Ion beam figuring （IBF） technology is an effective technique for fabricating continuous phase plates （CPPs） with small feature structures. This study proposes a multi-pass IBF approach with different beam diameter...Ion beam figuring （IBF） technology is an effective technique for fabricating continuous phase plates （CPPs） with small feature structures. This study proposes a multi-pass IBF approach with different beam diameters based on the frequency filtering method to improve the machining accuracy and efficiency of CPPs during IBF. We present the selection principle of the frequency filtering method, which incorporates different removal functions that maximize material removal over the topographical frequencies being imprinted. Large removal functions are used early in the fabrication to figure the surface profile with low frequency. Small removal functions are used to perform final topographical correction with higher fre- quency and larger surface gradient. A high-precision surface can be obtained as long as the filtering frequency is suitably selected. This method maximizes the high removal efficiency of the large removal function and the high corrective capability of the small removal function. Consequently, the fast convergence of the machining accuracy and efficiency can be achieved.展开更多
Deep learning-assisted facial expression recognition has been extensively investigated in sentiment analysis,human-computer interaction,and security surveillance.Generally,the recognition accuracy in previous reports ...Deep learning-assisted facial expression recognition has been extensively investigated in sentiment analysis,human-computer interaction,and security surveillance.Generally,the recognition accuracy in previous reports requires high-quality images and powerful computational resources.In this work,we quantitatively investigate the impacts of frequency-domain filtering on spatial-domain facial expression recognition.Based on the Fer2013 dataset,we filter out 82.64% of high-frequency components,resulting in a decrease of 3.85% in recognition accuracy.Our findings well demonstrate the essential role of low-frequency components in facial expression recognition,which helps reduce the reliance on high-resolution images and improve the efficiency of neural networks.展开更多
A 3rd-order Butterworth active-RC complex band-pass filter was presented for Zig Bee(IEEE802.15.4) transceiver applications. The filter adopted cascaded complex pole stages to realize the 3 MHz bandwidth with a centre...A 3rd-order Butterworth active-RC complex band-pass filter was presented for Zig Bee(IEEE802.15.4) transceiver applications. The filter adopted cascaded complex pole stages to realize the 3 MHz bandwidth with a centre frequency of 2 MHz which was required by the Zig Bee transceiver applications. An automatic frequency tuning scheme was also designed to accommodate the performance deterioration due to the process, voltage and temperature(PVT) variations. The whole filter is implemented in a 0.18 μm standard process and occupies an area of 1.3 mm×0.6 mm. The current dissipation is 1.2 m A from a 1.8 V single power supply. Measurement results show that the image rejection ratio(IRR) of the filter is 24.1 d B with a pass-band ripple less than 0.3 d B. The adjacent channel rejection is 29.8 d B@7 MHz and alternate channel rejection 47.5 d B@12 MHz, respectively.展开更多
By using a loop mirror filter, a novel wavelength-tunable single-frequency ytterbium-doped fiber laser is developed to select single longitudinal modes in a linear cavity. The output wavelength could be tuned 2.4 nm i...By using a loop mirror filter, a novel wavelength-tunable single-frequency ytterbium-doped fiber laser is developed to select single longitudinal modes in a linear cavity. The output wavelength could be tuned 2.4 nm intervals range from 1063.3 to 1065.Tnrn with the temperature change of the fiber Bragg grating. The maximum output power could reach 32 m W while the pump power increases to 120 m W. The corresponding optical-to-optical conversion efficiency is 26.7% and the slope efficiency is 33.9%, respectively. The output power fluctuation is below 2%, and its highest signal-to-noise ratio is 60 dB.展开更多
In the mechanical fault detection and diagnosis field, it is more and more important to analyze the instantaneous frequency （IF） character of complex vibration signal. The improved IF estimation method is put forwar...In the mechanical fault detection and diagnosis field, it is more and more important to analyze the instantaneous frequency （IF） character of complex vibration signal. The improved IF estimation method is put forward aiming at the shortage of traditional Hilbert transform. It is based on Hilbert transform in wavelet domain. With the help of relationship between the real part and the imaginary part obtained from the complex coefficient of continuous wavelet transform or the analyti- cal signal reconstructed in wavelet packet decomposition, the instantaneous phase function of the subcomponent is extracted. In order to improve the precise of IF estimated out, some means such as Linear regression, adaptive filtering, resampling are applied into the instantaneous phase obtained, then, the central differencing operator is used to get desired IF. Simulation results with synthetic and gearbox fault signals are included to illustrate the proposed method.展开更多
