COMMISSION A:
Electromagnetic Metrology, Electromagnetic
standards(November 2016 – October 2020)

measurements

andEdited by
Hidekazu Hachisu (National Institute of Information and Communications Technology;
NICT) andMasami Yasuda (National Institute of Advanced Industrial Science and Technology, National
Metrology Institute of Japan; AIST, NMIJ)
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 (−1.1± 2.5) × 10-16. Furthermore, by measuring the frequency of NMIJ-F2 with changes of the tilt angleof the fountain, the frequency correction and uncertainty for the distributed cavity phase shift
were evaluated to be (0 ± 3.4) × 10-16. By these, the uncertainty evaluation of NMIJ-F2 wascompleted. The type A uncertainty for measurement for 20 d and the type B uncertainty are
typically 1.9 × 10-16 and 5.5 × 10-16, respectively. Ultrastable microwave oscillators: The 3rd cryorefrigerator-cooled cryogenic sapphire-resonator oscillator (cryoCSO) has been set up. The Allan
deviations of 3 cryo-CSOs were evaluated by the three-cornered-hat method, to be 2 × 10-15, 3 ×
10-15, and 4 × 10-15 at an averaging time of 1 s, respectively. One of the cryoCSOs has been
continuously operating, except during an annual scheduled power outage due to an inspection ofelectrical facilities. At present three active hydrogen maser frequency standards and one cesium
atomic clock with high-performance beam tubes (Agilent 5071A) 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
a frequency stepper (AOG). At NMIJ, Dual frequency carrier phase GPS receiver is one of themain international time and frequency transfer tools. NMIJ has the Two Way Satellite Time andFrequency Transfer (TWSTFT) facilities for Asia Pacific link and for Asia-European link.

Frequency Calibration Service at NMIJ; 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 19 in 2021.
NICT maintains Japan Standard Time (JST) and disseminates it domestically. From 2016 to
2020, the time difference of UTC(NICT) from UTC was kept within approximately 20 ns. In 2018,a substation in Kobe was opened with the purpose of distributed and integrated management ofJST. Currently, it continually operates as an emergency backup station for the Tokyo headquarters.
NICT established a new precise frequency transfer method for two-way satellite time andfrequency transfer (TWSTFT), named two-way satellite carrier-phase frequency transfer (TWCP)
and developed a frequency measurement system of optical clocks without a flywheel oscillator[Fujieda et al., 2016]. Additionally, NICT and KRISS succeeded in the optical clock comparisonof Sr and Yb optical lattice clocks by TWCP, where an uncertainty at the mid-10−16 level wasachieved after a total measurement time of 12 hours [Fujieda et al., 2018]. NICT subsequently
developed a new digital TWSTFT modem to enable TWCP and time transfer by code phase[Fujieda et al., 2020]. The performance of the new modems has been evaluated in Japanese andAsian TWSTFT links in collaboration with KRISS and TL since 2019. In National Metrology
Institutes (NMIs), the implementation of software defined receiver (SDR) has actively proceeded
into the TWSTFT earth stations to reduce instabilities with daily variation [Jiang et al., 2018]. By
adapting TWCP to wireless communication modules, wireless two-way interferometry (Wi-Wi),
was developed at NICT [Shiga et al., 2017]. Wi-Wi has already been applied to monitor distancevariations [Bohla et al., 2019] and water vapor in the atmosphere [Yasuda et al., 2019] at a mm
level of accuracy. The development of a microfabricated atomic clock has been started in NICT.
By using piezoelectric MEMS (Micro Electro-Mechanical System) and CMOS technologies, anultra-compact RF oscillator for a Rb atomic clock was developed. Its operation was verified byincorporating it into a CPT atomic clock system [Hara et al., 2018]. Furthermore, to compress thephysics package height, a reflection-type gas cell was developed by integrating an optical MEMS
device into the gas cavity [Nishino et al., 2019]. An atomic clock test bench and a fast CPT
simulator were also developed to accelerate the development activity [Yano et al., 2017] [Yano etal., 2019]. By using a custom-designed broadband feed [Ujihara et al., 2018], NICT developed abroadband VLBI (Very Long Baseline Interferometry) system for long-distance precise frequency
transfer. Transportable 2.4 m diameter VLBI terminals were installed at NICT (Japan) and INAF
(National Institute for Astrophysics, Italy) for frequency ratio measurement between the Sr opticallattice clock at NICT and an Yb optical lattice clock at INRIM (National Institute of MetrologicalResearch, Italy). VLBI observations were conducted pairing these two small antennas with the
Kashima 34 m radio telescope in 2018-2019 [Pizzocaro et al., 2021] [Sekido et al., 2021]. The

Kashima 34 m radio telescope used in this project was forced to end its operation due to serious
damage caused by the typhoon Faxai on 9 Sep. 2019 and it was dismantled in 2020. This telescope
had been constructed as an element of the Western Pacific Radio Interferometer in 1988 andplayed an important role in VLBI technology developments and international observations in thefield of geodesy and astronomy.
[References]
Bhola R P, Kido K, Yasuda S, Hanado Y, Kawamura S, Hanado H, Takizawa K, Inoue M, andShiga N [2019], “Distance Variation Monitoring with Wireless Two-way Interferometry (Wi-Wi),”
Sens. Mater. 31 (7), 2313-2321.
Fujieda M, Ido T, Hachisu H, Gotoh T, Takiguchi H, Hayasaka K, Toyoda K, Yonegaki K, Tanaka
U, and Urabe S [2016], “Frequency measurement system of optical clocks without a flywheel
oscillator,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control. 63 (12), 2231-2236
Fujieda M, Yang S-H, Gotoh T, Hwang S-W, Hachisu H, Kim H, Lee Y-K, Tabuchi R, Ido T,
Lee W-K, Heo M-S, Park C-Y, Yu D-H, Petit G [2018], “Advanced Satellite-based Frequency
Transfer at the 10−16 Level,” IEEE Ultrason. Ferroelectr. Freq. Control 65 (6), 973-978.
Fujieda M, R. Tabuchi, T. Gotoh [2020], “DEVELOPMENT OF A NEW DIGITAL TWSTFT
MODEM”, Int. J. Electr. Eng. 27 (4), 141-145.
Hara M, Yano Y, Kajita M, Nishino H, Ibata Y, Toda M, Hara S, Kasamatsu A, Ito H, Ono T, and
Ido T [2018], “Microwave oscillator using piezoelectric thin-film resonator aiming forultraminiaturization of atomic clock,” Rev. Sci. Instrum. 89 (10), 105002.
Jiang Z, Zhang V, Huang Y-J, Achkar J, Piester D, Lin S-Y, Wu W, Naumov A, Yang S-H,
Nawrocki J, Sesia I, Schlunegger C, Yang Z, Fujieda M, Czubla A, Esteban H, Rieck C,
Whibberley P [2018], “Use of software-defined radio receivers in two-way satellite time andfrequency transfers for UTC computation,” Metrologia 55, 685-698.
Nishino H, Yano Y, Hara M, Toda M, Kajita M, Ido T, and Ono T [2019], “Reflection-type vapor
cell for micro atomic clocks using local anodic bonding of 45° mirrors,” Opt. Lett. 46 (10), 22722275.
Pizzocaro M, Sekido M, et al. [2021] “Intercontinental comparison of optical atomic clocks

