Description:TECHNICAL FIELD
[0001] The present disclosure relates to the field of strain measurement, and more specifically to a device and a system for detecting axial strain in material specimens based on variations in resonant frequency.

BACKGROUND
[0002] In mechanical testing of materials, particularly under uniaxial tension, accurate measurement of strain is critical for evaluating material properties such as elasticity, ductility, and yield strength. Devices used to measure strain are typically integrated into tensile test rigs or experimental setups where they monitor deformation under applied loads.
[0003] Traditional strain measurement techniques primarily include resistive strain gauges and contact extensometers. Resistive strain gauges, while compact, provide only localized strain data and require adhesive bonding to the test specimen, which may affect the mechanical behavior of compliant or soft materials. Contact extensometers, on the other hand, require mechanical gripping or knife edges and are sensitive to slippage, alignment errors, and specimen geometry constraints. Gauge lengths of the contact extensometers are fixed, making them unsuitable for specimens of varying sizes or for applications requiring adaptable measurement zones.
[0004] Moreover, in dynamic testing environments, contact-based systems may not respond adequately to rapid strain changes, leading to signal lag or loss of fidelity. The bulkiness of the equipment, complex calibration procedures, and physical interference with the specimen further limit the practical utility of conventional extensometers in advanced experimental workflows, especially where minimal mechanical intrusion is preferred.
[0005] To address at least the aforementioned challenges, there exists a need for a strain measurement device and system that enables non-intrusive integration with test specimens, accommodates flexible gauge length configurations, and facilitates high-resolution detection of axial strain without compromising structural fidelity or experimental accuracy.
OBJECTS OF THE PRESENT DISCLOSURE
[0006] A general object of the present disclosure is to provide a device and system for measuring axial strain in material specimens using radio frequency sensing principles.
[0007] Another object of the present disclosure is to provide a strain sensing device including a monopole antenna and a displaceable coupling pole, wherein strain-induced deformation alters the effective radiating length of the antenna.
[0008] Another object of the present disclosure is to facilitate frequency-based strain measurement through controlled mechanical displacement and electromagnetic contact between the antenna and a sliding conductive element.
[0009] Another object of the present disclosure is to enable integration of the strain sensing device with standard tensile testing setups, allowing real-time monitoring of strain without intrusive contact or adhesive bonding.
[0010] Another object of the present disclosure is to provide a system that includes a force application mechanism, a radio frequency measurement unit, and a strain-responsive antenna structure configured for multi-band operation and strain detection.

SUMMARY
[0011] Aspects of the present disclosure generally relate to the field of strain measurement, and more specifically to a device and a system for detecting axial strain in material specimens based on variations in resonant frequency.
[0012] An aspect of the present disclosure pertains to a device for measuring axial strain in a test specimen. The device includes a monopole antenna and a coupling pole slidably attached to and in electromagnetic contact with the monopole antenna. The monopole antenna and the coupling pole are mounted to the test specimen and are configured such that deformation of the test specimen causes relative displacement between the coupling pole and the monopole antenna. The displacement of the coupling pole alters an effective length of the monopole antenna, causing a shift in resonant frequency of the monopole antenna.
[0013] In one embodiment, the coupling pole and the monopole antenna are configured to have an overlapping region.
[0014] In one embodiment, the monopole antenna is fed by a coplanar waveguide.
[0015] In one embodiment, the monopole antenna and the coupling pole are fabricated on a dielectric substrate.
[0016] In one embodiment, the dielectric substrate includes an FR4 epoxy laminate.
[0017] In one embodiment, the coupling pole includes a conductive strip and is configured to slide along a mechanical guide associated with the monopole antenna.
[0018] Another aspect of the present disclosure pertains to a system for measuring axial strain in a test specimen. The system includes a device having a monopole antenna and a coupling pole slidably attached to and in electromagnetic contact with the monopole antenna, wherein the coupling pole is configured to be displaceable with respect to the monopole antenna in response to deformation of the test specimen. The system also includes a mounting arrangement configured to secure the test specimen, a force application mechanism configured to apply tensile force to the test specimen to induce strain, and a radio frequency measurement unit configured to detect a shift in resonant frequency of the monopole antenna during deformation of the test specimen.