Based on time correlation characteristic, width correlation characteristic and frequency correlation characteristic of detecting pulses, several methods are introduced to control random or periodic noise whose width i...Based on time correlation characteristic, width correlation characteristic and frequency correlation characteristic of detecting pulses, several methods are introduced to control random or periodic noise whose width is narrower than 1 ms or wider than 3 ms in Frequency Selection Detecting Radar System. The software flow chart and the results of the experiment are also given.展开更多
In this paper human face machine identification is experienced using optical correlation techniques in spatial frequency domain. This approach is tested on ORL dataset of faces which includes face images of 40 subject...In this paper human face machine identification is experienced using optical correlation techniques in spatial frequency domain. This approach is tested on ORL dataset of faces which includes face images of 40 subjects, each in 10 different positions. The examined optical setup relies on optical correlation based on developing optical Vanderlugt filters and its basics are described in this article. With the limitation of face database of 40 persons, the recognition is examined successfully with nearly 100% of accuracy in matching the input images with their respective Vanderlugt synthesized filters. Software simulation is implemented by using MATLAB for face identification.展开更多
The backscattering signal, which arises from the pulsed laser traveling through water, has limited the lidar system sensitivity and underwater target contrast. The transmitted optical carrier is modulated to be ultras...The backscattering signal, which arises from the pulsed laser traveling through water, has limited the lidar system sensitivity and underwater target contrast. The transmitted optical carrier is modulated to be ultrashort pulsed laser and it is effective to suppress the backscattering to adopt the coherent detection technology by identifying the modulation envelope. A nonstationary light field is formed in seawater by the ultrashort pulsed laser. The inherent relationship between the nonstationary light field formed by modulated lidar and the stationary light field formed by conventional lidar was discussed and the backscattering light model of the stationary light field for the ultrashort pulsed laser was proposed. The backscattering signal in modulated lidar system was processed and analyzed in the frequency domain on the basis of the model.展开更多
In recent years,WiFi indoor positioning technology has become a hot research topic at home and abroad.However,at present,indoor positioning technology still has many problems in terms of practicability and stability,w...In recent years,WiFi indoor positioning technology has become a hot research topic at home and abroad.However,at present,indoor positioning technology still has many problems in terms of practicability and stability,which seriously affects the accuracy of indoor positioning and increases the complexity of the calculation process.Aiming at the instability of RSS and the more complicated data processing,this paper proposes a low-frequency filtering method based on fast data convergence.Low-frequency filtering uses MATLAB for data fitting to filter out low-frequency data;data convergence combines the mean and multi-data parallel analysis process to achieve a good balance between data volume and system performance.At the same time,this paper combines the position fingerprint and the relative position method in the algorithm,which reduces the error on the algorithm system.The test results show that the strategy can meet the requirements of indoor passive positioning and avoid a large amount of data collection and processing,and the average positioning error is below 0.5 meters.展开更多
A hybrid image allows multiple image interpretations to be modulated by the viewing distance.Originally,it can be constructed by combining the low and high spatial frequencies of two different images.The original hybr...A hybrid image allows multiple image interpretations to be modulated by the viewing distance.Originally,it can be constructed by combining the low and high spatial frequencies of two different images.The original hybrid image synthesis was limited to similar shapes of source images that were aligned in the edges,e.g.,faces with a different expression,to produce an effective double image interpretation.In our previous work,we proposed a noiseinserted method for synthesizing a hybrid image from dissimilar shape images or unaligned images.In this work,we propose a novel method for adding an image to be seen from a middle viewing distance.The middlefrequency(MF)image is extracted by a special bandpass filter,which generates ringing while extracting only specified frequency bands.With this method,the middle frequency should be perceived as a meaningless pattern when viewed from a far distance and close up.A parameter tuning experiment was performed to determine the suitable cutoff frequencies for designing the filter for the MF image.We found that ringings of a suitable size could be used to make the middle frequency less noticeable when seen from far away.展开更多