through very long baseline interferometry,” Nat. Phys. 17(2), 223-227, DOI: 10.1038/s41567020-01038-6.
Sekido M, et al., [2021] “A broadband VLBI system using transportable stations for geodesy andmetrology - An alternative approach to the VGOS concept -,” J Geod 95 (41), DOI:
10.1007/s00190-021-01479-8 25.
Shiga N., Kido K, Yasuda S, Patna B, Hanado Y, Kawamura S, Hanado H, Takizawa K, and Inoue
M[2017],“Demonstrationofwireless

two-wayinterferometry(Wi-Wi),”

IEICE

Communications Express 6 (2), 77-82.
Ujihara H, et al. [2019], “Development of wideband antennas”, International Symposium on
Advancing Geodesy in a Changing World, DOI: 10.1007/1345_2018_41.
Yano Y, Goka S and Kajita M [2017], “Two-step pulse observation to improve resonance contrast
for coherent population trapping atomic clocks,” Appl. Phys. B 123, 67 1-8
Yano Y, Kajita M, Ido T, and Hara M [2019], “Fast numerical analysis of the time response incoherent population trapping resonance based on Galerkin spectral method,” Jpn. J. Appl. Phys
58 (SG), SGGB05.
Yasuda S, Ichikawa R, Hanado Y, Kawamura S, Hanado H, Iwai H, Namba K, Okamoto Y,
Fukunaga K, Iguchi T, Shiga N [2019], “Horizontal atmospheric delay measurement using
wireless two-way interferometry (Wi-Wi),” Radio Sci. 54, 572.

A2. Laser Stabilization & Frequency Measurement
The research and development on laser stabilization and frequency measurement at several
institutes in Japan.
NICT reported the absolute frequency of an 87Sr optical lattice clock by reference toInternational Atomic Time (TAI) at an uncertainty of less than 10−15 [Hachisu et al., 2017a], andreached an uncertainty at the low 10−16 level after this [Hachisu et at., 2017b]. This contributed to
the 2017 update of the CIPM recommendation value. NICT was first to use an optical clock to
generate an actual time scale signal for nearly half a year. The measurements over that interval
were also used to evaluate the TAI scale interval [Hachisu et al., 2018]. The clock wasconsequentially recognized as a secondary frequency standard in 2018, and has formallyparticipated in TAI calibration after this. The clock measurements also contributed to aninternational dark matter search led by the Nicolaus Copernicus University in Poland [Wcisło etal., 2018]. At NICT, a new frequency standard based on the In+ 1S0-3P0 transition frequency is
now in development [Ohtsubo et al., 2019]. In 2017, a new measurement of the clock frequencyof this standard was reported with an uncertainty of 10−15 order, which contributed to the updateof the CIPM recommended value [Ohtsubo et al., 2017]. In 2020, the frequency ratio of In+/Sr
was measured with an uncertainty of 7.7 × 10−16 [Ohtsubo et al., 2020]. In theoretical work at
NICT, the attainable uncertainty of the vibrational transition frequencies of O2+ molecular ion was
estimated to be lower than 10−17 [Kajita, 2017]. The possibility to establish the frequency standard
in the terahertz region was discussed. The (J, F) = (0,1/2) – (1,1/2) (J: rotational state, F:
hyperfine state) transition of QH+ (Q: even isotope of alkali earth atom or rare gas atom) is freefrom the electric quadrupole shift. Using these molecular ions, trapped in a linear trap andsympathetically cooled, a measurement uncertainty below 10−15 is attainable when the magnetic
field is maintained to below 1 mG [Kajita et al., 2020a] [Kajita et al., 2020b]. NICT also
developed an apparatus for the frequency comparison of two THz waves at separate locations[Nagano et al., 2017].
At NMIJ, the systematic uncertainty of the 171Yb lattice clock (1S0-3P0 transition) has been
evaluated to be 3.6 × 10-16 in 2018 [Kobayashi et al., 2018]. This robust Yb lattice clock with
automatic laser frequency re-lock systems [Kobayashi et al., 2019] was successfully used forcalibrating TAI with uptime ratio of 80 % for six months [Kobayashi et al., 2020]. The frequency
ratio of the clock transitions in Sr and Yb was measured by an optical direct frequency link
between two independent optical lattice clocks of Sr and Yb in 2021. The fractional uncertaintyof the measurement was 4.1 × 10-16 [Hisai et al., 2021].
Katori group at the University of Tokyo and RIKEN has developed optical lattice clocks toestablish accurate frequency standards, and is exploring applications in fundamental physics andrelativistic geodesy. They have investigated higher-order lattice light shifts to reduce theuncertainty of the clock to less than 10-18, and determined the optimal parameters for thefrequency and intensity of the lattice laser with Sr [Ushijima et al., 2018] and Yb atoms [Nemitz
et al., 2019]. The frequency ratio between the different clock transitions gives insight into
exploring fundamental physics and validation of measurements that support the redefinition of
the second. They have demonstrated cooling of Cd atoms as a new candidate for OLCs
[Yamaguchi et al., 2019], developed stable single-branch Er-combs for frequency comparison[Ohmae et al., 2017], compared 87Sr and 88Sr isotopes [Takano et al., 2017], and completed theloop closure over the frequency ratios among Sr, Yb, and Hg atoms [Ohmae et al., 2020]. They
have also developed a transportable optical lattice clock that operates with an uncertainty of
10-18 even in the field environment. A pair of clocks was transported to TOKYO Skytree to test
general relativity with an uncertainty of 10-5, comparable to that of space experiments[Takamoto et al., 2020]. A long-distance optical fiber link was developed between RIKEN, theUniversity of Tokyo, and NTT for application in future optical lattice clock networks [Akatsuka
et al., 2020]. Other applications of magic-wavelength protocols have also been explored, suchas atomic interferometry in magic-wavelength dipole traps [Akatsuka et al., 2017], superradiantclocks inside hollow-core fibers [Okaba et al., 2019], and mid-infrared laser cooling inmetastable states of Sr atoms for continuous operation of OLCs [Hashiguchi et al., 2019].
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 [Ikeda et al., 2020]. They have also developed an iodine-stabilized
laser at telecom wavelength for applications including optical frequency standards [Ikeda et al.,2020]. Prof. Hong has summarized recent research activities of optical frequency standards in areview article [Hong, 2017].
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. Micromotion minimization has been improved in three dimensions for aconventional RF trap and a linear RF trap. Optical frequency-ratio measurement systems has
been developed using octave-spanning optical frequency combs based on a mode-lockedtitanium-sapphire laser [Hatanaka et al., 2017] and a ytterbium-doped potassium-yttriumtungstate (Yb:KYW) lasers [Mitaki et al., 2018] [Mitaki et al., 2021].
Nakagawa group at University of Electro-communications (UEC) has developed an opticalfrequency synthesizer for the precision spectroscopy of Rydberg states of Rb atoms using an
Er fiber-based optical frequency comb. They demonstrate the high resolution spectroscopy ofthe nD (n=53-92) and nS (n=60-90) Rydberg states of 87Rb and measure the absolute
frequencies of these transitions with an uncertainty of 250 kHz [Watanabe et al., 2017]. They
have also developed a quantum simulator based on cold Rydberg atoms in microtrap arrays,

