Shangchun Fan

Analyzing the applicability of miniature ultra-high sensitivity Fabry–Perot acoustic sensor using a nanothick graphene diaphragm

A miniature Fabry–Perot interferometric acoustic sensor with an ultra-high pressure sensitivity was constructed by using approximately 13 layers of graphene film as the diaphragm. The extremely thin diaphragm was transferred onto the endface of a ferrule, which had an inner diameter of 125 μm, and van der Waals interactions between the graphene diaphragm and its substrate created a low finesse Fabry–Perot interferometer with a cavity length of 98 μm. Acoustic testing demonstrated a pressure-induced deflection of 2380 nm kPa−1 and a noise equivalent acoustic signal level of ~2.7 mPa/Hz1/2 for a 3 dB bandwidth with a center frequency of 15 kHz. The sensor also exhibited a dynamic frequency response between 1 and 20 kHz, which conformed well to the result obtained by a reference microphone. The use of a suspended graphene diaphragm has potential applications in highly sensitive pressure/acoustic sensors.

Measurement of thermal expansion coefficient of graphene diaphragm using optical fiber Fabry–Perot interference

Application of the Fabry–Perot (FP) interference method for determining the coefficient of thermal expansion (CTE) of a graphene diaphragm is investigated in this paper. A miniature extrinsic FP interferometric (EFPI) sensor was fabricated by using an approximate 8-layer graphene diaphragm. The extremely thin diaphragm was transferred onto the endface of a ferrule with an inner diameter of 125 μm, and van der Waals interactions between the graphene diaphragm and its substrate created a low finesse FP interferometer with a cavity length of 36.13 μm. Double reference FP cavities using two cleaved optical fibers as reflectors were also constructed to differentially cancel the thermal expansion effects of the trapped gas and adhesive material. A temperature test demonstrated an approximate cavity length change of 166.1 nm °C−1 caused by film thermal expansion in the range of 20–60 °C. Then along with the established thermal deformation model of the suspended circular diaphragm, the calculated CTE ranging from −9.98 × 10−6 K−1 to −2.09 × 10−6 K−1 conformed well to the previously measured results. The proposed method would be applicable in other types of elastic materials as the sensitive diaphragm of an EFPI sensor over a wide temperature range.

Room-Temperature Pressure-Induced Optically-Actuated Fabry-Perot Nanomechanical Resonator with Multilayer Graphene Diaphragm in Air

We demonstrated a miniature and in situ ~13-layer graphene nanomechanical resonator by utilizing a simple optical fiber Fabry-Perot (F-P) interferometric excitation and detection scheme. The graphene film was transferred onto the endface of a ferrule with a 125-μm inner diameter. In contrast to the pre-tension induced in membrane that increased quality (Q) factor to ~18.5 from ~3.23 at room temperature and normal pressure, the limited effects of air damping on resonance behaviors at 10−2 and 105 Pa were demonstrated by characterizing graphene F-P resonators with open and micro-air-gap cavities. Then in terms of optomechanical behaviors of the resonator with an air micro-cavity configuration using a polished ferrule substrate, measured resonance frequencies were increased to the range of 509–542 kHz from several kHz with a maximum Q factor of 16.6 despite the lower Knudsen number ranging from 0.0002 to 0.0006 in damping air over a relative pressure range of 0–199 kPa. However, there was the little dependence of Q on resonance frequency. Note that compared with the inferior F-P cavity length response to applied pressures due to interfacial air leakage, the developed F-P resonator exhibited a consistent fitted pressure sensitivity of 1.18 × 105 kHz3/kPa with a good linearity error of 5.16% in the tested range. These measurements shed light on the pre-stress-dominated pressure-sensitive mechanisms behind air damping in in situ F-P resonant sensors using graphene or other 2D nanomaterials.

Measurement of the Adhesion Energy of Pressurized Graphene Diaphragm Using Optical Fiber Fabry–Perot Interference

Van der Waals adhesion between graphene and substrate has an important impact on the graphene-based sensor performance. Here, we proposed a simple in situ measurement method for the adhesion energy of the graphene diaphragm suspended on the endface of a ferrule. The interaction between the diaphragm and its substrate created a low finesse Fabry-Perot (FP) interferometer. The analytical relationship between prestress and adhesion energy was modeled on the basis of the initial dip along the edges of the suspended regions. Then, the deflection deformations of pressurized graphene diaphragm were examined using the FP interference technology. The obtained adhesion energies for monolayer and two to five layer graphene membranes on SiO2 conformed exceedingly well to the previously measured results and yielded a cross-correlation coefficient of 0.999 with the latter. Furthermore, an experimental setup for acoustic pressure test was developed to determine the adhesion energies for ~7-layer and ~13-layer graphene diaphragms with a zirconia substrate to be 0.286 and 0.275 J/m2, respectively. The highly consistent experimental data confirmed the accuracy of our method. This method presented in this paper could be further extended for measuring the adhesion energy of other 2-D materials.

