COMMISSION A:
Electromagnetic Metrology, Electromagnetic
standards(November 2020 – May 2023)

measurements

andEdited by
Hidekazu Hachisu (National Institute of Information and Communications Technology;
NICT)
A1. Time and Frequency Standards and Time Transfer Technique
The research and development on time and frequency standards as well as time and frequency
transfer in Japan are mainly carried out at the National Metrology Institute of Japan (NMIJ) andthe National Institute of Information and Communications Technology (NICT).
At NMIJ, the second cesium fountain, NMIJ-F2, for primary frequency standards has beendeveloped. We evaluated the frequency shifts due to the microwave leakage and distributed cavity
phase. By measuring the frequency of NMIJ-F2 as a function of the microwave pulse area, thefrequency correction and uncertainty for the microwave leakage shift were evaluated to be(−1.2 ± 2.5) × 10−16. Furthermore, by measuring the frequency of NMIJ-F2 with changes of thetilt angle of the fountain, the frequency correction and uncertainty for the distributed cavity phaseshift were evaluated to be (0 ± 3.4) × 10−16. By these, the uncertainty evaluation of NMIJ-F2 wascompleted [1]. The type A uncertainty for measurement for 20 d and the type B uncertainty are
typically 1.7 × 10−16 and 4.6 × 10−16, respectively. Ultrastable microwave oscillators: We havedeveloped three cryo-refrigerator-cooled cryogenic sapphire-resonator oscillators (cryoCSOs)
with a frequency stability of an order of 10−15 at an averaging time of 1 s. One of them iscontinuously operating, except during an annual scheduled power outage due to an inspection ofelectrical facilities and works as a local oscillator of the cesium fountain NMIJ-F2.
At present two active hydrogen maser frequency standards are operated at NMIJ for time
keeping. Those atomic clocks are kept in individual chambers, whose temperature variations are
kept to within 0.2 deg C. One of the hydrogen masers is used as a source oscillator for generating
UTC(NMIJ), which is created by frequency-steering of the hydrogen maser output signal using afrequency stepper (AOG). At NMIJ, Dual frequency carrier phase GPS receiver is one of the maininternational time and frequency transfer tools. NMIJ has been providing the remote frequency
calibration service using the GPS common-view method and Internet since 2006. The CMCs of
the service are 1.1 × 10−13 (baseline: 50 km), 1.4 × 10−13 (baseline: 500 km) and 4.9 × 10−13(baseline: 1,600 km) at an averaging time of one day. The number of users is 18 in 2023.
NICT maintains Japan Standard Time (JST) and disseminates it domestically. From November

2020 to May 2023, the difference between the Coordinated Universal Time (UTC) andUTC(NICT) has been kept within 20 nanoseconds. Since August 2021 NICT’s strontium opticallattice clock NICT-Sr1 is used as an additional reference, remarkably reducing the difference towithin 5 nanoseconds, a quarter of the previous difference. Throughout the period, NICT’s Kobe
JST substation has continued to keep the standard time, which is constantly monitored and steeredby the distributed and integrated management of JST stations. Kobe substation operates as an
emergency backup station for the Tokyo headquarters.
Regarding the next-generation TWSTFT modem (SRS modem), NICT conducted time andfrequency (T&F) transfer experiments with national metrology institutes of three European
countries, the Physikalisch-Technische Bundesanstalt (PTB) in Germany, the Observatoire deParis (OP) in France, and the Istituto Nazionale di Ricerca Metrologica (INRiM) in Italy, andreported its results at international meetings including the CCTF (Consultative Committee forTime and Frequency) working group. Starting 2022, a collaboration contract has been concluded
among the Research Institute of Sweden (RISE) in Sweden and the above three national
metrology institutes, and a T&F transfer experiment with SRS modems within the European
region is being planned. Domestically, a regular time comparison link among four stations (twolow frequency (LF) Stations, Kobe substation, and Koganei headquarters) has been constructedusing the SRS modem. Frequency comparison using a global navigation satellite system (GNSS)
precise point positioning (PPP) method was started among NICT, MMIJ, and the Korea ResearchInstitute of Standards and Science (KRISS) to realize regular mutual comparison of their opticalfrequency standards. NICT started nearly-real-time time comparison using the augmentation
service MADOCA-PPP broadcast by Michibiki (Quasi-Zenith Satellite System) in order toincrease the accuracy and robustness of the time comparison link used in the decentralization ofJST. It was confirmed that almost the same accuracy can be obtained as using satellite orbit
information provided by the International GNSS Service (IGS) with a delay of several hours.
Participating in the "Task Force GNSS Traceability" established under the CCTF GNSS WG in
June 2020, the results of the discussions were published in [2].
Wireless two-way interferometry (Wi-Wi) developed at NICT was applied to low latency
communication [3-5], to physical layer security [6] and to automatic mobility following [7].
Considering the cost reduction and mass production of miniaturized atomic frequency
standards, NICT developed a GHz-band MEMS oscillator using a legacy process (line width of
150 nm or more), and a VCSEL with MEMS wavelength tuner [8]. In addition, for wafer-level
fabrication of gas cells, NICT successfully synthesized a solid Rb source (RbN3) that does not
generate reaction products undesired for wafer processes [9]. To transfer these technologies tocompanies in the future, a joint research program with companies and universities has been started.
To reduce the size of the physics package further, NICT started developing the laser handlingtechniques for the atomic clock, such as steering, polarization, or collimation, using metasurface
patterns [10].
NICT has started development of a distributed time synchronization system utilizing small
atomic clocks to construct a resilient time synchronization network. Simulations using a statespace model of small atomic clocks were performed to investigate the effect of network topology,
connection method and number of atomic clocks on the stability of timescale generation using a
Kalman filter in a network of multiple atomic clocks [11].
The redefinition of the SI second requires the stable operation of optical atomic clocks, and so
it is important to understand frequency changes caused by solid-earth tides that often range from10 to 20 cm in amplitude, by oceanic tidal loading, crustal deformations due to earthquakes, andground movements with groundwater changes. NICT has begun observations and data analysis toevaluate how these effects interact with optical atomic clocks [12]. Since early 2021, NICT and
the Geospatial Information Authority of Japan (GSI) have been jointly conducting levelingsurveys and relative gravimeter observations at the NICT’s headquarters in Koganei. Theseobservations reduce the contribution of gravitational redshift to the total uncertainty of NICT-Sr1
to the 10−19 level. With the support of the National Institute of Polar Research (NIPR), absolutegravity measurements were performed in August 2019 and May 2022 to evaluate the effects ofthe 2011 off the Pacific coast of Tohoku Earthquake on coseismic vertical crustal displacement.
The obtained absolute gravity change between the two periods was −43.8 μGal. This matches thetrend of GNSS results obtained by the GNSS Earth Observation Network system (GEONET) of
GSI, which show a vertical displacement of up to 31.5 mm from August 2019 to May 2022
(equivalent to about −10 μGal gravity change) even though the values do not agree precisely.
NICT has introduced the Micro-g LaCoste's gPhoneX gravimeter for continuous gravity
measurements near the optical clocks at the end of 2021. The preliminary results over sevenmonths detect stable gravity change due to solid earth tide with about 22 μGal precision. NICT isalso monitoring vertical crustal displacement by geodetic GNSS measurement.
[References][1]

A. Takamizawa, S. Yanagimachi, and K. Hagimoto, “First uncertainty evaluation of the cesium fountain primary
frequency standard NMIJ-F2,” Metrologia 59(3), 035004 (2022).