and demonstrate quantum many-body dynamics of Ising-type quantum spin model with up to six
interacting spins [Tamura et al., 2020].
Musha group at UEC has developed the space-borne precision microwave frequency reference
for Japanese next-generation quasi-zenith satellite, whose frequency stability reaches 10-15 level
for averaging time of more than 1000 s. The optical frequency reference from the iodine-stabilized
fiber DFB laser at 1 um is down-converted to the microwave region without phase noise
degradation by using an optical frequency comb. For the space-borne optical frequency comb, therobust fiber mode-lock laser has been developed which consists of all-PM figure-8 type NALM
oscillator [Takeuchi et al., 2020]. For the compact and robust trapping light source for the Sr
optical lattice clock, a Tm-doped ZBLAN fiber MOPA (master oscillator power amplifier) has
developed. By utilizing self-breaching effect for compensating photodarkening, a stable operationof 2-W narrow-linewidth 813-nm light has been achieved [Kajikawa et al., 2019]. We have also
developed a space borne high-power and highly-stabilized laser for the space gravitational wave
detector DECIGO [Suemasa et al., 2017, 2018]
Goka group at Tokyo Metropolitan University (TMU) is developing chip-scale atomic clocks.
They have developed gas-cell based miniature atomic clocks with better frequency stabilities byusing improvement methods. A frequency drift detection method was demonstrated using a dual
alkali microelectromechanical system (MEMS) cell to improve the long-term stability [Furuse etal., 2017]. A two-step pulse observation method in a two-step Raman–Ramsey scheme wasproposed and showed a good contrast and lower light-shift of the coherent population trapping(CPT) resonances [Yano et al., 2017]. A miniaturized ultralow-power atomic clock (ULPAC) withthe frequency stability of 2.2 × 10-12 at an averaging time of 105 s and 59.9 mW power
consumption was demonstrated [Zhang et al., 2019]. The ULPAC was operated with a proposedfrequency drift reducing method [Yanagimachi et al., 2020].
[References]
Akatsuka T, Takahashi T, and Katori H [2017], “Optically guided atom interferometer tuned to
magic wavelength,” Appl. Phys. Express 10, 112501.
Akatsuka T, Goh T, Imai H, Oguri K, Ishizawa A, Ushijima I, Ohmae N, Takamoto M, Katori H,
Hashimoto T, Gotoh H, and Sogawa T [2020], “Optical frequency distribution using laser repeater
stations with planar lightwave circuits,” Opt. Express 28, 9186.
Furuse Y, Kase Y, Goka S [2017], “Frequency drift detection method using dual alkali gas forcoherent population trapping atomic clocks,” 2017 Joint Conference of the European Frequency
and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS), 328-331.

