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Articles & White Papers

White Papers from our highly respected engineers who are considered experts in their field.

  • Designing an Efficient and Effective iMRI Facility - July 2014
    Intra-Operative MRI (iMRI) is quickly becoming the go to technology in the ever evolving integration of various radiologic modalities for invasive and non-invasive patient procedures and treatments. Intra-Operative MRI is defined by the use of an MRI magnet during a surgical or treatment procedure. This can be achieved with a moving magnet that is brought into the theatre or by moving the patient to the room containing the magnet. In both cases, imaging is performed prior to, during and after the surgical or treatment procedure. The real time availability of the high resolution MR images is improving patient outcomes in a widening arena including, but not limited to, neurosurgery, cardiovascular and radiation oncology. This article will provide an overview of current iMRI technology and review design, location, safety and performance considerations to ensure an optimally functioning iMRI facility. Following a successful installation, maintenance guidelines are provided to protect your iMRI investment for years to come of optimal imaging and patient care.

  • Reverberation Chambers for Wireless Applications - May 2014
    Owing to the beauty of its statistical behavior, reverberation chambers can be utilized as a measurement environment[1]. In a metallic cavity, numerous resonance modes can be excited. Each mode is induced by standing waves of the electrical fields that resonate with crests and troughs residing spatially. Such field variation due to resonance is seemingly contrary to the concept to establish a constant field with which the measurement can be repeated accurately inside the test volume. Repeatability is the key to the construction of a feasible measurement system. Although each individual resonance mode shows field deviation, the averaged field over sufficient modes can statistically achieve certain field uniformity that the measurement is then repeatable.

  • Real-time,high-tech healthcare. Strategies for designing an efficient intra-operative magnetic resonance imaging space - May 2014
    Intra-operative magnetic resonance imaging is quickly becoming the leading technology in the integration of various radiologic modalities for medical procedures. iMRI refers to the use of an MRI magnet during a surgical or treatment procedure — either a moving magnet brought into the theater or by moving the patient to the room containing the magnet. In both cases, imaging of precise locations is performed prior to, during and after the surgical or treatment procedure.

  • MIMO Wireless Terminals OTA Performance Test Based on Boundary Array Methodology - May 2014
    MIMO antenna technology is commonly used in high speed wireless communication (LTE, WIFI, WIMAX) as well as in high performance radar (MIMO radar). There are more and more wireless terminals with MIMO antenna around the current market. However, there are no current standardized measurement methodologies to evaluate the new technology. The main international standardization organizations, including 3GPP, CTIA and the national organization of China (CCSA), are working to standardize the test methodology. Part of the difficulty in completing a standard of the test method is due to the fact that channel models of multi-path environments complicate the test system to a large degree. Such complexity can be taken into account by the methodology based on boundary array OTA method that makes it a very important evaluation candidate for MIMO OTA performance test. The paper presents a real MIMO OTA test system. After the introduction of boundary array concept, the system calibration is described, including input and output calibration of the entire system. Subsequently, the system validation is examined from several aspects, such as power validation, filed mapping, temporal correlation and so on. Finally, the measurement results of an actual wireless product, with three different antennas, are provided to further elaborate the test methodology. At the end, the current status of the MIMO OTA test methodology standardization is provided to conclude the paper.

  • EMC Test Laboratory Sofware Program Development: A Proven Process - October 2013
    Asymmetric filter designs are gaining popularity in industry because of their lower cost and size, however, although this design is successful in eliminating common mode signal issues this paper will show that for certain applications such as TEMPEST these filters offer little to no protection. Symmetric filters, although physically larger and more costly due to the use of more components, provide better filtering in these applications.

  • Facility Power Filters: Symmetric vs. Asymmetric Performance - September 2013
    Asymmetric filter designs are gaining popularity in industry because of their lower cost and size, however, although this design is successful in eliminating common mode signal issues this paper will show that for certain applications such as TEMPEST these filters offer little to no protection. Symmetric filters, although physically larger and more costly due to the use of more components, provide better filtering in these applications.

