共查询到20条相似文献,搜索用时 31 毫秒
1.
使用MEMS技术研制出一种高灵敏度热温差式流量传感器。器件采用热隔离性能良好的衬底挖空结构,且热敏电阻器与热源距离可调,保证了系统的灵敏度和响应速度。同时热敏电阻器、加热电阻器与电桥电阻器集成在传感器片内,提高了系统的稳定性。实验表明:合适的电阻器间距可以获得较高的灵敏度,而在0~20 mL/min的量程范围内系统线性度较好,因此,在生化检测、医疗等领域具有良好的推广前景。 相似文献
2.
A novel single-chip microelectromechanical systems (MEMS) capacitive microphone with a slotted diaphragm for sound sensing
is developed to minimize the microphone size and improve the sensitivity by decreasing the mechanical stiffness of the diaphragm.
The behaviors of the microphones with clamped and slotted diaphragms are analyzed using the finite element method (FEM). According
to the results, a clamped microphone with a 2.43 × 2.43 mm 2 diaphragm and a slotted one with a 1.5 × 1.5 mm 2 diaphragm have the same mechanical sensitivity, but the size of slotted microphone is at least 1.62 times smaller than clamped
structure. The results also yield a sensitivity of 5.33 × 10 −6 pF/Pa for the clamped and 3.87 × 10 −5 pF/Pa for the slotted microphone with a 0.5 × 0.5 mm 2 diaphragm. The sensitivity of the slotted diaphragm is increased 7.27 times. The pull-in voltage of the clamped microphone
is 105 V, and slotted one is 49 V. The pull-in voltage of the slotted microphone is about 53% decreased. 相似文献
3.
The use of a laser to provide localised heating is an ideal solution to the problem of packaging micro-electro-mechanical-systems
(MEMS) whilst maintaining a low device temperature to avoid changes in temperature-sensitive materials in the device. In this
paper we present localised laser bonding of glass to silicon (normally used as the MEMS substrate) by using a fibre-delivered
high power laser diode array to cure an intermediate layer of the thermosetting polymer Benzocyclobutene (BCB). In our experiments,
we use two techniques to realise localised heating: one is to use an axicon together with a conventional positive lens to
generate a ring focus; the other is to use a scanning focused laser beam. In both cases localised cooling is required to confine
the elevated temperatures to the bonding area. Finite Element (FE) simulation indicates that both techniques should keep the
temperature in the centre of the package to approximately that of the ambient environment (300 K) during the process. However,
experiments show that the temperature in the centre of the package rises to a value of around 500 K, likely due to poor contact
between silicon and cooling sink. Experimentally, we confirmed that either technique can be used to obtain excellent bonding
of glass to silicon with leak rate at a level of 10 −10 mbar l s −1, whilst keeping the centre of device at a lower temperature. 相似文献
4.
This paper presents an approach for generating a well-defined cooling pattern over an area of tissue. An array of solid-state
microcoolers is used, which could be included in a probe that provides local cooling. This medical instrument can be used
for removal of scar tissue in the eye or for the rapid stopping of bleeding due to micro-cuts, which makes it a useful tool
to medical doctors and could make surgery more secure to the patient. The array of microcoolers is composed of 64 independent
thermo-electric elements, each controlled using an integrated circuit designed in CMOS. The independent control allows the
flexible programming of the surface temperature profile. This type of control is very suitable in case abrupt temperature
steps should be avoided. Cooling by lateral heat flow was selected in order to minimize the influence of heat by dissipation
from the electronic circuits. Moreover, a thermo-electric component with lateral heat allows fabrication of the cooling elements
using planar thin-film technology, lithography and wet etching on top of the silicon wafer. This approach is potentially CMOS
compatible, which would allow for the fabrication of the thermo-electric elements on top of a pre-fabricated CMOS wafer as
a post-process step. Each pixel is composed of thin-films of n-type bismuth telluride, Bi 2Te 3 and p-type antimony telluride, Sb 2Te 3, which are electrically interconnected as thermocouple. These materials have excellent thermoelectric characteristics, such
as thermoelectric figures-of-merit, ZT, at room temperatures of 0.84 and 0.5, respectively, which is equivalent to power-factors, PF, of 3.62 × 10 −3 W K −1 m −2 and 2.81 × 10 −3 W K −1 m −2, respectively. The theoretical study presented here demonstrates a cooling capability of 15°C at room temperature (300 K ≈ 27°C).
