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• A highly sensitive magnetostrictive sensor is achieved by combination of MZI and Terfenol-D. • The highest sensitivity reaches -1.113nm/mT. • The Terfenol-D provides a protection for fiber sensor. • Low cost simple structure. In this article, we propose and experimentally testified a highly sensitive magnetostrictive sensor with well-sealed and sensitivity tunability. The sensor is consisted of a Terfenol-D cylinder and a fiber-optic Mach-Zehnder interferometer (MZI) affixed inside the cylinder. As an energy transducer, the Terfenol-D converts the external magnetic field into stress, which is applied to the fiber structure inside the cylinder. Here, the inside MZI is composed by symmetrical-polished plane (SPP) and inclined structure. With alternative depth of the SPP, the sensitivity tunability can be realized. The experimental results present that the sensor displays linear response to magnetic field and temperature, which adapts to simultaneous measurement. The highest magnetic field sensitivity reaches −1.113 nm/mT. Furthermore, the cylinder structure provides well-sealed property for inside sensor, which indicates actual application in future. [ABSTRACT FROM AUTHOR]

Efficient CO 2 electrodes require optimized catalytic activity and a delicate electrode structure. However, it is often insufficient to consider only a single factor when constructing a high-performance electrode. In this study, we elaborately prepare the freestanding Fe-doped CoP catalysts on N-doped carbon cloth (Fe-CoP@N-CC) substrates, which synergistically realizes electronic structure tuning of the catalysts and electrode structure modification. The experimental and theoretical calculations reveal that the electrode structure, consisting of fully covered nanowires on an N-CC skeleton, promotes mass transfer and accommodates products. The introduction of N atoms in Fe-CoP@N-CC leads to increased defects and strong Co–N–C bonds at the interface, enhancing interfacial electron transfer. Furthermore, Fe doping optimizes the electronic structure of Fe-CoP@N-CC. This synergistic enhancement facilitates the kinetics of both CO 2 reduction reaction (CO 2 RR) and CO 2 evolution reaction (CO 2 ER), resulting in the formation of large-size spherical morphologies following the solution pathway. The improved electrocatalytic performance of Fe-CoP@N-CC electrodes was demonstrated by their high discharge capacity of 4127 mAh g−1 and cycling stability of 446 h in Li–CO 2 batteries. These findings emphasize the significance of compatibility between electrode structure and catalytic activity in the design of CO 2 electrode. • Fe-doped CoP on N-doped carbon cloth (Fe-CoP@N-CC) substrates were fabricated. • Enlarged reaction active area and promoted mass transfer. • Strong Co–N–C bonds at the interface can facilitate interfacial electron transfer. • Enhanced CO 2 RR and CO 2 ER kinetics are realized. • Optimizing morphology and discharge product pathways. [ABSTRACT FROM AUTHOR]

We propose and experimentally investigate a spiral-polished single-multi-single-mode (SP-SMS) fiber sensor for the simultaneous measurement of strain and temperature. This special spiral shape on a multimode fiber is fabricated by a high-frequency CO2 laser, which excites higher order cladding modes in the interference process and leads to high strain sensitivity. Experimental results show that the strain sensitivity for the proposed structure in the transmission spectrum of two marked interference dips is − 17 pm/με and − 1 pm/με in the range of 0–600 με. Moreover, temperature sensitivities of 10 pm/℃ and 13.3 pm/℃ are obtained in the range of 30–150 ℃. Furthermore, the proposed sensor is inexpensive, is easy to fabricate and has a compact structure. [ABSTRACT FROM AUTHOR]

In this paper, a novel torsion sensor based on Mach-zehnder interferometer (MZI) is proposed and demonstrated. The proposed sensor is fabricated by the single-mode fiber (SMF) and multi-mode fiber (MMF) shear splicing, further employing CO 2 laser to modulate the MMF surface into triangular prism form. And compare the number of different triangular prism pairs structure on torsion sensitivity. By increasing the number of triangular prism pairs effectively improve the torsion sensitivity. The experimental results show that in the range of 0–9.617 rad/m, the highest sensitivity fiber sensor can be obtained with a sensitivity of 3.3133 nm/(rad/m). Meanwhile, the temperature characteristic of the sensor is investigated, which presents a sensitivity of 21.67 pm/℃ in the range from 30 ℃ to 100 ℃. Therefore, the temperature crosstalk is 0.0065 (rad/m)/℃, which results in a low temperature crosstalk. In addition, the structure also has the advantages of low cost and simple manufacturing process. [Display omitted] • A high sensitive torsion optical fiber sensor is achieved by using CO 2 laser polished method. • The highest torsion sensitivity of the UITP-SMS reaches 3.3133 nm/(rad/m). • A low-temperature crosstalk is obtained, which is 0.0065 (rad/m)/℃. • Low cost, simple structure and easy fabrication. [ABSTRACT FROM AUTHOR]

