Enhanced optical coherence vibration tomography for subnanoscale-displacement-resolution calibration of piezoelectric actuators

We report a subnanoscale-displacement-resolution optical coherence vibration tomography (SOCVT) systemfor real-time calibration of piezoelectric actuators. The calibrations of the actuators at nanoscale or microscale displacement ranges were performed by varying the input voltage over the entire range in the ascending and descending directions. The computational and experimental results demonstrated that the developed SOCVT could be used to characterizethe dynamic hysteretic behaviour, nonlinear effect, and impulsive behaviour of piezoelectric actuators. The SOCVT technique is non-contact and non-invasive in nature, making it ideal for real-time and in situ ultra-precision calibration of piezoelectric actuators, which are widely used in active vibration control and nanopositioning

Sine-modulated wavelength-independent full-range complex spectral optical coherence tomography with an ultra-broadband light source

We present a full-range complex spectral domain optical coherence tomography with an ultra-broadband light source based on sinusoidal modulation. For the sinusoidal modulation strategy, a lead zirconate titanate stack actuator is employed to achieve the sinusoidal vibration of a mirror and therefore to get a series of spectral interferogram with different phase delays. The purpose of this strategy is to get higher performance complex-conjugate artifact elimination. Bessel separation of the signal sequence at each wavelength of the spectrometer was used to reconstruct the real and imaginary components of interference fringes; however, the sinusoidal modulation method is independent of light source wavelength. The experimental results demonstrated that the method had an excellent performance in a complex-conjugate suppression of 50 dB for a full width at half maximum bandwidth of 236 nm, and it has better anti-artifact ability and more flexible range in phase shifting than the conventional wavelength-dependent phase-shifting method on a full-range complex spectral optical coherence tomography system. Furthermore, the effect of the hysteresis error of lead zirconate titanate actuators on the performance of complex-conjugate artifact elimination was investigated and the solution of lead zirconate titanate positioning performance for both conventional phase-shifting and sine-modulation methods was suggested

Two-dimensional optical coherence tomography for real-time structural dynamical characterization

We present a two-dimensional optical coherence vibration tomography (2DOCVT) system with an ultra-precision displacement resolution of ~0.1 nm that is capable of in site real-time absolute displacement measurement of structural line vibrations. Experimental results of sinusoidal, sweep and impulse vibrations were reported. The key figures of merit such as the 2DOCVT system could obtain fast line vibration measurement without scanning and it also could be used to capture structural modal parameters in one single impulse excitation measurement without any vibration excitation input information, making it attractive for the application in low-frequency vibration measurement and response-only modal analysis

Five-Frame Variable Phase-Shifting Method for Full-Range Spectral-Domain Optical Coherence Tomography

In order to achieve a better complex conjugate artifacts (CCA) suppression, we propose a five-frame variable phase-shifting (FVP) method for spectral domain optical coherence tomography (SD-OCT). The traditional five-frame invariant phase-shifting (FIP) method employs five phase shifts correlate with the center wavelength. However, due to the effects of polychromatic errors, the FIP method cannot get excellent CCA suppression. In the present work, we employ FVP method using variable phase shifts which is dependent on all the wavelengths and therefore, theoretically, the system would have no effects of polychromatic errors. This is the reason why the FVP method would achieve better CCA suppression than the FIP method. Comparative studies between FIP and FVP methods are investigated in the work. Subsequently, we develop a homemade SD-OCT system involving a homemade spectrometer, by which the anterior segment of a rat’s eyeball is measured. The experimental results demonstrate that the quality of OCT images is significantly improved by using FVP method with an increase by a factor of 1.7 on the CCA suppression of SD-OCT. FVP provides a new strategy for complex conjugate artifacts suppression for spectral domain optical coherence tomography

Vehicle Tracking Algorithm Based on Deep Learning in Roadside Perspective

Traffic intelligence has become an important part of the development of various countries and the automobile industry. Roadside perception is an important part of the intelligent transportation system, which mainly realizes the effective perception of road environment information by using sensors installed on the roadside. Vehicles are the main road targets in most traffic scenes, so tracking a large number of vehicles is an important subject in the field of roadside perception. Considering the characteristics of vehicle-like rigid targets from the roadside view, a vehicle tracking algorithm based on deep learning was proposed. Firstly, we optimized a DLA-34 network and designed a block-N module, then the channel attention and spatial attention modules were added in the front of the network to improve the overall feature extraction ability and computing efficiency of the network. Next, the joint loss function was designed to improve the intra-class and inter-class discrimination ability of the tracking algorithm, which can better discriminate objects of similar appearance and the color of vehicles, alleviate the IDs problem and improve algorithm robustness and the real-time performance of the tracking algorithm. Finally, the experimental results showed that the method had a good tracking effect for the vehicle tracking task from the roadside perspective and could meet the practical application demands of complex traffic scenes

Parameterized Instantaneous Frequency Estimation Method for Vibration Signal with Nonlinear Frequency Modulation

The vibration signal from the rotatory machinery condition monitoring under time-varying speed is usually amplitude-modulated (AM) and frequency-modulated (FM). It is important to efficiently and accurately estimate the instantaneous frequency (IF) of the vibration signal. In this paper, a novel parameterized IF estimation method is proposed. The method employs a high-order polynomial function to approximate the nonlinear IF and subsequently constructs overdetermined systems of linear equations by calculating the Fourier transform of the derivative of the signal. The IF can be estimated by using least squares estimation to solve the equations. The proposed method has high computational efficiency because it can obtain the estimation of IF over a period of time simultaneously; it differs from traditional time-frequency analysis methods that need to calculate the IF at each point in the time axis. It is demonstrated that the proposed method is not only particularly powerful for the nonlinear FM mono-component signal but also applicable to the multi-component signal constructed by multiple harmonics. The numerical simulation validates the effectiveness of the proposed method, and the experiment’s results show that the method is suitable for the IF estimation of the vibration signal from the varying-speed rotor system

Parameterized Instantaneous Frequency Estimation Method for Vibration Signal with Nonlinear Frequency Modulation

The vibration signal from the rotatory machinery condition monitoring under time-varying speed is usually amplitude-modulated (AM) and frequency-modulated (FM). It is important to efficiently and accurately estimate the instantaneous frequency (IF) of the vibration signal. In this paper, a novel parameterized IF estimation method is proposed. The method employs a high-order polynomial function to approximate the nonlinear IF and subsequently constructs overdetermined systems of linear equations by calculating the Fourier transform of the derivative of the signal. The IF can be estimated by using least squares estimation to solve the equations. The proposed method has high computational efficiency because it can obtain the estimation of IF over a period of time simultaneously; it differs from traditional time-frequency analysis methods that need to calculate the IF at each point in the time axis. It is demonstrated that the proposed method is not only particularly powerful for the nonlinear FM mono-component signal but also applicable to the multi-component signal constructed by multiple harmonics. The numerical simulation validates the effectiveness of the proposed method, and the experiment’s results show that the method is suitable for the IF estimation of the vibration signal from the varying-speed rotor system

Research on the application of the ultra-small GRIN fiber probe

A swept source optical coherence tomography(SS-OCT)system based on the ultra-small gradient-index(GRIN)fiber probe wasset up to measure the thickness of a thin glass. The application effecton this system was analyzed. The comparison analysis of the experimental results with the same thin glass measured by a bare single-mode optical fiber probe proves that the ultra-small GRIN fiber probe has superior focusing performance and signal collection ability