- Détails du magazine
- Format
- Magazine
- eISSN
- 1335-8871
- Première publication
- 07 Mar 2008
- Période de publication
- 6 fois par an
- Langues
- Anglais

#### Chercher

- Accès libre

Sparse Signal Acquisition via Compressed Sensing and Principal Component Analysis

Pages: 175 - 182

#### Résumé

This paper presents a way of acquiring a sparse signal by taking only a limited number of samples; sampling and compression are performed in one step by the analog to information conversion. The signal is recovered with minimal information loss from the reduced data record via compressed sensing reconstruction. Several methods of analog to information conversion are described with focus on numerical complexity and implementation in existing embedded devices. Two novel analog to information conversion methods are proposed, distinctive by their computational simplicity - direct subsampling and subsampling with integration. Proposed sensing methods are intended for and evaluated with real water parameter signals measured by a wireless sensor network. Compressed sensing proves to reduce the data transfer rate by >80 % with very little signal processing performed at the sensing side and no appreciable distortion of the reconstructed signal.

#### Mots clés

- Compressed sensing
- analog-to-information conversion
- sparse signal
- signal compression

- Accès libre

A Novel Dynamic Method to Improve First-order Natural Frequency for Test Device

Pages: 183 - 192

#### Résumé

It is important to improve the natural frequency of test device to improve measurement accuracy. First-order frequency is basic frequency of dynamic model, which generally is the highest vibration energy of natural frequency. Taking vector force test device (VFTD) as example, a novel dynamic design method for improving first-order natural frequency by increasing structure stiffness is proposed. In terms of six degree-of-freedom (DOF) of VFTD, dynamic model of VFTD is built through the Lagrange dynamic equation to obtain theoretical natural frequency and mode shapes. Experimental natural frequency obtained by the hammering method is compared with theoretical results to prove rationality of the Lagrange method. In order to improve the stiffness of VFTD, increase natural frequency and meet the requirement of high frequency test, by using the trial and error method combined with curve fitting (TECF), stiffness interval of meeting natural frequency requirement is obtained. Stiffness of VFTD is improved by adopting multiple supports based on the stiffness interval. Improved experimental natural frequency is obtained with the hammering method to show rationality of the dynamic design method. This method can be used in improvement of first-order natural frequency in test structure.

#### Mots clés

- Natural frequency
- dynamic analysis
- Lagrange dynamic method
- structure improvement
- test device

- Accès libre

Analysis of Influence of Coil Gradient System on Vibration Properties and Acoustic Noise Level Generated by the Low Field MRI Device

Pages: 193 - 200

#### Résumé

The paper focuses on investigation of influence of the volume inserted in the scanning area of the magnetic resonance imaging (MRI) device working with a low magnetic field generated by a pair of permanent magnets on vibration and acoustic noise. In addition, its aim is to evaluate the influence of different types of used scan sequences, different settings of slice orientation and scan parameters on the energy and spectral properties of vibration and noise generated by the gradient coil system of the MRI device. Two basic measurements were performed within this work: mapping of sound pressure levels in the MRI device vicinity and parallel acquisition of vibration signals by sensors mounted on the lower and upper parts of the MRI gradient system. The paper next analyzes changes in properties of the vibration signals for the examined person lying in the scanning area compared with the situation of using only the testing phantom. Spectral characteristics of the recorded vibration signals are then analyzed statistically, and compared visually and numerically. The obtained results of the detailed analysis will be used for improvement of noise suppression algorithms applied to a speech signal recorded simultaneously with scanning of the human vocal tract for its 3D modeling.

#### Mots clés

- Vibration and acoustic noise measurement
- magnetic resonance imaging
- signal processing
- statistical analysis

- Accès libre

Application of Coordinate Measuring Arm for Accurate Measurement of Child Growth

Pages: 201 - 206

#### Résumé

The article describes an approach to measure child growth using a coordinate measuring arm. For this purpose, a test set up has been built to measure the lower leg length directly on the knee surface and with the help of a plate. The use of the plate resulted in the distribution of pressure on the surface to be measured. Based on the results, the LLV (a lower leg growth velocity) was determined and studies were carried out to estimate the uncertainty of this factor. The obtained LLV results at 0.4 mm/week, correspond to the results of studies conducted on specialist test set-ups for knemometric measures described in the literature. The obtained results also allow recognizing periods of good health and bad health of the child.

#### Mots clés

- Dimensional metrology
- coordinate measurements
- child growth

- Accès libre

Pseudorandom Dynamic Test Power Signal Modeling and Electrical Energy Compressive Measurement Algorithm

Pages: 207 - 217

#### Résumé

With the rapid construction of smart grid, many applications of the new generation and the large power dynamic loads are revolutionizing the electrical energy measurement of electricity meters. The dynamic measurement errors produced by electricity meters are intolerable. In order to solve the dynamic error measurement of electrical energy, firstly, this paper proposes a three-phase pseudorandom dynamic test power signal model to reflect the main characteristics of dynamic loads. Secondly, a compressive measurement algorithm is proposed by the means of steady-state optimization to accurately measure the electrical energy. The experimental results confirm the effectiveness of the three-phase pseudorandom dynamic test signal model, the maximum errors of compressive measurement algorithm are superior to 1×10^{-13}, the high precision enables the algorithm to accurately measure the electrical energy under different dynamic conditions.

#### Mots clés

- Compressive measurement
- dynamic load
- electricity meter
- electrical energy

- Accès libre

A Non-Destructive Impedance Method Using Resonance to Evaluate the Concentration of Steel Fibers in Concrete

Pages: 218 - 226

#### Résumé

Steel-fiber reinforced concrete is a composite material characterized by outstanding tensile properties and resistance to cracking. The concrete, however, exhibits such characteristics only on the condition that the steel fibers in the final, hardened composite are distributed evenly. Current methods to evaluate the distribution and concentration in a fiber composite are either destructive or exhibit a limited capability of evaluating the concentration and orientation of the fibers. In this context, the paper discusses auxiliary techniques and laboratory tests that evaluate the density and orientation of the fibers in a composite material, presenting an innovative approach to impedance-based non-destructive testing. The actual methodology utilizes the resonance of the measuring device and the measured sample set; the desired state occurs within the interval of f = 10 kHz and 2 GHz.

#### Mots clés

- Concrete
- electric impedance
- electromagnetic field
- non-destructive testing
- resonance
- steel fiber