[2]

P. Defraigne, J. Achkar, M. J. Coleman, M. Gertsvolf, R. Ichikawa, J. Levine, P. Uhrich, P. Whibberley, M.
Wouters, and A. Bauch, "Achieving traceability to UTC through GNSS measurements,” Metrologia 59, 064001(2022).

[3]

D. Koyama, Y. Wang, N. Shiga, S. Yasuda, N. Chauvet, and M. Naruse, "Low latency information transfer basedon precision time synchronization via wireless interferometry, "Nonlinear Theory and Its Applications, IEICE 12,2, 225–235 (2021).

[4]Y. Yamasaki, N. Chauvet, N. Shiga, S. Yasuda, K. Takizawa, R. Horisaki, and M. Naruse, "Delay-bounded
Wireless Network Based on Precise Time Synchronization Using Wireless Two-way Interferometry," IEEE
Access 9, 85084 (2021).

[5]

H. Tanaka, Y. Yamasaki, S. Yasuda, N. Shiga, K. Takizawa, N. Chauvet, R. Horisaki, and M. Naruse,"Experimental Demonstration of Delay-Bounded Wireless Network Based on Precise Time Synchronization,"
IEEE Access 10, 94285 (2022).

[6]

N. Shiga, S. Yasuda, K. Yonaga, K. Takizawa, M. Yoshida, "Virtual Wiretap Channel Based on Wireless Twoway Interferometry," in Proc. the 2022 IEEE Global Communications Conference (GLOBECOM 2022), 6188
(2022).

[7]

R. Isogai, S. Yasuda, N. Shiga, Y. Shoji, "Extremely High-accuracy Automatic Following between Mobilities
Using Wireless Two-way Interferometry," in Proc. 2023 IEEE 20th Consumer Communications & Networking
Conference (CCNC), 829, (2023).

[8]

M. Hara, S. Shinada, Y. Yano, T. Ido, Z. Zhao, M. Toda, T. Ono, and H. Ito, “FBAR Oscillator and MEMS Tunable
VCSEL to Generate the Probe Lasers for Microfabricated Atomic Clock”, in Proc. 2022 IEEE International
Ultrasonics Symposium (IUS), 1-4 (2022).

[9]

M. Hara, Y. Yano, M. Toda, T. Ono, and T. Ido, “Evaluation of New Solid Rubidium Source Using Atomic Clock
Stabilization Loop”, in Proc. 2021 21st International Conference on Solid-State Sensors, Actuators andMicrosystems (Transducers), 1158-1161 (2021).

[10] P. Prutphongs, K. Aoki, S. Ikezawa, M. Hara, and K. Iwami, “Multifunctional Metasurface for a Miniaturized
Reflection-type Atomic Vapor Cell”, in Proc. 2023 22nd International Conference on Solid-State Sensors,
Actuators and Microsystems (Transducers), (in Press).
[11] Y. Yano, M. Hara, and I. Ido, “Time Estimation of a Miniature Atomic Clock Using Instantaneous Frequency
Information,” URSI Radio Science Letters 4, 48 (2023).
[12] R. Ichikawa, H. Hachisu, M. Sekido, T. Ido, Y. Hiraoka, E. Harima, S. Fukaya, K. Matsuo, M. Nakashima, Y.
Aoyama, A. Hattori, and Y. Fukuda, “Geodetic measurements and quantitative evaluation for reduced
gravitational redshift uncertainty of NICT optical frequency standards,” IFCS-EFTF 2023, in Proc. 2023 Joint
Conference of the IEEE International Frequency Control Symposium and the European Frequency and Time
Forum (IEEE IFCS-EFTF 2023) (in press).

A2. Laser Stabilization & Frequency Measurement
Several institutes in Japan conduct research and development on laser stabilization andfrequency measurement.
NICT’s strontium optical lattice clock NICT-Sr1 is recognized as a secondary frequency
standard since 2018. An updated evaluation of its frequency against remote primary standards
was reported in 2021, with an uncertainty of 1.8 × 10−16 [1]. NICT began the continuous
generation of an optically steered, physical timescale signal in July 2021, using NICT-Sr1 todetermine adjustments to the frequency of an active hydrogen maser [2]. From August 2021, thistimescale is referenced in the generation of JST, which has reduced its deviation from UTC [3].
NICT-Sr1 also contributed calibration data for the interval of International Atomic Time (TAI)each month from August 2021 to August 2022. NICT has established a collaboration with NMIJ
and KRISS to share measurement results of the optical lattice clocks at these institutes. Data is
exchanged in terms of frequency evaluations for hydrogen masers and the local realization of
UTC at each institute with respect to their optical lattice clocks, combined with comparisons ofthese local UTC realizations by the GNSS PPP technique.
At NICT, an In+ frequency standard based on sympathetic cooling with Ca+ is in development,
and in 2020 the frequency ratio of In+/Sr was measured with a fractional uncertainty of 7.7 × 10−16[4]. The major contribution to the uncertainty comes from the evaluation of micro- and secularmotion of the In+. A new approach replacing Ca+ with Yb+ for sympathetic cooling is in progress
to reduce the mass ratio from 3 to 1.5 for better control of the In+ motion.
NICT is developing frequency standards in the THz region. A 3.1 THz quantum-cascade laser
was stabilized to J = 27−26 rotational transition of CO molecules and the uncertainty wasevaluated to be 3.6 × 10−8. A portable 0.3 THz standard based on the difference-frequency
generation of two C2H2-stabilized 1.5 m lasers was developed simultaneously, with anuncertainty of 4.5 × 10−8. A theoretical study on the possibility of the precision measurement ofvibrational-rotational transition frequencies in the THz region was presented for the HeH+, NeH+,
and ArH+ molecular ions, with an expected uncertainty of 10−15 [5]. In further work, a highprecision THz counter with wide measurable bandwidth was developed using a semiconductorsuperlattice harmonic mixer, attaining an uncertainty below 1 × 10−16 over 4 octaves from 0.1 THz
to 3 THz [6].
At NMIJ, the Yb optical lattice clock NMIJ-Yb1 participated in the on-time calibration ofinternational atomic time for 13 months during the period 2021-2023, with an operating period of
5 - 30 days per month and an availability rate of more than 80%. Particularly high availability
rates of 94.5% for 30 days in August 2021 and 97.0% for 20 days in March 2022 were achieved.
In addition, the Yb optical lattice clock NMIJ-Yb1 is routinely compared with the Cs fountainclock NMIJ-F2, and a dark matter search was conducted using the data from 2020-2021. The