In this paper, the problem of parameter estimation of the combined radar signal adopting chaotic pulse position modulation （CPPM） and linear frequency modulation （LFM）, which can be widely used in electronic count...In this paper, the problem of parameter estimation of the combined radar signal adopting chaotic pulse position modulation （CPPM） and linear frequency modulation （LFM）, which can be widely used in electronic countermeasures, is addressed. An approach is proposed to estimate the initial frequency and chirp rate of the combined signal by exploiting the second-order cyclostationarity of the intra-pulse signal. In addition, under the condition of the equal pulse width, the pulse repetition interval （PRI） of the combined signal is predicted using the low-order Volterra adaptive filter. Simulations demonstrate that the proposed cyclic autocorrelation Hough transform （CHT） algorithm is theoretically tolerant to additive white Gaussian noise. When the value of signal noise to ratio （SNR） is less than 4 dB, it can still estimate the intra-pulse parameters well. When SNR = 3 dB, a good prediction of the PRI sequence can be achieved by the Volterra adaptive filter algorithm, even only 100 training samples.展开更多
The ring microresonator filter considering resonator inner loss is analyzed theoretically, which has one input port and two output ports. Some universal relations for coupling of optical power between microresonator a...The ring microresonator filter considering resonator inner loss is analyzed theoretically, which has one input port and two output ports. Some universal relations for coupling of optical power between microresonator and dielectric waveguides are presented. The analytical expressions of filter bandwidth or the full width at half maximum(FWHM), free spectral range and finesse of resonator are derived. The characteristics of the ring microresonator filter are discussed numerically. It is demonstrated that the loss of the ring resonator reduces the peak value of transmission, widens the filter bandwidth, and reduces the finesse of the resonator filter.展开更多
Associated with ITU-T G.719,a post-processing method in frequency domain for enhancing the perceptual quality of the decoded transient audio is proposed only to the audio decoder with no side information from the enco...Associated with ITU-T G.719,a post-processing method in frequency domain for enhancing the perceptual quality of the decoded transient audio is proposed only to the audio decoder with no side information from the encoder.The proposed post-filter is used to filter the frequency coefficients of the decoded transient frame and consists of a short-term post-filter and a spectral tilt compensation filter which are derived from linear predictive coding（LPC） predictor based on the discrete cosine transform（DCT） coefficients of the decoded transient frame.As a result,the post-filter in frequency domain shapes the temporal noise in time domain and controls the pre-echo noise effectively while enhancing the transient perception.Listening test results show that the preferring ratio of the post-processed transient signal is higher than that of the original decoded signal at a low bit rate of 32 kbit/s in G.719 and the post-processing module brings a complexity of 12.399 WMOPS to the decoder.展开更多
The theoretical model of spatial noise passing through a spatial filter is established in high power laser system under the small signal approximation. The transmission characteristic for a noise signal passing throug...The theoretical model of spatial noise passing through a spatial filter is established in high power laser system under the small signal approximation. The transmission characteristic for a noise signal passing through spatial filters with different magnifications is analyzed by numerical simulation, according to the actual structure of the high power laser system. The results show that the spatial modulation period of low-frequency noise getting through the pinhole will be proportional to the magnification of the spatial filter. When the magnification is less than 1, the safe low-frequency noise will be extruded into the high-frequency region, which is the fast increasing part, and finally develops into the most dangerous part which can damage the optical devices. The conclusion of this research improves the relay imaging theory of a spatial filter and provides an important theoretical basis for a general design of high power laser systems.展开更多
A fourth-order Gm-C Chebyshev low-pass filter is presented as channel selection filter for reconfigurable multi-mode wireless receivers. Low-noise technologies are proposed in optimizing the noise characteristics of b...A fourth-order Gm-C Chebyshev low-pass filter is presented as channel selection filter for reconfigurable multi-mode wireless receivers. Low-noise technologies are proposed in optimizing the noise characteristics of both the Gm cells and the filter topology. A frequency tuning strategy is used by tuning both the transconductance of the Gm cells and the capacitance of the capacitor banks. To achieve accurate cut-off frequencies, an on-chip calibration circuit is presented to compensate for the frequency inaccuracy introduced by process variation. The filter is fabricated in a 0.13 m CMOS process. It exhibits a wide programmable bandwidth from 322.5 k Hz to20 MHz. Measured results show that the filter has low input referred noise of 5.9 n V/（Hz）^（1/2） and high out-of-band IIP3 of 16.2 d Bm. It consumes 4.2 and 9.5 m W from a 1 V power supply at its lowest and highest cut-off frequencies respectively.展开更多
