جستجوی مقالات مرتبط با کلیدواژه « حساسیت » در نشریات گروه « مکانیک »

Diaphragm pressure sensors are used in various industries. Much research has been done to optimize and improve the quality of these sensors. This paper investigates "sensitivity" as a critical variable in diaphragm pressure sensors based on MEMS technology. Aperture geometry is one of the most influential variables in the sensitivity of a diaphragm sphygmomanometer, which in addition to sensitivity, can affect other variables such as operating range, sensor accuracy, dimensions, and even price. To increase the performance and sensitivity of pressure sensors, the sensor aperture was simulated in AbaqusFEA software, and while validating the computational solver, different geometries were evaluated. The results showed that the circular diaphragm has the best performance. Then the effect of corrugations on the surface of the diaphragm was investigated, and different forms of waves were simulated. The results showed that creating a circular wave with a radius of 15 μm at the end of the diaphragm surface increases the sensor's sensitivity by 18%.

Auxetic structures (negative Poisson’s ratio) are a group of materials that expand (contract) under tensile (compression) longitudinal loading. In this work, the effect of re-entrant auxetic structure geometry on Poisson’s ratio was investigated under large tensile loading experimentally and numerically and showed that the location and stiffness of rotation joints are two new important parameters affecting the value of Poisson’s ratio. Poisson's ratio increases as the rotation joints tighten and move away from the center of the structure. Therefore, by changing the location and stiffness of the rotation joints, it will be easy to obtain re-entrant auxetic structures with different Poisson's ratios, which makes it possible to build piezoresistant auxetic sensors with different sensitivities. A highly sensitive, stretchable piezoresistant auxetic sensor made of silicon rubber and chopped carbon fibers is proposed for low strain values. The main feature of this sensor is its high sensitivity for strains less than 6%, which previous works have been unable to detect this range of strains. Shifting strain is the value of strain in which the Poisson's ratio of the structure changes from negative to positive. The provided auxetic sensor performs exceptionally well until the shifting strain and then performs as conventional sensors. This improvement in sensing performance is about 150% (in terms of gauge factor).

In this paper, the resonant frequency and sensitivity of vibration modes of an atomic force microscope (AFM) with an assembled cantilever probe (ACP) are analyzed utilizing the modified couple stress theory. The proposed ACP comprises a horizontal microcantilever, a vertical extension and two tips located at the free ends of the cantilever and the extension, which make AFM capable of scanning the top surface and the sidewall of the sample, simultaneously. To derive the exact solution of the proposed ACP vibration behaviour, the horizontal cantilever is modeled as two beam. Having obtained the equation of motion, boundary and continuity conditions, the resonant frequency and sensitivity are studied. The results predicted by the current theory are compared to those obtained by the numerical methods presented by Kahrobaiyan et al. and the comparison shows that there is some errors in the numerical method results. The results of the couple stress theory are also compare with those of the classical beam theory. The evaluation indicates that the vibration behaviour of the proposed ACP is completely size-dependent.

In this paper, behavior of a lateral comb capacitive micro accelerometer including system noise, sensitivity, and response time has been modeled and improved. Also, dynamic behavior of system has been studied based on three different functions of the input acceleration including the constant, step, and impulse functions. Hence, at first system has been investigated based on the constant input acceleration function and the simulation results has been verified with the experimental results of the existed research. Following, the improved distance between the capacitor plates has been obtained based on the minimum amount of the system total noise. Additionally, sensitivity of system has been maximized by evaluation of the proof mass amount and considering the maximum possible displacement between capacitor plates, as a constraint, to avoid connection of the electrodes. Results show that the distance between capacitor plates was reduced by 90% and the length and width of proof mass were increased by 41.5%. Eventually, sensitivity of the system was doubled. In addition, response time of the system was decreased, significantly. Also, the results of choosing different input functions for input acceleration including the impulse and step functions show that the input function is an effective factor of the model based designing. It changes both the amount of the designing parameters and prediction of the system performance.

In this paper, the resonant frequency and sensitivity of an atomic force microscope (AFM) with an assembled cantilever probe (ACP) are analyzed utilizing the modified couple stress theory. The proposed ACP comprises a horizontal microcantilever, an extension and a tip located at the free end of the extension, which make AFM capable of scanning the sample sidewall. First, the governing differential equation and boundary conditions for dynamic analysis are obtained by a combination of the basic equations of the modified couple stress theory and Hamilton principle. Then, a closed form expression for the resonant frequency are derived, and using this expression the sensitivity are also investigated. The results of the proposed model are compared with those of the classic beam theory. The comparison shows that the difference between the results predicted by these two theories becomes significant when the horizontal cantilever thickness comes approximately close to the material length scale parameter, in which for some values of contact stiffness the difference reaches its maximum. It can also be inferred that a decrease in the microcantilever thickness could have a knock on effect on the shifts of first frequency and first sensitivity caused by an increase in the extension length.

Terfenol-D, known as a giant magnetostrictive material, is used in many sensors such as force sensor. In these sensors, external force is measured due to variation of magnetic flux density passing through Terfenol-D. To improve the performance, Terfenol-D is exposed to bias magnetic field and mechanical pre-stress. In this paper, Effects of bias magnetic field and mechanical pre-stress on sensitivity and linear measurement range of a force sensor are studied and optimum values of them are recognized. Initially based on magnetomechanical coupling equations, theoretical model of sensor that includes effective parameters on sensitivity and linear measurement range is developed. Then using experimental set-up, magnetomechanical properties of Terfenol-D are investigated and values of essential parameters for theoretical model are extracted. Finally, employing theoretical model and experimental results, the response of sensor under dynamic external forces is simulated and effects of bias magnetic field and mechanical pre-stress on sensitivity and linear measurement range of the sensor are studied. Based on the obtained results, to increase sensitivity and linear measurement range of sensor, values of bias magnetic field and mechanical pre-stress should be relatively determined considering the amplitude of external force.