This cooling performance is sufficient to maintain a local tissue temperature at 25°C, which makes it suitable for the intended
application. A first prototype was successfully fabricated to demonstrate the concept. 相似文献
5.
This paper describes the microfocusing in a microchannel using the thermal actuation of a pair of microbubbles. A microbubble
was produced from de-ionized (DI) water with an integrated microheater, and the volume was controlled by applying voltage.
The microfocusing was demonstrated with a polydimethylsiloxane (PDMS) device consisting of two layers. The top layer included
a microchannel that was 300 μm wide and 50 μm high. It was flanked by a pair of reservoirs. The bottom layer provided a microheater
underneath the reservoir. Upon heating, DI water boiled immediately over the microheater and formed a microbubble that came
out of the reservoir in a perpendicular direction toward the fluid. The fluid was focused from 300 to 22 μm, as the distance
between the apexes of the arch-shaped microbubbles was shortened due to expansion, which was maintained at a flow velocity
up to approximately 17.8 mm s −1. The temperature of the water in the reservoir was estimated to reach the boiling point within 62 or 160 ms, depending on
the substrate. 相似文献
6.
The present study investigates a large power thermal bubble micro-ejector with induction heating device. The traditional thermal-bubble ejectors adopted resistors as the heating resources, it can only work with lower power and convey liquid with lower flow rate. Induction heating devices are adopted to replace the resistor for heating liquid in this paper. With this heating method, there is no physical contact between the heating core and the external power supply circuit. The liquid in the chamber of micro-ejector is heated by the induction heating device and changes from liquid phase to gas phase, generating vapor bubbles in the micro chamber of the micro ejector. The bubble expands rapidly and ejects droplets through the nozzle. The prototype of the micro-ejector is fabricated and experiments are carried out. Continuous droplets are ejected out from the nozzle as the applied AC current is 0.6–0.65 A with the power frequency of 100 kHz. The total volume of the continuous droplets is ranging from 18.84 to 49.87 nL, and the corresponding flow rate is about 0.52–1.36 μL/min. Furthermore, this new micro-ejector can be adopted in conveying of micro-scale liquid, the injection of trace drugs and the 3D printing. 相似文献
7.
This work presents a polydimethylsiloxane (PDMS) microfluidic device for packaging CMOS MEMS impedance sensors. The wrinkle
electrodes are fabricated on PDMS substrates to ensure a connection between the pads of the sensor and the impedance instrument.
The PDMS device can tolerate an injection speed of 27.12 ml/h supplied by a pump. The corresponding pressure is 643.35 Pa.
The bonding strength of the device is 32.44 g/mm 2. In order to demonstrate the feasibility of the device, the short circuit test and impedance measurements for air, de-ionized
water, phosphate buffered saline (PBS) at four concentrations (1, 2 × 10 −4, 1 × 10 −4, and 6.7 × 10 −5 M) were performed. The experimental results show that the developed device integrated with a sensor can differentiate various
samples. 相似文献
8.
In this paper, a new S-shaped piezoelectric PZT cantilever is microfabricated for scavenging vibration energy at low frequencies
(<30 Hz) and low accelerations (<0.4 g). The maximum voltage and normalized power are 42 mV and 0.31 μW g
−2, respectively, at input acceleration of 0.06 g. For acceleration above 0.06 g, the vibration of PZT cantilever changes from a linear oscillation to a nonlinear impact oscillation due to the displacement
constraint introduced by a mechanical stopper. Based on theoretical modeling and experimental results, the frequency broadening
effect of the PZT cantilever is studied with varying stop distances and input accelerations. The operation bandwidth of the
piezoelectric PZT cantilever is able to extend from 3.4 to 11.1 Hz as the stop distance reduces from 1.7 to 0.7 mm for an
acceleration of 0.3 g, at the expense of the voltage and normalized power at resonance decreasing from 40 to 16 mV and from 17.8 to 2.8 nW g −2, respectively. 相似文献
9.