Lithium niobate (LiNbO_(3))and lithium tantalate (LiTaO_(3))are a class of multifunctional materials with excellent piezoelectric/ferroelectric,electro-optic,and nonlinear optical properties,which have wide applicatio...Lithium niobate (LiNbO_(3))and lithium tantalate (LiTaO_(3))are a class of multifunctional materials with excellent piezoelectric/ferroelectric,electro-optic,and nonlinear optical properties,which have wide applications in high-performance radio fre-quency filters,optical communications,integrated photonics,quantum information,and other fields.With the advent of the post-Moore era of integrated circuit technology,LiNbO_(3)/LiTaO_(3) thin-film also shows great potential and advantages in new concept chip applications.High-quality single-crystal thin films lay the foundation for high-performance radio frequency,optoelectronic,and quantum devices and their integration.This review first introduces the main characteristics of LiNbO_(3)/LiTaO_(3) single-crystal thin films,such as ferroelectricity,piezoelectricity,electro-optic effect and nonlinear optical effect,then introduces the preparation methods of LiNbO_(3)/LiTaO_(3) single-crystal thin films represented by smart-cut and their application progress in different fields such as waveguides,modulators,laterally excited bulk acoustic wave resonators,and quantum devices.The application prospects and challenges of LiNbO_(3)/LiTaO_(3) single-crystal thin films in post-Moore era chips are also discussed in this article,aiming to provide valuable references for their development and application.展开更多
In this paper, we study a composite preconditioner that combines the modified tangential frequency filtering decomposition with the ILU（O） factorization. Spectral property of the composite preconditioner is examined...In this paper, we study a composite preconditioner that combines the modified tangential frequency filtering decomposition with the ILU（O） factorization. Spectral property of the composite preconditioner is examined by the approach of Fourier analysis. We illustrate that condition number of the preconditioned matrix by the composite preconditioner is asymptotically bounded by O（hp -2/3） on a standard model problem. Performance of the composite preconditioner is compared with other preconditioners on several problems arising from the discretization of PDEs with discontinuous coefficients. Numerical results show that performance of the proposed composite preconditioner is superior to other relative preconditioners.展开更多
In order to enhance the signal-to-noise-ratio of a distributed acoustic sensing system based on phase-sensitive optical time-domain reflectometry （φ-OTDR）, we have proposed a combination of segmented unwrapping alg...In order to enhance the signal-to-noise-ratio of a distributed acoustic sensing system based on phase-sensitive optical time-domain reflectometry （φ-OTDR）, we have proposed a combination of segmented unwrapping algorithm, averaging estimation of phase difference, and infinite impulse response （IIR） filtering method. The enhancement of signal quality is numerically demonstrated. Moreover, we have studied the influence resulted from the light source noise on the φ-OTDR performance. The result has shown that when the linewidth of light source used in the φ-OTDR system is narrower, the performance of the system is better. In a word, such a φ-OTDR system could obtain higher quality demodulated signals when the narrower linewidth light source is chosen and the method of averaging estimation phase difference is used.展开更多
In wireless communication, the space-time anti-jamming method is widely applied because it shows better performance than the pure airspace and pure temporal anti-jamming methods. However, its application is limited by...In wireless communication, the space-time anti-jamming method is widely applied because it shows better performance than the pure airspace and pure temporal anti-jamming methods. However, its application is limited by its computational complexity, and it cannot suppress narrowband interference that is in the same direction as the navigation signal. To solve these problems, we propose improved frequency filter to filter the narrowband interference from the desired signal direction in advance, meanwhile, an improved variable step Least Mean Square （LMS） method is proposed to complete the space-time array weights with fast iteration, thereby reducing computational complexity. The simulation results show that, compared with conventional methods, the anti-jamming capability of the proposed algorithm is significantly enhanced; and its complexity is significantly reduced.展开更多
This paper studies an algorithm about separating spectrally overlapping signals using the cyclostationary properties of signals.On the basis of direct sequence spread system(DSSS),frequency shift filter is added into ...This paper studies an algorithm about separating spectrally overlapping signals using the cyclostationary properties of signals.On the basis of direct sequence spread system(DSSS),frequency shift filter is added into the re-ceiver of the communication system.Although the structure of frequency shift filter is more complicated than the time-domain filter,it uses both time correlations and fre-quency spectrum correlations so it can achieve better per-formances on separating the overlapping signals.After the analysis of cyclostationary characteristic and frequency spec-trum correlation,the structure of the frequency shift filter can be gained.Then,a self-adaptive algorithm is utilized for the purpose of achieving optimum multidimensional tap weights of frequency shift components.The simulation results indi-cate that this method can efficiently separate overlapping signals,and its error rate is lower than the time-domain filter or DSSS system by two orders of magnitude on the condition that high-power interference is added into the system.展开更多
基金Acknowledgements We gratefully acknowledge the support of the National Natural Science Foundation of China （Grant Nos. 91323302 and 61505259） and the Program for New Century Excellent Talents in University （NCET- 13 -0165）.
