Strain Transfer Research Articles

Inverse analysis of strain distributions sensed by distributed fiber optic sensors subject to strain transfer

Strains measured by distributed fiber optic sensors with protective coatings can be different from the real strains in host matrix due to strain transfer effect. This study presents a novel inverse method to determine the real strain distributions in host matrix using strain distributions measured from distributed fiber optic sensors. Two different scenarios of strain distributions in host matrix are investigated, which have known and unknown types of strain fields, respectively. Three representative metaheuristic algorithms are respectively utilized in the inverse analysis, which are colliding bodies optimization algorithm, particle swarm optimization algorithm, and genetic algorithm. The performance of the proposed method was evaluated by analytical case studies and experimental testing of a prestressed concrete beam subjected to four-point bending. The results demonstrated high accuracy and efficiency of the proposed method. This study is expected to greatly advance distributed fiber optic sensing capabilities in measuring strain distributions for structural health monitoring.

Crystalline‐Phase‐Recognition‐Induced Domino Phase Transition and Luminescence Switching for Advanced Information Encryption

AbstractHerein, a new mechanism, namely, crystalline phase recognition (CPR), is proposed for the single‐crystal‐to‐single‐crystal (SCSC) transition of metal halides. Chiral β‐[Bmmim]2SbCl5 (Bmmim=1‐butyl‐2,3‐methylimidazolium) can recognize achiral α‐[Bmmim]2SbCl5 on the basis of a key–lock feature through intercontact of their single crystals, resulting in a domino phase transition (DPT). The concomitant photoluminescence (PL) switching enables observation of the DPT in situ. The liquid eutectic interface, stress–strain transfer, and feasible thermodynamics are key issues for the CPR. DFT calculations and PL measurements revealed that the optical absorption and emission of the isomers mainly originate from [SbCl5]2− anions. The structural effects (e.g., supramolecular interactions and [SbCl5]2− distortion) on the optical emission are clarified. As a novel type of stimuli response, the CPR‐induced DPT and luminescence switching exhibit potential for application in advanced time‐resolved information encryption.

Error analysis and experimental research of joint fiber-optic displacement sensor based on shear lag model

Landslide displacement monitoring is an efficient method to mitigate casualties and economic losses caused by landslide disasters. In recent years, distributed fiber-optic sensing technology, due to distributed and long-distance advantages, was widely used in subsurface displacement monitoring of landslides. However, existing fiber-optic displacement sensors has a large monitoring error when the landslide has multi-sliding surfaces. Aiming at solving this issue, a new joint fiber-optic displacement sensor which can achieve accurate displacement monitoring, was designed. Its measurement error was analyzed and the feasibility was demonstrated by theory and laboratory experiment. Based on the shear lag model, the error caused by strain transfer was studied by fiber-optic cable pull-out experiment. Finally, the feasibility of the sensor was verified by calibration experiment and soil shear experiment. The results show that the displacement sensor has high sensitivity and accuracy, and can realize distributed displacement monitoring inside the slope with multi-sliding surfaces.

Ferromagnetic, ferroelectric, and magnetoelectric properties in individual nanotube-based magnetoelectric films of CoFe2O4/BaTiO3 using electrically resistive core-shell magnetostrictive nanoparticles

Since 2010, two-phase magnetoelectric (ME) films consisting of magnetostrictive and piezoelectric phases have been continuously developed with regard to their promising ME responses, for potential applications such as ultra-sensitive magnetic sensing, magnetic-field induced energy harvesting, and nano-transduction. Generally, one-dimensional piezoelectric nanowires, nanorods, and nanotubes are used to enlarge the active area for strain transfer between the piezoelectric and magnetostrictive phases of ME films. In this study, we developed 1–2 type individual nanotube-based ME films of CoFe2O4/BaTiO3 with main considerations in the optimization of magnetostrictive phase, piezoelectric phase, and interface between the phases, respectively. First, core-shell magnetostrictive nanoparticles were improved with a high resistivity of 3.89 MΩ·cm and saturation magnetization of 20.8 emu/g via a sufficient TiO2 coating on the CoFe2O4 nanoparticles. Then, individually free-standing TiOx nanotubes were prepared with an optimal structure exhibiting a large pore size of 220 nm and high interspace distance of 80 nm. Final 1–2 type ME films of CoFe2O4/BaTiO3 were successfully prepared by magnetostrictive particle electrodeposition and perovskite conversion in sequence. Enhanced dipole moments through high amounts of BaTiO3 phase were achieved with a maximal remnant polarization (Pr) of 0.192 µC/cm2 from the AC-electrodeposited (AC-) ME films exhibiting a dense film structure. Maximal ME coefficient of the AC-ME films was achieved with magnitude of 27.39 mV/cm∙Oe at Hbias = 1000 Oe. As a result, considering the investigations, the 1–2 type ME films could be expected for possible applications such as high-sensitive magnetic sensors or low-power energy harvesters.

