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Canalithiasis is a common vestibular system disorder, which may lead to a specific form of vertigo known as BPPV or top-shelf vertigo. In this paper, based on the actual geometric parameters of the human semicircular canal, we designed a 4-fold in vitro one-dimensional semicircular canal model using technologies such as 3D printing, image processing, and target tracking. We investigated the essential characteristics of the semicircular canal, such as the time constant of the cupula and the relationship between the number, density, and size of the canalith and the cupular deformation during canalith settlement. The results showed a linear relationship between the number and size of the canalith and the amount of cupular deformation. We also found that when the number of canaliths reached a particular scale, the interaction between the canaliths exerted an additional disturbance on the cupular deformation (‘Z’ twist). In addition, we explored the latency time of the cupula during canalith settlement. Finally, we verified that the canaliths had little effect on the frequency characteristics of the semicircular canal by a sinusoidal swing experiment. All the results validate the reliability of our 4-fold in vitro one-dimensional semicircular canal model.

Recently, the CNC/GEL (cellulose nanocrystals/gelatin) composite hydrogel has been used as a biomaterial for 3D printing of tissue engineering scaffolds. Rheological properties of hydrogel have been regarded as one of the most important factors affecting printing quality, especially the viscosity recover time. However, there is still a lack of comprehensive research on the rheology property of the CNC/GEL hydrogel in the process of 3D printing. In this study, the CNC was isolated from Humulus japonicus, and a CNC/GEL hydrogel system was prepared. The rheological properties of CNC/GEL hydrogel were evaluated using a rotary rheometer. The viscosity recovery time of the CNC/GEL hydrogel was measured using a special method. The optimal ratio of hydrogel was obtained by rheology experiment and mechanical test. The flow field distribution of the hydrogel in the flow passage of 3D printer was analyzed using fluent simulation. The rheological parameters of a hydrogel can be adjusted by changing the printing conditions. Thus, the effect of printing conditions on the formation of CNC/GEL filaments was also investigated. Finally, the biocompatibility of the printed CNC/GEL scaffold after crosslinking treatment was verified using CCK-8 and Hoechst 33342/PI double-staining assays. The present study shows a new approach for the analysis of rheological properties of CNC/GEL and also provides some suggestions for 3D printing of CNC/GEL scaffolds.

To date, there are three main hypotheses explaining why the human semicircular canals (HSCCs) cannot sense linear accelerations. To further study this issue, we designed a bionic ampulla (BA) instrumented with a symmetrical metal core polyvinylidene fluoride fiber as a bionic sensor, which imitates the structure and function of the human ampulla. The BA was confirmed to have a good sensing ability in experiments with a straight tube. Additionally, we designed a bionic semicircular canal model, a blocking model, and a square model. We compared the perception performance of these three models to test the “density hypothesis,” the “closed loop hypothesis,” and the “circular hypothesis.” The outcomes of these experiments verified the “density hypothesis” and “circular hypothesis,” but did not support the “closed loop hypothesis,” shedding light on why the HSCC is sensitive to angular acceleration, but not to linear acceleration.

A human vestibular system is a group of devices in the inner ear that govern the balancing movement of the head, in which the saccule is responsible for sensing gravity accelerations. Imitating the sensing principle and structure of the Sensory Hair (SH) cell in the saccule, a Bionic Sensory Hair (BSH) was developed, and 9 BSH arrays were arranged in the bionic macular at the bottom of the spherical shell to prepare a Bionic Saccule (BS). Based on the piezoelectric equation, the electromechanical theoretical models of the BSH cantilever and BS were deduced. They were subjected to impact oscillations using an exciter, and their output charges were analyzed to check their sensing ability. The results showed that BSH could sense its bending deflection, and the BS could sense its position change in the sagittal plane and in space. They exhibited a sensitivity of 1.6104 Pc s2/m and a fast response and similar sensing principles and low resonance frequency to those of the human saccule. The BS is expected to be used in the field of robotics and clinical disease diagnosis as a part of the artificial vestibular system in the future.

A BA (bionic ampulla) was designed and fabricated using an SMPF (Symmetric electrodes Metal core PVDF Fiber) sensor, which could imitate the sensory hair cells to sense the deformation of the cupula of the BA. Based on the BA, a bionic semicircular canal with membrane semicircular canal (MBSC) and a bionic semicircular canal without membrane semicircular canal (NBSC) were designed and fabricated. The biomechanical models of the MBSC and NBSC were established. The biomechanical models were verified through the perception experiments of the MBSC and the NBSC. The results showed that the SMPF could sense the deformation of the cupula. The MBSC and NBSC could sense the angular velocity and accelerations. What's more, it was speculated that in a human body, the endolymph probably had a function of liquid mass while the membranous semicircular canal and the cupula had a function similar to a spring in the human semicircular canal.

