Volumen 4 (2013): Heft 1 (January 2013)

The bioimpedance of tissues under compression is a field in need of study. While biological tissues can become compressed in a myriad of ways, very few experiments have been conducted to describe the relationship between the passive electrical properties of a material (impedance/admittance) and its underlying mechanical properties (stress and strain) during deformation. Of the investigations that have been conducted, the exodus of fluid from samples under compression has been thought to be the cause of changes in impedance, though until now was not measured directly. Using a soft tissue-mimicking phantom material (tofu) whose passive electrical properties are a function of the conducting fluid held within its porous structure, we have shown that the mechanical behavior of a sample under compression can be measured through bioimpedance techniques.

This paper is concerned with a physical model of an interdigitated sensor working in a frequency range from 100 Hz to 10 MHz. A theoretical approach is proposed to optimize the use of the sensor for bioimpedance spectroscopy. The correlation between design parameters and frequency behavior in coplanar impedance sensors are described. CoventorWare^® software was used to model the biological medium loaded interdigital sensor in three dimensions to measure its electrical impedance. Complete system simulation by a finite element method (FEM) was used for sensor sensitivity optimization. The influence of geometrical parameters (number of fingers, width of the electrodes) on the impedance spectroscopy of the biological medium was studied. The simulation results are in agreement with the theoretical equations of optimization. Thus, it is possible to design a priori such sensor by taking into account the biological medium of interest that will load the sensor.

Alternating current sources are mainly used in bioelectrical impedance devices. Nowadays 50 – 100 kHz bioelectrical impedance devices are commonly used for body composition analysis. High frequency bioelectrical impedance analysis devices are mostly used in bioimpedance tomography and blood analysis. High speed op-amps and voltage comparators are used in this circuit. Direct current feedback is used to prevent delay. An N-Channel J-FET transistor was used to establish the voltage controlled gain amplifier (VCG). A sine wave signal has been applied as input voltage. The value of this signal should be constant in 170 mV rms to keep the output current in about 1 mA rms. Four frequencies; 100 kHz, 1 MHz, 2 MHz and 3.2 MHz were applied to the circuit and the current was measured for different load resistances. The results showed that the current was stable for changes in the resistor load, bouncing around an average point as a result of bouncing DC feedback.

Reasoned by its dynamical behavior, the memristor enables a lot of new applications in analog circuit design. Since some realizations have been shown (e.g. 2007, Hewlett Packard), the development of applications with memristors becomes more and more interesting. Besides applications in neural networks and storage devices, analog memristive circuits also promise further applications. Therefore, this article proposes a frequency dependent rectifier memristor bridge for different purposes, for example, using as a programmable synaptic membrane voltage generator for Spike-Time-Dependent-Plasticity and describes the circuit theory. In this context it is shown that the Picard Iteration is one possibility to analytically solve the system of nonlinear state equations of memristor circuits. An intuitive picture of how a memristor works in a network in general is given as well and in this context some research on the dynamical behavior of a HP memristor should be done. After all it is suggested to use the memristor bridge as a neuron.

Electrical Impedance Tomography (EIT) has successive wide range in impedance imaging, but still it is difficult to extract cardiac-related conductivity changes and respiratory-related conductivity changes in spontaneous breathing subjects. Quite a few methods are attempted to extract these two signals such as electrocardiogram gated averaging, frequency domain filtering and principal component analysis. However, such methods are not able to take apart these components properly or put some effort in real time imaging and have their own limitations. The purpose of this paper is to introduce a new method in the EIT clinical application field, Independent Component Analysis (ICA) to extract cardiac and respiratory related signals in electrical impedance tomography. Independent component analysis has been introduced to use in electrical impedance tomography but this is the first attempt ever to implement this method to separate these two signals and image those independent conductivity distribution of respiration and cardiac changes independently. Data has been collected from a spontaneous breathing subject. Filtration technique has been used to remove random noise and multi level spatial ICA has been applied to obtain independent component signals which has been later used in reconstruction algorithm for imaging.

