Surface waves on a grounded dielectric slab covered by a periodically slotted conducting plane

The surface-wave modes in a dielectric slab covered by a periodically slotted conducting plane are investigated. Two methods-sampling and variational-are used to obtain the surface-wave modes. The dispersion curves obtained by the two methods agree very well. The experimental and the theoretical results are in good agreement, except close to the stopband.     

Ultrasonic measurement of density of liquids flowing in tubes

This paper presents the implementation of the relative reflection method for the ultrasonic measurement of the density of liquids, which may be flowing in pipelines, at different temperatures. This technique will be shown to be valid for large-diameter tubes containing flowing liquids. It employs a double-element transducer, consisting of a piezoelectric ceramic transmitter and a large aperture PVDF membrane receiver, separated by a polymethylmethacrylate buffer rod. Between the receiver and the liquid is a PMMA reference rod. The density is obtained from the reflection coefficient of the reference rod-liquid interface and the transit time between this interface and a reflector placed in the opposite wall of the tube. The DET is calibrated once to account for temperature effects. The calibration is incorporated during signal processing, so that the actual density measurement is temperature compensated. In testing this method, a system was implemented and measurements of several liquids, stationary and flowing in a pipeline, were conducted. The error of measurements obtained by this method for distilled water, tap water, castor oil, and ethanol, when compared to data in the literature or obtained by a pycnometer, is less than 1.5%     

Calculation by the Method of Finite Differences of the Temperature Distribution in Layered Tissues

A numerical approach to obtain the temperature distribution in layered tissues with thermal source and cooling inside the tissues is presented in this paper. This approach can be applied to problems with a distributed internal thermal source produced by external radiation such as microwave, ultrasound, and shortwave, or by internal increase of metabolic rate in live subjects. The exact mechanism of cooling is not discussed here, but it is assumed to be due to blood flow in vivo. The calculation of the temperature distribution in layered tissues is based on a linear model of the tissues that consists of several layers of different kinds of tissues separated by parallel boundaries. Some simple mathematical forms of the cooling functions are also assumed in this paper. The results obtained agree well with six available experiments.     

Micropower Pulse Frequency Modulator for Use in an Optically Isolated Catheter System

A micropower pulse frequency modulator (PFM) has been developed for implementing an opticaily isolated system capable of making sensor voltage measurements. The PFM circuit is powered with an array of solar cells which converts light energy into electrical energy. An input port receives the sensor voltage. The PFM signal generated by the circuit drives an infrared emitting diode which provides the frequency-modulated output signal. The PFM circuit can accept sensor output voltages in the range ±500 mV and has a minimum bandwidth of 500Hz.     

Scattering of Ultrasound by Blood

The ultrasonic volumetric scattering cross section of the erythrocyte has been measured over a range of frequencies by comparing the rms value of the gated backscattered signal from the blood with that of a wave reflected from a flat reflector with known reflection coefficient. It is found to be proportional to the fourth power of the frequency predicted by the wave scattering theory for small particles in the frequency range from 5 MHz to 15 MHz. The relation between the scattering coefficient and the hematocrit is also examined up to a hematocrit of 45 percent. This coefficient is found to increase along with the hematocrit until it reaches a maximum around hematocrit = 26 percent and then decreases as the hematocrit increases. Twersky's wave scattering theory is applied to describe this result.     

Calculations Of Therapeutic Heat Generated by Ultrasound in Fat-Muscle-Bone Layers

An analytical approach to obtain the relative heating pattern due to the propagation of ultrasonic waves in a fat-muscle-bone layered tissue system is presented. The effects on the relative heating pattern due to the change of incident angle and the change of frequency are discussed in this paper. The contribution to heating due to mode conversion at the bone surface is also discussed.     

Angular Dependence of Scattering of Ultrasound from Blood

The angular scattering of 5-MHz ultrasonic waves by blood was measured in the range from 60 to 1500. Experimental and theoretical results agree very well. A discussion on the use of angular scattering for determining the mechanical properties of the erythrocyte is presented.     

Radiation from periodic structures excited by an aperiodic source

In the past, periodic structures have been extensively studied for guided waves along the surface, or for plane wave excitation. However, very little has been reported concerning the problem of exciting periodic structures by a localized source. The essential difficulty of this problem is due to the aperiodic nature of the source. This paper presents a study of a two-dimensional periodic structure excited by a magnetic line source. The structure consists of a grounded dielectric slab covered by a periodically slotted conducting plane. From the continuity of the fields in the slots, an infinite system of integral equations for the aperture fields is derived. Under the assumption of narrow slots, these equations are converted into a single integral equation by the use of the sampling technique, and the solution is expressed in an inverse Fourier transform. The integrand is then converted into a form of space harmonics which contains an infinite number of poles and branch points. The relationship between these singularities and thek-betadiagram is clearly demonstrated. The radiation pattern is calculated and compared with experimental data. The Wood anomalies associated with leaky waves and the Rayleigh wavelength, and in particular, the relationship between the behavior of the field near the Rayleigh wavelength and the lateral waves are discusssed.     

Ultrasonic Measurement of Blood Coagulation Time

A feasibility study indicates that ultrasound backscattering may be used to determine the onset of the formation of a fibrin clot in plasma and whole blood. Experimental results with blood and plasma containing different amounts of fibrinogen are presented.