Simulate, test, and manage with confidence
Many types of software programs are accommodated under the EMC umbrella. One large category is precompliance/compliance test automation software such as EMC32 from Rohde & Schwarz, emcware from AR RF/Microwave Instrumentation, NEXIO’s BAT-EMC, and TILE! from ETS-Lindgren. To be accepted as a solutions provider, a company must offer viable test systems. Often, a customer has one or more constituent parts, so this type of software generally accommodates instrument idiosyncrasies within the instrument driver—the routine that adapts the general-purpose software to the specific instrument. As new test equipment is produced, corresponding drivers are provided for the software programs.
ETS’ TILE! program is an acronym for Totally Integrated Lab Environment and has added several incremental improvements during the last year. I attended the company’s TUG meeting during the 2014 EMC Symposium at which these changes were discussed along with a range of user problems and questions.
The TILE! profile is the file that actually sets up the test. You create one—generally by starting with something similar that already exists—by dragging and dropping successive actions/icons. The program’s virtual instrumentation facility allows you to develop and troubleshoot profiles without needing to have all the actual instruments. TILE!’s test executive runs the chosen profiles with the necessary parameters so a technician with little actual TILE! understanding can run tests.
There was some discussion about dividing the present profiles into a list of actions and a separate list of relevant instruments rather than continuing to embed the instruments within the profile. This would allow a “universal” list of instruments to be compiled that the profiles simply referenced. Although the idea sounded good, one attendee said he ran several instances of the same test in parallel, sometimes with different but equivalent instruments. He used VISA commands within each profile to allow drilling down to individual instruments. The change was a proposal and clearly needs some more thought before implementation.
In common with several other software programs I encountered at the symposium, video has been included in TILE! to monitor EUT behavior that may not be associated with an easily measured signal. For example, in automotive dashboard testing, a video camera could determine that an immunity test had caused a direction indicator to begin blinking. This capability also provides galvanic isolation.
Overall, about 50 people attended the TUG meeting. The message was that TILE! is “connected, flexible, faster, and powerful; had more drivers and networking; and offered more training.” Each of these topics was discussed in detail.
AR RF/Microwave Instrumentation’s emcware EMC software suite features an equipment management function that requires you to only enter instrument details once. That instrument subsequently can be accessed from any of the modules. In addition, the equipment manager keeps track of calibration dates.
emcware is a comprehensive solution that supports radiated and conducted emissions testing to CISPR standards, radiated and conducted emissions and susceptibility testing to MIL-STD-461 and RTCA DO-160, and testing to several automotive, telecomm, and IEC standards.
AR specializes in amplifiers, so it’s not surprising that emcware drivers exist for a large number of AR amplifiers and few amplifiers from other vendors. This is not the case for other instruments and accessories that AR either does not manufacture or only has a couple of models, such as signal generators. There are at least 50 generators listed for other manufacturers and only two from AR.
Similarly, the mix of supported equipment listed in the R&S EMC32 software datasheet indicates those kinds of instruments and accessories that R&S provides. Test receivers, spectrum analyzers, signal generators, and power meters are almost all R&S models. Lists of other equipment, such as antenna masts and turntables, field sensors, and amplifiers may include R&S units where they exist but also reference ETS, Agilent Technologies (now Keysight Technologies), and AR products. A large number of options extend the basic EMC32 emission/immunity test capabilities to include automotive and MIL standards, reverberation chamber tests, and 3-D result evaluation.
According to NEXIO literature, this company is the French leader in the market for automated EMC test. NEXIO’s BAT-EMC all-in-one EMC test software comprises six parts: four fairly specialized modules and separate emissions and susceptibility sections. In this regard, it is similar to the R&S EMC32—emissions and immunity modules can be bought separately.
Olivier Roffe, head of the company’s test and measurement department, said that NEXIO was focused totally on the control and measurement software product. This made them distinct from their competitors, which often gave preference to supporting their own products. Like TILE! and EMC32, video can be integrated into the test setup.
Another large category is simulation software including FEKO’s cable harness radiation solutions and Keysight Technologies’ EEsof EDA EMPro 3-D simulation and modeling software. Because the physical chassis/board/cable characteristics greatly influence EMC, many simulation programs allow you to import CAD files so you don’t have to describe the structure twice. On the other hand, a CAD file has all the required detail to build the part, and much of that detail may not be relevant to the EMC performance. Some programs provide a way to simplify the imported data to minimize simulation time.