[0019] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The accompanying drawings, which are incorporated herein, and constitute a part of this disclosure, illustrate exemplary embodiments of the disclosed methods and systems which like reference numerals refer to the same parts throughout the different drawings. Components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Some drawings may indicate the components using block diagrams and may not represent the internal circuitry of each component. It will be appreciated by those skilled in the art that disclosure of such drawings includes the disclosure of electrical components, electronic components, or circuitry commonly used to implement such components.
[0021] FIG. 1 illustrates an exemplary schematic diagram of a device for measuring axial strain in a test specimen, in accordance with an embodiment of the present disclosure.
[0022] FIG. 2 illustrates an exemplary schematic diagram of a system for measuring axial strain in a test specimen, in accordance with an embodiment of the present disclosure.
[0023] FIG. 3 illustrates a plot illustrating the variation of resonant frequency (GHz) with respect to the displacement (mm) of coupling pole, in accordance with an embodiment of the present disclosure.
[0024] FIG. 4 illustrates a graph showing the variation of resonant frequency with cross-head displacement, in accordance with an embodiment of the present disclosure.
[0025] FIG. 5 illustrates a graph showing the variation of resonant frequency with respect to tensile strain in a thermoplastic polyurethane (TPU) specimen, in accordance with an embodiment of the present disclosure.
[0026] FIG. 6 illustrates a graph showing the variation of resonant frequency with coupling pole displacement, in accordance with an embodiment of the present disclosure.
[0027] FIG. 7 illustrates a graph showing the repeatability analysis of the proposed RF strain sensor, in accordance with an embodiment of the present disclosure.
[0028] The foregoing shall be more apparent from the following more detailed description of the disclosure.

DETAILED DESCRIPTION
[0029] In the following description, for the purposes of explanation, various specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent, however, that embodiments of the present disclosure may be practiced without these specific details. Several features described hereafter can each be used independently of one another or with any combination of other features. An individual feature may not address all of the problems discussed above or might address only some of the problems discussed above. Some of the problems discussed above might not be fully addressed by any of the features described herein.
[0030] The ensuing description provides exemplary embodiments only and is not intended to limit the scope, applicability, or configuration of the disclosure. Rather, the ensuing description of the exemplary embodiments will provide those skilled in the art with an enabling description for implementing an exemplary embodiment. It should be understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the disclosure as set forth.
[0031] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0032] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0033] In conventional strain measurement systems, strain gauges and mechanical extensometers are limited by their contact-based nature, fixed gauge lengths, and susceptibility to alignment errors or surface preparation requirements. These systems often require physical bonding to the specimen or complex mechanical gripping arrangements, which can interfere with the material's natural deformation or introduce measurement inaccuracies. Additionally, conventional sensors offer limited adaptability across specimen geometries and may not support dynamic reconfiguration of sensing zones during testing. The inability to flexibly adjust the gauge length and the challenges associated with reliable signal acquisition in compact or high-strain environments present further limitations in existing strain sensing approaches.
[0034] To address the aforementioned challenges, the present disclosure provides a strain sensing device and system based on radio frequency principles, wherein a monopole antenna is mechanically and electrically coupled with a displaceable conductive element. The antenna structure is fabricated on a dielectric substrate and configured to respond to mechanical deformation by shifting its resonant frequency in proportion to the relative displacement of the coupled element. The device may be integrated with a test specimen in a manner that allows axial strain to alter the overlapping region between the antenna and the conductive element, thereby adjusting the antenna's effective electrical length. The system further includes a force application mechanism and a radio frequency measurement unit to monitor changes in resonant frequency during strain events.
[0035] The disclosed configuration enables a compact, contact type strain sensing solution that translates mechanical strain into a measurable frequency shift without requiring surface bonding or intrusive contact. The interaction between the radiating element and the displaceable conductive structure facilitates strain-responsive adaptation of antenna geometry, allowing for real-time strain monitoring with high sensitivity and linearity. The planar fabrication and CPW-fed design further support easy integration with standard test setups, while the multi-band resonant behavior provides enhanced measurement resolution and sensing flexibility across a range of frequencies. Overall, the solution allows for accurate, repeatable, and reconfigurable strain detection in experimental and applied mechanical testing environments.
