Single and bundled carbon nanofibers as ultralightweight and flexible piezoresistive sensors

This work demonstrates the application of electrospun single and bundled carbon nanofibers(CNFs)as piezoresistive sensing elements in flexible and ultralightweight sensors.Material,electrical,and nanomechanical characterizations were conducted on the CNFs to understand the effect of the critical synthesis parameter—the pyrolyzation temperature on the morphological,structural,and electrical properties.The mechanism of conductive path change under the influence of external stress was hypothesized to explain the piezoresistive behavior observed in the CNF bundles.Quasi-static tensile strain characterization of the CNF bundle-based flexible strain sensor showed a linear response with an average gauge factor of 11.14(for tensile strains up to 50%).Furthermore,conductive graphitic domain discontinuity model was invoked to explain the piezoresistivity originating in a single isolated electrospun CNF.Finally,a single piezoresistive CNF was utilized as a sensing element in an NEMS flow sensor to demonstrate air flow sensing in the range of 5-35 m/s.

Transformer components impact on compatibility of measured PDs:comparison of IEC60270 and RF methods

Power transformer partial discharge signal measurement using Radio Frequency method has advantages over IEC 60270‘apparent charge’measurement method for online monitoring due to greater immunity against external interference.However,the lack of a well-defined calibration relationship between the two methods is main disadvantage of RF method.Simultaneous measurements,using these two methods,carried out on various transformer PD source models,in laboratory,to investigate main parameters that affect the relationship of results of these two methods.In this paper,factors that influence this relationship are classified into three groups:(i)type of PD sources,(ii)transformer windings as PD signal transmitter,and(iii)the inner structure of the transformer.Firstly,the relationship between these two methods has been investigated for some simple types of PD sources.Subsequently,by adding the winding structure model to the void,which is the PD source,its impact on each measurement method and the relationship between them have been studied.The impact of inner structure on the relation between the two methods is compensated through a formula which is proposed as a means for calibration of the RF partial discharge measurement setup.However to compensate for internal insulating system effects more research is required.

Non-intrusive flow measurement based on a distributed feedback fiber laser

We propose a new non-intrusive flow measurement method using the distributed feedback fiber laser(DFB-FL)as a sensor to monitor flow in the pipe.The relationship between the wavelength of the DFB-FL and the liquid flow rate in the pipeline is derived.Under the guidance of this theory,the design and test of the flow sensor is completed.The response curve is relatively flat in the frequency range of 10 Hz to 500 Hz,and the response of the flow sensor has high linearity.The flow from 0.6 m^3/h to 25.5 m^3/h is accurately measured under the energy analysis method in different frequency intervals.A minimum flow rate of 0.046 m/s is achieved.The experimental results demonstrate the feasibility of the new non-intrusive flow measurement method based on the DFB-FL and accurate measurement of small flow rates.