Economic strain, parental education and psychotic experiences among college students in the United States: Findings from the Healthy Minds Study 2020.

Socioeconomic status (SES) is linked to psychosis, and much can be learned by examining how various indicators of SES-specifically economic strain and intergenerational transfer of resources-are related to sub-threshold psychotic experiences among college students. Using data from the Healthy Minds Survey (September 2020-December 2020), we used multivariable logistic regression models to examine the associations between five SES indicators and 12-month psychotic experiences, adjusting for age, gender and race/ethnicity. We also examined the count of predictors and psychotic experiences. Each indicator of economic strain was associated with greater odds of psychotic experiences. In particular, increasing levels of financial stress (current, childhood and pandemic-related) were associated with greater odds of psychotic experiences in a dose-response fashion. Food insecurity was associated with double the odds of psychotic experiences. In terms of intergenerational transfer of resources, having either one or no parents who attended college was associated with significantly greater odds of having psychotic experiences, when compared with having both parents who attended college. Examining all predictors in the same model, only childhood and current financial stress and food insecurity were significantly associated with psychotic experiences. The count of predictors was significantly associated with greater odds of having psychotic experiences in a dose-dependent fashion. Among college students, economic strain and intergenerational transfer of resources were associated with recent psychotic experiences, highlighting the importance of economic interventions targeting young adults to influence risk for psychosis.

A theoretical strain transfer model between optical fiber sensors and monitored substrates

This study proposed an analytical model to investigate strain transfer mechanism between FBG sensor and measured geogrid. Both geometric and mechanical parameters (bonding length, bonding thickness, bonding width, and Young's modulus) of interaction interface can be taken into account in this model. Both laboratory tensile tests of geogrid and experimental data in published literatures were used to verify the developed model. Validation study shows that the maximum relative error between experimental values and theoretical values is 8.2%, indicating that this theoretical model can be used to reflect geogrid deformation. Parametric study indicates that bonding length, bonding thickness, bonding width, Young's modulus of adhesive layer, and substrate layer have significant influence on strain transfer coefficient. Grey Relational Analysis (GRA) method was used to analyze influencing sensitivity of different parameters. GRA parameter values of bonding width and length are higher than 0.72, indicating that bonding width and bonding length are relatively dominant factors affecting average strain transfer coefficient in comparison with bonding thickness, Young's moduli of substrate and adhesive layers (their related GRA values are all lower than 0.692).

A General Solution to Determine Strain Profile in the Core of Distributed Fiber Optic Sensors under Any Arbitrary Strain Fields.

Despite recent publications, the strain transfer in distributed optical fiber sensors is still often overlooked and poorly understood. In the first part of this paper, strain transfer is shown to be driven by a second-order differential equation, whether the optical fiber is embedded into the host material or surface-mounted. In this governing equation, only the value of a key parameter, called strain lag parameter, varies according to the attachment configuration and the type of optical fiber used as a sensor. Then, a general solution of the governing equation is proposed. It is an analytical expression established from new boundary conditions that are more adequate than those used previously in the literature and allows the determination of the strain profile in the core of a distributed optical fiber sensor under any arbitrary strain fields. This general solution has been validated by two experiments presented in the third part of the paper. A very good agreement between the analytical solutions and measured strain profiles using a high spatial resolution optical interrogator for both uniform and non-uniform strain fields has been obtained. These results highlight the importance of the strain lag parameter which must be taken into account for a correct interpretation of measurements, especially in the case of important strain gradients.

Strain Transfer of Fiber Bragg Grating Sensor Externally Bonded to FRP Strip for Structural Monitoring after Reinforcement.

