Dynamic electric field sensing using modified optical fiber structures

Abstract

A dynamic electric field sensing system includes an optical fiber sensor assembly having a fiber core with fiber Bragg grating that reflects light at a characteristic wavelength. A sensing material layer surrounds the fiber core and vibrates in response to alternating electric fields. The vibrations induce mechanical strain in the fiber core, causing wavelength shifts in the reflected light. An optical interrogation system detects these wavelength shifts, and a signal processing unit converts the shifts into electric field measurements. The sensing material layer may include polyimide coatings, polystyrene tubes, thermoplastic elastomer buffers, or suspended-in-coating configurations where chemical etching creates an air gap between the fiber and a fluoropolymer coating. The system enables distributed electric field sensing along optical fibers without requiring direct electrode contact or field gradients. Multiple fiber Bragg gratings at different wavelengths along a single fiber provide spatially-resolved field measurements at numerous locations.

Description

Docket No.: 222204-2990DYNAMIC ELECTRIC FIELD SENSING USING MODIFIED OPTICAL FIBER STRUCTURESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 694,290, filed September 13, 2024, titled “DYNAMIC ELECTRIC FIELD SENSING USING MODIFIED OPTICAL FIBER STRUCTURES,” the entire contents of which is hereby incorporated herein by reference.GOVERNMENT LICENSE RIGHTS

[0002] This invention was made with government support under Grant No. DE- SC0023984 awarded by the United States Department of Energy. The government has certain rights in the invention.BACKGROUND

[0003] Electric field sensing has applications in various technical fields including power system monitoring, medical diagnostics, atmospheric research, and industrial process control. Optical fiber-based sensing systems have been explored for electric field detection due to certain characteristics such as electromagnetic immunity and the potential for remote monitoring.

[0004] Various approaches to electric field sensing have been developed. Some sensing systems employ piezoelectric materials that respond to electric fields. Other approaches have utilized electrostrictive materials or interferometric techniques. Certain electric field sensing implementations have been designed for point measurements at specific locations. In some applications, there may be interest in monitoring electric fields over extended distances or areas. Additionally, different applications may uses different levels of sensitivity, with some applications potentially benefiting from detection capabilities below one volt per meter, including sensitivities in the millivolt per meter range.SUMMARY

[0005] The present disclosure relates to dynamic electric field sensing systems and methods using modified optical fiber structures that detect electric fields throughDocket No.: 222204-2990 vibration-induced strain measurements. The disclosed technology enables distributed electric field monitoring along optical fibers without requiring direct electrode contact or field gradients.

[0006] In accordance with various aspects of the disclosure, a dynamic electric field sensing system includes an optical fiber sensor assembly, an optical interrogation system, and a signal processing unit. The optical fiber sensor assembly includes a fiber core with fiber Bragg grating configured to reflect light at a characteristic wavelength and a sensing material layer surrounding the fiber core. The sensing material layer vibrates in response to alternating electric fields, inducing mechanical strain that shifts the reflected wavelength. The optical interrogation system detects these wavelength shifts, which the signal processing unit converts into electric field measurements.

[0007] The vibrations in the sensing material layer may result from lateral forces generated when alternating electric fields interact with space charges or dielectric dipoles within the material. In uniform electric fields, space charge contributions may dominate, while in non-uniform fields, dipole gradient interactions may contribute additional sensing mechanisms.

[0008] Various sensing material configurations can be implemented. In certain implementations, the sensing material layer includes a polyimide coating applied during fiber drawing, which may detect electric fields as low as approximately 2.5 volts per meter. Other implementations may include a polystyrene tube configuration where the fiber core resides within an internal cavity with an air gap between the fiber and tube wall. Alternative configurations may employ a thermoplastic elastomer buffer, such as Hytrel® material, surrounding the fiber core.

[0009] An advanced implementation includes a suspended-in-coating configuration where an air gap exists between the fiber core and a fluoropolymer coating. This configuration may be achieved through chemical etching using hydrofluoric acid that reduces fiber diameter while leaving the fluoropolymer coating intact. The suspended configuration may exhibit frequency doubling characteristics where a 60 hertz alternating electric field produces mechanical vibrations at 120 hertz due to electrostatic interactions occurring twice per field cycle.

[0010] The optical interrogation system may include an optical circulator for bidirectional signal routing between light sources and the fiber sensor assembly. TheDocket No.: 222204-2990 signal processing unit may include multiple components such as a wavelength analyzer for extracting wavelength shift data, a noise filter for removing environmental interference, and a field strength calculator for converting wavelength measurements to electric field values. A calibration module may provide calibration coefficients to maintain measurement accuracy over time.

[0011] For distributed sensing applications, the fiber core may contain multiple fiber Bragg gratings positioned at intervals along the fiber length, with each grating reflecting at a different wavelength. This configuration enables spatially-resolved electric field measurements at numerous locations using a single optical fiber, with the number and spacing of sensing points adaptable to specific monitoring requirements.

[0012] Methods for detecting dynamic electric fields include positioning an optical fiber containing fiber Bragg gratings in an electric field environment, where the fiber includes a material layer that vibrates in response to field variations. The method includes transmitting light through the fiber, detecting wavelength shifts in reflected signals, and converting these shifts to field measurements. Fiber preparation may include applying coatings during manufacturing, chemical etching to create suspended configurations, or assembling fibers within dielectric structures.

[0013] Optional enhancements may include electrical conditioning to align dipoles or inject charges into sensing materials, thermal treatments to stabilize material properties, or environmental monitoring to compensate for temperature and vibration effects. The systems and methods can be calibrated to correlate wavelength shifts with known electric field strengths for various material configurations.

[0014] Optional enhancements may include at least one electrically conductive element positioned proximate to the optical fiber sensor assembly. A single grounded conductive element can stabilize the charge environment, reducing noise and baseline drift. Dual conductive elements with applied alternating voltage can generate a reference electric field that enables detection of static fields through field distortion patterns. The conductive elements may extend along distributed sensing implementations, providing enhanced detection capabilities across multiple sensing regions.

[0015] The disclosed technology provides flexible solutions for electric field sensing applications ranging from power system monitoring to perimeter security, withDocket No.: 222204-2990 sensitivities adaptable from sub-volt-per-meter to kilovolt-per-meter ranges depending on the selected configuration and materials.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 depicts a block diagram of a dynamic electric field sensing system according to an example implementation.

[0017] FIG. 2A depicts a cross-sectional view of a polyimide-coated fiber configuration for electric field sensing according to an example implementation.

[0018] FIG. 2B depicts a cross-sectional view of a polystyrene tube configuration for electric field sensing according to an example implementation.

[0019] FIG. 2C depicts a cross-sectional view of a thermoplastic polyester elastomer buffer configuration for electric field sensing according to an example implementation.

[0020] FIG. 2D depicts a cross-sectional view of a suspended-in-coating configuration for electric field sensing according to an example implementation.

[0021] FIG. 2E depicts a cross-sectional view of a polyimide-coated fiber configuration with a grounded conductive element for electric field sensing according to an example implementation.

[0022] FIG. 2F depicts a cross-sectional view of a suspended-in-coating configuration with dual conductive elements for electric field sensing according to an example implementation.

[0023] FIG. 3A depicts a longitudinal view of a distributed electric field sensing fiber assembly according to an example implementation.

[0024] FIG. 3B depicts a longitudinal view of a distributed electric field sensing fiber assembly with conductive elements for enhanced field detection according to an example implementation.

[0025] FIG. 4A depicts experimental data showing an electric field response of a polyimide coating configuration of a distributed electric field sensing fiber according to an example implementation.

[0026] FIG. 4B depicts experimental data showing an electric field response of a polystyrene tube configuration of a distributed electric field sensing fiber according to an example implementation.Docket No.: 222204-2990

[0027] FIG. 4C depicts experimental data showing an electric field response of a thermoplastic polyester elastomer buffer configuration of a distributed electric field sensing fiber according to an example implementation.

[0028] FIG. 4D depicts experimental data showing a suspended-in-coating configuration of a distributed electric field sensing fiber according to an example implementation.

[0029] FIG. 5 depicts a flowchart of a method for electric field sensing using optical fiber with fiber Bragg gratings (FBGs) according to an example implementation.

[0030] FIG. 6 depicts a flowchart of a method for fabricating and operating a dynamic electric field sensing system according to an example implementation.DETAILED DESCRIPTION

[0031] The present disclosure relates to optical fiber-based systems and methods for detecting and measuring electric fields through distributed sensing architectures. Electric field monitoring has applications across diverse technical domains including power system diagnostics, medical device operation, atmospheric research, industrial process control, and electromagnetic compatibility testing. The ability to accurately detect and characterize electric fields, particularly at low field strengths and across extended spatial regions, presents ongoing technical challenges.

