Development of capacitive pure bending strain sensor for wireless spinal fusion monitoring

2007 ◽  
Vol 138 (2) ◽  
pp. 276-287 ◽  
Author(s):  
Ji-Tzuoh Lin ◽  
Kevin W. Walsh ◽  
Douglas Jackson ◽  
Julia Aebersold ◽  
Mark Crain ◽  
...  
2006 ◽  
Vol 1 (2) ◽  
pp. 159-164 ◽  
Author(s):  
J. W. Aebersold ◽  
W. P. Hnat ◽  
M. J. Voor ◽  
R. M. Puno ◽  
D. J. Jackson ◽  
...  

Lumbar arthrodesis or spinal fusion is usually performed to relieve back pain, and regain functionality from degenerative disc disease, trauma, etc. Fusion is determined from radiographic images (X-ray) or computed tomography scans, yet these inspection procedures are subjective methods of review. As a result, exploratory surgery is performed if the presence of fusion cannot be confirmed. Therefore, a need exists to provide objective data to determine the presence of fusion that could avoid the cost, pain, and risk of exploratory surgery. One method to achieve this objective is to observe bending strain from spinal rods implanted during surgery. A system has been developed that will attach to the spinal instrumentation rods, transmit strain information wirelessly, and without the use of batteries. Major components of the system include a strain transferring sensor housing, a microelectromechanical (MEMS)-based strain sensor, telemetry circuitry, and antennae. Only discussed herein are the design, testing, and results of the housing without a cover and its ability to transfer strain from the rod to an internal surface where a foil strain gage is attached to characterize strain transfer efficiency. Strain gauges rather than the MEMS sensor were employed for housing characterization due cost and limited availability. Design constraints for the housing are long-term implantation, small size, greater than 95% transfer of bending strain from the spinal rods to the internal strain sensor, and ease of installation. ABAQUS finite element modeling software was employed to develop a working model that was fabricated using polyetheretherkeytone. The housing underwent cycle testing in a material testing system to simulate long-term implantation along with static testing to determine if creep was present. Both series of tests showed that the housing’s response did not degrade over a period of time and there was no indication of creep. The experimental results also validated the results of the ABAQUS finite element model.


Author(s):  
Muhammad Irsyad Abdul Mokti ◽  
Inzarulfaisham Abd. Rahim ◽  
Asrulnizam Abd Manaf ◽  
Othman Bin Sidek ◽  
Muhamad Azman Bin Miskam

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Muhammad Irsyad Abdul Mokti ◽  
Inzarulfaisham Abd Rahim

This study evaluates the sensitivity of microelectromechanical system (MEMS) capacitive bending strain sensor with a double layer cantilever designed to meet the requirements of spinal fusion monitoring. The cantilever structure of the sensor consists of two parallel substrate plates which constitute the electrodes, attached to an anchor made of silicon dioxide. The sensor was able to monitor bending strain value ranging from 0 to 1000 με. In order to evaluate the sensitivity of the sensor, parametric study was carried out by varying electrode gap, anchor length, and dielectric coverage between the electrodes. The nominal capacitive strain sensor for various applications has sensitivity ranging from 255 aF/μεto 0.0225 pF/με. An increase in the sensitivity was observed on reducing the electrode gap and the anchor length and increasing the dielectric coverage, resulting in a highest sensitivity value of 0.2513 pF/με. It was also observed that dielectric constant has a significant effect on the sensitivity behavior of the sensor.


2007 ◽  
Vol 17 (2) ◽  
pp. 2591-2594 ◽  
Author(s):  
L. Muzzi ◽  
A. della Corte ◽  
A. Di Zenobio ◽  
S. Turtu ◽  
L. Zani ◽  
...  
Keyword(s):  

