This article proposes a multimode neuromorphic event-frame integrated vision sensor that enables event detection (ED) with simultaneous brightness measurement based on the pulse width modulation mechanism. The logarit...
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This article proposes a multimode neuromorphic event-frame integrated vision sensor that enables event detection (ED) with simultaneous brightness measurement based on the pulse width modulation mechanism. The logarithmic voltage is directly taken as intensity information. Brightness measurement involves in-pixel voltage-to-pulse conversion and out-pixel pulse coding. The maximum event bandwidth is improved to 366 Meps by pipelining the time-prior arbiter along with the address-events grouping circuit. A wide intensity dynamic range of 105 dB can theoretically be achieved through logarithmic photoelectric conversion and pulse coding. Our sensor supports a 128x64 frame-like image with an improved signal-to-noise ratio of 49 dB. The experimental results indicate that the log sensitivity of the optimized logarithmic photoreceptor was measured as 164 mV/dec. The equivalent frame rate for both event and intensity reaches kilo fps, making it a promising candidate in high-speed wireless sensing applications.
Underwater distance/length sensing serves a fundamental function and plays a crucial role in a wide range of applications, including topography and geomorphology in remote sensing. Advanced light detection and ranging...
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Underwater distance/length sensing serves a fundamental function and plays a crucial role in a wide range of applications, including topography and geomorphology in remote sensing. Advanced light detection and ranging (LiDAR) systems and algorithms are significant for underwater tasks, such as objection positing, target searching, and rescuing. In this article, we propose a dual-comb interferometer-based LiDAR system to achieve accurate underwater absolute distance measurement. Specifically, the system applies a well-designed pulse coding strategy that significantly expands the nonambiguity range (NAR) for underwater distance measurements, allowing for precise long-distance measurements in a single attempt. Besides, we introduce a correction process to handle the water group refractive index problem. Compared with reference values, experimental results show that the range fluctuation is within +/- 15 m at a 12 m measurement range, and the Allan deviation is 0.62 mu m over an average time of 100 s. In practice, this LiDAR solution with a micrometer-level precision is promising for various applications in ocean engineering.
Distributed optical fiber vibration sensor (DOFVS) is suitable for remote monitoring of vibration signals generated by external perturbations. In order to improve the sensing performance, various pulse coding techniqu...
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Distributed optical fiber vibration sensor (DOFVS) is suitable for remote monitoring of vibration signals generated by external perturbations. In order to improve the sensing performance, various pulse coding techniques are applied in DOFVS, which have attracted an increasing amount of research attention. In this paper, recent advances of pulse coding methods used in DOFVS are reviewed, from pulse compression, including linear frequency modulation (LFM) and nonlinear frequency modulation (NLFM), pulse coding modulation based on the linear combination and correlation operation, such as Simplex code, Golay code and random code, as well as pulse sequence modulation (PSM), such as phase-shift pulses, differential frequency pulses, etc. Characteristics, working principles and the latest research results of pulse coding methods are discussed. Furthermore, some application progresses of pulse coding for performance enhancement in DOFVS are also introduced. By combining these technologies, the sensing performance could be improved in aspects of sensing distance, spatial resolution (SR), and frequency response, which show considerable potential applications in perimeter security, oil and gas monitoring, pipeline leakage, and structural health monitoring.
This paper introduces two pulse coding control methods for generating notch frequency automatically in noise spread spectrum for switching DC-DC converters;these are based on our previously proposed method. Our two me...
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ISBN:
(纸本)9781665420082
This paper introduces two pulse coding control methods for generating notch frequency automatically in noise spread spectrum for switching DC-DC converters;these are based on our previously proposed method. Our two methods here generate the notch frequency F-n automatically according to the received frequency F-in. The first one is a constant frequency PWM-controlled buck DC-DC converter where the clock frequency and codingpulse width are automatically set according to the frequency of the received signal to generate notch characteristics. The second one is a pulse frequency modulation (PFM) pulse coding DC-DC converter which generates a composite notch characteristic where both the constant pulse width and the periodic modulation codingpulse width are automatically matched with input frequency F-in. Our simulation results show that the transient response is fast and the output voltage overshoot is small.
This paper proposes a noise reduction technology for a specific frequency band that uses the pulse coding controlled method to automatically set the notch frequency in DC-DC switching converters of communication equip...
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This paper proposes a noise reduction technology for a specific frequency band that uses the pulse coding controlled method to automatically set the notch frequency in DC-DC switching converters of communication equipment. For reducing the power levels at the frequency and its harmonics in the switching converter, we often use a frequency-modulated clock. This paper investigates a technology that prevents modulated clock frequency noise from spreading into protected frequency bands;this proposed noise reduction technology does not distribute the switching noise into some specified frequency bands. The notch in the spectrum of the switching pulses is created by the pulse Width coding (PWC) method. In communication devices, the noise in the receiving signal band must be as small as possible. The notch frequency is automatically set to the frequency of the received signal by adjusting the clock frequency using the equation F-n = (P + 0.5)F-ck. Here F-n is the notch frequency, F-ck is the clock frequency, and P is a positive integer that determines the noise spectrum location. Therefore, simply be setting the notch frequency to the received signal frequency can suppress the noise present. We confirm with simulations that the proposed technique is effective for noise reduction and notch generation. Also we implement a method of automatic switching between two receiving channels. The conversion voltage ratio in the pulse width coding method switching converter is analyzed and full automatic notch frequency generation is realized. Experiments on a prototype circuit confirm notch frequency generation.
A new method of reducing coherent Rayleigh noise (CRN) by using Phase Shift Keying (PSK) pulse coding is characterized and demonstrated theoretically and experimentally. A phase modulator driven by an arbitrary functi...