[0032] Electric field sensing technologies face several technical constraints that limit their deployment in practical applications. Sensitivity specifications vary significantly across applications, with some applications requiring detection of fields below one volt per meter while others monitor fields exceeding kilovolts per meter (kV / m). Spatial coverage presents another challenge, as many applications may benefit from monitoring electric fields over extended areas or along lengthy perimeters rather than at discrete points. Real-time monitoring capabilities become critical in dynamic environments where field characteristics change rapidly. Environmental factors including temperature variations, mechanical vibrations, and electromagnetic interference can compromise measurement accuracy. Additionally, safety considerations in high-voltage environments necessitate sensing approaches that avoid direct electrical contact with field sources.Docket No.: 222204-2990

[0033] The disclosed technology addresses at least these challenges through optical fiber-based sensing that converts electric field-induced mechanical effects into measurable optical wavelength shifts. The sensing mechanism operates on the principle that certain materials experience mechanical forces when exposed to electric fields, described by the relationship F = QE + jl - E = F + F2, where Q represents assembled space charges, p represents dielectric dipoles, E represents the local electric field, and VE represents the field gradient. In uniform electric fields where VE equals zero, the force component F = QE enables sensing without requiring field gradients.

[0034] The optical fiber can incorporate fiber Bragg gratings (FBGs) that reflect specific wavelengths of light. When mechanical strain from field-induced forces affects the fiber, the reflected wavelength shifts proportionally to the strain magnitude. An optical interrogation system detects these wavelength shifts and signal processing converts them into calibrated electric field measurements. The fiber may extend over considerable distances with multiple sensing regions, enabling distributed field monitoring along the entire fiber length.

[0035] Various electric field sensing approaches have been developed for different applications. Piezoelectric-based sensors utilizing materials such as polyvinylidene fluoride (PVDF) generate electrical signals in response to mechanical deformation. However, certain piezoelectric configurations may require specific operating conditions such as electric field gradients or particular temperature ranges. Capacitive sensors measure field-induced charge redistribution but typically provide point measurements rather than distributed sensing. Electro-optic sensors employ materials with fielddependent refractive indices, though these may require high field strengths for measurable effects. Rotating vane electrometers mechanically modulate electric fields for measurement but involve moving parts that can affect reliability.

[0036] The disclosed optical fiber sensing approach provides several technical capabilities. The distributed sensing architecture enables simultaneous field monitoring at multiple locations along a single fiber, with potential for continuous spatial coverage over kilometers of fiber length. The optical nature of the sensing mechanism provides immunity to electromagnetic interference that might affect electronic sensors. The absence of electrical components at the sensing location enables operation in high-voltage environments without safety concerns associated with conductive connections.Docket No.: 222204-2990

[0037] Multiple sensor configurations accommodate different application requirements. A polyimide coating configuration integrates the sensing material directly with the fiber during manufacturing, achieving demonstrated sensitivity to approximately 2.5 V / m. A suspended-in-coating configuration, created through chemical etching to form an air gap between the fiber and its coating, provides enhanced mechanical response with potential for sub-volt-per-meter sensitivity. Modular configurations using polystyrene tubes or thermoplastic elastomer buffers enable adaptation of standard optical fibers for electric field sensing.

[0038] The sensing mechanism operates effectively in uniform electric fields, eliminating requirements for field gradients that constrain certain sensing approaches. The system can detect both alternating current (AC) and direct current (DC) fields across frequency ranges from DC to several kilohertz (kHz). Temperature compensation and environmental monitoring capabilities maintain measurement accuracy across varying operating conditions. Digital signal processing enables real-time field characterization including magnitude, frequency, and temporal variations.

[0039] The complete sensing system integrates multiple subsystems to achieve comprehensive electric field monitoring. An optical fiber sensor assembly incorporates the field-sensitive materials and FBG sensing elements in various configurations. An optical interrogation system generates broadband light, routes signals bidirectionally through an optical circulator, and detects wavelength shifts in reflected signals. A signal processing unit performs analog-to-digital conversion, digital filtering, noise reduction, field strength calculation, and frequency analysis. Supporting subsystems provide calibration, environmental compensation, power distribution, and data output through display, storage, and communication interfaces.

[0040] This architecture supports scalable deployment from laboratory instruments to industrial monitoring networks. The modular design allows optimization of individual subsystems while maintaining system compatibility. Standard optical components and established signal processing techniques facilitate implementation using commercially available technologies while the novel sensing configurations provide the enhanced electric field detection capabilities.

[0041] FIG. 1 depicts a block diagram of a dynamic electric field sensing system 100 according to an example implementation. The dynamic electric field sensing systemDocket No.: 222204-2990100 can detect electric fields ranging from below one V / m to several kV / m through distributed optical fiber sensing. The dynamic electric field sensing system 100 operates by converting electric field-induced mechanical vibrations in dielectric or electret materials into measurable optical wavelength shifts, eliminating requirements for direct electrode contact or electric field gradients that limit conventional sensing approaches.

[0042] An electric field 101, represented by multiple horizontal arrows directed toward sensing components, interacts with an optical fiber sensor assembly 102. The electric field 101 may include uniform fields where field vectors maintain consistent magnitude and direction across the sensing region, such as fields between parallel plate capacitors or at distances from point sources where field variation becomes negligible. Alternatively, the electric field 101 may include non-uniform fields exhibiting spatial gradients, such as fields near conductors, electrical equipment, or biological tissues. The electric field 101 may operate at various frequencies, including DC fields, power frequency AC fields at 50 or 60 Hz, or higher frequency fields up to several kHz as may be encountered in switching power supplies or communication systems.

[0043] The optical fiber sensor assembly 102 employs a concentric layered construction where each successive layer contributes to the electric field sensing mechanism. At the core of the optical fiber sensor assembly 102, a fiber core with FBG 104 provides an optical strain sensing element. The fiber core with FBG 104 may include, for example, a single-mode fiber with a core diameter between 8 and 10 micrometers (pm) or a multimode fiber with core diameters of 50 or 62.5 pm. The FBG within this element can include periodic modulations in the refractive index of the fiber core, typically created through ultraviolet laser inscription or phase mask techniques. The periodic structure may include thousands of index modulations spaced at intervals of approximately 500 nanometers (nm) for operation in the 1550 nm telecommunications wavelength band. When broadband light propagates through the fiber core with FBG 104, wavelengths matching the Bragg condition= 2nA reflect, where n represents the effective refractive index and A represents the grating period. Mechanical strain on the fiber alters both the grating period and the effective refractive index through the photoelastic effect, causing the reflected wavelength to shift according to = Kex s, where Kerepresents the strain-A optic coefficient (approximately 0.78 for silica fibers) and e represents the applied strain.Docket No.: 222204-2990

[0044] A sensing material layer 106 surrounds the fiber core with FBG 104 and provides the electric field responsive mechanism. The sensing material layer 106 may include various materials selected for specific electric field interaction properties. Dielectric materials with high relative permittivity, such as barium titanate (er> 1000) or lead zirconate titanate (PZT), can experience strong forces in electric field gradients. Electret materials, including corona-charged polymers like polytetrafluoroethylene (PTFE) or polypropylene, maintain quasi-permanent electric charges or dipole orientations that interact with external fields. Polymer materials such as polyvinylidene fluoride (PVDF) or polyimide can exhibit electrostrictive or charge accumulation properties. The sensing material layer 106 responds to the electric field 101 through lateral force generation described by F = QE + ■ VE, where Q represents assembled space charges, p represents assembled dielectric dipoles, E represents the local electric field, and VE represents the field gradient. In uniform fields where VE equals zero, the force F = QE dominates, enabling sensing without field gradients. The generated forces cause mechanical vibrations or deformations in the sensing material layer 106 at frequencies corresponding to the applied field frequency for DC fields with AC noise, at the field frequency for AC fields, or at twice the field frequency for certain nonlinear material responses.

[0045] A protective layer 108 may surround the sensing material layer 106 to provide mechanical protection, moisture barriers, or chemical resistance. The protective layer 108 may include polymer jackets such as polyethylene or polyurethane with thicknesses ranging from 100 pm to several mm. The protective layer 108 material selection balances protection requirements against mechanical coupling efficiency, as excessive stiffness or damping in the protective layer 108 can attenuate the transmission of field-induced vibrations to the fiber core with FBG 104.

