We summarize the pertinent electrical phenomena relevant to the application of the impedance technique in vivo and discuss the relations between electrical measurements and biological conductor volumes. Whole-body impedance-what does it measure?ДЄlthough the bioelectrical impedance technique is widely used in human nutrition and clinical research, an integrated summary of the biophysical and bioelectrical bases of this approach is lacking. Furthermore, this technique is used in investigating the acoustic properties of reticulated vitreous carbon (RVC) in the range of 250-1100 Hz. The values of characteristic impedance and complex propagation constant extracted from the reconstruction agree well with predicted values. Measurements of the acoustic properties of a material having square cross-section pores is used to check the validity of the technique. In this paper, a multiple microphone technique is investigated to reconstruct the pressure field inside an impedance tube. Muehleisen and Beamer improved upon a four-microphone method by interchanging microphones to reduce errors due to uncertainties in microphone response. In this method two microphones are used to determine the complex pressure amplitudes for each side of a sample. Song and Bolton's four-microphone method is one of the most widely employed techniques. Knowledge of acoustic properties such as characteristic impedance and complex propagation constant is useful to characterize the acoustic behaviors of porous materials. Technique for measurement of characteristic impedance and propagation constant for porous materials In order to model the bio- impedance spectrum, we analyzed layered samples with different thickness and material composition.

We compared different anatomical body regions, some of them with less subcutaneous body fat (frontal, anterior tibial, knee, and frontal regions) others with more subcutaneous body fat (pectoral, abdominal, and internal calf regions). We studied the variability of the body impedance spectrum (from 1 Hz to 1 MHz) in a group of subjects compared to the values obtained from commercial apparatus. The multi-frequency option of the bio- impedance technique has still a lot of challenges to overcome. However these apparatus have significant variability in the BCM values. This technique, in the single frequency mode, has some commercial versions to perform BCM. The use of bio- impedance analysis (BIA) has been very useful in BCM. Reviewing the methods and physical principles used in body composition measurements (BCM), it is evident that more accurate, reliable, and easily handled methods are required. On the use of The Bio- Impedance technique for Body Composition Measurements

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