Displacement Sensitivity Research Articles

Validation and sensitivity of model-predicted proximal tibial displacement and tray micromotion in cementless total knee arthroplasty under physiological loading conditions

The initial fixation of cementless tibial trays after total knee arthroplasty is crucial to bony ingrowth onto the porous surface of the implants, as micromotion magnitudes exceeding 150 μm may inhibit bone formations and limit fixation. Experimental measurement of the interface micromotions is still very challenging. Thus, previous studies investigated micromotions at the bone-tray interface via finite element methods, but few performed direct validation via in vitro cadaveric testing under physiological loading conditions. Additionally, previous models were validated by solely considering relative displacements of the marker couples placed around the tray-bone interface. In this paper, we present an experimental-computational validation framework for investigating micromotions at the tray-bone interface under physiological conditions. Three cadaveric specimens were implanted with cementless rotating-platform implants and tested under gait, deep knee bending, and stair descent loads. Corresponding subject-specific finite element models were developed and used to predict the marker (tray-bone) relative displacements and tibial surface displacements. Experimental measurements were used to validate model estimations. Subsequent sensitivity analyses were performed on implantation and friction parameters to represent model uncertainties.The models appropriately differentiated between locations, activities, and specimens. The average root-mean-square (RMS) differences and correlations between measured marker relative displacements and predictions from the ‘best-matching’ models were 13.1 μm and 0.86. RMS differences and correlations between measured surface displacements and predictions were 78.9 μm and 0.84. Full-field interface micromotions were investigated and compared with predicted marker relative displacements. The marker relative displacements underestimated the actual interface micromotions. Initial tray-bone alignment in anterior-posterior, flexion-extension, and varus-valgus degrees of freedom have a considerable impact on the interface micromotions. The validated cadaveric models can be further used for pre-clinical assessments of new TKR tray design. The outcomes of the sensitivity analyses provide further insights into reducing interface micromotions via clinical techniques.

An Angular Displacement Sensor Based on Microstrip Wideband Impedance Transformer With Quasi-Chebyshev Frequency Response

In this paper, the design methodology of a microstrip angular displacement sensor based on an impedance transformer with a quasi-Chebyshev frequency response is proposed. This sensor with impedance transforming function can realize the angular displacement detection by bandwidth sensing, and matching sensing simultaneously. The insertion loss in stopband achieves 24.9 dB to 32.6 dB with an average bandwidth selectivity of 2.25 MHz/degree of the sensor centered at 2.4 GHz with two poles of 1.71 GHz and 2.81 GHz. Meanwhile, the average matching level of return loss for displacement sensitivity are 0.18 dB/degree and 0.15 dB/degree, respectively. It is the first time to apply an impedance transformer into the angular displacement sensor design for both bandwidth and matching level sensing among reviewed literatures. In this design, the load-to-source impedance transformation is designed for 250-to-50 Ω, and by adding a rotated stub on the proposed microstrip transformer, the sensing function is developed with angular displacement.

Imaging of cranio-cervical junction traumas

The craniocervical junction (CCJ) or upper cervical spine (UCS) has anatomic features and a biomechanics completely different from the other spinal segment of the spine. Several ligaments and muscles control its motion and function and ensure the maximum mobility and the visual and auditory spatial exploration. UCS traumas represent approximately one-third of all cervical spine injuries. Most of UCS traumas results from blows to the head and sudden deceleration of the body. Thanks to the improvement of the Advanced Trauma Life Support protocols dissociative injuries of CCJ have become less lethal onsite. In other less severe but unstable injuries, patients are neurologically intact at presentation, but they may deteriorate during the stay in hospital, with important clinical and medico-legal consequences. Knowing the peculiarities of UCS is fundamental for the early detection of imaging findings that influences the patient management and outcome. The classification of UCS traumas is mechanistic. More than in any other spinal segment, fractures of CCJ bones can occur without generating instability; on the contrary highly unstable injuries may not be associated with bone fractures. An early and correct diagnosis of occipito-cervical instability may prevent secondary neurological injury. The goal of imaging is to identify which patients can benefit of surgical stabilization and prevent secondary neurologic damage. Actual helical multidetector-CT (MDCT) offers high sensitivity and specificity for bone lesions and displacements in cervical spine traumas, but magnetic resonance imaging (MRI) is increasingly being used to evaluate soft tissues and ligaments, and mainly to identify possible spinal cord injury.

