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Narieda S.,Akashi National College of Technology
IEEE Transactions on Vehicular Technology

This paper presents a novel network lifetime extension technique that uses probabilistic transmission control for distributed estimation in wireless sensor networks. In conventional techniques, only a few sensors are selected to transmit messages, and the remaining sensors are not used for measurement. Furthermore, as measurements cannot be carried out when the batteries of the selected sensors are exhausted, network lifetimes strongly depend on the battery capacity of the selected sensors. The presented technique increases the number of available sensors relative to conventional techniques. Sensors that are not selected in conventional techniques can be incorporated into the presented technique to obtain final estimates. As a result, the number of potentially usable sensors in networks increases. These newly available sensors are partitioned into several sensor sets to maintain the same estimation performance. Since observation and transmission for each sensor set are not carried out for every observation period, the network lifetime can be expected to be extended for a given estimation performance. Numerical examples are presented to validate the effectiveness of the presented technique. © 2012 IEEE. Source

In this study, new ultrasound reflection and backscatter measurements in cancellous bone using a membrane-type hydrophone are proposed. A membrane hydrophone made of a piezoelectric polymer film mounted on an annular frame allows an incident ultrasound wave to pass through its aperture because it has no backing material. Therefore, in measurements using the membrane hydrophone, the receiving area could be located independently from the transmitting area. In addition, the size and shape of the receiving area, which corresponded to those of the electrode deposited on the piezoelectric film, could be arranged in various ways. To investigate the validity of the proposed measurements, before bench-top experiments, the reflected and backscattered waves from cancellous bone were numerically simulated using a finite-difference time-domain method. The reflection and backscatter parameters were measured on various receiving areas, and their correlation coefficients with the structural parameters in the cancellous bone were derived. The simulated results suggested that appropriate receiving areas for the reflection and backscatter measurements could exist and that the proposed measurements could be more effective for evaluating bone properties than conventional measurements. © 2013 Elsevier B.V. All rights reserved. Source

The purpose of this study is to numerically investigate the basic reflection properties of fast and slow longitudinal waves propagating in cancellous bone in the direction parallel to the strong orientation of the trabecular network. Finite-difference time-domain simulations with microcomputed tomographic models of bovine cancellous bone were performed to calculate the reflected waveforms at the boundary layers of 100-0% bones. The reflection coefficients of the fast and slow waves were derived by comparing with the waveform simulated for the cancellous bone model with an artificial absorbing boundary. For the fast wave, the reflection coefficients were positive at the boundaries of the 100 and 80% bone layers, but negative at the other boundaries. Moreover, the reflection coefficient at the 100% bone boundary increased with cancellous bone porosity. As the density of the boundary layer decreased, the porosity dependence became weaker, and the reflection coefficient at the 0% bone boundary was almost constant. For the slow wave, at the 100% bone boundary, the reflection coefficient increased with porosity but decreased at the other boundaries. These variations could be associated with the degrees of conversions between the fast and slow waves. © 2014 The Japan Society of Applied Physics. Source

Hosokawa A.,Akashi National College of Technology | Nagatani Y.,Kobe City College of Technology
Japanese Journal of Applied Physics

Fast and slow longitudinal waves can propagate through cancellous bone in the direction of the strong trabecular orientation. In in vivo experiments, the cortical bone layer surrounding cancellous bone is considered to affect the fast and slow wave propagations. In this study, the effects of the cortical bone layer were investigated using the stratified models of cancellous bone. In the experimental and simulated results, it was shown that the boundary condition between the cancellous and cortical bone regions affected both the fast and slow waves, particularly the slow wave. The slow wave could be clearly observed for the stratified bone model with a distinct boundary, but the slow wave amplitude decreased as the boundary became less distinct. This was because the generation of the slow wave was interrupted by the gradually varying pore spaces. Moreover, it was shown that the reflected waves within the cortical bone layer could affect the observation of the fast and slow waves. Despite the effects of the cortical bone layer, both the fast and slow waves could be observed for all stratified bone models. © 2012 The Japan Society of Applied Physics. Source

Hosokawa A.,Akashi National College of Technology
IEEE International Ultrasonics Symposium, IUS

Numerical analysis of ultrasound backscattering in cancellous bone was performed by using three-dimensional finite-difference time-domain (FDTD) simulations with numerical models reconstructed from microcomputed tomographic images of bovine bone. In the simulations, two cancellous bone models with different thicknesses were used. In each model, an artificial absorbing boundary was set at the back surface opposite to the front surface toward which an ultrasound pulse wave was transmitted from a concave transmitter/receiver in water. From the difference between the simulated waveforms for the two bone models, the reflected wave from the front surface could be canceled, and only the backscattered waves inside the bone could be extracted. For the ultrasound transmission parallel to the main orientation of the trabecular network, the backscattered waves from various bone depths were analyzed. The peak-to-peak amplitudes of the backscattered waves from the deep bone depths were moderately correlated with porosity [R2 = 0.43-0.54 (P < 0.001)]. The backscattered waves from the deeper bone depth could be more clearly separated into the fast and slow waves, and the backscattered wave amplitude could be regarded as the slow wave amplitude. © 2014 IEEE. Source

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