[0046] Configuration options 110 presents a selection of four validated sensing assembly implementations, each offering distinct advantages for specific applications or operating conditions. A polyimide coating 112 represents a configuration where polyimide polymer applies directly to the fiber cladding during the fiber drawing process at temperatures exceeding 200 degrees Celsius. The polyimide coating 112 typically measures 10 to 30 pm in thickness and can function as both protective coating and sensingDocket No.: 222204-2990 material. Laboratory testing has demonstrated polyimide-coated fibers detecting electric fields as low as approximately 2.5 V / m, with linear response characteristics up to 200 V / m.

[0047] A polystyrene tube 114 configuration employs a rigid dielectric tube structure within which a standard optical fiber resides. The polystyrene material, having a relative permittivity of approximately 2.6, experiences mechanical forces when exposed to electric fields. The polystyrene tube 114 may have an outer diameter of approximately 9.5 millimeters (mm) (3 / 8 inch) with wall thickness of approximately 1 mm, creating an internal cavity where the optical fiber can move in response to tube vibrations. The mechanical coupling between the vibrating polystyrene tube 114 and the enclosed fiber enables electric field detection with sensitivity in the range of 100 V / m.

[0048] A thermoplastic polyester elastomer buffer 116 utilizes thermoplastic elastomer material to create a compliant buffer layer around the optical fiber. For example, the thermoplastic polyester elastomer buffer 116 can be Hytrel®, which is a polyester- based elastomer with a relative permittivity of approximately 3.7 that can be extruded onto fibers to build up the cable diameter to 900 pm or larger. The thermoplastic polyester elastomer buffer 116 deforms under electric field forces, directly straining the embedded fiber. The elastomeric properties of the thermoplastic polyester elastomer buffer 116 enable recovery from deformation while maintaining consistent coupling between field- induced forces and fiber strain.

[0049] A suspended-in-coating 118 configuration represents an advanced implementation where chemical etching creates a gap between the fiber core with FBG 104 and the surrounding coating. Starting with a fluoropolymer-coated fiber, hydrofluoric acid selectively etches the glass fiber through the intact coating, reducing the fiber diameter from approximately 125 pm to approximately 110 pm while preserving the coating structure. The resulting air gap allows the fiber to vibrate freely within the coating cavity. Charge separation between the fluoropolymer coating (affinity for negative charges) and the silica glass fiber (affinity for positive charges) enhances the electric field interaction, producing dramatically improved sensitivity with potential for sub-volt-per- meter detection.

[0050] An optical interrogation system 120 generates, routes, and analyzes optical signals for wavelength-based strain detection. A light source 122 within the optical interrogation system 120 produces optical radiation for fiber interrogation. The lightDocket No.: 222204-2990 source 122 may include superluminescent light-emitting diodes (SLEDs) providing broadband emission with spectral widths of approximately 40 to 80 nm, tunable laser sources capable of wavelength sweeping across the FBG reflection spectrum, or amplified spontaneous emission (ASE) sources. The light source 122 power levels typically range from -10 decibels per milliwatt (dBm) to +13 dBm, balanced between signal-to-noise requirements and nonlinear effects in the fiber.

[0051] An optical interrogation signal 124 propagates from the light source 122 to an optical circulator 126. The optical circulator 126 provides non-reciprocal routing of optical signals. The optical circulator 126 directs the optical interrogation signal 124 from a first port (connected to the light source 122) to a second port (connected to the optical fiber sensor assembly 102) with minimal loss, typically less than 1 dB. Simultaneously, the optical circulator 126 can route a reflected optical signal 128 returning from the optical fiber sensor assembly 102 (entering the second port) to a third port (connected to downstream detection components) with high isolation from the first port, typically greater than 40 dB. The connection between the optical circulator 126 and the optical fiber sensor assembly 102 represents a bidirectional optical path where the optical interrogation signal 124 (solid line) and the reflected optical signal 128 (dashed line) can share the same physical fiber.

[0052] An interrogator unit 130 receives the reflected optical signal 128 from the optical circulator 126. The interrogator unit 130 may implement various detection architectures. Tunable filter-based systems use Fabry -Perot filters or fiber Bragg gratings to scan across wavelengths while measuring reflected power. Spectrometer-based systems use diffraction gratings or arrayed waveguide gratings with photodetector arrays to measure the complete reflection spectrum simultaneously. Interferometric systems detect wavelength shifts through phase changes in interferometer arms. Commercial interrogator units, such as a commercially available data acquisition system (DAS) (e.g., picoDAS from EME Corporation) systems can achieve wavelength resolution better than 1 picometer (pm) with sampling rates exceeding 1 kHz, enabling detection of strain levels below 1 microstrain.

[0053] The interrogator unit 130 generates an electrical data signal 132 containing digitized wavelength information. A wavelength analyzer 134 processes the electrical data signal 132 to extract wavelength shift data 136. The wavelength analyzer 134 may employDocket No.: 222204-2990 peak detection algorithms to identify FBG reflection wavelengths, correlation techniques to track wavelength changes, or curve fitting methods to determine wavelength shifts with sub-pm resolution. The wavelength shift data 136 output represents temporal variations in the reflected wavelength corresponding to dynamic strain induced by the electric field 101.

[0054] A signal processing unit 136 transforms the wavelength shift data 136 into calibrated electric field measurements through cascaded processing stages. An analog / digital (A / D) converter 138 digitizes any analog signal components, typically operating at sampling rates of 10 to 100 kilosamples per second with 16 to 24-bit resolution. A digital signal processing (DSP) module 140 executes digital signal processing algorithms such as finite impulse response (FIR) or infinite impulse response (IIR) filtering, fast Fourier transforms (FFT) for frequency analysis, and wavelet transforms for time-frequency analysis.

[0055] A noise filter 142 removes unwanted signal components that could corrupt electric field measurements. The noise filter 142 may implement bandpass filtering centered on expected field frequencies, notch filters to remove power line interference at 50 or 60 Hz and harmonics thereof, adaptive filtering to track and remove time-varying noise, or median filtering to eliminate impulse noise from electrical transients. Environmental vibrations from machinery, acoustic noise, or seismic activity can be distinguished from electric field-induced vibrations through frequency analysis and correlation techniques.

[0056] A field strength calculator 144 converts wavelength shift measurements to electric field magnitude values in volts per meter. The conversion process applies multiple transfer functions: wavelength shift to strain Asstrain to mechanical displacementbased on the sensing material properties and geometry, and mechanical displacement to electric field strength using calibration curves determined experimentally for each configuration option 110. For example, the polyimide coating 112 configuration may exhibit a transfer function of 0.1 pm wavelength shift per volt per meter of electric field, while the suspended- in-coating 118 configuration may achieve 1.0 pm wavelength shift per V / m due to enhanced mechanical coupling.

[0057] A frequency analyzer 146 determines the spectral content of detected electric fields. The frequency analyzer 146 can identify fundamental frequencies such as 60 HzDocket No.: 222204-2990 from power systems, 400 Hz from aircraft electrical systems, or variable frequencies from switching converters. Harmonic analysis reveals nonlinear effects, with odd harmonics indicating asymmetric field distributions and even harmonics suggesting rectification effects. Certain configurations, particularly the suspended-in-coating 118, may exhibit frequency doubling where a 60 Hz applied field produces a 120 Hz mechanical response due to electrostatic attraction occurring twice per field cycle.

[0058] Output data 148 from the signal processing unit 136 contains comprehensive electric field characterization including instantaneous field magnitude, root-mean-square (RMS) values for AC fields, frequency spectrum with magnitude and phase information, field direction for multi-axis sensor configurations, and time-stamped data for temporal analysis.

[0059] A data output interface 150 manages the distribution and presentation of the output data 148. A display 152 may include graphical user interfaces (GUIs) showing real-time field strength meters, frequency spectrum analyzers, historical trend plots, or spatial field maps for distributed sensing configurations. Data storage 154 archives measurements using formats such as hierarchical data format (HDF5) for scientific data, comma-separated values (CSV) for compatibility with analysis software, or binary formats for efficient storage of high-rate data streams. External communication 156 enables integration with broader systems through interfaces such as Ethernet for network connectivity, RS -485 for industrial environments, and / or wireless protocols for remote monitoring applications.

[0060] A calibration module 158 maintains measurement accuracy through bidirectional interaction with the signal processing unit 136. The calibration module 158 provides calibration coefficients derived from laboratory or field calibration procedures, temperature compensation curves accounting for thermal expansion and thermo-optic effects, aging compensation for long-term drift in material properties or optical components, and zero-point adjustments for offset corrections. The calibration module 158 receives performance metrics from the signal processing unit 136 including signal-to- noise ratios, wavelength stability indicators, and self-test results that trigger recalibration when predetermined thresholds are exceeded.