Uniformly sized droplets of soybean oil, MCT (medium-chain fatty acid triglyceride) oil and n-tetradecane with a Sauter mean diameter of d
3,2 = 26–35 μm and a distribution span of 0.21–0.25 have been produced at high throughputs using a 24 × 24 mm silicon microchannel
plate consisting of 23,348 asymmetric channels fabricated by photolithography and deep reactive ion etching. Each channel
consisted of a 10-μm diameter straight-through micro-hole with a length of 70 μm and a 50 × 10 μm micro-slot with a depth
of 30 μm at the outlet of each channel. The maximum dispersed phase flux for monodisperse emulsion generation increased with
decreasing dispersed phase viscosity and ranged from over 120 L m −2 h −1 for soybean oil to 2,700 L m −2 h −1 for n-tetradecane. The droplet generation frequency showed significant channel to channel variations and increased with decreasing
viscosity of the dispersed phase. For n-tetradecane, the maximum mean droplet generation frequency was 250 Hz per single active channel, corresponding to the overall
throughput in the device of 3.2 million droplets per second. The proportion of active channels at high throughputs approached
100% for soybean oil and MCT oil, and 50% for n-tetradecane. The agreement between the experimental and CFD (Computational Fluid Dynamics) results was excellent for soybean
oil and the poorest for n-tetradecane. 相似文献
10.
This paper presents the design and fabrication of a micro Pirani gauge using VO
x
as the sensitive material for monitoring the pressure inside a hermetical package for micro bolometer focal plane arrays
(FPAs). The designed Pirani gauge working in heat dissipating mode was intentionally fabricated using standard MEMS processing
which is highly compatible with the FPAs fabrication. The functional layer of the micro Pirani gauge is a VO
x
thin film designed as a 100 × 200 μm pixel, suspended 2 μm above the substrate. By modeling of rarefied gas heat conduction
using the Extended Fourier’s law, finite element analysis is used to investigate the sensitivity of the pressure gauge. Also
the thermal interactions between the micro Pirani gauge and bolometer FPAs are verified. From the fabricated prototype, the
measured device TCR is about −0.8% K −1 and the sensitivity about 1.84 × 10 −3 W K −1 mbar −1. 相似文献
11.
In this paper, a model is presented that describes the pressure drop of gas–liquid Taylor flow in round capillaries with a
channel diameter typically less than 1 mm. The analysis of Bretherton (J Fluid Mech 10:166–188, 1961) for the pressure drop
over a single gas bubble for vanishing liquid film thickness is extended to include a non-negligible liquid film thickness
using the analysis of Aussillous and Quéré (Phys Fluids 12(10):2367–2371, 2000). This result is combined with the Hagen–Poiseuille
equation for liquid flow using a mass balance-based Taylor flow model previously developed by the authors (Warnier et al.
in Chem Eng J 135S:S153–S158, 2007). The model presented in this paper includes the effect of the liquid slug length on the
pressure drop similar to the model of Kreutzer et al. (AIChE J 51(9):2428–2440, 2005). Additionally, the gas bubble velocity
is taken into account, thereby increasing the accuracy of the pressure drop predictions compared to those of the model of
Kreutzer et al. Experimental data were obtained for nitrogen–water Taylor flow in a round glass channel with an inner diameter
of 250 μm. The capillary number Ca
gl varied between 2.3 × 10 −3 and 8.8 × 10 −3 and the Reynolds number Re
gl varied between 41 and 159. The presented model describes the experimental results with an accuracy of ±4% of the measured
values. 相似文献
12.
We have developed SWCNT sensors for air-flow shear-stress measurement inside a polymethylmethacrylate (PMMA) “micro-wind tunnel”
chip. An array of sensors is fabricated by using dielectrophoretic (DEP) technique to manipulate bundled single-walled carbon
nanotubes (SWCNTs) across the gold microelectrodes on a PMMA substrate. The sensors are then integrated in a PMMA micro-wind
tunnel, which is fabricated by SU-8 molding/hot-embossing technique. Since the sensors detect air flow by thermal transfer
principle, we have first examined the I– V characteristics of the sensors and confirmed that self-heating effect occurs when the input voltage is above ~1 V. We then
performed the flow sensing experiment on the sensors using constant temperature (CT) configuration with input power of ~230 μW.
The voltage output of the sensors increases with the increasing flow rate in the micro-wind tunnel and the detectable volumetric
flow is in the order of 1 × 10 −5m 3/s. We also found that the activation power of the sensors has a linear relation with 1/3 exponential power of the shear stress
which is similar to conventional hot-wire and polysilicon types of convection-based shear-stress sensors. Moreover, measurements
of sensors with different overheat ratios were compared, and results showed that sensor is more sensitive to the flow with
a higher overheat ratio. 相似文献
13.