Optical coherence tomography and its applications in experimental mechanics: A review

Optical coherence tomography (OCT) is a low-coherence interferometry based optical technique capable of imaging internal structures of transparent/semitransparent objects with micrometer resolution and millimeter range. It features distinct advantages of non-invasive and fast-imaging, and has been widely applied in biology, medicine, and material science. After combining with digital image/volume correlation (DIC/DVC) or phase-contrast, OCT can also be used as an elastography method, known as OCT elastography, for measuring full-field displacements and strains inside objects. Recently, OCT elastography has already been developed as an effective tool for investigating mechanical behaviors of inside bio-tissues and materials, such as cornea, skin, tumor, polymer, and polymer composite. In this work, we introduce the basic principles of OCT elastography, summarize the typical experimental mechanics applications of OCT elastography, and finally discuss the remaining problems and limitations of the technique. OCT was originally developed by D. Huang et al. in 1991. The early OCT technique detects depth information of a specimen by means of mechanical scanning, and therefore it is also called time-domain OCT (TD-OCT). Owing to the limitation of mechanical scanning manner, the imaging speed and signal-to-noise (SNR) of this first-generation OCT is relatively low, which makes it unable to meet the requirements of most measurement situations. In 1995, A. F. Fercher et al. developed another type of OCT, called Fourier-domain OCT (FD-OCT). This second-generation OCT uses parallel detection instead of mechanical scanning to improve the imaging speed and SNR, and greatly accelerated the extension of OCT application. Recently, OCT has also been combined with some other techniques and forms a lot of functional OCT methods, including Doppler OCT, polarization-sensitive OCT, OCT elastography, and spectroscopic OCT. Among them, OCT elastography can realize displacement and strain fields measurement inside objects, which is a promising technique in the field of experimental mechanics. The development of OCT elastography can be traced back to 1998, J. M. Schmitt et al. measured the in-plane and out-of-plane displacement fields inside specimens by using the combination of OCT and DIC. However, owing to the low resolution and poor SNR of the early OCT systems, the imaging quality of the method is unsatisfactory. In addition, the displacement sensitivity of the method is at sub-pixel level (micrometer or sub-micrometer level), which is insufficient for most measurement scenarios. For these reasons, DIC-based OCT elastography hasn’t been widely accepted by the researchers. In 2006, R. K. Wang et al. proposed an alternative method that combines OCT and phase-contrast for achieving OCT elastography. The method uses phase sensitive characteristic of OCT for measuring displacements, and makes the displacement sensitivity reach to nanometer level or even higher. Benefiting from the significant improved displacement sensitivity, OCT elastography has received increasing attention in the last decade. Though OCT elastography developed rapidly in recent years, there still remain some problems: (1) Current OCT elastography is only available of measuring transparent and semitransparent objects. For measuring non-transparent objects, it is helpless. Therefore, in the future work, improving penetrating capability is required for OCT elastography. (2) Despite the fact that the development of FD-OCT greatly improved the imaging speed of OCT elastography, it is still insufficient for measuring full-field deformations of inside objects dynamically. Therefore, improving the imaging speed of OCT elastography is also on demand. (3) The employment of phase-contrast can significantly improve the displacement measurement sensitivity of OCT elastography, but it also makes the method lose its in-plane displacement measurement capability. Therefore, developing a novel OCT elastography enabling both in-plane and out-of-plane displacement measurements with high sensitivity is required in the further research.