To date, a method of attaching a FRP (fiber-reinforced polymer) to concrete members with epoxy has been widely applied to increase the strength of the member. However, there are cases in which the adhesion of the epoxy deteriorates over time and the reinforcing effect of the FRP is gradually lost. Therefore, monitoring whether or not the reinforcing effect is properly maintained is needed in order to prevent a decrease in the structural performance of the member improved by FRP reinforcement. In this regard, this study examines FRP with OF (optical fiber) sensors to monitor the reinforcing effect of FRP in concrete structural members. In particular, this paper seeks to determine an appropriate adhesion length when FBG (fiber Bragg grating) based OF sensors are externally bonded to FRP strips with epoxy resin. To this end, a tensile test was carried out to evaluate the sensing performance according to the adhesion length. In addition, an analytical approach was performed and the result were compared with test result. The results of the experimental and analytical studies showed that the strain generated in the FRP is sufficiently transferred to the OF if the total adhesion length of it is 40 mm or more in consideration of the error in the epoxy thickness.

Temperature compensated diaphragm based Fiber Bragg Grating (FBG) sensor for high pressure measurement for space applications

A temperature compensated diaphragm-type Fiber Bragg Grating (FBG) sensor for high pressure measurement, with a maximum pressure up to 700 bar, has been developed and packaged for different applications including space. In this device, a pressure sensitive FBG is bonded at the centre of a Martensitic Stainless Steel (APX-4) diaphragm and a temperature compensation FBG is bonded in the strain-free region of the same diaphragm. The experimental results obtained indicate a pressure sensitivity of 3.64 pm/bar and a non-linearity + Hysteresis error of 0.75% of full-scale pressure in the range of 0 to 700 bar, with a correlative coefficient of 99.99%. Structural and thermal stress analyses of the diaphragm and strain transfer analysis from the diaphragm to FBG have been carried out using Comsol Multiphysics software, to validate the experimental results. Shock tube and vibration tests have also been carried out to study the dynamic characteristics and stability of the sensor. The pressure sensor developed, can be used to measure both static/dynamic pressures of cryogenic propellants as well as pneumatic pressure in rockets, missiles and launch vehicles.

Induction of cell migration by transient Wolbachia pipientis infection in Aedes albopictus cell line

• The effect of transient Wolbachia infection was investigated in vitro. • Transient Wolbachia infection induced the migration of Aedes albopictus cells. • Wolbachia infection induced production of nitrite and reactive oxygen species. • Wolbachia infection elevated the expression of Toll pathway-related genes. • Early adaptation of Wolbachia in original host insect affects insect cell features. Wolbachia is a genus of maternally transmitted bacteria having an endosymbiotic relationship with arthropod and nematode species. These bacteria manipulate host development, sex-determination, and reproduction. In addition, they are known to potentially suppress vector-borne diseases by interfering with pathogen transmission. Although the occurrence of Wolbachia infection in insects has been known, the underlying mechanisms that mediate their interactions remain unclear. To examine the influence of Wolbachia adaptation on the host, we infected w AlbA and w AlbB strain from Aedes albopictus into the C6/36 cell line derived from Ae. albopictus . The transient Wolbachia infection was characterized by induction of cell migration without cell proliferation. The production of nitrite and reactive oxygen species (ROS) was induced by transient Wolbachia infection. Cells with transient Wolbachia infection exhibited elevated expression of Toll-like receptor 6 (TLR6) and myeloid differentiation primary response 88 (Myd88). Conversely, the expression of TLR2, TLR4, TLR7, Cactus, Ankyrin, and Argonaute2 (AGO2) was inhibited upon Wolbachia infection. These results suggest that Wolbachia has an influence on the cell migration ability as well as host innate immune response in vitro . Considering these results, transient Wolbachia strain transfer in C6/36 cells might be an important approach for studying Wolbachia- host interactions and might help gain a deeper understanding of the early adaptation of Wolbachia in the original host insect.

Control of substrate strain transfer to thin film photovoltaics via interface design

Brittle thin film photovoltaics (PV) that are integrated with load-bearing structures can be subjected to large strains that lead to fragmentation and performance degradation. Such adverse effects can be mitigated, or altogether eliminated, by mechanically isolating a thin PV module from the underlying load-bearing structure. We developed an effective and efficient strain attenuation strategy to eliminate strain transfer from a stiff unidirectional Carbon Fiber Reinforced Polymer (CFRP) laminate to an integrated thin amorphous Si PV module. An analytical model of the three-layer material system (CFRP laminate, interface layer and PV module) was employed to create strain attenuation maps that depend on the length of the PV module and capture the coupled effects of the shear modulus and the thickness of the interface layer (G2, t2), and the Young’s modulus and the thickness of the PV module (E3, t3) through the terms G2/t2 and E3t3, respectively. Based on these strain attenuation maps, polydimethylsiloxane (PDMS) was identified as an effective and versatile interface material, which provided up to 100% strain attenuation between the CFRP laminate and the PV module. After accounting for confinement effects on the effective modulus of the PDMS interface layer, a very good agreement was achieved between the measured and the predicted strain attenuation. Importantly, the PDMS interfacial layer preserved the initial fill factor of the PV module until CFRP laminate failure at 1.7% strain, while in the absence of the PDMS interface the fill factor decreased when the CFRP laminate strain exceeded 0.80%.

