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Keywords = broadband guided waves

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18 pages, 5657 KiB  
Article
Guided Lamb Wave Array Time-Delay-Based MUSIC Algorithm for Impact Imaging
by Fei Zheng and Shenfang Yuan
Sensors 2024, 24(6), 1882; https://doi.org/10.3390/s24061882 - 15 Mar 2024
Viewed by 1675
Abstract
Composite materials, valued in aerospace for their stiffness, strength and lightness, require impact monitoring for structural health, especially against low-velocity impacts. The MUSIC algorithm, known for efficient directional scanning and easy sensor deployment, is gaining prominence in this area. However, in practical engineering [...] Read more.
Composite materials, valued in aerospace for their stiffness, strength and lightness, require impact monitoring for structural health, especially against low-velocity impacts. The MUSIC algorithm, known for efficient directional scanning and easy sensor deployment, is gaining prominence in this area. However, in practical engineering applications, the broadband characteristics of impact response signals and the time delay errors in array elements’ signal reception lead to inconsistencies between the steering vector and the actual signal subspace, affecting the precision of the MUSIC impact localization method. Furthermore, the anisotropy of composite materials results in time delay differences between array elements in different directions. If the MUSIC algorithm uses a fixed velocity value, this also introduces time delay errors, further reducing the accuracy of localization. Addressing these challenges, this paper proposes an innovative MUSIC algorithm for impact imaging using a guided Lamb wave array, with an emphasis on time delay management. This approach focuses on the extraction of high-energy, single-frequency components from impact response signals, ensuring accurate time delay measurement across array elements and enhancing noise resistance. It also calculates the average velocity of single-frequency components in varying directions for an initial impact angle estimation. This estimated angle then guides the selection of a specific single-frequency velocity, culminating in precise impact position localization. The experimental evaluation, employing equidistantly spaced array elements to capture impact response signals, assessed the effectiveness of the proposed method in accurately determining array time delays. Furthermore, impact localization tests on reinforced composite structures were conducted, with the results indicating high precision in pinpointing impact locations. Full article
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15 pages, 8181 KiB  
Article
Multi-Order Mode Excitation and Separation of Ultrasonic Guided Waves in Rod Structures Using 2D-FFT
by Gang Li, Jing Zhang, Juke Cheng, Kang Wang, Dong Yang and Ye Yuan
Sensors 2023, 23(20), 8483; https://doi.org/10.3390/s23208483 - 16 Oct 2023
Cited by 4 | Viewed by 1877
Abstract
The ultrasonic guided wave technique is extensively used for nondestructive structural testing, and one of the key steps is to extract a single mode with certain purity from multi-order mixed modes. In this paper, the propagation of ultrasonic guided waves in the cylindrical [...] Read more.
The ultrasonic guided wave technique is extensively used for nondestructive structural testing, and one of the key steps is to extract a single mode with certain purity from multi-order mixed modes. In this paper, the propagation of ultrasonic guided waves in the cylindrical rod is simulated first; the appropriate broadband excitation signal is selected to excite the multi-order modes in a specific frequency range; and the time–space signal containing multi-order modes is converted to the frequency-wavenumber domain signal by two-dimensional Fourier transform. In the frequency-wavenumber domain, the frequency-wavenumber ridge is extracted from the multi-mode frequency-wavenumber domain based on the dynamic programming method, and then the time-domain signal corresponding to a single mode can be reconstructed. By comparing the excited multi-order mode and the separated single mode with the theoretical results, it is observed that the two results are consistent. Thus, the employed mode-excitation method can accurately excite the multi-order modes in rod structures. Furthermore, the proposed method enables the separation of a single-mode wave with high purity, providing a foundation for future utilization of isolated modes. Full article
(This article belongs to the Section Physical Sensors)
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12 pages, 23476 KiB  
Article
Low-Profile Millimeter-Wave Metasurface-Based Antenna with Enhanced Bandwidth
by Ke Han, Yuchu Yan, Ze Yan and Chongwei Wang
Micromachines 2023, 14(7), 1403; https://doi.org/10.3390/mi14071403 - 10 Jul 2023
Cited by 5 | Viewed by 2697
Abstract
A millimeter-wave broadband metasurface-based antenna with a low profile is proposed. In order to guide the mode excitation, the characteristic mode analysis (CMA) is used for the design and optimization of the proposed antenna. Four sets of coplanar patches with different dimensions on [...] Read more.
