Analysis of Resonating Microcantilevers Operating in a Viscous Liquid Environment

The characteristics of resonant cantilevers in viscous liquids are analyzed. Various rectangular cantilevers geometries are studied in pure water, glycerol and ethanol solutions of different concentrations, and the results are described in terms of the added displaced liquid mass and the liquid damping force for both, the resonance frequency and the quality factor (Q-factor). Experimental results using a set of magnetically actuated resonant cantilevers vibrating in the out-of-plane (“weak-axis bending”) mode are presented and compared to theoretical calculations. The importance of the study is in the use of resonant cantilevers as biochemical sensors in liquid environments

Micro Electromechanical Systems (MEMS) Based Microfluidic Devices for Biomedical Applications

Micro Electromechanical Systems (MEMS) based microfluidic devices have gained popularity in biomedicine field over the last few years. In this paper, a comprehensive overview of microfluidic devices such as micropumps and microneedles has been presented for biomedical applications. The aim of this paper is to present the major features and issues related to micropumps and microneedles, e.g., working principles, actuation methods, fabrication techniques, construction, performance parameters, failure analysis, testing, safety issues, applications, commercialization issues and future prospects. Based on the actuation mechanisms, the micropumps are classified into two main types, i.e., mechanical and non-mechanical micropumps. Microneedles can be categorized according to their structure, fabrication process, material, overall shape, tip shape, size, array density and application. The presented literature review on micropumps and microneedles will provide comprehensive information for researchers working on design and development of microfluidic devices for biomedical applications

Master of Science

thesisThe design, working principle, fabrication, and characterization of ultrasensitive ferromagnetic and magnetoelectric magnetometer are discussed in this thesis. Different manufacturing techniques and materials were used for the fabrication of the two versions of the magnetometer. The ferromagnetic microelectromechanical systems (MEMS) magnetometer was fabricated using low-pressure chemical vapor deposition (LPCVD) of silicon nitride, yielding low compressive stress, followed by patterning. The built-in stress was found to be -14 Mpa using Tencor P-10 profilometer. A neodymium magnet (NdFeB) was used as a foot-mass to increase the sensitivity of the device. A coil (Ø=3 cm), placed at a distance from the sensor (2.5-15 cm), was used to produce the magnetic field. The response of the ferromagnetic MEMS magnetometer to the AC magnetic field was measured using Laser-Doppler vibrometer. The ferromagnetic sensor's average temperature sensitivity around room temperature was 11.9 pV/pT/-C, which was negligible. The resolution of the ferromagnetic sensor was found to be 27 pT (1 pT = 10-12 T). To further improve the sensitivity and eliminate the use of the optical detection method, we fabricated a Lead Zirconate titanate (PZT) based magnetoelectric sensor. The sensor structure consisted of a 9 mm long, and 0.17 mm thick PZT beam of varying widths. A neodymium permanent magnet was used as a foot-mass in this case as well. The magnetic field from the coil generated a driving force on the permanent magnet. The driving force displaced the free end of the PZT beam and generated a proportional voltage in the PZT layer. The magnetoelectric coupling, i.e., the coupling between mechanical and magnetic field, yielded a sensor resolution of ~40 fT (1 fT = 10-15 T); an improvement by three orders of magnitude. We used high permeability Mu sheets (0.003"") attached to copper plates (0.125"") to shield stray magnetic fields around the sensor. For both the ferromagnetic MEMS and the magnetoelectric magnetometer, the initial output was improved by using external bias and parametric amplification. By applying an external DC magnetic field bias to the sensor, the effective spring compliance of the sensor was modified. Electronic feedback reduced the active noise limiting the sensor's sensitivity. We used magnetic coupling to enhance the sensors' sensitivity and to reduce the electronic noise. Two identical sensors, with identical foot-mass (permanent magnet), was used to show coupling. The magnet on one of the sensors was mounted in NS polarity, whereas, on the other it was in SN polarity. When excited by the same external AC magnetic field (using coil), one of the sensors was pulled towards the coil and the other was pushed away from it. Adding the individual sensor output, using a preamplifier, an overall increase in sensors' output was observed. The techniques mentioned above helped to improve the output from the sensor. The sensitivity of the sensor can be improved further by using a 3-axis magnetic field cancellation system, by eliminating the AC and DC stray magnetic field, by using coupled-mode resonators and by increasing the surface field intensity of the foot-mass. The magnetometers, thus, developed can be used for mapping the magnetic print of the brain

