Hamamatsu Photonics KK Research Articles

Feasibility study of CSNS as an ATLAS ITk sensor QA irradiation site

The current ATLAS Inner Detector will undergo a complete upgrade in order to meet the requirements of the High Luminosity Large Hadron Collider (HL-LHC). The new Inner Tracker (ITk) will be made completely of silicon sensors fabricated by Hamamatsu Photonics K.K. (HPK). Quality Assurance (QA) is focused on providing confidence that quality requirements will be fulfilled in production such as irradiation tolerance and testing specification for the mini sensors. The Associated Proton beam Experiment Platform (APEP) beam line at the China Spallation Neutron Source (CSNS) was commissioned in 2022. This study focused on verifying the feasibility of CSNS as an ITk sensor QA irradiation site. A low-temperature Peltier cold box has been developed to keep the irradiation sensor samples at −15 °C. Several fluence points have been studied from 5.1×1014 neq/cm2 to 1.6×1015 neq/cm2, measured with the activation of the aluminium foils. The post-irradiation measurements (IV, CV, and CCE) are done under cold temperatures (−8 °C for IV and CV, −20 °C for CCE), after annealing for 80 min at 60 °C. Test results show CSNS could be a suitable proton irradiation site for the ATLAS ITk sensor project, after formal site qualification.

Cryogenic characterization of Hamamatsu HWB MPPCs for the DUNE photon detection system

The Deep Underground Neutrino Experiment (DUNE) is a next generation experiment aimed to study neutrino oscillation. Its long-baseline configuration will exploit a Near Detector (ND) and a Far Detector (FD) located at a distance of ∼1300 km. The FD will consist of four Liquid Argon Time Projection Chamber (LAr TPC) modules. A Photon Detection System (PDS) will be used to detect the scintillation light produced inside the detector after neutrino interactions. The PDS will be based on light collectors coupled to Silicon Photomultipliers (SiPMs). Different photosensor technologies have been proposed and produced in order to identify the best samples to fullfill the experiment requirements. In this paper, we present the procedure and results of a validation campaign for the Hole Wire Bonding (HWB) MPPCs samples produced by Hamamatsu Photonics K.K. (HPK) for the DUNE experiment, referring to them as `SiPMs'. The protocol for a characterization at cryogenic temperature (77 K) is reported. We present the down-selection criteria and the results obtained during the selection campaign undertaken, along with a study of the main sources of noise of the SiPMs including the investigation of a newly observed phenomenon in this field.

Analysis of the performance of low gain avalanche diodes for future particle detectors

Low-Gain Avalanche Diodes (LGAD) are the sensor of choice for the timing detectors of the ATLAS and CMS experiments at the High Luminosity Large Hadron Collider (HL-LHC). This paper presents the results of static and dynamic performance evaluations of LGADs manufactured by Hamamatsu Photonics K.K. (HPK) and Brookhaven National Laboratory (BNL). Timing performance was measured using β-scopes after a static characterization of the device (current-voltage and capacitance-voltage curves) and a time resolution better than 35 ps was extracted under high operational bias voltage before irradiation. This value is considered within the nominal requirements of the ATLAS project for un-irradiated sensors. Transient Current Technique (TCT) was used to observe and analyze a gain suppression mechanism, i.e. a decrease in gain correlated with increased laser intensities. TCAD simulations were carried out to interpret the gain suppression of the BNL sensors under different conditions of bias voltage and laser intensity. A good correspondence between experimental observations and TCAD simulations was found.

Evaluation of HPK [formula omitted] planar pixel sensors for the CMS Phase-2 upgrade

To cope with the challenging environment of the planned high luminosity upgrade of the Large Hadron Collider (HL-LHC), scheduled to start operation in 2029, CMS will replace its entire tracking system. The requirements for the tracker are largely determined by the long operation time of 10 years with an instantaneous peak luminosity of up to 7.5 × 1034cm−2s−1 in the ultimate performance scenario. Depending on the radial distance from the interaction point, the silicon sensors will receive a particle fluence corresponding to a non-ionising energy loss of up to Φeq= 3.5 × 1016cm−2. This paper focuses on planar pixel sensor design and qualification up to a fluence of Φeq = 1.4 × 1016cm−2.For the development of appropriate planar pixel sensors an R&D program was initiated, which includes n+-p sensors on 150mm (6”) wafers with an active thickness of 150µm with pixel sizes of 100×25 µm2 and 50×50 µm2 manufactured by Hamamatsu Photonics K.K. (HPK). Single chip modules with ROC4Sens and RD53A readout chips were made. Irradiation with protons and neutrons, as well was an extensive test beam campaign at DESY were carried out. This paper presents the investigation of various assemblies mainly with ROC4Sens readout chips. It demonstrates that multiple designs fulfil the requirements in terms of breakdown voltage, leakage current and efficiency. The single point resolution for 50×50 µm2 pixels is measured as 4.0µm for non-irradiated samples, and 6.3µm after irradiation to Φeq = 7.2 × 1015cm−2.

