Piezoresistive sensors often suffer from poor signal-to-noise ratios, limiting their use for measuring small pressure differentials. As the pressure range is reduced, and the sensitivity of the sensor increased, the effect of noise on the output signal becomes the limiting factor in the sensor design. In this paper, the optimization of the design to enhance the signal-to-noise ratio of a piezoresistive-type pressure sensor is performed considering different noise components commonly present with these types of sensors. The optimal design for the cases of constant voltage and current is achieved by maximizing the performance index, which is defined as the output signal versus noise. The output voltage and noise are separately analyzed and experimentally tested with respect to the geometric parameters of the piezoresistor and the applied voltage and current. Brownian, Johnson and flicker (1/f) noises are modeled, the latter two of which are dominant for piezoresistive sensors operated at low frequencies to dc. The experimental results show that the optimal design with respect to the resistor length, and number of turns is significantly different when noise is considered. For the special case of the piezoresistive sensor tested, the flicker noise required more turns and longer active elements than if only the effective and non-effective resistances were considered. The optimal Vout/Vnoise was over twice that of the sensor designed maximizing Vout alone.
Glaucoma is an eye disease which is caused by abnormal high intraocular pressure (IOP) in the eye. If the condition of the patient becomes serious, the use of an implant device is recommended, which decreases the IOP compulsory. Active implants for glaucoma implants are capable of controlling the IOP actively and coping with the personal differences of patients. However, the conventional active valves for the glaucoma implant are not convenient for the patient and feasibility is not shown for the glaucoma treatment. In this paper, we propose, analyze, fabricate and experiment on the pressure regulating valve for the active implant. Based on the analysis, we carry out optimal design of the proposed valve. The in vitro experiments are performed extensively both using and not using a rabbit in open- and closed-loop pressure control. The various experimental results verify the possibility of the proposed valve for a glaucoma implant.
Since the eddy-current problem usually depends on the geometry of the moving conductive sheet and the pole shape, there is no general method to find an analytical solution. The analysis of the eddy currents in a rotating disk with an electromagnet is performed in the case of time-invariant field with the consideration of the boundary conditions of the rotating disk and induced magnetic flux. First, the concept of Coulomb’s law and the method of images are introduced with the consideration of the boundary conditions. Second, the induced magnetic flux density is calculated by using Ampere’s law. Third, the net magnetic flux density is introduced by defining the magnetic Reynolds number Rm as the ratio of the induced magnetic flux density to the applied magnetic flux density. Finally, the braking torque is calculated by applying the Lorentz force law and the computed results are compared with experimental ones.
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