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A new method of reducing coherent Rayleigh noise (CRN) by using Phase Shift Keying (PSK) pulse coding is characterized and demonstrated theoretically and experimentally. A phase modulator driven by an arbitrary function generator is employed to encode pulses with PSK modulation, the traces obtained by coded pulses with different coding orders are superposed and averaged to reduce CRN. The experimental results validate that our method can realize about 0.49 dB amplitude fluctuation in 10 km optical fiber with 10 m spatial resolution when the coding length is 6bit. Compared with the method of FSAV, the method presented in this paper has almost the same CRN reduction effect at different spatial resolutions. From a practical point of view, the proposed method may be attractive in reducing the CRN for the Rayleigh scattering distributed optical fiber sensing system especially when the high spatial resolution and high accuracy are the main concerns.
Optical pulse coding phase-sensitive optical time-domain reflectometry (phi-OTDR) sends a series of pulses into the sensing fiber to enhance signal-to-noise ratio (SNR). And the spatial resolution is determined by the...
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Optical pulse coding phase-sensitive optical time-domain reflectometry (phi-OTDR) sends a series of pulses into the sensing fiber to enhance signal-to-noise ratio (SNR). And the spatial resolution is determined by the subpulse duration. The current challenges in optical pulse coding phi-OTDR include long measurement time, complex coding design, and intricate modulation process. In this paper, pulse intensity coding and mismatched filtering is introduced, which could reach the theoretical measurement time determined by the fiber length. Additionally, it also simplifies coding design and modulation process. In order to obtain satisfactory decoding results, the least-squares criterion is used to design the mismatched filter. Experimental result demonstrates a 6.6 dB improvement in the SNR of the demodulated signal using a 10-bit codingpulse.
This paper proposes a new vector Brillouin optical time-domain analysis optical fiber sensor with large dynamic range and high signal-to-noise ratio that combines distributed Raman amplification with optical pulse cod...
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ISBN:
(纸本)9781510624931
This paper proposes a new vector Brillouin optical time-domain analysis optical fiber sensor with large dynamic range and high signal-to-noise ratio that combines distributed Raman amplification with optical pulse coding. The optimized Raman pumping configurations are numerically simulated by solving the coupled differential equations of the hybrid Brillouin-Raman process, and experimentally investigated with respect to the Brillouin pump pulse. A vector network analyzer is adopted to extract both the amplitude and phase spectrograms of the Brillouin interaction in a distributed fashion which effectively lessens the impact of the Raman relative intensity noise transfer problem and achieve high accuracy measurement over a long sensing distance. Advanced pulse coding is further introduced to increase the sensing range under high spatial resolution. Initial experimental results of phase and amplitude from a custom built BOTDA system is presented. Compared to typically tens of kilometers measurement distance of conventional Brillouin optical time-domain analysis techniques, the proposed optical fiber Brillouin sensor has the potential to greatly enhances sensing range up to one hundred kilometers or greater, providing distributed temperature and strain monitoring of high spatial resolution and high sensing resolution in structures such as oil and natural gas pipelines.
With phase-sensitive optical time-domain reflectometry (Phi-OTDR), an optic fiber can be used as a distributed vibration sensor to perceive the external disturbance along the fiber through the phase variation of the R...
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With phase-sensitive optical time-domain reflectometry (Phi-OTDR), an optic fiber can be used as a distributed vibration sensor to perceive the external disturbance along the fiber through the phase variation of the Rayleigh backscatter light. However, due to the inevitable interference fading phenomenon, the signal-to-noise ratio (SNR) of Rayleigh backscatter light at certain points is insufficient, thus affecting the fidelity of vibration sensing. In this paper, we propose the spectrum extraction and the rotated-vector-sum (SERVS) method to suppress the interference fading in the pulse-intensity-coding Phi-OTDR, which applies Golay complementary sequence through acousto-optic modulator (AOM). Benefited from the easier implementation, the experimental results demonstrate that the percentage of fading points can be reduced from 2.98% to 0.33% significantly and the standard deviation of differential phase is also decreased from 0.6556 rad to 0.2901 rad. Also the minimum level of averaged power spectral density (PSD) of the differential phase at whole locations along the fiber is reduced about 6 dB/Hz effectively. For the demodulated disturbance signal, no influence on the SNR is observed thus it maintains a SNR improvement of 8.6 dB compared to the traditional single pulse Phi-OTDR system, achieving a noise floor of 2.38 pe/root Hz.
Phase-sensitive optical time-domain reflectometry (Phi-OTDR), which utilizes the phase information of Rayleigh scattered lightwave inside optical fiber, could turn a fiber cable into a massive sensor array for distrib...
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Phase-sensitive optical time-domain reflectometry (Phi-OTDR), which utilizes the phase information of Rayleigh scattered lightwave inside optical fiber, could turn a fiber cable into a massive sensor array for distributed acoustic sensing (DAS), i.e., an emerging infrastructure for Internet of Things. Given a certain fiber length, there are tradeoffs among the sensing bandwidth, the sensitivity, and the spatial resolution. In this paper, the concept of linearization and Golay pulse-coding for heterodyne Phi-OTDR are proposed and experimentally verified for the first time. First, we gave a full theoretical treatment on how an intensity-coded yet phase-retrieved Phi-OTDR can be built up as a fully linear system, therefore a significant enhancement of signal-to-noise ratio becomes viable and the sensing bandwidth equals the four-times averaging case. Second in the proof-of-concept experiment, submeter gauge length and nano-strain resolution were realized with 10 km sensing range, in other words, more than ten thousand sensitive sensing units were realized along the fiber. This paper makes a significant step toward high-performance DAS with orders-of-magnitude performance enhancement.
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