Hachisu H, Petit G, and Ido T [2017a] “Absolute frequency measurement with uncertainty below
1×10−15 using International Atomic Time,” Appl. Phys. B 123, 34 1-5.
Hachisu H, Petit G, Nakagawa F, Yuko Y, and Ido T [2017b], “SI-traceable measurement of an
optical frequency at the low 10−16 level without a local primary standard,” Opt. Express 25, 8511.
Hachisu H, Nakagawa F, Hanado Y, and Ido T [2018], “Months-long real-time generation of atime scale based on an optical clock,” Sci. Rep. 8, 4243.
Hashiguchi K, Akatsuka T, Ohmae N, Takamoto M, and Katori H [2019], “Frequency
measurement on the 5s5p 3P2 - 5s4d 3D3 transition of 88Sr atoms using the photon-momentumtransfer technique,” Phys. Rev. A 100, 042513.
Hatanaka S, Sugiyama K, Mitaki M, Misono M, Slyusarev S N, and Kitano M [2017], “Phaselocking of a mode-locked titanium-sapphire laser-based optical frequency comb to a reference
laser using a fast piezoelectric actuator,” Appl. Opt. 56(12), 3615-3621.
Hisai Y, Akamatsu D, Kobayashi T, Hosaka K, Inaba H, Hong F-L, Yasuda M [2021], “Improved
frequency ratio measurement with 87Sr and 171Yb optical lattice clocks at NMIJ,” Metrologia 58,
015008.
Hong F-L [2017], “Optical frequency standards for time and length applications,” Meas. Sci.
Technol. 28, 012002.
Ikeda K, Yamada Y, Kato H, Yoshii K, Okubo S, Inaba H, and Hong F-L [2020], “Developmentof 19.8-MHz-repetition-rate optical frequency combs for dual-comb spectroscopy,” Jpn. J. Appl.
Phys. 59, 028002.
Ikeda K, Okubo S, Wada M, Kashiwagi K, Yoshii K, Inaba H, and Hong F-L [2020], “Iodinestabilized laser at telecom wavelength using dual-pitch periodically poled lithium niobate
waveguide,” Opt. Express 28, 2166.
Kajikawa E, Ishii T, Kubo T, Takeuchi Y, Ogawa K, Musha M [2019], “Dual-wavelengthpumped Tm3+-doped ZBLAN fiber MOPA at 813 nm,” Opt. Lett. 44, 2875-2878.
Kajita M [2017], “Accuracy estimation of the 16O2+ transition frequencies targeting the search forthe variation in the proton-electron mass ratio,” Phys. Rev. A 95, 023418 1-6.
Kajita M, Bala R, and Abe M [2020a], “Attainable accuracies of QH+ rotational transition
frequencies (Q:40Ca, 24Mg, 202Hg),” J. Phys. B At. Mol. Opt. Phys. 53, 085401.
Kajita M and Kimura N [2020b], “Prospect in rare-gas hydride ions for terahertz frequency
standards,” J. Phys. B At. Mol. Opt. Phys. 53, 135401.
Kobayashi T, Akamatsu D, Hisai Y, Tanabe T, Inaba H, Suzuyama T, Hong F-L, Hosaka K, Yasuda
M [2018], “Uncertainty evaluation of an 171Yb optical lattice clock at NMIJ,” IEEE Trans.
Ultrason. Ferroelectr. Freq. Control, 65(12), 2449.
Kobayashi T, Akamatsu D, Hosaka K, Yasuda M [2019], “A relocking scheme for optical phaselocking using a digital circuit with an electrical delay line,” Rev. Sci. Instrum. 90, 103002.
Kobayashi T, Akamatsu D, Hosaka K, Hisai Y, Wada M, Inaba H, Suzuyama T, Hong F-L, Yasuda
M [2020], “Demonstration of the nearly continuous operation of an 171Yb optical lattice clock forhalf a year,” Metrologia 57, 065021.
Mitaki M, Sugiyama K, and Kitano M [2018], “Octave-spanning optical frequency comb basedon a laser-diode pumped Kerr-lens mode-locked Yb:KYW laser for optical frequency
measurement,” Appl. Opt. 57(18), 5150-5160.
Mitaki M and Sugiyama K [2021], “Phase-locking of octave-spanning optical frequency comb
based on Kerr-lens mode-locked Yb:KYW laser to reference laser,” Jpn. J. Appl. Phys. 60(2),22003.
Nagano S, Kumagai M, Ito H, Kajita M, and Hanado Y [2017], “Phase-coherent transfer andretrieval of terahertz frequency standard over 20 km optical fiber with 4×10−18 accuracy,” Appl.
Phys. Express 10, 012502 1-4.
Nemitz N, Jørgensen A, Yanagimoto R, Bregolin F, and Katori H [2019], “Modeling light shifts
in optical lattice clocks,” Phys. Rev. A 99, 033424.
Ohmae N, Kuse N, Fermann M E, and Katori H [2017], “All-polarization-maintaining, singleport Er:fiber comb for high-stability comparison of optical lattice clocks,” Appl. Phys. Express

10, 062503.
Ohmae N, and Katori H [2019], “626-nm single-frequency semiconductor laser system operated
near room temperature for mW-level second-harmonic generation at 313 nm,” Rev. Sci. Instrum.
90, 063201
Ohmae N, Bregolin F, Nemitz N, and Katori H [2020], “Direct measurement of the frequency
ratio for Hg and Yb optical lattice clocks and closure of the Hg/Yb/Sr loop,” Opt. Express 28,
15112.
Ohtsubo N, Li Y, Matsubara K, Ido T, and Hayasaka K [2017], “Frequency measurement of theclock transition of an indium ion sympathetically-cooled in a linear trap,” Opt. Express 25, 11725.
Ohtsubo N, Li Y, Nemitz N, Hachisu H, Matsubara K, Ido T, and Hayasaka K [2019], “Opticalclock based on a sympathetically-cooled indium ion,” Hyperfine Interactions 240, 39.
Ohtsubo N, Li Y, Nemitz N, Hachisu H, Matsubara K, Ido T, and Hayasaka K [2020], “Frequency
ratio of an 115In+ ion clock and a 87Sr optical lattice clock,” Opt. Lett. 45, 5950.
Okaba S, Yu D, Vincetti L, Benabid F, and Katori H [2019], “Superradiance from lattice-con ﬁned
atoms inside hollow core ﬁbre,” Commun. Phys. 2, 136.
Suemasa A, Shimo-oku A, Nakagawa K, Musha M, [2017], “Developments of high frequency
and intensity stabilized lasers for space gravitational wave detector DECIGO/B-DECIGO,”
CEAS space journal 9, 485-491.
Suemasa A, Shimo-oku A, Ohtsuka S, Nakamori M, Musha M [2018], “Stable and high power
515-nm lasers for the space gravitational wave detector: DECIGO,” Proceedings of ICSO2018
3c, 1220.
Takamoto M, Ushijima I, Ohmae N, Yahagi T, Kokado K, Shinkai H, and Katori H [2020], “Testof general relativity by a pair of transportable optical lattice clocks,” Nat. Photonics 14, 411-415.
Takano T, Mizushima R, and Katori H [2017], “Precise determination of the isotope shift of 88Sr
– 87Sr optical lattice clock by sharing perturbations,” Appl. Phys. Express 10, 072801.