[0036] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosures as defined by the appended claims.
[0037] Embodiments explained herein relate to the field of strain measurement, and more specifically to a device and a system for detecting axial strain in material specimens based on variations in resonant frequency.
[0038] The various embodiments throughout the disclosure will be explained in more detail with reference to FIGs. 1-7.
[0039] Referring now to FIG. 1, an exemplary schematic diagram of a device (120) for measuring axial strain in a test specimen (106) is illustrated, in accordance with one or more embodiments of the present disclosure. The device (120) may include a monopole antenna (102) configured for radio frequency (RF) operation and a coupling pole (104) slidably attached to the monopole antenna (102). The monopole antenna (102) may be formed on a dielectric substrate (108) and may include one or more conductive segments (102A) arranged in an extended configuration. The coupling pole (104) may be made from a conductive strip (104A), may be positioned in electromagnetic contact with the monopole antenna (102). The coupling pole (104) may be supported in a manner that allows linear sliding relative to the monopole antenna (102). Various examples of the test specimen (106) may include, but are not limited to, flexible or semi-flexible materials such as polymeric films, elastomeric substrates, thermoplastic polymers (e.g., thermoplastic polyurethane), or other deformable materials suitable for uniaxial tensile testing.
[0040] In one embodiment, the monopole antenna (102) and the coupling pole (104) may be mounted to the test specimen (106) such that axial deformation of the specimen causes a relative displacement between the monopole antenna (102) and the coupling pole (104). As tensile force is applied to the specimen (106), the coupling pole (104) slides along the surface of the monopole antenna (102), varying the overlapping length between the two conductive structures (102A and 104A). The mechanical displacement (i.e., the sliding) may alter the effective electrical length of the monopole antenna (102), resulting in a shift in its resonant frequency. The change in resonant frequency may be measured using external RF instrumentation.
[0041] In one embodiment, the electromagnetic contact between the coupling pole (104) and the monopole antenna (102) may ensure continuity in the radiating surface along the overlapping region. Such configuration may enable the antenna to respond to strain-induced displacement as a function of structural elongation, without requiring bonding to resistive strain gauges or optical sensing components. The device (120) may provide a compact and adaptable sensing mechanism suitable for integration with standardized test specimens under axial strain conditions.
[0042] In one embodiment, the monopole antenna (102) may be fed by a coplanar waveguide (112) (as shown in FIG. 2) formed on a dielectric substrate (108). The coplanar waveguide (112) may include a central signal conductor flanked on either side by ground planes on the same layer of the substrate (108), defining a controlled impedance transmission line. Such configuration may allow the monopole antenna (102) to be excited with a well-matched RF signal over a wide frequency range, enabling reliable detection of resonant behavior under mechanical deformation.
[0043] The coplanar waveguide (CPW) (112) may be designed in accordance with standard high-frequency layout principles, such that the width of the signal line and the spacing to adjacent ground planes are selected to achieve a desired characteristic impedance, typically 50 ohms, but not limited thereto. The CPW-fed configuration may offer mechanical simplicity and ease of integration with planar antenna structures, and may also minimize parasitic radiation and mode conversion. A feed line may terminate at the base of the monopole antenna (102), providing a direct RF path to the radiating structure. In some embodiments, the coplanar waveguide (112) may also facilitate surface mounting of connectors or soldered coaxial transitions for connection with external RF measurement instruments.
[0044] In one embodiment, the monopole antenna (102) and the coupling pole (104) may be fabricated on a dielectric substrate (108) that provides mechanical support and suitable electromagnetic properties for radio frequency (RF) operation. The substrate (108) may serve as the structural base for patterning the monopole antenna (102) and the coupling pole (104), and may be selected to achieve desired performance characteristics such as impedance matching, minimal signal loss, and thermal stability.