A millimeter-wave broadband metasurface-based antenna with a low profile is proposed. In order to guide the mode excitation, the characteristic mode analysis (CMA) is used for the design and optimization of the proposed antenna. Four sets of coplanar patches with different dimensions on a thin printed circuit board are used to generate four adjacent broadside modes, which are directly fed by a coaxial probe. Then, to expand low-frequency bandwidth, a new resonant mode is introduced by etching slots on the parasite patch. Meanwhile, the extra mode introduced does not significantly change the radiation performance of the original modes. Moreover, dual slots are etched on the mid patch fed by the coaxial probe, which moves the orthogonal modes of the chosen modes out of the operating band to reduce cross-polarization levels. The proposed antenna realized 25.02 % (30–38.58 GHz) impedance bandwidth with dimensions of 1.423×1.423×0.029λ0 3 (λ0 is the wavelength at 34 GHz in free space), and the realized gain in the band is 8.35–11.3 dB. Full article
(This article belongs to the Special Issue Advanced Antennas for Wireless Communication Systems)
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18 pages, 7017 KiB  
Article
Intercoupling of Cascaded Metasurfaces for Broadband Spectral Scalability
by Shaolin Zhou, Liang Liu, Qinling Deng, Shaowei Liao, Quan Xue and Mansun Chan
Materials 2023, 16(5), 2013; https://doi.org/10.3390/ma16052013 - 28 Feb 2023
Cited by 4 | Viewed by 2641
Abstract
Electromagnetic metasurfaces have been intensively used as ultra-compact and easy-to-integrate platforms for versatile wave manipulations from optical to terahertz (THz) and millimeter wave (MMW) ranges. In this paper, the less investigated effects of the interlayer coupling of multiple metasurfaces cascaded in parallel are [...] Read more.
Electromagnetic metasurfaces have been intensively used as ultra-compact and easy-to-integrate platforms for versatile wave manipulations from optical to terahertz (THz) and millimeter wave (MMW) ranges. In this paper, the less investigated effects of the interlayer coupling of multiple metasurfaces cascaded in parallel are intensively exploited and leveraged for scalable broadband spectral regulations. The hybridized resonant modes of cascaded metasurfaces with interlayer couplings are well interpreted and simply modeled by the transmission line lumped equivalent circuits, which are used in return to guide the design of the tunable spectral response. In particular, the interlayer gaps and other parameters of double or triple metasurfaces are deliberately leveraged to tune the inter-couplings for as-required spectral properties, i.e., the bandwidth scaling and central frequency shift. As a proof of concept, the scalable broadband transmissive spectra are demonstrated in the millimeter wave (MMW) range by cascading multilayers of metasurfaces sandwiched together in parallel with low-loss dielectrics (Rogers 3003). Finally, both the numerical and experimental results confirm the effectiveness of our cascaded model of multiple metasurfaces for broadband spectral tuning from a narrow band centered at 50 GHz to a broadened range of 40~55 GHz with ideal side steepness, respectively. Full article
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15 pages, 7669 KiB  
Article
Ultrasonic Testing of Mechanical Changes in a Water-Filled Pipe with Multi-Mode and Broadband Signals and Two-Level Compensation
by Taeho Ju and Alp T. Findikoglu
Sensors 2022, 22(22), 8647; https://doi.org/10.3390/s22228647 - 9 Nov 2022
Cited by 3 | Viewed by 2474
Abstract
Ultrasonic testing (UT) has been widely used for the Nondestructive Evaluation (NDE) of pipes due to its many favorable characteristics. However, one of the main challenges in the general use of UT for real-world pipelines is the sensitivity of this method to environmental [...] Read more.