Nonreciprocity Applications in Acoustics and Microfluidic Systems

Breaking reciprocity in linear acoustic systems and designing a novel actuator for the nonreciprocal valveless pumps are studied in this dissertation. The first part was started by deriving the acoustic governing equations in a moving wave propagation medium. It was shown thatthe Coriolis acceleration term appears ina cross-product term with the wave vector. It means the main reason for breaking reciprocity in the circular fluid flow is the Coriolis acceleration term. Finally, the governing equations were solved numerically by COMSOL Multiphysics software. Moreover, Green`s second identity was used as a complimentary method to prove breaking reciprocityin such a system with moving medium. It is concluded that the non-reciprocity is magnified by increasing the angular velocity of the fluid system. The second part of this thesis is about achieving non-reciprocity utilizing the arrangement of a nozzle and diffuser as the inlet and outlet ports. This part’s goal is to design a novel flexible actuator design for a valveless pump. The actuation mechanism which is novel in its own term, uses liquid metal called galinstan, a non-magnetic but electrically conducting alloy. In the designed device, an alternating current (AC) is applied onto a microchannel filled with galinstan. This device is placed between two permanent magnets with opposing poles. Due to the Lorentz force law, there will be radial in-plane forces on the polymeric flexible substrate. These in-plane forces radially contract and expand the circular diaphragm to provide an upward and downward out of plane bending moment, which causes an oscillatory reciprocating movement similar to a piezoelectric actuator`s movement. Compared to the traditional piezo electric materials such as Lead Zirconate Titanate (PZT), this actuator has numerous advantages such as being flexible, having the ability to be scaled down, being formed as an integrated structure, and being fabricated by a considerably simple process. The prototype of the pump could be fabricated easily with Platinum Silicone rubber and some low-cost 3D printed elements. Although the prototype has been fabricated in a relatively large size, it is considered as a proper conceptual model representing the performance of the pump

A model of a fundamental-mode Lorentz force actuated flexural plate wave resonator

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (leaves 37-38).by Misha K. Hill.M.Eng

Inertial MEMS Sensors

In this work, novel electrostatic micro-electro-mechanical system (MEMS) sensor and sensors are introduced and demonstrated. First, a novel bifurcation-based MEMS ethanol vapor sensor is demonstrated. In contrast to traditional gas sensors that measure in analog mode (quantify) gas concentration, this sensor does not quantify the gas concentration. Rather, it detects its gas concentration in binary mode, reporting (1) for concentrations above a preset threshold and (0) for concentrations below the threshold. The sensing mechanism exploits the qualitative difference between the sensor state before and after the static pull-in bifurcation in electrostatic MEMS. The transition between these states is the bifurcation used in detection. A driving circuit with a resolution of 1 mV was used to drive the sensor at a point close to the pull-in limit to achieve maximum sensitivity. The sensor was able to detect concentrations as low as 5 ppm of ethanol vapor in dry nitrogen, equivalent to a detectable mass of 165 pg. Gas detection was verified electrically and optically through a detection circuit and a CCD camera, respectively. Second, a novel tunable MEMS magnetic field sensor is demonstrated in this work. It measures torsional vibrations excited via Lorentz force. The sensor sensitivity and dynamic range can be tuned by varying a bias voltage. Experimental demonstration shows that the sensor sensitivity can be changed from 0.436 (mm/s)/mT at 6 V bias to 0.87 (mm/s)/mT at 1 V bias. Unlike most commercial magnetic sensors, this magnetic sensor achieves a higher bandwidth (182 kHz) and a tunable sensitivity adjustable on-the-fly.1 yea