faster with well-validated CFD results across a wide range of applications, and with ANSYS Fluent users are able to do just that; delivering reliable and accurate results.

Join Padt’s CFD Team Lead Engineer, Clinton Smith for a look at what new capabilities are available for the latest version of Fluent, in ANSYS 2019 R1.

Register Here


Mechanical Updates in ANSYS 2019 R1
Wednesday, March 13th – 11:00 am – 12:00 pm MST AZ

From designers and occasional users looking for quick, easy, and accurate results, to experts looking to model complex materials, large assemblies, and nonlinear behavior, ANSYS Mechanical enables engineers of all levels to get answers fast and with confidence. With applications for everything form strength analysis to topology optimization, it’s no wonder this comprehensive suite of tools continues to serve as the flagship mechanical engineering software solution.

Join PADT’s Simulation Support Manager, Ted Harris for a look at what new capabilities are available for ANSYS Mechanical, in the latest version; 2019 R1.

Register Here


High Frequency Electromagnetics Updates in ANSYS 2019 R1
Wednesday, April 10th – 11:00 am – 12:00 pm MST AZ

In today’s world of high performance electronics and advanced electrification systems, the effects of electromagnetic fields on circuits and systems cannot be ignored. ANSYS software can uniquely simulate electromagnetic performance across component, circuit and system design, evaluating temperature, vibration and other critical mechanical effects.

Join PADT’s Electrical Engineer, Michael Griesi for a look at what new capabilities are available with regards to High Frequency Electromagnetics, in the latest version of ANSYS; 2019 R1

Register Here


Discovery Updates in ANSYS 2019 R1
Wednesday, May 8th – 11:00 am – 12:00 pm MST AZ

The ANSYS 3D Design family of products enables CAD modeling and simulation for all design engineers. Since the demands on today’s design engineer to build optimized, lighter and smarter products are greater than ever, using the appropriate design tools is more important than ever.

Join PADT’s Simulation Support Manager, Ted Harris for a look at what exciting new features are available for design engineers in both Discovery Live and AIM, in ANSYS 2019 R1.

Register Here


If this is your first time registering for one of our Bright Talk webinars, simply click the link and fill out the attached form. We promise that the information you provide will only be shared with those promoting the event (PADT).

You will only have to do this once! For all future webinars, you can simply click the link, add the reminder to your calendar and you’re good to go!


Discussing Tools for AM with Softwareconnect.com

With the substantial growth of more advanced manufacturing technologies over the past decade, the engineering world has seen additive manufacturing lead the way towards the future of innovation.


While the process of additive manufacturing, has proven to yield valuable results that can drastically reduce lead time and overall cost, without an effective design and an in-depth understanding of the process behind it end users of the tool will struggle to achieve the high-quality results they initially envisioned.

PADT’s Principle and Co-Owner Eric Miller sat down with David Budiac of Software Connect to discuss the use of software when it comes to Additive Manufacturing, including integrating MES & QMS into your process, specific steps for ensuring success with AM software.

Check out the blog post featuring notes from their discussion here.

You can also view a recording of PADT’s webinar discussing design for Additive Manufacturing below:

 

Explore the Latest Advancements in Design Engineering with ANSYS 19.2 – Webinar

Don’t miss this informative presentation – Secure your spot today!

If this is your first time registering for one of our Bright Talk webinars, simply click the link and fill out the attached form. We promise that the information you provide will only be shared with those promoting the event (PADT).

You will only have to do this once! For all future webinars, you can simply click the link, add the reminder to your calendar and you’re good to go!

Don’t compromise your composite tooling design – Streamline your Sacrificial tooling with FDM

FDM Sacrificial Tooling: Using Additive Manufacturing for Sacrificial Composite Tool Production

Additive manufacturing has seen an explosion of material options in recent years. With these new material options comes significant improvements in mechanical properties and the potential for new applications that extend well beyond prototyping; one such application being sacrificial tooling.