The Forward Fuselage Rigidity Design Based on Sensitivity Analysis of The Aircraft

In this paper, structural characteristics of the forward fuselage of an aircraft were analyzed. Loadbearing characteristics of longitudinal members and transverse members of the forward fuselage were summarized. After analysis, longitudinal members were identified as main factors that affected structural deformation. Then, finite element analysis and sensitivity analysis methods were combined to determine accurate stiffness sensitivity parameters of the forward fuselage structure. Through analysis of the displacement sensitivity curve, the law of changes in stiffness of the forward fuselage with changes in sizes of longitudinal members was found out. Design requirements on stiffness of the forward fuselage were well satisfied by controlling parameters on purpose. Then, some experiments were designed to compare calculated displacements of the forward fuselage. Experiment results proved the accuracy of the proposed analysis method, allowing designers to get rid of their experience-based the forward fuselage stiffness design methods and providing a theoretical basis for the forward fuselage stiffness design. The proposed method could also provide some reference for structural design of new or retrofitted planes.

A knotted shape core cladding optical fiber interferometer for simultaneous measurement of displacement and temperature

A novel composite structured all-fiber sensor was designed and experimentally demonstrated for simultaneous measurement of displacement and temperature. The sensor consists of a knotted shape core cladding optical fiber. The interferometer notch of a knotted shape fiber was found to be highly sensitive to the micro-displacement as well as environmental temperature, while the core-offset fiber was sensitive to temperature only. Thus the different features of these interferometer notchs of two parts can be used to measure the displacement and temperature. The experimental results showed that the sensor exhibited a high displacement sensitivity of −528.57 pm/μm ranges from 0 mm to 0.012 mm. And the temperature sensitivities of the knotted shape core cladding optical fiber were −114.86 pm/℃ and 31.66 pm/℃ ranges from 35 ℃ to 60℃, respectively. Due to the compact size and dual-parameters measurability, the sensor had a great potential in diverse sensing application.

Model Prediction of Microcantilever using DOE for Stress and Eigen Frequency Analysis for Force Measurement

In this paper, stress and eigen frequencies are analyzed through prediction of microcantilever model using design of experiment approach. The important factors affecting displacement sensitivity, stress and eigen frequencies were identified such as geometrical dimensions of microcantilever (length, breadth and thickness), modulus of elasticity of materials, applied force. Based on the selection of factors and levels, experiments were designed using L9 orthogonal array. The designed experiments were simulated with finite element method in COMSOL Multiphysics software. Further, optimum values of dimensions of microcantilever and material property are used for stress and eigen frequencies analysis. The evaluated frequencies under eigen frequency analysis revealed that designed and simulated Gallium Arsenide (GaAs) microcantilever is prone to vibrate at these frequencies, whereas stress analysis illustrates the response of structure and material properties towards reliability.

Miniature Fabry-Perot interferometer based on a movable microsphere reflector.

We propose and demonstrate a miniature Fabry-Perot interferometer (FPI) based on a movable microsphere reflector. The movable microsphere acts as a good reflector, with the reflections occurring at the spliced single-mode fiber/hollow-core fiber interface and the surface of a microsphere, resulting in two-beam interference. The silica microsphere is formed at the tip of a half-tapered optical fiber, and its diameter can be reduced to miniaturize the FPI. The movable microsphere interferometer exhibits a highly linear response to external displacement change, and a high displacement sensitivity of 11.9 pm/nm with a nanoscale resolution of 1.7 nm is achieved. Wide-range displacement can also be measured by monitoring the changes in the free spectral range of the reflection spectrum. Therefore, this miniaturized FPI may find use in applications in nano-displacement measurement fields, and the concept of a movable microsphere reflector is of great significance for the miniaturization of micro-photonic devices.

Probabilistic seismic landslide hazard assessment: a case study in Tianshui, Northwest China

