Doppler ultrasound system is of great importance among the diagnostic modalities. To ensure the output of such systems that measure the physiological quantities, performance tests were carried out using AIUM and BSI protocols on 20 pulsed wave Doppler systems in 9 reference centers in Tehran. In these tests, velocity of Doppler ultrasound systems as an acoustic parameter was assessed. To evaluate the performance of pulsed wave Doppler, an in-house string phantom was designed for the first time in the country. This phantom was used to investigate pulsed Doppler ultrasound systems. The results show that the minimum and maximum errors in blood flow velocity measurement on 20 Doppler systems were 23 (cm/s) and 83 (cm/s), respectively. The mean±SD for velocity measurement errors in 6 Doppler systems (7.5 MHz) and 12 systems (3.5 MHz) were 11±16 and 28±9 (cm/s), respectively, the velocities ranged 10-140 (cm/s). These errors emphasize the necessity for doing performance tests in Doppler ultrasonic systems.
 

The purpose of this article is to provide an analytical model of the vibroacoustic for an elastic beam submerged in low subsonic flows with mean velocities. In general, vibroacoustic modeling refers to the combined effects of sound propagation and mechanical vibration of the structure. Sound radiations from submerged structures are coupled with physical phenomena because the sound pressures acting on structure surfaces and the dynamic responses of structures will impact each other. The Rayleigh Theory has been used to derive the beam vibration equations, and Green's functions are used to find the response of vibrations and the propagation of sound waves from the elastic beam. Initially, we solve the differential equation governing the Rayleigh beam under harmonic load. Then, the sound wave propagation equation around the beam is solved. The solution of the vibration and sound propagation differential equations must be done in the form of couplings so that at first distinct Green's function is obtained for each of the differential equations, and then by combining these two Green's functions, a coupled response function is found to solve the problem. Further, the vibroacoustic response of the beam was obtained by applying the boundary conditions at the interface between the beam and the fluid. In order to evaluate the process of analysis and validation, the results are compared with the results of other researchers and a good match between the results is observed; then, the effects of fluid velocity and useful parameters on the sound field have been investigated.

According to evidences, it has been observed that the reverberation time is longer than expected and that the cause is a horizontal reverberant field established in the region near the ceiling and far from the audience. Although there are no unfavorable comments about it, this has been also observed in the Boston Symphony Hall, Massachusetts, and the Stadthalle Göttingen. This study is on based of two scaled modeling that the walls and ceiling contained openings in which either plane or scattering panels could be placed. With plane panels, the model reverberation time (RT) was measured as 53% higher than the Sabine prediction, compared with 8% higher with scattering panels. But the second model was lecture theatre with a movable 6 m or 8 m high. In this case, the amount of absorption was increased until the point was reached where speech had acceptable intelligibility, with the early energy fraction, D > 0.5. For this acceptable speech condition, the measured mid-frequency T15 was 1.47s, whereas the Sabine predicted RT was 1.06 s. The sound decay was basically non-linear with T30 > T15 > EDT. Exploiting a high-level horizontal reverberant field offers the possibility of acoustics that are better adapted as suitable for both speech and unamplified music, without any physical change in the auditorium. Optimum using of this secondary reverberation in an auditorium for a wide variety of music might also be beneficial.