Traditional composite manufacturing techniques work well to produce basic shapes with constant cross sections. However, complex composite parts with hollow interiors present unique manufacturing challenges. However, with FDM sacrificial tooling, no design compromise is necessary.

Download the white paper to discover how FDM sacrificial tooling can dramatically streamline the production process for complicated composite parts with hollow interiors.

This document includes insight into:

  • Building for optimal results
  • Consolidating composites
  • Finding application best fits

Best practices for composite tooling with additive manufacturing

Additively Manufactured: Best Practices for Composite Tooling with 3D Printing

The advanced composites industry has a continual need for innovative tooling solutions. Conventional tooling is typically heavy, costly and time-consuming to produce. New applications, product improvements and the demand for faster, lower-cost tool creation challenge composite product manufacturers to innovate and remain competitive.

The use of additive manufacturing (or “3D printing”), and specifically FDM, for composite tooling has demonstrated considerable cost and lead time reductions while providing numerous other advantages such as immense design freedom and rapid iteration, nearly regardless of part complexity.

Download the white paper to learn more about the various advantages and capabilities of composite tooling with additive over traditional manufacturing methods, and discover the best practices for ensuring that your composite tooling process is efficient as possible.

This document includes best practices for:

  • Testing and characterization
  • Tool Design, Production, & Use
  • Analyzing results

Getting to Know PADT: Medical Device Product Development

 This post is the thirteenth installment in our review of all the different products and services PADT offers our customers. As we add more, they will be available here.  As always, if you have any questions don’t hesitate to reach out to info@padtinc.com or give us a call at 1-800-293-PADT.

The development of medical devices is difficult.  The regulatory challenges, quality requirements,  and technical hurdles of dealing with the complex system that is the human body make the processes required to bring products for this industry to market unique and difficult. That is why PADT has a team in our Engineering Services department that is focused on one thing: Medical Device Development.

If you read our article on Product Development Services or watched the flashy video then you know how we do product development differently.  That our processes and staff are proven, that we are all about solving problems and using project management intelligently, all geared towards to deliver a complete solution.  Every one of those characteristis is true for our Medical Device team as well, we just add more on top to give our customers the confidence to work with us on their product development.

We sometimes get involved in projects all the way from defining specifications to coordinating with manufacturing. We also provide assistance at every step along the way: testing, concept modeling, trade studies, material evaluations, quality consulting, design for manufacturing, and testing to name just a few areas that we can help.  That is one of the things that makes PADT unique in this particular industries. Most companies will only do the full product development, whereas we serve as an outside resource for the whole thing, or only where our customers need additional help.

Solving the Tough Problems

There are a lot of medical device design companies out there.   We often get asked how we can stay busy in this industry, especially when we are not located in a hot-bed of device design and manufacturing like California, Boston, or Minneapolis.   The answer is simple.  Customers from those locations and other markets come to Tempe to work with us because we are good at solving the difficult problems.  Most of this capability comes from the skill and experience of our staff.  They know their stuff and they know how to systematically investigate and solve the most difficult problems.  They also have access to advanced tools like 3D Printing and world-class simulation in-house. Combine this with solid project management and a well-provisioned lab, and you have a winning combination.

Understanding Medical Devices

The other key requirement for anyone doing medical device product development is a thorough understanding of Medical Devices themselves. Every industry has its buzzwords and acronyms, but medical devices are in a category all their own. They are a bridge between the world of mechanical engineering and medicine, so they terminology and operating environment are different then say aerospace devices or consumer products.  To work on medical devices you have to understand all the physics, manufacturing, software, and electronics that every mechanical device needs. You also need to understand biology and treatment.  PADT’s staff walks that fine line between the two worlds and often serves as a translator between the end user (doctors and nurses) and engineering, even within our customer’s organizations.