Hierarchical enhancement of stress–strain transfer and flame retardancy of wood plastic composite

AbstractMechanical strength of multiphase material depends on mechanical properties of components and interface bonding states, which has always been a research hot spot. In this work, a hyperbranched polyethyleneimine‐grafted nano SiO2 (pSiO2)‐decorated ammonium polyphosphate (APP) was applied to synergistically improve the flame retardancy and toughness of wood plastic composite (WPC). With nonpolar carbon skeleton and polar amine groups on it, pSiO2 could successfully coated on APP via ionic bonding and improve the compatibility between wood fiber and high‐density polyethylene (HDPE). According to digital image correlation (DIC), pSiO2 improved the strain transfer from HDPE molecular to wood fiber, thus an increased high‐deformation region was observed in WPC/pSiO2 and WPC/APP‐pSiO2 . pSiO2 provided numerous of stress concentration area,to induce the formation and inhibit the convergence of craze. As a result, WPC/APP with 30% pSiO2 addition showed a 47.9% increment in impact strength compared to WPC/APP. Besides, pSiO2 also showed a synergistic effect with APP and further improved the flame retardancy of flame retardant WPC. This work provides a route for interface design and internal stress–strain study of multiphase composites.

<i>In situ</i> Tracking of Individual Collagen Fibre Bundles in Intact Loaded Intervertebral Discs Exposes Damage-Susceptible Collagen Organisations

Many soft tissues, such as the intervertebral disc (IVD), have a hierarchical fibrous composite structure which suffers from regional damage. We hypothesise that clinical injury patterns in these tissues occur in localised regions where there is an integrated requirement for both marked compliance and significant load transfer. Here we used synchrotron computed tomography (sCT) to resolve collagen fibre bundles (~5μm width) in 3D throughout an intact native rat lumbar IVD under increasing compressive load. Using intact samples meant that tissue boundaries (such as endplate-disc or nucleus-annulus) and residual strain were preserved; this is vital for characterising both the inherent structure and structural changes upon loading in tissue regions functioning in a near-native environment. Nano-scale displacement measurements along >10,000 individual fibres were tracked, and fibre orientation, curvature and strain changes were compared between the failure-prone posterior-lateral region and the more robust anterior region. These methods can be widely applied to other soft tissues, to identify fibre structures which cause tissue regions to be more susceptible to injury and degeneration. Our results demonstrate for the first time that highly-localised changes in fibre orientation, curvature and strain indicate differences in regional strain transfer and mechanical function (e.g. tissue compliance), correlating directly with locations clinically at risk of damage. This included decreased fibre reorientation at higher loads, specific tissue morphology which reduced capacity for flexibility and high strain at the disc-endplate boundary.

Strain engineering 2D MoS2 with thin film stress capping layers

We demonstrate a method to induce tensile and compressive strain into two-dimensional transition metal dichalcogenide (TMDC) MoS2 via the deposition of stressed thin films to encapsulate exfoliated flakes. With this technique we can directly engineer MoS2 strain magnitude by changing deposited thin film stress, therefore allowing variable strain to be applied on a flake-to-flake level. These thin film stressors are analogous to SiN x based stressors implemented in industrial complementary metal-oxide-semiconductor (CMOS) processes to enhance Si mobility, suggesting that our concept is highly scalable and may be applied for large-scale integration of strain engineered TMDC devices. We choose optically transparent stressors to allow us to probe MoS2 strain through Raman spectroscopy. Combining thickness dependent analyses of Raman peak shifts in MoS2 with atomistic simulations, we can explore layer-by-layer strain transfer. MoS2 on conventional substrates (SiO2, MgO) show strain transfer into the top two layers of multilayer flakes with limited strain transfer to monolayers due to substrate adhesion. To mitigate this limitation, we also explore stressors on van der Waals heterostructures constructed of monolayer (1L) MoS2 on hexagonal boron nitride (h-BN). This concept frees the 1L-MoS2 allowing for a 0.85% strain to be applied to the monolayer with a corresponding strain induced bandgap change of 75 meV. By using thin films with higher stress, strain may be engineered to be even higher. Various stressors and deposition methods are considered, showing a stressor material independent transfer of strain that only depends on stressor film force with negligible defects induced into MoS2 when thermal evaporation is used.