During the last decades the use of electrical bioimpedance (EBI) in the medical field has been the subject of extensive research, as an affordable, harmless and non-invasive technology. In some specific applications, such as body composition assessment where EBI has proven a good degree of effectiveness and reliability, the use of textile electrodes and measurement garments have shown good performance and reproducible results. Impedance cardiography (ICG) is a modality of EBI that can benefit from the implementation and use of wearable sensors. ICG is based on continuous impedance measurements of a longitudinal segment across the thorax taken at a single frequency. The need for a specific electrode placement on the thorax and neck can be easily ensured with the use of a garment with embedded textile electrodes, also known as “textrodes.” The first step towards the implementation of garment-based ICG is to determine the quality of ICG measurements with textile sensors to allow estimation of fundamental ICG parameters. In this work, the measurement performance of a 2-belt set with incorporated textrodes for thorax and neck is compared against ICG measurements obtained with Ag/AgCl electrodes. The analysis is based on the quality of the fundamental ICG signals (ΔZ, dZ/dt and ECG), systolic time intervals and other ICG parameters. The results indicate the feasibility of using textrodes for ICG measurements with consistent measurements and relatively low data dispersion. Thus, enabling the development of measuring garments for ICG measurements.

The real-time monitoring of alcoholic fermentation (sugar consumption) is very important in industrial processes. Several techniques (i.e., using a biosensor) have been proposed to realize this goal. In this work, we propose a new method to follow sugar yeast consumption. This novel method is based on the changes in the medium resistance (Rm) that are induced by the CO₂ bubbles produced during a fermentative process. We applied a 50-mV and 700-Hz signal to 75 ml of a yeast suspension in a tripolar cell. A gold electrode was used as the working electrode, whereas an Ag/AgCl electrode and a stainless-steel electrode served as the reference and counter electrodes, respectively. We then added glucose to the yeast suspension and obtained a 700% increase in the Rm after 8 minutes. The addition of sucrose instead of glucose as the carbon source resulted in a 1200% increase in the Rm. To confirm that these changes are the result of CO₂ bubbles in the fermentation medium, we designed a tetrapolar cell in which CO₂ gas was insufflated at the bottom of the cell and concluded that the changes were due to CO₂ bubbles produced during the fermentation. Consequently, this new method is a low-cost and rapid technology to follow the sugar consumption in yeast.

Focused impedance measurement (FIM) is a technique where impedance can be measured with the optimum level of localization without much increase in complexity of measuring instrument. The electrodes are applied on the skin surface while the organs inside also contribute to the measurement, as the body is a volume conductor. In a healthy and disease free lung region, the air enters at breathe-in, increases the impedance of the lung, and impedance reduces during breathe-out. In contrast, for a diseased lung, where part of the lungs is filled with water or some fluid, air will not enter into this zone reducing impedance change between inspiration and expiration. With this idea, the current work had been executed to have general view of localized impedance change throughout thorax using 6-electrode FIM. This generated a matrix mapping from both the front and from the back of the thorax, which showed how impedance change due to ventilation varies from frontal plane to back plane of human bodies.

Advancement of wireless technology leads to some developments in current wireless electroencephalography. Through improving the transmission method of brainwaves, it would be possible to bring more convenience for the patients in need and give this opportunity to others for discovering other aspects of the amazing brainwave. What has been proposed in this study is a new type of adjustable backward quantization method which exploits the nature of the brainwave signal. This method is based on the nature of the captured brainwave and its quantization boundary changes based on the amplitude of each EEG captured signal. The proposed quantization scheme has been analyzed with uniform and Gaussian distribution of quantization level. Consequently, the Backward Gaussian Quantization with Adjustable Boundary and two Word Memories beside the Backward Uniform Quantization with Adjustable Boundary and two Word Memories are introduced by this experiment. In addition, the performance of wireless transmission system and the proposed quantizer’s efficiency for very low frequency (up to 100 Hz) and amplitude EEG signal have been noticed. With doing so, we simulated the transmitter and receiver by MATLAB^® software. To model the medium, channel was assumed as Additive White Gaussian Noise (AWGN). Meanwhile analysis is done for the whole wireless system performance in terms of transmission range, compared with current available wireless transmission systems on the market. It should be noticed that the transmission range of the proposed wireless transmission system is compared to the transmission range of current wireless EEG systems when there is no obstacle between transmitter and receiver. Furthermore, some relevant parameters to evaluate the quality of the proposed quantization method were examined. To sum up, the proposed quantization schemes show considerable performance in terms of Quantization Rate for constant MSQE and SQNR in comparison with Uniform Quantization method and the achieved transmission range of our wireless system by using this method is higher than available wireless EEG systems on market.

This paper reports on the impedimetric investigation of glucose concentrations present in the human blood by using impedance sensing devices with different working electrode areas. It is evident from the experiment that, the impedance value increases with the increase of glucose concentration in blood and the trend follows in all the devices with various electrode areas. The measured complex admittance plot shows two semicircles which are due to double layer and coating capacitances respectively. Lower values of relative standard deviation in impedance data infer the reproducibility of these devices. A quantitative relationship, developed between the impedance and glucose concentration establishes a positive correlation between the blood glucose values and impedance.