ABSTRACT
We propose a novel, to the best of our knowledge, distance recovery method via swept frequency mixing for frequency-modulated continuous wave (FMCW) light detection and ranging (LiDAR) to overcome the Nyquist limit and obtain high data efficiency. A one dimensional (1D) experiment was conducted to recover the optical fiber length; in addition, a 3D image was obtained by recovering the distances of several targets in free space. Compared to conventional methods based on fast Fourier transform (FFT), beat frequency up to 14 times the Nyquist limit for sampling frequency was successfully measured without aliasing. The proposed method dramatically increases the data efficiency in FMCW LiDAR by reducing the number of complex algorithms and experimental resources required.
Subject(s)
Algorithms , Optical FibersABSTRACT
Coherent light detection and ranging (LiDAR), particularly the frequency-modulated continuous-wave LiDAR, is a robust optical imaging technology for measuring long-range distance and velocity in three dimensions (3D). We propose a spatio-spectral coherent LiDAR based on a unique wavelength-swept laser to enable both axial coherent ranging and lateral spatio-spectral beam scanning simultaneously. Instead of the conventional unidirectional wavelength-swept laser, a flutter-wavelength-swept laser (FWSL) successfully decoupled bidirectional wavelength modulation and continuous wavelength sweep, which overcame the measurable distance limited by the sampling process. The decoupled operation in FWSL enabled sequential sampling of flutter-wavelength modulation across its wide spectral bandwidth of 160 nm and, thus, allowed simultaneous distance and velocity measurement over an extended measurable distance. Herein, complete four-dimensional (4D) imaging, combining real-time 3D distance and velocity measurements, was implemented by solid-state beam scanning. An acousto-optic scanner was synchronized to facilitate the other lateral beam scanning, resulting in an optimized solid-state coherent LiDAR system. The proposed spatio-spectral coherent LiDAR system achieved high-resolution coherent ranging over long distances and real-time 4D imaging with a frame rate of 10 Hz, even in challenging environments.
ABSTRACT
The depletion of high-grade and coarse-grain ores has led to an increasing demand for the development of efficient separation technologies for low-grade and fine-grain ores. However, conventional froth flotation techniques are not adequate to efficiently recover fine and ultrafine particles (typically <10-15 µm) due to the low collision probability between these particles and the relatively large bubbles used in the process. The introduction of microbubbles has shown promise in enhancing particle recovery, making it a subject of significant interest. Thus, this review focuses on microbubble generation methods that have the potential to be scaled up for industrial applications, with a specific emphasis on their suitability for froth flotation. The methods are categorized based on their scalability: high-hydrodynamic cavitation, porous media/medium-dissolved air, electrolysis/low-microfluidics, and acoustic methods. The bubble generation mechanisms, characteristics, advantages and limitations of each method and its applications in froth flotation are discussed to provide suggestions for improvement. There is still no appropriate technology that can optimize bubble size distribution, production rate and cost together for industrial froth flotation application. Therefore, novel approaches of combining multiple methods are also explored to achieve the potential synergic effects. By addressing the limitations of current microbubble generation methods and proposing potential enhancements, this review aims to contribute to the development of efficient and cost-effective microbubble generation technologies for fine and ultrafine particles in the froth flotation industry.