EMCoS’ EMC Studio v8.0 offers geometry healing and cleaning. Healing refers to the process of rationalizing points within a design. For example, an excessive number of points could be used to define an arc. One of the healing actions is to eliminate the unnecessary points. Similarly, points close to intersecting with other design elements could be moved to intersect. Cleaning simplifies an imported CAD design by removing aspects that don’t materially affect the EMC performance.
Although EMC Studio v8.0 is a general-purpose tool, it includes special capabilities to deal with many automotive applications such as smart entry systems, rear-window antennas and the connections to them, and high-power shielded cables as found in hybrid and all-electric vehicles.
Typically, the 3-D model of a physical structure such as a car or PCB would be represented by a tetrahedral mesh (Figure 1). The finer the mesh, the greater the computing load and the longer the simulation will take to run. Keysight’s EMPro brochure states that the finite element method (FEM) is a frequency-domain approach best suited to electrically small problems. In contrast, the finite difference time-domain (FDTD) method, also supported in EMPro, updates the field values within rectangular and conformal curved cells while stepping through time. FDTD is good for broadband applications and uses less memory than FEM for electrically large problems. For FDTD solutions, a fixed-point meshing feature automatically aligns the mesh with object boundaries.
|Figure 1. Section of PCB assembly meshed for FEM analysis
Courtesy of Keysight Technologies
ANDRO Computational Solutions has developed E3 Expert software, a U.S. Air Force and Navy-funded program. According to company literature, the software provides…“the electromagnetic environment effects engineer a new type of user-friendly capability to perform interactive electromagnetic interference/compatibility computer modeling, simulation, and analysis of large, complex systems.” The brochure lists cosite analysis as a major application of E3 Expert—determining how best to have all the emitters on an airplane coexist without interfering with each other.
Computer Simulation Technology’s (CST’s) STUDIO SUITE features a co-simulation capability that couples 3-D EM field simulation and SPICE equivalent network calculation. This approach makes it possible, for example, to investigate the interaction between a complex cable harness and 3-D EM fields without having to mesh the whole problem space.
EMC/EMI is one of several modules within STUDIO SUITE and includes emissions, susceptibility, and E3 subsections. An automotive article on the company’s website provides a good example of how several STUDIO SUITE capabilities can work together. CST BOARDCHECK applies a rule-checker to PCB designs, the rules being chosen by the PCB designer. Violations automatically are flagged. This kind of tool helps find more obvious problems.
Simulating the PCB allows virtual test signals to be injected and the signal flow monitored under various conditions. Simulation also can provide S-parameters, eye diagrams, and impedance profiles, all without building any hardware. Power integrity has become critical in many designs that support very fast signals, and in addition to circuit simulation, EM field simulation also is needed to thoroughly characterize these PCB designs. With a 3-D EM simulation, interference arising from other signals within the car can be applied to the PCB design to investigate susceptibility problems. Of course, emissions from the PCB itself also can be estimated.1
CST’s MICROWAVE STUDIO is one of the modules within the STUDIO SUITE. MICROWAVE STUDIO, in turn, comprises several sections: the front end, a transient solver, a time-domain transmission-line solver, a frequency-domain solver, an Eigenmode solver, an integral equation solver, a multilayer solver, and an asymptotic solver.
FEKO from EM Software and Systems, now part of Altair, also features several types of solvers to deal with a range of applications. The June 2014 Altair-EMSS purchase announcement helps to clarify how the newly combined capabilities might be deployed. “Typical applications of FEKO include antenna design, antenna placement, electromagnetic compatibility analysis, bioelectromagnetics, radio frequency components, three-dimensional electromagnetic circuits, design and analysis of radomes, and radar cross-section analysis. Altair HyperWorks contains a number of… solvers, including Opti-Struct, RADIOSS, MotionSolve, and AcuSolve. The addition of FEKO will help to address coupled electromagnetic-thermal and electromagnetic-mechanical problems, among others.”
Like ANDRO, DELCROSS Technologies also analyzes cosite problems, but through the company’s EMIT simulation software (Figure 2). The EMIT library contains information about the various types of radios used in both military and commercial applications. However, even for radios for which you have little information, EMIT’s multifidelity parametric models support meaningful simulation. As described in DELCROSS literature, “When CST STUDIO SUITE is used to simulate antenna isolation, EMIT provides a direct link that will automatically create an EMIT project using the CST STUDIO model. Only the radios need to be specified in EMIT to perform the full cosite simulation.”
|Figure 2. Drone 3-D RF cosite and coexistence simulation
Courtesy of DELCROSS Technologies
In addition, DELCROSS provides the Signa radar signature analysis software for electrically large and complex targets. The company has developed the shooting and bouncing ray asymptotic technique to predict a target’s radar signature.