  • High Performance 10-meter EMC Chamber Design - August 2013
    In recent years, the need for a large, high performance EMC chamber is more and more pressing due to the increased likelihood of spectrum contaminates to the open area test site (OATS) environment. A high performance 10-meter EMC chamber with a 2 dB NSA design is discussed in this paper.

  • Mitigation of EMP Effects (pages 1-4) & HEMP Protection of ESA/Filters (page 5) - April 2012
    Mitigation of EMP Effects & HEMP Protection of ESA/Filters Electromagnetic pulse (EMP) protection requires absolute performance and reliability of a shielding system to assure the survival of sensitive data, equipment and systems in an environment threatened by both high altitude electromagnetic pulse (HEMP) and intentional electromagnetic interference (IEMI). A critical component of a shielding system is the specialty filters required to allow protected points of entry (POE) of electrical power, computer networking, control and communication lines penetrating the shield. Electrical surge arrestors (ESA) provide added protection.

  • Automating EMC Testing (or what did we do with all the time we saved?) - August 2011
    I was introduced to commercial electromagnetic interference (EMI) testing in 1984. While working at Intergraph Corp. in Huntsville, Alabama, I got to work in the coolest looking building in town. It was an oversized pool cover that we called ‘The Bubble’. The bubble building was on a hillside that allowed the Open Area Test Site (OATS) ground plane to be a bit above the surrounding terrain, free of conductive building materials and large enough for a 10 meter ellipse, though we primarily used it for 3 meter testing.

  • Practical Considerations for Radiated Immunities Measurement using ETS-Lindgren EMC Probes - May 2011
    For radiated immunities applications from 10 MHz - 40 GHz, especially in an open air environment, it is recommended to select HI-6053/6153 probes. These probes provide the best isotropic response in this frequency range (provided with probe electronics positioned away from the incident field). The dynamic range is 2 V/m – 800 V/m, with an option for 1200 V/m.

  • On the Radiation Patterns of Common EMC Antennas - May 2011
    Antennas have been used in EMC measurements since the early days. Knowledge of the antenna pattern was not a requirement of the standards. While MIL STD 461 and some SAE standards called for information on the half power beamwidth, most standards did not require any knowledge of the antenna radiation characteristics. With the evolution of standards to cover frequencies above 1 GHz knowledge of the pattern has become more important. Since above 1 GHz most antennas are very directive and very un-dipole-like, information on the pattern has become very important, especially when it comes to understanding how much area the main beam is covering. The present paper starts by giving the reader a refresher on antenna pattern parameters and then shows typical patterns for the most common antennas used in EMC. The antennas covered are biconicals, log periodic dipole arrays, hybrid antennas and dual ridge horns. Measured data is presented except for patterns above 18 GHz.

  • Automotive Component EMC Testing: CISPR 25, ISO 11452-2 and Equivalent Standards - April 2011
    Automotive Component EMC Testing: CISPR 25, ISO 11452-2 and Equivalent Standards

  • No Sleeping in Seattle (Part 2) - April 2011
    In this second installment of a two part article, we continue our review of the recent meeting of IECCISPR held in October 2010 in Seattle. In the first part of this article, we have described the current changes affecting the basic standard CISPR 16 and the activities of its experts within CISPR sub-committee (SC) A. We now take a look at the activities of the other CISPR sub-committees responsible for preparing the CISPR product standards. We also describe some of the projects shared by CISPR and IEC TC 77B (High Frequency Phenomena).

  • Confronting Challenges to Urban-Based MRI Facilities - March 2011
    MRI systems can be negatively impacted by electromagnetic interference generated by a variety of sources including moving metal, subways, electric buses, transformers, and electric lines. Typically, EMI sources will impact gradient echo sequences, functional MRI (fMRI), and spectroscopy. While OEMs and end-users will try to avoid situating in areas impacted by EMI, it can be very difficult to find “quiet” sites in densely populated urban areas.