Semi-passive vibration control with the Synchronized Switching Damping on Inductor (SSDI) technique has attracted significant attention in recent years. However, the damping performance of the SSDI technique will be decreased by the lag in detection of switching time. In order to detect switching time without lag, the paper proposes a self-powered semi-passive vibration damping system based on self-sensing approach. In the proposed technique, the switching control signal is obtained by properly processing the voltage of one piezoelectric element which is also used for vibration damping at the same time. Compared with other self-powered SSDI techniques, the proposed approach can detect switching time without lag, while keeping simplicity of implementation with a small number of piezoelectric elements. The proposed technique is also experimentally implemented by a self-powered circuit in the paper. The theoretical analysis, the experimental validation and the drawback of the proposed technique are discussed in the paper.

Crickets, similar to some other insects, have highly sensitive filiform hairs on their cerci that can detect miniscule changes in airflow. This study imitates the perception mechanism of these filiform sensory hairs of crickets by designing and fabricating a Multi-electrode Metal Core Piezoelectric Fiber (MMPF)-based airflow sensor. Four longitudinal conductive sheets were coated symmetrically on their surfaces with Metal-core Piezoceramic Fibers (MPF). The four fan-shaped piezoelectric ceramics with surface electrode covers were polarized. After successful polarization, the cantilevered MMPF could be used as an airflow sensor. The four electrodes on the surface were symmetrically divided into two groups. Therefore, two signals can be produced by a single fiber sensor. The theoretical model of an MMPF airflow sensor has been established. The model indicates that the ratio of the two signals is equivalent to the tangent of the airflow angle. Furthermore, the sum of the squares of the two signals is not dependent on the angle, but reflects the velocity of the airflow. Therefore, a single MMPF can be used to measure both the direction and amplitude for a given airflow. The theoretical model has been confirmed via experimental measurements.

This paper proposes a new energy harvesting architecture that optimizes the energy conversion under broadband vibrations, which is called adaptive synchronized switch harvesting (ASSH) technique. This technique is derived from the enhanced synchronized switch harvesting (ESSH) technique and based on a new and effective switch control law, which can prevent the switch in energy transferring circuit from over-frequent on-and-off and accordingly enhance the extracted power under multimode vibration. Compared with the ESSH technique, theoretical and experimental results demonstrate the new technique can improve electromechanical conversion efficiency when the piezoelectric energy harvester is excited under two-mode vibration, especially in the case of higher vibration amplitude of the second mode. The extracted power with the new technique is more than three times the ESSH technique in the case of the exciting signal of amplitude ratio (3:6). Furthermore, a self-powered circuit which implements the technique (ASSH) is proposed, which validates that the new technique can be truly self-powered, thus addressing the issue of harvesting environmental energy by autonomous devices.

In recent years, semi-passive vibration damping using Synchronized Switching Damping on Inductor (SSDI) technique has been intensively investigated. In this paper, a self-powered semi-passive vibration damping system based on self sensing approach is proposed and investigated. With the self-sensing technique, the same piezoelectric element can be used as a sensor and an actuator. Compared with the other self-powered SSDI approaches, this technique can not only detect switching time without lag, but also reduce the number of piezoelectric elements. Furthermore, a low-power circuit for semi-passive piezoelectric vibration control based on self-sensing technique is designed. Experimental results demonstrate that the self-sensing SSDI system has good damping performance. The performance of the self-sensing SSDI system is also compared with the externally powered system.

Energy harvesting systems are interesting for use in remote power supplies. Many such systems utilize the motion or deformation associated with vibration, converting the mechanical energy to electrical energy, and supplying power to other electronic devices. In terms of energy harvesting from mechanical vibrations, piezoelectric conversion has received much attention as it can directly convert applied strain energy into useable electric energy and easily be integrated into a microsystem. The removal of mechanical energy from a vibrating structure necessarily leads to a damping effect. This paper addresses the damping associated with a piezoelectric energy harvesting system which is called the adaptive synchronized switching harvesting (ASSH) technique. Furthermore, a self-powered circuit which implements the technique (ASSH) is proposed, which validates that the new technique can be truly self-powered. Experimental results show that the vibration amplitudes of the first two modes are reduced by about 9.27 dB and 0.96 dB in the case of the exciting signal of same amplitude ratio (3:3), respectively. Compared with other self-powered vibration damping technique, this technique not only shows its robustness, but also harvests the energy and supply power to other electronic circuits.

