4
Fundamental Electromagnetic Technologies and Standards
This chapter addresses the Fundamental Electromagnetic Technologies and Standards (FETS) research focus area. FETS is supported by the Radio Frequency Technology Division, which provides solutions by capitalizing on and leveraging its expertise in the following four research groups: (1) Guided Wave Electromagnetics, (2) Electromagnetic Fields, (3) High-Speed Waveform Metrology, and (4) Superconductor Electronics. The last group was added during the recent reorganization. Outcomes of the FETS focus area address specific high-impact fundamental problems and provide solutions that support the five other research focus areas in the Communications Technology Laboratory (CTL).
To ensure future impact and keep advances in CTL technologies and standards relevant, CTL collaborates with four other National Institute of Standards and Technology (NIST) laboratories—the Physical Measurement Laboratory, the Information Technology Laboratory, the Material Management Laboratory (MML), and the Engineering Laboratory. The work with the MML is on the Material Measurement Laboratory mega-qubit Innovations in Measurement Science (IMS) project, which CTL leads, and the electric-acoustic spectroscopy project, which the MML leads. The aim is to address grand challenge–like problems of key interest to industry and the nation through the IMS program as either lead or support.
OVERALL DISCUSSION
To perform its research mission on metrology, CTL’s funding is adequate and stable. The Radio Frequency Technology Division does, however, need to continue to seek support to upgrade facilities that are currently lacking. The current state of these facilities hinders its ability to provide services related to standards testing. The team of scientists and technologists is excellent, highly productive, and actively engaged across CTL divisions and NIST laboratories, which provides enhanced productivity and a strong interdisciplinary technical culture.
CTL staff have identified important metrology projects to support current and future communications needs. It has a strong foundation in solving fundamental problems and good strategies for near-term
measurement challenges. Since the reorganization, it also has a clearer strategy for establishing emerging measurement methods (e.g., over-the-air testing) and is actively pursuing beta testing of such ideas in projects associated with its inter-laboratory IMS collaborations. Because of the number of projects and the high level of integration with other projects, the effort from the Radio Frequency Technology Division with different focus areas and laboratories needs to show the depth and breadth of connectivity. Due to the fundamental nature of the work, it was difficult to see the full impact until after all other presentations were given. In addition, it was unclear how to determine which projects are emerging, active, sunsetting, or required for legacy purposes. Clarification of these would better convey the relevance, value, and impact of the FETS focus area by this division within CTL.
The importance of the work within the Radio Frequency Technology Division is evident, and a highly trained workforce is necessary to maintain such high-quality work. CTL’s commitment to hiring excellent people is clear, and its understanding of the need to diversify its future workforce more urgently was evident by the staff and programs being developed at the management and leadership level. Specific strategies at the division level to support the diversification of its technical workforce were less clear. Developing these strategies in collaboration with divisions would allow for a more synergistic approach for implementation. Efforts to make select versions of the work accessible to lay audiences and youth could help with NIST branding nationwide and support CTL’s goals for diversifying its workforce, especially in locations where demographics are less diverse. CTL’s goals to diversify the future workforce are embedded into the highest leadership level.
The CTL metrology staff are experts with years of experience in providing consistent and diligent dissemination of their scientific and technical findings to the broader community of technical professionals and stakeholders.
The FETS focus area is important and it has the capacity to grow, especially if the facility’s challenges are addressed regarding the emerging needs of new technology and application areas. Its growth will play an important role in serving the nation’s needs and expansions in communication technology. It was clearly communicated that equipment upgrades are needed. With the pandemic constraints, the Radio Frequency Technology Division made significant efforts to move forward by developing alternative solutions for in-person and remote access to work in response to the pandemic. Some conventional measurement and standard services were impacted by equipment limitations due to building upgrade delays. Equipment and facilities are discussed in Chapter 9.