results show that in the very low mass region (10−22 - 10−21 eV), the coupling constants between
dark matter and electrons are more strongly constrained than in previous studies [7]. In addition,
the comparison uncertainty with UTC using the optical frequency comb could become abottleneck due to the higher accuracy of NMIJ's 171Yb optical lattice clock. To overcome thisproblem, the comparison accuracy between UTC and optical lattice clocks was improved to 4
× 10−18 by improving the precision of the system that frequency synthesizes the frep of the
optical frequency comb from 10 MHz of UTC(NMIJ) [8].
Katori group at the University of Tokyo and RIKEN is developing a transportable opticallattice clock [9] for applications in relativistic geodesy [10, 11]. The entire setup, including
lasers, optics, electronics, and physics package, has a volume of 250 L (27% of existing
systems) and a weight of 150 kg (40%), making it the most compact clock system with a target
uncertainty of ~10−18. They also propose a scheme of longitudinal Ramsey spectroscopy thatallows continuous interrogation of atoms in the lattice to improve the instability of the clockby 𝜎 ∝ 1⁄𝜏 [12]. They have succeeded in continuously extracting atoms from the magnetooptical trap with moving lattice [13]. They started developing a nuclear clock based on the lowenergy nuclear transition of thorium-229 (Th-229). The nuclear clock is expected to achieve
unprecedented accuracy because the resonance frequency of the nuclear transition is thought
to be insusceptible to the fluctuations of the environment due to the shielding by thesurrounding electron shells. Toward a nuclear clock, they trapped triply charged Th-229 ionsand performed laser spectroscopy. They also trapped Th-229 ions in the isomer state (thenuclear-excited state at 8.3 eV) and determined its nuclear properties by measuring thehyperfine constants [14].
Hong group at Yokohama National University is developing optical frequency combs andfrequency stabilized lasers. They have developed a low-repetition-rate dual comb spectrometerfor molecular spectroscopy at visible wavelengths [15]. They have also developed a 3D Yb
magneto-optical trap using a dispenser atomic source [16] and an iodine-stabilized laser at 556
nm for Yb cold atom experiments [17]. They also performed laser frequency measurement in
the short-wavelength region using an intermediate laser and a frequency noise cancellation
method [18].
Sugiyama group at Kyoto University has been developing Yb+ and Ba+ ion clocks. The groupaims at search for a temporal variation of the fine-structure constant and precise measurementof isotope shifts. Three-dimensional cooling technique has been established and the second trapsystem is being developed for Yb+ ions [19]. Optical frequency-ratio measurement systems has
been developed using octave-spanning optical frequency combs based on a mode-locked
ytterbium-doped potassium-yttrium-tungstate (Yb:KYW) laser [20].
Nakagawa group at University of Electro-Communications (UEC) have developed

transportable atomic gravimeters based on cold Rb atoms for the field applications under thenational quantum technologies program. The transportable atomic gravimeters are required forthe precision gravity measurements in the fields of geophysics, metrology, and navigation. We
developed a compact sensor head (a height of 60 cm and a diameter of 24 cm) and a transportablelaser system for the atomic gravimeter based on telecom lasers and fiber optics [21]. We achieved
a sensitivity of 1.5 × 10−8 g for the integration time of 1000 s [22].
Musha group at UEC has been developing space-borne photonic microwave frequency
references for the next-generation Japanese quasi-zenith satellite in which the frequency of afrequency-stabilized light source is down-converted to the microwave region by using an opticalfrequency comb. As an optical frequency reference, the frequency of 3rd harmonics of a 1545-nm
ECLD is stabilized in reference to the saturated absorption of iodine molecule at 515 nm. The
frequency stability of this laser is evaluated by using the H-maser-locked optical frequency comb
at NICT, and it reaches 8 × 10−15 at 1000 s. This frequency-stabilized light source will be alsoutilized for the light source of Japanese space gravitational wave detector DECIGO. The NALMtype figure-8 Er mode-lock fiber laser around 1.5 m has been also developed for the opticalfrequency comb, and self-starting of the mode-lock operation and low phase noise are achieved
which has been hardly obtained in the conventional figure-8 fiber mode-lock lasers. Our fibermode-lock lasers passed the disturbance and the thermal vacuum tests which shows their highrobustness as the space-borne laser. For the formation flying of multiple satellites in space whichis indispensable technique for DECIGO project, we propose and develop the 3-dimentional
satellite position tracking system which consists of single-frequency laser and acousto-optic
deflector (AOD). Our system has the angle resolution of 2 micro radian and length resolution of
2 m, and now plan to install it on a small engineering test satellite for the precision formation
flying in space.
Goka group at Tokyo Metropolitan University (TMU) is developing chip-scale atomic clocks.
They have developed improved measurement method in gas-cell based miniature atomic clocks
for better frequency stabilities. A simple light-shift measurement method using multiple photodetectors (MPDs) suitable for chip-scale atomic clocks (CSACs) and miniature atomic clocks(MACs) has proposed [23]. A new observation method of Ramsey–coherent population trapping(CPT) characteristics has developed by employing different laser sideband combinations as thetwo interrogation pulses [24].
[References][1]

N. Nemitz, T. Gotoh, F. Nakagawa, H. Ito, Y. Hanado, T. Ido, and H. Hachisu, “Absolute frequency of 87Sr at
1.8 × 10−16 uncertainty by reference to remote primary frequency standards,” Metrologia 58, 025006 (2021).

[2]

H. Hachisu, F. Nakagawa, Y. Hanado, and T. Ido, “Months-long real-time generation of a time scale based on anoptical clock,” Sci. Rep. 8, 4243 (2018).
[3]

H. Hachisu, H. Ito, N. Nemitz, N. Ohtsubo, Y. Miyauchi, M. Morikawa, K. Matsubara, and T. Ido, “UTC(NICT)
Referenced to a Timescale Based on the Optical Clock NICT-Sr1,” in Proc. 2023 Joint Conference of the IEEE
International Frequency Control Symposium and the European Frequency and Time Forum (IEEE IFCS-EFTF
2023) (in press).

