Design and evaluation of a monostable symmetric piezoelectric energy harvester based on cantilever structure and magnetic excitation action.

This work proposes a monostable symmetric piezoelectric energy harvester based on the cantilever structure and magnetic excitation action (M-PEH). The governing equations of M-PEH are derived based on its kinematic properties. The intrinsic frequency of the piezoelectric cantilever beam was obtained by modal simulation. It has been demonstrated that the mode of arrangement of the magnetic poles has a significant effect on the output voltage of the energy harvester. The proposed M-PEH has four driving magnets with a mass of 6 g and a radial driving distance of 15 mm for more efficient energy harvesting. The experimental results show that the maximum voltage of the M-PEH with the double U-type rotor was 31.2 V at 240 rpm and 110 kΩ external resistance. The average power of the PEH with the double U-type rotor was 16.562 mW at a speed of 240 rpm with an outer resistance of 20 kΩ. The energy harvester with a double U-type rotor can realize a voltage output of not less than 10 V in the range of 60-300 rpm when the same poles of the tip magnets are arranged outward. The M-PEH can also easily light up LEDs or miniature electronic watches with speeds of 120 rpm and 240 rpm. This further proves that the proposed piezoelectric energy harvester (M-PEH) has a better energy harvesting effect and great potential for practical applications.

Water-durability and high-performance all-fiber humidity sensor using methyldiethanolamine-photopolymer-PDMS structure.

In the context of optical fiber humidity sensing, the long-term stability of sensors in high humidity and dew environments such as bathrooms or marine climates remains a challenge, especially since many humidity sensitive materials are water soluble. In this study, we use methyldiethanolamine, pentaerythritol triacrylate and Eosin Y to form a liquid-solid structure humidity sensitive component, the outermost layer is coated with PDMS passivating layer to ensure the stability and durability of the humidity sensor under the conditions of dew and high humidity. The liquid microcavity of the sensor consists of methyldiethanolamine-pentaerythritol triacrylate composite solution, and the sensitivity is several times higher than that of the liquid-free cavity sensor. The sensitivity of the sensor to temperature is verified (0.43 nm/°C and 0.30 nm/°C, respectively) and temperature crosstalk is compensated using a matrix. The compact structure allows for ultra-fast response (602 ms) and recovery time (349 ms). Our work provides a promising platform for efficient and practical humidity and other gas monitoring systems.

Refractive index SPR sensor with high sensitivity and wide detection range using tapered silica fiber and photopolymer coating.

This paper introduces a surface plasmon resonance (SPR) sensor using tapered silica fiber and photopolymer coating for enhanced refractive index (RI) detection. Tapering the silica fiber to a diameter of 10 µm ensures the evanescent wave leaks into a 1.8-µm thick photopolymer film, which increases the average waveguide RI and broadens the RI detection range accordingly. A 50-nm thick single-side gold film is coated on the photopolymer film, exciting SPR and causing less light transmission loss than a double-side gold film. The method avoids the complex microfabrication processes of conventional polymer optical fiber SPR sensors, while the waveguide RI can be controlled by altering the curing time of the photopolymer during fabrication. The sensor has an overall sensitivity of 3686.25 nm/RIU, enabling RI detection of 1.333 - 1.493. Moreover, the sensor has an ultrahigh sensitivity of 6422.9 nm/RIU in the RI range of 1.423 - 1.493. The temperature response is about 1.43 nm/°C at 20 - 50 °C, which has little impact on RI detection. Finally, we demonstrate that the sensor can grade the severity of hepatic steatosis by measuring the RIs of cytoplasm/triglyceride emulsions with superior sensing performance.

Wearable Fiber SPR Respiration Sensor Based on a LiBr-Doped Silk Fibroin Film.