Probabilistic analysis in the field of seismic landslide hazard assessment is often based on an estimate of uncertainties of geological, geotechnical, geomorphological and seismological parameters. However, real situations are very complex and thus uncertainties of some parameters such as water content conditions and critical displacement are difficult to describe with accurate mathematical models. In this study, we present a probabilistic methodology based on the probabilistic seismic hazard analysis method and the Newmark’s displacement model. The Tianshui seismic zone (105°00′–106°00′ E, 34°20′–34°40′ N) in the northeastern Tibetan Plateau were used as an example. Arias intensity with three standard probabilities of exceedance (63%, 10%, and 2% in 50 years) in accordance with building design provisions were used to compute Newmark displacements by incorporating the effects of topographic amplification. Probable scenarios of water content condition were considered and three water content conditions (dry, wet and saturated) were adopted to simulate the effect of pore-water on slope. The influence of 5 cm and 10 cm critical displacements were investigated in order to analyze the sensitivity of critical displacement to the probabilities of earthquake-induced landslide occurrence. The results show that water content in particular, have a great influence on the distribution of high seismic landslide hazard areas. Generally, the dry coverage analysis represents a lower bound for susceptibility and hazard assessment, and the saturated coverage analysis represents an upper bound to some extent. Moreover, high seismic landslide hazard areas are also influenced by the critical displacements. The slope failure probabilities during future earthquakes with critical displacements of 5 cm can increase by a factor of 1.2 to 2.3 as compared to that of 10 cm. It suggests that more efforts are required in order to obtain reasonable threshold values for slope failure. Considering the probable scenarios of water content condition which is varied with seasons, seismic landslide hazard assessments are carried out for frequent, occasional and rare earthquake occurrences in the Tianshui region, which can provide a valuable reference for landslide hazard management and infrastructure design in mountainous seismic zones.

Temperature Compensated FBG Displacement Sensor for Long-Range Applications

This letter presents an improved fiber Bragg grating (FBG) displacement sensor for long-range measurements. A mechanical transfer structure is designed and developed, which converts the displacement of a measurement wire to the elastic deflection of a sensing arm. The wavelength shift difference between two FBGs symmetrically pasted on the sensing arm is found to be proportional to the displacement. The experimental results show that this design has a displacement sensitivity of 23.80 pm/mm within a measurement range of 0–150 mm. This improved displacement sensor shows good temperature compensation with the very low temperature sensitivity of 0.076 pm/°C for a temperature range of −40–120 °C. This sensor can be utilized for long-range and high endurance displacement measurement applications in harsh industrial environment.

Coherent Optical Transduction of Suspended Microcapillary Resonators for Multi-Parameter Sensing Applications.

Characterization of micro and nanoparticle mass has become increasingly relevant in a wide range of fields, from materials science to drug development. The real-time analysis of complex mixtures in liquids demands very high mass sensitivity and high throughput. One of the most promising approaches for real-time measurements in liquid, with an excellent mass sensitivity, is the use of suspended microchannel resonators, where a carrier liquid containing the analytes flows through a nanomechanical resonator while tracking its resonance frequency shift. To this end, an extremely sensitive mechanical displacement technique is necessary. Here, we have developed an optomechanical transduction technique to enhance the mechanical displacement sensitivity of optically transparent hollow nanomechanical resonators. The capillaries have been fabricated by using a thermal stretching technique, which allows to accurately control the final dimensions of the device. We have experimentally demonstrated the light coupling into the fused silica capillary walls and how the evanescent light coming out from the silica interferes with the surrounding electromagnetic field distribution, a standing wave sustained by the incident laser and the reflected power from the substrate, modulating the reflectivity. The enhancement of the displacement sensitivity due to this interferometric modulation (two orders of magnitude better than compared with previous accomplishments) has been theoretically predicted and experimentally demonstrated.

Improved Sensitivity of Intramolecular Strand Displacement Based on Localization of Probes

Effective intermolecular interaction is required between probe and target molecules for successful detection of biomarkers. Here, we demonstrate that localization of probes on DNA nanostructures improves detection sensitivity and reaction rate. The structural flexibility of DNA nanostructures enabled frequent intramolecular interactions among the localized probes. The Smoluchowski coagulation method and the coarse-grained molecular dynamic software oxDNA were used for theoretical estimation of inter- and intramolecular behaviors of the DNA nanostructures as well as adequate experiments verifying the improvements in sensitivity with probe localization. Remarkably, the probe-localized DNA nanostructure had an increased sensitivity up to 274 times higher than that of the same probes without localization. We believe this achievement represents a wide applicability as a potential design strategy for robust, reliable, and sensitive biosensors.