The CTL physical infrastructure was mostly sufficient for its previous programs. Since the pandemic began in early 2020, however, delays in facilities access have made such upgrades even more important for the Radio Frequency Technology Division. Despite these delays, CTL has been extremely productive in its FETS focus area, and the outcomes of this effort could be observed in the other focus area projects and IMS projects presented.
CTL’s work in electromagnetics and quantum science for communications are outstanding and important for next-generation advancements. Over-the-air testing standards development has emerged over several years, and CTL is leading in that effort, which is revitalizing the measurement space for antenna research related to communications and the advanced systems and standards developed over the past two decades. Finally, the strength of CTL’s microwave measurements for materials and electronics by the Radio Frequency Technology Division for many decades has provided and continues to provide important test and measurement methods, standards, and data. These efforts help industry establish protocols, especially for integrated circuit chips, for determining acceptable performance metrics and standards for high-speed communication circuits and devices used frequently in consumer electronics and scientific government applications. CTL’s development of quantum-based technologies advances FETS standards and traceability into a new generation of accuracy.
The FETS research area stakeholders comprise diverse community members (i.e., industry, government, academia, and research communities). Moreover, the FETS research focus area stakeholders have a wide range of needs from basic science and engineering to applied research and technology that can benefit from the development of different test and measurement capabilities, research facilities, and experts who can address the different stakeholder projects. The IMS projects may have similar needs and
requirements for unique test and measurement capabilities, facilities, and experts. While performance metrics for the different technologies are easier to quantify at the fundamental level, clarification of how uniquely designed integrated systems platforms are evaluated needs to be included.
CTL has diverse technical expertise in its world-class staff. CTL’s restructured research focus areas makes it easier to see the collaborations between the laboratories of divisions and inter-laboratory collaborations between IMS projects (e.g., with the Physical Measurement Laboratory, Information Technology Laboratory, and Engineering Laboratory). The reorganization created tremendous strength in CTL.
Area-Wide Challenges and Opportunities
The collaboration between the superconducting and electromagnetic research groups within the Radio Frequency Technology Division offers even greater potential for advancement by applying these technologies to support the other research focus areas. Continued investigation in enabling quantum computing and sensing can revolutionize communication, networking, and other related industries through high-performance and energy-efficient components. CTL’s fundamental research and development can serve as an incubator and seedling for further government, academic, and industry innovation as components evolve and systems are integrated. CTL’s creation of precise measurement equipment based on quantum and superconducting electromagnetic concepts also has the potential to provide independent test and measurement evaluation of candidate systems from other research organizations—an ideal testbed.
Recommendation 4-1: CTL should continue to advance its work in quantum information science and engineering and leverage the strengths of the superconductor group, recently added to the Radio Frequency Technology Division. It should also continue to find ways to co-integrate different technological systems (e.g., electrical, optical, and quantum) effectively to support the direction of industry and government.
Integration of CTL projects with the work of other NIST laboratories, both as lead and collaborator, was strong and needs to be continued to ensure that the efforts within CTL are tracking with new directions and emerging fields.
Key Recommendation 4: Given the fundamental nature of FETS, the Radio Frequency Technology Division should create a system or database that tags key projects and links them to other work within or between different CTL focus areas, divisions, or NIST laboratory projects. Such a system would provide tracking of the work throughout CTL and allow others to better understand the connections, impacts, uses, evolution, and sunsetting of the work.
ASSESSMENT OF TECHNICAL PROGRAMS
The Radio Frequency Technology Division executes various projects within the four major program areas of
- Electromagnetic traceability,
- Microwave measurements for materials and electronics,
- Over-the-air testing, and
- Quantum traceability for communications.
These major program areas can be further broken down into interdisciplinary projects requiring the contribution of multiple research groups within the Radio Frequency Technology Division. Figure 4.1 provides a Venn diagram depicting the relationships of those projects with the four Radio Frequency Technology Division research groups and their connection to other research focus areas.