Ultrasonic testing (UT) has been widely used for the Nondestructive Evaluation (NDE) of pipes due to its many favorable characteristics. However, one of the main challenges in the general use of UT for real-world pipelines is the sensitivity of this method to environmental and operational condition changes. This paper proposes a new UT method with enhanced compensation for environmental effects and operational condition changes. In particular, the effectiveness of the new method is tested in the presence of temperature variations, and changes in water flow rate inside a stainless-steel pipe. The proposed UT method uses multi-mode and broadband guided ultrasonic waves in the pipe walls, excited and received by single-element ultrasonic sensors that are spatially separated, forming a measurement zone between any pair of such transmit and receive sensors. Amplitude changes, time shifts, and frequency content variations in the ultrasonic signal due to temperature changes and water flow are evaluated and compensated for reliable UT of mechanical changes in the pipe. It is observed that spurious effects of water flow on ultrasonic response, if not properly compensated, can dominate over effects due to actual mechanical changes, but such liquid-boundary effects can be compensated effectively by the proposed time- and frequency-filtering method. Full article
(This article belongs to the Section Physical Sensors)
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11 pages, 3774 KiB  
Article
Coupled Plasmon Wave Dynamics beyond Anomalous Reflection: A Phase Gradient Copper Metasurface for the Visible to Near-Infrared Spectrum
by Hosna Sultana
Optics 2022, 3(3), 243-253; https://doi.org/10.3390/opt3030024 - 15 Jul 2022
Cited by 4 | Viewed by 2949
Abstract
In nanoscale photonic devices, the demand for multifunctionality from 2D metasurface optics has increased rapidly. To explore the required fine-tuning in the design metrics, we reinvestigated the trapezoid-shape copper metasurface using finite-difference time-domain simulation to efficiently utilize linearly polarized light for two different [...] Read more.
In nanoscale photonic devices, the demand for multifunctionality from 2D metasurface optics has increased rapidly. To explore the required fine-tuning in the design metrics, we reinvestigated the trapezoid-shape copper metasurface using finite-difference time-domain simulation to efficiently utilize linearly polarized light for two different functionalities. From the plasmonic band structure, we could see how the degree of asymmetry in the geometry affected the efficient resonance coupling of the traveling plasmonic modes, along with the different types of mode hybridization profiles that were related to the nanoantenna’s geometric shape. By tuning the nanoantenna’s length, we could excite the effective plasmon mode that was supported by this configuration and guide surface waves unidirectionally from the normal incidence free-space light within the visible to infrared range. The directed surface plasmon polaritons had both antisymmetric and symmetric modes that oscillated between the top and bottom surfaces of the continuous metal layer, depending on the nanoantenna’s length and wavelength. This proposed copper metasurface was optimized for a far-field application of broadband (600–900 nm) anomalous beam steering for an average of 60% efficiency with a maximum angle of 64°. This work offers more understanding of a metasurface being implemented in small plasmonic devices, waveguide mode controlling and beam steering with wavelength-dependent functionalities. Full article
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16 pages, 8422 KiB  
Article
A Compact Broadband Analog Complex Correlator with High Correlation Efficiency for Passive Millimeter-Wave Imaging System
by Wangdong He, Anyong Hu, Xi Chen, Jianhao Gong and Jungang Miao
Electronics 2022, 11(14), 2165; https://doi.org/10.3390/electronics11142165 - 11 Jul 2022
Cited by 2 | Viewed by 1976
Abstract
In this paper, the design, fabrication, and measurement of a compact broadband (4–8 GHz) analog complex correlator for a passive millimeter-wave imaging system are presented. To achieve high sensitivity and high integration of the imaging system, the wideband and miniaturization of the correlator [...] Read more.
