Keinosuke Nagai

Pruning the decimation-in-time FFT algorithm with frequency shift

Fourier transformed components within desired narrow-band can be efficiently calculated by the pruned version of the decimation-in-time FFT algorithm. A new pruning method is proposed here which invloves frequency shift. The shifting simplifies the pruning algorithm because its flowgraph has a repetitive pattern of butterflies between adjacent stages.

Acoustic Measurement of Temperature Distribution in a Room Using a Small Number of Transducers

We propose a method for noncontact measurement of room temperature distribution using a small number of acoustic transducers. The sound propagation velocity is dependent on the air temperature, and it is acquired from the time of flight of sound. The mean temperature parallel to the sound probe is acquired using an acoustic delay line consisting of a pair of transducers. The measured object is a room of size 4,000 mm (D)× 4,200 mm (W) partitioned into a 3×3 grid, with 9 unit cells. By arranging a certain geometrical property of the sound propagation path, we can formulate an expression for the temperature distribution as a matrix function of the sound velocity. Twelve transducers are installed in contact with the four walls. We create a temperature gradient throughout the room using an electrical heat source. Experimental reconstruction results of the room temperature distribution were in agreement with the distributions estimated from the temperature profiles of the heat sources. This technique has the advantages of noncontact sensing, quicker response time and simpler calculation of room temperature distribution, in comparison with conventional temperature measurement systems.

Measurement of Temperature Distribution in Space Using Ultrasound Computerized Tomography

We propose a method for measuring the temperature distribution in space using ultrasound computerized tomography (CT). We verified by simulations and experiments that reconstruction of the air temperature distribution is possible using a time of flight profile. Good experimental results were obtained in the reconstruction of a point heat source 30° hotter than room temperature in an area of 100 mm × 100 mm using ultrasound with a frequency of 40 kHz.

Temperature Distribution in Circular Space Reconstructed from Sampling Data at Unequal Intervals in Small Numbers Using Acoustic Computerized Tomography (A-CT)

The propagation velocity of sound is often used to measure temperature. The sound probe has the advantage of non-contact sensing and quick response. By combining a sound probe with computerized tomography (CT) and data interpolation, an image of temperature distribution through space can be reconstructed. We have proposed a method for measuring the temperature distribution in two-dimensional space using an acoustic CT (A-CT) method with a very small number of acoustic transducers. The measured object is a circular space with a radius of 1,480 mm. Sixteen transducers are installed on the circular stage. Without a mechanical motion, projection data for the reconstruction is acquired by electronic scanning. We reconstruct the temperature distribution by interpolation from a small number of data set. Electrical heaters create a temperature gradient in space. The temperature profile is measured by 19 thermocouples and used for a computer simulation. Experimentally reconstructed images are in agreement with the simulated images. The measurement system proposed in this paper has advantages for use in atmospheric monitoring, air conditioning and heat management.

Generation of Bessel Beam from Equiamplitude-Driven Annular Transducer Array Consisting of a Few Elements

We present a method for generating a nondiffraction beam using an annular transducer array. In this method, each element is driven with equiamplitude and with an antiphase from its neighboring elements. Theoretical and experimental analyses of an array of this type have been carried out, and the feasibility of this method is confirmed. The beam from a continuous wave is shown using radiated pressure magnitude distributions and it is shown that there exist most suitable values of the width and number of elements. When the array is driven by a burst signal, the beam propagates as a plane wave which has an amplitude corresponding to the zeroth-order Bessel function of the first kind, J0. Since this beam is realized by an annular array consisting of a few elements, it suggests the possibility of a transducer of this form developing into a source which generates nondiffraction beams.

Ultrasonic imaging using the Doppler effect caused by a moving transducer

An imaging method using the Doppler effect is proposed in this paper. An object is illuminated by a sinusoidal wave from a linearly moving transducer. The frequency components of the reflected wave can be considered to be projections along lines at specified corresponding angles from the transducer. One can reconstruct images by applying conventional CT (computerized tomography) algorithms to the projections thus obtained. The theory is derived for coherent and incoherent processing. Theoretical results are confirmed by numerical simulations. Experimental results show that coherent Doppler tomography is much higher in resolution but more noisy than incoherent Doppler tomography.

Fast Method for Visualization of Temperature Distribution Using Acoustic Computerized Tomography

Sound velocity is dependent on medium temperature and is estimated from the time of flight of sound. We propose a fast method for the visualization of temperature distribution using acoustic computerized tomography (A-CT). In this study, considering the property of a temperature gradient field, which is the visualization object and is approximated by a Gaussian function, the number of data points required by the CT is optimized and the speed of visualization is improved. As a result of noncontact measurements of the temperature distribution in the circular space of 100 mm radius which includes a high-temperature area of about 40 mm radius, sufficient spatial resolution is obtained by the data acquisition system which combines linear scanning of 11 measurement points and rotational scanning with a 22.5° angular step. In addition to the optimization of the data acquisition geometry, an aerial delay-line oscillator is used for the detection of sound velocity, in order to sensitize and simplify the system. Visualized results obtained by the A-CT agree well with the measurements taken by thermocouples. The fast visualization scheme proposed in this paper has an advantage over conventional methods in such applications as air conditioning, reactor monitoring and atmospheric monitoring among others.

Calculation of Acoustic Near Field from Bessel Beam Transducers with Annular Transducer Array

This paper describes acoustic fields radiated from Bessel beam transducers with an annular ring array. We calculate the fields without the para-axial approximation such as the Fresnel one, in order to elucidate the near fields from the transducers. We find that field intensities from some transducers abruptly increase and decrease in the near region. This makes the transducers inappropriate for imaging applications. Annular transducer elements of width less than 1 wavelength prove to be effective in avoiding the abrupt changes.

Space Thermometry Using a Double Acoustic Delay Line Oscillator

Acoustic thermometry in space using a double-delay line oscillator is described. The delay line oscillator is an important component in the sensor systems. In this paper, the adverse effect of a discontinuous oscillation was solved by adopting an acoustic technique which uses multiple oscillators. An experimental result at 40 kHz shows that the error in measured room temperature is 1.5% in a room 4,020 mm (D)×4,200 mm (W)×3,550 mm (H) with air conditioning. The acoustic thermometry proposed in this paper has advantages over conventional methods for such applications as atmospheric monitoring and air conditioning.

Optical Measurement of Sound Fields Information Using Mach-Zehnder Interferometer

An optical method for measuring information of sound fields using the Mach-Zehnder interferometer is described. The Mach-Zehnder interferometer is advantageous for obtaining quantitative measurements of phase values in comparison to other visualization methods. In this study, we simultaneously investigate a two-dimensional data acquisition system for the projection image of an optical phase deviation in proportion to sound fields below the frequency of 2.16 MHz. In the experiment, the charge-coupled device (CCD) camera is used as a function of a mean value detector. The experimental results of the optical phase deviation along the ultrasound axis are useful as primary data for estimating the sound pressure. The two-dimensional measurement system using a CCD camera proposed in this paper has the advantages of acquiring the data in a short time when used in an environment where the measurement conditions change.