In the ordinary type of Wöhler machine used for testing materials in fatigue under reversed bending stresses, the load system is stationary in space, and variation of the stress system with respect to the test piece is obtained by rotating the test piece. It is, of course, essential to the success of the test that the system of displacements caused by the application of the load system to the test piece should remain stationary in space; but, since the test piece rotates, this requirement can only be fulfilled if the material of the test piece is isotropic. Thus, if an attempt were made to test a single crystal in a Wöhler machine it might be anticipated that either actual elastic antisotropy or the virtual anisotropy due to restricted slip movement would cause the deformation to vary with the orientation of the stress system relative to the axes of the crystal and that "whipping" of the specimen would occur. Three such attempts have indeed been made: but in spite of great care exercised in setting up the specimens and in applying the loads, only in one case, in which the orientation of the crystal was such as to provide effective symmetry about the axis of the specimen, was the test successful. A new type of testing machine recently developed at the N. P. L. for testing specimens in fatigue under systems of combined bending and torsional stresses, differs in principle from the Wöhler machine in that the variation of stress is produced by actual variation of load. In this machine both me test piece and the orientation of the stress system remain stationary, only the magnitude of the stresses being varied. The deformation of the test piece is therefore only that due to one type of stress system fixed in relation to the orientation of the test piece and varying only in magnitude. Moreover, the construction of the machine is such that the strain of the test piece is not required to be of the same type as the stress system applied, e. g ., the application of pure bending moment does not restrict the test piece to pure bending strain and the test piece remains free to twist also if necessary. These conditions render this type of machine perfectly suitable for test on single crystals. Accordingly, tests have been carried out in this machine on three single crystals of aluminium; the first was tested under reversed flexural stresses, the second under reversed torsional stresses and the third under a combination of reversed flexural and reversed torsional stresses.


2006 ◽  
Vol 34 ◽  
pp. 124-129 ◽  
Author(s):  
J Aebersold ◽  
K Walsh ◽  
M Crain ◽  
M Voor ◽  
M Martin ◽  
...  
Keyword(s):  

Author(s):  
Ali Limam ◽  
Liang-Hai Lee ◽  
Stelios Kyriakides

Previous work by the authors investigated the inelastic response and stability of pipes bent in the presence of internal pressure [1,2]. It was shown that internal pressure tends to stabilize the pipe by reducing initial geometric imperfections and reducing the induced ovalization. Consequently pressurized pipe can sustain significantly higher bending strains before collapse than pipe bent in the absence of pressure. Pipelines have girth welds and other local imperfections such as dents. The present phase of this work uses experiment and analysis to investigate the effect of local dents on the collapse capacity of pressurized pipes under pure bending. A series of experiments was conducted on stainless steel 321 seamless tubes with diameters of 1.5 inches and D/t of 52. Small imperfections in the form of transverse dents were introduced to the specimens using a custom technique that limits the axial and circumferential spans of the dents. The dented tubes were loaded by pure bending at a fixed internal pressure (approximately one half the yield pressure) to collapse. Tubes with dent depths ranging from very small to about 1.7 times the pipe wall thickness were tested. It was found that such local imperfections tend to reduce the bending strain capacity of the pipe quite significantly. Smaller depth dents tend to cause relatively larger reduction in the bending strain at collapse whereas at larger depths the bending strain at collapse tends to level off. The inelastic response and the eventual localized collapse are being simulated using FE models. The material is represented as an anisotropic elastic-plastic solid using the flow theory of plasticity. The modeling includes simulation of the denting process followed by pressurization and bending. It will be shown that all aspects of the observed behavior including the sensitivity of collapse strain to the local imperfection are reproduced well by the models.


1986 ◽  
Vol 108 (2) ◽  
pp. 141-146 ◽  
Author(s):  
G. S. A. Shawki ◽  
S. A. R. Naga

This paper presents the results of experiments conducted on lamellar graphite grey cast iron of rectangular section subjected to pure bending. Strain measurements confirm the traditional speculation that plane sections remain plane under strain. Owing to the nonlinear relationship between stress and strain, however, the neutral axis of a loaded specimen is shown to shift away from the centroidal axis. This shift is evidently amplified with increased loading. A computer program is herein specially devised for calculating the shift in neutral axis through satisfaction of the conditions of equilibrium together with checking for possible crack initiation at the extension side. While the simple flexural formula holds very nearly true for the compression side, it fails, however, to predict stresses on the extension side, the situation being further aggravated by higher bending moments. The apparent high bending strength of grey cast iron is fully accounted for.


2006 ◽  
Vol 16 (5) ◽  
pp. 935-942 ◽  
Author(s):  
J Aebersold ◽  
K Walsh ◽  
M Crain ◽  
M Martin ◽  
M Voor ◽  
...  

2007 ◽  
Vol 546-549 ◽  
pp. 1975-1978
Author(s):  
Zhao Yang Lu ◽  
Xu Qiang Huang ◽  
Yan Fa He ◽  
Jing Sun ◽  
Jin Xing Wang

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