Daitaro Okuyama

Ultrasonic Imaging by Impulse Ultrasound

An impulsive ultrasound wave as membrane radiated from a transmitter, a thick piezoceramic transducer, is used for ultrasonic imaging. The transmitter is fixed and a probe type hydrophone with tiny piezoceramic transducer moves just a few millimeters from the radiation surface. An object is set very close to or put onto the radiator surface. The image is characterized by the amplitude and the transit-time of the penetrating wave through the object. A coded ultrasonic pulse train is also used to make ultrasonic images.

Development of a Detector of Variation of Underground Water Level Using Ultrasound

A system which measures the variation of underground water level in a bored hole using ultrasound is proposed. The principle of the measurement is the ultrasonic pulse echo method. A transducer is hung in the underground water and sends 1 MHz of ultrasound with a 50 µs pulse width upward to the water surface. The equipment has the ability to measure a depth of about 15 m with almost 3 cm resolution. An experiment using a telemeter system was carried out in a landslide area where there was much snow and no commercial power supply; the rising of the water level was observed with the thawing of the snow.

Positron Emission Tomography計測における重み付け積分法による3コンパートメントモデル3速度定数の推定

A simulation study to evaluate the errors in rate constants of the three compartment model using the weighted integral method was performed. Ten combinations of 7 kinds of weight functions, the errors were tested in 18F fluorodeoxyglucose (18FDG) study. The error factors arising in PET measurement were statistical noise, cerebral blood volume, time shift and scanning time of PET measurement. Errors in each rate constant were within the range of 10 percent and those in k1k3/(k2+k3) within 1 percent. The weighted integral method was confirmed to be a faster method than the conventional least squares method within a reasonable error range.

Detection of Starved Joints in Plywood by Acoustic Emissions

The automatic evaluatation of the adhesive strength of plywood is beyond the capabilities of methods proposed to date, and development of such a test methods is most important. Detection of starved joints in plywood by acoustic emissions (AE) method was therefore attempted. Test specimens with and without starved joints were prepared of 2-ply plywood. AEs generated from plywood specimens with and without starved joints were measured during the cooling of plywood thermally stressed by a hot press, and AE characteristics of the two kinds of specimens were compared.

Inspection of Interior Adhesion in Plywood by Means of Acoustic Emission

A trial inspection was made of interior adhesion in plywood using the acoustic emission (AE) method. A bending test investigated the relation between AE characteristics and samples with and without adhesion in plywood. It was found that for sample C without adhesion AE started to count at an early stage of mechanical load. Also, sample C gave various amplitudes in the range from 30 kHz to 100 kHz even at an early stage of mechanical load.