Sojun Sato

A method for measuring the frequency response of photodetector modules using twice-modulated light

In this paper, a novel method is proposed for measuring the frequency response of a photodetector (PD) and its associated amplifier, which is called a PD module in this paper, by using light whose intensity is modulated twice. A distinctive feature of the twice-modulated light is that it contains two frequency components that essentially have equal intensities. A measurement system was constructed consisting of an He-Ne laser source and two acoustooptic modulators to verify the method. This study shows the resolution to a problem caused by the use of acoustooptic modulators (AOMs). This method can be readily used for determining the frequency responses of a PD module in the frequency range of up to tens of megaHertz.

Quantitative Estimation of the Amount of Fibrosis in the Rat Liver Using Fractal Dimension of the Shape of Power Spectrum

This paper describes the quantitative measurement of the amount of fibrosis in the rat liver using the fractal dimension of the shape of power spectrum. The shape of the power spectrum of the scattered echo from biotissues is strongly affected by its internal structure. The fractal dimension, which is one of the important parameters of the fractal theory, is useful to express the complexity of shape of figures such as the power spectrum. From invitro experiments using rat liver, it was found that this method can be used to quantitatively measure the amount of fibrosis in the liver, and has the possibility for use in the diagnosis of human liver cirrhosis.

Ultrasonic Power Measurement by the Radiation Force Balance Method –Experimental Results using Burst Waves and Continuous Waves–

Results of ultrasonic power measurements using a radiation force balance system constructed at National Institute of Advanced Industrial Science and Technology (AIST) are described. The aim of this research is to establish the ultrasonic power standard for medical ultrasonics. The experimental results of the linearity of the system under 1 mW to about 60 mW for the continuous and the burst waves are presented. It is also confirmed that the measured ultrasonic power is not affected by the repetition rate of the burst wave.

Influence of Ultrasonic Nonlinear Propagation on Hydrophone Calibration Using Two-Transducer Reciprocity Method

In this study, the influence of ultrasonic nonlinear propagation on hydrophone calibration by the two-transducer reciprocity method is investigated quantitatively using the Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation. It is proposed that the correction for the diffraction and attenuation of ultrasonic waves used in two-transducer reciprocity calibration can be derived using the KZK equation to remove the influence of nonlinear propagation. The validity of the correction is confirmed by comparing the sensitivities calibrated by the two-transducer reciprocity method and laser interferometry.

Final report on key comparison APMP.AUV.A-K1

A regional key comparison APMP.AUV.A-K1 has been carried out for the pressure sensitivity of laboratory standard microphones. The National Metrology Institute of Japan (NMIJ) piloted this project. Two LS1P microphones were circulated through nine national metrology institutes and calibrated in the frequency range from 63 Hz to 8 kHz. Deviations from the mean value are below ? 0.05 dB for all the frequencies. Results have been linked to CIPM key comparison CCAUV.A-K1 by introducing a correction factor. For every participant, the degree of equivalence with a key comparison reference value is within the corresponding expanded uncertainty. Main text. To reach the main text of this paper, click on Final Report. The final report has been peer-reviewed and approved for publication by the CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

A new traceability system in Japan

In 1993, the measurement law was revised and enacted in Japan. The old law had provided only the use of legal metrology units and the approval and verification systems for measuring equipment. The new one has added the provision of a traceability system to match the needs for a high accuracy measurement technique and international mutual recognition. In the Electrotechnical Laboratory (ETL), the national standard of sound‐pressure level has been established and maintained in an audible frequency range. The type approval test and verification of sound level meters have been carried out in the Japan Quality Assurance Organization (JQA). Now, in conformity with the law, ETL has started to construct the new traceability system for the acoustical standards in cooperation with JQA. An outline, is made of the traceability system in Japan and of the newly constructed pressure calibration systems for laboratory standard microphones.

Three-Dimensional Imaging by Synthetic Aperture Focusing Technique Using a Large Aperture Plane Ultrasonic Transducer

This paper describes a new method for obtaining three-dimensional (3-D) images of point scatterers using a large aperture plane ultrasonic transducer (LAPUT). The surface of the LAPUT was tilted towards its rotation axis. Scattered signals from point scatterers are received and recorded at each rotation angle. The images of the point scatterers can be reconstructed three-dimensionally by synthesizing these signals. This method is expected to provide 3-D images more easily than the conventional methods. The theoretical analysis and the images obtained by both simulations and experiments are described.

An Estimation of Randomness of Scattering Media by Power Spectrum of Ultrasonic Scattering Wave

Two methods are shown for characterizing shapes of a power spectrum to estimate distribution (randomness) of the spacings of the scatterers. One method is FFT of cepstrum (FFTC). The other is fractal-based analysis which is useful for characterization of complex figures such as geometry. Using a one-dimensional scattering model, trial estimations of the randomness of the scatterers were performed, and it was found that the randomness could be discriminated by both methods.

Development and performance evaluation of virtual auditory display system to synthesize sound from multiple sound sources using graphics processing unit

Head-related transfer function (HRTF) is characterized as sound transmission from sound source to listeners eardrum. When a listener hears a sound that is filtered with the HRTFs, the listener can localize a virtual target (sound image) as if the sound had come from the position corresponding to that at which the HRTFs were measured. A moving sound image can be generated to switch HRTFs of successive direction in real-time. While many virtual auditory displays (VADs) based on synthesis of HRTFs have been proposed, most of them can synthesize only a few sound images due to lack of computation power. In this article, the VAD system implemented based on graphics processing unit (GPU) was introduced. In our system, the convolution of HRTFs is parallelized on GPU to realize a high-speed processing. In addition, the multiple HRTFs each of which is corresponding to sound sources at different position are processed in parallel to control multiple sound image simultaneously. In this article, the performance of ou...

Free‐field calibration of 1/4 inch microphones for ultrasound by reciprocity technique

Recently, equipment that radiates ultrasound radiation at frequencies far beyond the audible range is increasing in our environment. Such electronic equipment has switching regulators or inverter circuits, and many devices are unintended sources of ultrasound radiation. However, the effects of airborne ultrasound on human hearing and the human body have not been well investigated. To estimate the potential damage of airborne ultrasound radiation quantitatively, it is necessary to establish an acoustic standard for airborne ultrasound because the standard is a basis of acoustic measurement. With the intention of establishing a standard on airborne ultrasound, a free‐field calibration system with an anechoic chamber was produced. The principle of free‐field calibration techniques is introduced in this presentation. Type WS3 microphones (B&K 4939) were calibrated in the system to examine the calibration ability to be achieved. Results showed that it can calibrate a microphone from 10 to 100 kHz with dispersi...