Quality Centric

Quality is the most important, and least understood, unique aspect of Medical Device Product Development.  Any team attempting to bring a product to market who does not know ISO 13485 and the FDA requirements will fail.  We also know that Quality is a tool, not a barrier.  We understand the client’s quality system and adapt our processes as efficiently as possible to get value from the entire quality process.

Let us Engineer your Medical Device Innovations

Here is a powerpoint we put together last year with even more information:

Product development for medical devices is something we are just plain good at.  Large corporations and startups come to PADT to because we get the job done.  You can see some great case studies here that tell the story in the words of our customers.  Reach out to us via email (info@padtinc.com) or give us a call at 480.813.4884 and we can talk about how our team can help engineer your medical device innovation.

PADT-Medical-Overview-Portfolio-2018_02_13-1

What’s New & Exciting in Mechanical Simulation – Webinar

Don’t miss this informative presentation – Secure your spot today!
Register Here

If this is your first time registering for one of our Bright Talk webinars, simply click the link and fill out the attached form. We promise that the information you provide will only be shared with those promoting the event (PADT).

You will only have to do this once! For all future webinars, you can simply click the link, add the reminder to your calendar and you’re good to go!

All Things ANSYS 013 – Lessons in simulation learned from Anaheim’s Pacific Design & Manufacturing Show

 

Published on: February 12, 2018
With: Joe Woodword, Tom Chadwick, Ted Harris, Eric Miller
Description: In this episode your host and Co-Founder of PADT, Eric Miller is joined by PADT’s Joe Woodword, Tom Chadwick, and Ted Harris, for a discussion on what they learned about the world of simulation by attending this year’s Pacific Design & Manufacturing show, North America’s largest Advanced Design and Manufacturing event. This talk includes tips for a variety of ANSYS tools, along with some general “how-to” points regarding overall process that will help to ensure your simulation runs smoothly.
Listen:
Subscribe:

 

Getting to Know PADT: Product Development Services

This post is the ninth installment in our review of all the different products and services PADT offers our customers. As we add more, they will be available here.  As always, if you have any questions don’t hesitate to reach out to info@padtinc.com or give us a call at 1-800-293-PADT.

The “D” in PADT stands for design.  It has been an integral part of PADT’s service offering since the company was started. Design, or more broadly Product Development, is the engineer process of defining, designing, testing, prototyping and transferring the manufacturing of a product.  From concept to manufacturing, or any point in between, PADT’s engineers can help with product development.

Doing product development with PADT is about defining product requirements and then stepping the team through a proven process that iterates efficiently and results in working hardware that has been tested and verified. This approach works across industries.  We have worked on products for golfing, designed the insides of an electric vehicle fast charger, designed and built an alpha-machine for semiconductor manufacturing, reconfigured the configuration of an avionics device, developed several medical devices through clinical trials, and tested the fittings on an artificial heart.

We specialize in working with companies that have an engineering staff, but don’t have the specialization or capacity need to complete a project entirely in-house.  Our engineers become part of the customer’s team and can work on specific tasks, a subsystem of the product, or complete the entire process.  Regardless of the scope, it comes down to our providing our customers with experienced and capable engineers that can plug in where they are needed.

There are four characteristics that set PADT apart from other design houses that help with product development:

Proven

We have been providing product development services since 1994.  As of this post being published, we have 30 engineers onstaff and we have helped over 400 customers with their product development needs.  Many of those customers choose to use PADT over and over again letting us design and test their products.

Problem Solvers

What sets PADT apart from most providers of design or product development is the fact that we are problem solvers.  Product development is primarily the process of identifying problems and finding solutions. And that is what our engineers excel at and thrive on.  We are brought in by customers because we can answer the tough questions.

Project Management

It does not matter how experienced your staff is, or how amazing your tools and equipment.  To be successful in product development you need to have a proven Project Management process.  PADT’s process has been developed over decades to provide a flexible methodology to ensure requirements are defined, that they are met on time.  It drives the entire process to achieve deliverables on-time and on-budget with minimal customer oversight.

