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Electromagnetics Electromagnetic Properties of Materials EMC Measurements and Facilities Magnetic Thin Films and Devices Near Fields Antenna Techniques Non-linear Device Characterization Scattering Parameters and Impedance Standard EM Fields and Transfer Probe Standards Superconductor Interfaces and Electrical Transport Superconductor Standards and Technology Return
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Electromagnetics Division Contact: Dennis Friday A system's output power level is frequently the critical factor in the design, and ultimately the performance, of almost all RF and microwave equipment. Accurate measurements of power and voltage allow designers and users of measuring and test equipment to determine whether performance specifications are met. Inaccurate measurements lead to over-design of products and, hence, increased costs. Economic gains are realized through improvements in accuracy. In a broad range of industries, state-of-the-art calibration services are needed so that customers can maintain quality assurance programs in the manufacture and distribution of their products. We presently offer calibration services in power over the frequency range from 10 MHz to 100 GHz. The availability of these services allows the customers to be globally competitive. Research and development efforts in power standards can be grouped into three categories. The first is the maintenance and improvement of existing standards and measurement services. The second is the increase in frequency range of these services. The increasing speed of the Internet, wireless technology, and FCC regulations on interference have created needs for calibration services at higher frequencies than previously required. Microwave power measurements are being extended so that all frequencies up to 110 GHz can be measured. It is expected that additional development of services above 110 GHz will begin in the next few years. The third area of research is the measurement of microwave field strength through the Rabi oscillation between two quantum states of atoms exposed to the field. If successful, this will be a fundamental shift in the traceability of microwave signal strength measurements from one based on DC power to one based on quantum mechanical principles. Contact: Thomas Crowley Magnetic Thin Films and Devices We develop measurements and standards for the magnetic data storage and magneto-electronics industries. These measurements and standards assist industry in the development of magnetic thin-film materials and devices required for advanced magnetic recording systems, magnetic solid-state memories, magnetic sensors, and magnetic microwave devices. The emphasis is on the performance of nanoscale devices, consisting of multilayer and multicomponent thin-film systems, operating at microwave frequencies. We have successfully devised better methods to measure and control the dynamical properties of magnetic devices operating in the gigahertz regime. We have fabricated magnetic nanostructures to measure new spin-dependent transport phenomena and to determine the resolution of magnetic imaging systems. In addition, we are developing new combinatorial materials techniques for magnetic thin films and new types of on-wafer magnetic metrology. Long-term goals include the development of metrology for advanced magnetic data storage on the nanometer size scale, metrology for emerging spin-electronics technologies, and novel electron spin resonance techniques (down to the single-spin limit). Contact: Stephen Russek In this project, we are developing instruments, techniques, and theory for the understanding of the high-speed response of commercially important magnetic materials. Techniques used include linear and non-linear magneto-optics, and pulsed inductive microwave magnetometry. Emphasis is on broadband (above 1 gigahertz), time-resolved measurements for the study of magnetization dynamics under large-field excitation. Research concentrates on the nature of coherence and damping in ferromagnetic systems and on the fundamental limits of magnetic data storage. Exploratory research on spin-electronic systems and physics is under way. The project provides results of interest to the magnetic-disk-drive industry, developers of magnetic random-access memory, and the growing spintronics community. Project members have measured deleterious magnetic turbulence during the magnetic switching process, evanescent flux-pulse propagation in metallic films, and anisotropic coupling (damping) between uniform excitations and the crystal lattice. Coherent-control methods have been used to switch magnetization without unwanted precessional ringing. An inductive current probe was developed to assess trace-suspension interconnects for disk-drive recording heads. Contact: Thomas Silva The large magnetic recording industry is continually and rapidly advancing the state-of-the-art in high-density information storage and read devices. To maintain their competitive advantage in rigid-disk manufacture, U.S. firms must constantly