Respiration is essential for supporting human body functions. However, a biocompatible fiber respiration sensor has rarely been discussed. In this study, we propose a wearable fiber surface plasmon resonance (SPR) respiration sensor using a LiBr-doped silk fibroin (SF) film. The SPR sensor monitors respiration by responding to airway humidity variation during inhalation and exhalation. We fabricated the SPR respiration sensor by depositing the core of a plastic-clad optical fiber with a gold film and an SF-LiBr composite film. The SF-LiBr composite film can absorb water through the interaction between water molecules and hydrogen bonds linking fibroin chains. Thus, humidity variation can change the SF-LiBr composite film's refractive index (RI), altering the phase-matching condition of the surface plasmon polaritons and shifting the SPR spectral dip. In experiments, we test the effect of the LiBr doping ratio on humidity response and confirm that the SF-22.1 wt % LiBr sensor has balanced performances. The SF-22.1 wt % LiBr sensor has a broad sensing range of 35-99% relative humidity (RH), a reasonable overall sensitivity of -6.5 nm/% RH, a fast response time of 135 ms, a quick recovery time of 150 ms, good reversibility, and good repeatability, which is capable of tracking different respiration states and patterns. Finally, we encapsulate this sensor in a conventional nasal oxygen cannula for wearable respiration monitoring, proving that the sensor is suitable for high-sensitivity, real-time, and accurate respiration monitoring.

Simultaneous Measurement of Microdisplacement and Temperature Based on Balloon-Shaped Structure.

An optical fiber sensor for the simultaneous measurement of microdisplacement and temperature based on balloon-shaped single-mode fibers cascaded with a fiber Bragg grating with two core-offset joints is proposed. The interference between the core mode and cladding mode is caused by the stimulation of the cladding mode by the core-offset joints' structure. The cladding of the core has a distinct refractive index, which causes optical path differences and interference. The balloon-shaped structure realizes mode selection by bending. As the displacement increases, the radius of the balloon-shaped interferometer changes, resulting in a change in the interference fringes of the interferometer, while the Bragg wavelength of the fiber grating remains unchanged. Temperature changes will cause the interference fringes of the interferometer and the Bragg wavelength of the fiber grating to shift. The proposed optical fiber sensor allows for the simultaneous measurement of microdisplacement and temperature. The results of the experiment indicate that the sensitivity of the interferometer to microdisplacement is 0.306 nm/µm in the sensing range of 0 to 200 µm and that the temperature sensitivity is 0.165 nm/°C, respectively. The proposed curvature sensor has the advantages of a compact structure, extensive spectrum of dynamic measurement, high sensitivity, and simple preparation, and has a wide range of potential applications in the fields of structural safety monitoring, aviation industry, and resource exploration.

Balloon-like optical fiber sensor for simultaneous displacement and temperature measurement based on an anti-resonance mechanism.

We propose and experimentally demonstrate a balloon-like optical fiber sensor with an anti-resonance mechanism for the simultaneous measurement of displacement and temperature. The sensor consists of a hollow-core fiber spliced between two single-mode fibers and bent into a balloon-like shape. The balloon-like structure not only increases the contrast of the spectral lines but also improves the displacement sensitivity. Theoretical and experimental results show that the incidence angle of light varies with the change in displacement, resulting in the variation of spectral intensity based on the anti-resonance mechanism. In addition, the temperature change causes the wavelength drift of the spectrum. Thus, by separately demodulating the intensity and wavelength of this sensor, it is possible to measure displacement and temperature simultaneously. The sensitivity of the displacement and temperature of the sensor is 0.043 dB/µm and 20.94 pm/°C, respectively. The proposed optical fiber sensor has a compact structure and simple preparation, making it an ideal choice for simultaneous measurement of displacement and temperature in the fields of micro-manufacturing and structural monitoring in the future.

Design and evaluation of a magnetically coupled piezoelectric energy harvester with parallel connection.

This work proposed a magnetically coupled piezoelectric energy harvester with parallel connections. The rectangular piezoelectric patch in the upper part of the device generates regular vibrations due to the nonlinear forces caused by magnetic coupling. The lower rectangular piezoelectric patch is deformed by contact collision excitation. The parallel connection effectively connects the two sets of piezoelectric patches together and fully exploits the performance of the piezoelectric energy harvester. The intrinsic frequency of the rectangular piezoelectric patch was simulated and verified experimentally. The rectangular piezoelectric patch generates a large vibration amplitude in high-speed operation due to its elasticity property. From the experimental results, it can be seen that the piezoelectric energy harvester can work well in different frequency bands. The parallel piezoelectric energy harvester with a three-contact rotor has a peak-to-peak voltage of 252 V at a speed of 120 r/min and 200 V at a speed of 240 r/min. The maximum voltage achieved by the piezoelectric energy harvester in parallel is 266 V at a speed of 180 r/min with a resistance of 1000 kΩ. The maximum voltage reached by a series-connected piezoelectric energy harvester is 256 V at a speed of 180 r/min and a resistance of 100 kΩ. The peak-to-peak power of the piezoelectric energy harvester connected in parallel is 0.313 W under a resistance of 100 kΩ and a speed of 180 r/min. Besides, the developed piezoelectric energy harvester can light up to 60 light-emitting diodes. Accordingly, the energy can be effectively harvested by the piezoelectric energy harvester and then supplied to the microelectronic device.