We fabricated a sensitive air flow detector that mimic the sensing mechanism found at the tail of some insects. [see Y. Yang, A. Klein, H. Bleckmann and C. Liu, Appl. Phys. Lett. 99(2) (2011); J. J. Heys, T. Gedeon, B. C. Knott and Y. Kim, J. Biomech. 41(5), 977 (2008); J. Tao and X. Yu, Smart Mat. Struct. 21(11) (2012)]. Our bionic airflow sensor uses a polyvinylidene difluoride (PVDF) microfiber with a molybdenum core which we produced with the hot extrusion tensile method. The surface of the fiber is partially coated with conductive silver adhesive that serve as surface electrodes. A third electrode, the metal core is used to polarize polyvinylidene difluoride (PVDF) under the surface electrodes. The cantilever beam structure of the prepared symmetric electrodes of metal core piezoelectric fiber (SMPF) is used as the artificial hair airflow sensor. The surface electrodes are used to measure output voltage. Our theoretical and experimental results show that the SMPF responds fast to air flow changes, the output charge has an exponential correlation with airflow velocity and a cosine relation with the direction of airflow. Our bionic airflow sensor with directional sensing ability can also measure air flow amplitude. [see H. Droogendijk, R. G. P. Sanders and G. J. M. Krijnen, New J. Phys. 15 (2013)]. By using two surface electrodes, our sensing circuit further improves sensitivity.

The metal core piezoelectric fiber (MPF) is one of the new typical sensors and actuators. The metal core is precisely located at the center of the fiber and surrounded by the ceramic. The metal core can be used as an electrode and the other electrode is coated on the outer surface of the fiber. When an external voltage is applied between the electrodes, the electric field is assumed to be in the radial direction of the fiber. Hence the direction of the polarization in the polarized ceramic is radial. Because two electric electrodes are available in each fiber, a single fiber can be used as a sensor or an actuator. When MPF is mounted on the surface of a cantilever beam, an axial strain will be generated on the fiber as a dynamic load is applied at the tip of the beam. And a dynamic electric charge will be generated on the electrodes of MPF because of the piezoelectric effect. Based on the piezoelectric constitutive equations, the mechanical model of the sensor is established. When the tip of cantilever beam subjected to a dynamic lateral force, the analytical expressions of the electric charges generated on the electrodes of MPF have been derived from the constitutive equations. The electric charges of the MPF with platinum core or wolfram core, and different metal core to fiber radius ratios were calculated, when the tip of cantilever beam subjected to a dynamic lateral force. The effects of the radius ratio on the electric charge of the MPF sensor are investigated based on the numerical results of these equations. The dynamic vibration sensing properties of MPF sensor were experimentally studied. The first mode natural frequencies of cantilever beam is obtained using MPF sensor. The results show that the sensor can give a high sensitivity for the vibration of cantilever beam.

The response principle of piezoelectric ceramic fibers with metal core (MPF) to Lamb waves is studied, and the factors which influence the response are analyzed, also verification experiments are carried out. First, the strain response principle of piezoelectric ceramic fibers with metal core to Lamb waves is studied, and the voltage formula of the response of fibers with metal core to Lamb waves is deduced; then, the MPF response formula to random angle A0 mode Lamb waves is deduced from the strain response principle, and the parallel incidence response formula as a special case is also deduced. The deduced result is validated through pencil-lead breaks performed on an aluminum plate in the end. The comparison between predictions and measurement is rather satisfactory in terms of both relative amplitude and spectral shape.

To track prey or avoid predators, many arthropods can detect variations in airflow and pressure gradients using an array of very thin and sensitive filiform hairs. In this study, metal core piezoelectric poly(vinylidene fluoride) (PVDF) fibers were prepared to mimic such hair sensors. The flexibility of the fibers was very good, which was helpful for overcoming the typical brittleness of piezoelectric ceramic fibers. At the same time, the diameter of the fibers was very small (down to 50 μm in diameter). In order to mimic the insects' hairs to the maximum extent, which was expected to greatly improve the sensitivity of such PVDF fiber-based sensors, a feasible process to prepare and extract electrodes on the surface of the fibers had to be developed. Compared with stainless steel filament-core fibers, the molybdenum filament-core PVDF fibers were easy to stretch. The molybdenum filament was then covered by a cylindrical PVDF layer with a diameter of 400 μm. One half of the longitudinal surface of the fibers was spray-coated with a conductive silver adhesive. The metal core was then used as one electrode, and the conductive silver adhesive was used as the other electrode. After polarization, a single metal-core PVDF fiber could be used as an airflow sensor. The surface structure and the sections of the PVDF fiber were analyzed by scanning electron microscopy. The results of the mechanical stretching tests showed that the metal core greatly enhanced the mechanical properties of the PVDF fibers. X-ray diffraction revealed that the greater the stretching ratio, the higher the α-to-β-phase conversion rate during the preparation of the PVDF fibers. A single metal-core PVDF fiber was used as a bionic airflow sensor, and a mechanical model of this sensor was derived. The airflow sensing capability of the PVDF fiber was experimentally confirmed in a miniature wind tunnel. The results showed that a cantilevered metal-core PVDF fiber is capable of detecting the range and direction of the surrounding airflow variations. The experimental results also verified the theoretical model.