Upper bound frequency-dependent strains imposed on deep underground box-shaped structures under shear wave field of motion with different incident angles

This article investigates seismic demands of underground structures with a rectangular section in a two-dimensional framework subjected to complete passage of shear wave field of motion. The wave field is considered to have different incident angles with the structure. Using the finite element approach, frequency-dependent strain transfer functions for different parts of the structure are estimated. The transfer functions convert maximum free field shear strains to the uppermost strains imposed on structural sections. It is shown that maximum demands would not happen simultaneously for different parts of the structure. Also, critical frequencies of excitation and dominant incident angles may differ from each structural section to the other one. In the last part, simplified equations that cover dynamic characteristics of the problem and influences of different incident angles are suggested as correction factors to modify the strains commonly calculated from traditional static approaches.

Polymer conformation-dependent piezoelectric properties and self-bias magnetoelectric responses in adhesive-free laminate composites of Ni-foam/PVDF/Ni-foam

In the past decade, polymer-based magnetoelectric (ME) laminate composites have been developed for feasible applications such as flexible energy harvesters and wearable sensors. The 2-2-type ME laminate composites have been typically prepared by epoxy adhesion of piezoelectric and magnetostrictive layers, which is a drawback that disrupts strain transfer from the magnetostrictive phase to the piezoelectric phase due to its strong hardness after epoxy curing. In this study, to overcome the disadvantage of insufficient strain transfer due to the adhesive layers, we designed adhesive-free laminate composites consisting of porous magnetostrictive nickel foam (NF) and soft poly (vinylidene fluoride) (PVDF) films, which exhibited good physical coupling via the sandwich hot-pressing of NF/PVDF/NF. In addition, the self-bias ME effect could be expected from NF, since it exhibits butterfly-shaped magnetostrictive hysteresis loops. Therefore, NF/annealed PVDF(AP)/NF and NF/hot-pressed PVDF(HP)/NF were prepared for investigating the polymer conformation during the fabrication process of ME laminates. Polymer conformation-dependent piezoelectric properties were investigated after annealing and hot-pressing, respectively. The NF/AP/NF laminates (mM/mP = 0.88) were found to exhibit a β/α phase ratio of 2.07, degree of crystallinity (χc) of 46.5%, piezoelectric charge constant (d33) of 17.7 pC/N, and self-bias ME response of 1.88 mV/cm Oe (94% of the maximal ME response at Hbias = 20 Oe). The NF/HP/NF laminates (mM/mP = 1.26) were found to exhibit a β/α phase ratio of 1.40, χc of 32.2%, d33 of 12.4 pC/N, and self-bias ME response of 2.27 mV/cm Oe (92% of the maximal ME response at Hbias = 10 Oe). The high β/α phase ratio were carried out sufficient stretching effect during hot-press laminating process. The optimal piezoelectric properties of β/α phase ratio and χc were induced by predominant stretching of PVDF chains rather than recrystallization during the hot-press. Further, reliable self-bias ME responses were obtained in the adhesive-free laminate composites by enhancement of coupling effect between magnetostrictive and piezoelectric phases. As a result, the sandwich laminate composites of NF/PVDF/NF were successfully prepared via hot-pressing and reliable ME responses were obtained without requiring the electroding process. This demonstrates the feasibility of ME laminate composites for use in wearable energy harvesters or sensors through removal of the hard adhesive layer.

Reliable packaging of optical fiber Bragg grating sensors for carbon fiber composite wind turbine blades

A sensing module composed of a carbon fiber reinforced polymer (CFRP) packaging and an embedded fiber Bragg grating (FBG) sensor is proposed for strain monitoring of wind turbine blades. The sensing unit is designed and manufactured with the aim of maximizing the strain transfer from a CFRP wind blade to the FBG sensor. The performance of the packaged FBG sensors is experimentally investigated through exhaustive aging and fatigue tests. Then, a series of CFRP-packaged FBG sensors is used to monitor a full-scale 56.85 m-long wind blade during flapwise and edgewise fatigue tests over a few million dynamic strain cycles. Results demonstrate that the independent sensing modules provide efficient strain transfer, verifying a longer lifetime and more reliable measurements compared to conventional electrical strain gauges.