look to new properties, such as giant magnetoresistance, of magnetic materials. The accurate characterization of new materials is often beyond the capability of small companies that are often the most eager to exploit them. Thus, NIST develops metrology to assist the magnetic recording industry. We also develop techniques to characterize the performance of ultrahigh-density magnetic recording systems and the performance of submicrometer magnetoresistive (MR) sensors. We have developed a scanning micromagnetic recording system to characterize ultrahigh-density recording using commercial or experimental media, heads, and sliders (recording heads on mechanical actuators). The system combines the ability to read and write conventional bit tracks under a variety of controlled conditions with the ability to image the magnetic structure, and allows the characterization of advanced sensors without the need for full head fabrication. Development is coordinated with the needs of commercial disk drive, head, and media manufacturers, and with the National Storage Industry Consortium heads program. We develop micromagnetic models of MR sensors and media to assist industry in the engineering and development of high-density magnetic recording. We also develop characterization techniques for magnetoresistive sensors for the new generation of submicrometer MR sensors to be used in ultrahigh-density magnetic recording. Contact: David Pappas By the mid 1990s, magnetic recording technology was a $50 billion worldwide industry consisting mainly of tape- and disk-drive manufacturers. Driven by domestic and foreign competition, U.S. industry has advanced to where nanometer-scale morphological, magnetic, and electrical properties play important roles in drive performance. Images showing microroughness, device dimensions, magnetic field patterns, and local electronic processes provide important information about the fundamental operation and ultimate limitations of drive components. In addition, images of components shipped for assembly can be used to determine quality before manufacture of the complete drive. Scanned probe microscopies (SPM) such as scanned tunneling microscopies, atomic-force microscopies, magnetic-force microscopies, and scanning potentiometry are uniquely qualified for many of these applications due to the nanometer-scale dimensions of the various types of probes. Industry needs the development and testing of SPM techniques, the demonstration of their usefulness, and generally a facilitating of the transfer of the latest innovations in SPM technology. By working closely with industry, we help to determine which kinds of SPM technology developed by the scientific community may have a commercial impact. We establish standard levels of instrument performance by optimizing techniques for a measurement. We maintain an active research program to develop new imaging and image measurement techniques tailored to specific problems which the magnetic recording industry has designated as areas of need where SPM will have commercial impact. Contact: John Moreland Superconductor Standards and Technology Manufacturers of superconducting wire need practical and accurate methods for characterizing critical current and ac loss. Large magnet systems require 5 percent uncertainty or less and critical-current values as high as possible. These require accurate measurements of magnetic field, voltage, current, temperature, fabrication, and precise control of magnetic-flux-pinning systems. In Nb-Ti wire, new artificial-pinning-center (APC) technology has complex materials science and analysis problems. APC wire is replacing conventional Nb-Ti wires in some applications. For Nb3Sn wires, the properties and handling of the sample mandrel can affect the measured critical current significantly. For high-temperature superconductors, sample damage, sample variability, and mounting variability can affect the measured critical current significantly. The accurate and unbiased feedback of conductor performance and measurement considerations are important to U.S. manufacturers to maintain their competitive position in support of magnetic resonance imaging, electric power, laboratory magnets, and other applications. NIST activity in national and international standards helps a fair market place. We provide standards, measurement techniques, quality assurance, reference data, and clarification of issues for both high- and low-temperature superconducting wire technology. We also develop standards for critical current measurements; conduct research, interlaboratory comparisons, and help create standards under the Versailles Project on Advanced Materials and Standards and the International Electrotechnical Commission Technical Committee 90 on superconductivity. We represent, update, and seek input from U.S. industry throughout the process of standards creation in order to protect U.S. interest in international trade. We contribute to the precise characterization of Nb3Sn wires for the International Thermonuclear Experimental Reactor in which a critical current accuracy of 2 percent