These projects cover a wide range of fundamental radio frequency measurement problems for both classical and quantum radio frequency metrology. CTL continues to pave the way in developing and delivering better measurement technologies. The world-class quality of its research in fundamental metrology is proven through successful international intercomparisons and dissemination of intrinsically accurate quantum artifact standards. Due to its standing, CTL’s Radio Frequency Technology Division provides various measurement services and is working on future measurements and standards identified as industry needs. Projects focused on characterizing uncertainty of radio frequency quantities, extending the frequency range coverage of measurement technology, and addressing emerging new applications are appropriately chosen to ensure that the Radio Frequency Technology Division can reach its technical objectives for stakeholders in academia, government, and industry.
Accomplishments
Projects chosen within the FETS research focus area simultaneously focus on enhancing existing classical radio frequency metrology and developing new quantum-based metrology to address industry trends and needs. CTL’s Radio Frequency Technology Division maintains the U.S. national standards for various radio frequency measurements and has deep expertise in International System of Units (SI)-
traceable radio frequency measurement technology.1 The division has continually focused on increasing the frequency range in which that expertise and standards exist. With the interest in higher and higher communication operating frequencies, both fundamental and harmonic frequencies within the microwave and millimeter-wave bands need to be characterized for all communication components. This has led CTL to execute multiple projects focused on
- Extending the NIST microwave uncertainty framework to include traceability for uncertainty above 100 GHz under dynamic conditions (change in time, position, or angle of arrival), and/or using correlative analysis;
- SI-traceable measurements, models, and tools for authenticity, design, security, characterization, and verification of hardware and materials to include semiconductors, on-wafer integrated circuits, optoelectronics and photonics, three-dimensional microelectronics, and microfluidic chips; and
- Over-the-air testing for high-frequency and complex radio frequency channels using synthetic aperture measurements under the SAMURAI project2 and developing test environments and performance tools for the design and verification of millimeter-wave, industrial Internet of Things applications.
In addition to its growth in classical radio frequency metrology, CTL has developed and delivered multiple innovations in quantum standards. One such accomplishment is the delivery of Programmable Josephson Voltage Standards Reference Instruments that are intrinsically accurate and based on quantum effects as a new SI traceable reference for the volt. The Programmable Josephson Voltage Standards Reference direct current-to-direct current comparison agreement is 3 × 10–11 V/V, an order of magnitude better than previous electrochemical battery artifacts. In addition, this technology has been leveraged to develop the Josephson Arbitrary Waveform synthesis at radio frequencies with statistical uncertainty below 1 × 10–7, which is more than two orders of magnitude better than current alternating current calibrators. These developments not only improve the accuracy of standards and measurements worldwide, but the technology opens doors to more promising applications of quantum-based sources for future radio frequency communication, computing, and qubit control. CTL is currently engaged in several projects to focus on these future applications.
The development, demonstration, and dissemination of the Rydberg atom-based sensors is another CTL achievement with significant potential to revolutionize communications. CTL continues to enhance the technology by working on the development of arrays of Rydberg sensors for direction finding and beamforming, the evolution of the original Rydberg atom-based radio receiver, and exploring other measurement and calibration possibilities. CTL recently demonstrated the ability to measure phase at different locations within a cell to determine the angle of arrival of an incoming radio signal. The continued evolution of such an environment-independent and electromagnetically sensitive sensor directly aligns with the need for extreme bandwidth, miniaturized, radio frequency sensor technology for all applications currently using antennas. The progression in Rydberg atom projects shows an intentional technical plan to continue to add capability that could lead to the replacement of conventional antennas for a number of communication-related applications.
In response to the 2019 assessment by the National Academies of Sciences, Engineering, and Medicine,3 CTL has participated in several IMS projects in collaboration with other NIST laboratories. These projects cover a range of topics by leveraging the Radio Frequency Technology Division’s
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1 When something is SI-traceable, it means that it can be traced back to established SI standards. The SI is the International System of Units.
