arXiv subjects

Tomofumi Shimoda

Publications and source records attributed to Tomofumi Shimoda.

12 recordsLinked to original sources

arXiv2026

Temperature dependence of broadband seismometer sensitivity

Broadband seismometers are widely used in global observation networks deployed for geophysics research. Recently, the calibration of their sensitivity has become an important factor for ensuring observation accuracy. One of the limiting factors of calibration uncertainty is the temperature dependence of the sensitivity because seismometers operate in a wide range of temperatures. However, systems that accurately measure the temperature coefficient in seismometers have not been established. Herein, we develop such a system using a triaxial vibration exciter combined with a thermostatic chamber. Using this system, we calibrated several broadband seismometers (Trillium Compact, Trillium Horizon 360, and CMG-3T) at various temperatures, ranging from $-15 ^\circ$C to $+45 ^\circ$C. We found that the temperature coefficient was $(0.11\pm0.01)$ %/$^\circ$C, which can be attributed to the internal magnet of the seismometers. The variation of the phase delay corresponded to a change of less than 2 ms in output time delay. Additionally, we found that the relative frequency response below 1 Hz was stable against temperature variations. These values are useful for evaluating the measurement accuracy of seismometer observation networks.

physics.geo-ph↗

arXiv2025

Accurate laboratory testing of low-frequency triaxial vibration sensors under various environmental conditions

Triaxial vibration sensor are widely used used in various application. Recently, low-cost sensors based on micro electro mechanical system (MEMS) technology are also becoming more widely adopted. However, their measurement accuracy can be affected by environmental factors such as temperature. In this study, we developed an environmental testing system integrated with a triaxial vibration exciter. The system can reproduce long-stroke, low-frequency triaxial vibrations -- such as those caused by huge earthquakes -- under temperatures ranging from $-30~^\circ\mathrm{C}$ to $+80~^\circ\mathrm{C}$. Using this system, the measurement accuracy of vibration sensors can be evaluated under different environmental conditions. The system provides highly accurate reference measurements using a laser interferometer and reference accelerometers that are primarily calibrated within the system. The overall accuracy of the reference vibration measurement is estimated to be approximately 0.23~\%. Based on these reference measurements, we investigated the accuracy of earthquake observations using a MEMS accelerometer as a demonstration. The system configuration and testing procedures are presented in this paper.

physics.ins-det↗

arXiv2025

Optical sound pressure measurement using Fabry-Pérot cavity for primary acoustic standards

Optical sound pressure measurement is a promising technology to establish primary acoustic standards without reliance on specific types of microphones. We developed a precision optical sound pressure measurement system by combining a Fabry-Pérot optical cavity, a phase-stabilized optical frequency comb, and a custom-made phasemeter. The optical cavity detects changes in the air's refractive index induced by sound waves as changes in its resonance frequency. A continuous-wave laser frequency is stabilized at the resonance, and the frequency comb detects the changes in the laser frequency. The frequency changes are measured with high sensitivity and accuracy using a phasemeter that we developed. The sound pressures measured by this system agreed with the measurement value obtained using a reference microphone within 5% at sound pressure levels of 78 dB and 84 dB, within a frequency range of 100 Hz to 1 kHz. A systematic deviation of 2.6% was observed, with the optical system yielding higher values than the microphone. To identify the cause of this deviation, we performed vibration displacement measurements of the cavity mirrors and finite element analysis, which revealed that fluctuations in the optical path length due to insufficient fixation of the mirrors were responsible.

physics.ins-det↗

arXiv2025

Measurement of the intrinsic sensitivity for a single-ended accelerometer without the influence of the mounting condition

The calibration technique for accelerometers has been internationally developed for up to 20 kHz to ensure the reliability of vibration measurement. However, it has been established that the calibrated sensitivity changes at over 10 kHz depending on the mounting conditions, and this makes it difficult to accurately measure the characteristics of accelerometers and degrades the accuracy of high-frequency vibration measurements. Thus, in this study, we developed a reversed-calibration method for measuring the intrinsic sensitivity of an accelerometer without the influence of the mounting conditions. Through demonstration experiment, the intrinsic resonance structure of the accelerometer at approximately 45.8 kHz was adequately determined. Furthermore, the result was independently confirmed by fitting the conventional adapter-calibration results up to 100 kHz with four different materials based on the dynamic three-body model. Concurrently, the material dependency observed during adapter calibration was quantitatively analyzed, after which its relationship with the Young's modulus was extracted. Overall, these results deepen our understanding of the performance of the accelerometer at above 10 kHz, which is essential in vibration metrology and accelerometer development.

physics.ins-det↗

arXiv2024

TOrsion-Bar Antenna: A Ground-Based Detector for Low-Frequency Gravity Gradient Measurement

The Torsion-Bar Antenna (TOBA) is a torsion pendulum-based gravitational detector developed to observe gravitational waves in frequencies between 1 mHz and 10 Hz. The low resonant frequency of the torsion pendulum enables observation in this frequency band on the ground. The final target of TOBA is to observe gravitational waves with a 10 m detector and expand the observation band of gravitational waves. In this paper, an overview of TOBA, including the previous prototype experiments and the current ongoing development, is presented.

