Chunjie Qiao

A novel DSSS based ToF measurement method for short baseline and its application in sound velocimeter

The short baseline framework is commonly used in ultrasonic parameter measurement, and ToF (time of flight) of which is essential in sound velocimeter and other applications. Different from conventional steady-state and transient methods, this paper proposed a new method using DSSS (Direct Sequence Spread Spectrum) signal to extract the ToF. DSSS signal possesses excellent auto-correlation features, thus it does not need to adjust path-length or the acoustic frequency, nor avoid the impact of the multiple echoes. The DSSS signal and measurement system are modeled and the detailed theoretical process of ToF estimation is derived to demonstrate the measurement principles, and the principles of echoesresistance are analyzed. Measurement experiments are carried out using distilled water at ambient pressure with temperature ranging from 19°C to 30°C. The test results indicate that the relative precision of ToF is in bounds of 2 ppm and the bias of sound speed derived is within 0.06m/s compared to Del Grossos equation.

Chaos and wavelet based colonic motility analysis for subjects with constipation

This paper proposes a method for analyzing the colonic motility of subjects with constipation based on chaos and wavelet. Using a capsule system with an application-specific integrated circuit (ASIC), the pressure data of human colon can be monitored accurately. Preprocessing of colonic pressure signal was performed primarily by applying threshold processing and wavelet de-noising. Then, wavelet with six-layer decomposition was implemented based on Daubechies 5 wavelet basis. Hilbert-Huang transform (HHT) was used for analyzing the frequency spectrum of detail signals. Particularly, six features include the peak frequency of detail signal at level 3, the peak frequency of detail signal at level 4, the Lyapunov index, correlation dimension, Kolmogorov entropy, and box dimension of were extracted for diagnosis purposes based on HHT spectrum and chaos. Moreover, the features space of 20 subjects was used to build the probabilistic neural network (PNN). As a consequence, the classification accuracy of the other 11 subjects based on PNN reached 81.8% in total.

Least-squares estimation for linear models with certain ranges

As a signal processing method, the least-squares method plays a crucial role in parameter estimation, and great progress has been made in recent decades. However, errors may occur when the parameters to be estimated have some actual physical meaning, e.g., if the human-body temperature is estimated to be 70 °C by a general least-squares method. In this study, we consider solving a particular problem, named ranged least-squares estimation (RLSE), where the parameters are restricted to certain meaningful ranges. By using a theoretical analysis, we prove that the solution of the RLSE problem is unique and can be obtained in finite number of steps when the system matrix has a full column rank. Two programmable algorithms are proposed: a basic algorithm and another with improved efficiency. We also present a numerical experiment of an actual RLSE problem for hydrological parameter estimation, which validates the proposed method.

Calibration Method of an Ultrasonic System for Temperature Measurement

System calibration is fundamental to the overall accuracy of the ultrasonic temperature measurement, and it is basically involved in accurately measuring the path length and the system latency of the ultrasonic system. This paper proposes a method of high accuracy system calibration. By estimating the time delay between the transmitted signal and the received signal at several different temperatures, the calibration equations are constructed, and the calibrated results are determined with the use of the least squares algorithm. The formulas are deduced for calculating the calibration uncertainties, and the possible influential factors are analyzed. The experimental results in distilled water show that the calibrated path length and system latency can achieve uncertainties of 0.058 mm and 0.038 μs, respectively, and the temperature accuracy is significantly improved by using the calibrated results. The temperature error remains within ±0.04°C consistently, and the percentage error is less than 0.15%.

A Method for Amplitude and Phase Calibration in a Spaceborne Multibeam Receiver

This paper presents a method for amplitude and phase calibration in a spaceborne multibeam receiver, which is based on the satellite-ground link, to solve the inconsistent problem in amplitude and phase between different channels. In this method, the calibrating signal is firstly immitted by a ground control station, and then the discrepancy of amplitude and phase between different channels and the reference channel in the receiver are determined by signal processing. And self-calibration would finally be achieved by some inversion operations. Additionally, this paper adopted an advanced discrete fourier transform method to determine the parameters which is help to overcome the spectral leakage caused by the doppler frequency shift. Results denote that errors of amplitude and phase would heavily influence the beam pointing and beam shape for a spaceborne multibeam receiver which will lead to a distinct decline in performance. However, this problem is meliorated after our adapting the method in this paper to calibrate the amplitude and phase errors of the receiver.

Precise ultrasonic ranging based on pseudo-random sequence modulated continuous signal processing

The ultrasonic ranging equipment usually need to measure the “time of flight”, that it takes for acoustic waves to travel the measured distance. Due to the influence of various noises, ultrasonic distance measurement using the pulse signal is difficult to obtain accurate measurement results. Continuous signal phase detected method can achieve the precision measurement of the transmission time, and has a strong noise resistance capability. When single-frequency signals are used, the measurement range is limited to a small extent. This problem can be solved by dual-tone or multi-frequency method. But in short distance ranging applications especial in the restricted space fields, there usually exists strong multiple echoes. Because of the echoes, the ranging accuracy will be significantly decreased. In this paper, a singlefrequency continuous signal modulated by a pseudo-random sequence is used, since the pseudo-random sequence has excellent autocorrelation properties. On the other hand, an improved signal phase estimation algorithm is used to realize the high-precision measurement of TOF. An experimental measurement system was built, and experiments showed that the method can get micron degree precision.

Transmitting pulse signal design for ultrasonic time of flight measurement in short baseline framework

The SBF (short baseline framework) is commonly used in ultrasonic parameter measurement, and ToF (time of flight) of which is essential in sound velocimeter and other applications. Different from general ultrasonic measurement research work mainly on ToF estimation method, this paper studies the criterion and way of establishing the optimum signal. For given transducers, the optimum signal achieves the most accuracy, and the pulsed form signal is stress here. To find the optimum signal, firstly, the transmitting is illustrated in its Fourier series form, which establishes the waveform, and the problem of transmitting wave design is converted into finding the optimum Fourier series. Secondly, as the accuracy is in inverse ratio to the sensitivity of the measured signal, the problem of finding the optimum Fourier series is equivalent to maximizing the sensitivity, resulting into a form of nonlinear optimization problem. For optimum parameter derivation, the sensitivity is expressed in form of vector and matrix, and a novel method based on SCHUR decomposition on the matrix is proposed to solve the nonlinear optimization problem. Simulation with a typical narrowband system testifies that the proposed method can synthesize transmitting waveform efficiently.

Sound speed measurement with direct-sequence spread spectrum signal combining time of flight and phase shift

Increasing demands for high accuracy and rapid measurement of sound speed have prompted the development of portable sound velocimeter in oceanography. Generally, sound speed can be established by CTD or TD (Time Delayed) method respectively. CTD method suffers from errors of corresponding sensors and application range of the converting equations. TD method, sing-around technique representative, is widely used in portable velocimeter. The accuracy of TD is proportional to receiving SNR and signal length. The duration of tone burst in convenient sing-around is limited by multi-echo, thus only a few valid data can be utilized. To address the problems, DSSS (Direct-Sequence-Spread-Spectrum) signal in continuous form is adopted to extract the TD directly, with which sound speed could be established related to laboratory derived equations, Del Grosso’s equation representative. Based on this method, two separate transducers were deployed with constant distance. Cross-correlation between received and transmitted ...