2 For more information see https://www.nist.gov/publications/welcome-samurais-software.
3 National Academies of Sciences, Engineering, and Medicine (NASEM), 2019, An Assessment of the Communications Technology Laboratory at the National Institute of Standards and Technology: Fiscal Year 2019, Washington, DC: The National Academies Press, https://doi.org/10.17226/25602.
expertise in measurement, uncertainty improvement, and electromagnetics. CTL has done well to ensure that each project supports the further expansion of its capability into higher frequencies (sometimes even leaving the radio frequency spectrum) and quantum technology (or at least investigating electromagnetics at a molecular level). These activities have contributed to capital investments in facilities for CTL as new ranges and laboratories are created in support of them.
Lastly, critical to the Radio Frequency Technology Division’s core function of providing accurate measurements, CTL completed a 5-year quality assessment of the division’s measurement services in 2020. In 2021, the Radio Frequency Technology Division also received re-approval from the Inter-American Metrology System and had the first quality management system that NIST accredited to the full requirements of the new ISO/IEC standard 7025:2017. This speaks well of CTL and the quality of its people and processes by reaching this milestone during the pandemic.
Challenges and Opportunities
The extension of traceability to include more complex factors to uncertainty becomes not only a challenge in the method of collection, but also in data recording. The scale of data required to characterize a measurement not only spectrally, but now temporally, spatially, and directionally, could be a significant big data problem. CTL currently develops and distributes various software packages for managing NIST traceability, uncertainty, and measurement data. Examples are the NIST Microwave Uncertainty Framework, classical and quantum calibration software modules, and software products from the NextG Channel Model Alliance.
Recommendation 4-2: CTL should continue to provide NIST software updates and additions to the broader community that evolve along with the growing complexity of its metrology data sets as one way of avoiding a future big data problem.
The Rydberg atom arrays are a prime opportunity for CTL to lead the way and warrant maximum effort, because more system-level analysis, design, and development are needed to mature the technology. There are a number of challenges in terms of realizable instantaneous bandwidth and system size, weight, and power. This could be done in partnership with external organizations, such as the Defense Advanced Research Projects Agency (DARPA), the Intelligence Advanced Research Projects Activity, the National Aeronautics and Space Administration, and military research laboratories, which have focus and experience in transitioning technologies from research into operational deployment. However, CTL’s experience would be critical to ensuring that performance gains are not lost.
Recommendation 4-3: CTL should continue to seek more Rydberg atom sensor-focused external partnerships with organizations like the Defense Advanced Research Projects Agency, the Intelligence Advanced Research Projects Activity, the National Aeronautics and Space Administration, and military research laboratories, which have focus and experience in transitioning technologies from research into operational deployment. Collaboration with other NIST laboratories to address size, weight, and power improvement and system-level issues through other advanced technology being developed in those laboratories would further advance the evolution of Rydberg atom-based capabilities.
Authenticity verification for communication hardware and microelectronics is of national concern. CTL has engaged stakeholders through workshops and reports. Although there are currently discussions on developing use cases, a primary enabler for this is the ability to perform the required measurements at different facilities with different equipment; this requires calibrated measurements traceable to NIST. The derived uncertainty of those measurements needs to be well below the tolerance of the authentication parameter to be measured. Given the current supply-chain issues in a post-pandemic economy, this is an
urgent problem. As materials and products become scarcer, the need to diversify sourcing becomes greater, which results in a growing reliance on foreign suppliers or multiple suppliers for the same component to avoid catastrophic delays. This reliance accelerates accepting the increased risk of acquiring suspect counterfeit or malicious components. This acceleration needs to be met by an equally accelerated effort to triage the potential counterfeit part epidemic.