This paper describes a flow reversal phenomenon for fluids with moderate conductivity. Fluids with conductivities of 2 × 10 −4 S/m, 0.02 S/m and up to 0.1 S/m were experimented at frequencies ranging from 1 to 110 kHz. Flow reversal was observed only
at ~1 kHz and 5.3 V
rms for σ = 0.02 S/m, and our analysis indicates that AC electrothermal effect could be responsible. Analysis of the system impedance
and simulation of power consumption show that the distribution of electric power consumption is dependent on conductivity
and AC frequency. At low frequencies, possibly more electric power is consumed at surface/electrolyte interface rather than
within the fluid, which consequently changes the location of temperature maximum and the directions of temperature gradients.
The direction of AC electrothermal force is reoriented, causing the flow reversal. Numerical simulation is also performed
and agrees within the experiments. 相似文献
14.
Many aging people and patients have difficulties in bladder control. Recent methods have been studied for non-invasive measuring
for bladder information. It must be improved to a more convenient and real time measurable system for accurately analyzing
and controlling individual bladder information. This paper presents the pressure sensor for the invasive bladder monitoring
system. The system has the pressure sensing resistor sensor (PSRS) which is set-up inside the bladder. The PSRS consists of
a flexible and contactable diaphragm which deforms towards an underlying substrate while a range of pressure is applied. The
flexible diaphragm has a thin metal film which acts as a switch and the underlying substrate has interdigitated electrodes
which serve as a variable resistor. The PSRS initially exhibits infinite electrical resistance with no external pressure applied
since the metal switch is not contact with the interdigitated electrodes. As the applied pressure increases above a threshold,
the contact area increases thus the resistance of the PSRS decreases. Based on the finite element analysis, proper ranges
for the diaphragm size and gap distance are determined. The sensor, the diaphragm size of which is 2.6 × 2.6 mm 2, has been fabricated through MEMS technology. The change of the electrical resistance is 0.5 Ω for the range of human bladder
pressure (0–10 kPa). This PSRS will be effectively used for reliability and stability of the research for the improvement
of bladder management. It can also be utilized for the future application. 相似文献
15.
While walking on an instrumented treadmill, 20 subjects were perturbed by lateral sinusoidal oscillations representative of those encountered in transport: frequencies in the range 0.5–2 Hz and accelerations in the range 0.1–2.0 ms −2 r.m.s., corresponding to velocities in the range 0.032–0.16 ms −1 r.m.s. Postural stability was assessed from the self-reported probability of losing balance (i.e., perceived risk of falling) and the movements of the centre of pressure beneath the feet. With the same acceleration at all frequencies, the velocities and displacements of the oscillatory perturbations were greater with the lower frequency oscillations, and these caused greater postural instability. With the same velocity at all frequencies, postural instability was almost independent of the frequency of oscillation. Movements of the centre of pressure show that subjects attempted to compensate for the perturbations by increasing their step width and increasing their step rate. 相似文献
16.
An electrothermally excited dual beams silicon resonant pressure sensor with temperature compensation is proposed in this
paper. One beam locates upon the diaphragm, whose resonant frequency changes with the measured pressure; the other beam is
on the fixed edge, isolated from the pressure effect but sensitive to the temperature variation. Taking the difference of
the dual beams’ resonant frequencies, temperature influence can be corrected. Compensation algorithm with consideration of
the fabrication errors is deducted theoretically and implemented by a homemade readout system. Experimental results of the
test sample indicates that the maxim pressure measurement residual errors without compensation is up to 53.9 kPa in the working
temperature range from −40 to 60°C; while with compensation the maxim residual errors decreased to 1.8 kPa from −40 to 60°C,
which is only 3.3% of the uncompensated sensor. The experimental results confirm that the new designed sensor has good temperature
compensation ability. 相似文献
17.
