Fourier Band-pass Filter Research Articles

The angle of arrival estimation of frequency-hopping cooperative object based on software-defined radio

The primary objective of this research is to propose and examine a technique for accurately determining the azimuth angle of cooperative objects. The proposed methodology aims were to achieve fast processing, increased precision, and enhanced safety. A transmitter emitting a continuous wave with a hopping frequency was utilized in combination with interferometry techniques to measure the angle of arrival (AOA) between two antennas. The efficient method incorporates a coarse-to-fine strategy that improves processing speed and azimuth angle accuracy and to effectively eliminate any signal interference, a Fourier bandpass filter is utilized. The coarse estimation is performed using the fast Fourier transform (FFT) algorithm, while the fine estimation is achieved using the multiple signal classification (MUSIC) algorithm. The fine estimation involves utilizing coarse angle input and a scan limit of 2.5° that is determined from the largest simulated root mean square error (RMSE) value. Modelling and outdoor testing using software defined radio (SDR) have been carried out to assess the proposed methodology. The results from the analysis indicate that the proposed method produces the desired RMSE estimation of less than 1°, thereby validating its accuracy and effectiveness.

Influence of surface roughness frequencies and roughness parameters on lubricant wettability transitions in micro-nano scale hierarchical surfaces

In this work, the influence of surface roughness frequencies and roughness parameters on mixed wetting and its transitions are discussed. Sessile drop experiments were conducted on hierarchical engineering surfaces having multiple roughness frequencies. Results show that the net roughness Ra or Rq (RMS roughness) solely cannot dictate the wettability behavior. Fourier Band Pass Filtering (FBPF) and Power Spectral Density (PSD) analysis revealed that all roughness frequencies in a hierarchical rough surface contribute to the net Ra and Rq; however, all need not contribute to wettability transitions. Rz and LSm were found to be the roughness parameters that could predict the range of spatial roughness frequencies that dictate wettability transitions to near Wenzel and Cassie-Baxter states.

Application of a New Combination Algorithm in ELF-EM Processing

With regards to the electromagnetic measurement while drilling (EM-MWD), the extremely-low frequency electromagnetic wave signal (ELF-EM) below 20 Hz is usually used as the carrier of downhole measurement data due to the transmission characteristics of the electromagnetic wave (EM). However, influenced by the low frequency noise of drilling, the ELF-EM signal will be inevitably interfered by field noise, which ultimately impedes decoding. The Fourier band-pass filter can effectively remove out-of-band noise but is incapable of handling in-band noise. Therefore, based on the traditional method, a hybrid algorithm of adaptive Wiener algorithm and correlation detection (AWCD) is designed, so as to enhance the in-band noise processing capability, and the effectiveness of such algorithm is well verified through coding and decoding simulation as well as experimental data. The proposed algorithm, as indicated by theoretical analysis and test data, can effectively solve actual engineering issues, providing methodological references to engineers and technicians.

Hollow-Core Fiber-Based All-Fiber FPI Sensor for Simultaneous Measurement of Air Pressure and Temperature

In paper, an all-fiber Fabry-Perot interferometer (FPI) sensor with cascaded micro-cavities is presented to measure air pressure and temperature simultaneously. The proposed sensor mainly consists of two tiny segments of hollow-core fiber (HCF) located at the end of lead-in single mode fiber (SMF), and there is a misalignment fusion splicing between the two HCFs with different core diameter. The sensor has minor length of about $210~\mu \text{m}$ since the two HCFs lengths are about $80~\mu \text{m}$ and $130~\mu \text{m}$ , respectively. Because the reflection spectrum of the sensor is formed by the fiber cavity, air cavity and their combined cavity, which can be processed by methods of fast Fourier transform (FFT) and Fourier band-pass filter (FBPF), so we can analyze the corresponding responses of every cavity from the reflection spectrum of sensor for temperature and pressure variations. The experiment results show that the sensor has not only two different linear temperature sensitivities but also two different linear pressure sensitivities, which can be used to distinguish air pressure and temperature simultaneously. The validity experiment shows the relative errors of 1.0% and 1.4% are obtained in simultaneous measurements of air pressure and temperature. The advantages of the presented sensor than other structure sensors are miniaturization, easier to manufacture and with lower fabrication cost, which is promising used in the harsh environment monitoring.

