The role of the concentration and distribution of water in the complex permittivity of breast fat tissue.

The structure of breast tissue is complicated and highly variable and presents a great challenge in the development of physical models that may be used to obtain its effective complex permittivity. Empirical models are commonly used by researchers to fit measured data and extrapolated to higher frequencies. However, these models have not been verified experimentally at higher frequencies. Theoretical models of tissue permittivity to explain the role of water are not available today. This communication is a systematic study of several models to estimate the complex permittivity of breast fat tissue based on volume content and distribution of water in the tissue. These models are implemented in (i) long wavelength, sparse concentration limit; (ii) full wave finite element simulation; and (iii) numerical implementation of dynamic multiple scattering theory. A comparison of the proposed models with experimental data is done at 3.2 GHz. Some of the measurement values are in fair agreement with the modeling. The results of the present study are useful for interpreting the large variability in experimentally measured values of the permittivity of breast fat tissue by taking the distribution of water into account.

Characterization of all the elastic, dielectric, and piezoelectric constants of uniaxially oriented poled PVDF films.

Polyvinylidene fluoride (PVDF), a piezoelectric material, has many useful applications, for example, as sensors, transducers, and surface acoustic wave (SAW) devices. Models of performance of these devices would be useful engineering tools. However, the benefit of the model is only as accurate as the material properties used in the model. The purpose of this investigation is to measure the elastic, dielectric and piezoelectric properties over a frequency range, including the imaginary part (loss) of these properties. Measurements are difficult because poled material is available as thin films, and not all quantities can be measured in that form. All components of the elastic stiffness, dielectric tensor, and electromechanical coupling tensor are needed in the models. The material studied here is uniaxially oriented poled PVDF that has orthorhombic mm2 symmetry. Presented are the frequency dependence of all nine complex elastic constants, three complex dielectric constants, and five complex piezoelectric constants. The PVDF was produced at Raytheon Research Division, Lexington, MA. Measurements were made on thin films and on stacked, cubical samples. The elastic constants c44D and C55D, the dielectric constants epsilon11T and epsilon22T, as well as the piezoelectric constants g15 and g24 reported here have not been published before. The values were determined by ultrasonic measurements using an impedance analyzer and a least square data-fitting technique.

Evaluation of a new self-contained, ambulatory, objective cough monitor.

OBJECTIVE AND BACKGROUND: Objective monitoring of cough may be preferred to subjective reporting of the symptom in clinical and research settings. Therefore, a self-contained, ambulatory cough monitoring system is needed that is non-invasive, usable for children and adults of all ages, inexpensive, and highly accurate with easy to use analysis software. METHODOLOGY: After development of a new device, 15 subjects with frequent coughing were recorded with the novel cough monitor and a simultaneous video recording in order to validate the monitor compared with a gold standard. Two investigators independently analyzed the recordings and counted the number of coughs during the study period from both the cough monitor and the video recording. RESULTS: When measuring agreement between the two investigators, the sample concordance correlation coefficient for audio counts was 0.998 (p < 0.001). In the comparison of video counts, the sample concordance correlation coefficient was 0.997 (p < 0.001). For the comparison of investigator 1's video counts to the corresponding audio counts, the sample concordance correlation coefficient was 0.968 (p = 0.026). For the comparison of investigator 2's video counts to the corresponding counts, the sample concordance correlation coefficient was 0.973 (p = 0.015). CONCLUSION: We have developed and piloted a new, valid, and reproducible method of objectively recording and analyzing cough. This device appears to be useful for subjects of any age and in clinical and research settings.