[4]

N. Ohtsubo, Y. Li, N. Nemitz, H. Hachisu, K. Matsubara, T. Ido, K. Hayasaka, “Frequency ratio of an 115In+ ion
clock and a 87Sr optical lattice clock,” Opt. Lett. 45, 5950 (2020).

[5]

M. Kajita and N. Kimura, “Prospects for vibrational transition frequency measurement of rare-gas hydride ions,”
J. Phys. Soc. Jpn. 90, 044302 (2020).

[6]

S. Nagano, M. Kumagai, H. Ito, Y. Hanado, and T. Ido, “Terahertz frequency counter based on a semiconductorsuperlattice harmonic mixer with four-octave measurable bandwidth and 16-digit precision,” Metrologia 58,
055001 (2021).

[7]

T. Kobayashi et al., Phys. Rev. Lett. 129, 241301 (2022).

[8]

M. Wada and H. Inaba. "Femtosecond-Comb Based 10 MHz-to-Optical Frequency Link with Uncertainty at the
10−18 Level." Metrologia 59(6), 065005 (2022).

[9]

N. Ohmae, M. Takamoto, Y. Takahashi, M. Kokubun, K. Araki, A. Hinton, I. Ushijima, T. Muramatsu, T.
Furumiya, Y. Sakai, N. Moriya, N. Kamiya, K. Fujii, R. Muramatsu, T. Shiimado, and H. Katori, “Transportable
Strontium Optical Lattice Clocks Operated Outside Laboratory at the Level of 10 −18 Uncertainty,” Adv. Quant.
Tech. 4, 2100015 (2021).

[10] Y. Tanaka, and H. Katori, “Exploring potential applications of optical lattice clocks in a plate subduction zone,”J. Geod. 95, 93 (2021).
[11] M. Takamoto, Y. Tanaka, and H. Katori, “A perspective on the future of transportable optical lattice clocks,” Appl.
Phys. Lett. 120, 140502 (2022).
[12] H. Katori, “Longitudinal Ramsey spectroscopy of atoms for continuous operation of optical clocks,” App. Phys.
Exp. 14, 072006 (2021).
[13] R. Takeuchi, H. Chiba, S. Okaba, M. Takamoto, S. Tsuji, and H. Katori, “Continuous outcoupling of ultracold
strontium atoms combining three different traps,” App. Phys. Exp. 16, 042003 (2022).
[14] A. Yamaguchi, Y. Shigekawa, H. Haba, M. Wada, and H. Katori, “Laser spectroscopy of triply charged thorium
ions towards a nuclear clock”, SMI-2023, Giessen, Germany, May 8-11th, 2023.
[15] Y. Sugiyama, T. Kashimura, K. Kashimoto, D. Akamatsu, and F-L. Hong, “Precision dual-comb spectroscopyusing wavelength-converted frequency combs with low repetition rates," Scientific Reports 13, 2549 (2023).
[16] J. Nomura, T. Momma, Y. Kojima, Y. Hisai, T. Kobayashi, D. Akamatsu, and F-L. Hong, “Direct loading of Yb
atoms into a 3D magneto-optical trap from a dispenser atomic source," AIP Advances 13, 025361 (2023).
[17] Y. Tanabe, Y. Sakamoto, T. Kohno, D. Akamatsu, and F-L. Hong, “Frequency references based on moleculariodine for the study of Yb atoms using the 1S0 – 3P1 intercombination transition at 556 nm," Opt. Express 30,
46487 (2022).

[18] Y. Kojima, K. Ikeda, Y. Tanabe, D. Akamatsu, and F-L. Hong, “Laser frequency measurement at the shortwavelength region using an intermediate laser and a frequency noise cancellation method," Opt. Lett. 47, 30(2022).
[19] K. Yoshida, M. Katagiri, H.-S. Jo, Y. Ueno, T. Morimoto, K. Sugiyama, Y. Imai, “Development of two single-ion
spectroscopy system for the 2S1/2 – 2D5/2 transition in ytterbium ions towards measurement of isotope shifts,” Joint
Conference of the IEEE International Frequency Control Symposium and the European Frequency and Time
Forum (IFCS-EFTF 2023), #7147 (2023).
[20] M. Mitaki and K. Sugiyama, “Phase-locking of octave-spanning optical frequency comb based on Kerr-lensmode-locked Yb:KYW laser to reference laser,” Jpn. J. Appl. Phys. 60(2), 22003 (2021).
[21] K. Nakagawa, Development of transportable atomic gravimeters for field applications, 4th International Forumon Quantum Metrology and Sensing / QUANTUM INNOVATION 2021, Online, 8 December, 2021.
[22] T. Hojo, K. Takamura, K. Nakagawa, Development of highly sensitive gravimeter based on atom interferometry
using hybrid system for field applications, 5th International Forum on Quantum Metrology and Sensing /QUANTUM INNOVATION 2022, Online, 29 November, 2022.
[23] M. Fukuoka, A. Hanatani and S. Goka, "Novel Light-shift Measurement Method with Multiple Photo Detectors
for Gas-cell Based Atomic Clocks," 2022 Joint Conference of the European Frequency and Time Forum andIEEE International Frequency Control Symposium (EFTF/IFCS), doi: 10.1109/EFTF/IFCS54560.2022.9850834(2022).
[24] M. Fukuoka and S. Goka, "Ramsey–CPT Resonance Observation Using Different Laser Sideband Combinations
for the Two Interrogation Pulses," 2022 Joint Conference of the European Frequency and Time Forum and IEEE
International Frequency Control Symposium (EFTF/IFCS), doi: 10.1109/EFTF/IFCS54560.2022.9850881(2022).

A3. Realization of Electrical Unit (DC & LF)
A3.1 Josephson Voltage
A3.1.1 PJVS operation in dilution refregirator system
At NMIJ, A liquid-helium-free PJVS cooled with a GM cooler has been utilized since 2015 forcalibrations of Zener voltage standards with the CMC values, 8 nV for 1 V and 45 nV for 10 V,
same as those for their conventional JVS system cooled with liquid helium. They are now
attempting to operate the PJVS chip on the 4 K stage in a dilution refrigerator system toward thequantum-metrology-triangle measurement and other general applications. Up to now, they havesucceeded in the stable temperature control of the sample stages and the stable generation of thequantized voltage steps.

Fig.1 Implementation of PJVS module in a dilution refriqerator, temperature stability of 10 K stage, andquantized voltage steps generated from the PJVS.

A3.1.2 Thermodynamic temperature measurement
NMIJ measured the thermodynamic temperature of the melting point of gallium TGa using a
Johnson noise thermometer (JNT) with an integrated quantum voltage noise source (IQVNS) asa reference. TGa was calculated using the fundamental constants recommended by the Committee
on Data for Science and Technology (CODATA) for the revision of the International System ofUnits (SI). The measured TGa is consistent with the value defined in the International Temperature
Scale of 1990. The power spectral density of output signal of IQVNS has been fixed so far. In
order to use IQVNS as a reference for the measurement of thermodynamic temperature at various
temperature fixed points, the power spectral density of the output signal of IQVNS should bevariable. They improved part of the design of the device to be able to change the power spectral
density of the output signal.