and a precision of 0.5 percent is a goal. We conduct research to improve the performance of new superconductors that use artificial flux-pinning-center technology. Contact: Loren Goodrich Superconductor Interfaces and Electrical Transport The high-temperature-superconductor (HTS) industry needs high-quality contacts and interfaces for both thin-film and bulk conductors. NIST has the measurement equipment and expertise to develop and understand HTS interfaces, and industry has looked to us for engineering help and an understanding of how to control the surfaces of these new materials. In magnet technology, both HTS and low-temperature-superconductor magnets are being developed with larger volumes and higher fields (nuclear magnetic resonance, for example). Both lead to higher magnetic loading of the superconductor which necessitates the need for measurements of the effect of stress on their electrical performance. The new HTS materials also have significant magnetic field anisotropy, which has opened a new set of measurement and modeling problems for conductor performance. NIST thus promotes the development of the HTS industry; many of the companies that have expressed a need for our expertise and the equipment are small start-up companies without extensive infrastructure. We provide experience and equipment for the study of superconductor interfaces not available in industry. Our expertise started with the development of the first HTS contact patent four weeks after the announcement of YBCO, and has continued through the issuing of additional patents. Our equipment is unequaled in the study of HTS interfaces. The thin-film fabrication equipment offers both sputter and laser-ablation deposition of HTS materials, reflection high-energy electron diffraction analysis, in situ characterization of process gas and background contaminants, ion-milling, and etching, all in the same vacuum chamber. In situ transfer capability to an Auger spectrometer is also available. The equipment to perform in situ scanning tunneling microscopy surface analysis of HTS films is developed to allow surface conductivity maps immediately after film fabrication. Our instrumentation in the electromechanical area is the only apparatus in the United States for electrical transport measurements of superconductors at high magnetic fields and, therefore, provides a national service to superconductor companies for conductor characterization and development. We are developing an automated high-field angle test apparatus to provide critical-current versus temperature, field, and field-angle maps at magnetic field levels not available in industry. Contact: Jack Ekin Scattering Parameters and Impedance Vector network analyzers (VNAs) are the single most important instrument in the microwave industry. These instruments are commonly found on production lines, in calibration laboratories, and in research laboratories. VNAs are typically calibrated daily, and the accuracy of their measurements can vary significantly after calibration depending on the operator's skill, the quality of the calibration standards, and the condition of the test ports. The microwave industry needs cost-effective techniques to monitor and verify the accuracy of VNA measurements. In addition, industry requires validation of techniques and procedures that they develop. NIST supports these needs by providing consultations on measurement techniques and uncertainty characterization. We also offer an extensive array of measurement services that allow VNA users to establish and gain confidence in their capability. The goals of the program are to provide traceability for microwave measurements in scattering parameters, impedance, and attenuation; to support the microwave industry by developing standards and new measurement techniques; and to develop methods for assessing and verifying the accuracy of vector network analyzers. Contact: Ronald Ginley Noise is a crucial consideration in designing or assessing the performance of virtually any electronic device or system that involves detection or processing of a signal. This includes communications systems, such as cellular phones and home entertainment systems, as well as systems with internal signal detection and processing, such as guidance and tracking systems or electronic test equipment. The global market for microwave and millimeter-wave devices in these areas is huge and growing. Important trends that must be addressed include the utilization of higher frequencies, the growing importance of low-noise amplifiers, the demand for and lack of repeatable and traceable on-wafer noise-measurement techniques, and the perpetual quest for faster, less expensive measurements. The two most important noise-related technical parameters requested by industry are the noise temperature of a one-port source and the noise figure of an amplifier. We are pursuing new work in three general areas: traditional noise-temperature measurements, characterization of amplifier noise characteristics, and on-wafer noise measurements. In traditional (connectorized) noise-temperature measurements, the