This paper presents a systematic review concentrating on the design and extensive applications of optical fiber sensors based on embedded long-period fiber gratings (LPFGs). First of all, the preparation procedures and the working principle is introduced in detail. Then, the applications of different types of sensors based on the embedded LPFG are investigated, which is explored to detect physical parameters such as temperature, strain, refractive index (RI), bending, torsion, liquid level. Also, the method for enhancing sensing performance is presented. Compared with LPFGs proposed in these years, the embedded LPFGs sensors with high selectivity and flexibility have proved to behave excellent sensing characteristic, especially in the recognition in bending and RI measurement. Furthermore, the sensors are briefly described according to the design scheme and sensing performance. Finally, the drawbacks of the sensors are analyzed and the future prospect is discussed. [ABSTRACT FROM AUTHOR]

• A highly sensitive strain optical fiber sensor is achieved by means of side-polishing and high-temperature oxyhydrogen flame heating. • The highest strain sensitivity of the M-LPFG reaches to −19.05 pm/ με. • A compact length is obtained, which is 5 mm. • Low cost, simple structure and easy fabrication. Optical sensors for strain measurement have been significantly concerned due to their unique characteristics of quick response, anti-electromagnetic interference and compact size. In this article, a brand-new type of "M"-shaped core long-period fiber grating (M-LPFG) based on core-modulated method is proposed and experimentally testified. By means of side-polishing and high-temperature oxyhydrogen flame heating, the cladding of fiber tends to be circular and the core will bend slightly towards the polished area. The micro-bending core is suffered strong refractive index modulation and this phenomenon also excites the evanescent field adequately. By analyzing the simulated light transmission and the transmission spectrum, considerable degree of micro-bending core is achieved. In the experiment, the proposed sensor with 10 periods (5 mm) displays a high strain sensitivity of −19.05 pm/ με with range of 0–500 με, and the temperature sensitivity of which is obtained as 51.16 pm/°C. Due to relatively small influence on cladding and self-circularity of structure, the M-LPFG possesses a high mechanical strength. With the above advantages of high sensitivity, compact size, low-cost and strong mechanical strength, the method of fabricating M-LPFG has great potential in strain measurement. [ABSTRACT FROM AUTHOR]

We propose and experimentally demonstrate an optical fiber torsion sensor based on symmetrically polished single-multi-single mode (SP-SMS) fiber structure. The polished structure enhances the torsion response effectively, which is fabricated by a high-frequency CO 2 laser. Experimental results show that the high sensitivity of the proposed torsion sensor reaches 1.032 nm/(rad m−1) in the range from − 10.261 rad/m to 10.261 rad/m. Meanwhile, the temperature response of the sensor is also investigated, which is 21 pm/°C in the range from 30 °C to 150 °C. Moreover, the structure has the features of low cost, simple fabricating method and small temperature crosstalk. Schematic diagram of the symmetrically polished SMS fiber structure (SP-SMS). The geometrical shape of the sensor is prepared by a high-frequency CO 2 laser, which enhances the torsion sensitivity of the structure. The structure achieves a high sensitivity of 1.032 nm/(rad m−1). Meanwhile, small temperature-torsion crosstalk of 0.03 (rad m−1)/°C is achieved. The fabricating method of the structure has the advantages of is non-contact and scalable. Hence, the proposed structure provides a new idea to the design of the fiber torsion sensor. [Display omitted] • The highest torsion sensitivity of the SP-SMS reaches to 1.032 nm/(rad m−1). • The low temperature-torsion crosstalk is obtained, which is 0.03 (rad m−1)/°C. • Low cost, compact structure and easy fabrication. [ABSTRACT FROM AUTHOR]

• A new type of waved core fiber structure is proposed and experimentally demonstrated. • The highest sensitivity of the sensor reaches 125.5 pm/με within the measuring range of 0–200 με. • Simultaneous measurement for strain and temperature can be achieved. • Compact in length and high mechanical strength. Strain and temperature, as two important parameters to evaluate structural health, is increasingly paid numerous attentions for years. In this article, we developed and experimentally tested a highly sensitive strain sensor based on SMS structure with waved core multi-mode fiber (MMF), which has ability to monitor temperature simultaneously. By introducing a section of bent-core fiber into the portion of MMF, the higher-order cladding mode is excited to enhance the sensitivity. Furthermore, the portion of bent-core displays significant influence on effective refractive index (ERI) of the MMF section as strain applied, which brings about higher strain sensitivity. The experimental results display that the highest sensitivity of the sensor reaches 125.5 pm/με within 0–200 με and the measuring range achieves 0–1200 με. By demodulating two dips, simultaneous measurement for strain and temperature is achieved by solving the equation matrix. This simple method displays minor influence on mechanical property and enhances the strain sensitivity considerably. It is strongly believed the proposed sensor brings about a competitive choice in engineering fields. [ABSTRACT FROM AUTHOR]