A3.2 ResistanceA3.2.1 Standard Resistors
At NMIJ, development of compact and ultra-stable 1 Ω and 1 kΩ standard resistors has been
finished, and resistors with 10 kΩ are in progress of evaluation and development. The best
resistors display extremely small average drift rates and temperature coefficients, and otherperformances, e.g.,⚫

1 Ω: 4.2 nΩ/(Ω year), 4 nΩ/(Ω ˚C) at 23 ˚C,⚫

10 Ω: 0.53 nΩ/(Ω year), 1 nΩ/(Ω ˚C) at 23 ˚C,⚫

100 Ω: 50 nΩ/(Ω year), < 20 nΩ/(Ω ˚C) at 23 ˚C, deviation by transportation: < 10 nΩ/Ω,power and humidity coefficients are negligible,⚫

1 kΩ: < 10 nΩ/(Ω year), 1.7 nΩ/(Ω ˚C) at 23 ◦C.

(note that the average drift rate and temperature coefficient of each resistance value does not comefrom the same resistor). It is demonstrated that this excellent performance is suitable for utilizationin national metrology institutes and international comparisons.
Development of stable high-resistance standard resistors at NMIJ is also undergoing, and thedeveloped resistors are now commercially available as type HVR10000 series from Japan
Finechem corporation. The development is done mainly in 100 GΩ and the developed resistors
show a small temperature coefficient of less than 5 (μΩ/Ω)/K and the other characteristics are also
good.

～90 mmFig. 2 Picture and temperature-resistance curve of developed 100 Ω standard resistor.

Fig. 3 Developed high-resistance standard resistor, HVR10000 series made by Japan Finechem
corporation.

A3.2.2 DC high-resistance comparison between NIST and NMIJ
A precise high resistance comparison was performed between the traveling dual source bridge
developed by NMIJ and the adapted Wheatstone bridge of the National Institute of Standards andTechnology (NIST) from 10 MΩ to 100 TΩ at NIST. The NMIJ traveling bridge was shipped to
NIST Gaithersburg and was installed right next to the NIST bridge and these bridges alternately
measured the resistance ratio of the high resistance standards, without moving the location of theresistors inside the temperature controlled air-bath. Having the bridges and resistance standards
in the same location for the comparison decreased the transportation and temperature coefficienteffects on the resistance standards, contributing to the excellent agreement of the measured values.
The NMIJ traveling bridge used an 8.5-digit digital multimeter and a relay switch box todetermine a resistance ratio by measuring the ratio of the voltages applied to the resistors. The
comparison was started from 10 MΩ based on the same 1 MΩ standard resistor calibrated using
a NIST two-terminal cryogenic current comparator bridge, and standard resistors from 10 MΩ to
100 TΩ were calibrated by repeating 10: 1 scaling measurements with both systems. Excellent
agreement was obtained within the uncertainty of all resistance ranges and the difference between
both systems was less than 1 μΩ/Ω up to 1 TΩ and the degrees of equivalence for 10 TΩ and
100 TΩ were less than 6 μΩ/Ω [1].

Fig. 4 .DoE for the measurements from 10 MΩ to 100 TΩ
between NIST and NMIJ [1].

A3.2.3 Contact Resistance Evaluation of Wire Harness
To establish a relationship between the physical structure of electrical contact boundary andcontact resistance, NMIJ developed a method for evaluating that using a physical simulated
sample created via nanofabrication. Several samples with various distribution of “contact area”
were made and their resistances were measured precisely. It was demonstrated experimentallythat our result is in good agreement with an expression for constriction resistance.
Impedance measurement was introduced as a degradation diagnosis method for contacts of wire

harness by a nondestructive test. It was found that the changes in reactance at a certain frequency
behave characteristically and independently of the DC resistance changes during accelerated test.
The degradation degree of contacts was estimated by the change in impedance. (Contact: Yasuhiro
Fukuyama, y.fukuyama@aist.go.jp).
A3.3 DC Current (single electron pumping)
Towards a realization of the current standard based on the single-electron pumping, NMIJ
investigates the physics of low-temperature electron transport phenomena in various types ofsingle-electron devices, i.e. superconductor-insulator-normal- insulator-superconductor (SINIS)
turnstiles, gate-confined quantum dots, and graphene- or nanotube-based single-electrontransistors. On SINIS turnstiles, in their early studies, they had discovered the new phenomenon
that is a reduction of the single-electron pumping error induced by a weak magnetic field applied
to the device. The origin of this phenomenon is related to the suppression of inverse-proximity
effect at the interface between superconducting leads and a normal metal island. The inverse
proximity effect causes the quasiparticle trap at the interface, namely it leads to the overheatingof the junction. The magnetic field weaken the inverse proximity effect and helps to lease thequasiparticle. They justify this scenario from numerical analysis and controlling the tunnel
resistance. Aiming at further reducing the pumping error, they extended the research to that basedon another pumping mechanism. In one instance, they investigated a GaAs-based gate-definedquantum dot and demonstrated single-parameter pumping. In addition, they developed an airbridge based parallel integration of this pump to demonstrate a synchronized parallel pumpingthat can generate a larger current otherwise unattained. In this study, they succeeded to operate
the GaAs single electron device with sigma-delta modulated pulses for the arbitrary wave
generation. This technique is thought to be useful for the calibration of current noise in the shotnoise measurement. Also they start to measure the Si single electron pump device in collaboration
with NTT group. At present they succeeded to operate single electron pumping at 1 GHz with 10–
6uncertainty. Also we are trying to operate this type of device in parallel to generate large (a few

nano ampere) current. Four silicon pump devices are simultaneously operated at 1 GHz with 10–
6uncertainty levels inside dilution refrigerator. To test the uncertainty of pumped current, we aretrying to compare the generated current each others. These single-electron devices are planned to
be integrated with the quantum metrology triangle experiment that combine the single-electron
device with the quantum Hall resistance and Josephson voltage standards. Towards this futuristic
experiment, they had introduced a dry dilution refrigerator; An ample open space offered by thisrefrigerator allows them to integrate the whole components required for the triangle experiment
including a cryogenic current comparator into one system. Electric noise filters and highfrequency wiring are now designed and constructed to complete this setup. Also to operate