[0061] An environmental control unit 160 monitors and potentially regulates environmental conditions affecting sensor performance. The environmental control unitDocket No.: 222204-2990160 may include temperature sensors such as thermocouples or resistance temperature detectors (RTDs) positioned near the optical fiber sensor assembly 102, vibration sensors such as accelerometers to detect mechanical disturbances, and humidity sensors for applications where moisture affects the sensing materials. The environmental control unit 160 provides data to both the calibration module 158 for triggering environment-based recalibration and the signal processing unit 136 for real-time compensation of environmental effects.

[0062] A power supply 162 provides electrical power to all active components within the dynamic electric field sensing system 100. The power supply 162 may include linear regulators for low-noise analog circuits, switching regulators for digital processing components, battery backup for uninterrupted operation during power failures, and isolation transformers or optical isolation for high-voltage environments. Power requirements typically range from 5 to 50 watts depending on system configuration and performance specifications.

[0063] The distributed sensing capability of the dynamic electric field sensing system 100 extends beyond single-point measurements. The optical fiber with the FBG 104 may include multiple gratings at different wavelengths, enabling wavelength-division multiplexed sensing at numerous locations along a single fiber. Alternatively, timedivision multiplexing using optical time-domain reflectometry techniques can provide continuous distributed sensing with spatial resolution of meters to centimeters along fiber lengths exceeding several kilometers.

[0064] FIG. 2A depicts a cross-sectional view of a polyimide-coated fiber configuration corresponding to the polyimide coating 112 option from the configuration options 110 shown in FIG. 1 according to an example implementation. This configuration integrates the sensing material 106 directly with the optical fiber during manufacturing, eliminating requirements for secondary assembly processes.

[0065] At the center, the fiber core 104 from FIG. 1 appears in cross-section as a circular region having a diameter between 8 and 10 pm for single-mode implementations or between 50 and 62.5 pm for multimode implementations, for example. The FBG structures within the fiber core 104, while not visible in FIG. 2A, extend longitudinally through the fiber providing wavelength-selective reflection as described with reference to FIG. 1.Docket No.: 222204-2990

[0066] A glass cladding 202 surrounds the fiber core 104, establishing the waveguide structure used for optical signal propagation. The glass cladding 202 typically includes pure silica or fluorine-doped silica with a slightly lower refractive index than the fiber core 104, creating total internal reflection conditions. The combined diameter of the fiber core 104 and glass cladding 202 measures approximately 125 pm, conforming to standard telecommunications fiber dimensions.

[0067] The polyimide coating 112 encapsulates the glass cladding 202, serving dual functions as both protective layer 108 and sensing material layer 106 referenced in FIG. 1. The polyimide coating 112 applies during the fiber drawing process when the glass reaches temperatures exceeding 200 degrees Celsius, creating a uniform layer with thickness ranging from 10 to 30 pm. The total fiber diameter including the polyimide coating 112 may range from approximately 250 to 300 pm depending on the specific coating thickness selected for the application requirements.

[0068] The electric field 101, shown by multiple arrows approaching from the left, interacts with the polyimide coating 112 to generate mechanical forces. The polyimide material exhibits dielectric properties that cause mechanical strain when exposed to electric fields, with the strain magnitude proportional to the strength of the electric field 101. This mechanical strain transfers through the glass cladding 202 to the fiber core 104, modulating the FBG reflection wavelength as described in the operation of the system 100 of FIG. 1.

[0069] The polyimide coating 112 configuration demonstrates minimum electric field detection of approximately 2.5 V / m with linear response characteristics extending to 200 V / m. The integrated nature of this configuration, where the sensing material layer 106 bonds directly to the glass cladding 202 during manufacturing, provides mechanical robustness and consistent strain transfer characteristics.

[0070] FIG. 2B depicts a cross-sectional view illustrates a polystyrene tube configuration corresponding to the polystyrene tube 114 option from the configuration options 110 shown in FIG. 1 according to an example implementation. The polystyrene tube 114 provides a modular sensing approach where standard optical fibers can be adapted for electric field detection.

[0071] The polystyrene tube 114 forms a rigid cylindrical structure with an outer diameter of approximately 9.5 millimeters (3 / 8 inch) and a wall thickness of approximatelyDocket No.: 222204-29901 millimeter in one example implementation, creating an internal cavity for fiber placement. The polystyrene material, having a relative permittivity of approximately 2.6, experiences mechanical forces when exposed to the electric field 101. These forces cause the walls of the polystyrene tube 114 to vibrate at frequencies corresponding to the applied field frequency for AC fields or in response to field variations for DC fields containing noise components.

[0072] A standard fiber 204 resides within the polystyrene tube 112, including the fiber core 104 containing FBGs as described with reference to FIG. 1, surrounded by glass cladding and a protective acrylate coating (not shown separately in the illustrated example). In some implementations, the standard fiber 204 can maintain a total diameter of approximately 250 pm, compatible with commercial telecommunications fiber specifications.

[0073] An air gap 206 separates the standard fiber 204 from the inner wall of the polystyrene tube 112. The air gap 206 enables mechanical coupling between the vibrating polystyrene tube 112 and the standard fiber 204 while allowing relative movement. When the polystyrene tube 112 vibrates in response to the electric field 101, acoustic waves propagate through the air gap 206 and induce periodic strain in the standard fiber 204. This strain modulates the reflection wavelength of the FBGs within the fiber core 104, creating detectable optical signals proportional to the strength of the electric field 101.

[0074] The polystyrene tube 114 configuration demonstrates electric field detection sensitivity in the range of approximately 100 V / m, with response characteristics dependent on the length of the polystyrene tube 114, fiber tension within the tube, and acoustic coupling efficiency across the air gap 206.

[0075] FIG. 2C depicts a cross-sectional view of a thermoplastic polyester elastomer configuration corresponding to the thermoplastic polyester elastomer buffer 116 of the configuration options 110 shown in FIG. 1 according to an example implementation. This configuration uses thermoplastic elastomer material to create a compliant buffer that transfers electric field-induced deformations directly to the embedded optical fiber.

[0076] The thermoplastic polyester elastomer buffer 116 includes a polyester-based thermoplastic elastomer extruded concentrically around a standard fiber 204. The thermoplastic polyester elastomer material (e.g., Hytrel®) builds up the overall cable diameter from approximately 250 pm to approximately 900 pm. Hytrel®, specifically,Docket No.: 222204-2990 exhibits a relative permittivity of approximately 3.7, providing enhanced interaction with electric fields compared to standard polymer coatings. The thermoplastic polyester elastomer buffer 116 applies through conventional cable manufacturing processes, either through pressure extrusion directly onto the fiber or through tubing extrusion followed by thermal forming.

[0077] The standard fiber 204 includes an acrylate protective coating surrounding the glass optical structure. The standard fiber 204 maintains a total diameter of approximately 250 pm, conforming to telecommunications industry standards for handling and connectivity.

[0078] Within the standard fiber 204, the glass cladding 202 establishes the optical waveguide structure with the fiber core 104. The glass cladding 202 can include silica glass with a refractive index slightly lower than the fiber core 104, creating the conditions for total internal reflection. The combined diameter of the fiber core 104 and glass cladding 202 measures approximately 125 pm.

[0079] The fiber core 104 contains the fiber Bragg gratings described with reference to FIG. 1, maintaining the wavelength-selective reflection properties essential for strain detection. The fiber core 104 diameter ranges from 8 to 10 pm for single-mode implementations or 50 to 62.5 pm for multimode configurations.

[0080] When the electric field 101 interacts with the thermoplastic polyester elastomer buffer 116, the thermoplastic polyester elastomer buffer 116 deforms in response to field-induced forces. The thermoplastic polyester elastomer buffer 116 bonds directly to the acrylate coating of the standard fiber 204, establishing continuous mechanical coupling from the buffer exterior to the fiber core 104. This bonded interface prevents slippage or relative movement, ensuring efficient strain transfer. The elastomeric properties enable reversible deformation, with the material compressing and expanding at the frequency of alternating fields or deforming statically in response to DC fields.

[0081] The deformation of the thermoplastic polyester elastomer buffer 116 directly strains the embedded standard fiber 204 and consequently the fiber core 104, modulating the Bragg wavelength proportionally to the electric field strength. The compliance of the thermoplastic polyester elastomer buffer 116 material allows measurable strain while maintaining mechanical integrity and enabling full recovery when the field removes.Docket No.: 222204-2990

[0082] FIG. 2D depicts a cross-sectional view of a suspended-in-coating configuration corresponding to the suspended-in-coating 118 option from the configuration options 110 shown in FIG. 1 according to an example implementation. This configuration employs chemical etching to create an air gap between the optical fiber and its surrounding coating, providing enhanced sensitivity through increased mechanical freedom.