Constructed fiber-optic FPI-based multi-parameters sensor for simultaneous measurement of pressure and temperature, refractive index and temperature

Abstract In paper, a multi-parameter measurement sensor based on single-mode fiber and ultra violet (UV) curable adhesive is proposed and fabricated for simultaneously distinguish gas temperature and pressure, liquid refractive index (RI) and temperature. The proposed sensor consists of a fiber Bragg grating (FBG) and three Fabry-Perot interferometers (FPIs) that are fabricated from a tiny segment of single-mode fiber, a section of UV curable adhesive and their integrations. The whole size of experimental sensor is below 1 mm since the combinations of micro-cavity. Interrogation of the sensor utilized Fourier band-pass filter (FBPF) and fast Fourier transform (FFT) signal processing of the reflection spectrum, allows for free extraction of individual cavity resonators’ frequency. Results show that the sensor not only has four different temperature response sensitivities, but also has higher resolutions as it is used in simultaneous distinguishing measurement of pressure and temperature, refractive index and temperature. The maximum resolutions of temperature, pressure and liquid RI are 0.07 °C, 6 × 10−3 MPa and 3 × 10−4 RIU, respectively. The sensor might be applied to distinguish physical parameters related to gas or liquid environment, and work in complex environments such as high pressure.

Simultaneous measurement of gas pressure and temperature with integrated optical fiber FPI sensor based on in-fiber micro-cavity and fiber-tip

Abstract In paper, an integrated optical fiber Fabry-Perot interferometer (FPI) sensor is proposed and fabricated. The all-fiber sensor is composed of an in-fiber micro-cavity machined by 193 nm excimer laser and a tiny segment of single-mode fiber (SMF). Due to the production of reflection mirrors, the composite FPI structure with different interference cavity is formed between every two surfaces of micro-cavity and fiber-tip. Resulting from the influences of thermal expansion effect of fiber and the thermo-optic effect of in-cavity gas, the interference spectrum of FPI sensor can shift with the temperature and pressure change with different rules. Experimental researches indicate, the low-frequency interference fringe of air cavity is sensitive to pressure change and insensitive to temperature change, but the high-frequency interference fringe of micro-fiber cavity is sensitive to temperature change and insensitive to pressure change. Through analyzing with fast Fourier transform (FFT) and Fourier band-pass filtering (FBPF) methods, we obtain the temperature and pressure sensitivities of the two different cavities. Owning to the different responses to gas pressure and temperature change, the fiber sensor can be used in simultaneous measurement of them, and has excellent merits of miniature size, strong tip structure, simple manufacturing and low cost.

Stratospheric ozone intrusion events and their impacts on tropospheric ozone in the Southern Hemisphere

Abstract. Stratosphere-to-troposphere transport (STT) provides an important natural source of ozone to the upper troposphere, but the characteristics of STT events in the Southern Hemisphere extratropics and their contribution to the regional tropospheric ozone budget remain poorly constrained. Here, we develop a quantitative method to identify STT events from ozonesonde profiles. Using this method we estimate the seasonality of STT events and quantify the ozone transported across the tropopause over Davis (69° S, 2006–2013), Macquarie Island (54° S, 2004–2013), and Melbourne (38° S, 2004–2013). STT seasonality is determined by two distinct methods: a Fourier bandpass filter of the vertical ozone profile and an analysis of the Brunt–Väisälä frequency. Using a bandpass filter on 7–9 years of ozone profiles from each site provides clear detection of STT events, with maximum occurrences during summer and minimum during winter for all three sites. The majority of tropospheric ozone enhancements owing to STT events occur within 2.5 and 3 km of the tropopause at Davis and Macquarie Island respectively. Events are more spread out at Melbourne, occurring frequently up to 6 km from the tropopause. The mean fraction of total tropospheric ozone attributed to STT during STT events is ∼ 1. 0–3. 5 % at each site; however, during individual events, over 10 % of tropospheric ozone may be directly transported from the stratosphere. The cause of STTs is determined to be largely due to synoptic low-pressure frontal systems, determined using coincident ERA-Interim reanalysis meteorological data. Ozone enhancements can also be caused by biomass burning plumes transported from Africa and South America, which are apparent during austral winter and spring and are determined using satellite measurements of CO. To provide regional context for the ozonesonde observations, we use the GEOS-Chem chemical transport model, which is too coarsely resolved to distinguish STT events but is able to accurately simulate the seasonal cycle of tropospheric ozone columns over the three southern hemispheric sites. Combining the ozonesonde-derived STT event characteristics with the simulated tropospheric ozone columns from GEOS-Chem, we estimate STT ozone flux near the three sites and see austral summer dominated yearly amounts of between 5. 7 and 8. 7 × 1017 molecules cm−2 a−1.