文摘Ion beam figuring （IBF） technology is an effective technique for fabricating continuous phase plates （CPPs） with small feature structures. This study proposes a multi-pass IBF approach with different beam diameters based on the frequency filtering method to improve the machining accuracy and efficiency of CPPs during IBF. We present the selection principle of the frequency filtering method, which incorporates different removal functions that maximize material removal over the topographical frequencies being imprinted. Large removal functions are used early in the fabrication to figure the surface profile with low frequency. Small removal functions are used to perform final topographical correction with higher fre- quency and larger surface gradient. A high-precision surface can be obtained as long as the filtering frequency is suitably selected. This method maximizes the high removal efficiency of the large removal function and the high corrective capability of the small removal function. Consequently, the fast convergence of the machining accuracy and efficiency can be achieved.
基金supported by the Project of Jiangsu Education Department(No.2023SJYB0677)the Natural Science Foundation of Jiangsu Province(No.BK20240005)+1 种基金the Fundamental Research Funds for the Central Universities(No.021314380268)the Science Research Project of Nanjing University of Science and Technology Zi Jin College(No.2022ZXKX0401012)。
文摘Deep learning-assisted facial expression recognition has been extensively investigated in sentiment analysis,human-computer interaction,and security surveillance.Generally,the recognition accuracy in previous reports requires high-quality images and powerful computational resources.In this work,we quantitatively investigate the impacts of frequency-domain filtering on spatial-domain facial expression recognition.Based on the Fer2013 dataset,we filter out 82.64% of high-frequency components,resulting in a decrease of 3.85% in recognition accuracy.Our findings well demonstrate the essential role of low-frequency components in facial expression recognition,which helps reduce the reliance on high-resolution images and improve the efficiency of neural networks.
基金Projects(61334003,61274026) supported by the National Natural Science Foundation of ChinaProject(K5051225006) supported by the Fundamental Research Fund for the Central Universities,China
文摘A 3rd-order Butterworth active-RC complex band-pass filter was presented for Zig Bee(IEEE802.15.4) transceiver applications. The filter adopted cascaded complex pole stages to realize the 3 MHz bandwidth with a centre frequency of 2 MHz which was required by the Zig Bee transceiver applications. An automatic frequency tuning scheme was also designed to accommodate the performance deterioration due to the process, voltage and temperature(PVT) variations. The whole filter is implemented in a 0.18 μm standard process and occupies an area of 1.3 mm×0.6 mm. The current dissipation is 1.2 m A from a 1.8 V single power supply. Measurement results show that the image rejection ratio(IRR) of the filter is 24.1 d B with a pass-band ripple less than 0.3 d B. The adjacent channel rejection is 29.8 d B@7 MHz and alternate channel rejection 47.5 d B@12 MHz, respectively.
基金Supported by the International Cooperation Projects of Ministry of Science and Technology under Grant No 2012DFB10120the National Natural Science Foundation of China under Grant No 61177059
文摘By using a loop mirror filter, a novel wavelength-tunable single-frequency ytterbium-doped fiber laser is developed to select single longitudinal modes in a linear cavity. The output wavelength could be tuned 2.4 nm intervals range from 1063.3 to 1065.Tnrn with the temperature change of the fiber Bragg grating. The maximum output power could reach 32 m W while the pump power increases to 120 m W. The corresponding optical-to-optical conversion efficiency is 26.7% and the slope efficiency is 33.9%, respectively. The output power fluctuation is below 2%, and its highest signal-to-noise ratio is 60 dB.
基金This project is supported by National Natural Science Foundation of China (No.50605065)Natural Science Foundation Project of CQ CSTC(No.2007BB2142).
