A Piezoelectrically Driven Microrobot Using a Novel Monolithic Spatial Parallel Mechanism as Its Hip Joint

Inspired by the fast,agile movements of insects,we present a 1.9 g,4.5 cm in length,piezoelectrically driven,quadrupedal microrobot.This microrobot uses a novel spatial parallel mechanism as its hip joint,which consists of two spatially orthogonal slider-crank linkages.This mechanism maps two inputs of two independent actuators to the decoupled swing and lift outputs of a leg,and each leg can produce the closed trajectories in the sagittal plane necessary for robot motion.Moreover,the kinematics of the transmission are analyzed,and the parameters of the flexure hinges are designed based on geometrical constraints and yield conditions.The hip joints,legs and exoskeletons are integrated into a five-layer standard laminate for monolithic fabrication which is composed of two layers of carbon fiber,two layers of acrylic adhesive and a polyimide film.The measured output force(15.97 mN)of each leg is enough to carry half of the robot’s weight,which is necessary for the robot to move successfully.It has been proven that the robot can successfully perform forward and turning motions.Compared to the microrobot fabricated with discrete components,the monolithically fabricated microrobot is more capable of maintaining the original direction of locomotion when driven by a forward signal and has a greater speed,whose maximum speed is 25.05 cm/s.

A Sub-100 mg Electromagnetically Driven Insect-inspired Flapping-wing Micro Robot Capable of Liftoff and Control Torques Modulation

Inspired by the unique,agile and efficient flapping flight of insects,we present a novel sub-100 mg,electromagnetically driven,tailless,flapping-wing micro robot.This robot utilizes two optimized electromagnetic actuators placed back to back to drive two wings separately,then kinematics of each wing can be independently controlled,which gives the robot the ability to generate all three control torques of pitch,roll and yaw for steering.To quantify the performance of the robot,a simplified aerodynamic model is used to estimate the generated lift and torques,and two customized test platforms for lift and torque measurement are built for this robot.The mean lift generated by the robot is measured to be proportional to the square of the input voltage amplitude.The three control torques are measured to be respectively proportional to three decoupled parameters of the control voltages,therefore the modulation of three control torques for the robot is independent,which is helpful for the further controlled flight.All these measured results fit well with the calculated results of the aerodynamic model.Furthermore,with a total weight of 96 mg and a wingspan of 3.5 cm,this robot can generate sufficient lift to take off.

On-chip chalcogenide microresonators with low-threshold parametric oscillation

Chalcogenide glass (ChG) is an attractive material for highly efficient nonlinear photonics,which can cover an ultrabroadband wavelength window from the near-visible to the footprint infrared region. However,it remains a challenge to implement highly-efficient and low-threshold optical parametric processes in chip-scale ChG devices due to thermal and light-induced instabilities as well as a high-loss factor in ChG films. Here,we develop a systematic fabrication process for high-performance photonic-chip-integrated ChG devices,by which planarintegrated ChG microresonators with an intrinsic quality (Q) factor above 1 million are demonstrated. In particular,an in situ light-induced annealing method is introduced to overcome the longstanding instability underlying ChG film. In high-Q ChG microresonators,optical parametric oscillations with threshold power as low as 5.4 mW are demonstrated for the first time,to our best knowledge. Our results would contribute to efforts of making efficient and low-threshold optical microcombs not only in the near-infrared as presented but more promisingly in the midinfrared range.

Microbubble resonators combined with a digital optical frequency comb for high-precision air-coupled ultrasound detectors

Fast and sensitive air-coupled ultrasound detection is essential for many applications such as radar,ultrasound imaging,and defect detection.Here we present a novel approach based on a digital optical frequency comb(DOFC)technique combined with high-Q optical microbubble resonators(MBRs).DOFC enables precise spectroscopy on resonators that can trace the ultrasound pressure with its resonant frequency shift with femtometer resolution and sub-microsecond response time.The noise equivalent pressure of air-coupled ultrasound as low as 4.4 m Pa∕pHz is achieved by combining a high-Q(~3×10~7)MBR with the DOFC method.Moreover,it can observe multi-resonance peaks from multiple MBRs to directly monitor the precise spatial location of the ultrasonic source.This approach has a potential to be applied in 3 D air-coupled photoacoustic and ultrasonic imaging.