Establishing the Quality Assurance programme for the strip sensor production of the ATLAS tracker upgrade including irradiation with neutrons, photons and protons to HL-LHC fluences

The successful pre-production delivery of strip sensors for the new Inner Tracker (ITk) for the upgraded ATLAS detector at the High Luminosity LHC (HL-LHC) at CERN was completed and based on their performance full production has commenced. The overall delivery period is anticipated to last 4 years to complete the approximately 22000 sensors required for the ITk. For Quality Assurance (QA), a number of test structures designed by the collaboration, along with a large area diode and miniature version of the main sensor, are produced in every wafer by the foundry Hamamatsu Photonics K.K (HPK). As well as Quality Control (QC) checks on every main sensor, samples of the QA pieces from each delivery batch are tested both before and after irradiation with results after exposure to neutrons, gammas or protons to fluences and doses corresponding to those anticipated after operation at the HL-LHC to roughly 1.5 times the ultimate integrated luminosity of 4000 fb-1. In this paper the procedures are presented and the studies carried out to establish that the seven ITk QA Strip Sensor irradiation and test sites meet all the requirements to support this very extensive programme throughout the strip sensor production phase for the ITk project.

INFIERI 2021: Hands-on Lab – LiDAR

LiDAR is an acronym of “Light Detection and Ranging”, which is to measure the distance to an object (“Ranging”) by detecting the light being reflected (“Light Detection”). The "hands-on" lab is made of two sections: (1) overviewing the technology, the application, and the key devices of LiDAR, and (2) a laboratory where we operate a LiDAR setup, do calibration, and look into signals in the electronics. In the section (1), we learn the “basics” of the LiDAR. In the section (2), we learn “real stuff” by using a LiDAR setup. We use a simple desktop LiDAR setup developed by Hamamatsu photonics K.K. (HPK), adapted for the hands-on lab in collaboration with the author. The LiDAR setup, which is using “cutting-edge” solid-state devices, is a direct time-of-flight LiDAR equipped with a 905 nm laser diode and a 16-ch MPPC photon counting image sensor. The light emitter is a pulsed solid-state laser (PLD) of 905 nm infra-red light. The light receiver (a photon counting image sensor (PCI)) is a linear-array of 16 channel MPPC (a solid-state photomultiplier) with a readout ASIC. The setup is also equipped with a visible-light camera, with which we correlate the visual image with the feature of the LiDAR setup. In the LiDAR laboratory, we do “aiming” (i.e., calibrate) by detecting the infra-red laser light, and correlating visual imaging and LiDAR “ranging”. We get insight into the LiDAR setup by monitoring time-of-flight (TOF) and energy (pulse height with time-over-threshold technology (TOT)) signals in the electronics with an oscilloscope. Through the process, we learn the real stuff of LiDAR and the issues associated.

Afterpulse measurement of JUNO 20-inch PMTs

In this study, we present the large photomultiplier tube (PMT) afterpulse measurement results obtained from the Jiangmen underground neutrino observatory (JUNO) experiment. A total of 11 dynode-PMTs (R12860) from the Hamamatsu company (Hamamatsu Photonics K.K. (HPK)) and 150 micro-channel plate PMTs (MCP-PMTs, GDB-6201) from the NNVT company (North Night Vision Technology Co., Ltd. (NNVT)) were tested. Subsequently, an afterpulse model was built according to the afterpulse time distribution and the probability of occurrence for these two types of PMTs. The average ratio of the total afterpulse charge with a delay between 0.5 \(\upmu\)s and 20 \(\upmu\)s to the primary pulse charge is \(\sim\) 5.7% (13.2%) for the tested MCP-PMTs (dynode-PMTs). The JUNO experiment will deploy 20,012 20-inch PMTs; this study will benefit detector simulation, event reconstruction, and data analysis regarding the JUNO experiment.