[0083] A fluoropolymer coating 208 forms the outer cylindrical structure, remaining intact throughout the chemical etching process. The fluoropolymer coating 208, which may include polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), or similar fluorinated polymers, maintains its original structural integrity with an outer diameter of approximately 250 micrometers. The inner diameter of the fluoropolymer coating 210 preserves the original dimension corresponding to the standard 125- micrometer fiber diameter before etching.

[0084] An air gap 206 separates the fluoropolymer coating 208 from an etched fiber 210, creating spacing that enables the enhanced sensing mechanism. The air gap 206 forms through selective etching with hydrofluoric acid, which penetrates through the fluoropolymer coating 208 to dissolve glass material from the fiber surface while leaving the coating structure unaffected. The resulting annular gap measures approximately 7.5 micrometers radially, providing sufficient clearance for unimpeded fiber movement within the coating cavity.

[0085] The etched fiber 210 exhibits a reduced diameter of approximately 110 micrometers, decreased from the original 125 -micrometer diameter through controlled chemical etching. The etching process removes glass material uniformly from the fiber circumference, maintaining concentricity with the fiber core 104 while reducing the overall glass cross-section. The etched fiber 210 remains mechanically continuous and maintains optical transmission properties despite the diameter reduction.

[0086] The fiber core 104 preserves its original dimensions and properties throughout the etching process, as the hydrofluoric acid removes material only from the outer cladding regions. The FBGs within the fiber core 104 continue to provide wavelength-selective reflection for strain detection as described with reference to FIG. 1.

[0087] When the electric field 101 interacts with the suspended-in-coating structure, the fluoropolymer coating 208 and the etched fiber 210 experience differential forces dueDocket No.: 222204-2990 to the distinct properties of each material. The fluoropolymer coating 208 exhibits an affinity for negative charge accumulation while the silica glass of the etched fiber 210 tends toward positive charge accumulation, creating an electrostatic interaction across the air gap 206. These charge differences generate attractive or repulsive forces depending on the applied field polarity and orientation.

[0088] The air gap 206 eliminates mechanical damping that would occur with direct contact between the etched fiber 210 and the fluoropolymer coating 208, allowing the fiber to oscillate freely in response to electric field variations. The suspended fiber can move laterally within the coating cavity, with the magnitude of displacement proportional to the electric field strength and the electrostatic forces between the charged surfaces.

[0089] This configuration may demonstrate frequency doubling phenomena where alternating fields at 60 Hz produce mechanical vibrations at 120 Hz, as electrostatic attraction occurs twice per field cycle independent of polarity. The combination of mechanical freedom provided by the air gap 206 and the charge separation between material surfaces enables detection of electric fields potentially below 1 V / m, representing the highest sensitivity among the configuration options 110.

[0090] The fabrication process uses precise control of etching parameters including hydrofluoric acid concentration typically between 20 and 50 percent, temperature maintained between 20 and 40 degrees Celsius, and exposure duration ranging from minutes to hours depending on the desired diameter reduction. The etching rate should be carefully monitored to achieve uniform fiber diameter while preventing over-etching that could compromise mechanical strength.

[0091] FIG. 2E depicts a cross-sectional view of a polyimide-coated fiber configuration 200E with an electrically grounded conductive element according to an example implementation. The configuration 200E builds upon the structure shown in FIG. 2A, incorporating a grounded conductor 212 positioned at a spacing 214 from the fiber assembly. The grounded conductor 212 may include a metallic wire, such as copper or aluminum, with a diameter ranging from approximately 0.5 to 2 millimeters. The grounding connection maintains the grounded conductor 212 at zero potential, enabling the grounded conductor 212 to function as an electron reservoir for neutralizing positive charges and as an electron drain for removing negative charges in the surrounding environment. This grounded configuration stabilizes the charge distribution around theDocket No.: 222204-2990 polyimide coating 112, reducing baseline drift and improving signal-to-noise ratio in the sensor response.

[0092] FIG. 2F depicts a cross-sectional view of a suspended-in-coating configuration 200F with dual conductive elements for active field sensing according to an example implementation. Building upon the suspended structure of FIG. 2D, a first conductor 216 and a second conductor 218 are positioned on opposite sides of the fluoropolymer coating 208. A first distance (“distance A”) 220A separates the first conductor 216 from the fiber centerline, while a second distance (“distance B”) 220B separates the second conductor 218 from the fiber centerline. These distances may be equal for symmetric field generation or may differ to create asymmetric field patterns. An AC source 222 applies an alternating voltage between the first conductor 216 and the second conductor 218, generating a reference electric field 224 in the region surrounding the suspended fiber. The reference electric field 224 interacts with the etched fiber 210 through the air gap 206, creating a controlled vibration pattern. When external static or dynamic electric fields are present (e.g., the electric field 101), these fields distort the pattern of the reference electric field 224, causing detectable changes in the mechanical response of the fiber. This active sensing approach enables detection of static electric fields that would not otherwise produce mechanical vibrations in the fiber, extending the sensor capability beyond alternating field detection.

[0093] FIG. 3A depicts a longitudinal view of a distributed electric field sensing fiber assembly 300A according to an example implementation. The distributed electric field sensing fiber assembly 300A can be configured for simultaneous electric field detection at multiple positions along a single optical fiber. The distributed electric field sensing fiber assembly 300A demonstrates the wavelength-division multiplexing capability that enables independent monitoring of electric fields at numerous locations without requiring separate fibers for each sensing point.

[0094] The sensing material layer 106, corresponding to the element described in FIG. 1, extends continuously along the fiber length and may include any of the configurations shown in FIGS. 2A-2F. The sensing material layer 106 surrounds the fiber core 104 containing multiple FBGs 302A-302N, providing electric fields 101A-101N in corresponding sensing regions 304A-304N.Docket No.: 222204-2990

[0095] The optical interrogation signal 124, corresponding to the signal from the optical interrogation system 120 of FIG. 1, enters the distributed electric field sensing fiber assembly 300 from the left. The optical interrogation signal 124 includes broadband light containing wavelengths spanning approximately 1540 to 1560 nm or wider, sufficient to interrogate all of the FBGs 302A-302N along the fiber.

[0096] The first sensing region 304 A contains the FBGi 302A configured to reflect light at wavelength Xi of 1545 nm. The vertical lines within the first sensing region 304A represent the periodic refractive index modulations that form FBGi 302A. The electric field Ei 101 A applied at the first sensing region 304A induces mechanical strain in the sensing material layer 106, which transfers to the FBGi 302 A, causing a wavelength shift proportional to the local field strength.

[0097] The second sensing region 304B, positioned approximately 10 m to 25 m along the fiber, contains the FBG2302B reflecting at wavelength X2 of 1550 nm. The 5 nm wavelength separation from FBGi 302A prevents spectral overlap while remaining within typical interrogation system bandwidths. The electric field E2 10 IB at the second sensing region 304B operates independently from Ei 101 A, with the FBG2 302B responding only to the local field conditions at its position.

[0098] The third sensing region 304C, located approximately 25 m to 40 m from the fiber input, contains a the FBG3 302C with reflection wavelength X3 of 1555 nm. The consistent 5 nm spacing between adjacent FBG wavelengths simplifies system design while maintaining adequate spectral separation for independent detection. The electric field E3 101C at this location produces wavelength shifts in the FBG3 302C that can be distinguished from shifts occurring at other FBGs 302 due to the unique operating wavelength.

[0099] Additional sensing regions extend to the nthsensing region 302N containing the FBGn304N with wavelength Xn. The notation indicates scalability to numerous sensing points, with practical implementations potentially incorporating 20 to 100 distinct FBGs along a single fiber. The specific wavelength for FBGn302N would be selected to avoid overlap with the other FBGs 302 in the system 100, typically continuing the progression with 5 nm spacing or adjusted based on available spectral range.

[0100] The electric fields Ei 101 A through En10 IN may vary independently in magnitude, frequency, and phase, representing different field conditions at each sensingDocket No.: 222204-2990 location. Each FBG 302 responds only to its local electric field, enabling spatial mapping of field distributions along the fiber path. The fields may originate from different sources or represent the spatial variation of a single extended field.

[0101] Reflected optical signals, shown as dashed arrows returning toward the input, carry the wavelength-encoded information from the FBGs 302. The reflected signals contain wavelengths Xi, X2, X3 through Xn, each shifted from its nominal value by an amount proportional to the strain at that FBG location. These reflected signals return through the same fiber to the optical circulator 126 described in FIG. 1, which routes the reflected signals (e.g., the reflected optical signal 128 in FIG. 1) to the interrogator unit 130 for detection and analysis.