Complete Solution

Project managers and design engineers work with simulation, test, software, and manufacturing engineers to address the needs of the complete product lifecycle.  Almost every capability that is needed is available within PADT’s walls, and a tested network of approved vendors fills in any missing needs.

One of the best ways to understand these difference is to watch our video on Product Development here:

You can also review some of our great case studies:

Satellite Messaging
Device
Electric Vehicle
Fast Charger

Tissue Expander

Smart Orthopedic
Sensor

Ultrasonic Skin
Treatment Device

Compact High Pressure
Hydrogen Pump

Or, check out our brochure:

If you are developing a product of any kind, then please contact PADT so we can explore where and how we can help with that process.  Our slogan is “We Make Innovation Work.” Join over 400 other companies who have trusted PADT to make their innovation work.

Leaving CAD Embedded Simulation Behind – Webinar

With simulation driven product design and development becoming the norm in the world of manufacturing, it has become increasingly relevant for companies to stay on the cutting edge in the search of the next best thing, in order to succeed in their respective industries.

Join PADT’s Co-Owner and Principal Engineer, Eric Miller for a live presentation on the benefits of ditching your current CAD-Embedded Software for state of the art ANSYS Simulation Solutions.

This webinar will dispel common misconceptions surrounding ANSYS Software, explain how to make the move away from CAD-Embedded tools, and present highly requested topics that ANSYS can provide solutions for, such as:

  • Understanding fluid flow: accurate and fast CFD
  • Real parts that exist in assemblies
  • The importance of robust meshing
  • Advanced capabilities and faster solvers

Cellular Design Strategies in Nature: A Classification

What types of cellular designs do we find in nature?

Cellular structures are an important area of research in Additive Manufacturing (AM), including work we are doing here at PADT. As I described in a previous blog post, the research landscape can be broadly classified into four categories: application, design, modeling and manufacturing. In the context of design, most of the work today is primarily driven by software that represent complex cellular structures efficiently as well as analysis tools that enable optimization of these structures in response to environmental conditions and some desired objective. In most of these software, the designer is given a choice of selecting a specific unit cell to construct the entity being designed. However, it is not always apparent what the best unit cell choice is, and this is where I think a biomimetic approach can add much value. As with most biomimetic approaches, the first step is to frame a question and observe nature as a student. And the first question I asked is the one described at the start of this post: what types of cellular designs do we find in the natural world around us? In this post, I summarize my findings.

Design Strategies

In a previous post, I classified cellular structures into 4 categories. However, this only addressed “volumetric” structures where the objective of the cellular structure is to fill three-dimensional space. Since then, I have decided to frame things a bit differently based on my studies of cellular structures in nature and the mechanics around these structures. First is the need to allow for the discretization of surfaces as well: nature does this often (animal armor or the wings of a dragonfly, for example). Secondly, a simple but important distinction from a modeling standpoint is whether the cellular structure in question uses beam- or shell-type elements in its construction (or a combination of the two). This has led me to expand my 4 categories into 6, which I now present in Figure 1 below.

Figure 1. Classification of cellular structures in nature: Volumetric – Beam: Honeycomb in bee construction (Richard Bartz, Munich Makro Freak & Beemaster Hubert Seibring), Lattice structure in the Venus flower basket sea sponge (Neon); Volumetric – Shell: Foam structure in douglas fir wood (U.S. National Archives and Records Administration), Periodic Surface similar to what is seen in sea urchin skeletal plates (Anders Sandberg); Surface: Tessellation on glypotodon shell (Author’s image), Scales on a pangolin (Red Rocket Photography for The Children’s Museum of Indianapolis)

Setting aside the “why” of these structures for a future post, here I wish to only present these 6 strategies from a structural design standpoint.