Recommendation 4-4: CTL should begin developing an authentication demonstrator based on existing measurement capabilities to provide a testbed to help develop and experiment with possible use cases; identify needed technology enablers; and quantify current performance gaps. The demonstrator would include selecting a component that can be acquired from multiple diverse suppliers, including known counterfeit versions, and quantifying variability across units in every parameter that CTL can currently measure. If external funding is not available at this time, an IMS project could be the best vehicle for such an investigation.
Calibrations—Ebbs and Flows
The Radio Frequency Technology Division quality assessment conducted in 2020 provided the number of calibrations performed each year from 2016 to 2020. The trend showed the number at nearly 4,000 in 2016, falling to 1,200 in 2018, and having a large increase to over 6,000 in 2019. It was not clear if this 500 percent increase in a single year was a result of the National Academies’ 2019 assessment.4 However, 2020 had less than 2,300 calibrations, which could be a result of multiple issues, including the pandemic or could just indicate that the number of calibrations in 2019 was an anomaly. Given that NIST is known for its calibration work and CTL is heavily investing in developing advanced calibration methods and tools, the amount of calibration work conducted by CTL may be an indicator of, or a contributor to, CTL’s accomplishments or issues.
Key Recommendation 5: CTL should investigate the reasons behind the trend in the number of calibrations performed annually. Specifically, CTL should understand (1) the significant drop in 2018, (2) the surge in 2019, and (3) the trend during the pandemic. The results of this investigation should inform a strategic plan for determining if there needs to be a goal for achieving the desired amount of CTL calibration work and what that amount might be.
PORTFOLIO OF SCIENTIFIC EXPERTISE
Accomplishments
The Radio Frequency Technology Division has four research groups, led by a group leader, with team members in either the technical staff or associate category.
- Radio Frequency Electronics has 9 staff and 11 associates.
- Radio Frequency Fields has 7 staff and 19 associates.
- High-Speed Measurements has 7 staff and 10 associates.
- Superconductivity has 11 staff and 6 associates.
The division headquarters has four staff and one associate. In total, there are 37 staff members and 46 associates. The Superconductivity group joined the division in fiscal year 2022.
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4 Ibid.
Due to the virtual format of the 2022 assessment, there was limited interaction with the Radio Frequency Technology Division staff. The interaction was limited to the division leaders and presentations from select team leads. However, the high-performing work product of the division demonstrates the expertise of the staff. The division team continues to lead SI-traceable measurements and has been focusing on improving the infrastructure capability to ensure that its constituents—other laboratories, industry, and government—receive the precision of measurements needed. This places CTL as a leader in the field. In addition, the Rydberg Atom-based Quantum Radio-Frequency Field Probe5 work is a highly productive effort that provides high visibility for CTL, increases its interagency collaboration within and outside of NIST, and positions it to play a key role in the upcoming NIST-on-a-chip funding effort.6 Other high-performing areas include leading efforts for precision materials measurements as well as quantum voltage measurements that are both essential for emerging topics of high priority to industry in heterogeneous integration and advanced devices as well as in computing.
Challenges and Opportunities
Since the National Academies’ 2019 assessment,7 the Radio Frequency Technology Division experienced several leadership changes resulting in acting personnel for division chief and three group leader roles. Currently, all roles are filled, starting with division chief in 2020 and various group leader roles in 2021. The new structure allows divisions to work on focus area projects as well as collaborative projects with other groups. It appears to be a good, and timely, fit and provides the organization with interconnections between the strong disciplinary nature of divisions to advance fundamentals while supporting and advancing the goals and objectives of the interdisciplinary nature of IMS projects.
As the complexity of collaborative and interdisciplinary projects grows, it may be necessary to consider hiring personnel who can cross the vertical and horizontal layers between fundamentals and applications, especially as materials, devices, and hardware systems become more integrated with software and software technologies like artificial intelligence and machine learning.
Recommendation 4-5: CTL should continue to evaluate the needs for testing between technologies—wired and wireless, electronic, optical, and quantum for communication and computing—and collaborate with other laboratories within NIST to help determine planning and funding needs.