Mass testing and characterization of 20-inch PMTs for JUNO

Main goal of the JUNO experiment is to determine the neutrino mass ordering using a 20 kt liquid-scintillator detector. Its key feature is an excellent energy resolution of at least 3% at 1 MeV, for which its instruments need to meet a certain quality and thus have to be fully characterized. More than 20,000 20-inch PMTs have been received and assessed by JUNO after a detailed testing program which began in 2017 and elapsed for about four years. Based on this mass characterization and a set of specific requirements, a good quality of all accepted PMTs could be ascertained. This paper presents the performed testing procedure with the designed testing systems as well as the statistical characteristics of all 20-inch PMTs intended to be used in the JUNO experiment, covering more than fifteen performance parameters including the photocathode uniformity. This constitutes the largest sample of 20-inch PMTs ever produced and studied in detail to date, i.e. 15,000 of the newly developed 20-inch MCP-PMTs from Northern Night Vision Technology Co. (NNVT) and 5000 of dynode PMTs from Hamamatsu Photonics K. K.(HPK).

Radiation hardness characterization of low gain avalanche detector prototypes for the high granularity timing detector

The high granularity timing detector (HGTD) is a crucial component of the ATLAS phase II upgrade to cope with the extremely high pile-up (the average number of interactions per bunch crossing can be as high as 200). With the precise timing information (<i>σ<sub>t</sub></i>～30 ps) of the tracks, the track-to-vertex association can be performed in the “4-D” space. The Low Gain Avalanche Detector (LGAD) technology is chosen for the sensors, which can provide the required timing resolution and good signal-to-noise ratio. Hamamatsu Photonics K.K. (HPK) has produced the LGAD with thicknesses of 35 μm and 50 μm. The University of Science and Technology of China(USTC) has also developed and produced 50 μm LGADs prototypes with the Institute of Microelectronics (IME) of Chinese Academy of Sciences. To evaluate the irradiation hardness, the sensors are irradiated with the neutron at the JSI reactor facility and tested at USTC. The irradiation effects on both the gain layer and the bulk are characterized by <i>I</i>-<i>V</i> and <i>C</i>-<i>V</i> measurements at room temperature (20 ℃) or −30 ℃. The breakdown voltages and depletion voltages are extracted and presented as a function of the fluences. The final fitting of the acceptor removal model yielded the <i>c</i>-factor of 3.06×10<sup>−16</sup> cm<sup>−2</sup>, 3.89×10<sup>−16</sup> cm<sup>−2</sup> and 4.12×10<sup>−16</sup> cm<sup>−2</sup> for the HPK-1.2, HPK-3.2 and USTC-1.1-W8, respectively, showing that the HPK-1.2 sensors have the most irradiation resistant gain layer. A novel analysis method is used to further exploit the data to get the relationship between the <i>c</i>-factor and initial doping density.

Characterisation of SiPM Photon Emission in the Dark.

In this paper, we report on the photon emission of Silicon Photomultipliers (SiPMs) from avalanche pulses generated in dark conditions, with the main objective of better understanding the associated systematics for next-generation, large area, SiPM-based physics experiments. A new apparatus for spectral and imaging analysis was developed at TRIUMF and used to measure the light emitted by the two SiPMs considered as photo-sensor candidates for the nEXO neutrinoless double-beta decay experiment: one Fondazione Bruno Kessler (FBK) VUV-HD Low Field (LF) Low After Pulse (Low AP) (VUV-HD3) SiPM and one Hamamatsu Photonics K.K. (HPK) VUV4 Multi-Pixel Photon Counter (MPPC). Spectral measurements of their light emissions were taken with varying over-voltage in the wavelength range of 450–1020 nm. For the FBK VUV-HD3, at an over-voltage of V, we measured a secondary photon yield (number of photons () emitted per charge carrier ()) of . The emission spectrum of the FBK VUV-HD3 contains an interference pattern consistent with thin-film interference. Additionally, emission microscopy images (EMMIs) of the FBK VUV-HD3 show a small number of highly localized regions with increased light intensity (hotspots) randomly distributed over the SiPM surface area. For the HPK VUV4 MPPC, at an over-voltage of V, we measured a secondary photon yield of . In contrast to the FBK VUV-HD3, the emission spectra of the HPK VUV4 did not show an interference pattern—likely due to a thinner surface coating. The EMMIs of the HPK VUV4 also revealed a larger number of hotspots compared to the FBK VUV-HD3, especially in one of the corners of the device. The photon yield reported in this paper may be limited if compared with the one reported in previous studies due to the measurement wavelength range, which is only up to 1020 nm.