Full-color holographic projection display system featuring an achromatic Fourier filter.

We propose a full-color complex holographic display system design comprised of three R/G/B amplitude-only spatial light modulators and an achromatic Fourier filter. A key feature of the design is a single achromatic Fourier bandpass filter for robust axial R/G/B color matching, whereby the R/G/B holographic image light fields can be three-dimensionally aligned. The synthesis algorithm producing the full-color computer-generated holograms for this system is described and a full-color optical reconstruction of the designed holographic three-dimensional images is experimentally demonstrated.

Optical Fiber Fabry–Pérot Interferometer Based on an Air Cavity for Gas Pressure Sensing

An optical fiber Fabry–Perot interferometer (FPI) based on an air cavity with a microchannel is proposed and demonstrated for gas pressure measurement. The inner air cavity is fabricated by fusion splicing a single-mode fiber (SMF) with a microhole at the end facet to another section of SMF, then creating a microchannel to vertically cross the air cavity to allow gas to flow in. As the air cavity is cascaded to a short section of SMF, a three-beam interference pattern is produced, which shifts with the gas pressure variation in the inner air cavity due to the refractive index change of the gas. In order to compensate the temperature effect, the multiple-dip tracing technique and the Fourier band pass filtering (FBPF) method are used simultaneously for gas pressure and temperature measurement. It is also found that by using the FBPF method, the gas pressure sensitivity does not depend on the resonant peaks/dips selected in the filtered spectrum of the device. The proposed device has a robust tip structure, miniature size, and high sensitivity (∼4.028 nm/MPa) and is easy to fabricate, which makes it attractive for highly sensitive and precise gas pressure measurement.

Vortex stretching in a homogeneous isotropic turbulence

Stretching vortices whose sizes are in the inertial subrange of a homogeneous isotropic turbulence are picked up, and the geometric relations with the neighboring vortices whose scales are twice larger are studied. Hierarchical vortices are extracted using a Fourier band-pass filter, and each extracted vortex is reconstructed as a set of short cylindrical segments along the vortex axis to discuss the vortex interactions. As a result, it is shown that the directions of larger vortices near the segments of the fast stretching vortices tend to be orthogonal to the direction of the stretching segments, and the locations of the larger vortices that contribute most to the stretching of smaller vortex segments are likely to be found in the direction with the relative angle of 45° from the axes of the stretching vortex segments. And, the vortices with the second highest contributions tend to be in the directions 45° from the stretching segments’ axes and orthogonal to the directions of the highest contributing vortices.

OBSERVATION AND SIMULATION OF TSUNAMIS INDUCED BY THE 2003 TOKACHI-OKI EARTHQUAKE (M 8.0)

The 2003 Tokachi-oki earthquake (MJ 8.0) occurred off the southeastern coast of Tokachi, Japan, and generated a large tsunami which arrived at Tokachi Harbor at 04:56 with a wave height of 4.3 m. Japan Marine Science and Technology Center (JAMSTEC) recovered records of water pressure and sea-bed acceleration at the bottom of the tsunami source region. These records are first introduced with some findings from Fourier analysis and band-pass filter analysis. Water pressure disturbance lasted for over 30 minutes and the duration was longer than those of accelerations. Predominant periods of the pressure looked like those excited by Rayleigh waves. Next, numerical simulation was conducted using the dynamic tsunami simulation technique able to represent generation and propagation of Rayleigh wave and tsunami, with a satisfactory result showing validity and usefulness of this technique.
 
 Keywords: Earthquake, Rayleigh wave, tsunami, near-field

Fourier analyses of commensurability oscillations in Fibonacci lateral superlattices

Magnetotransport measurements have been performed on Fibonacci lateral superlattices---two-dimensional electron gases subjected to a weak potential modulation arranged in the Fibonacci sequence $LSLLSLS\dots{}$ with $L/S=\ensuremath{\tau}$ (golden ratio). Complicated commensurability oscillation (CO) is observed, which can be accounted for as a superposition of a series of COs each arising from a sinusoidal modulation representing the characteristic length scale of one of the self-similar generations in the Fibonacci sequence. Individual CO components can be separated out from the magnetoresistance trace by performing a numerical Fourier band-pass filter. From the analysis of the amplitude of a single-component CO thus extracted, the magnitude of the corresponding Fourier component in the potential modulation can be evaluated. By examining all the Fourier contents observed in the magnetoresistance trace, the profile of the modulated potential seen by the electrons can be reconstructed with some remaining ambiguity about the interrelation of the phase between different components.