Fiber liquid-pressure sensor with high sensitivity and a wide measurement range using photopolymer.

This paper presents a novel fiber liquid-pressure sensor that uses photopolymer glue to generate Fabry-Perot (F-P) interference, resulting in high sensitivity and a wide measurement range. The sensor comprises a single-mode fiber and photopolymer glue; the latter adheres to the fiber's end face and is decomposed by a 405-nm laser to create an air channel with a diameter of 5.9 µm and a length of 50 µm. When the air channel is placed underwater, a 17.5-µm air cavity forms between the fiber core and the air-liquid boundary due to the pressure balance, creating an F-P interferometer. Based on experimental results, the sensor has an average pressure sensitivity of 5.68 nm/kPa over 0.49-2.94 kPa. The sensitivity can be maintained at this level across different pressure measurement ranges (up to about 500 kPa) by using a 980-nm laser's radiation pressure to reset the air-liquid boundary. Besides its high sensitivity and wide measurement range, the sensor's straightforward structure, durability, affordability, compactness, and simple construction make it an appealing choice for liquid pressure measurement applications in various fields.

Light-induced microdroplet suspension and directional self-driving.

In this Letter, we show stable suspension and directional manipulation of microdroplets on a liquid surface employing simple-mode fiber with a Gaussian beam at 1480-nm wavelength using the photothermal effect. The intensity of the light field generated by the single-mode fiber is used to generate droplets of different numbers and sizes. In addition, the effect of the heat generated at different heights from the liquid surface is discussed through numerical simulation. In this work, the optical fiber is not only free to move at any angle, solving the difficulty that a certain working distance is needed to generate microdroplets on free space, it can also allow the continuous generation and directional manipulation of multiple microdroplets, which is of tremendous scientific relevance and application value in promoting the development and cross-fertilization of life sciences and other interdisciplinary fields.

Development of a piezoelectric actuator based on stick-slip principle inspired by the predation of snake.

A new piezoelectric actuator based on the stick-slip working principle inspired by the predation of the snake is proposed and developed in this work. A lead zirconate titanate (PZT) stack is used and inserted into the stator with an asymmetric configuration. Then, the elongation of the PZT stack can be transmitted into the vertical and horizontal displacements on the driving foot. They are used to press and drive the slider, respectively. In this design, the motion of the actuator imitates the predation process of the snake. The principle of the proposed actuator is clarified in detail. The statics characteristics are conducted by using the FEM method. The dynamics model of the actuator was established to show the motion behavior of the slider in theory. Finally, the output characteristics of the developed piezoelectric actuator are tested. The results stated that this actuator obtained the maximum output speed of 11.44 mm/s under a voltage of 100 V and a frequency of 600 Hz. The output force of the developed actuator was 2.8N under the preload force of 3N. In conclusion, the feasibility of the proposed piezoelectric stick-slip type actuator inspired by the predation of the snake is verified.

All-optically modulated nonvolatile optical switching based on a graded-index multimode fiber.

Photonic switches have attractive application prospects in optical communication data networks that require dynamic reconfiguration. Integrating optical switching devices with optical fiber, the most widely deployed photonic technology platform, can realize signal transmission and processing in practical applications. Here, we demonstrate the multilevel optical switching using the phase-change material Ge2Sb2Te5 (GST) integrated on a graded-index multimode fiber. This switching process works by exploiting the significant difference in extinction coefficient between the crystalline state and the amorphous state of the GST. Using GST to achieve the switch function, no external energy source is needed to maintain the existing state of the switch, and the device is nonvolatile. This multi-level optical switch is an all-fiber integrated device. We apply GST to the end facets of the graded-index multimode fiber by magnetron sputtering, which is a reflective structure. A pulsing scheme is used to control the optical propagation state of the optical modulation signal to realize the switching function. It can store up to 11 non-volatile reliable and repeatable levels encoded by the pump source laser with a wavelength of 1550 nm. At the same time, the switching process between states is on the order of hundreds of nanoseconds. The present experimental results demonstrate the feasibility of 11 multilevel states in the field of optical fibers commonly used in communications. It can be well coupled with the all-fiber terminal device. It also shows that the device is still applicable in the 1525 nm∼1610 nm broadband range, promising for designing future multilevel photonic switches and memory devices.