EFFECTIVE DISSEMINATION OF OUTPUTS
Publications and patents were a consistent mechanism for the delivery of outcomes and showcased the high quality, significance, and visibility of research such as the Rydberg Atom-based Quantum Radio Frequency Field Probe and quantum voltage efforts.
Accomplishments
The Radio Frequency Technology Division has had the following accomplishments:
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5 For more information see https://www.nist.gov/programs-projects/rydberg-atom-based-quantum-rf-field-probes.
6 For more information about NIST-on-a-chip, see https://www.nist.gov/noac.
7 NASEM, 2019, An Assessment of the Communications Technology Laboratory at the National Institute of Standards and Technology: Fiscal Year 2019, Washington, DC: The National Academies Press, https://doi.org/10.17226/25602.
- Five direct current/alternating current quantum-based voltage standards, with four more planned for 2022;
- Continued maintenance of U.S. national standards for S-parameters, radio frequency power, inter-frequency phase, antenna gain, thermal noise, field strength, and Josephson volt work; and
- Research outcomes in top-tier journals in the following projects with high productivity (over 100 publications), high visibility, and inter-agency support for CTL across the four research groups:
- Rydberg Atom-based Quantum Radio Frequency Field Probe: five programs at other agencies, 47 publications, 6 patents (3 granted, 2 filed, 1 with NIST legal), 2 related IMS programs, NIST-on-a-chip funding, and 1 Cooperative Research and Development Agreement (CRADA);
- Microwave Materials: 2 DARPA programs, 20 publications, 2 patent applications, 1 CRADA, 2 related IMS programs, and related NIST-on-a-chip funding;
- Quantum Voltage: 1 Intelligence Advanced Research Projects Activity program, 25 publications, 2 patents granted, 1 patent filed, 2 related IMS programs, and NIST-on-a-chip funding; and
- High-Frequency Electronics: 2 DARPA programs, 11 publications, patent application, 1 CRADA, and 2 related IMS programs.
Challenges and Opportunities
Technically, as communication systems continue to evolve in complexity and diversity to accommodate the broad range of applications, users (i.e., people and things), and system requirements, supporting the development of the next generation of innovations and personnel needs to continue to be a priority. CTL has established a very strong organizational structure that should position it to continue to make significant contributions to emerging applications in the communications field. The strong interactions between CTL and other NIST laboratories, industry, as well as with other government agencies, are catalyzed by its mission and role in establishing and influencing the formation of precision standards and measurement methods for the field. The development of advanced concepts around probe technologies and measurement techniques for over-the-air transmission and voltages for quantum computing is both forward-thinking and influential to industry and other government agencies.
Diversity is one of NIST’s core values.8 CTL has put in place a very forward-thinking strategy to support its current workforce more holistically and to diversify its workforce in terms of race, ethnicity, and gender. It was developed with input from many stakeholders and is striving to create a better outward facing NIST that is learning from the past. Their past effort, when the organization was structured differently, did not seem to work as well. While those efforts didn’t work as well as intended, diversity goals seem to be better integrated into the new CTL structure. One challenge specific to this division is that electrical engineering students are on the decline, these students in the electromagnetic and radio frequency subfields relevant to the Radio Frequency Technology Division have been on a steeper decline, and those students that are U.S. citizens of diverse ethnicities are particularly difficult to find due to their rarity. This calls for particular attention when attempting to build a more diverse workforce for the Radio Frequency Technology Division.
Recommendation 4-6: When recruiting its future workforce, CTL should (1) define specific strategies that integrate diversity goals into the Radio Frequency Technology Division’s workforce generation strategies to account for its unique challenges in recruiting diverse researchers in this field, and (2) use select projects from the FETS focus area that will impact the broader lay community to
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support national awareness of CTL’s research, offer technical access, and expose the broader community to science, technology, engineering, and mathematics work opportunities.