[0102] The distance scale indicates the fiber extends from 0 meters at the input to length (L), which may reach several kilometers in some implementations. The spacing between sensing regions can be tailored to application requirements, from sub-meter intervals for high-resolution field mapping to hundreds of meters for long-distance monitoring. The total number and spacing of sensing regions depends on factors including the required spatial resolution, available optical power, wavelength range of the interrogation system, and acceptable signal-to-noise ratio.

[0103] The distributed sensing fiber assembly 300A operates continuously along the length of the assembly, with the sensing material layer 106 and the fiber core 104 maintaining consistent properties between discrete FBG locations. While the FBGs 302 provide discrete sensing points, the continuous nature of the sensing material allows for future implementations using distributed sensing techniques such as optical time-domain reflectometry to provide fully continuous field measurements between FBG locations.

[0104] FIG. 3B depicts a longitudinal view of a distributed electric field sensing fiber assembly 300B with conductive elements for enhanced field detection according to an example implementation. Building upon the configuration of FIG. 3 A, the assembly 300B incorporates a first conductor 216 positioned above the fiber and a second conductor 218 positioned below the fiber, both extending along the entire fiber length L. The conductors may include metallic wires with diameters ranging from approximately 0.5 to 2 millimeters, positioned at controlled distances from the fiber axis to optimize field coupling.Docket No.: 222204-2990

[0105] An AC voltage source 222 at the input end applies an alternating voltage between the first conductor 216 and the second conductor 218, generating a reference electric field 224 along the length of the assembly 300B. The reference electric field 224, indicated by vertical arrows between the conductors, can extend through all sensing regions 304A-304N (although not shown extending through all sensing regions in the illustrated example), creating a controlled electromagnetic environment. The voltage source 222 may operate at frequencies from a few Hz to several kHz, with 60 Hz or 120 Hz commonly selected for power system monitoring applications.

[0106] The reference electric field 224 interacts with the sensing material layer 106 to produce baseline mechanical vibrations detectable by each FBG 302A-302N. When external electric fields Ei 101 A through EN 10 IN are present at their respective sensing regions 304A-304N, these fields locally distort the pattern of the reference electric field 224. Each FBG 302 detects the distortion at its specific location through changes in the vibration-induced strain pattern, enabling spatially-resolved measurement of both static and dynamic external fields along the entire fiber length.

[0107] This dual-conductor configuration provides enhanced capabilities for distributed sensing applications. Static electric fields, which would not normally induce mechanical vibrations, become detectable through their interaction with the reference electric field 224 The reference electric field 224 also improves signal-to-noise ratio by providing a carrier signal that can be demodulated to extract field information. Additionally, when the voltage source 222 is disabled, the conductors 216, 218 can be grounded to provide charge stabilization as described for the single conductor configuration in FIG. 2E, offering operational flexibility for different sensing scenarios.

[0108] FIG. 4A depicts a graph 400A of experimental data showing an electric field response of the polyimide coating 112 configuration of a distributed electric field sensing fiber according to an example implementation. The vertical axis represents |P(f)|, the magnitude of the optical response signal in arbitrary units, while the horizontal axis shows the applied electric field strength in volts per meter. Data points demonstrate linear response from the minimum detection threshold of approximately 2.5 V / m through 50 V / m. The dashed trend line confirms the linear relationship between field strength and optical response, validating the sensing mechanism for the polyimide coating 112 whereDocket No.: 222204-2990 the polyimide material serves dual functions as protective coating and sensing material layer 106.

[0109] FIG. 4B depicts a graph 400B of experimental data showing an electric field response of the polystyrene tube 114 configuration of a distributed electric field sensing fiber according to an example implementation. The response data spans from 0 to 800 V / m, with measurable detection beginning around 100 V / m. The linear trend line through the data points demonstrates consistent proportionality between field strength and sensor response throughout the measurement range. The higher detection threshold of this configuration compared to the polyimide coating 112 (FIG. 4A) reflects the mechanical coupling through the air gap 206 between the vibrating polystyrene tube 114 and the enclosed standard fiber 204 (shown in FIG. 2B).

[0110] FIG. 4C depicts experimental data showing an electric field response of the thermoplastic polyester elastomer buffer 116 configuration of a distributed electric field sensing fiber according to an example implementation. The experimental data exhibits linear behavior from near-zero field strength through 800 V / m. The thermoplastic polyester elastomer buffer 116 configuration demonstrates intermediate sensitivity between the polyimide and polystyrene implementations, with the thermoplastic elastomer material providing direct mechanical coupling to the embedded fiber while maintaining flexibility for field-induced deformation.

[0111] FIG. 4D depicts experimental data showing an electric field response of the suspended-in-coating 118 configuration of a distributed electric field sensing fiber according to an example implementation. The data reveals two distinct operating regions separated by frequency response. Below approximately 1000 V / m, the distributed electric field sensing fiber responds at 60 Hz as shown by the dotted line with gradual slope. Above this threshold, the response transitions to 120 Hz operation, indicated by the dashed line with significantly steeper slope. This frequency doubling phenomenon occurs because electrostatic forces between the fluoropolymer coating 210 and the etched fiber 208 attract twice per alternating current cycle, independent of field polarity. The enhanced sensitivity at 120 Hz, approaching 0.003 |P(f)| units at 1750 V / m, demonstrates the superior performance achieved through the suspended fiber architecture with the air gap 206.

[0112] The experimental data presented in FIGS. 4A-4D confirm the theoretical predictions for each configuration option 110 from FIG. 1. The linear responseDocket No.: 222204-2990 characteristics enable calibrated electric field measurements, with sensitivity ranges spanning from 2.5 V / m for the polyimide coating 112 to potential sub-V / m detection for the suspended-in-coating 118 configuration. These performance variations allow selection of appropriate configurations based on specific application requirements, from sensitive laboratory measurements to robust industrial field monitoring.

[0113] FIG. 5 depicts a flowchart of a method 500 for electric field sensing using optical fiber with FBGs according to an example implementation. It should be understood that the operations of the methods disclosed herein are not necessarily presented in any particular order and that performance of some or all of the operations in an alternative order(s) is possible and is contemplated. The operations have been presented in the demonstrated order for ease of description and illustration. Operations may be added, omitted, and / or performed simultaneously, without departing from the scope of the appended claims. It also should be understood that the illustrated methods disclosed herein can be ended at any time and need not be performed in their respective (or collective) entireties.

[0114] For purposes of illustrating and describing the concepts and technologies of the present disclosure, the methods disclosed herein are described as being performed generally by the system 100 or components thereof. It should be understood that additional and / or alternative systems, devices, and / or network nodes can provide the functionality described herein via execution of one or more modules, applications, and / or other software. Thus, the illustrated implementations are illustrative, and should not be viewed as being limiting in any way.

[0115] The method 500 begins at block 502 with initialization of the optical interrogation system 120. Specifically, at block 50 includes powering and configuring the light source 122, optical circulator 126, and interrogator unit 130 to establish baseline operating parameters.

[0116] At block 504, the light source 122 generates a broadband optical signal containing wavelengths sufficient to interrogate all FBGs along the sensing fiber (e.g., the optical interrogation signal 124 in FIG. 1). For the distributed configuration shown in FIGS. 3 A, 3B, for example, this includes wavelengths spanning the reflection bands of the FBGi 304A through the FBGn304N.Docket No.: 222204-2990

[0117] At block 506, the optical circulator 126 interrogates multiple FBGs positioned along the fiber by transmitting the optical interrogation signal 124 through the fiber core 104 and collecting reflected wavelengths in the reflected optical signal 128. Each FBG reflects its characteristic wavelength while transmitting others, enabling simultaneous monitoring of multiple the sensing regions 302A-302N.

[0118] At block 508, the interrogator unit 130 and the wavelength analyzer 134 detects wavelengths in the reflected optical signal(s) 128. The wavelength shifts correspond to mechanical strain induced in the fiber by electric field interactions with the sensing material layer 106.

[0119] At decision block 510, the wavelength analyzer 134 determines whether a measurable wavelength shift has been detected above the noise floor of the system 100. If no significant shift is detected (NO path), the method 500 returns to block 506 to continue interrogation. If a wavelength shift is detected (YES path), the method 500 proceeds to block 512.