Takeuchi Y, Saito R, Endo S, Matsusaka K, Musha M [2020], “Development of an all PM mode
lock fiber laser for space borne frequency reference,” Proceeding of SPIE 11852, 118523O-2.
Tamura H, Yamakoshi T and Nakagawa K [2020], “Analysis of coherent dynamics of a Rydbergatom quantum simulator,” Phys. Rev. A 101, 043421 1-8.
Ushijima I, Takamoto M, Katori H [2018], “Operational Magic Intensity for Sr Optical Lattice
Clocks,” Phys. Rev. Lett. 121, 263202.
Watanabe N, Tamura H, Musha M, and Nakagawa K [2017], “Optical frequency synthesizer for
precision spectroscopy of Rydberg states of Rb atoms,” Jpn. J. Appl. Phys. 56, 112401 1-5.
Wcisło P., P. Ablewski, K. Beloy, S. Bilicki, M. Bober, R. Brown, R. Fasano, R. Ciuryło, H.
Hachisu, T. Ido, J. Lodewyck, A. Ludlow, W. McGrew, P. Morzyński, D. Nicolodi, M. Schioppo,
M. Sekido, R. Le Targat, P. Wolf, X. Zhang, B. Zjawin, and M. Zawada [2018], “New bounds ondark matter coupling from a global network of optical atomic clocks,” Sci. Adv. 4, eaau4869.
Yamaguchi A, Safronova M S, Gibble K, and Katori H [2019], “Narrow-line Cooling andDetermination of the Magic Wavelength of Cd,” Phys. Rev. Lett. 123, 113201.
Yanagimachi S, Harasaka K, Suzuki R, Suzuki M, Goka S [2020], “Reducing frequency driftcaused by light shift in coherent population trapping-based low-power atomic clocks,” Appl. Phys.
Lett. 116, 104102.
Yanagimoto R, Nemitz N, Bregolin F, and Katori H [2018], “Decomposed description of Ramsey
spectra under atomic interactions,” Phys. Rev. A 98, 012704.
Yano Y, Goka S, Kajita M [2017], “Two‑step pulse observation to improve resonance contrast forcoherent population trapping atomic clock,” Appl. Phys. B 123, 67.
Zhang H, Herdian H, Narayanan A T, Shirane A, Suzuki M, Harasaka K, Adachi K, Goka S,
Yanagimachi S, Okada K [2019], “ULPAC: A Miniaturized Ultralow-Power Atomic Clock,” inIEEE Journal of Solid-State Circuits 54(11), 3135-3148.

A3. Realization of Electrical Unit (DC & LF)
Research works and developments on dc and low frequency electrical standards are
implemented in the electrical standards area of Research Institute for Physical Measurement in
NMIJ, partly in collaboration with several other institutes in the Advanced Industrial Science andTechnology (AIST). In the five research groups of the electrical standards area, the Applied
Electrical Standards Group and the Quantum Electrical Standards Group covers A3 Field.
A liquid-helium-free PJVS has been utilized since 2015 for calibrations of Zener voltage
standards with the CMC values, 8 nV for 1 V and 45 nV for 10 V, same as those for ourconventional JVS system cooled with liquid helium. We are now attempting to develop an AC
voltage calibration system using PJVS. Development of Zener voltage standards are also now inprogress in collaboration with ADC Corporation. We are continuing to investigate theenvironmental-condition dependences of the voltage outputs of prototype Zener modules (Fig.
3.1). Excelent stability in the nominal 10 V and 7.2 V outputs for temperature, ambient-pressure
and relative-humidity changes has been confirmed.

Fig.3.1 Prototype of a Zener votage standard and its relative-humidity dependence.

We 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 fixedso 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 be variable. We improved part of the design of the device to be able to change the power
spectral density of the output signal.
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 other performances (Fig.
3.2), 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.
～90 mmFig. 3.2 Picture and temperature-resistance curve of developed 100 Ω standard resistor.

Some 1 MΩ quantum Hall array devices were fabricated and evaluated (Fig. 3.3). The devices
have simple configuration and consist of 88 Hall bars. They have the nominal quantized resistancevalue of 106×(1 + 246.289×10-6) Ω and its quantized value was evaluated using a cryogenic
current comparator (CCC) bridge at NIST. The below graph shows the magnetic field dependenceof the device. At the center of the plateau, the measurement was repeated some times and themeasured value was scattered from –18 nΩ/Ω to +17 nΩ/Ω and the averaged value was +4 µΩ/Ω. The devices showed flat magnetic field dependence for more than 1 T.

Fig. 3.3 Picture and the magnetic field dependence of the 1 MΩ array device.