ANSYS offers several applications used for EMC simulation. The HFSS program includes an automated adaptive meshing technique that, as described in the company’s brochure, “generates the most appropriate, efficient, and accurate mesh for the simulation.” SIwave is a separate signal and power integrity application specifically for PCB, package, and IC design. Like HFSS, it creates a thorough 3-D simulation.
The ANSYS Workbench platform provides a central user interface to facilitate multiphysics simulations. For example, HFSS results can be used as inputs to thermal- and fluid-based problems. HFSS develops full-wave SPICE models that can be used in tools such as Ansoft Designer for signal integrity investigations. In EMC simulation, the choice of the most appropriate solver type is important. HFSS includes multiple solvers based on FEM.
The integral equation solver is optionally available and complements the FEM solvers by improving far-field accuracy or reducing the overall size of the FEM domain. A transient solver based on the discontinuous Galerkin time-domain method supports TDR simulations and uses the same automated meshing technique as HFSS. For very large EM structures, a physical optics solver is appropriate for reflector antennas, satellites, or antenna platforms.
For these very large designs, the FEM mesh can be partitioned through domain decomposition and each section solved on a separate machine. Similarly, a broadband frequency sweep can be partitioned into frequency bands that are each addressed by a separate computer. This idea can be extended to user-defined design parameters allocated among separate computers to develop a distributed solution. These capabilities reduce the total simulation time and include the means to reassemble the separate solutions into a single result.
Christian Orta, vice president of product and marketing at OnRule, gave me a thorough demo of the software package. According to the company’s website, “OnRule is a cloud-based platform…to help organizations exercise better control and increase visibility over their product regulatory compliance.”
Various dashboards allow you to determine, for example, what standards a new product must meet to be sold into South Africa and Canada. You need to describe the type of product under consideration and select the countries in which you hope to sell it. The program provides the list of required standards. Once a project is underway, the approval status is logged, and automatic alerts are provided if any certificates are about to expire. For an organization with many products at various stages in their life cycles, the various reports the program generates, as noted on the company’s website, “provide accurate and timely visibility to relevant stakeholders.”
OnRule seems to fill a need that design- and test-oriented EMC software does not. In this sense, the features in OnRule are more like those you might find in construction planning that also helps organizations comply with a range of standards. More general-purpose project planning programs also may have a certification element.
Hardware and Software Systems
EMSCAN is a Canadian company with a range of real-time distributed EMC field sensors. In this case, distributed applies to an array of sensors located a few centimeters below a nonmetallic work surface. When a powered-up PCB or small piece of equipment is put on the surface, the sensor array is sampled and very-near-field measurements made.
As described in EMSCAN literature, “EMxpert consists of a patented scanner and compact adaptor and a customer-supplied spectrum analyzer and PC running EMxpert software. The benchtop scanner combines … 1,218 H-field (magnetic) probes spaced every 7.5 mm into an electronically switched array, which provides an effective 3.75-mm resolution. The system operates from 50 kHz to 4 GHz, enabled with optional software keys.”
Erkan Ickam, director of EMSCAN marketing, explained that several models of the scanner and software are available. RFX2 offers a 32 x 32 cm scan area for antenna testing. The accompanying software calculates far-field patterns, bisections, EIRP, and TRP. EHX features a 32 x 22 cm scan area and operates from 150 kHz to 4 GHz, optionally 8 GHz. EHX+ is similar but includes a 100-MHz bandwidth spectrum analyzer. ERX+ adds motion to the scanner to effectively increase the spatial resolution. You can choose among seven levels of resolution from 7.5 mm to 120 microns.
NEXIO also developed a 3-D near-field scanner, the BAT-SCANNER, which is a reasonably large three-axis mechanical scanner that positions a single probe relative to the DUT. By scanning a volume up to 400 x 400 x 200 mm, the probe and associated software can map the DUT fields. Although a particular scanner is shown in the company’s literature, 10 drivers are available to adapt the BAT-SCAN software to a robotic system.
There certainly is no shortage of EMC software. However, especially for simulation applications, the match between the simulation software capabilities and the problem being investigated is key. The correct choice of solver and meshing scheme is necessary to optimize both the solution accuracy and run time.
Sjiariel, R., “Analyze Automotive PCB Layouts Efficiently with Simulation,” Extension Media, November 2013.