773 research outputs found
A three-axis accelerometer for measuring heart wall motion
This thesis presents the work carried out in the design, simulation, fabrication and
testing of miniaturised three-axis accelerometers. The work was carried out at the
Faculty of Science and Engineering at Vestfold University College (Tønsberg, Norway),
the MIcroSystems Engineering Centre (MISEC) at Heriot-Watt University
and in collaboration with the Interventional Centre at Rikshospitalet University
Hospital (Oslo, Norway). The accelerometers presented in this thesis were produced
to be stitched to the surface of human hearts. In doing so they are used to
measure the heart wall motion of patients that have just undergone heart bypass
surgery. Results from studies carried out are presented and prove the concept of
using such sensors for the detection of problems that can lead to the failure of heart
bypasses. These studies were made possible using commercially available MEMS
(MicroElectroMechanical Systems) three-axis accelerometers. However, the overall
size of these sensors does not meet the requirements deemed necessary by the medical
team (2(W) 2(H) 5(L) mm3) and fabrication activities were necessary to produce
custom-made sensors. Design verification and performance modelling were carried
out using Finite Element Analysis (FEA) and these results are presented alongside
relevant analytical calculations. For fabrication, accelerometer designs were submitted
to three foundry processes during the course of the work. The designs utilise the
piezoresistive effect for the acceleration sensing and fabrication was carried out by
bulk micromachining. Results of the characterisaton of the sensors are presente
Bi-stable buckled energy harvesters actuated via torque arms.
Vibrational energy harvesters (VEH) are one way to generate electricity. Though the energy quantities are not enough to run desktop computers, they can power remote devices such as temperature, pressure, and accelerometer sensors or power biological implants. New versions of the Bluetooth protocol can even be used with VEH technology to send wireless data. An important aspect of VEH devices is the power output, operating frequency, and bandwidth. This dissertation investigates a novel method of actuating the primary buckled energy harvesting structure using torque arms as a force amplification mechanism. Buckled structures can exhibit snap-through and has the potential to broaden the operating frequency for the VEH. Macro and MEMS size prototypes are fabricated and evaluated via a custom made shaker table. The effect of compliance arms, which pin the center beam with piezoelectric strips, are also evaluated along with damping ratios. ANSYS models evaluating generated power are created for use in future optimization studies. Lastly, high energy orbitals (HEO) are observed in the devices. Results show that buckling lowers and broadens the output power of the new devices. Reverse sweeps drastically increase the operating frequency during snap-through. Rectangular compliance arms made of poly-lactic acid (PLA) generated the most power of all compliance arms tested. HEO performance can be induced by perturbing the system while maintaining the same input force which increases power output
Hybrid Energy Harvesting for Self Powered Human Applications
Continuing progress in reduction of size and power consumption of semiconductors, and significant improvement in their capability to compute sense and communicate data, have enabled a new area of wearable electronics and smart garments. Mobile electronics devices such as smart phones, tablets, laptops, e-readers and GPS devices have shaped and defined the world of consumer electronics. As such those devices interact with us on every day level, keeping us connected with environment through the use of sensors, imagers, location based services and data networks. Looking beyond typical consumer applications, there is an increasing demand for a wearable and energy efficient electronics capable of operating from human harvested energy. This study will present a solution that is capable of providing basic human bio-parametric data such as: body temperature, pressure, man down indication, impact occurrence indication as well as data on orientation and inclination. All those functions will be embedded as wearable electronics and be able to operate from the energy that was harvested from human body. The need to have this kind of data collected on the human subject in especially demanding environments and situations is greatly appreciative in applications related to search and rescue agencies, paramedics, firefighters and security and police. The solution presented in this thesis is focusing on energy harvesting from human body and the environment, together with utilization of such energy for wearable electronic
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