  • No Sleeping in Seattle (Part 1) - February 2011
    A Recap of CISPR Projects from the 74th IEC General Meeting. October 2010 saw the 74th IEC General meeting in Seattle, Washington, USA. Within the IEC, its special committee CISPR (Comite International Special des Perturbations Radioelectriques –International Special Committee on Radio Interference) came together and this article reviews some of the key projects discussed at that meeting. The activities of IEC TC 77, a parallel committee to CISPR developing the IEC 61000 series and of equal importance, did not meet in Seattle and hence will not be discussed here except for the JTFs (Joint Task Forces) that exist in common with CISPR Subcommittee A, responsible for the basic standard CISPR 16, which will be the main focus of this first part of a two part article.

  • A Brief History of Horns - November 2010
    Unlike so many technologies in use today, horn antenna history actually started more than a hundred years ago. This short article introduces the reader to the history of horns from the early experiments of radio pioneers to the “horn boom” during the 1940s and 1950s. The article ends with the latest evolution of horn antennas.

  • Creating a Complex Multipath Environment Simulation in an Anechoic Chamber - August 2010
    Techniques for measuring over-the-air (OTA) performance of wireless devices with single antennas do not work as well for multiple antennas because they assume that the radiation pattern of the device is fixed such that the measured result is a snapshot of the device performance at any given instant in time.

  • Choosing the Right Chamber for Your Test Requirements - May 2010
    Developments within the standards community have led to new chamber validation procedures above 1 GHz and alternative test methods using FARs

  • Anechoic Chambers for Evaluating and Validating Telecommunication Equipment - April 2010
    In recent years, enforcement of test and measurement standards for both performance validation and product conformity testing have provided a level platform for certifying telecommunication equipment as well as other electronic equipment. Unlike previous decades where the majority of this testing was conducted on outdoor test sites, today indoor shielded anechoic chambers are the primary hosting environment to facilitate the vast majority of test requirements. In addition to the obvious benefits of independence to weather and ambient-free test conditions, the close proximity and reliable test environment provided by an anechoic chamber also greatly accelerates the R&D and certification period.

  • EMC Test Site Qualifications - January 2010
    Everyone in the EMC business is familiar wtih the traditional Normalized Site Attenuation test (NSA). However, in February of 2007 CISPR 16-1-4 was published complete with the new Site Voltage Standing Wave Ratio (SVSWR) test. At the time, the American National Standards Institute (ANSI) Accredited Standards Committee (ASC) C63® had developed a draft proposal fro C63.4 (Draft 1 - May 20, 2005) called the Time Domain Reflectivity (TDR) measurement. The critical question addressed by this article is which method - SVSWR or TDR - more accurately provides an assessment of the test site.

  • Site Planning for Medical Imaging Equipment - January 2010
    Designing space for medical imaging equipment can be quite complex and involved as there are many items that must be addressed in order to successfully develop a site. Good site planning must thoroughly evaluate both the impact of the imaging equipment on teh surroundings (environmental concerns) and the impact of the space itself on the performance of the imaging equipment and the personnel using the equipment (performance concerns).

  • Designing and Building a Low-Noise Hemi-Anechoic Chamber - October 2009
    Noise emission and noise control are common topics in the field of acoustics. Noise emission from devices needs to be measured to comply with noise standards and to develop quieter devices. To make these measurements, a quiet noise-controlled environment is required. A large convertible hemi-anechoic chamber was constructed at ETS-Lindgren's headquarters in Cedar Park, Texas for that purpose. The project was a noise control project unto itself with the goal to measure the noise produced by a wide variety of test specimens.

  • Update on CISPR Standards - August 2009
    The global recession has not prevented EMC standardization work from marching relentlessly forward. Work within CISPR is no exception and this year delegates and experts will meet in Lyon, France in September under the auspices of the current chairman Don Heirman (US) and secretary Steve Colclough (UK). For those of you new to EMC, CISPR is an international special committee on radio interference within the International Electrotechnical Commission (IEC).

  • New Acoustic Research Lab Open for Business - July 2009
    ETS-Lindgren has opened its new Acoustic Research Laboratory featuring state-ofthe- art chambers for acoustic test services. With a hemi-anechoic chamber, two reverberation chambers, impedance tubes and supporting acoustical test equipment and software, the laboratory now offers product noise emission testing and structural/ architectural acoustic testing.