  1. Volumetric – Beam: These are cellular structures that fill space predominantly with beam-like elements. Two sub-categories may be further defined:
    • Honeycomb: Honeycombs are prismatic, 2-dimensional cellular designs extruded in the 3rd dimension, like the well-known hexagonal honeycomb shown in Fig 1. All cross-sections through the 3rd dimension are thus identical. Though the hexagonal honeycomb is most well known, the term applies to all designs that have this prismatic property, including square and triangular honeycombs.
    • Lattice and Open Cell Foam: Freeing up the prismatic requirement on the honeycomb brings us to a fully 3-dimensional lattice or open-cell foam. Lattice designs tend to embody higher stiffness levels while open cell foams enable energy absorption, which is why these may be further separated, as I have argued before. Nature tends to employ both strategies at different levels. One example of a predominantly lattice based strategy is the Venus flower basket sea sponge shown in Fig 1, trabecular bone is another example.
  2. Volumetric – Shell:
    • Closed Cell Foam: Closed cell foams are open-cell foams with enclosed cells. This typically involves a membrane like structure that may be of varying thickness from the strut-like structures. Plant sections often reveal a closed cell foam, such as the douglas fir wood structure shown in Fig 1.
    • Periodic Surface: Periodic surfaces are fascinating mathematical structures that often have multiple orders of symmetry similar to crystalline groups (but on a macro-scale) that make them strong candidates for design of stiff engineering structures and for packing high surface areas in a given volume while promoting flow or exchange. In nature, these are less commonly observed, but seen for example in sea urchin skeletal plates.
  3. Surface:
    • Tessellation: Tessellation describes covering a surface with non-overlapping cells (as we do with tiles on a floor). Examples of tessellation in nature include the armored shells of several animals including the extinct glyptodon shown in Fig 1 and the pineapple and turtle shell shown in Fig 2 below.
    • Overlapping Surface: Overlapping surfaces are a variation on tessellation where the cells are allowed to overlap (as we do with tiles on a roof). The most obvious example of this in nature is scales – including those of the pangolin shown in Fig 1.

Figure 2. Tessellation design strategies on a pineapple and the map Turtle shell [Scans conducted at PADT by Ademola Falade]

What about Function then?

This separation into 6 categories is driven from a designer’s and an analyst’s perspective – designers tend to think in volumes and surfaces and the analyst investigates how these are modeled (beam- and shell-elements are at the first level of classification used here). However, this is not sufficient since it ignores the function of the cellular design, which both designer and analyst need to also consider. In the case of tessellation on the skin of an alligator for example as shown in Fig 3, was it selected for protection, easy of motion or for controlling temperature and fluid loss?

Figure 3. Varied tessellation on an alligator conceals a range of possible functions (CCO public domain)

In a future post, I will attempt to develop an approach to classifying cellular structures that derives not from its structure or mechanics as I have here, but from its function, with the ultimate goal of attempting to reconcile the two approaches. This is not a trivial undertaking since it involves de-confounding multiple functional requirements, accounting for growth (nature’s “design for manufacturing”) and unwrapping what is often termed as “evolutionary baggage,” where the optimum solution may have been sidestepped by natural selection in favor of other, more pressing needs. Despite these challenges, I believe some first-order themes can be discerned that can in turn be of use to the designer in selecting a particular design strategy for a specific application.

References

This is by no means the first attempt at a classification of cellular structures in nature and while the specific 6 part separation proposed in this post was developed by me, it combines ideas from a lot of previous work, and three of the best that I strongly recommend as further reading on this subject are listed below.

  1. Gibson, Ashby, Harley (2010), Cellular Materials in Nature and Medicine, Cambridge University Press; 1st edition
  2. Naleway, Porter, McKittrick, Meyers (2015), Structural Design Elements in Biological Materials: Application to Bioinspiration. Advanced Materials, 27(37), 5455-5476
  3. Pearce (1980), Structure in Nature is a Strategy for Design, The MIT Press; Reprint edition

As always, I welcome all inputs and comments – if you have an example that does not fit into any of the 6 categories mentioned above, please let me know by messaging me on LinkedIn and I shall include it in the discussion with due credit. Thanks!