We are investigating on precise acoustic measurement technology including airbone ultrasound and infrasound which are related to human auditory, noise pollution and safety. The precise ultrasonic measurement techniques related mainly to medical applications including ultrasonic power and pressure standards are also developed. We also carry out research on vibration acceleration standards, hardness standards and material impact strength standards necessary to ensure the safety and quality control of transport equipment and structures. Hardness in microstructure, advanced vibration measurements and ultrasound measurements are investigated to support next-generation industry.    

Precise acoustic measurements in the audible frequency range rely on absolutely calibrated pressure sensitivity (ratio of the output voltage to the sound pressure on the microphone diaphragm) of laboratory standard microphones. The pressure calibration system developed by NMIJ covers a frequency range of 20 Hz to 20 kHz and is capable of calibration with the measurement uncertainty of approximately 0.04 dB (0.4%) in the major frequency rage. NMIJ also carries out R&D for the acoustic standards outside the audible frequency range to realize accurate infrasonic-noise measurement and to estimate safe levels of airborne ultrasound accurately.     [ Acoustics and Ultrasonics Section ]

For medical applications, it is important for safety of human body to evaluate the characteristics of ultrasonic field precisely. At the NMIJ, an ultrasonic power measurement system by using "a radiation force balance method" is now developing. When a target suspended in water is irradiated with ultrasound emitted by an ultrasonic transducer, small radiation force is generated at the target. By measuring the force with an electrobalance precisely, ultrasonic power can be measured with high accuracy.     [ Acoustics and Ultrasonics Section ]

Precise and reliable measurements of vibration and shock are frequently required from diverse fields of industry. They are also requested to construct structures such as high-rise buildings or large bridges which are resistant to earthquakes. Vibration measurement to ensure safety and quality of life is growing increasingly important and the sensitivity and the phase response of vibration transducers should be accurately known. Vibration calibration system by using laser interferometer enables relative uncertainty of about 1% for vibration transducer sensitivity calibration in the range of 1 Hz to 5 kHz.     [ Vibration and Hardness Section ]

Hardness measurement is a common testing method used in a wide range of industrial fields. It is an important technique for quality evaluation of various materials and mechanical parts since it is simple and non-destructive. The standard Rockwell hardness machine is capable of accurate measurements of indentation load and displacement, and the shape of the diamond indenter equipped with the machine is precisely evaluated. It is used to maintain primary scales of Rockwell hardness. The measurement uncertainty is estimated to be 0.3 HRC.     [ Vibration and Hardness Section ]