文摘In the mechanical fault detection and diagnosis field, it is more and more important to analyze the instantaneous frequency （IF） character of complex vibration signal. The improved IF estimation method is put forward aiming at the shortage of traditional Hilbert transform. It is based on Hilbert transform in wavelet domain. With the help of relationship between the real part and the imaginary part obtained from the complex coefficient of continuous wavelet transform or the analyti- cal signal reconstructed in wavelet packet decomposition, the instantaneous phase function of the subcomponent is extracted. In order to improve the precise of IF estimated out, some means such as Linear regression, adaptive filtering, resampling are applied into the instantaneous phase obtained, then, the central differencing operator is used to get desired IF. Simulation results with synthetic and gearbox fault signals are included to illustrate the proposed method.
基金Supported by the 86 3High Technology Project of China( 86 3-8180 2 )
文摘Based on time correlation characteristic, width correlation characteristic and frequency correlation characteristic of detecting pulses, several methods are introduced to control random or periodic noise whose width is narrower than 1 ms or wider than 3 ms in Frequency Selection Detecting Radar System. The software flow chart and the results of the experiment are also given.
文摘In this paper human face machine identification is experienced using optical correlation techniques in spatial frequency domain. This approach is tested on ORL dataset of faces which includes face images of 40 subjects, each in 10 different positions. The examined optical setup relies on optical correlation based on developing optical Vanderlugt filters and its basics are described in this article. With the limitation of face database of 40 persons, the recognition is examined successfully with nearly 100% of accuracy in matching the input images with their respective Vanderlugt synthesized filters. Software simulation is implemented by using MATLAB for face identification.
文摘The backscattering signal, which arises from the pulsed laser traveling through water, has limited the lidar system sensitivity and underwater target contrast. The transmitted optical carrier is modulated to be ultrashort pulsed laser and it is effective to suppress the backscattering to adopt the coherent detection technology by identifying the modulation envelope. A nonstationary light field is formed in seawater by the ultrashort pulsed laser. The inherent relationship between the nonstationary light field formed by modulated lidar and the stationary light field formed by conventional lidar was discussed and the backscattering light model of the stationary light field for the ultrashort pulsed laser was proposed. The backscattering signal in modulated lidar system was processed and analyzed in the frequency domain on the basis of the model.
文摘In recent years,WiFi indoor positioning technology has become a hot research topic at home and abroad.However,at present,indoor positioning technology still has many problems in terms of practicability and stability,which seriously affects the accuracy of indoor positioning and increases the complexity of the calculation process.Aiming at the instability of RSS and the more complicated data processing,this paper proposes a low-frequency filtering method based on fast data convergence.Low-frequency filtering uses MATLAB for data fitting to filter out low-frequency data;data convergence combines the mean and multi-data parallel analysis process to achieve a good balance between data volume and system performance.At the same time,this paper combines the position fingerprint and the relative position method in the algorithm,which reduces the error on the algorithm system.The test results show that the strategy can meet the requirements of indoor passive positioning and avoid a large amount of data collection and processing,and the average positioning error is below 0.5 meters.
文摘A hybrid image allows multiple image interpretations to be modulated by the viewing distance.Originally,it can be constructed by combining the low and high spatial frequencies of two different images.The original hybrid image synthesis was limited to similar shapes of source images that were aligned in the edges,e.g.,faces with a different expression,to produce an effective double image interpretation.In our previous work,we proposed a noiseinserted method for synthesizing a hybrid image from dissimilar shape images or unaligned images.In this work,we propose a novel method for adding an image to be seen from a middle viewing distance.The middlefrequency(MF)image is extracted by a special bandpass filter,which generates ringing while extracting only specified frequency bands.With this method,the middle frequency should be perceived as a meaningless pattern when viewed from a far distance and close up.A parameter tuning experiment was performed to determine the suitable cutoff frequencies for designing the filter for the MF image.We found that ringings of a suitable size could be used to make the middle frequency less noticeable when seen from far away.