  • A-GPS Over-The-Air Test Method: Business and Technology Implications - July 2009
    Once the complete EIS pattern is determined, the TIS, UHIS, and PIGS - all of which are isotropic sensitivity measurements - can be calculated.

  • Mitigation of EMP effects using shielded rooms and enclosures - June 2009
    The most cursory assessment of news and events around the globe during this first decade of the Twenty-First Century leads to the inescapable conclusion that we live in perilous times. Around the globe, political, ethnic, and religious strife results in violence. This paper does not discuss the capabilities or readiness of the United States military or that of its allies, nor does it focus on developing effective standards for first-responder communications both inside and outside challenging environments such as skyscrapers and tunnels.

  • An Overview of WiMAX Radiated Performance Test Requirements - December 2008
    At present, more than 500 companies representing all aspects of the WiMAX ecosystem have become members of the WiMAX Forum. The forum is an industry-led, not-for-profit association organized to certify and promote broadband wireless products based upon the harmonized IEEE 802.16/ ETSI HiperMAN standard. Member companies are service providers, regulators, equipment manufacturers, test equipment manufacturers, certification labs, and application service providers working together to ensure global adoption of a common platform for the delivery of broadband wireless services. There is a considerable emphasis on making sure that WiMAX technology provides an exceptional, out of the box user experience.

  • The Importance of Antenna Calibration - December 2008
    In the United States and many parts of the world, antennas are calibrated per the American National Standards Institute C63.5: American National Standard for Electromagnetic Compatibility— Radiated Emission Measurements in Electromagnetic Interference (EMI) Control—Calibration of Antennas (9 kHz – 40 GHz). A standard sets uniform methods, processes, and practices for the industry. Some standards may be mandatory while others are voluntary.

  • The State of Antenna Calibration Standards in the United States Using ANSI C63.5 - November 2008
    Methods for calibrating antennas have been around since antennas were first used. Over the years our understanding of antennas and their performance in their intended applications has continued to evolve. In this article we seek to discuss the past, present, and future state of our antenna calibration work in the Accredited Standards Committee C63® (ASC C63®), which has resulted in the publication of the American National Standard, C63.5 “Radiated Emission Measurements in Electromagnetic Interference (EMI) Control–Calibration of Antennas (9 kHz to 40 GHz).” This work is performed by experts in ASC C63® which maintains the currency of ANSI C63.5.

  • An Overview of WiMAX™ Radiated Performance Test Requirements and Related Test System Solutions - June 2008
    At present, more than 500 companies representing all aspects of the WiMAX™ ecosystem have become members of the WiMAX Forum®. The forum is an industry-led, not-for-profit organization organized to certify and promote broadband wireless products based upon the harmonized IEEE 802.16/ETSI HiperMan standard.

  • Electromagnetic Interference (EMI) and Structural Vibration Effects on MRI Site Construction and Installation Requirements - May 2008
    Electromagnetic interference (EMI) and structural vibrations can impact the diagnostic performance of imaging equipment. MRIs, for example, are susceptible to EMI and structural vibrations and these disturbances can impact the quality of clinical images or data collected for spectroscopy, functional MR, and other MR diagnostics.

  • Shielding for Intra-Operative MRI - May 2008
    Clinical-use MRI scanners have been around for more than 20 years. Periodically, new developments and applications in this technology increase demand for more innovative MRI scanners or MRI technology.

  • Business Decisions: Specifying the Modern Hearing Test Environment - April 2008
    Considerations in the purchase and set-up of a sound room
    The key factors in the successful selection of a sound room are:
    1) Determining your working space based upon application;
    2) Creating customer comfort through appearance upgrades; and
    3) Having realistic expectations of product noise reduction, cost, and performance.

  • Radiated Performance Testing of WiMAX Mobile Devices - March 2008
    Given the potential cost of higher network densities, wireless carriers need to be concerned about the RF performance of mobile devices on the network.

  • Determining Radiated Performance of Mobile WiMAX Devices - March 2008
    The past year has seen a flurry of activity related to bringing the next generation of broadband wireless technology, commonly referred to as Mobile WiMAX, to the market. Based on the IEEE 802.16e standard for local and metropolitan area networks, released in 2005, Mobile WiMAX promises wireless data connections of 10 to 15 megabits per second in a typical cellular radius, far exceeding the capabilities of today's 2.5-3G wireless networks.

