Towards an ideal data acquisition channel

A method is presented for compensating in real time for a nonideal transfer function of a data acquisition channel by means of a digital IIR (infinite impulse response) filter. Real-time compensation of the amplitude and phase characteristics of an acquisition channel so that the long-term error is less than ±0.01 dB and ±0.1°, respectively, has been obtained experimentally. It is shown that stability and linearity are the main requirements for the components of the data acquisition channel. Careful selection of the components and outlining of the antialias filter and the programmable amplifier is no longer necessary     

Novel estimation of the electrical bioimpedance using the local polynomial method. Application to in vivo real-time myocardium tissue impedance characterization during the cardiac cycle

Classical measurements of myocardium tissue electrical impedance for characterizing the morphology of myocardium cells, as well as cell membranes integrity and intra/extra cellular spaces, are based on the frequency-sweep electrical impedance spectroscopy (EIS) technique. In contrast to the frequency-sweep EIS approach, measuring with broadband signals, i.e., multisine excitations, enables to collect, simultaneously, multiple myocardium tissue impedance data in a short measuring time. However, reducing the measuring time makes the measurements to be prone to the influence of the transients introduced by noise and the dynamic time-varying properties of tissue. This paper presents a novel approach for the impedance-frequency-response estimation based on the local polynomial method (LPM). The fast LPM version presented rejects the leakage error's influence on the impedance frequency response when measuring electrical bioimpedance in a short time. The theory is supported by a set of validation measurements. Novel preliminary experimental results obtained from real-time in vivo healthy myocardium tissue impedance characterization within the cardiac cycle using multisine excitation are reported.     

Creating water-repellent and super-hydrophobic cellulose substrates by deposition of organic nanoparticles

A series of organic nanoparticles is synthesized by imidization of poly(styrene-maleic anhydride) copolymers under pure conditions or in presence of palm oil. The nanoparticles are applied as a coating onto paper substrates, offering enhanced water-repellence and hydrophobicity. The latter properties can be further tuned by thermal curing of the coatings. After depositing the nanoparticles onto tissue papers, super-hydrophobic surfaces with self-cleaning properties can be prepared. The presented materials offer an attractive alternative for surface treatments of textiles, avoiding the use of environmental unfriendly fluorderivates.     

An improved sliding-load calibration procedure using asemiparametric circle-fitting procedure

Circle-fitting problems often occur in microwave engineering when dealing with variable delays, e.g., during calibration using a sliding load. This paper proposes an efficient semiparametric circle-fitting procedure, which takes into account the phase relationships over the frequencies. It produces more accurate results than the standard sliding-load calibration, requires only three positions on the sliding load for the whole frequency band, and is more robust to the settings of the positions of the sliding load. The proposed method also has the ability to detect whether or not the sliding load is defective or out of its specifications. This can be done by using only three positions on the sliding load. Optimal-position settings are then proposed. The performance of the proposed method is illustrated on sliding-load measurements up to 50 GHz, demonstrating the ability of detecting modeling errors and showing that the accuracy of the proposed method using three positions is comparable to the standard method with six positions     

Electrochemical impedance spectroscopy in the presence of non-linear distortions and non-stationary behaviour: Part I: theory and validation

In order to investigate non-linear and non-stationary electrochemical systems, this series of two papers describes a new measurement method for electrochemical impedance spectroscopy (EIS), using specially designed broadband excitation signals. During one single experiment, the impedance, the level of the disturbing noise, the level of the non-linear distortions, and the level of the non-stationary behaviour are simultaneously measured.Part I of the paper presents the measurement strategy and validates it on a linear and a non-linear electrical circuit.In part II the described measurement strategy is applied to the pitting corrosion of aluminium (99.5 wt.%) immersed in an aerated sodium chloride solution.     

Measurement of frequency response functions in noisy environments

The geometric mean is proposed as an alternative averaging technique for frequency response function (FRF) measurements of a linear system. It is shown that it produces almost unbiased measurements even if the input and output measurements are both disturbed with (normal distributed) noise. The properties of the arithmetic and geometric mean of expression are compared to those of the H₁ and H₂ methods. It is shown that if the S/N ratio on the input and the output measurements is higher than 3 dB, then it is possible to generate measurements without systematic errors     

Silkworm and spider silk scaffolds for chondrocyte support

Objective To create scaffolds with silkworm cocoon, spider egg sac and spider dragline silk fibres and examine their use for chondrocyte attachment and support. Methods Three different kinds of scaffolds were developed with Bombyx mori cocoon, Araneus diadematus egg sac and dragline silk fibres. The attachment of human articular cartilage cells were investigated on these bioprotein matrices. The chondrocytes produced an extracellular matrix which was studied by immunostaining. Moreover, the compression behaviour in relation to the porosity was studied. Results The compression modulus of a silkworm silk scaffold was related to its porosity. Chondrocytes were able to attach and to grow on the different fibres and in the scaffolds for several weeks while producing extracellular matrix products. Conclusion Porous scaffolds can be made out of silkworm and spider silk for cartilage regeneration. Mechanical properties are related to porosity and pore size of the construct. Cell spreading and cell expression depended on the porosity and pore-size.     

Amplitude-only versus amplitude-phase estimation

The feasibility of transfer function estimation based on amplitude-only measurements is verified. Its properties are compared to those of a full complex estimation using both the magnitude and the phase information of the estimated transfer function. The Fisher information matrix is used as a basis of comparison. It is found that the amplitude-only estimation has a larger standard deviation on the transfer function parameters. Optimal excitation for the analyzed examples is calculated for both methods. The main difference between them is that amplitude estimates require more energy further in the transition band. The variance of the amplitude estimates is highly dependent on the excitation bandwidth used. Care has to be taken to provide sufficient excitation in the transition band(s) of the device under test to obtain sensible results with amplitude estimates     

Robust identification of transfer functions in the s- andz-domains

A frequency-domain maximum-likelihood estimator (MLE) for estimating the transfer function of linear continuous-time systems developed by J. Schoukens et al. (1988) assumes independent Gaussian noise on both the input and the output coefficients. A Gaussian frequency-domain MLE for transfer functions of linear continuous or discrete time invariant systems in an errors-in-variables model is presented. It is demonstrated that most of the properties of the estimator remain unchanged when it is applied to measured input and output Fourier coefficients corrupted with non-Gaussian errors. The result is a robust Gaussian frequency-domain estimator that is very useful for the practical identification of linear systems. The theoretical results are verified by simulations and experiments     

Peak factor minimization of input and output signals of linearsystems

An overview is given of existing analytical and numerical methods for the comparison of the peaks of discrete, finite sum of sines. A novel method that compresses the signals optimally or almost optimally is presented. The algorithm is extended to the simultaneous compression of the input and output signals of a linear system. The implications of strong signal compression for the signal-to-noise ratio lead to the formulation of a two-step optimal experimental setup for system identification and parameter estimation of linear systems