[0045] The dielectric substrate (108) may include commercially available materials used in RF and microwave engineering such as, but not limited to, FR4 epoxy laminate, Rogers RO4003C, or RT/duroid 5880, depending on the application requirements. In one example implementation, the monopole antenna (102) and the coupling pole (104) may be patterned using copper or other conductive materials on an FR4 epoxy substrate having a dielectric constant of approximately 4.4 and a standard thickness of 1.6 mm, but not limited thereto. The fabrication process may involve standard photolithographic techniques, etching, or additive manufacturing methods. In some embodiments, the conductive traces may be laminated or screen-printed onto the substrate, enabling low-cost, repeatable production of the sensing device.
[0046] In one embodiment, the coupling pole (104) may include a conductive strip formed from a metallic or metallized layer, such as copper, aluminium, or a conductive ink material. The coupling pole (104) may be shaped and dimensioned to partially overlap the monopole antenna (102) along its longitudinal axis and may be configured to translate linearly with respect to the monopole antenna (102) as the test specimen (106) deforms under load.
[0047] To facilitate controlled and repeatable displacement, the coupling pole (104) may be configured to slide along a mechanical guide (110) associated with the monopole antenna (102). The mechanical guide (110) may include a channel, rail, slot, or raised edge formed on or affixed to the dielectric substrate (108), or it may be realized as a discrete structural frame in which the conductive strip is retained.
[0048] Referring now to FIG. 2, an exemplary schematic diagram of a system (100) for measuring axial strain in a test specimen (106) is illustrated, in accordance with one or more embodiments of the present disclosure. The system (100) may include a strain-sensing device (120), a mounting arrangement (110), a force application mechanism (130), and a radio frequency (RF) measurement unit (140). The device (120) may also include a monopole antenna (102) and a coupling pole (104) that is slidably attached to and in electromagnetic contact with the monopole antenna (102), as described in earlier embodiments. Various examples of the radio frequency measurement unit (140) may include, but are not limited to, instruments such as vector network analyzers (VNA), spectrum analyzers, software-defined radios, or any other RF signal detection systems capable of measuring input reflection coefficients, resonant frequencies, or frequency shifts corresponding to axial strain.
[0049] The mounting arrangement (110) may be configured to securely hold the test specimen (106) in place during testing. The mounting arrangement (110) may include fixed and movable grips, clamps, or frame structures commonly used in uniaxial tensile testing machines. The force application mechanism (130) may be implemented using mechanical actuators, pneumatic rams, or dead-weight systems that apply a controlled tensile load to the test specimen (106). As tensile force is applied, the specimen elongates, causing relative displacement between the monopole antenna (102) and the coupling pole (104) mounted on the specimen. The displacement may alter the effective length of the monopole antenna (102), resulting in a shift in its resonant frequency.
[0050] The RF measurement unit (140) may include a vector network analyser (VNA), spectrum analyser, or any suitable signal detection device configured to monitor the input reflection coefficient (S11) or resonant frequency response of the monopole antenna (102) during deformation. The RF measurement unit (140) may be connected to the feed point of the monopole antenna (102), for example, via a coaxial cable or RF connector, and may record the frequency shift as a function of applied load or strain. The combination of these components enables the system (100) to non-invasively quantify axial strain in the test specimen (106) based on RF resonance characteristics.
[0051] In one embodiment, the monopole antenna (102) may be configured to operate over multiple resonant frequency bands as a function of its physical dimensions and electrical length, including contributions from the coupling pole (104). When the coupling pole (104) is positioned in contact with and overlapping the monopole antenna (102), the effective length of the radiating structure may change in accordance with the overlap, resulting in distinct resonant modes. The resonant modes may correspond to quarter-wavelength or higher-order resonances determined by the geometry and material properties of the antenna structure.
[0052] By way of example, the monopole antenna (102), as implemented on a dielectric substrate (108) and fed via a coplanar waveguide (112), may exhibit resonant frequency behavior at approximately 1.36 GHz, 2.80 GHz, and 4.47 GHz under initial configuration. The resonant frequencies may represent the first, second, and third harmonic modes of the antenna structure in one experimental embodiment. The multi-band nature of the monopole antenna (102) may enhance strain measurement resolution, as shifts in different resonant frequencies may be used to evaluate strain with varied sensitivity or spatial resolution. The multi-resonant characteristic also allows for flexible sensing schemes, such as band-selective monitoring or redundancy-based validation.
