Akashi National College of Technology

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Akashi, Japan
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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.


Hosokawa A.,Akashi National College of Technology
Japanese Journal of Applied Physics | Year: 2014

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.


Narieda S.,Akashi National College of Technology
IEEE Transactions on Vehicular Technology | Year: 2012

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.


Hosokawa A.,Akashi National College of Technology
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2013

The basic reflection properties of fast and slow waves propagating in cancellous bone were numerically investigated using finite-difference time-domain (FDTD) simulations with 18 microcomputed tomographic (μCT) models of bovine cancellous bone. The simulated results showed that both reflection coefficients of the fast and slow waves linearly increased with porosity. © 1986-2012 IEEE.


Hosokawa A.,Akashi National College of Technology
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2010

Cancellous bone is a porous material composed of numerous trabecular elements, and its porosity changes according to its position within a bone. In this study, the effect of porosity distribution in the propagation direction on ultrasound waves through cancellous bone was numerically investigated using finite-difference time-domain (FDTD) simulations. Fiftyfour numerical models of cancellous bone were reconstructed from 3-D X-ray microcomputed tomographic (CT) images at 6 positions in a bovine femoral bone. To generate trabecular structures with distinct porosity distributions, 3 erosion procedures were performed in which the trabecular elements in each cancellous bone model were eroded. In one procedure, erosion was uniformly distributed over the whole spatial region of the cancellous bone model, but in the other 2 procedures, the spatial distribution of erosion was changed in a specific direction. Fast and slow waves propagating through the 3-D CT cancellous bone models in the porosity-distributed direction were simulated using the viscoelastic FDTD method. The wave amplitudes and propagation speeds of the fast and slow waves were measured for the cancellous bone models eroded by each procedure, and the effect of porosity distribution was investigated in terms of change in the trabecular microstructure. The results suggest that both wave amplitudes increased when porosity distribution was low and when trabecular structure was more uniform, but that the speed of the fast wave increased when porosity distribution was high and when longer trabecular elements were present. © 2006 IEEE.


Narieda S.,Akashi National College of Technology
Electronics Letters | Year: 2012

Presented is a novel downsampling technique for narrowband wireless communication systems. The presented technique employs digital notch filters for downsampling in a low IF receiver. The presented results are compared with conventional results. Although these are found to be almost the same, the presented technique has lower computational complexity than the conventional technique. © 2012 The Institution of Engineering and Technology.


Hosokawa A.,Akashi National College of Technology
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2011

Ultrasound propagation through cancellous bone can be greatly affected by the trabecular structure. In the present study, the ultrasound propagation for the oblique orientation of the trabecular network was numerically investigated using 3-D finite-difference time-domain (FDTD) simulations. The models of cancellous bone were reconstructed from X-ray microcomputed tomographic (μCT) images of a bovine bone. Cancellous bone models with various orientations of the trabecular network were realized by cutting the μCT images rotated from 0 to 90°. Ultrasound waveforms propagating through these cancellous bone models were simulated while changing the receiving position. The refraction of the ultrasound wave for the oblique angle of the main orientation was investigated on the basis of the variation in the arrival time and peak amplitude. As the propagation direction approached the direction parallel to the main orientation, the arrival time of the first peak became less and the peak amplitude became smaller. This means that the wave of the first peak, which corresponded to a fast wave, propagated in the direction perpendicular to the main orientation. In addition, a strong correlation between the first-peak amplitude and the arrival time was observed in the porosity range of 0.68 to 0.85, in which the slope of the amplitude with respect to time increased linearly with porosity. © 2011 IEEE.


Hosokawa A.,Akashi National College of Technology
AIP Conference Proceedings | Year: 2012

Cancellous bone remodeling, which is a couple of bone formation and resorption on the trabecular surface, was numerically simulated using finite difference time-domain (FDTD) method with a voxel finite element (VFE) model of bovine cancellous bone. Assuming that the bone formation/resorption could be generated on the trabecular surface where the local stress under the mechanical load was larger/smaller than the surrounding stress, the voxel elements in the cancellous bone model were added/removed. An ultrasound wave at 100 kHz was applied to cancellous bone as the mechanical load, and the local stress was calculated using the FDTD method. In the case of the ultrasound transmission in the direction parallel to the main orientation of the trabecular network, both orientations in the trabecular and pore structures became stronger as the bone remodeling advanced. On the other hand, in the case of the transmission in the perpendicular direction, these orientations became weaker. In the remodeling simulation, the realistic change in the trabecular structure with the porosity could be observed. © 2012 American Institute of Physics.


Hosokawa A.,Akashi National College of Technology
IEEE International Ultrasonics Symposium, IUS | Year: 2014

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.


Narieda S.,Akashi National College of Technology
2011 IEEE Radio and Wireless Week, RWW 2011 - 2011 IEEE Topical Conference on Wireless Sensors and Sensor Networks, WiSNet 2011 | Year: 2011

This paper presents a probabilistic transmission control technique for the distributed estimation in WSNs. The presented technique is based on a novel transmission control which is to minimize a mean squared error of estimation by increasing the packet transmission success probability of only sensors having the high observation SNR. In the presented method, the transmission of sensors is probabilistically decided whether the SNR of sensor is greater than the threshold whereas the transmission of sensors is deterministically decided in the conventional method. To achieve the presented method, we introduce a probabilistic transmission control function that gives each sensor a probabilistic value (from 0 to 1) as the transmission probability. Also, since the presented method can allows sensors to retransmit messages, it can be expected that the reliability of estimate increases. We employed the collision channel model where the transmission from the sensor to the FC is successful only when no other sensors are transmitting in the same time slot. Also, we assume that each sensor observe unknown at the beginning of the limited observation period, and each sensor can transmits observation only the limited retransmission time. Based on the model, theoretical packet transmission success probability of the presented and conventional method is derived. Numerical results are presented to valid the effectiveness of the presented method. © 2011 IEEE.

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