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 ofwire 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.
Towards a realization of the current standard based on the single-electron pumping, weinvestigate 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 our early studies, we had discovered the new phenomenon that is areduction of the single-electron pumping error induced by a weak magnetic field applied to thedevice. 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 theoverheating of the junction. The magnetic field weaken the inverse proximity effect and helps tolease the quasiparticle. We justify this scenario from numerical analysis and controlling the tunnel
resistance. Aiming at further reducing the pumping error, we extended the research to that basedon another pumping mechanism. In one instance, we investigated a GaAs-based gate-definedquantum dot and demonstrated single-parameter pumping. In addition, we 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, we 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 shot noise
measurement. Also we start to measure the Si single electron pump device in collaboration withNTT group. At present we succeeded to operate single electron pumping at 1 GHz with 10-6
uncertainty. Now we try to operate this type of device in parallel to generate large (a few nanoampere) current.
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 andJosephson voltage standards. Towards this futuristic experiment, we had introduced a dry dilution
refrigerator; An ample open space offered by this refrigerator allows us to integrate the whole
components required for the triangle experiment including a cryogenic current comparator into
one system. Electric noise filters and high-frequency 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, we are installing additional cold stage and try to operate thesequantum standards.
AC resistor calibration service has been kept in the range of 10 Ω up to 100 kΩ at 1 kHz and
10 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 kHz, 1.592 kHz.
NMIJ has started a development of precision measuring techniques for diagnosis of the energy
storage devices such as lithium-ion batteries and super-capacitors by using an impedance
spectroscopy method. We have a plan to establish a metrology for evaluating the storage powerdevices. Preliminary impedance measurements for lithium-ion battery cells in the range of 10mHz – 10 kHz demonstrated that the impedance value for unused cells is clearly distinguishedfrom that for used-up cells. Impedance spectra for the unused cells which are obtained under 100mΩ indicate that the evaluations of the uncertainties should be required for detecting a faint signor a symptom of degradations of storage devices. We have developed 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 (Fig .3.4, Fig.3.5).
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 toresearch for innovative environmental and energy technologies, including in the fields ofrenewable energy, storage batteries, hydrogen, and so on. NMIJ joined in GZR and has started theresearch of the safety and reliability evaluation method for solid oxide electrochemical cells andlithium ion batteries by using precision impedance and charge-discharge measurements.

Fig. 3.4 Photograph of the electrochemical impedance measurement system developed using theFrequency 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

Z' (m)

4000

6000

8000

10000

Z' (m)Fig. 3.5 Nyquist plot of the impedance spectra for the 18650-type lithium-ion batteries: (a) theunused samples and (b) used-up samples. Obvious change in impedance spectra was observed withthe progression of the charge/discharge cycle.

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. We have been participating in APMP Comparison for "APMP.EM-K12" of AC/DC current transfer difference, and “CCEM-K6a/K9” of AC/DC voltage
transfer difference.
The thin film multi-junction thermal converters with a novel design have been developed at
NMIJ/AIST in collaboration with NIKKOHM Co. Ltd.

We have introduced a new thermopile

pattern to improve the performance of our thin film MJTC [Amagi et al., 2015a]. 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 [Amagai et al., 2019]. Thinfilm AC-DC resistor on an AlN substrate with negligible voltage dependence have been fabricatedfor measuring AC voltages up to 1000 V. Toward next-generation AC/DC current transfer standard,high-current multijunction thermal converters on Si substrates up to 1 A have been designed andfabricated through the collaborative project with NIST in Gaithersburg. The results were
presented at NCSLI/CPEM2020 and a joint paper was submitted.

Fig. 6
Toward quantum AC voltage standards, a differential sampling measurement system using an

AC-programmable Josephson voltage standard (AC-PJVS) system has been developed [Amagai
et al., 2020]. To extend the voltage range of the system, we have combined a two-stage inductive
voltage divider and an 10 V AC-programmable Josephson voltage standard chip.

Fig. 7

Toward a waste-heat recovery with thermoelectric conversion, we have developed advanced
metrology techniques and apparatus using a precise ac and dc electrical measurement technique.
In particular, the Seebeck coefficient is an essential indicator of the conversion efficiency and themost widely measured property specific to these materials. So far, we have developed a method
to precisely measure Thomson effect to determine the absolute Seebeck coefficient of platinumreference material [Amagai et al., 2015b] [Amagai et al., 2019b] [Amagai et al., 2020]. We havealso precisely measured the absolute Seebeck coefficient of the fine Pt sample at low temperature
below 100 K using a high-Tc superconductor as a reference [Amagai 2020].

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. 8[References]
Amagai Y, Fujiki H, Shimizume K, Kishino K and Hidaka S [2015a], “Improvements in the LowFrequency Characteristic and Sensitivity of a Thin-Film Multijunction Thermal Converter in
Vacuum,” IEEE Trans. Instrum. Meas. 64(6), 1570-1575, doi: 10.1109/TIM.2014.2385133.
Amagai Y, Fujiki H, Okawa K and Kaneko N [2019a], “Low-Frequency AC–DC Differences ofa Series–Parallel Circuit of Thermal Converters,” IEEE Trans. Instrum. Meas. 68(6), 1907-1912,
doi: 10.1109/TIM.2018.2882929.
Amagai Y, et al. [2020], Meas. Sci. Technol. 31, 065010.
Amagai Y, Yamamoto A, Akoshima M, Fujiki H and Kaneko N [2015b], “AC/DC Transfer
Technique for Measuring Thomson Coefficient: Toward Thermoelectric Metrology,” IEEE Trans.
Instrum. Meas. 64(6), 1576-1581, doi: 10.1109/TIM.2014.2381752.
Amagai Y, Shimazaki T, Okawa K, Fujiki H, Kawae T, and Kaneko N-H, [2019b] AIP Advances
9, 065312, https://doi.org/10.1063/1.5095485.
Amagai Y, Shimazaki T, Okawa K, Kawae T, Fujiki H, and Kaneko N-H, [2020a], Appl. Phys.
Lett. 117, 063903, https://doi.org/10.1063/5.0018593.
Amagai Y, Shimazaki T, Okawa K, Kawae T, Fujiki H, and Kaneko N-H, [2020b], Rev. Sci.
Instrum. 91, 014903, https://doi.org/10.1063/1.5122226.