[0053] In one embodiment, the displacement of the coupling pole (104) relative to the monopole antenna (102) may result in a measurable and continuous shift in the resonant frequency of the antenna structure. When the device (120) is mounted on a test specimen (106) subjected to axial loading, the extent of overlap between the monopole antenna (102) and the coupling pole (104) decreases, thereby increasing the effective electrical length of the antenna and lowering the resonant frequency. The frequency shift may serve as a direct indicator of the strain experienced by the test specimen.
[0054] In an experimental implementation, the device (120), fabricated on a dielectric substrate (108) and interrogated via a radio frequency measurement unit (140), demonstrated a strain sensitivity of approximately 0.867 kilohertz per microstrain (kHz/με) in the third resonant band. Furthermore, the frequency shift exhibited a substantially linear correlation with the applied strain, with a coefficient of determination (R²) of approximately 0.97. The linear response may enable accurate calibration and repeatable strain estimation using standard RF measurement techniques. The system (100) may therefore provide a consistent and quantifiable means of translating mechanical deformation into a high-resolution electromagnetic response.
[0055] In one embodiment, the device (120) may be implemented as a strain-sensing structure including a coplanar waveguide (CPW)-fed extended monopole antenna (102), which may be used to detect axial strain based on variations in the resonant frequency. The antenna structure may be designed to operate over multiple resonant bands and may be fabricated on a planar dielectric substrate (108), such as FR4, to enable low-cost integration with material test specimens (106). To introduce adaptability in gauge length and enable frequency-based sensing, the monopole antenna (102) is mechanically coupled with a displaceable conductive coupling pole (104), which may slide relative to the antenna body and remains in electromagnetic contact along an overlapping region.
[0056] The effective length of the antenna, and therefore the resonant frequency, may be influenced by the overlap between the monopole antenna (102) and the coupling pole (104). As axial strain is applied to the test specimen (106), the mechanical elongation may cause the coupling pole (104) to slide, changing the extent of the electrical overlap and thereby modifying the radiating length. The effective pole length of the antenna under deformation may be expressed as:
…(1)
[0057] where represents the fixed length of the second pole segment and denotes the displacement of the coupling pole (104) relative to the monopole antenna (102). The equation (1) assumes that the coupling pole (104) remains in contact with the antenna throughout the displacement, forming a continuous conductive path that influences the antenna’s electrical length.
[0058] In one embodiment, the effective electrical length of the monopole antenna (102) under strain is modeled based on the initial antenna geometry and the displacement caused by axial elongation of the test specimen (106). As the coupling pole (104) slides relative to the monopole antenna (102), the extent of overlap between the two conductors changes, thereby modifying the resonant behavior. The effective pole length under deformation, denoted as may be expressed as:
…(2)
[0059] Here, is the total electrical length of the monopole antenna (102) prior to deformation, is the strain-induced displacement, and is a geometric correction factor that accounts for coupling effects and field overlap between the monopole and the coupling pole.
[0060] The initial effective length of the antenna, is defined by the sum of two physical segments of the monopole structure, expressed as:
…(3)
[0061] Where is the length of the first segment and is the length of the second segment of the monopole antenna (102).
[0062] The displacement term , which captures the relative change in electrical length due to mechanical strain, is computed as the difference between the initial pole length and the instantaneous overlapping length, , expressed as:
…(4)
…(5)
[0063] Where is the instantaneous length of the overlap between the monopole antenna (102) and the coupling pole (104). As axial strain is applied to the test specimen (106), the coupling pole (104) displaces by an amount , reducing the overlapping region and increasing the effective length of the antenna, which results in a corresponding downshift in its resonant frequency.
