Noninvasive Determination of Central Blood Pressure by Impedance Plethysmography

A new algorithm based on impedance plethysmography provides reliable determinations, on an experimental basis, of arterial blood pressure. Signals over the brachial artery are picked up by four Velcro-type electrodes attached to the skinward side of a regular blood pressure cuff. Mathematical formulas are used to define those impedance pulses that correspond to systolic, diastolic, and mean arterial blood pressure values. The envelope of the impedance pulses recorded during cuff deflation can be defined by linear regressions, function of just one normalized independent variable, which is the ratio between the amplitude of the pulse with maximum amplitude and of the amplitude of the pulses with constant amplitude. These linear regressions are assumed to be universally applicable, the influence of individual anatomic variations having been eliminated by the use of a normalized variable. The results of this study prove that the variable pulse amplitude obtained during a cuff deflation is a quantifiable reaction of the circulatory system to arterial constriction.     

Full-wave analysis of aperture-coupled microstrip lines

Two methods are presented for the analysis of aperture-coupled microstrip lines. Assuming a quasi-transverse electromagnetic traveling wave incident on the feeding line, an expression for the wave on the coupled line is derived. First, the moment method is used and the current on the coupled line is represented by a traveling wave propagating away from the slot. In the second method, the reciprocity theorem is applied to the coupled line. Both the moment method and the reciprocity method make use of the exact Green functions and produce results that are in very close agreement. An equivalent circuit is derived and the S-parameters are computed. Theoretical results are verified with measurements     

Circularly polarized single-fed wide-band microstrip patch

For more than 25 years, the circularly polarized single-fed microstrip patch was considered to be extremely narrow-band. The reported performances are almost exclusively related to single patches printed on a dielectric substrate, which partially explains the frequency characteristics. The antenna proposed is a variation of the "almost square" patch and exhibits measured axial radio of less than 2.5 dB over a 13% bandwidth. The antenna was designed for wireless applications.     

Low-sidelobe arrays fed by a uniform-distribution feeding network

Low-sidelobe arrays typically use feeding networks with appropriate amplitude and phase distributions, which, in some cases, can be lossy and narrow-band as a result of their complexity. In the new approach presented in this paper, a simple uniform distribution feeds the array elements, which are not uniformly positioned in the traditional uniform grid. The location of the array elements is such that the sidelobes of the array factor are “pushed” in the end-fire direction. There, the element pattern is low enough in amplitude to effectively suppress the array-factor sidelobes to the required level. The combination of the simple uniform-distribution feeding network and the spatial distribution of the array elements results in a simple design for a low-sidelobe array     

A simple cosec2-microstrip array: the shovel-microstriparray

A novel application of a microstrip array is presented. Although microstrip arrays are often made on mechanically flexible substrates for conformal applications, this approach uses such flexibility to achieve cosecant-squared beam shaping. The antenna developed is the shovel-microstrip array antenna     

A concise conjugate gradient computation of plate problems withmany excitations

One of the major difficulties in the application of the conjugate gradient algorithm for the analysis of electromagnetic scattering problems is the necessity to carry out the calculation separately for each incident wave. In the approach suggested, rather than handling the incident waves directly, a class of possible excitations is represented by a set of strip-type basis functions. For these functions, convergence is predictable and rapid because the majority of the strips are located away from the edges of the scatterer. This choice also facilitates the use of the physical optics approximation as a good initial guess. Once the solutions for all the unit basis functions over the body are known, they can be combined to synthesize the solution for any excitation using the weighting coefficients associated with the expansion of the incident field. Numerical examples are given, and they demonstrate the substantial savings achieved by adopting this approach for the analysis of multiple excitations     

The aperture-coupled helix antenna

Planar arrays with circular polarization are frequently used in a large variety of applications. The typical choices are quite limited when size, bandwidth, efficiency, and simplicity are important. The paper proposes a new type of radiating element that seems to cope with all these requirements. The well-known helix antenna is fed by a slot in the ground plane of a microstrip-feeding line. The measurements show a successful combination of the excellent characteristics of the helix antenna, with the simplicity of fabrication of the microstrip networks     

Hybrid reverse osmosis — ultrafiltration membranes

A new group of asymmetric non-cellulosic membranes having a performance intermediate between that of a conventional RO membrane and an ultrafilter has been developed. Its main characteristics are high fluxes (4–10 m³/m² day) at low pressures (6–10 at) and moderate rejections for various salts. From 200 mg/l solutions of NaNO₃, Na₂SO₄ and KH₂PO₄ rejections up to 40%, 70% and 90%, respectively, were obtained. The new membranes can withstand large variations in pH (1 to 13) and have excellent chemical and biological stability. The membranes have been tested in a mobile SUF pilot plant operating on oxidation pond effluent. High rejections for BOD, COD, bacteria and suspended solids as well as a 20% reduction in salinity have been obtained.     

New considerations in the design of microstrip antennas

Printed microstrip antennas and arrays are known to have limitations in terms of bandwidth and efficiency, all imposed by the very presence of the dielectric substrate. Microstrip arrays printed on a very thin film and separated from the ground-plane by foam were successfully designed; however, the fabrication difficulties associated with the use of foam considerably increases the fabrication cost. In this paper, a new concept is presented. Rather than using a superstrata geometry, the “printed circuit” is etched out of metal and supported at “strategic points” by (metallic or nonmetallic) posts. The main motivation for this work was to obtain large microstrip arrays, which exhibit a higher efficiency than conventional ones, and can be fabricated using inexpensive large quantity production techniques. However, this technology was also used to develop many new types of microstrip antennas. Microstrip elements and arrays based on this technology were designed and fabricated for the L, S, and C bands     

Minimal distance lexicographic codes over an infinite alphabet

The author investigates the properties of minimal distance lexicographic codes, or lexicode, over the ordered infinite alphabet N={0,1,2…}. The author presents a method for computing the basis of such a code. It is shown that any lexicographic code S with minimal distance d has a unique basis where each basis vector is a one followed by a string of zeros, followed by d-1 nonzero digits a_ij. Furthermore, the matrix A=(a_ij) has no singular minors over the nim-field. The dual code when S has finite length is also computed. The author develops a systematic approach to determine which words belong to these lexicodes