  • Choosing the Right Chamber Depends on the Application - February 2008
    Anechoic chambers are used today for performing EMC measurements according to a variety of different published EMC standards. There are many different fields of application including...

  • Safety for the MRI Suite of the Future - September 2007
    This article discusses how imperative it is that magnet manufacturers and hospital or imaging personnel that come into contact with the magnets truly understand all the issues concerning MRI safety.

  • Shielding Issues for Medical Products - May 2007
    This article provides the reader with an overview of the basic principles of magnetic shielding for magnetic resonance (MRI) systems. It pre-supposes only a rudimentary understanding of magnetic shielding as it relates to MRI Systems, and will...

  • A Self-Contained Portable Antenna Measurement System - March 2007
    ETS-Lindgren pioneered the over-the-air(OTA) performance testing market, designing and building the first CTIA Authorized Test Lab (CATL) for mobile station over-the-air antenna performance testing. Since then, the company has designed and built test chambers that have performed tests at some of the largest and best-known manufacturers of mobile wireless products. ETS-Lindgren’s efficient and accurate test systems...

  • Hearing Aid Compatibility for Wireless Devices - January 2007
    The use of wireless devices for both personal and business use continues to rise exponentially in developed and now in many immerging countries. The U.S. government has taken a strong position that the hearing impaired should have access to the networks through digital wireless phones. The testing and enforcements of...

  • A Multi-Octave, Open Boundary, Quad-ridged Horn Antenna for Use in the S- to Ku-bands - March 2006
    This article introduces a new antenna design to be used in anechoic chambers as a source antenna for 3D pattern measurements. When measuring 3D patterns, the receiving antenna in the anechoic chamber must be able to sense the two orthogonal components of the field that exist in the far field. This can be accomplished by...

  • An Update ON SAR Standards And The Basic Requirements For SAR Assessment - April 2005
    For many years the general public has been concerned about the possible health effects of exposure to radio frequency (RF) radiation. High levels of RF fields are known to cause a variety of physical effects on the human body. With the dramatic increase in public use...

  • Making Better Electric Field Measurements - April 2005
    The subject of this article is the factors involved in selection and use of the electric field (E-field) probes typically found in the feedback loops of immunity test setups, and anywhere else field strength values need to be measured.

  • Anechoic Chambers, Past and Present - February 2005
    This article will review the historical development of absorber materials and anechoic chambers, which play an important role in the work of today's EMC test engineer. We will discuss early attempts to achieve correlation between Anechoic Chambers and Open Area Test Sites and trace the improvements made through the years that...

  • CTIA test requirements cover over-the-air performance - November 2004
    Phones destined for the US market must undergo stringent over-the-air performance tests. Martin Wiles explains the procedure, which could soon be adopted by Europe and Asia.

  • Magnetic Active Compensation System (MACS) for Electron Microscopy - December 2003
    Since the invention of the compound microscope by Zecharias Janssen in 1595, and its extensive use by Galileo in the early 1600s, the microscope has proved to be one of the most valuable research and information tools used by the scientific community. Yet, as researchers began to delve deeper, beyond the mere cellular structures of biological...

  • Tabletop Shielded Enclosures - April 2003
    The space-saving table-top family of shielded test enclosures has gained popularity in recent years, primarily because of the evolution of smaller electronic devices. Besides conserving space, these units cost less than the traditional, full-size walk-in shielded rooms and offer...

  • Antenna Pattern Measurement: Concepts and Techniques - January 2002
    The first article of this two-part series explores the basic concepts and techniques of antenna pattern measurement and evaluates the benefits and drawbacks of various measurement methods. The concepts relating to near-field and far-field pattern testing are discussed as well. The second article presents the theory and equations governing antenna properties and includes a complete description of a site calibration for pattern-measurement testing.

  • Spotlight on Anechoic Chambers - April 2001
    In the next few pages, this article will review the development of absorber materials and anechoic chambers to meet the needs of the EMC test engineer. It will discuss early attempts to achieve correlation between anechoic chambers and open area test sites and will trace the...