Josephson voltage standard and quantum Hall array device inside the dilution refrigerator, they
are installing additional cold stage and try to operate these quantum standards. As a result, theysucceeded to operate Josephson voltage standard inside a dilution refrigerator. They obtained 1 Vwith 4.8 × 10–10 and 2 mV with 4.3 × 10–8.
A3.4 LF-Impedance
At NMIJ, AC resistor calibration service has been kept in the range of 10 kΩ at 1 kHz. Standard
capacitor (dry-nitrogen or used silica dielectric) calibration service has been kept in the range of
10 pF up to 1000 pF at 1.592 kHz. They have started a development of precision measuring
techniques for diagnosis of the energy storage devices such as lithium-ion batteries and supercapacitors by using an impedance spectroscopy method. They have a plan to establish a metrology
for evaluating the storage power devices. Preliminary impedance measurements for lithium-ion
battery cells in the range of 10 mHz – 10 kHz demonstrated that the impedance value for unused
cells is clearly distinguished from that for used-up cells. Impedance spectra for the unused cells
which are obtained under 100 mΩ indicate that the evaluations of the uncertainties should be
required for detecting a faint sign or a symptom of degradations of storage devices. They havedeveloped an electrochemical impedance measurement system and have evaluated the type-A
uncertainty for the impedance spectra which was estimated to be less than 0.2 mΩ.
National institute of Advanced Industrial Science and Technology (AIST) established the Global
Zero Emission Research Center (GZR) in 2020. GZR has a mission for an international joint
research base for zero emission technologies. GZR started to research for innovativeenvironmental and energy technologies, including in the fields of renewable energy, storage
batteries, hydrogen, and so on. NMIJ joined in GZR and has started the research of the safety andreliability evaluation method for solid oxide electrochemical cells and lithium ion batteries byusing precision impedance and charge-discharge measurements.

Fig. 5 Photograph of the electrochemical impedance measurement system developed using the Frequency
Response Analyzer and the Potentio-Galvano Stat.

20

10000

(a)

10

10 Hz

(b)

10 mHz

a

8000

a

-10

Z'' (m)Z'' (m)

0

1 Hz

1 kHz

#b1
#b2
#b3

-20

6000

4000

#c1
#c2
#c3

2000

-30

10 mHz

10 kHz-4030

32 mHz

1 Hz

0

40

50

60

70

80

90

0

2000

4000

Z' (m)

6000

8000

10000

Z' (m)Fig. 6 Nyquist plot of the impedance spectra for the 18650-type lithium-ion batteries: (a) the unused
samples and (b) used-up samples. Obvious change in impedance spectra was observed with theprogression of the charge/discharge cycle.

A3.5 AC/DC transfer
NMIJ has provided ac-dc voltage difference transfer calibration of thermal converters in thevoltage range from 10 mV to 1000 V and in the frequency range from 10 Hz to 1 MHz, and AC
voltage calibration below 10 Hz. They have been participating in APMP. EM-K12 comparison[2], and CCEM-K6a/K9 key comparison [3]. The thin film multi-junction thermal converters witha novel design have been developed in collaboration with NIKKOHM co. ltd. We have introduced
a new thermopile pattern to improve the performance of their thin film MJTC [4]. Using these
thermal converters, novel thermal converter circuits arranged in an 2 by 2 matrix have been
fabricated to improve the low-frequency AC-DC transfer differences [5]. Thin-film AC-DC
resistor on an aluminum nitride (AlN) substrate with negligible voltage dependence have been
fabricated for measuring AC voltages up to 1000 V [6]. Toward next-generation AC/DC current
transfer standard, high-current multijunction thermal converters on a Si substrate up to 1 A havebeen designed and fabricated through the collaborative project with National Institute ofStandards and Technology in Gaithersburg [7].

Fig. 7

Toward quantum AC voltage standards, a differential sampling measurement system using an
AC-programmable Josephson voltage standard (AC-PJVS) system has been developed at NMIJ
[8]. To extend the voltage range of the system, they have combined a two-stage inductive voltage
divider and an 10 V AC-programmable Josephson voltage standard chip.

Fig. 8

Toward a waste-heat recovery with thermoelectric conversion, they have developed advanced
metrology techniques and apparatus using a precise ac and dc electrical measurement technique.
The Seebeck coefficient is an essential indicator of the conversion efficiency and the most widely
measured property specific to these materials. So far, they have developed a method to precisely
measure Thomson effect to determine the absolute Seebeck coefficient of platinum referencematerial [9,10].

ΔT
TC
TH
x=0

VoltageV

μI/K = 3

0.5

ΔT

x

emissivity = 0
emissivity = 0.3[T(x*)-T0]/(TH-TC )AC/DC current

TH
TC

Reduction by radiative heat loss

1

μI/K = 0μI/K = -30TCHeat reservoirs
Reservoir

0

TC

0.5
x* = x/l

1Fig. 9A3.6 PowerAn improved evaluation system for a wideband resistive voltage divider (WRVD) is underdevelopment at NMIJ. The fabrication of an accurate and precise WRVD based on the extended
Hamon method has been realized by direct soldering of series resistor and by soldering on theedge of round substrates for parallel resistor with suitable fixtures. The improved evaluation
system was verified with calibrated IVDs. By replacing with a phase standard, the difference fromthe calibration result by Thompson’s method has been effectively reduced comparing with theprevious system. An error simulation of the equivalent circuit of the IVDs based on the calibration
result has revealed the large quadrature error of the improved system at 50 kHz. It was considered
due to the phase error of the phase standard.

Fig. 10[References][1]

T. Oe, S. Payagala, A. R. Panna, S. Takada, N.-H. Kaneko, and D. G. Jarrett, “Precise high resistance comparison
between the NMIJ traveling dual source bridge and the NIST adapted Wheatstone bridge,” Metrologia 59(6),065007 (2022).
[2]

APMP. EM-K12, Key comparison of AC-DC current transfer standards.
(https://www1.bipm.org/kcdb/comparison?id=509)[3]

CCEM-K6.a/K9, CIPM Key Comparison of AC-DC Voltage Transfer Standards.

[4]

H. Fujiki, Y. Amagai, K. Shimizume, K. Kishino, S. Hidaka, “Fabrication of Thin Film Multijunction Thermal
Converters With Improved Long-Term Stability,” IEEE. Trans. Instrum. Meas. 64(6) (2015).

[5]

Y. Amagai, H. Fujiki, K. Okawa, N.-H. Kaneko, “Low-Frequency AC–DC Differences of a Series–Parallel Circuitof Thermal Converters,” IEEE. Trans. Instrum. Meas. 68(6) (2019).

[6]

H. Fujiki, Y. Amagai, and K. Okawa, “Establishment of High-Voltage AC–DC Voltage Transfer Standards in 1–
100-kHz Range at NMIJ,” IEEE. Trans. Instrum. Meas. 68(6) (2019).

