Delay Time Of Echo Research Articles

Fractional Fourier transform‐based detection and delay time estimation of moving target in strong reverberation environment

In ocean environments, reverberation is an inevitable interference for active sonar system. The reverberation has many characteristics quite similar to target echo, thus resulting in high false probability during active sonar detection. In this study, a novel method is proposed for both target detection and delay time estimation in environments experiencing strong reverberation. By utilising the focus characteristics of linear frequency modulated signal in fractional Fourier domain and Doppler shift of moving target, optimal transform angle of received signal is applied to detect targets based on fractional Fourier transform (FrFT). The authors have deduced a relationship among delay time, Doppler shift, and transform angle as the energy distribution in fraction Fourier domain is related with the delay time and Doppler shift of target echo. Simulation results have shown that the proposed method can achieve better performance with higher detection probability and lower root-mean-square errors in terms of delay time estimation under low signal-to-reverberation ratio environments as compared with match filter (MF). The experimental results have shown that multiple targets can be detected successfully. In addition, the accuracy of estimated delay time is even higher than MF in severe reverberant environment. It is pertinent to mention that reverberation may be suppressed by setting velocity threshold.

Coherent longitudinal acoustic phonon approaching THz frequency in multilayer Molybdenum Disulphide.

Coherent longitudinal acoustic phonon is generated and detected in multilayer Molybdenum Disulphide (MoS2) with number of layers ranging from 10 to over 1300 by femtosecond laser pulse. For thin MoS2, the excited phonon frequency exhibits a standing wave nature and shows linear dependence on the sample thickness. The frequency varies from 40 GHz to 0.2 THz (10 layers), which promises possible application in THz frequency mechanical resonators. This linear thickness dependence gradually disappears in thicker samples above about 150 layers, and the oscillation period shows linear dependence on the probe wavelength. From both the oscillation period of the coherent phonon and the delay time of acoustic echo, we can deduce a consistent sound velocity of 7.11*103 m/s in MoS2. The generation mechanisms of the coherent acoustic phonon are also discussed through pump power dependent measurement.

Pattern recognition and signal processing of ultrasonic echo signal on two-phase flow

This paper presents a novel measurement method using ultrasonic echo signals on the flow of air–water mixtures. This method has the capability of measuring an instantaneous echo intensity profile along an ultrasonic beam, so it is expected to apply to pattern recognition of two-phase flow. Additionally, this method has an advantage compared with conventional techniques because of the clump-on type. The principle of the flow pattern recognition is based on the delay time and strength of the pulse echo. In this paper, first of all, the transmission of ultrasound through solid plates, which are made of plexiglass and carbon steel, has been investigated and the effective incidence angles for these materials were found. Then, echo signals reflected off a boundary between water and air in a vertical pipe, having a diameter of 50 mm, were obtained using an ultrasound system, and the effects estimated of a two-phase pattern, from bubbly to slug flow, on the signals. In addition, water flows down the inner surface of a pipe as annular flow, and the echo signals then also investigated.

D308 二探触子パルス反射法を用いたタンク内オイルの計測

Pulse ultrasound technique has been applied to measure the reflected echo signals from vapor bubbles in boiling two-phase flow. In this study, an ultrasonic transducer, which has allowable temperature limit of 120°C, was developed for ultrasonic measurement in boiling two-phase flow under atmospheric pressure. The pulse ultrasound transmitted from an ultrasonic transducer enters into a vessel through the wall 1mm thick made of carbon steel, and echo signals are received by the same transducer. So the delay time and strength of a pulse echo is obtained from this measurement, and the effect of boiling phenomena is estimated by the echo distribution.

D307 沸騰二相流の超音波エコー信号による可視化

Pulse ultrasound technique has been applied to measure the reflected echo signals from vapor bubbles in boiling two-phase flow. In this study, an ultrasonic transducer, which has allowable temperature limit of 120°C, was developed for ultrasonic measurement in boiling two-phase flow under atmospheric pressure. The pulse ultrasound transmitted from an ultrasonic transducer enters into a vessel through the wall 1mm thick made of carbon steel, and echo signals are received by the same transducer. So the delay time and strength of a pulse echo is obtained from this measurement, and the effect of boiling phenomena is estimated by the echo distribution.

C310 超音波パルスを用いた気液二相流の流動様式判別

This paper presents a novel measurement method using pulse ultrasound on air-water mixtures flow. The method has the capability to measure an instantaneous echo intensity profile along an ultrasonic beam, so it is expected to apply on pattern recognition of two-phase flow. The principle of the flow pattern recognition is based on delay time and strength of a pulse echo. In this paper, the echo signals reflected on a boundary between water and air, were obtained using an ultrasonic system with a clamp-on transducer, and estimated the effects of two-phase flow pattern, which is from bubbly to slug flow, on the signals.

Analytical efficiency of the molecular rotational quantum echo

The sensitivity of the delay time of the molecular rotational quantum echo to change in the rotational constants of molecules was investigated with a model of the rotational quantum echo considered as an optically induced quantum synchronization of the Fourier rotational modes of an asymmetric molecular top. The J-echo and the K-echo were investigated for the A- and C-configurations of rotation of a top molecule. The contour maps of the dependence of the sensitivity of the delay time of these types of echo to changes in the rotational constants on the parameters of the molecular tops have been obtained for all the rotational constants. They show that the delay time of the rotational quantum echo is greatly dependent on the configuration of rotation of the top molecule and on the rotational constants. It is shown that the optical probing of the rotational quantum echo can also be performed by the optical rotation of the investigated molecule, and in this case the rotational force is dependent on the intramolecular orientation of the magnetic dipole moment. It was determined that a high sensitivity of the delay time of the echo to changes in the rotational constants can be responsible for the broadening of the echo pulse and even for its disappearance.

Bit error rate and power penalty in MSK coherent optical communication systems with a single interfering echo

AbstractIf an echo is generated during transmission, then along with the principal wave (directly transmitted wave), an echo with a certain time delay arrives at the receiver, which causes degradation of receiver performance.In this paper, the bit error rate for optical MSK communication systems with a limiter‐discriminator‐integrator‐type receiver is analyzed and the influence of echo is evaluated qualitatively as well as quantitatively.In general, there exists a floor value on the error rate curve due to the phase fluctuation of laser light in the coherent optical communication systems, which is not reduced upon increasing the received optical power. It is shown that this floor value increases due to the presence of echo and its value is a maximum when the delay time of echo with respect to the principal wave is an integral multiple of the bit duration. Moreover, when the spectral linewidth of the light with high bit rate is narrow, then the effect of echo becomes even stronger.A relationship between the received optical power and bit error rate is derived, and the power penalty is determined for given echo amplitude, delay time, and linewidth‐bit duration product. the conditions under which the effect of echo cannot be neglected are clarified. Moreover, the optical MSK system is compared with the optical DPSK system and it is shown that the MSK signal is degraded by echo greater than the DPSK‐signal.The special feature of this paper is an exact analysis of the case when some phase correlation exists between the principal wave and echo due to coding considerations.