Experimental Study and Implementation of a Novel Digital Closed-Loop Control System for Coriolis Mass Flowmeter

Closed-loop control system undertakes the foundational task of maintaining the permanent vibration of the measuring tube for Coriolis Mass Flowmeter (CMF). In order to overcome the disadvantages of bad anti-jamming, slow response speed and high zero drift existing in conventional analog closed-loop system, a novel digital closed-loop control system is proposed in which the Multiplying Digital to Analog Converter is introduced to track the vibration signal of CMF in real time, together with the non-linear amplitude control method to vary the amplitude gain of the excitation signal, so that the measuring tube can be adjusted to vibrate with stable amplitude promptly. The real flow calibration experimental result shows that the maximum steady state relative error and repeatability are 0.147% and 0.039%, respectively. In addition, the start-up time of measuring tube can reach to 2.75 s.

Microscale liquid marble-based tilt motion sensor using optical fiber fabry-perot interference

We demonstrate a miniature and low-cost liquid marble-based optical fiber tilt angle sensor prototype with advantages of simple fabrication, immunity to electromagnetic interference, high linearity and available differential detection by using Fabry-Perot (F-P) interferometric detection. A mercury marble, working as a light reflector, is dispensed into a capillary tube preprocessed by hydrophobic agent. The gravitational acceleration solved by tilt angle in the range of 0–90° exhibits a fitted linear sensitivity of 3.72 μm/ms−2, in agreement well with the governing model incorporating with the effect of contact angle hysteresis between the droplet and the substrate.

The Effect of Viscous Air Damping on an Optically Actuated Multilayer MoS2 Nanomechanical Resonator Using Fabry-Perot Interference

We demonstrated a multilayer molybdenum disulfide (MoS2) nanomechanical resonator by using optical Fabry-Perot (F-P) interferometric excitation and detection. The thin circular MoS2 nanomembrane with an approximate 8-nm thickness was transferred onto the endface of a ferrule with an inner diameter of 125 μm, which created a low finesse F-P interferometer with a cavity length of 39.92 μm. The effects of temperature and viscous air damping on resonance behavior of the resonator were investigated in the range of −10–80 °C. Along with the optomechanical behavior of the resonator in air, the measured resonance frequencies ranged from 36 kHz to 73 kHz with an extremely low inflection point at 20 °C, which conformed reasonably to those solved by previously obtained thermal expansion coefficients of MoS2. Further, a maximum quality (Q) factor of 1.35 for the resonator was observed at 0 °C due to viscous dissipation, in relation to the lower Knudsen number of 0.0025~0.0034 in the tested temperature range. Moreover, measurements of Q factor revealed little dependence of Q on resonance frequency and temperature. These measurements shed light on the mechanisms behind viscous air damping in MoS2, graphene, and other 2D resonators.

Theory and experiment research for ultra-low frequency maglev vibration sensor

A new maglev sensor is proposed to measure ultra-low frequency (ULF) vibration, which uses hybrid-magnet levitation structure with electromagnets and permanent magnets as the supporting component, rather than the conventional spring structure of magnetoelectric vibration sensor. Since the lower measurement limit needs to be reduced, the equivalent bearing stiffness coefficient and the equivalent damping coefficient are adjusted by the sensitivity unit structure of the sensor and the closed-loop control system, which realizes both the closed-loop control and the solving algorithms. A simple sensor experimental platform is then assembled based on a digital hardware system, and experimental results demonstrate that the lower measurement limit of the sensor is increased to 0.2 Hz under these experimental conditions, indicating promising results of the maglev sensor for ULF vibration measurements.

Design and Simulation of a Fused Silica Space Cell Culture and Observation Cavity with Microfluidic and Temperature Controlling

We report a principle prototype of space animal cell perfusion culture and observation. Unlike previous work, our cell culture system cannot only realize microfluidic and temperature controlling, automatic observation, and recording but also meet an increasing cell culture at large scale operation and overcome shear force for animal cells. A key component in the system is ingenious structural fused silica cell culture cavity with the wedge-shaped connection. Finite volume method (FVM) is applied to calculate its multipoint flow field, pressure field, axial velocity, tangential velocity, and radial velocity. In order to provide appropriate flow rate, temperature, and shear force for space animal cell culture, a closed-loop microfluidic circuit and proportional, integrating, and differentiation (PID) algorithm are employed. This paper also illustrates system architecture and operating method of the principle prototype. The dynamic culture, autofocus observation, and recording of M763 cells are performed successfully within 72 h in the laboratory environment. This research can provide a reference for space flight mission that carries an apparatus with similar functions.

Design of IIR filter in capacitive rotary position sensor based on FPGA

In the capacitive rotary position sensor, noise jamming generated by the motor is mixed in the response signal, so it is difficult to measure precisely. This paper presents an IIR filter solution with cascade structure. An IIR band-pass filter of 8-order is designed by Matlab, and then be disintegrated into 4 sub-filters. The band-pass frequency of the filter ranges from 18 kHz to 22 kHz with date sample rate of 400 kHz. All coefficients of the sub-filters are quantized by 214 to satisfy the multiplication requirement in FPGA. The filter is described modularly by Verilog HDL and implemented in FPGA of Cyclone III series. The filter has been tested well with square wave. Signal attenuation outside the band-pass frequency is more than 50 dB. Modular structure makes it very convenient to design filters with different characteristics. At present, the solution is applied in a capacitive rotary position sensor.