[0120] At block 512, the signal processing unit 136 processes the detected signals, including operations performed by the A / D converter 138, the DSP module 140, the noise filter 142, and the frequency analyzer 146. Particularly, the A / D converter 138 can digitize analog signal components from the interrogator unit 130, typically operating at sampling rates of 10 to 100 kilosamples per second with 16 to 24-bit resolution. The DSP module 140 can execute digital signal processing algorithms, such as finite impulse response (FIR) or infinite impulse response (IIR) filtering, fast Fourier transforms (FFT) for frequency analysis, and wavelet transforms for time-frequency analysis. The noise filter 142 can remove unwanted signal components that could corrupt electric field measurements, implementing bandpass filtering centered on expected field frequencies, notch filters to remove power line interference at 50 or 60 Hz and harmonics thereof, adaptive filtering to track and remove time-varying noise, or median filtering to eliminate impulse noise from electrical transients. The frequency analyzer 146 can determine the spectral content of detected electric fields, identifying fundamental frequencies such as 60 Hz from power systems, Hz from aircraft electrical systems, or variable frequencies from switching converters, and can identify harmonic content including frequency doubling effects. This processing extracts the electric field information from the optical wavelength data.Docket No.: 222204-2990

[0121] At block 514, the field strength calculator 144 calculates electric field. In particular, the field strength calculator 144 can apply configuration-specific transfer functions to convert wavelength shift measurements into calibrated field values in V / m.

[0122] At block 516, the data output interface 150 outputs measurement data (i.e., the output data 148 in FIG. 1) through the data output interface 150, providing real-time field measurements via the display 152, archiving data in the storage 154, and / or transmitting results through the external communication 156.

[0123] At block 518, the environmental control unit 150 can adjust for environmental conditions. This operation compensates for temperature variations, mechanical vibrations, or other environmental factors affecting sensor performance.

[0124] At block 520, the calibration module 158 provides calibration feedback, with the calibration path returning to block 506 to enable continuous or periodic recalibration during operation of the system 100. The calibration maintains measurement accuracy by compensating for drift, aging, or changing environmental conditions.

[0125] The method 500 can operate continuously, providing real-time electric field monitoring at multiple locations along the distributed fiber sensor.

[0126] FIG. 6 depicts a flowchart of a method 600 for fabricating and operating a dynamic electric field sensing system according to an example implementation. The method 600 can detect electric fields ranging from mV / m to kV / m through chemical modification of optical fibers and strategic material coupling.

[0127] At block 602, an optical fiber undergoes chemical treatment to enhance electric field sensitivity. The chemical treatment may include applying specialized coatings during the fiber drawing process, such as the polyimide coating 112 from the configuration options 110 that replaces standard acrylate protective layers. Alternatively, the chemical treatment may include post-fabrication modifications for creating the suspended-in-coating 118 configuration through hydrofluoric acid etching that selectively removes glass material while preserving surrounding polymer coatings. For hydrofluoric acid etching, parameters may include acid concentrations between 20 and 50 percent by weight, temperatures maintained between 20 and 40 degrees Celsius, and exposure durations ranging from 30 minutes to 4 hours depending on the desired diameter reduction from 125 pm to approximately 110 pm as shown in FIG. 2D. The chemical treatment may also include surface functionalization processes that modify the charge accumulationDocket No.: 222204-2990 properties of the fiber surface, such as plasma treatment, corona discharge, or chemical vapor deposition of charge-trapping layers.

[0128] At block 604, the chemically treated optical fiber couples with a selected material that enhances field detection capabilities, forming the sensing material layer 106 described with reference to FIG. 1. The coupling process depends on the material type and desired sensing mechanism corresponding to the configuration options 110. For electret materials, the coupling may include thermal bonding where the electret material melts and adheres to the fiber surface at temperatures between 100 and 200 degrees Celsius, creating a permanent charge layer. For the thermoplastic polyester elastomer buffer 116 configuration, the coupling may include extrusion coating where the thermoplastic elastomer flows around the standard fiber 204 during a continuous manufacturing process, building up the diameter to 900 pm while ensuring uniform thickness and adhesion. The coupling may also include mechanical assembly for the polystyrene tube 114 configuration where the fiber inserts into pre-formed tubes having an inner cavity with the air gap 206 as shown in FIG. 2B. In the suspended- in-coating 118 configuration, the coupling creates the air gap 206 between the etched fiber 208 and the fluoropolymer coating 210 through selective etching that removes fiber glass while preserving the outer coating structure.

[0129] At block 606, the system 100 monitors changes in the optical interrogation signal 124 transmitted through the fiber core with FBG 104. The monitoring employs the optical interrogation system 120, specifically the interrogator unit 130 described with reference to FIG. 1, which receives the reflected optical signal 128 containing wavelength information from FBGs. The monitoring process detects wavelength shifts on the order of picometers that correspond to mechanical strain induced by electric field interactions with the sensing material layer 106. For alternating electric fields at 60 Hz, the monitoring system may sample at rates exceeding 1 kHz to capture field-induced vibrations and their harmonics. The monitoring can distinguish between different vibration modes, including fundamental frequency responses where the fiber vibrates at the same frequency as the applied field, and frequency-doubled responses where electrostatic attraction occurs twice per field cycle, producing vibrations at 120 Hz for a 60 Hz applied field as demonstrated in FIG. 4D for the suspended-in-coating 118 configuration.Docket No.: 222204-2990

[0130] At block 608, the optical signal changes convert to quantitative electric field measurements using the signal processing unit 136. The conversion process applies calibration factors determined through controlled testing corresponding to the performance data shown in FIGS. 4A-4D. For the polyimide coating 112 configuration, a wavelength shift of 1 pm may correspond to an electric field of approximately 2.5 V / m as indicated by the data in FIG. 4A, establishing the transfer function of the sensor. The conversion employs the field strength calculator 144 described with reference to FIG. 1, which accounts for temperature effects using data from the environmental control unit 160, as a 1 degree Celsius temperature change can produce wavelength shifts comparable to those from electric fields. The DSP module 140 and frequency analyzer 146 may apply fast Fourier transform analysis to extract frequency components, lock-in amplification to enhance signal-to-noise ratio for specific frequencies, and time-domain averaging processed by the noise filter 142 to reduce random noise contributions.

[0131] At block 610, the method optionally applies specific treatments to enhance sensitivity beyond initial fabrication parameters. These treatments may include electrical conditioning where high-voltage fields up to 10 kilovolts per meter temporarily apply to the optical fiber sensor assembly 102, aligning dipoles or injecting charges that increase subsequent field responsiveness. Thermal annealing at temperatures between 80 and 150 degrees Celsius for durations of 1 to 24 hours can stabilize properties of the sensing material layer 106 and enhance charge retention in electret coatings. Humidity conditioning in controlled environments with relative humidity between 20 and 80 percent can modify surface charge accumulation properties, particularly for the polyimide coating 112 that absorbs moisture. Mechanical pre-straining of the fiber core with FBG 104 to tensions between 50 and 200 grams can increase sensitivity by modifying the fiber's mechanical response characteristics. Corona charging using point electrodes at potentials of 5 to 20 kV can implant charges into dielectric coatings, creating quasi-permanent electric fields that enhance sensitivity to external fields.

[0132] At block 612, the method adjusts for dielectric dipole responses based on the operating environment and field characteristics. In non-uniform electric fields where gradients exist, the dipole contribution F2 = p VE becomes significant and requires different signal processing approaches than uniform field sensing where Fi = QE dominates as described with reference to FIG. 1. The adjustment may include modifyingDocket No.: 222204-2990 parameters of the optical interrogation system 120 such as sampling rate of the interrogator unit 130 or wavelength range of the light source 122 based on the expected field frequencies and magnitudes. For multi-layer configurations combining elements from the configuration options 110, the adjustment accounts for different dielectric constants of each layer, as the polyimide coating 112 with dielectric constant of 3.4 and the fluoropolymer coating 210 with dielectric constant of 2.1 create complex field distributions. The adjustment may also compensate for environmental factors detected by the environmental control unit 160, such as atmospheric pressure changes that affect dimensions of the air gap 206 in the suspended-in-coating 118 configuration, or electromagnetic interference that can couple into the optical interrogation signal 124 through metallic components.

[0133] The method 600 enables fabrication of electric field sensors with sensitivities ranging from below 1 V / m for the optimized suspended- in-coating 118 configuration to several hundred V / m for robust implementations using the polystyrene tube 114 or the thermoplastic polyester elastomer buffer 116 configurations. The systematic approach ensures reproducible sensor performance across different fiber types, coating materials, and operating environments while maintaining compatibility with the distributed sensing architecture shown in FIGS. 3 A, 3B.

[0134] Methods for enhanced electric field detection may further include positioning at least one electrically conductive element proximate to the optical fiber sensor assembly. For single conductor implementations, a method can include grounding the conductive element to provide charge stabilization, reducing baseline drift and improving measurement stability (see FIG. 2E). For dual conductor implementations, a method can include applying an alternating voltage between first and second conductive elements to generate a reference electric field. For instance, a method may include characterizing baseline mechanical response patterns with only the reference field present, then detecting deviations from the baseline when external static or dynamic fields distort the reference field pattern. The voltage amplitude and frequency of the reference field can be adjusted based on the expected characteristics of external fields to be detected.