Digital switch boards for IV and CV measurements of large-array Low Gain Avalanche Detectors

The High-Granularity Timing Detector (HGTD), with a time resolution of approximately 30 ps, is proposed for the ATLAS Phase II upgrade to address the challenge of greatly increased pile-up interactions. The HGTD is based on the technology of Low Gain Avalanche Detectors (LGADs). The current–voltage (IV) and capacitance–voltage (CV) measurements are important methods to study the main characteristics that can be exploited for quality controlling LGADs during production. A single probe can be controlled via computer to switch channels when using an automatic probe station, but this leaves the remaining, adjacent channels floating and results in inaccurate measurements due to the punch-through effect. We designed the digital switch boards for the IV and CV measurements of 5 × 5 and 15 × 15 LGADs arrays. With the digital switch board and probe cards, channels on a large-array LGADs can be scanned automatically during the measurement, which greatly improves the measurement efficiency. The results show that the leakage currents and noise of all channels induced by the two digital switch boards are lower than 10 pA. We show the IV and CV curves of all channels on two LGADs from Hamamatsu Photonics K. K. (HPK) with our digital switch boards. Compared with the results measured by HPK with an automatic probe station, the IV and CV curves that we measured have better uniformity and accuracy, demonstrating that the quality control of the large-array LGADs can be conducted well with our digital switch board.

Reflectance of Silicon Photomultipliers at Vacuum Ultraviolet Wavelengths

Characterization of the vacuum ultraviolet (VUV) reflectance of silicon photomultipliers (SiPMs) is important for large-scale SiPM-based photodetector systems. We report the angular dependence of the specular reflectance in a vacuum of SiPMs manufactured by Fondazionc Bruno Kessler (FBK) and Hamamatsu Photonics K.K. (HPK) over wavelengths ranging from 120 nm to 280 nm. Refractive index and extinction coefficient of the thin silicon-dioxide film deposited on the surface of the FBK SiPMs are derived from reflectance data of a FBK silicon wafer with the same deposited oxide film as SiPMs. The diffuse reflectance of SiPMs is also measured at 193 nm. We use the VUV spectral dependence of the optical constants to predict the reflectance of the FBK silicon wafer and FBK SiPMs in liquid xenon.

Annealing of proton radiation damages in Si-PM at room temperature

We report the radiation damage results of two new types of Multi-Pixel Photon Counter (MPPC) under the 200 MeV proton beam, for cosmic gamma-ray observations with CubeSats. The new MPPCs, S13360-6050CS and S14160-6050HS, have recently become commercially available by Hamamatsu Photonics K.K. (HPK). After 100 rad irradiation, the dark current increased by a factor of ∼100 and the threshold energy of gamma-ray detection by CsI scintillator increased, but S14160-6050HS was less degraded. We then confirmed the annealing effects of the dark current and threshold energy for both. The decrease rate of the dark current in both MPPCs were similar to those in the previous works. At 20 °C, the threshold energies of both MPPCs reduced by several tens of percent after irradiation, but below 0 °C, the threshold energy of S14160-6050HS was not significantly lowered. We also confirmed that annealing began before one month post-irradiation.

Quality Assurance methodology for the ATLAS Inner Tracker strip sensor production

The production of the strip sensors for the ATLAS Inner Tracker (ITk) will start in 2020. Nearly 22,000 large area sensors will be produced over a period of about five years by Hamamatsu Photonics K.K. (HPK). The institutes involved in the sensor development and production are committed to deliver and maintain the highest quality sensors for the experiment. A Quality Assurance (QA) strategy has been prepared to be carried out during the whole production period. Once the process has been characterized as providing the required pre-irradiation specifications and the proper radiation hardness, the onus is on the manufacturer to rigidly stick to that qualified process. Still, sample testing with specific device-element structures and irradiation of devices should be implemented by the ITk sensor collaboration.A detailed irradiation and testing plan has been prepared by the ATLAS-ITk Collaboration, together with a newly designed test chip with specific structures to monitor different key technological and device parameters during the whole production. The tests and irradiations will be carried out on a sample basis. In order to have a practical methodology, samples from alternating batches will be sent for irradiations with protons, neutrons and gammas, and then tested in order to check that the characteristics remain within specifications. The detailed plan and the design and test methods for the structures in the test chip are presented here.