goal is to cover the frequency range from 8.2 GHz to 65 GHz for waveguide sources, and 30 MHz, 60 MHz, and 1 GHz to 50 GHz for coaxial sources. Concurrently, redesign of systems and test procedures is reducing the time required for such measurements, thereby reducing the costs to our customers. The second general thrust of the project is in amplifier noise-parameter measurements. The long-term goals in this area are to improve techniques for measurement of noise parameters of amplifiers (especially low-noise amplifiers), to develop measurement capability for noise parameters of amplifiers with coaxial connectors from 1 to at least 12 GHz, and to provide a means for industry to access this capability, either through measurement comparisons or a measurement service. The third area of new work is noise measurements on a wafer or substrate. We are currently developing on-wafer noise sources suitable for use in interlaboratory comparisons of noise-temperature measurements, and as the noise parameter work progresses, it will be extended to measurements of noise parameters of on-wafer amplifiers and devices. Contact: James Randa The rapid advance in the speed of modern telecommunications and computing systems drives this project. The explosion of optical and wireless telecommunications is fueling the demand for microwave and radio-frequency microelectronics, and advances in the silicon industry continue to drive the size of digital circuits down and their clock rates up to microwave frequencies. Characterizing signal integrity in a microprocessor with a 2 GHz clock rate requires at least 10 GHz of calibrated measurement bandwidth on lossy silicon substrates. Limited available bandwidth is pushing wireless systems into the millimeter-wave region of 30 to 100 GHz. New 40 GB/s optical links require electrical metrology to 200 GHz. These extraordinary advances in technology require new high-speed frequency-domain and waveform measurements. However, current commercial sampling oscilloscopes are limited to a 50 GHz bandwidth, and current broadband single-sweep network analyzers are limited to 110 GHz. This project supports the microwave, telecommunications and computing industries through research and development of high-frequency on-wafer metrology. The goal of the project is to develop electrical metrology for new 40 GB/s optical links, 30 to 100 GHz wireless systems, and high-speed microprocessors by establishing accurate on-wafer waveform and frequency-domain metrology to 200 GHz. Contact: Dylan Williams Electromagnetic Properties of Materials The trend in microelectronic applications is toward higher frequencies, variable temperatures, and thinner materials. Substrate-based components employing thin films form the basis for microelectronic circuitry. Substrate electronic materials are used in printed wiring boards (PWB), low-temperature cofired ceramics (LTCC), CPU chips, and microwave components. Industry requires new measurement methods, with well-characterized uncertainties, at microwave and millimeter frequencies and over variable temperatures. Knowledge of temperature-dependent dielectric and loss properties of ceramics, substrates, and crystals are crucial in the wireless and time-standards arena at microwave and millimeter frequencies. For example, computer-based design methods require very accurate data on the dielectric and magnetic properties of these materials over wide frequency and temperature ranges. Various applications require composite dielectrics that emulate the human body's electrical properties for testing metal detectors and analyzing electromagnetic interference (EMI) of implant medical devices. Liquid permittivity measurements are needed to support biotechnology research. To support the evolving microelectronics industry, methods for characterizing metamaterial properties will be necessary for the development of novel new technologies. On-chip, microscale-to-nanoscale permittivity measurements are important for the microelectronic industry. Dielectric reference materials are needed to provide measurement traceability to NIST and measurement intercomparisons provide assessments of the quality of material characterization. An understanding of loss mechanisms in low-loss crystals is important in interpreting measurement results. The project objectives are to develop, improve, and analyze measurement methods, uncertainties, and theory for the characterization of the complex permittivity and permeability of dielectric and magnetic materials in the RF and microwave spectrum, as a function of temperature and bias fields. We plan to extend measurement capability to higher frequencies and a broader range of temperature, and to develop new methods for thin films and on-chip measurement of permittivity. We also plan to develop models for underlying relaxation phenomena that occur in dielectric and magnetic materials. Finally, we will provide measurement services, become active on standards committees, and develop Standard Reference Materials (SRMs). Contact: James Baker-Jarvis Non-linear Device Characterization Radio-frequency measurements are applied extensively in the deployment of commercial wireless communication systems. They are crucial to all stages of system development, from device modeling to circuit design and system performance characterization. NIST's RF and microwave measurement teams are addressing the critical need for accurate measurements of nonlinear electrical networks and supporting industrial standards development. The Non-linear Device