gr-qc↗

arXiv2022

Primary accelerometer calibration with two-axis automatic positioning stage

In this study, we developed an automated, multipoint primary accelerometer calibration system using a two-axis positioning stage and a heterodyne laser interferometer. The proposed system offers low-cost, convenient, and automated multipoint accelerometer calibration, enabling less calibration lead time. The positioning stage also offers better positioning repeatability of 1 um, which is impossible through manual alignments. We measured the surface deformation of a laser reflection adaptor for a single-ended accelerometer by measuring more than 450 measurement positions. Visualizing the deformation of laser reflection surfaces facilitates understanding the effects of deformation or nonrectilinear motion, which are among the most significant uncertainty components in high-frequency accelerometer calibrations.

physics.ins-det↗

arXiv2022

Precise sinusoidal signal extraction from noisy waveform in vibration calibration

Precise extraction of sinusoidal vibration parameters is essential for the dynamic calibration of vibration sensors, such as accelerometers. However, several standard methods have not yet been optimized for large background noise. In this work, signal processing methods to extract small vibration signals from noisy data in the case of accelerometer calibration is discussed. The results show that spectral leakage degrades calibration accuracy. Three methods based on the use of a filter, window function, and numerical differentiation are investigated with theoretical calculations, simulations, and experiments. These methods can effectively reduce the contribution of the calibration system noise. The uncertainty of micro vibration calibration in the National Metrology Institute of Japan is reduced by two orders of magnitudes using the proposed methods. The theoretical analyses in this work can lay the foundation for the optimization of signal processing in vibration calibration, and can be applied to other dynamic calibration fields.

eess.SP↗

arXiv2020

Compact integrated optical sensors and electromagnetic actuators for vibration isolation systems in the gravitational-wave detector KAGRA

This paper reports on the design and characteristics of a compact module integrating an optical displacement sensor and an electromagnetic actuator for use with vibration-isolation systems installed in KAGRA, the 3-km baseline gravitational-wave detector in Japan. In technical concept, the module belongs to a family tree of similar modules called OSEMs, used in other interferometric gravitational-wave detector projects. After the initial test run of KAGRA in 2016, the sensor part, which is a type of slot sensor, was modified by increasing the spacing of the slot from 5 mm to 15 mm to avoid the risk of mechanical interference with the sensor flag. We confirm the sensor performance is comparable to that of the previous design despite the modification. We also confirm the sensor noise is consistent with the theoretical noise budget. The noise level is 0.5 nm/rtHz at 1 Hz and 0.1 nm/rtHz at 10 Hz, and the linear range of the sensor is 0.7 mm or more. We measured the response of the actuator to be 1 N/A, and also measured the resistances and inductances of coils of the actuators to confirm consistency with theory. Coupling coefficients among the different degrees of freedom were also measured and shown to be negligible, varying little between designs. A potential concern about thermal noise contribution due to eddy current loss is discussed. As of 2020, 42 of the modules are in operation at the site.

astro-ph.IM↗

arXiv2019

Mirror actuation design for the interferometer control of the KAGRA gravitational wave telescope

KAGRA is a 3-km cryogenic interferometric gravitational wave telescope located at an underground site in Japan. In order to achieve its target sensitivity, the relative positions of the mirrors of the interferometer must be finely adjusted with attached actuators. We have developed a model to simulate the length control loops of the KAGRA interferometer with realistic suspension responses and various noises for mirror actuation. Using our model, we have designed the actuation parameters to have sufficient force range to acquire lock as well as to control all the length degrees of freedom without introducing excess noise.

physics.ins-det↗

arXiv2019

Nonlinear vibration transfer in torsion pendulums

Torsion pendulums have been widely used in physical experiments, because their small restoring forces are suitable for tiny force measurement. Recently, some applications such as low-frequency gravity gradiometers have been proposed by focusing on their low resonant frequencies. Torsion pendulums with low resonant frequencies enable the suspended masses to be isolated from the ground, allowing for good response to the fluctuation of local gravity field at low frequencies. However, translational ground vibration can be transferred to the horizontal rotation of the torsion pendulum nonlinearly. This effect can have a non-negligible contribution to the sensitivity of torsion pendulums as gravity gradiometers. This paper evaluates the amount of nonlinear vibration noise, and discusses how to reduce it.

physics.ins-det↗

arXiv2019

Torsion-bar antenna: a ground-based mid-frequency and low-frequency gravitational wave detector

Expanding the observational frequency of gravitational waves is important for the future of astronomy. Torsion-Bar Antenna (TOBA) is a mid-frequency and low-frequency gravitational wave detector using a torsion pendulum. The low resonant frequency of the rotational mode of the torsion pendulum enables ground-based observations. The overview of TOBA, including the past and present status of the prototype development is summarized in this paper.

physics.ins-det↗

arXiv2018

Seismic Cross-coupling Noise in Torsion Pendulums

Detection of low frequency gravitational waves around 0.1 Hz is one of the important targets for future gravitational wave observation. One of the main sources of the expected signals is gravi- tational waves from binary intermediate-mass black hole coalescences which is proposed as one of the formation scenarios of supermassive black holes. By using a torsion pendulum, which can have a resonance frequency of a few millihertz, such signals can be measured on the ground since its rotational motion can act as a free mass down to 0.01 Hz. However, sensitivity of a realistic tor- sion pendulum will suffer from torsional displacement noise introduced from translational ground motion in the main frequency band of interest. Such noise is called seismic cross-coupling noise and there have been little research on it. In this paper, systematic investigation is performed to identify routes of cross-coupling transfer for standard torsion pendulums. Based on the results this paper also proposes reduction schemes of cross-coupling noise, and they were demonstrated experimen- tally in agreement with theory. This result establishes a basic way to reduce seismic noise in torsion pendulums for the most significant coupling routes.

physics.ins-det↗