In this paper, the design, fabrication, and measurement of a compact broadband (4–8 GHz) analog complex correlator for a passive millimeter-wave imaging system are presented. To achieve high sensitivity and high integration of the imaging system, the wideband and miniaturization of the correlator are required. The correlator achieves wide bandwidth by using the add-and-square method, which is composed of a six-port circuit and a detection circuit. In order to realize the miniaturization of the correlator, the six-port circuit is realized on the chip base on the 0.15-μm gallium arsenide (GaAs) process. The influence of mismatch of the detection circuit that employs zero-bias Schottky diodes on the correlator is also analyzed to guide the design of the correlator. The measurement results of the designed chips and detector are consistent with the simulation result. Finally, a Sweep-frequency test is applied to the designed correlator, and the measurement results show that, within the frequency range of 4–8 GHz, the correlation amplitude fluctuation is less than 1.9 dB and the correlation efficiency is larger than 99%, which reveal that the correlator is suited for interferometric passive millimeter-wave imaging applications. Full article
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11 pages, 5879 KiB  
Article
Broadband Acoustic Sensing with Optical Nanofiber Couplers Working at the Dispersion Turning Point
by Xu Gao, Jiajie Wen, Jiajia Wang and Kaiwei Li
Sensors 2022, 22(13), 4940; https://doi.org/10.3390/s22134940 - 30 Jun 2022
Cited by 9 | Viewed by 2577
Abstract
Herein, a broadband ultrasensitive acoustic sensor based on an optical nanofiber coupler (ONC) attached to a diaphragm is designed and experimentally demonstrated. The ONC is sensitive to axial strain and works as the core transducing element to monitor the deformation of the diaphragm [...] Read more.
Herein, a broadband ultrasensitive acoustic sensor based on an optical nanofiber coupler (ONC) attached to a diaphragm is designed and experimentally demonstrated. The ONC is sensitive to axial strain and works as the core transducing element to monitor the deformation of the diaphragm driven by acoustic waves. We first theoretically studied the sensing property of the ONC to axial strain and the deformation of the diaphragm. The results reveal that ONC working at the dispersion turning point (DTP) shows improved ultra-sensitivity towards axial strain, and the largest deformation of the circular diaphragm occurs at the center. Guided by the theoretical results, we fabricated an ONC with a DPT at 1550 nm, and we fixed one end of the ONC to the center of the diaphragm and the other end to the edge to construct the acoustic sensor. Finally, the experimental results show that the sensor can achieve accurate measurement in the broadband acoustic wave range of 30~20,000 Hz with good linearity. Specifically, when the input acoustic wave frequency is 120 Hz, the sensitivity reaches 1923 mV/Pa, the signal-to-noise ratio is 42.45 dB, and the minimum detectable sound pressure is 330 μPa/Hz1/2. The sensor has the merits of simple structure, low cost, and high performance, and it provides a new method for acoustic wave detection. Full article
(This article belongs to the Special Issue Micro-/Nano-Fiber Sensors and Optical Integration Devices)
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13 pages, 8787 KiB  
Article
Impact Damage Detection Using Chirp Ultrasonic Guided Waves for Development of Health Monitoring System for CFRP Mobility Structures
by Langxing Tan, Osamu Saito, Fengming Yu, Yoji Okabe, Taku Kondoh, Shota Tezuka and Akihiro Chiba
Sensors 2022, 22(3), 789; https://doi.org/10.3390/s22030789 - 20 Jan 2022
Cited by 13 | Viewed by 3161
Abstract
When impact damage occurs in carbon fiber-reinforced plastic (CFRP) structures, it is barely visible but may cause significant degradation in the mechanical properties of the structure. Hence, a structural health monitoring (SHM) system that can be installed in CFRP mobility structures and is [...] Read more.
When impact damage occurs in carbon fiber-reinforced plastic (CFRP) structures, it is barely visible but may cause significant degradation in the mechanical properties of the structure. Hence, a structural health monitoring (SHM) system that can be installed in CFRP mobility structures and is sensitive to impact damage is needed. In this study, we attempted to establish an SHM system based on ultrasonic guided waves, which are generated by inputting a broadband chirp signal into a film-like piezoelectric actuator. The relationship between impact damage size and maximum time-of-flight (ToF) delay was investigated for three types of CFRP plates: woven, non-woven, and hybrid laminates. As a result, it was found that the maximum ToF delay increased linearly with an increase in the damage size for all CFRP laminates. Moreover, the amplitude of the A0 mode was found to be significantly affected by the damage length in the wave propagation direction. Thus, this SHM method using chirp ultrasonic waves can quantitatively evaluate the size and extent of the impact damage in CFRP laminates. Full article
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20 pages, 25537 KiB  
Article
Guided Waves for Damage Detection in Complex Composite Structures: The Influence of Omega Stringer and Different Reference Damage Size
by Jochen Moll, Christian Kexel, Jens Kathol, Claus-Peter Fritzen, Maria Moix-Bonet, Christian Willberg, Marcel Rennoch, Michael Koerdt and Axel Herrmann
Appl. Sci. 2020, 10(9), 3068; https://doi.org/10.3390/app10093068 - 28 Apr 2020
Cited by 39 | Viewed by 7432
Abstract
The third dataset dedicated to the Open Guided Waves platform aims at carbon fiber composite plates with an additional omega stringer at constant temperature conditions. The two structures used in this work are representative for real aircraft components. Comprehensive measurements were recorded in [...] Read more.