This study designs and characterizes a novel MEMS-based flow-rate micro-sensor consisting of a platinum resistor deposited
on a silicon nitride-coated silicon cantilever beam. Due to the difference between the thermal conductivities of the silicon
nitride film and the silicon beam, the tip of the cantilever structure bends slightly in the upward direction. As air travels
across the upper surface of the sensor, it interferes with the curved tip and displaces the beam in either the upward or the
downward direction. The resulting change in the resistor signal is then used to calculate the velocity of the air. A flow-direction
micro-sensor is constructed by arranging eight cantilever structures on an octagonal platform. Each cantilever is separated
from its neighbors by a tapered baffle plate connected to a central octagonal pillar designed to attenuate the aerodynamic
force acting on the cantilever beams. By measuring the resistor signals of each of the cantilever beams, the micro-sensor
is capable of measuring both the flow rate and the flow direction of the air passing over the sensor. A numerical investigation
is performed to examine the effects of the pillar height and pillar-to-tip gap on the airflow distribution, the pressure distribution,
the bending moment acting on each beam, and the sensor sensitivity. The results show that the optimum sensor performance is
obtained using a pillar height of 0.75 mm and a pillar-to-tip gap of 5 mm. Moreover, the sensitivity of the octagonal sensing
platform is found to be approximately 90% that of a single cantilever beam. 相似文献
18.
This paper presents a novel micro-fabricated formaldehyde gas sensor with enhanced sensitivity and detection resolution capabilities. The device comprises a quartz substrate with Pt heaters as a micro-hotplate and deposited formaldehyde-sensing layer on it. A sputtered NiO thin film is used as the formaldehyde-sensing layer. A specific orientation of NiO becomes more apparent as the substrate temperature increases in the sputtering process, which helps the formation of NiO material with a correct stoichiometric ratio. The gas sensor incorporates Pt heating resistors integrated with a micro-hotplate to provide a heating function and utilizes Au inter-digitated electrodes. When formaldehyde is present in the atmosphere, oxydation happens near the sensing layer with a high temperature caused by the micro-hotplate and causes a change in the electrical conductivity of the NiO film. Therefore, the measured resistance between the inter-digitated electrodes changes correspondingly. The application of a voltage to the Pt heaters causes the temperature of the micro-hotplate to increase, which in turn enhances the sensitivity of the sensor. The nanometer scale grain size of the sputtered oxide thin film is conducive to improving the sensitivity of the gas sensor. The experimental results indicate that the developed device has a high stability (0.23%), a low hysteresis value (0.18%), a quick response time (13.0 s), a high degree of sensitivity (0.14 Ω ppm−1), and a detection capability of less than 1.2 ppm. 相似文献
19.
Porous anodic alumina has been of an increasing interest to applications of on-chip biosensors and bioseparations. However,
the characteristics of molecular diffusion in alumina nanopores have not been fully explored. Here, we have investigated an
ultra-thin freestanding alumina membrane fabricated on a silicon substrate as a new on-chip diffusion system. Sub-1,000 Da
molecules such as caffeine were diffused through alumina pores with a pore diameter of 40 nm and a pore length of 1.2 μm.
The diffusion dynamics was characterized by modeling the molecular transport as one-dimensional convective Fickian flow. The
diffusion coefficients were calculated to be on the order of 10 −8 cm 2 s −1. The transport rate of coions was enhanced by increasing the ionic strength of diffusion solution. Relative to thick alumina
membranes, the thin-film alumina was able to achieve a significantly higher flux rate, making it more favorable for rapid
molecular transport. The characterizations we present here have contributed important experimental data to alumina nanofluidics,
and are believed to be valuable for applications such as drug deliveries, molecular separations, and membrane biosensors. 相似文献
20.
We studied an imaging-based technique for the rapid quantification of bio-particles in a dielectrophoretic (DEP) microfluidic
chip. Label-free particles could be successively sorted and trapped in a continuous flow manner under the applied alternating
current (AC) conditions. Both 2 and 3 μm polystyrene beads at a concentration of 1.0 × 10 7 particles ml −1 could be rapidly quantified within 5 min in our DEP system. Capturing efficiencies higher than 95% could be 2 μm polystyrene
beads with a linear flow speed, applied voltage and frequency of 0.89 mm s −1, 20 V p-p and 5 MHz. Yeast cells ( Candida glabrata and Candida albicans) could also be captured even at a lower concentration of 2.5 × 10 5 cells ml −1. Images of aggregative particles taken from the designed trapping area were further processed based on the intensity of relative
greyscale followed by correction of the particle numbers. The imaging-based quantification method showed higher agreement
than that of the conventional counting chamber method and proved the stability and feasibility of our AC DEP system. 相似文献
|