  • Site Validation Theory 101: Techniques and Methods - August 2000
    Understanding available techniques for site validation is critical to improving methods for achieving accurate and meaningful results. Much discussion about site validation methods has appeared in the EMC press lately, coinciding with a considerable amount of work being done by the ANSI committee to...

  • Comparing Ground Plane Coupling Effects for Bicon/Log Hybrid Antennas With or Without Capacitively Loaded Bowtie Elements - February 1999
    The bicon/log hybrid antenna was developed by the University of York in 1993. It gained great popularity since then because a single sweep of the antenna can cover the whole frequency range of 30 MHz to 1 GHz. The antenna was originally designed for emissions measurement, which could...

  • Understanding the measurement uncertainties of the bicon/log hybrid antenna - January 1999
    Measurement uncertainty associated with the bicon/log hybrid antenna for radiated emissions and site validation tests relate to many factors, including height dependency, polarization and loading.

  • EMC Antenna Parameters and Their Relationships - June 1997
    The basics of the EMC profession often get buried under the day-to-day effort of continuous measurement and the volume of test and reporting paperwork. The fundamental parameter of the most common of technical tools, the EMC antenna, is used...

  • Field Homogeneity in Different TEM Waveguides - January 1996
    The testing of electromagnetic interference presents, in general, enormous problems due to the very high costs involved in constructing and preparing test equipment. Over the past few years, investigations have been carried out as to how these very complex field tests could be...

  • FCC Expands use of GTEM Cells for Equipment Authorization Measurements - July 1995
    FCC Expands Use of GTEM Cells for Equipment Authorization Measurements. On December 2, 1993, the Commission released Public Notice 40830 announcing that, under limited conditions, it would accept GTEM cells as...

  • GTEM to OATS Correlation Testing - March 1994
    This paper discusses the requirements, procedures and technical approach for submission of requests to the Federal Communications Commission (FCC) for the acceptance of type certification data measured in wide bandwidth TEM cells, often called Gigahertz Transverse Electromagnetic (GTEM!) cells. This paper is limited to the description of a...

  • A User's Perspective on GTEM Testing - December 1993
    Today electromagnetic compatibility (EMC) engineering is seeing one of the most exciting test technologies coming to maturity. Since their development at the National Institute of Standards and Technology (NIST) by Dr. Myron Crawford, transverse electromagnetic (TEM) cells and their spawn have...

  • GTEM - FCC Notice - December 1993
    FCC Will Accept GTEM Measurement Data Under Limited Conditions. The Authorization and Evaluation of the Office of the Chief Engineer has recently begun to receive requests from equipment manufacturers asking that radiate emissions data collected using a Gigahertz Transverse Electromagnetic (GTEM) cell be accepted for...

  • Properities of Metals Used for RF Shielding - December 1993
    Understanding the basic principles that influence a radio-frequency (RF) shielded enclosure's performance can be a tremendous help to someone tasked wtih specifying or purchasing a shielded enclosure. The choice of shielding materials and how they are assembled are crucial to the performance of the enclosure.

  • Using an Oscilloscope And Sniffer Probe To Solve EMI Problems - February 1987
    Few tools are more helpful to an engineer wrestling with EMI problems than a good set of nearfield sniffer probes. Used with an oscilloscope, this tool is very useful in quickly answering key questions.

  • Monitoring Measuring Repeatability at Radiated Emissions Testing Facility - January 1987
    Maintaining adequate measuring accuracy and repeatability at radiated emissions testing facilities (e.g., open field sites and semi-anechoic chambers) is necessary to maintain credibility. Although catastrophic failures are usually readily apparent, slow changes to measurement accuracy or minor failures are difficult to detect. Annual or semi-annual preventative maintenance is necessary to insure accuracy, but cannot insure repeatability (i.e., continued accuracy) between...

  • Using LISN as an Electronic System EMC Diagnostic Tool - January 1986
    Most EMC engineers consider a Line Impedance Stabilization Network (LISN) to be a device that presents the ac power line of the equipment under test (EUT) with a precise impedance over a designated frequency range. This is the required function of a LISN. A LISN can also be used as...

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