Considerations for ultrasound exposure during transcranial MR acoustic radiation force imaging

The aim of this study was to improve the sensitivity of magnetic resonance-acoustic radiation force imaging (MR-ARFI) to minimize pressures required to localize focused ultrasound (FUS) beams, and to establish safe FUS localization parameters for ongoing ultrasound neuromodulation experiments in living non-human primates. We developed an optical tracking method to ensure that the MR-ARFI motion-encoding gradients (MEGs) were aligned with a single-element FUS transducer and that the imaged slice was prescribed at the optically tracked location of the acoustic focus. This method was validated in phantoms, which showed that MR-ARFI-derived displacement sensitivity is maximized when the MR-ARFI MEGs were maximally aligned with the FUS propagation direction. The method was then applied in vivo to acquire displacement images in two healthy macaque monkeys (M fascicularis) which showed the FUS beam within the brain. Temperature images were acquired using MR thermometry to provide an estimate of in vivo brain temperature changes during MR-ARFI, and pressure and thermal simulations of the acoustic pulses were performed using the k-Wave package which showed no significant heating at the focus of the FUS beam. The methods presented here will benefit the multitude of transcranial FUS applications as well as future human applications.

Super-sensitive measurement of angular rotation displacement based on the hybrid interferometers.

We theoretically study the angular rotation displacement based on the hybrid interferometers, which contain a beam splitter (BS) and an optical parameter amplication (OPA) for beam splitting and recombination. Two schemes with different orders of an OPA and a BS are discussed and both of them can realize the super resolving and sensitive angular rotation displacement. The sensitivity of angular rotation displacement can surpass the shot noise limit 12l N with the orbital angular momentum input beams. The squeezing strength of an OPA and the reflectivity of the BS play a decisive role on the resolutions and sensitivities while the losses play a negative effect on the sensitivity.

Characterization of oviduct ciliary beat frequency using real time phase resolved Doppler spectrally encoded interferometric microscopy.

Ciliary activity, characterized by the coordinated beating of ciliary cells, generates the primary driving force for oviduct tubal transport, which is an essential physiological process for successful pregnancies. Malfunction of the cilium in the fallopian tube, or oviduct, may increase the risk of infertility and tubal pregnancy that can result in maternal death. While many ex-vivo studies have been carried out using bright field microscopy, this technique is not feasible for the in-vivo investigation of oviduct ciliary beating frequency (CBF). Optical coherence tomography (OCT) has been able to provide in-vivo CBF imaging in a mouse model, but its resolution may be insufficient to resolve the spatial and temporal features of the cilium. Our group has recently developed the phase resolved Doppler (PRD) OCT method to visualize ciliary strokes at ultra-high displacement sensitivity. However, the cross-sectional field of view (FOV) may not be ideal for visualizing the surface dynamics of ciliated tissue. In this study, we report on the development of phase resolved Doppler spectrally encoded interferometric microscopy (PRD-SEIM) to visualize the oviduct ciliary activity within an en face FOV. This novel real time imaging system offers micrometer spatial resolution, sub-nanometer displacement sensitivity, and the potential for in-vivo endoscopic adaptation. The feasibility of the approach has been validated through ex-vivo experiments where the porcine oviduct CBF has been measured across different temperature conditions and the application of a drug. CBF ranging from 8 to 12 Hz have been observed at different temperatures, while administration of lidocaine decreased the CBF and deactivated the motile cilia. This study will serve as a stepping stone to in-vivo oviduct ciliary endoscopy and future clinical translations.

Investigating Impaired Aircraft's Flight Envelope Variation Predictability Using Least-Squares Regression Analysis

Aircraft failures alter the aircraft dynamics and cause the maneuvering flight envelope to change. Such envelope variations are nonlinear and generally unpredictable by the pilot, as they are governed by the aircraft’s complex dynamics. Hence, to prevent in-flight loss of control, it is crucial to practically predict the impaired aircraft’s flight envelope variation due to any a priori unknown failure degree. This Paper investigates the predictability of the number of trim points within the maneuvering flight envelope and its centroid using both linear and nonlinear least-squares estimation methods. To do so, various polynomial models and nonlinear models based on the hyperbolic tangent function, which incorporate the influencing factors on the envelope variations as the inputs and estimate the centroid and the number of trim points of the maneuvering flight envelope at any intended failure degree, are developed and compared. Results indicate that both the polynomial and hyperbolic tangent function-based models are capable of predicting the impaired fight envelope variation with good precision. Furthermore, it is shown that the regression equation of the best polynomial fit enables direct assessment of the impaired aircraft’s flight envelope contraction and displacement sensitivity to the specific parameters characterizing aircraft failure and flight condition.