[0064] The interaction between the overlapping conductive regions of the monopole antenna (102) and coupling pole (104) may introduce localized electromagnetic effects that may modify the antenna's input impedance and resonant characteristics. The overlapping structure may behave as a coupled transmission line segment exhibiting both inductive and capacitive components, which may vary as a function of overlap area and displacement. The inductive reactance and capacitive reactance introduced by the overlapping configuration may be approximately modeled as:
(6)
(7)
[0065] where 𝑓 is the operating frequency, and are the permeability and permittivity of free space respectively, is the length of the overlapping region between the monopole antenna (102) and the coupling pole (104), 𝐴 is the effective cross-sectional area of overlap, and 𝑔 is the gap (if any) between the conductive layers. These quantities describe the behavior of the antenna as its structure adapts in response to mechanical input, giving rise to frequency modulation.
[0066] Referring again to FIG. 1, the geometry of the monopole antenna (102) and the coupling pole (104) is defined using a set of dimensional parameters that influence both the mechanical layout and the radio frequency behavior of the device (120). The length of the first segment of the monopole antenna (102) is represented by Lp1, while Lp2 denotes the second segment, which together contribute to the total effective length of the antenna under static conditions. The coupling pole (104) may have a total length defined by Lcp, and a portion of it, defined by Lpl, may remain in overlapping and electromagnetic contact with the monopole antenna (102) during strain sensing. The width of the radiating trace is represented by Wp, while the coplanar waveguide (112) feeding the antenna is defined by ground width Wg and ground length Lg. The dimensional parameters may be selected based on impedance matching requirements, target resonant frequencies, and fabrication constraints to ensure predictable frequency shifts in response to axial strain.
[0067] Through careful design of the antenna geometry, choice of substrate material, and controlled coupling between the monopole antenna (102) and the coupling pole (104), the sensor may be configured to respond predictably to strain-induced displacements.
[0068] Referring now to FIG. 3, a plot illustrating the variation of resonant frequency (GHz) with respect to the displacement (mm) of coupling pole is shown, in accordance with one or more embodiments of the present disclosure. The graph presents experimental results obtained by translating the coupling pole (104) linearly with respect to the monopole antenna (102) while the system remained mounted on a fixed test specimen (106). As shown in the plot, incremental increases in the displacement of the coupling pole (104) result in a measurable and nearly monotonic shift in the resonant frequency of the monopole antenna (102). Such behavior reflects the change in the effective monopole length due to the alteration in overlapping region between the two conductive structures. The vertical axis represents S₁₁ (in dB), which is the input reflection coefficient indicating how much radio frequency power is reflected at the antenna’s input port. The resonant frequency corresponds to the frequency at which S₁₁ reaches a minimum, indicating optimal impedance matching and effective radiation. The plot substantiates the antenna’s sensitivity to mechanical displacement and establishes a quantitative relationship between overlap distance and the associated resonant frequency shift. The displacement range explored in the experiment aligns with the strain conditions typically encountered in standardized tensile testing protocols. The coupling due to overlapping region introduces electromagnetic coupling, which is captured in constant , which represents contribution of over the calculation of . For the proposed sensor the value of may be substantially estimated as 0.56.
[0069] Referring now to FIG. 4, a graph illustrating the variation of resonant frequency with cross-head displacement is shown, in accordance with one or more embodiments of the present disclosure. The graph presents experimental data collected during uniaxial tension, where the test specimen (106) was elongated using a mechanical testing machine. The cross-head displacement refers to the linear movement of the machine’s loading head, which indirectly reflects the applied strain.
[0070] Referring now to FIG. 5, a graph illustrating the variation of resonant frequency with respect to tensile strain in a thermoplastic polyurethane (TPU) specimen is shown, in accordance with one or more embodiments of the present disclosure. The plot presents the extracted strain values corresponding to the resonant frequency shifts observed in prior experimental data.
[0071] Referring now to FIG. 6, a graph illustrating the variation of resonant frequency with coupling pole displacement is shown, in accordance with one or more embodiments of the present disclosure. The plot compares the sensor’s frequency deviation characteristics using three approaches: analytical modeling, finite element method (FEM) simulation, and experimental results.