In this paper, we developed and experimentally evaluated a new type of long-period fiber grating. This structure is fabricated by CO 2 laser polishing and subsequent heating with an oxyhydrogen flame. Firstly, a single-mode fiber is produced using a high-frequency CO 2 laser to form periodic trapezoidal structures. It is then heated with an oxyhydrogen-flame-based fiber optic tapering system to bend the core slightly toward the polished area. The micro-bent cores exhibit strong refractive index modulation, which make the core-modulated LPFG more sensitive to tensile strain. The experimental results show that the proposed sensor exhibits a strain sensitivity as high as 30.43 pm/ μ ε over the 0–100 μ ε range and a temperature sensitivity of 9.29 pm/ ∘ C. Based on the results of a general theoretical analysis and simulations, we attribute the threshold point of its strain sensitivity to the degree of micro-bending of the core. Furthermore, the structure is low cost and compact and exhibits high mechanical strength and thus can be used in a variety of applications in several fields. • A new method for fabricating LPFGs is proposed and experimentally demonstrated. • The microbent core exhibits strong refractive index modulation, which makes the core-modulated LPFG more sensitive to tensile strain. • The strain sensitivity of the fabricated CM-LPFG is as high as 30.43 pm/ μ ε for the 0–100 μ ε. • Low cost, compact size, high mechanical strength. [ABSTRACT FROM AUTHOR]

The upper shift of the d-band level of Fe active sites was realized by regulating electronic structure of NiFe 2 O 4 /MoS 2 heterostructure, fundamentally improving the electrocatalytic performance of NiFe 2 O 4 /MoS 2. [Display omitted] The electronic structure of cathode catalysts dominates the electrochemistry reaction kinetics in lithium-oxygen batteries. However, conventional catalysts perform inferior intrinsic activity due to the low d-band level of the active sites makes it difficult to bond with the reaction intermediates, which results in poor electrochemical performance of lithium-oxygen batteries. Herein, NiFe 2 O 4 /MoS 2 heterostructures are elaborately constructed to reach an electronic state balance for the active sites, which realizes the upper shift of the d-band level and enhanced adsorption of intermediates. Density functional theory calculation suggests that the d-band center of Fe active sites on the heterostructure moves toward the Fermi level, demonstrating the heterointerface engineering endows Fe active sites with high d-band level by the transfer and balance of electron. As a proof of concept, lithium-oxygen battery catalyzed by NiFe 2 O 4 /MoS 2 exhibits a large specific capacity of 21526 mA h g−1 and an extended cycle performance for 268 cycles. Moreover, NiFe 2 O 4 /MoS 2 with strong adsorption to intermediates promotes the uniform growth of discharge products, which is favor of the reversible decomposition during cycling. This work presents the energy band regulation of the active sites in heterostructure catalysts has great feasibility for enhancing catalytic activities. [ABSTRACT FROM AUTHOR]

• A high sensitive curvature optical fiber sensor is achieved by using CO 2 laser polished method. • The highest bending sensitivity of the AP-LPFG reaches to 30.85 nm/m−1. • A compact length is obtained, which is 7.39 mm. • Low cost, simple structure and easy fabrication. In this paper, we experimentally propose and theoretically investigate a two-dimensional vector curvature sensor based on asymmetrically polished long period fiber grating (AP-LPFG). This sensor is fabricated by a high-frequency CO 2 laser in order to polish periodic asymmetrical V-shaped grooves on a single mode fiber (SMF). Such grooves efficiently enhances the bending sensitivity of sensor and shorten the length of the structure to 7.39 mm. Experimental results show that the sensitivity of AP-LPFG reaches 30.85 nm/m−1 in the direction of the X-axis and −0.97 nm/m−1 in the direction of the Y-axis. Meanwhile, the temperature response of AP-LPFG is carried out, which is 76 pm/℃ in range of 30-160℃. Moreover, the AP-LPFG has the features of compact length and simple structure, which shows the potential in curvature sensing. [ABSTRACT FROM AUTHOR]

A simple fiber sensor for dual-parameters measurement of curvature and temperature is proposed and demonstrated, which is prepared by sandwiching a section of deformed multimode fiber (D -MMF) into two single-mode fibers (SMFs). This structure is processed by CO 2 laser etching and hydrogen-oxygen flame melting method. The micro-bent core of MMF constructs in-fiber composite interference, which effectively improves the bending sensitivity of the structure. It is found that the dips at 1310 nm and 1376 nm in the interference spectrum show different curvature and temperature responses. The curvature sensitivities of two dips are up to − 23.2 nm/m−1 and − 11.64 nm/m−1 in the range of 0–1.1733 m−1. Moreover, the temperature sensitivities of two monitored dips are − 52.1 pm/°C and − 19.7 pm/°C, respectively. [Display omitted] • A high sensitive curvature optical fiber sensor is achieved by using CO 2 laser polished method and hydrogen-oxygen flame heating stretching. • The highest curvature sensitivity of the D-MMF reaches to − 23.2 nm/m−1 • Dual parameters measurement of curvature and temperature. • Low cost, compact structure and easy fabrication. [ABSTRACT FROM AUTHOR]