Genetic and behavioral adaptation of Candida parapsilosis to the microbiome of hospitalized infants revealed by in situ genomics, transcriptomics, and proteomics

BackgroundCandida parapsilosis is a common cause of invasive candidiasis, especially in newborn infants, and infections have been increasing over the past two decades. C. parapsilosis has been primarily studied in pure culture, leaving gaps in understanding of its function in a microbiome context.ResultsHere, we compare five unique C. parapsilosis genomes assembled from premature infant fecal samples, three of which are newly reconstructed, and analyze their genome structure, population diversity, and in situ activity relative to reference strains in pure culture. All five genomes contain hotspots of single nucleotide variants, some of which are shared by strains from multiple hospitals. A subset of environmental and hospital-derived genomes share variants within these hotspots suggesting derivation of that region from a common ancestor. Four of the newly reconstructed C. parapsilosis genomes have 4 to 16 copies of the gene RTA3, which encodes a lipid translocase and is implicated in antifungal resistance, potentially indicating adaptation to hospital antifungal use. Time course metatranscriptomics and metaproteomics on fecal samples from a premature infant with a C. parapsilosis blood infection revealed highly variable in situ expression patterns that are distinct from those of similar strains in pure cultures. For example, biofilm formation genes were relatively less expressed in situ, whereas genes linked to oxygen utilization were more highly expressed, indicative of growth in a relatively aerobic environment. In gut microbiome samples, C. parapsilosis co-existed with Enterococcus faecalis that shifted in relative abundance over time, accompanied by changes in bacterial and fungal gene expression and proteome composition.ConclusionsThe results reveal potentially medically relevant differences in Candida function in gut vs. laboratory environments, and constrain evolutionary processes that could contribute to hospital strain persistence and transfer into premature infant microbiomes.FVTWG-mFNui5xgWwFcfPTvVideo abstract

Mechanical Properties and Strain Transfer Behavior of Molybdenum Ditelluride (MoTe2) Thin Films

Abstract Transition metal dichalcogenides (TMDs) offer superior properties over conventional materials in many areas such as in electronic devices. In recent years, TMDs have been shown to display a phase switching mechanism under the application of external mechanical strain, making them exciting candidates for phase change transistors. Molybdenum ditelluride (MoTe2) is one such material that has been engineered as a strain-based phase change transistor. In this work, we explore various aspects of the mechanical properties of this material by a suite of computational and experimental approaches. First, we present parameterization of an interatomic potential for modeling monolayer as well as multilayered MoTe2 films. For generating the empirical potential parameter set, we fit results from density functional theory calculations using a random search algorithm known as particle swarm optimization. The potential closely predicts structural properties, elastic constants, and vibrational frequencies of MoTe2 indicating a reliable fit. Our simulated mechanical response matches earlier larger scale experimental nanoindentation results with excellent prediction of fracture points. Simulation of uniaxial tensile deformation by molecular dynamics shows the complete non-linear stress-strain response up to failure. Mechanical behavior, including failure properties, exhibits directional anisotropy due to the variation of bond alignments with crystal orientation. Furthermore, we show the deterioration of mechanical properties with increasing temperature. Finally, we present computational and experimental evidence of an extended c-axis strain transfer length in MoTe2 compared to TMDs with smaller chalcogen atoms.

Double-frequency passive deformation sensor based on two-layer patch antenna

To avoid the issues of incomplete strain transfer ratio and insufficient bonding strength of a monolithic stressed antenna, this paper presents an unstressed deformation sensor based on two-layer patch antenna for structural health monitoring. The proposed sensor is composed of a monolithic patch antenna and a stacked patch generating two fundamental resonant frequencies within a 3-to-7 GHz band. The resonant frequencies' shifts caused by the offset of the stacked patch were selected as the sensing parameters. An equivalent circuit was used to analyze the sensing method, which shows the relative displacement to be linear to the shift of resonant frequencies. This phenomenon was then checked by numerical simulation using the Ansoft High Frequency Structure Simulator 15 (HFSS15) and experiments in laboratory using both wired and wireless setups. Furthermore, the accuracy of measurement is verified to be increased by combining two resonant frequencies.