[0072] Referring now to FIG. 7, a graph illustrating the repeatability analysis of the proposed RF strain sensor is shown, in accordance with one or more embodiments of the present disclosure. The plot presents box plots of resonant frequency measurements obtained at various displacement positions of the coupling pole (104) during repeated experimental trials. The sensor was tested multiple times without altering environmental or loading conditions to evaluate its measurement stability. It is observed from the experimental data that the proposed sensor exhibits a sensitivity of approximately 0.867 kHz per microstrain, with a correlation coefficient (R²) of 0.968, indicating strong linearity between applied strain and resonant frequency shift. A standard deviation of less than 0.01 was recorded across all trials, and a relative uncertainty of approximately 0.9% was observed, demonstrating excellent repeatability and measurement precision of the device (120) for real-time axial strain sensing.
[0073] It will be appreciated that one or more additional components may be incorporated, modified, or omitted in the implementation of the present disclosure without departing from the scope as defined by the appended claims. The described embodiments are merely illustrative, and variations in design, structure, or material selection may be made to suit specific applications. Any such modifications, equivalents, or substitutions are intended to be within the scope and spirit of the present disclosure as defined by the claims.
[0074] While the foregoing describes various embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof. The scope of the present disclosure is determined by the claims that follow. The present disclosure is not limited to the described embodiments, versions, or examples, which are included to enable a person having ordinary skill in the art to make and use the present disclosure when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE PRESENT DISCLOSURE
[0075] The present disclosure provides a device and system for strain measurement that enables contact type sensing using radio frequency resonance principles, eliminating the need for bonded strain gauges or mechanical extensometers.
[0076] The present disclosure provides an antenna-based sensing approach that allows strain detection through frequency shift, enabling continuous monitoring without requiring physical alteration of the specimen surface.
[0077] The present disclosure provides a displaceable coupling pole integrated with a monopole antenna, wherein strain-induced displacement alters the effective antenna length, supporting a mechanically adaptive and structurally simple sensing mechanism.
[0078] The present disclosure provides a strain sensing structure fabricated on a planar dielectric substrate, allowing for compact form factor, ease of manufacturing, and compatibility with standard PCB-based testing systems.
[0079] The present disclosure provides a multi-band monopole antenna configuration that supports strain detection across multiple resonant frequencies, enabling enhanced measurement resolution and redundancy.
[0080] The present disclosure provides a mechanically reconfigurable gauge length enabled by the sliding interaction between the antenna and coupling pole, allowing the device to adapt to test specimens of varying lengths and geometries.
, Claims:1. A device (120) for measuring axial strain in a test specimen (106), the device (120) comprising:
a monopole antenna (102); and
a coupling pole (104) slidably attached to and in electromagnetic contact with the monopole antenna (102);
wherein the monopole antenna (102) and the coupling pole (104) are mounted to the test specimen (106) and are configured such that deformation of the test specimen (106) causes relative displacement between the coupling pole (104) and the monopole antenna (102); and
wherein the displacement of the coupling pole (104) alters an effective length of the monopole antenna (102), causing a shift in resonant frequency of the monopole antenna (102).
2. The device (120) as claimed in claim 1, wherein the coupling pole (104) and the monopole antenna (102) are configured to have an overlapping region.
3. The device (120) as claimed in claim 1, wherein the monopole antenna (102) is fed by a coplanar waveguide.
4. The device (120) as claimed in claim 1, wherein the monopole antenna (102) and the coupling pole (104) are fabricated on a dielectric substrate (108).
5. The device (120) as claimed in claim 4, wherein the dielectric substrate (108) comprises an FR4 epoxy laminate.
6. The device (120) as claimed in claim 1, wherein the coupling pole (104) comprises a conductive strip and is configured to slide along a mechanical guide (110) associated with the monopole antenna (102).
7. A system (100) for measuring axial strain in a test specimen (106), the system (100) comprising:
a device (120) comprising:
a monopole antenna (102); and
a coupling pole (104) slidably attached to and in electromagnetic contact with the monopole antenna (102), the coupling pole (104) configured to be displaceable with respect to the monopole antenna (102) in response to deformation of the test specimen (106);
a mounting arrangement (110) configured to secure the test specimen (106);
a force application mechanism (130) configured to apply tensile force to the test specimen (106) to induce strain; and
a radio frequency measurement unit (140) configured to detect a shift in resonant frequency of the monopole antenna (102) during deformation of the test specimen (106).