[7]

Y. Amagai, S. Cular. J. A. Hagmann, T. E. Lipe, N.-H. Kaneko “Low-Frequency Characteristics of Silicon-Based
High-Current Multijunction Thermal Current Converters Fabricated by Wet Chemical Etching” IEEE. Trans.
Instrum. Meas. 70 (2021).

[8]

Y. Amagai, M. Maruyama, H. Yamamori, T. Shimazaki, K. Okawa, H. Fujiki, and N.-H. Kaneko, “Extending
voltage range to 10 V rms in AC–DC difference measurements with AC programmable Josephson voltage
standard” Meas. Sci. Technol. 31, 065010 (2020).

[9]

Y. Amagai, T. Shimazaki, K. Okawa, T. Kawae, H. Fujiki, and N.-H. Kaneko, “High-accuracy compensation ofradiative heat loss in Thomson coefficient measurement,” Appl. Phys. Lett. 117, 063903 (2020).

[10] Y. Amagai, T. Shimazaki, K. Okawa, T. Kawae, H. Fujiki, and N.-H. Kaneko, “Precise absolute Seebeckcoefficient measurement and uncertainty analysis using high- Tc superconductors as a reference,” Rev. Sci.
Instrum. 91, 14903 (2020).

A4. EM Field, Power Density and Antenna Measurement
Calibration service at NMIJ for the free-space antenna factor of loop antenna is available in thefrequency range of 20 Hz to 30 MHz. The expanded uncertainty of the magnetic antenna factor
is from 0.4 dB to 0.7 dB in the frequency range from 9 kHz to 30 MHz [1]. As a result of the
improvement mentioned above, NICT started to provide the magnetic-field antenna factor of loop
antennas with lower expanded uncertainty than before since June 2023. In addition, two kinds ofloop antenna calibration methods developed by NMIJ and NICT are standardized by IEC/CISPR(International Special Committee on Radio Interference) in 2022 [2].
AC Magnetic field sensor evaluation service at NMIJ is available in a range of 1 T to 150 Tfrom 50 Hz to 100 kHz. The realizable field strength depends on frequency points [3].
Novel EM-sensor and an EM visualization method by using quantum phenomena of vapor
cesium atoms are currently under development at NMIJ [4-6].
At NMIJ, calibration of the dipole antenna factor above a ground plane from 30 MHz to 1 GHz
in the specific conditions (with horizontal polarization at 2.0 m from the ground plane surface) isavailable. Since EMC (electromagnetic compatibility) measurements are ordinarily carried out infree space above 1 GHz, the dipole antenna factor from 1 GHz to 2 GHz is calibrated in an
anechoic chamber. The free space dipole factor is one of the traceability sources of the E-fieldstrength calibration in free space. The free space antenna factor calibration services for broadband
antenna for Biconical antenna (30 MHz to 300 MHz), Log periodic dipole array antenna (300
MHz to 1000 MHz) and Super broadband antenna (30 MHz to 1000 MHz) are being performed
using their original three antenna calibration method. In 2022, calibration certificates forbroadband antennas were digitized. Four digitized calibration certificates (DCCs) were issued in
December 2022. An antenna factor calibration service for the broadband horn antenna (1 GHz to
18 GHz) is available using the time-domain single antenna extrapolation method in the semianechoic chamber [7, 8]. An antenna gain calibration service for millimeter-wave standard gainhorn antenna are being performed form 50 GHz to 110 GHz and 220 GHz to 330 GHz using atime-domain processing and extrapolation technique. Compact antenna test range for 6G wirelesssystem (the frequency range of 110 GHz to 330 GHz) are now developing using offset Gregoriantype parabolic reflector (Fig.11) This system will be able to evaluate sub-THz antenna radiation
pattern and also RCS pattern of RIS (Reconfigurable Intelligent Surface) for improving 6G radio
propagation environment.

Fig.11. Offset Gregorian type parabolic reflector for evaluating 6G sub-THz antenna and RIS.

The E-field strength is one of the important quantities in the electromagnetic free field metrology
and the E-field is ordinarily measured by using a calibrated field probe. At NMIJ/AIST, thecorrection factors of the E-field probe are calibrated against the standard field levels of 10 V/m
and 20 V/m generated in a G-TEM cell. Three appropriate methods to generate standard E-field
are employed in calibrating the response of the primary optical field transfer probe depending on
the measurement frequency. A TEM cell is employed as a standard E-field generator at lower
frequencies below 900 MHz, and the E-field level generated in the anechoic chamber from
0.8 GHz to 2.2 GHz is calibrated by using the free space dipole antenna factor and measured
power at the antenna port. Transmitting antenna gain and the net power flowing into the antenna
are the traceability sources for the standard field from 2 GHz to 4 GHz. The optical E-field transfer
probe calibrated against these standard E-fields transfers the E-field level into the G-TEM cell,and then the ordinary field probe is calibrated [9].
NICT performs the calibration service for frequency standard, RF measurement instruments
such as RF power meters, RF attenuators, DC/AC calibrators, DMM and antennas to maintain theradio station licensing system according with the radio low in Japan. Especially, calibration
service of RF power meters in the frequency range up to 330 GHz has been available since 2021.
The initial purpose of the service was spurious measurements in accordance with the ITU-R
recommendation SM.32-10, however, it contributes to licensing to radio stations using 300 GHz
band, too. It has been worked out by a collaboration between NICT and NMIJ.
For electromagnetic interference (EMI) measurements in the frequency range below 30 MHz, a
test site validation method was developed by NICT [10, 11]. The method was standardized by
IEC/CISPR [12]. In addition, NICT also contributed to determination the compliance test method
standardized by IEC/CISPR [13].
[References][1]

M. Ishii, “Improvement of Uncertainty in Calibrating Primary Standard Loop Antenna by Three-antenna Method,”

2022 Conference on Precision Electromagnetic Measurements (CPEM) (2022).
[2]

IEC/CISPR, Specification for radio disturbance and immunity measuring apparatus and methods - Part 1-6: Radio
disturbance and immunity measuring apparatus - EMC antenna calibration, edition 1.2 (CISPR 16-1-6, Ed.1.2)(2022).

[3]

M. Ishii and M. Suzuki, “Impedance of Helmholtz Coils to Generate Standard AC Magnetic Fields in HighFrequency,” 2020 Conference on Precision Electromagnetic Measurements (CPEM) (2020).

[4]

M. Ishii, “A study of frequency extension of AC magnetic field sensor using radio-optical multiple resonance in
133Cs,” EMC europe 2020 (2020).

[5]

M. Ishii and M. Kinoshita, “A feasibility study of a real-time visualization method for electromagnetic fields,”
Microw. Opt. Technol. Lett. 63, 399-403 (2021).