Dynamics of exciton energy renormalization in monolayer transition metal disulfides

Fundamental understandings on the dynamics of charge carriers and excitonic quasiparticles in semiconductors are of central importance for both many-body physics and promising optoelectronic and photonic applications.Here,we investigated the carrier dynamics and many-body interactions in two-dimensional(2D)transition metal dichalcogenides(TMDs),using monolayer WS2 as an example,by employing femtosecond broadband pump-probe spectroscopy.Three time regimes for the exciton energy renormalization are unambiguously revealed with a distinct red-blue-red shift upon above-bandgap optical excitations.We attribute the dominant physical process in the three typical regimes to free carrier screening effect,Coulombic exciton-exciton interactions and Auger photocarrier generation,respectively,which show distinct dependence on the optical excitation wavelength,pump fluences and/or lattice temperature.An intrinsic exciton radiative lifetime of about 1.2 picoseconds(ps)in monolayer WS2 is unraveled at low temperature,and surprisingly the efficient Auger nonradiative decay of both bright and dark excitons puts the system in a nonequilibrium state at the nanosecond timescale.In addition,the dynamics of trions at low temperature is observed to be significantly different from that of excitons,e.g.,a long radiative lifetime of^108.7 ps at low excitation densities and the evolution of trion energy as a function of delay times.Our findings elucidate the dynamics of excitonic quasiparticles and the intricate many-body physics in 2D semiconductors,underpinning the future development of photonics,valleytronics and optoelectronics based on 2D semiconductors.

Screening for musculoskeletal system malformations and birth injuries in newborns:Results of a screening program in two hospitals in Shenzen,China

Importance:There are a variety of musculoskeletal malformations and injuries that can occur in newborns.These can be a significant cause of perinatal death or a reason for miscarriage and can lead to long-term functional issues if not managed appropriately.There is no systematic and well-established screening program for neonatal musculoskeletal malformations and injuries in China now.Objective:To report the incidence and types of congenital musculoskeletal malformations in two hospitals in Shenzhen City,to explore and discuss the details of the screening procedure and improve future prevention and treatment.Methods:From October 2013 to May 2014,2564 one-day-old newborns were screened by a pediatric orthopedic physical examination,in combination with ultrasonography when required,and the incidence and variety of diseases were recorded statistically.Results:Among 2564 screened newborns,the following musculoskeletal conditions were identified:congenital muscular torticollis(CMT)(seven cases,0.27%),hip subluxation(four cases,0.16%),hip dysplasia(47 cases,1.83%),congenital talipes equinovarus(CTEV)(two cases,0.08%),congenital talipes calcaneovalgus(15 cases,0.58%),polydactyly(nine cases,0.35%),syndactyly(one case,0.04%),and spinal hemivertebra(one case,0.04%).Additionally,there were five(0.19%)neonates with birth injuries.Interpretation:It is feasible to carry out neonatal screening and identification of musculoskeletal malformations and birth injuries in China.This is helpful as timely detection and early intervention for many of these conditions can avoid permanent functional impairment in these children.

Perovskite polariton parametric oscillator

Optical parametric oscillators(OPOs)have been widely applied in spectroscopy,squeezed light,and correlated photons,as well as quantum information.Conventional OPOs usually suffer from a high power threshold limited by weak high-order nonlinearity in traditional pure photonic systems.Alternatively,polaritonic systems based on hybridized exciton–photon quasi-particles exhibit enhanced optical nonlinearity by dressing photons with excitons,ensuring highly nonlinear operations with low power consumption.We report an on-chip perovskite polariton parametric oscillator with a low threshold.Under the resonant excitation at a range of angles,the signal at the ground state is obtained,emerging from the polariton-polariton interactions at room temperature.Our results advocate a practical way toward integrated nonlinear polaritonic devices with low thresholds.

Microcavity exciton polaritons at room temperature

The quest for realizing novel fundamental physical effects and practical applications in ambient conditions has led to tremendous interest in microcavity exciton polaritons working in the strong coupling regime at room temperature.In the past few decades,a wide range of novel semiconductor systems supporting robust exciton polaritons have emerged,which has led to the realization of various fascinating phenomena and practical applications.This paper aims to review recent theoretical and experimental developments of exciton polaritons operating at room temperature,and includes a comprehensive theoretical background,descriptions of intriguing phenomena observed in various physical systems,as well as accounts of optoelectronic applications.Specifically,an in-depth review of physical systems achieving room temperature exciton polaritons will be presented,including the early development of ZnO and GaN microcavities and other emerging systems such as organics,halide perovskite semiconductors,carbon nanotubes,and transition metal dichalcogenides.Finally,a perspective of outlooking future developments will be elaborated.

Near-infrared carbon-implanted waveguides in Tb^3+doped aluminum borosilicate glasses

Ion implantation has played a unique role in the fabrication of optical waveguide devices.Tb'-doped aluminum borosilicate(TDAB)glass has been considered as an important magneto-optical material.In this work,near-infrared waveguides have been manufactured by the(5.5+6.0)MeV C^3+ion implantation with doses of(4.0+8.0)×10^13 ions·cm^-2 in the TDAB glass.The modes propagated in the TDAB glass waveguide were recorded by a prism-coupling system.The finite-difference beam propagation method(FD-BPM)was carried out to simulate the guiding characteristics of the TDAB glass waveguide.The TDAB glass waveguide allows the light propagation with a single-mode at 1.539μm and can serve as a potential candidate for future waveguide isolators.