All-fiber nonvolatile broadband optical switch using an all-optical method.

Optical switches based on phase change materials have enormous application potential in optical logic circuits and optical communication systems. Integration of all-optical switching devices with optical fibers is a promising approach for realizing practical applications in enabling the optical fiber to transmit and process signals simultaneously. We describe an all-fiber nonvolatile broadband optical switch using an all-optical method. We use a single optical pulse to modulate the phase change material deposited on the tapered fiber to achieve logical control of the transmitted light. The response time of our optical switch is 80 ns for SET and 200 ns for RESET. Our optical switches can operate in the C-band (1530-1565 nm). The optical switching contrast is 40%. Our approach paves the way for all-optical nonvolatile fiber optic communication.

Supercontraction of spider dragline silk for humidity sensing.

The spider dragline silk (SDS) has a supercontraction characteristic, which may cause the axial length of the SDS to shrink up to 50% when the SDS is wet or the relative humidity is higher than 58% RH. In this manuscript, we employ the supercontraction characteristic of the SDS to measure relative humidity. We connect two sections of a single-mode fiber (SMF) and a section of multimode fiber (MMF) with a sandwich structure to fabricate a single-mode-multimode-single-mode (SMS) interferometer. Then we fix the SDS on two SMFs to configure a bow-shaped sensing unit. The increase of environmental humidity will cause the supercontraction of the SDS, which will cause the change of the SDS length. The excellent mechanical properties of the SDS will generate a strong pulling force and change the bending of the arch, whose interference spectrum will shift correspondingly. In this way, we may perform relative humidity sensing. In the relative humidity range of 58% RH to 100% RH, the average sensitivity is as high as 6.213 nm/% RH, higher than most fiber-based humidity sensors. Compared with the traditional sensing structure with humidity-sensitive materials, the proposed sensor improves the sensitivity with environmental friendliness. The results suggest that the SDS can be used for high-sensitivity humidity sensors, and its degradability and biocompatibility also have a vast development space in biochemical sensors.

Light-induced micro-vibrator with controllable amplitude and frequency.

We propose and demonstrate a light-induced micro-vibrator that can perform an adjustable reciprocating vibration based on the Δα-typed photophoretic force. The vibration amplitudes and periods can be precisely controlled and modulated in real-time, and the maximum average restoring speed is as high as 23.26 µm/s. In addition, by using the self-healing properties of the Bessel-like beam, we achieve the simultaneous driving and modulating of three absorbing micro-vibrators. The proposed absorbing micro-vibrator can be used as a novel light-driven micromotor, which is considered to have potential application value in the field of targeted drug delivery, biosensing, and environmental detection.

Mode division multiplexing for multiple particles noncontact simultaneous trap.

We propose and demonstrate an optical trap on the basis of a normal single-mode fiber (SMF), which is used to trap two particles in the axial direction at the same time without contact based on mode division multiplexing technology. We design and manufacture a tapered fiber probe. The LP11 mode beam is excited by docking a normal SMF to a 980 nm SMF with a 2 µm offset. Then the beams of LP01 and LP11 are both transmitted in the fiber. To converge the LP11 mode beam, a SMF with a tapered end is used to produce a cage for trapping the first microparticle. This particle acts as a lens to converge the LP01 mode beam to trap the second microparticle. We verify the feasibility of trapping two particles simultaneously through simulation. With this function, the proposed optical trap is easier to manipulate different individual particles for comparison and testing, which can promote the development of the biological, biophysical, colloidal, and soft matter fields.

SPR sensor based on Bessel-like beam.

