A wavelength demultiplexer based on two dimensional photonic crystal waveguides is proposed. By using the finite differ-ence time domain (FDTD) method and plane wave extension (PWE) method,the transmission spectra and...A wavelength demultiplexer based on two dimensional photonic crystal waveguides is proposed. By using the finite differ-ence time domain (FDTD) method and plane wave extension (PWE) method,the transmission spectra and the distributions of mode field are obtained,and the wavelength demultiplexer has been synthesized. The characteristics of the device are obtained.展开更多
The ultrasonic echo in liquid density measurement often suffers noise,which makes it difficult to obtain the useful echo waveform,resulting in low accuracy of density measurement.A denoising method based on improved v...The ultrasonic echo in liquid density measurement often suffers noise,which makes it difficult to obtain the useful echo waveform,resulting in low accuracy of density measurement.A denoising method based on improved variational mode decomposition(VMD)for noise echo signals is proposed.The number of decomposition layers of the traditional VMD is hard to determine,therefore,the center frequency similarity factor is firstly constructed and used as the judgment criterion to select the number of VMD decomposition layers adaptively;Secondly,VMD algorithm is used to decompose the echo signal into several modal components with a single modal component,and the useful echo components are extracted based on the features of the ultrasonic emission signal;Finally,the liquid density is calculated by extracting the amplitude and time of the echo from the modal components.The simulation results show that using the improved VMD to decompose the echo signal not only can improve the signal-to-noise ratio of the echo signal to 20.64 dB,but also can accurately obtain the echo information such as time and amplitude.Compared with the ensemble empirical mode decomposition(EEMD),this method effectively suppresses the modal aliasing,keeps the details of the signal to the maximum extent while suppressing noise,and improves the accuracy of the liquid density measurement.The density measurement accuracy can reach 0.21%of full scale.展开更多
This paper uses a reduced model for simulating propagation of acoustic signals in fluid filled pipelines. The study allows a better understanding of the multipath environment found in a pipeline system with the goal o...This paper uses a reduced model for simulating propagation of acoustic signals in fluid filled pipelines. The study allows a better understanding of the multipath environment found in a pipeline system with the goal of finding optimum solutions for monitoring the pipeline integrity. Data provided both from the simplified model and from an equivalent experimental test rig are implemented using classical time delay estimation algorithms. It is observed an improved accuracy when closing gradually the pipeline end as a result of cancelling the multipath effect at the system＇s terminal.展开更多
文摘A wavelength demultiplexer based on two dimensional photonic crystal waveguides is proposed. By using the finite differ-ence time domain (FDTD) method and plane wave extension (PWE) method,the transmission spectra and the distributions of mode field are obtained,and the wavelength demultiplexer has been synthesized. The characteristics of the device are obtained.
文摘The ultrasonic echo in liquid density measurement often suffers noise,which makes it difficult to obtain the useful echo waveform,resulting in low accuracy of density measurement.A denoising method based on improved variational mode decomposition(VMD)for noise echo signals is proposed.The number of decomposition layers of the traditional VMD is hard to determine,therefore,the center frequency similarity factor is firstly constructed and used as the judgment criterion to select the number of VMD decomposition layers adaptively;Secondly,VMD algorithm is used to decompose the echo signal into several modal components with a single modal component,and the useful echo components are extracted based on the features of the ultrasonic emission signal;Finally,the liquid density is calculated by extracting the amplitude and time of the echo from the modal components.The simulation results show that using the improved VMD to decompose the echo signal not only can improve the signal-to-noise ratio of the echo signal to 20.64 dB,but also can accurately obtain the echo information such as time and amplitude.Compared with the ensemble empirical mode decomposition(EEMD),this method effectively suppresses the modal aliasing,keeps the details of the signal to the maximum extent while suppressing noise,and improves the accuracy of the liquid density measurement.The density measurement accuracy can reach 0.21%of full scale.
文摘This paper uses a reduced model for simulating propagation of acoustic signals in fluid filled pipelines. The study allows a better understanding of the multipath environment found in a pipeline system with the goal of finding optimum solutions for monitoring the pipeline integrity. Data provided both from the simplified model and from an equivalent experimental test rig are implemented using classical time delay estimation algorithms. It is observed an improved accuracy when closing gradually the pipeline end as a result of cancelling the multipath effect at the system＇s terminal.