The third dataset dedicated to the Open Guided Waves platform aims at carbon fiber composite plates with an additional omega stringer at constant temperature conditions. The two structures used in this work are representative for real aircraft components. Comprehensive measurements were recorded in order to study (I) the impact of the omega stringer on guided wave propagation, and (II) elliptical reference damages of different sizes located at three separate positions on the structure. Measurements were recorded for narrowband excitation (5-cycle toneburst with varying carrier frequencies) and broadband excitation (using chirp waveforms). The paper presents the results of a technical validation including numerical modelling, and enables further research, for example related to probability of detection (POD) analysis. Full article
(This article belongs to the Special Issue Guided Wave-Based Damage Identification for Composite Structures)
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11 pages, 1282 KiB  
Article
Terahertz Hollow Core Antiresonant Fiber with Metamaterial Cladding
by Jakeya Sultana, Md. Saiful Islam, Cristiano M. B. Cordeiro, Alex Dinovitser, Mayank Kaushik, Brian W.-H. Ng and Derek Abbott
Fibers 2020, 8(2), 14; https://doi.org/10.3390/fib8020014 - 17 Feb 2020
Cited by 28 | Viewed by 7656
Abstract
A hollow core antiresonant photonic crystal fiber (HC-ARPCF) with metal inclusions is numerically analyzed for transmission of terahertz (THz) waves. The propagation of fundamental and higher order modes are investigated and the results are compared with conventional dielectric antiresonant (AR) fiber designs. Simulation [...] Read more.
A hollow core antiresonant photonic crystal fiber (HC-ARPCF) with metal inclusions is numerically analyzed for transmission of terahertz (THz) waves. The propagation of fundamental and higher order modes are investigated and the results are compared with conventional dielectric antiresonant (AR) fiber designs. Simulation results show that broadband terahertz radiation can be guided with six times lower loss in such hollow core fibers with metallic inclusions, compared to tube lattice fiber, covering a single mode bandwidth (BW) of 700 GHz. Full article
(This article belongs to the Special Issue Microstructured Optical Fibers and Applications)
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18 pages, 3028 KiB  
Article
Broadband Linear High-Power Amplifier Based on the Parallel Amplification Architecture for Electromagnetic Ultrasonic Guided Wave
by Jinjie Zhou and Yang Zheng
Sensors 2019, 19(13), 2924; https://doi.org/10.3390/s19132924 - 2 Jul 2019
Cited by 5 | Viewed by 5657
Abstract
The linear power amplifier with high-output power in the broadband frequency is the critical component required by exciting the electromagnetic acoustic transducer (EMAT) to generate ultrasonic guided wave (UGW). The methods to realize the output of a high-power signal in the linear amplification [...] Read more.