[6]

M. Ishii, “A Feasibility Study of AC Magnetic Field Sensor in kHz-band Based on Quantum Phenomena in 133Cs,”
2022 Conference on Precision Electromagnetic Measurements (CPEM) (2022).

[7]

Y. She, S. Matsukawa, S. Kurokawa, "Uncertainty Analysis of Far-Field Gain Measuement of DRGH Using
Single-Antenna Extrapolation Method from 1 GHz to 18 GHz," 2022 MJWRT, Malaysia, (Hybrid workshop)(2022).

[8]

Y. She, S. Matsukawa, "A measurement test for antenna alignment using image processing and uncertainty
estimation, " IEICE Communications Express 12(6), 260–264 (2023).

[9]

T. Morioka, "Systematic and random errors in the net power measurement using a reflectometer," IEEE Trans.
Instrum. Meas. 70, 1010110 (2021).

[10] K. Fujii, “Basic characteristics of magnetic field antenna factor of loop antennas for EMI measurement,” IEICE
Communications Express 11(10), 643-648 (2022).
[11] K. Fujii, “Effects of feed gap arrangements of loop antennas on site validation for EMI measurements below 30
MHz,” IEICE Communications Express 11(11), 721-726 (2022).
[12] IEC/CISPR, Specification for radio disturbance and immunity measuring apparatus and methods - Part 1-4: Radio
disturbance and immunity measuring apparatus - Antennas and test sites for radiated disturbance measurements,
edition 4.2 (2023).
[13] IEC/CISPR, Specification for radio disturbance and immunity measuring apparatus and methods - Part 2-3:
Methods of measurement of disturbances and immunity - Radiated disturbance measurements, edition 4.2, (2023).

A5. Power Attenuation and Impedance Measurements
A5.1 RF-PowerNMIJ developed a WR-5 waveguide-based calorimeter for the frequency range of 140-220 GHz
in collaboration with NICT. Direct comparison calibration was demonstrated for commerciallyavailable power meters using the calorimeter as a reference standard. We have begun to provide
reference values for the WR-5 band to domestic organizations.
A5.2 RF-Attenuation and Phase Shift
NMIJ has established national standard for RF andmicrowave attenuation in the frequency range ofBlock diagram of the

1 kHz to 110 GHz, and provides its calibration
services mainly with the Japan Calibration Service
System (JCSS) scheme. All measurement andcalibration systems work based on the intermediate

attenuation measurement
system in the frequency range of
1 kHz to10 MHz works based on

frequency (IF) substitution method using the highly

the dual channel null balancing

accurate null detection and employing an inductive

techniquevoltage divider (IVD) as the reference standard. A
recent improvement was the inclusion of a newmeasurement system in the frequency range of 1 kHz

Fig.12
Fig.11

to 100 kHz, as shown in Fig. 12 to meet industry requirements for electromagnetic compatibility(EMC) [1]. These systems have been commercially manufactured by 7Gaa Corporation(https://7gaa.co.jp/) and several have been shipped to overseas NMIs for use as their national RF
attenuation standards.
NMIJ established national standard for RF phase shift in the frequency range of 10 MHz to
1 GHz. The expanded uncertainties are 0.029° for DUT with losses up to 20 dB, 0.031° for 40 dB,
and 0.056° for 60 dB loss. The frequency range is currently being expanded to 18 GHz [2, 3].
NMIJ took an initiative to organize a CIPM Key Comparison of attenuation at 18 GHz, 26.5 GHz
and 40 GHz using a step attenuator (CCEM.RF-K26) [4]. Measurements of both the first andsecond round loop were completed in February 2018. It can be said successful, although there
were some delays in the delivery of the traveling standards between the participants. The Draft B
Report is currently under review by the CCEM members.
A5.3 RF-Impedance and related measurement technology
NMIJ researched the precision on-wafer measurement techniques over 100 GHz and developed
a full-automatic RF probing system establishing high reproducibility of measurements. Balanced
type circular disk resonator method has been developped and commarcialized, in addition, themethod will be published as an IEC standardization. The method cannot only measure dielectric
permittivity but also conductivity at millimeter wave frequency (Fig.13). Furthermore,
electromagnetic sensing techniques is also researching for the agriculture products, food andinfrastructure, etc.
NMIJ as a pilot laboratory is managing the CCEM key comparison (CCEM.RF-K5c.CL: Sparameter for PC3.5 in the range from 50 MHz to 33 GHz) [5], the APMP supplemental
comparison (APMP.EM.RF-S5.CL: Dimensionally-derived characteristic impedance for PC7,
PC2.4 and PC1.85) [6] and the pilot study for material characterization.
Calibration certificates for S-parameter measurements using the vector network analyzers havebeen digitized at NMIJ. Six calibration certificates were issued in November 2022.

Fig. 13 Balanced type circular disk resonator at millimeterwave frequency

A5.4 Terahertz Metrology

Fig. 14 Photograph of the THz attenuation calibration system for free-space beams.

NMIJ developed a method for measuring terahertz (THz) attenuation for free-space beams (Fig.
14). It employs a photo-acoustic detector to compare THz attenuation to audio-frequency (AF)attenuation. The AF attenuation is directly calibrated by an inductive voltage divider as a reference
standard. Using a metalized-film attenuator, we have demonstrated attenuation measurements up

to 20 dB for 0.11 THz collimated beams.
A5.5 Material Characterization

Fig. 15 Photographs of Balanced-type circular-disk resonator(BCDR) and Measurement Results of cyclic
olefin polymers (COP) up to 120 GHz

NMIJ is researching and develops material characterization, i.e. dielectric permittivity
measurements, at the millimeterwave frequency. NMIJ developed the Balanced-type circular-disk
resonator (BCDR) and analytical software for dielectric permittivity of low loss materials.
Measurement can be performed in broad band frequency and up to 120 GHz (Fig. 15). The method
is now being standardized in the IEC standard, then the system has been provided by themeasurement instrument company. Furthermore, NMIJ as a pilot laboratory manages the Pilot
study for dielectric permittivity measurement proposed by NIST as a former pilot laboratory in it.
[References][1]

A. Widarta, “Primary standard of attenuation in the frequency range of 1 kHz to 10 MHz,” in CPEM Dig., Denver,
Co, Aug. 2020, virtual.

[2]

A. Widarta, “Precision phase shift measurement system in the frequency range of 1-18 GHz,” 50th European
Microwave Conf., Utrecht, The Netherlands, Jan. 2021, virtual.

[3]

A. Widarta, “Working Standard for RF Attenuation and Phase-shift Calibrations,” in CPEM Dig., Wellington, NZ,
Dec. 2022.

[4]

https://www.bipm.org/kcdb/comparison?id=1016[5]

https://www.bipm.org/kcdb/comparison?id=599

[6]https://www.bipm.org/kcdb/comparison?id=333