基金supported by the National Natural Science Foundation of China under Grant 61172116
文摘In this paper, the problem of parameter estimation of the combined radar signal adopting chaotic pulse position modulation （CPPM） and linear frequency modulation （LFM）, which can be widely used in electronic countermeasures, is addressed. An approach is proposed to estimate the initial frequency and chirp rate of the combined signal by exploiting the second-order cyclostationarity of the intra-pulse signal. In addition, under the condition of the equal pulse width, the pulse repetition interval （PRI） of the combined signal is predicted using the low-order Volterra adaptive filter. Simulations demonstrate that the proposed cyclic autocorrelation Hough transform （CHT） algorithm is theoretically tolerant to additive white Gaussian noise. When the value of signal noise to ratio （SNR） is less than 4 dB, it can still estimate the intra-pulse parameters well. When SNR = 3 dB, a good prediction of the PRI sequence can be achieved by the Volterra adaptive filter algorithm, even only 100 training samples.
基金Key Project Foundation from Depart ment of Education of Hubei Province(D200512011)
文摘The ring microresonator filter considering resonator inner loss is analyzed theoretically, which has one input port and two output ports. Some universal relations for coupling of optical power between microresonator and dielectric waveguides are presented. The analytical expressions of filter bandwidth or the full width at half maximum(FWHM), free spectral range and finesse of resonator are derived. The characteristics of the ring microresonator filter are discussed numerically. It is demonstrated that the loss of the ring resonator reduces the peak value of transmission, widens the filter bandwidth, and reduces the finesse of the resonator filter.
基金Supported by the Cooperation Between BIT and Ericsson
文摘Associated with ITU-T G.719,a post-processing method in frequency domain for enhancing the perceptual quality of the decoded transient audio is proposed only to the audio decoder with no side information from the encoder.The proposed post-filter is used to filter the frequency coefficients of the decoded transient frame and consists of a short-term post-filter and a spectral tilt compensation filter which are derived from linear predictive coding（LPC） predictor based on the discrete cosine transform（DCT） coefficients of the decoded transient frame.As a result,the post-filter in frequency domain shapes the temporal noise in time domain and controls the pre-echo noise effectively while enhancing the transient perception.Listening test results show that the preferring ratio of the post-processed transient signal is higher than that of the original decoded signal at a low bit rate of 32 kbit/s in G.719 and the post-processing module brings a complexity of 12.399 WMOPS to the decoder.
文摘The theoretical model of spatial noise passing through a spatial filter is established in high power laser system under the small signal approximation. The transmission characteristic for a noise signal passing through spatial filters with different magnifications is analyzed by numerical simulation, according to the actual structure of the high power laser system. The results show that the spatial modulation period of low-frequency noise getting through the pinhole will be proportional to the magnification of the spatial filter. When the magnification is less than 1, the safe low-frequency noise will be extruded into the high-frequency region, which is the fast increasing part, and finally develops into the most dangerous part which can damage the optical devices. The conclusion of this research improves the relay imaging theory of a spatial filter and provides an important theoretical basis for a general design of high power laser systems.
基金Project supported by the National Natural Science Foundation of China(No.61574045)
文摘A fourth-order Gm-C Chebyshev low-pass filter is presented as channel selection filter for reconfigurable multi-mode wireless receivers. Low-noise technologies are proposed in optimizing the noise characteristics of both the Gm cells and the filter topology. A frequency tuning strategy is used by tuning both the transconductance of the Gm cells and the capacitance of the capacitor banks. To achieve accurate cut-off frequencies, an on-chip calibration circuit is presented to compensate for the frequency inaccuracy introduced by process variation. The filter is fabricated in a 0.13 m CMOS process. It exhibits a wide programmable bandwidth from 322.5 k Hz to20 MHz. Measured results show that the filter has low input referred noise of 5.9 n V/（Hz）^（1/2） and high out-of-band IIP3 of 16.2 d Bm. It consumes 4.2 and 9.5 m W from a 1 V power supply at its lowest and highest cut-off frequencies respectively.
基金supported by Key R&D Program of Zhejiang(Grant Nos.2024SSYS0043)the National Natural Science Foundation of China(Grant Nos.61921005,62074075)Zhejiang Province introduces and cultivates leading innovation and entrepreneurship teams(Grant Nos.2023TD1035).
