Biotelemetric systems, especially those that employ implanted devices, work with inductive links, where usually large circular external coils are separated by relatively large distances (dimensions of centimeters) from the small (millimeter- or submillimeter-size) implanted coils. This paper shows that, under these conditions, a simplified method for calculation of the mutual inductance (M) between the coils, avoiding elliptic integrals, can be obtained. A procedure for coil design, with maximum M between them, is also described.
In this study, the analysis of a three-coil wireless power transfer (WPT) system, which can be divided into source, communication and load circuits, is discussed in details. Among the three-coil WPT systems features, it is demonstrated, for instance, that maximum efficiency (η MAX) and maximum power transferred to the load (P 3MAX) do not depend on the load resistance, neither on the mutual inductance between communication and load coils. In fact, it is shown that η MAX and P 3MAX depend only on source and communication circuits parameters. Practical results are also presented, showing good agreement with the developed theory and validating the proposed analysis.
An expression relating the red blood cell (RBC) volume and membrane surface area to the pore minimum radius /maximum length which the cell is able to traverse is derived. The application of this analytical model to design/specification of filters for RBC deformability evaluation is presented. The passage of the RBC's through relatively long (10 microns or more) submicron radii pores, which the developed model demonstrates, is also discussed.
In this paper, a novel and simple method to measure the phase difference between two sinusoidal signals is presented. Basically, the method consists of subtracting two sinusoidal signals with same frequencies and measuring the resulting signal amplitude: this amplitude being a minimum whenever there is a coincidence between both signal phases. In order to test this method, an adjustable phase reference signal has been generated using a direct digital synthesizer device. Employing this reference signal, it can be demonstrated that the phase difference between two signals can be evaluated with errors smaller than 0.3° for signals with frequencies up to 1.25 MHz.
The filtration method for the evaluation of the RBC deformability has been further refined to simulate the deformations encountered in the recticuloendothelial system (in particular the spleen), a recognized site of aged and sickled cells removal. The core of the developed measuring system is a very thin (0.4 micron thick) filter that consists of single micropore (diameters down to 1 micron) on a Si3N4 film which has been constructed using silicon microfabrication techniques. Individual RBC's deformability is quantified measuring the cell pore passage time. From one blood sample 200 passage times are analyzed by a computer, displaying mean and median values as deformability indexes, and class and cumulative histograms for studying the passage times distribution. In this paper the effectiveness of the developed system as a routine clinical evaluation tool is demonstrated by studying several factors that are known to affect the RBC deformability, such as temperature, addition of diamide and glutaraldehyde, and blood storage conditions. In addition, it is experimentally demonstrated that the human RBC can traverse a pore with a diameter as small as 1 micron when the pore length is very short, thus broadening the experimental conditions under which the RBC deformability (fluidity) can be studied.
In wireless power transfer (WPT) systems with more than two coils, the intermediary or relay circuits are used to extend the link distance. Thus, to achieve this extension efficiently in terms of power transfer, these relay circuits must have low losses. However, there are several instances in which there are restrictions in reducing the ohmic losses in all the relay circuits of the system. This is the case of biomedical applications where commonly there are size and access restrictions since one of the circuits can be implanted and also in applications using high-temperature superconductor (HTS) coils due to the difficulty in implementing the necessary cooling system for all the coils of the system. Therefore, in these situations, the designer need to choose which relay circuit will be optimized. In this work, it is presented an analysis on the impact that losses in individual relay circuits have on efficiency, and power transfer, of typical four-coil wireless power transfer systems consisting of circuit 1 (transmitter), relay circuits 2 and 3, and circuit 4 (load). It is shown that the losses on relay circuit 2 have greater impact on efficiency, while the losses of relay circuit 3 have a greater impact on power transfer for a given condition. Practical experiments confirm the developed analysis.
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