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Ultra-wide band (UWB) microwave imaging is a promising method for the breast cancer detection based on the large contrast of electric parameters between the malignant tumor and its surrounded normal organisms. In this paper, a two-dimensional model of the breast organisms is numerically carried by the finite difference time domain (FDTD) method. The dispersion characteristics of the breast media are taken into account by single pole Debye model to approach the actual properties of the breast organism. In this method, a tumor is assumed in the model with two cases. The standard Capon beamforming (SCB) and doubly constrained robust Capon beamforming (DCRCB) algorithm performed to reconstruct the image is described in detail. The tumor can be detected and localized using the proposed algorithm and the result demonstrates a good stability of DCRCB algorithm.

An implicit high-order compact unconditionally stable finite-difference time-domain (FDTD) method is proposed here for numerical solution of point sources over an impedance plane. In this method, the linearized Euler equations are split into three directional sets and twelve simple wave components, or six when equivalent sources are adopted with no mean flow. Each component is solved using a fourth-order Padé approximant in space and second-order trapezoidal integration in time. The concept of reflection coefficient is used and algebraically modeled to develop time-domain impedance-equivalent boundary conditions. Comparisons with established methods for reflections of harmonic or impulsive sources demonstrate the applicability of this method for general impedance value, source type, or their arbitrary distributions. Examples of using typical wool felt and grass ground impedances are given to illustrate its practicality and effectiveness. This method provides a means through which time-domain theories and procedures for in-situ characterization of impedance surfaces can be developed.

Modeling of acoustic pulse propagation in nonideal fluids requires the inclusion of attenuation and its causal companion, dispersion. For the case of propagation in a linear, unbounded medium Szabo developed a convolutional propagation operator which, when introduced into the linear wave equation, accounts for attenuation and causal dispersion for any medium whose attenuation possesses a generalized Fourier transform. Utilizing a one dimensional Finite Difference Time Domain (FDTD) model Norton and Novarini showed that for an unbounded isotropic medium, the inclusion of this unique form of the convolutional propagation operator into the wave equation correctly carries the information of attenuation and dispersion into the time domain. This paper addresses the question whether or not the operator can be used as a basic building block for pulse propagation in a spatially dependent dispersive environment. The operator is therefore used to model 2-D pulse propagation in the presence of an interface separating two dispersive media. This represents the simplest description of a spatially dependent dispersive media. It was found that the transmitted and backscattered fields are in excellent agreement with theoretical expectations demonstrating the effectiveness of the local operator to model the field in spatially dependent dispersive media. [Work supported by ONR/NRL.]

This paper describes the relationship between the eigenfrequencies of CT scanned realistic human head model and the subjective detecting pitch, which is given by providing the bone-conducted ultrasound. Our goal is to develop the optimal bone-conducted ultrasonic hearing aid for profoundly hearing-impaired persons. An ascent of a speech intelligibility is the requirement of hearing aid. To improve it, the perception mechanism of the bone-conducted ultrasound must be clarified, but the conclusive agreement of it has not been reached yet, although many hypotheses were reported.

The authors feel an interest in the detecting pitch of bone-conducted ultrasound with no frequency-dependence and predict that the cochleae are related to the perception mechanism for bone-conducted ultrasound, since it has been verified that the auditory cortex responds to bone-conducted ultrasound by MEG study.

In this paper, waves propagating from the mastoid to both cochleae are numerically analyzed and the characteristics of transfer functions are estimated as a first step to clarifying the perception mechanism for detecting pitch of bone-conducted ultrasonic stimuli.

Finite-difference time-domain (FDTD) method has been successfully developed to model electromagnetic systems in recent years. Since acoustics and electromagnetism share certain undulatory properties, a natural adaptation of this technique has been developed too. Several acoustics problems, such as room acoustics, require the use of fibrous tangles to attenuate the propagation speed of sound waves. Notwithstanding, although free air acoustic propagation is known, FDTD technique is not developed yet to model fibrous materials. To characterize this behavior, only a few and measurable set of parameters must be considered. In this paper, a new approach for modeling fibrous materials analysis using FDTD is presented and validated. A set of simulations covering various packing densities of a real fibrous material is performed. Loudspeaker cabinets, virtual acoustics and room acoustics are situations in which this method can be applied.

In this paper, the radiation characteristics with respect to the suitability of using homogeneous phantom for testing the compliance of radiation frequency devices are assessed. The Finite-Difference Time-Domain (FDTD) method is applied to analyze the variations of a 900 MHz half-wavelength dipole antenna's biological effects and link performance depending on distance between antenna and human body model. The distance between the surface of the model and the outside exposure source is changed from 25 mm to 1 mm within the range of λ/2π. The distributions of the specific absorption rates (SARs) and the electric fields for various vertical slices of a simplified homogeneous phantom and three anatomical human body trunk models are calculated, respectively. The legs and head have little influence on the radiation characteristics of body-worn, ingestible or implantable wireless devices. The results demonstrate that a homogenous representation of human body is suited for assessing the averaged SARs in human body and confirm that the local energy absorption details and communication link performance need to be analyzed by using the anatomical models or by combining with the worst-case consideration.