Characterization (NDC) Project is developing and verifying measurement-based
descriptions of devices, circuits, and systems that contain non-linear
elements. The RF power amplifier is a key non-linear component with which
engineers are currently contending. Industrial experts estimate that the
RF power amplifiers account for 60 to 70 percent of base station costs
and 20 to 30 percent of the total wireless link cost. Traditional microwave
circuit design has relied on the ability to cascade circuit elements through
simple linear operations and transformations, but engineers lose the ability
to predict circuit performance across operating environments, or states,
when their circuits include a non-linear element. Presently, there is
a critical need for fundamental RF measurement techniques to develop and
validate non-linear models and commonly applied figures of merit. Contributions
in this area will significantly improve design-cycle efficiency and trade
between manufacturers and eventually will facilitate improvements in communications
through the full incorporation of non-linear models at the system design
level. Contact: Don DeGroot Near Fields Antenna Techniques Microwave antenna hardware continues to become more sophisticated. High-performance systems, especially those that are satellite-based, require improved accuracy and maintenance of tighter tolerance. Operational frequencies are increasing with millimeter-wave applications up to 500 GHz proposed. Military and commercial communications applications increasingly require side lobe levels of 50 dB below peak, or better, a range where measurement by standard techniques is difficult. Large, often electronically steerable phased arrays require special diagnostic tests to ensure full functionality. Many systems cannot be simply transported to a measurement laboratory, and robust techniques are needed for on-site testing. These demands require constant improvement in antenna metrology. NIST is currently upgrading special test services to include the band 75 to 110 GHz. A further upgrade of services to include the band 110 to 170 GHz is planned. Measurements, especially at millimeter-wave frequencies, often require probe-positioning tolerances that are difficult to maintain. Probe position-correction software has been completed for planar near-field scanning and is near completion for spherical near-field scanning. One of the larger sources of error in near-field measurements is multiple interactions between the probe and test antenna. A study on compensation for multiple-interaction errors, possibly involving a simplified scattering model for electrically small probes, is near completion. Additional work is being carried out on planar scanning truncation errors (a finite plane is sampled versus the infinite plane required by theory) and on improving the near-field extrapolation method. NIST research on near-field antenna techniques seeks to develop, refine, and extend measurement techniques to meet current requirements and to anticipate future needs for accurate antenna characterization. Contact: Michael Francis Standard EM Fields and Transfer Probe Standards Well-defined electromagnetic (EM) reference fields are necessary for antenna calibrations, antenna research and development, evaluation of EM field probes, and EM interference measurements. Standards requirements need references to establish traceability and international compatibility. Industry requires a NIST-traceable EM field measurement capability to reduce barriers to worldwide acceptance of U.S. products and practices. NIST is working with industry and standards groups to extend methods for generating a standard EM field to frequencies up to 50 GHz. NIST is investigating the facilities used to generate standard fields. These include open area test sites (OATS) and anechoic chambers as are recommended by many standards. Work includes how to better use an OATS in the presence of high ambient fields, methods to improve repeatability at OATS, and how to better quantify uncertainties. The use of these facilities requires accurate measurements of EM fields. NIST is a leader in developing EM field probes and transfer standards. Standard probes are designed both so that response can be calculated from first principles, if possible, and to minimize errors that occur from pickup of unwanted signals. We have demonstrated a loop antenna with double gaps that simultaneously measures both the electric and magnetic components of the field. NIS has developed resistively tapered dipole probes with frequency responses up to 40 GHz. Probes based on this design are now being produced commercially by private