Study of interpad-gap of HPK 3.1 production LGADs with Transient Current Technique

The Phase-2 upgrade of the Large Hadron Collider (LHC) to High-Luminosity LHC (HL-LHC) allows an increase in the operational luminosity value by a factor of 5–7 that will result in delivering 3000 fb−1 or more integrated luminosity. Due to high luminosity, the number of interactions per bunch crossings (pileup) will increase up to a value of 140–200. To cope with high pileup rates, a precision minimum ionising particles (MIPs) timing detector (MTD) with a time resolution of ∼30–40 ps and hermetic coverage up to a pseudo-rapidity of |η|=3 is proposed by the Compact Muon Solenoid (CMS) experiment. An endcap part (1.6<|η|<3) of the MTD, called the endcap timing layer, will be based on low-gain avalanche detector (LGAD) technology. LGADs provide a good timing resolution due to a combination of a fast signal rise time and high signal-to-noise ratio. The performance of the ETL depends on optimising the crucial features of the sensors, namely; gain, signal homogeneity, fill factor, leakage current, uniformity of multiple-pad sensors and long term stability. The paper mainly focuses on the study of the fill factor of LGADs with varying temperature and irradiation at varying proton fluences as these sensors will be operated at low temperatures and are subjected to a high radiation environment.The 3.1 production of LGADs from Hamamatsu Photonics K.K. (HPK) includes 2x2 sensors with different structures, in particular, different values of narrower inactive region widths between the pads, called the no-gain region. In this paper, the term interpad-gap is used instead of no-gain region in order to follow the conventional terminology. These sensors have been designed to study their fill factor, which is the ratio of the area within the active region (gain region) to the total sensor area. A comparative study on the dependence of breakdown voltage with the interpad-gap width for the sensors has been carried out. Using infrared light (as the electron–hole pair creation by IR laser mimics closely to the traversing of MIPs) from the Scanning-Transient Current Technique (Scanning-TCT) set-up shows that the fill factor does not vary significantly with a variation in temperature and irradiation at high proton fluences.

Reflectance of silicon photomultipliers in linear alkylbenzene

Reflectance of silicon photomultipliers (SiPMs) is an important aspect to understand large scale SiPM-based detector systems and evaluate the performance of SiPMs. We design and produce a new experimental setup to measure the reflectance in air or in a liquid at visible wavelengths for various samples. With the new setup, we establish the measurement methods and validate its measurement results. The systematic errors are estimated to be 1.9% and 3.4% for measuring the reflectance in air and in a liquid, respectively. The reflectance of two SiPMs, NUV-HD-lowCT and S14160-60-50HS manufactured by Fondazione Bruno Kessler (FBK) and Hamamatsu Photonics K.K. (HPK) respectively, is measured in linear alkylbenzene (LAB) and in air at visible wavelengths. Our results show that the reflectance of the FBK SiPM in air varies in the range of 14% to 23% , depending on wavelengths and angle of incidence, which is two times larger than that of the HPK device. This indicates that the two manufacturers are using different designs of anti-reflective coating on the SiPM surfaces. The reflectance is reduced by about 10% when the SiPMs are immersed in LAB, compared with that measured in air. The profiles of the reflected light beams are also measured by a charge-coupled device (CCD) camera.

Physical image properties of a complementary metal-oxide-semiconductor imager for mammography systems.

We acquired a direct-type flat panel detector (FPD) developed for mammography systems and investigated its physical image properties, as its characteristics may affect future mammography in the clinic. The pixel size of the detector is 50µm, the smallest size used in clinical mammography. Amorphous selenium (a-Se) film is used in direct-type FPDs. Due to its inferior temperature properties, the temperature of the imaging room should be set to approximately 25°C. A novel a-Se film with superior heat resistance has been developed by the HAMAMATSU photonics KK Electron Tube Division that is suitable for high electric field driving. However, the associated trade-offs in image properties are unknown. The purposes of the current study were to investigate whether the detector maintains a high image quality in the presence of a high electric field, and to evaluate the image properties. The signal readout mechanism incorporates a complementary metal-oxide-semiconductor with superior noise properties. We measured the input-output characteristics, resolution, noise properties, and detection quantum efficiency, and investigated the effects of the exposure of the a-Se film to different applied voltages under standard mammography conditions prescribed by the International Electrotechnical Commission. The resolution and noise properties associated with the direct-type FPD were not affected by differences in applied voltage. The CMOS imager had a higher resolution than conventional systems with an equivalent pixel size. It also had a high detective quantum efficiency value. Thus, this detector may be useful in mammography.