The linear power amplifier with high-output power in the broadband frequency is the critical component required by exciting the electromagnetic acoustic transducer (EMAT) to generate ultrasonic guided wave (UGW). The methods to realize the output of a high-power signal in the linear amplification mode and to expand the bandwidth at high-output power are seldom reported. To solve these problems, a power amplifier with differential structure is developed by using the parallel amplification architecture and the broadband feedback circuits. The proposed power amplifier uses a differential structure to suppress the even harmonic waves and remove the disruptions. Each branch of the differential structure consists of five linear power amplifier modules with output terminals connected in parallel to increase the output power. Also, the negative voltage feedback is used to extend the bandwidth of the power amplifier. The experimental results show that the −3 dB bandwidth of the amplifier is from 40 kHz to 2.5 MHz, and the transient output power is greater than 1 kW. The power amplifier can drive the EMATs to generate ultrasonic guided waves. Because of the high-output power and good linearity, the proposed power amplifier has excellent potential for EMAT UGW applications. Full article
(This article belongs to the Section Physical Sensors)
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11 pages, 3406 KiB  
Article
Design and Fabrication of Moth-Eye Subwavelength Structure with a Waist on Silicon for Broadband and Wide-Angle Anti-Reflection Property
by He Lin, Mingzhao Ouyang, Bingxu Chen, Qifan Zhu, Jinshuang Wu, Nan Lou, Litong Dong, Zuobin Wang and Yuegang Fu
Coatings 2018, 8(10), 360; https://doi.org/10.3390/coatings8100360 - 9 Oct 2018
Cited by 24 | Viewed by 8080
Abstract
Reflection loss on the optical component surface is detrimental to performance. Several researchers have discovered that the eyes of moths are covered with micro- and nanostructured films that reduce broadband and wide-angle light reflection. This research proposes a new type of moth-eye subwavelength [...] Read more.
Reflection loss on the optical component surface is detrimental to performance. Several researchers have discovered that the eyes of moths are covered with micro- and nanostructured films that reduce broadband and wide-angle light reflection. This research proposes a new type of moth-eye subwavelength structure with a waist, which is equivalent to a gradient refractive index film layer with high–low–high hyperbolic-type fill factor distribution. The diffraction order characteristics of a moth-eye subwavelength structure are first analyzed using a rigorous coupled wave analysis. The moth-eye structural parameters are optimized within the spectral range of 2–5 μm using the finite-difference time-domain method. The experimental fabrication of the moth-eye structure with a waist array upon a silicon substrate is demonstrated by using three-beam laser interferometric lithography and an inductively coupled plasma process. The experimental and simulation results show good agreement. The experimental results show that the reflectivity of the moth-eye structure with a waist is less than 1.3% when the incidence angle is less than 30°, and less than 4% when the incidence angle is less than 60°. This research can guide the development of AR broadband optical components and wide-angle applications. Full article
(This article belongs to the Special Issue Applications of Optical Thin Film Coatings)
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15 pages, 4289 KiB  
Article
Dispersed Sensing Networks in Nano-Engineered Polymer Composites: From Static Strain Measurement to Ultrasonic Wave Acquisition
by Yehai Li, Kai Wang and Zhongqing Su
Sensors 2018, 18(5), 1398; https://doi.org/10.3390/s18051398 - 2 May 2018
Cited by 19 | Viewed by 5670
Abstract
Self-sensing capability of composite materials has been the core of intensive research over the years and particularly boosted up by the recent quantum leap in nanotechnology. The capacity of most existing self-sensing approaches is restricted to static strains or low-frequency structural vibration. In [...] Read more.
Self-sensing capability of composite materials has been the core of intensive research over the years and particularly boosted up by the recent quantum leap in nanotechnology. The capacity of most existing self-sensing approaches is restricted to static strains or low-frequency structural vibration. In this study, a new breed of functionalized epoxy-based composites is developed and fabricated, with a graphene nanoparticle-enriched, dispersed sensing network, whereby to self-perceive broadband elastic disturbance from static strains, through low-frequency vibration to guided waves in an ultrasonic regime. Owing to the dispersed and networked sensing capability, signals can be captured at any desired part of the composites. Experimental validation has demonstrated that the functionalized composites can self-sense strains, outperforming conventional metal foil strain sensors with a significantly enhanced gauge factor and a much broader response bandwidth. Precise and fast self-response of the composites to broadband ultrasonic signals (up to 440 kHz) has revealed that the composite structure itself can serve as ultrasound sensors, comparable to piezoceramic sensors in performance, whereas avoiding the use of bulky cables and wires as used in a piezoceramic sensor network. This study has spotlighted promising potentials of the developed approach to functionalize conventional composites with a self-sensing capability of high-sensitivity yet minimized intrusion to original structures. Full article
(This article belongs to the Special Issue Selected Papers from IWSHM 2017)
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