industry. Projections for future spectrum usage indicate that probes with millimeter-wave and terahertz responses need to be developed. NIST maintains parallel efforts both to generate standard reference fields and to develop the probes required for their accurate measurement. We seek to maintain this measurement capability in support of U.S. industry through traceability and international compatibility of antenna standards. Contact: Keith Masterson EMC Measurements and Facilities We are working to develop reliable measurement standards, test methods, and services to support the electromagnetic compatibility (EMC) needs of U.S. industry. These needs are related to electromagnetic emissions (intentional or unintentional signals transmitted by the test device) and immunity (ability to resist external electromagnetic energy) of electronic devices, components, and systems. The characterization of support hardware such as cables, connectors, enclosures, and absorbing or shielding material is an integral part of these measurements. Major challenges are to provide reliable and cost-effective test methods over a large frequency range (10 kHz to 40 GHz and, eventually, higher) and for large test volumes. The efficiencies and uncertainties of EMC measurements directly impact both the competitiveness of U.S. manufacturers and the reliability of their products. Our research quantifies and, in some cases, reduces these measurement uncertainties. We are investigating a variety of facilities used in EMC measurements including reverberation techniques, transverse electromagnetic (TEM) structures, anechoic chambers, time-domain ranges, open-area test site (OATS), and other new innovative techniques. A good example of a facility with a wide range of capabilities is the reverberation chamber. Reverberation chamber work includes developing techniques for characterizing the efficiency and mismatch characteristics of antennas in complex environments, investigating techniques for rapid evaluation and/or calibration of multiple electromagnetic field sensors, developing methods for measuring the shielding effectiveness of highly non-homogenous materials such as advanced composites, and developing emission and immunity test methods for commercial electronics. Another approach being investigated is the use of time domain free field metrology, which uses swept frequency or direct pulse systems to perform ultrawideband electromagnetic measurements. These systems exhibit high spatial resolution that and extract useful information quickly and accurately. Applications include determining the material properties of dielectric panels (low-loss and high-loss), evaluating RF absorbers at both normal and oblique incidence angles, characterizing electromagnetic EMC facilities, performing ultrawideband RCS measurements, and evaluating the shielding performance of large cavities, such as commercial aircraft. NIST is working to improve existing EMC measurement facilities and to develop new measurement methods to meet the needs of emerging technologies. The main objectives are to ensure harmony and international recognition of U.S. measurements for trade, to provide physically correct test methods, to provide national calibration services, and to serve as an impartial expert body for resolving measurement inconsistencies. Contact: Galen Koepke Radar cross section (RCS) measurements on complex targets, such as aircraft, ships, missiles, are made at different types of RCS measurement ranges such as, a compact range (indoor static), an outdoor static or an outdoor dynamic facility. Measurements taken at various ranges on the same targets must agree with each other within stated uncertainties to increase confidence in RCS measurements industry wide. NIST researchers are working on calibration artifacts to enhance and assess calibration accuracy, on defendable range specific uncertainty analyses throughout the RCS industry, and on an RCS interlaboratory comparison program. Another antenna system metrology area is satellite communication. Satellite communication is a finely tuned technology requiring accurate measurements of antenna gain, noise temperature, G/T (system gain divided by system temperature), and EIRP (effective isotropic radiated power) to ensure optimum performance. Ground stations and test ranges that monitor the performance of commercial and government satellites require traceability to NIST standards. New capabilities are needed to support anticipated technologies, such as anticollision radars. NIST traceability is also required by law-enforcement agencies to ensure the accuracy of their speed measurement devices, including down-the-road radar, across-the-road radar, and lidar. We are developing the metrology for system parameter measurements. Our research on antenna systems metrology seeks to develop and improve standards, methods, and instrumentation for measuring critical performance parameters of RCS test objects, earth terminal, satellite, and other critical antenna systems, such as those associated with public safety. Contact: Lorant Muth
Date
created:November
8, 2001 |