Test beam evaluation of newly developed n-in-p planar pixel sensors for use in a high radiation environment

Radiation-tolerant n-in-p planar pixel sensors have been under development in cooperation with Hamamatsu Photonics K.K. (HPK). This is geared towards applications in high-radiation environments, such as for the future Inner Tracker (ITk) placed in the innermost part of the ATLAS detector in the high luminosity LHC (HL-LHC) experiment. Prototypes of those sensors have been produced, irradiated, and evaluated over the last few years. In the previous studies, it was reported that significant drops in the detection efficiency were observed after irradiation, especially under bias structures. The bias structures are made up of poly-Si or Al bias rails and poly-Si bias resistors. The structure is implemented on the sensors to allow quality checks to be performed before the bump-bonding process, and to ensure that charge generated in floating pixels due to non-contacting or missing bump-bonds is dumped in a controlled way in order to avoid noise. To minimize the efficiency drop, several new pixel structures have been designed with bias rails and bias resistors relocated. Several test beams have been carried out to evaluate the drops in the detection efficiency of the new sensor structures after irradiation. Newly developed sensor modules were irradiated with proton-beams at the Cyclotron and Radio-Isotope Center (CYRIC) in Tohoku University to see the effect of sensor-bulk damage and surface charge-up. An irradiation with γ-rays was also carried out at Takasaki Advanced Radiation Research Center, with the goal of decoupling the effect of surface charge-up from that of bulk damage. Those irradiated sensors have been evaluated with particle beams at DESY and CERN. Comparison between different sensor structures confirmed significant improvements in minimizing efficiency loss under the bias structures after irradiation. The results from γ-irradiation also enabled cross-checking the results of a semiconductor technology simulation program (TCAD).

Preterm Infants Exhibit Greater Variability in Cerebrovascular Control than Term Infants.

Sudden infant death syndrome (SIDS) remains an important cause of infant death, particularly among infants born preterm. Prone sleeping is the major risk factor for SIDS and this has recently been shown to alter cerebrovascular control in term infants. As preterm infants are at greater risk for SIDS than those born at term, we hypothesized that their cerebrovascular control in the prone position would be reduced compared to term infants. There were 35 preterm (mean gestation 31.2 ± 0.4 w) and 17 term (mean gestation 40.1 ± 0.3 w) infants. Infants underwent daytime polysomnography at 2-4 w, 2-3 mo, and 5-6 mo postterm age. Infants slept both prone and supine and were presented with cardiovascular challenges in the form of 15° head-up tilts (HUT). Cerebral tissue oxygenation index (TOI) was recorded using near-infrared spectroscopy (NIRO-200 spectrophotometer, Hamamatsu Photonics KK, Japan) and mean arterial pressure (MAP) was recorded using a Finometer cuff (Finapres Medical Systems, Amsterdam, The Netherlands). In the prone position TOI increased following the HUT (P < 0.05), whereas no change was seen in the supine position. The overall pattern of response was similar in both groups, but more variable in preterm than term infants (P < 0.05). Cerebrovascular control differs between the prone and supine positions in preterm infants. Although overall the responses to head-up tilts were similar between term and preterm infants, greater variability of responses in preterm infants suggests persisting immaturity of their cerebrovascular control in the first year of life, which may contribute to their increased risk of sudden infant death syndrome.

Anthropometric Characteristics of Elite Japanese Female Wrestlers

ABSTRACT.The purposes of this study were to disclose the anthropometrical characteristics of elite Japanese female wrestlers and to compare them with those of other athletes reported in the literature. To this end, we tested 17 elite Japanese female wrestlers (nine and eight wrestlers, in light and heavyweight categories, respectively), most of who had won gold medals at the internationally recognized tournaments. Body composition, circumferences, and limb lengths were tested based on multi-frequency bioimpedance analysis (InBody 730, Biospace, Inc.) and whole-body scanning system (Body Line Scanner, Hamamatsu Photonics KK). The main results indicate that the participants are characterized as having great FFMI (fat-free mass divided by height squared, 18.8 ± 0.8 in light and 20.5 ± 0.8 in heavyweight groups) with intensely enlarged circumference especially within the arms (30.0 ± 2.7 cm for upper arms and 24.2 ± 1.5 cm for forearms). These findings suggest that elite female wrestlers have site-specific hy...