A4. EM Field, Power Density and Antenna Measurement
At NMIJ, a calibration service for the free-space antenna factor on loop antenna is maintainedin the frequency range of 20 Hz to 30 MHz. The expanded uncertainty of the magnetic antenna
factor was improved to be from 0.4 dB to 0.7 dB in the frequency range from 9 kHz to 30 MHz
in December 2019.
AC Magnetic field sensor calibration service is maintained in a range of 1 uT to 150 uT from50 Hz to 100 kHz. The realizable field strength depends on frequency points.
NMIJ is also developing a novel EM-sonsor and an EM visualization method by using quantum
phenomena of vapor cesium atoms.
[References][1] M. Ishii and M. Kinoshita, “A feasibility study of a real-time visualization method forelectromagnetic fields,” Microw. Opt. Technol. Lett. 63, 399-403 (2021).
[2] M. Ishii, “A study of frequency extension of AC magnetic field sensor using radio-opticalmultiple resonance in 133Cs,” EMC europe 2020, 2020.
[3] M. Ishii and M. Suzuki, “Impedance of Helmholtz Coils to Generate Standard AC Magnetic
Fields in High Frequency,” 2020 Conference on Precision Electromagnetic Measurements(CPEM), 2020.
[4] M. Kinoshita and M. Ishii, “Visualization of radio-frequency waves via double resonancespectroscopy of cesium atoms,” Jpn. J. Appl. Phys. 58(5), 052004-1-5 (2019).
[5] M. Ishii, “A feasibity study of AC magnetic field sensor in low-frequency using multiradiooptical resonance in 133Cs,” vol. 1, pp. 760, Proceedings of EMC Sapporo & APEMC
2019 (2019).
[6] M. Ishii, J. H. Kim, Y. Ji, and C. H. Cho, “Final report on APMP.RF-S21.F,” Metrologia
55(1A), 01003 (2018).
Calibration of the dipole antenna factor above a ground plane from 30 MHz to 1 GHz with thespecific conditions (with horizontal polarization and 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 a traceability source of the E-field strength.
[References][1] T. Morioka, “Time-domain mixed-mode site attenuation measurement," IEEE Trans. on
Electromagn. Compat. 62(6), 2650-2660 (2020).
[2] T. Morioka, “Improvement of anechoic chamber performance by the time-domain analysis,”

in Proc. of EMC Sapporo and APEMC 2019, Sapporo, Japan, 2019.
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 our original three antenna
calibration method. The eight calibration services have been provided to the client in between
2018 and the present.
[References][1] S. Matsukawa and S. Kurokawa, “Antenna gain self-calibration for Double Ridged Guide
Horn Antenna using bi-directional optical fiber link transceiver,” ECTI-CON2019, pp. 1-4,
Pattaya, Thailand, 10-13 July 2019.
[2] S. Matsukawa, S. Kurokawa and, M. Hirose, “Uncertainty Analysis of Far-Field Gain
Measurement of DRGH Using the Single-Antenna Method and Amplitude Center Distance,”
IEEE Tran. Instrum. Meas. 68(6), 1756-1754 (2019).
[3] S. Matsukawa, S. Kurokawa, M. Ameya and Y. She, “Influence of reflection area on
calibration accuracy by single antenna method using broadband antenna,” CPEM2018, pp. 12, Paris, France, 8-13 July, 2018.
An antenna factor calibration service for the broadband horn antenna (1 GHz to 18 GHz) isavailable using the time-domain single antenna extrapolation method in the semi-anechoic
chamber.
An antenna gain calibration service for millimeter-wave standard gain horn antenna are being
performed form 50 GHz to 75 GHz and 75 GHz to 110 GHz using a time-domain processing andextrapolation technique. Standard gain horn antenna calibration service for 220 GHz to 330 GHz
has been started from March 2020. The expanded uncertainty of antenna gain was estimated to
between 0.34 dB to 0.5 dB. The mm-wave antenna gain calibration by single antenna
extrapolation method with moving flat-reflector is also studied.
[References][1] M. Ameya, S. Matsukawa and S. Kurokawa, “Antenna Gain Self-calibration Method with
Moving Flat Reflector for Millimeter-wave Frequency Band,” Proceedings of 2018 IEEE
Conference on Antenna Measurements & Applications (CAMA), 2018[2] M. Ameya and S. Kurokawa, “Development of Antenna Gain Calibration System in 300 GHz
Frequency Band,” Proceedings of 2019 URSI-Japan Radio Science Meeting, A2-4, 2019.
[3] M. Ameya, S. Matsukawa, and S. Kurokawa, “Uncertainty Estimation of Antenna Gain Self-

Calibration Method with Moving Flat Reflector for 5G Standard Gain Horn Antenna,”
Proceedings of IEEE CAMA 2019, pp.277-280, 2019.

Fig. 12 Antenna gain calibration system
to 330 GHz

Fig. 13 Estimated antenna gain that compare for 220
with MoM results

Radar Cross Section (RCS) calibration service for cylindrical metal reflector and square metal
plate in W-band has been started from March 2019. The expanded uncertainty of RCS forcylindrical metal reflector in W-band was estimated to between 1.1 to 1.6 dB. The expanded
uncertainty of RCS for square metal plate reflector in W-band was estimated to between 1.4 dB
to 2.1 dB.

Fig. 14 RCS calibration results in W-band and an example of a cylindrical reflector

The E-field strength is one of the important quantities in the electromagnetic free field
metrology and the field measurement is ordinarily carried out by using a calibrated E-field probe.
In NMIJ/AIST, the correction factors of the E-field probe are calibrated against the field level of
10 V/m and 20 V/m generated in a G-TEM cell. Three appropriate methods to generate thestandard E-field depending on the measurement frequency are employed in calibrating the
response of the primary optical probe. A TEM cell is employed as a standard E-field generator atlower frequencies below 900 MHz, and the E-field level from 0.8 GHz to 2.2 GHz is calibrated