文摘Lithium niobate (LiNbO_(3))and lithium tantalate (LiTaO_(3))are a class of multifunctional materials with excellent piezoelectric/ferroelectric,electro-optic,and nonlinear optical properties,which have wide applications in high-performance radio fre-quency filters,optical communications,integrated photonics,quantum information,and other fields.With the advent of the post-Moore era of integrated circuit technology,LiNbO_(3)/LiTaO_(3) thin-film also shows great potential and advantages in new concept chip applications.High-quality single-crystal thin films lay the foundation for high-performance radio frequency,optoelectronic,and quantum devices and their integration.This review first introduces the main characteristics of LiNbO_(3)/LiTaO_(3) single-crystal thin films,such as ferroelectricity,piezoelectricity,electro-optic effect and nonlinear optical effect,then introduces the preparation methods of LiNbO_(3)/LiTaO_(3) single-crystal thin films represented by smart-cut and their application progress in different fields such as waveguides,modulators,laterally excited bulk acoustic wave resonators,and quantum devices.The application prospects and challenges of LiNbO_(3)/LiTaO_(3) single-crystal thin films in post-Moore era chips are also discussed in this article,aiming to provide valuable references for their development and application.
基金The authors thank the anonymous reviewers for their useful comments and suggestions that considerably improve the paper. The first author is indebted to L. Grigori, F. Nataf and P. Kumar for many helpful discussions. The work of the first author was supported in part by the National Natural Science Foundation of China （Grant No. 11301420）.
文摘In this paper, we study a composite preconditioner that combines the modified tangential frequency filtering decomposition with the ILU（O） factorization. Spectral property of the composite preconditioner is examined by the approach of Fourier analysis. We illustrate that condition number of the preconditioned matrix by the composite preconditioner is asymptotically bounded by O（hp -2/3） on a standard model problem. Performance of the composite preconditioner is compared with other preconditioners on several problems arising from the discretization of PDEs with discontinuous coefficients. Numerical results show that performance of the proposed composite preconditioner is superior to other relative preconditioners.
文摘In order to enhance the signal-to-noise-ratio of a distributed acoustic sensing system based on phase-sensitive optical time-domain reflectometry （φ-OTDR）, we have proposed a combination of segmented unwrapping algorithm, averaging estimation of phase difference, and infinite impulse response （IIR） filtering method. The enhancement of signal quality is numerically demonstrated. Moreover, we have studied the influence resulted from the light source noise on the φ-OTDR performance. The result has shown that when the linewidth of light source used in the φ-OTDR system is narrower, the performance of the system is better. In a word, such a φ-OTDR system could obtain higher quality demodulated signals when the narrower linewidth light source is chosen and the method of averaging estimation phase difference is used.
基金supported by the National High-Tech Research and Development (863) Program of China (No.2015AA016901)the International Cooperation Project of Shanxi Province (No.201603D421012)the National Natural Science Foundation of China (Nos.61371062, 61572346, and 61303207)
文摘In wireless communication, the space-time anti-jamming method is widely applied because it shows better performance than the pure airspace and pure temporal anti-jamming methods. However, its application is limited by its computational complexity, and it cannot suppress narrowband interference that is in the same direction as the navigation signal. To solve these problems, we propose improved frequency filter to filter the narrowband interference from the desired signal direction in advance, meanwhile, an improved variable step Least Mean Square （LMS） method is proposed to complete the space-time array weights with fast iteration, thereby reducing computational complexity. The simulation results show that, compared with conventional methods, the anti-jamming capability of the proposed algorithm is significantly enhanced; and its complexity is significantly reduced.
基金supported by the National Natural Science Foundation of China(No.60472053)the Natural Science Foundation of Jiangsu Province(No.BK2003055)+1 种基金the Specialized Research Foundation for the Doctoral Program of Higher Education(No.20030286017)the Science and Technology Brainstrom Program of Jiangsu Province(No.BE2004008).
文摘This paper studies an algorithm about separating spectrally overlapping signals using the cyclostationary properties of signals.On the basis of direct sequence spread system(DSSS),frequency shift filter is added into the re-ceiver of the communication system.Although the structure of frequency shift filter is more complicated than the time-domain filter,it uses both time correlations and fre-quency spectrum correlations so it can achieve better per-formances on separating the overlapping signals.After the analysis of cyclostationary characteristic and frequency spec-trum correlation,the structure of the frequency shift filter can be gained.Then,a self-adaptive algorithm is utilized for the purpose of achieving optimum multidimensional tap weights of frequency shift components.The simulation results indi-cate that this method can efficiently separate overlapping signals,and its error rate is lower than the time-domain filter or DSSS system by two orders of magnitude on the condition that high-power interference is added into the system.