[0135] The disclosed dynamic electric field sensing technology provides optical fiber-based detection of alternating electric fields through vibration-induced mechanical strain, eliminating requirements for direct electrode contact, field gradients, orDocket No.: 222204-2990 piezoelectric materials that characterize conventional approaches. The sensing mechanism operates through lateral force generation when electric fields interact with dielectric or electret materials surrounding modified optical fibers, enabling detection in uniform fields where gradient-based sensors cannot function.

[0136] The technology offers multiple implementation pathways, from polyimide coatings achieving approximately 2.5 V / m sensitivity to suspended-in-coating configurations exhibiting frequency-doubled response for enhanced detection capabilities. The distributed sensing architecture enables simultaneous electric field monitoring at numerous locations along a single optical fiber through wavelength-division multiplexing of multiple fiber Bragg gratings, providing spatial field mapping without requiring separate sensors at each measurement point. The adaptable material configurations, combined with optical interrogation immunity to electromagnetic interference and capability for remote monitoring over kilometer-scale distances, enable deployment across diverse applications from power system diagnostics to perimeter security monitoring, with sensitivity ranges spanning mV / m to kV / m through appropriate configuration selection.

[0137] Numerical data related to electric field measurements, fiber dimensions, wavelength values, frequencies, temperatures, and other parameters may be expressed herein in a range format. Such range format should be interpreted flexibly to include not only the explicitly recited limits, but also all individual values and sub-ranges within that range as if each were explicitly recited. For example, an electric field detection range of “approximately 2.5 V / m to 200 V / m” includes individual measurements (such as 10 V / m, 50 V / m, 100 V / m) and sub-ranges (such as 5-25 V / m, 40-80 V / m) within the indicated range. Similarly, a fiber diameter range of “110 to 125 pm” includes all intermediate values. The term “approximately” can include traditional rounding according to measurement precision and typical variations in optical fiber manufacturing and electric field sensing applications.

[0138] The features, structures, and configurations described above may be combined in various implementations in any suitable maimer, and features discussed across different configurations are interchangeable where technically feasible. While specific details regarding fiber Bragg grating structures, coating materials, etching processes, and interrogation systems are provided for complete understanding, those skilled in optical sensing will appreciate that the electric field sensing technology may beDocket No.: 222204-2990 practiced with modifications to specific details. Alternative optical components, coating materials, chemical processes, or signal processing techniques may be employed. Well- known aspects of optical fiber technology, FBG interrogation, and signal processing are not exhaustively described to maintain focus on the novel aspects of electric field sensing.

[0139] Relative terms such as “surrounding,” “inner,” “outer,” “above,” and “below” describe component relationships as illustrated in the drawings for convenience. These spatial relationships may vary based on fiber orientation or system configuration. When a sensing material layer “surrounds” a fiber core, this may indicate direct contact with the fiber surface, indirect coupling through intermediate layers, or spatial proximity with an intervening gap, as in the suspended- in-coating configuration. The term “coupled” encompasses both direct physical contact and configurations where components interact through intermediate structures or fields.

[0140] The articles “a,” “an,” and “the” indicate presence of one or more elements unless context clearly dictates otherwise. Terms such as “include,” “comprise,” “have,” and “contain” are open-ended and encompass additional elements, materials, or processing steps beyond those explicitly listed, except as limited by the claims. For instance, an optical fiber sensor assembly that “includes” a fiber core with FBG and a sensing material layer may incorporate additional protective layers, strength members, or optical components.

[0141] Terms such as “first,” “second,” and “third” when applied to sensing regions, FBGs, or configuration options serve as identifiers rather than indicating quantity, preference, or sequence unless explicitly stated. Multiple FBGs along a fiber may be designated as first through nth gratings solely for reference purposes.

[0142] Disjunctive language such as “polyimide, polystyrene, or thermoplastic elastomer” presents options that may be implemented individually or in combination unless technically incompatible. An optical fiber sensor may employ one sensing material in certain regions and different materials in other regions, or may include hybrid configurations combining multiple materials.

[0143] The described implementations represent examples for understanding the principles of distributed electric field sensing using modified optical fiber structures. Variations and modifications may be made without departing from the core sensingDocket No.: 222204-2990 mechanisms and system architecture. Such modifications and variations fall within the scope of this disclosure as defined by the following claims.

Claims

Docket No.: 222204-2990CLAIMSWhat is claimed is:

1. A dynamic electric field sensing system, comprising: an optical fiber sensor assembly including: a fiber core with at least one fiber Bragg grating configured to reflect light at a characteristic wavelength, a sensing material layer surrounding the fiber core, wherein the sensing material layer vibrates in response to alternating electric fields; an optical interrogation system configured to detect at least one wavelength shift in light reflected from the at least one fiber Bragg grating, wherein the at least one wavelength shift results from mechanical strain induced by vibrations of the sensing material layer; and a signal processing unit configured to convert the at least one wavelength shift into electric field measurements.

2. The dynamic electric field sensing system of claim 1, wherein the vibrations result from lateral forces generated when the alternating electric fields interact with space charges or dielectric dipoles in the sensing material layer.

3. The dynamic electric field sensing system of claim 1, wherein the sensing material layer comprises a polyimide coating applied during fiber drawing.

4. The dynamic electric field sensing system of claim 1, wherein the sensing material layer comprises a polystyrene tube, and wherein the fiber core resides within an internal cavity of the polystyrene tube with an air gap therebetween.

5. The dynamic electric field sensing system of claim 1, wherein the sensing material layer comprises a thermoplastic polyester elastomer buffer.

6. The dynamic electric field sensing system of claim 1, wherein the fiber core is separated from a fluoropolymer coating by an air gap, wherein the air gap is formed byDocket No.: 222204-2990 chemical etching that reduces fiber diameter while leaving the fluoropolymer coating intact.

7. The dynamic electric field sensing system of claim 1, further comprising at least one grounded conductive element positioned proximate to the optical fiber sensor assembly.

8. The system of claim 1, further comprising first and second conductive elements and a voltage source configured to apply alternating voltage between the first and second conductive elements to generate a reference electric field.

9. The dynamic electric field sensing system of claim 1, wherein the signal processing unit comprises: a wavelength analyzer configured to extract wavelength shift data; a noise filter configured to remove environmental noise; and a field strength calculator configured to convert wavelength shifts to electric field values.

10. The dynamic electric field sensing system of claim 1, wherein the fiber core contains multiple fiber Bragg gratings at different positions, each reflecting at a different wavelength.

11. A method for detecting dynamic electric fields, comprising: positioning an optical fiber containing at least one fiber Bragg grating in an alternating electric field, wherein the optical fiber comprises a material layer that vibrates in response to the alternating electric field; transmitting light through the optical fiber; detecting at least one wavelength shift in light reflected from the at least one fiber Bragg grating, wherein the at least one wavelength shift results from mechanical strain induced by the vibrations; and converting the at least one wavelength shift to electric field measurements.Docket No.: 222204-299012. The method of claim 11, further comprising applying a polyimide coating to the optical fiber during fiber drawing to form the material layer.

13. The method of claim 11, further comprising etching the optical fiber with hydrofluoric acid to reduce fiber diameter while preserving a surrounding coating.

14. The method of claim 13, wherein the etching creates an air gap between the optical fiber and the surrounding coating.

15. The method of claim 11, wherein detecting the at least one wavelength shift comprises detecting vibrations at twice a frequency of the alternating electric field.

16. The method of claim 11, further comprising calibrating the optical fiber to correlate the at least one wavelength shift with at least one known electric field strength.

17. The method of claim 11, wherein the material layer comprises at least one of polyimide, polystyrene, or thermoplastic elastomer.

18. A suspended-in-coating electric field sensor, comprising: an optical fiber containing at least one fiber Bragg grating; a fluoropolymer coating surrounding the optical fiber; and an air gap between the optical fiber and the fluoropolymer coating formed by chemical etching, wherein the optical fiber vibrates within the fluoropolymer coating in response to alternating electric fields.

19. The suspended-in-coating electric field sensor of claim 18, wherein the optical fiber has been etched from a first diameter to a smaller second diameter using hydrofluoric acid.Docket No.: 222204-299020. The suspended-in-coating electric field sensor of claim 18, wherein electrostatic forces between the optical fiber and the fluoropolymer coating cause vibrations at twice a frequency of an applied alternating electric field.

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