by using the free space dipole antenna factor in the anechoic chamber. Antenna gain and the net
power flowing into the transmitting antenna are the traceability sources for the standard field
generation in the anechoic chamber from 2 GHz to 6 GHz. The calibrated optical E-field probe
against these standard E-fields transfers the E-field level into the G-TEM cell, and then theordinary field probe is calibrated up to 4 GHz.
[References][1] T. Morioka, “Reflectometer calibration for net power measurement and uncertainty,” in CPEM
Dig., pp. 1-2, Denver CO, USA, Aug. 2020. (Virtual conference)
For the Radio Low in Japan, Calibration service of RF measurement instruments such as RF
power meters, RF attenuators, and antennas has been performed by NICT.
Calibration service of RF power meters in the frequency range from 170-220 GHz and 220330 GHz have been started in 2021 and 2018, respectively to realize spurious measurements inaccordance with the ITU-R recommendation SM.32-10. It has been worked out by a collaboration
between NICT and NMIJ [Tojima et al., 2020] [Kinoshita et al., 2018]. In addition, calibration
service of RF power meter for 75 Ω system which is based on the Japan Calibration Service
System (JCSS) has been started in 2019 to prepare with becoming widely use 4K/8K televisionsystem [Sakai et al., 2017]. Calibration service of RF power meters at 10 W (+40 dBm) in thefrequency range from 10 MHz to 9 GHz is available, too.
Calibration service of loop antennas which is based on the JCSS has been performed using ouroriginal calibration method, which will be standardized by IEC/CISPR in 2022 [Fujii et al., 2017].
Calibration services of dipole antennas for 25-1,000 MHz, biconical antennas for 25-300 MHz,
standard gain horn antennas for 1-40 GHz, and double-ridged guide antennas for 1-18 GHz are
available.
[References]
Tojima Y, Kinoshita M, Iida H, and Fujii K [2020], “Calibrating Power Meters in the 140–220GHz Frequency Range Using an Absolute-Power Reference Calorimeter,” IEEE Trans. on Intrum.
Meas. 70, 1002709.
Kinoshita M, Inoue T, Shimaoka K, and Fujii K [2018], “Precise power measurement with asingle-mode waveguide calorimeter in the 220–330 GHz frequency range,” IEEE Trans. Instrum.
Meas. 67(6), 1451–1460.
Sakai K, Sugiyama T, Sebata K, Nishiyama I, and Fujii K [2017], “Power Meter Calibration 2 (1mW, 75 Ω),” Journal of NICT 63(1), 23-31.
Fujii K, Sakai K, Sugiyama T, Sebata K, and Nishiyama I [2017], “Calibration of Loop
Antennas for EMI Measurements in the Frequency Range Below 30 MHz,” Journal of NICT
63(1), 71-81.

A5. Power Attenuation and Impedance Measurements
The Applied Electronics Standards Group, the Radio-Frequency Group and theElectromagnetic Measurement Group in the elctrical standards area of NMIJ covers the A5
fields.
The phase difference measurement system based on the three-voltmeter method (3VM) and adifferential thermal voltage converter (TVC) has been checked for frequency range from 1 kHz
to 1 MHz (Fig. 5.1). It has been found that the differential thermal voltage converter has a large
amount of differential voltage measurement error over the frequency of 100 kHz. A
measurement method of a differential TVC AC/DC difference has been developed to make thelarge error reduced for the frequency range.

Fig. 5.1

JEMIC has provided the primary active/reactive power/energy standards for the power
frequencies in the voltage range from 50 V to 120 V and in the current range from 2.5 A to 50 A.
The standard individually measures voltage U and current I with two precise voltmeters and ashunt resistor, and phase θ with a precise digital phase meter. After these measurements, the active
and reactive powers are calculated by UIcosθ and UIsinθ, respectively. The representative
expanded uncertainties under conditions of 100 V and 5 A are 22 μW/VA (power factor 1) and 10
μW/VA (power factor 0). In 2019, we calibrated approximately 10 power meters and 70 energy
meters.
NMIJ developed a WR-5 waveguide-based calorimeter for the frequency range of 140-220
GHz in collaboration with NICT. Direct comparison calibration was demonstrated forcommercially available power meters using the calorimeter as a reference standard. We havebegun to provide reference values for the WR-5 band to domestic organizations.

NMIJ has established national standard for RF and microwave attenuation in the frequency
range of 100 kHz to 110 GHz, and provides its calibration services mainly with the Japan
Calibration Service System (JCSS) scheme. All measurement and calibration systems work basedon the intermediate frequency (IF) substitution method using the highly accurate null detectionand employing an inductive voltage divider (IVD) as the reference standard. Improvements
including measurement system in the 1 kHz to 100 kHz frequency range (Fig. 5.2) are conducting
to meet industry requirements regarding electromagnetic compatibility (EMC).

Fig. 5.2

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.
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. Measurements of both the first and second round loop
were completed on February 2018. It can be said successful, although there were some delays inthe delivery of the traveling standards between the participants. Preparation of the Draft A report
is started.
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, themethod will be published as an IEC standardization. The method cannot only measure dielectric
permittivity but also conductivity at millimeter wave frequency (Fig. 5.3). Furthermore,
electromagnetic sensing techniques is also researching for the agriculture products, food andinfrastructure, etc.. In addition, scanning microwave microscopy (SMM) technique areresearching and NMIJ originally developed matching circuit to establish high sensitivity and lowsignal-to-noise ratio. Recently, NMIJ demonstrated percoemance comparison for three SMM
system.

Fig. 5.3

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), the APMP supplemental comparison(APMP.EM.RF-S5.CL: Dimensionally-derived characteristic impedance for PC7, PC2.4 andPC1.85) and the pilot study for material characterization.
NMIJ has developed a highly sensitive terahertz calorimeter using a broadband absorber (Fig.
5.4). A magnetically loaded epoxy having a pyramidal surface was used as the absorber. The
calorimeter enabled the measurement of absolute power from 110 GHz to several THz. The
measurement uncertainties were 6.2% for 13 μW at 300 GHz and 5.6% for 1.5 μW at 1 THz (k=2).
We also have demonstrated a THz power measurement of tens of nanowatts at room temperatureusing the calorimeter with vacuum insulation panels utilized for thermal insulation. The absolute
power of 26.7 nW was measured at 1 THz with the expanded uncertainty of 4.2% (k=2).

Fig. 5.4

NMIJ developed a method for measuring terahertz (THz) attenuation for free-space beams (Fig.
5.5). 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.

Fig. 5.5

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 sofware for dielectroic permittivity of low loss materials.
Measurement can be performed in broad band frequency and up to 120 GHz (Fig. 5.6). The
method is now being standardized in the IEC standard, then the system has been provided by themeasurement instrument company.

Fig. 5.6