查看更多>>摘要：Wearable flexible sensors attached on the neck have been developed to measure the vibration of vocal cords during speech.However,high-frequency attenuation caused by the frequency response of the flexible sensors and absorption of high-frequency sound by the skin are obstacles to the practical application of these sensors in speech capture based on bone conduction.In this paper,speech enhancement tech-niques for enhancing the intelligibility of sensor signals are developed and compared.Four kinds of speech enhancement algorithms based on a fully connected neural network(FCNN),a long short-term memory(LSTM),a bidirectional long short-term memory(BLSTM),and a convolutional-recurrent neural network(CRNN)are adopted to enhance the sensor signals,and their performance after deployment on four kinds of edge and cloud platforms is also investigated.Experimental results show that the BLSTM performs best in improving speech quality,but is poorest with regard to hardware deployment.It improves short-time objective intelligibility(STOI)by 0.18 to nearly 0.80,which corresponds to a good intelligibility level,but it introduces latency as well as being a large model.The CRNN,which improves STOI to about 0.75,ranks second among the four neural networks.It is also the only model that is able to achieves real-time processing with all four hardware platforms,demonstrating its great potential for deployment on mobile platforms.To the best of our knowledge,this is one of the first trials to systematically and specifically develop processing techniques for bone-conduction speed signals captured by flexible sensors.The results demonstrate the possibility of realizing a wearable lightweight speech collection system based on flexible vibration sensors and real-time speech enhancement to compensate for high-frequency attenuation.
查看更多>>摘要：The World Health Organization has declared COVID-19 a pandemic.The demand for devices or systems to diagnose and track COVID-19 infections noninvasively not only in hospitals but also in home settings has led to increased interest in consumer-grade wearables.A common symptom of CO VID-19 is dyspnea,which may manifest as an increase in respiratory and heart rates.In this paper,a novel piezoelectric strain sensor is presented for real-time monitoring of respiratory and heartbeat signals.A highly sensitive and stretchable piezoelectric strain sensor is fabricated using a piezoelectric film with a serpentine layout.The thickness of the patterned PVDF flexible piezoelectric strain sensor is only 168 μm,and the voltage sensitivity reaches 0.97 mV/με.The effective modulus is 13.5 MPa,which allows the device to fit to the skin and detect the small strain exhibited by the human body.Chest vibrations are captured by the piezoelectric sensor,which produces an electrical output voltage signal conformally mapped with respiratory-cardiac activities.The separate heart activity and respiratory signals are extracted from the mixed respiratory-cardiac signal by an empirical mode decomposition data processing algorithm.By detecting vital signals such as respiratory and heart rates,the proposed device can aid early diagnosis and monitoring of respiratory diseases such as COVID-19.
查看更多>>摘要：Isolating rare circulating tumor cells(CTCs)from blood is critical for the downstream analysis that is important in cancer-related research,diagnosis,and medicine,and efforts are ongoing to increase the efficiency and purity of CTC isolation in microfluidics.Reported in this paper is a two-stage integrated microfluidic chip for coarse-to-fine CTC isolation from whole blood.First,blood cells are removed by filtration using a micropore-array membrane,then CTCs and other cells that are trapped in the micropores are peeled off the membrane by a novel release method based on air-liquid interfacial tension,which significantly increases the recovery rate of CTCs.The second stage is CTC capture based on an on-chip dense immuno-magnetic-bead clump,which offers high capture efficiency and purity.Both the micropore filtration and immuno-magnetic-bead capture are validated and optimized experimentally.Overall,the integrated microfluidic chip can realize a recovery rate of 85.5％and a purity of 37.8％for rare cancer cells spiked in whole blood.
查看更多>>摘要：This paper proposes an air-coupled piezoelectric micromachined ultrasonic transducer(PMUT)for detection and imaging of surface stains.A 508 kHz PMUT array is designed,fabricated,and characterized in terms of its electrical and acoustic properties,and it is used in a pulse echo validation test.Imaging of stains on metal blocks is successfully demonstrated.Compared with existing optical methods for stain detection,the proposed approach can work in a dark environment without color requirements.This work provides a new and promising route for the development of miniaturized stain detection systems.
查看更多>>摘要：The presence of chemical warfare agents(CWAs)in the environment is a serious threat to human safety,but there are many prob-lems with the currently available detection methods for CWAs.For example,gas chromatography-mass spectrometry cannot be used for in-field detection owing to the rather large size of the equipment required,while commercial sensors have the disadvantages of low sensitivity and poor selectivity.Here,we develop a portable gas sensing instrument for CWA detection that consists of a MEMS-fabricated micro-preconcentrator(μPC)and a film bulk acoustic resonator(FBAR)gas sensor.The μPC is coated with a nanoporous metal-organic framework material to enrich the target,while the FBAR provides rapid detection without the need for extra car-rier gas.Dimethyl methylphosphonate(DMMP),a simulant of the chemical warfare agent sarin,is used to test the performance of the instrument.Experimental results show that the μPC provides effective sample pretreatment,while the FBAR gas sensor has good sensitivity to DMMP vapor.The combination of μPC and FBAR in one instrument gives full play to their respective advantages,reduc-ing the limit of detection of the analyte.Moreover,both the μPC and the FBAR are fabricated using a CMOS-compatible approach,and the prototype instrument is compact in size with high portability and thus has potential for application to in-field detection of CWAs.
查看更多>>摘要：Differential reflectance spectroscopy(DRS)is a powerful tool to study processes during thin-film growth,especially that of transition metal dichalcogenides and organic thin films.To satisfy the requirements for in situ and real-time monitoring of film growth,including spec-tral resolution and sensitivity at the level of monolayers and even sub-monolayers,the most challenging technical task in DRS is to reduce noise to an extremely low level so that the best possible signal-to-noise ratio can be achieved.In this paper,we present a simplified and cost-effective DRS apparatus,with which we show that the measurement noise is mainly composed of thermal drift noise and explore the temperature-dependence of the DRS signal.Based on the results obtained,we propose an easily realized and effective scheme aiming to reduce the noise.Experimental results demonstrate that this scheme is effective in stabilizing reliable signals for a long period of several hours.Significant noise reduction is achieved,with the typical average noise of the DRS system being decreased to 0.05％over several hours.The improved DRS system is applied to study the growth of an organic semiconductor layer for an organic field-effect transistor device.The results indicate that the apparatus proposed in this paper has potential applications in fabrication of devices on the nanoscale and even the sub-nanoscale.
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