A proposal toward the enhancement in the sensitivity of a fiber-based surface plasma resonance (SPR) refractive index (RI) sensor is explored experimentally using a Bessel-like beam as the input source. We splice a section of single-mode fiber and a section of multimode fiber to construct the Bessel-like beam, which contains a series of concentric rings for the consistency of the resonance angle configuration to improve the performance of the SPR sensor. We fabricate a dual-truncated-cone (DTC) structure of the fiber to excite and receive the SPR signals. The larger the number of concentric rings, the higher the sensitivity. The number of concentric ring is determined by the length of the multimode fiber. When the grinding angle of the DTC-sensing probe is 15° and the length of the multimode fiber is 500 µm, the maximum testing average sensitivity is 6908.3 nm/RIU, which is more sensitive than the previous SPR sensor introduced by the Gaussian beam as the input source in multimode fibers.

Simultaneous measurement of temperature and refractive index based on a hybrid surface plasmon resonance multimode interference fiber sensor.

We propose and demonstrate a hybrid fiber-based sensor combining a multimode interference (MMI) structure and a surface plasmon resonance (SPR) structure for simultaneous measurement of temperature and refractive index (RI) of a liquid sample. We configure the MMI structure by connecting a single-mode fiber, a no-core fiber, and a single-mode fiber sequentially. We set up the SPR structure by coating a gold film with a thickness of 50 nm on the surface of the no-core fiber. We measure the sensitivity of RI and the temperature of the MMI and SPR structure, respectively. Then we obtain the coefficient matrix to simultaneously measure the temperature and RI of a liquid sample and obtain the highest RI sensitivity of 2061.6 nm/RIU and temperature sensitivity of 37.9 pm/°C. We verify the feasibility of the sensor in liquid alcohol. The testing results indicate that the proposed sensor and testing method are feasible, accurate, and convenient.

X-typed curvilinear transport of strongly absorbing particle in a dual-beam fiber optical trap.

We propose and demonstrate a novel approach to transport a strongly absorbing particle in an X-typed trajectory reciprocally in pure liquid glycerol based on a dual-beam optical fiber trap. We perform the X-typed light field by integrating a glass microsphere on the tip of a two-core fiber. The motion of the absorbing particle in pure liquid glycerol is dominated by the Δα-type photophoretic forces (FΔα). The incident laser power determines the direction of FΔα. Therefore, we may perform the reciprocating transport of the absorbing particle by changing and controlling the laser power. It is simple to manufacture the fiber probe and convenient to operate the transport of the microparticle. Our research expands the applications of absorbing particles in targeted drug delivery, biological sampling, and optically mediated particle clearing.

Super-low-power optical trapping of a single nanoparticle.

We propose and demonstrate a simple approach for noncontact, three-dimensional, and stable trapping of a single nanoparticle with a super-low incident laser power (0.7 mW) via the single-fiber optical tweezers. We splice a section of single-mode fiber and a section of multimode fiber to construct a Bessel-like beam, which produces narrow output laser beams. We integrate a high-refractive-index glass microsphere on the tip of the multimode fiber to focus the narrow output laser beams. The focused beams provide a nanoscale optical trap for a single nanoparticle (polystyrene sphere, diameter of 200 nm). This optical fiber probe has the advantages of high laser transmission efficiency, high spatial resolution, and minimum joule heating. The proposed approach extends the application potential of fiber-based optical manipulations, such as nanoparticle sorting, single-cell organelle analysis, and bio-sensing.

Optical attraction of strongly absorbing particles in liquids.

Although optical tweezers function well for the majority of transparent particles, the absorbing particles experience a considerably high absorption force that can destroy the stable optical traps. Photophoretic force is an alternative mechanism that can be used to trap the absorbing particles. The major difficulty that is associated with the utilization of photophoretic forces for trapping strongly absorbing particles in liquids is the presence of considerable absorption on the illuminated side; a positive photophoretic force is usually induced, thereby pushing away the absorbing particles from the high-intensity region of the laser source. Here, we demonstrate a novel principle for the optical trapping and manipulation of strongly absorbing particles by harnessing strong Δα-type photophoretic forces while suppressing their stochastic nature in pure liquid glycerol using a normal divergent Gaussian beam and a Bessel-like beam. Further, our approach expands the optical manipulation of strong absorbing particles to liquid media and provides position control over the trapped particles, including the optical transportation and pinpoint positioning of the 3-µm objects over a distance of a millimeter.