A broadband piezoelectric energy harvester for IoT based applications

Advancement in fabrication technology and increasing levels of integration have enhanced the features of microelectronic systems. Growth of small structures or microsystems has developed the sensor network and “Internet of Things” revolution, thus providing a substantial portion of a digitized, automated and linked system around smart industries, housing, health, etc. Frequent maintenance and battery refurbishment are not desirable in microsystems, which require very low power (μW − mW) to operate. Hence, the battery-less operation is the most demanding area of micro-scale harvesting research. In this study, a low-frequency wide-band energy harvester based on see-saw structure is simulated and analyzed. See-saw design has provided a peak power of 0.175 mW. Mechanical response is studied in the form of tip displacement and stress on piezoelectric layer while the electrical response is obtained in current, voltage and power output. See-saw structure, when compared with conventional cantilever shows a betterment of 19.8, 13.3 and 23.3% in displacement, charge and voltage sensitivity bandwidth product per unit volume respectively.

Lossy Mode Resonance Generation on Sputtered Aluminum-Doped Zinc Oxide Thin Films Deposited on Multimode Optical Fiber Structures for Sensing Applications in the 1.55 µm Wavelength Range

In this work, we demonstrated lossy mode resonance (LMR) generation in optical fiber structures based on multimode fibers coated with aluminum-doped zinc oxide (AZO) films. AZO thin films were deposited by using radio frequency magnetron sputtering. In order to exhibit the usefulness of the LMR effect for sensing applications in optical fiber based systems, the deposition conditions of the AZO film coatings were set to obtain the second LMR order within the 1.55 µm wavelength range. An optical transmission configuration setup was used to investigate the LMR effect on fiber structures based on the use of no-core and cladding-removed multimode fibers coated with AZO films synthesized from metallic sputtering targets with different proportions of Zn:Al, 92:8% and 98:2%, at atomic concentrations. The optical and electrical/chemical features of the AZO films were characterized with UV–vis and XPS spectroscopy, respectively. The optical response of the proposed sensing configuration to refractive index (RI) variations was experimentally demonstrated. For the best approach, the sensitivity of wavelength displacement to RI variations on the liquid surrounding media was found to be 1214.7 nm/RIU.

Design Guidelines for MEMS Optical Accelerometer based on Dependence of Sensitivities on Diaphragm Dimensions

This work deals in specifying the design considerations while constructing a Micro Electro Mechanical Systems (MEMS) optical accelerometer working on capacitive sensing technique. Sensitivity is one of the most demanded characteristics of any sensor. The sensor considered is a MEMS capacitive accelerometer in which both displacement and capacitance are the primary sensing characteristics. This differential capacitive accelerometer causes change in displacement due to applied acceleration and further produces change in capacitance. So, the main focus in this work is to improve or select the suitable diaphragm dimensions of the differential capacitor in order to get optimal capacitive and displacement sensitivity. This is done for an Optical MEMS (MOEMS) based sensor where slight change has a large-scale impact. The electrical signal is converted to optical by adding an Optical Interferometer. Mach–Zehnder Interferometer (MZI) is used to carry out the intensity modulation which also gives protection in inflammable surroundings. This makes the system suitable for working in high temperature regions.

Super-resolution imaging of a low frequency levitated oscillator.

We describe the measurement of the secular motion of a levitated nanoparticle in a Paul trap with a CMOS camera. This simple method enables us to reach signal-to-noise ratios as good as 106 with a displacement sensitivity better than 10-16 m2/Hz. This method can be used to extract trap parameters as well as the properties of the levitated particles. We demonstrate continuous monitoring of the particle dynamics on time scales of the order of weeks. We show that by using the improvement given by super-resolution imaging, a significant reduction in the noise floor can be attained, with an increase in the bandwidth of the force sensitivity. This approach represents a competitive alternative to standard optical detection for a range of low frequency oscillators where low optical powers are required.