Jae-Geun Oh

Strain-based piezoelectric energy harvesting for wireless sensor systems in a tire

Vehicle safety can be improved by tire pressure monitoring with a wireless sensor system. Since a battery-powered wireless sensor system for tire pressure information is limited by the life of the battery, energy harvesting technology is applied. In order to develop an energy harvester based on a piezoelectric material for the tires, modeling of tire behavior and the energy harvester, and the validation of the modeling were performed. The structural behavior of a tire was numerically modeled and verified by comparing the simulation results with experimental data. In order to compare the generated voltages between the modeling and the experiment, comparisons of the root-mean-square voltage values for various velocities and loads, the distortion factor using the root-mean-square value of the wave form, and the crest factor for verifying the efficiency of the peak value of the wave form were conducted. The results showed that the differences are on average 10% for the loads between 300 and 700 kgf and velocities between 20 and 60 km/h (430 r/min). For the improvement of the energy harvester’s performance, the thickness of substrate was controlled and the generated voltage was increased. If a sensor for measuring radius is applicable to the tire, the strain on the tire can be collected, and thus the loads applied to the tire can be estimated. With a wireless sensor system for measuring radius driven by energy harvesting, we can be one step closer to the embodiment of an intelligent tire.

The viscosity deviation of magnetic fluids for microactuator due to temperature changes

Experiments were performed to investigate the characteristics of magnetic fluids on a micro scale for the purpose of applications to a micro pump, which is the core device of lab on a chip in medicine and biology. This work took an advantage of the phenomenon that the viscosity of a magnetic fluid decreases sharply as the temperature increases gradually. The magnetic fluid flowing through a trapezoidal silicon microchannel was heated below the temperature at which the magnetism in the magnetic fluid is not lost. As the temperature increases, the magnetic fluid became less viscid. This in turn made the pressure drop in the microchannel. Thus, this pressure drop of the heated magnetic fluid and the corresponding temperature were measured. The microchannel was fabricated by MEMS technology. Since the sheet resistance is as high as 10.6 /spl mu//spl Omega/, platinum was selected as the material of the folded film heater with the length and the thickness of 7.26 cm and 1000 /spl Aring/ on Pyrex glass, respectively. At a proper temperature, if a magnetic fluid is applied to the magnetic field and its viscosity decreases, the response time and the net unidirectional flow of actuators such as a micro pump are expected to be improved.

The energy conversion system with piezoelectric effect for wireless sensor network

The wireless sensors play an important role in USN. However, the power source is a critical obstacle for wireless sensor nodes. This research provides a solution to overcome the critical problem of constructing wireless sensor networks. The system with piezo materials converts the scavenged mechanical energy - vibration and rotation to electrical energy for powering a sensor and transmitting sensor value using wireless networks. This study explains the properties of piezo material and demonstrates powering sensor and transmitting data with 35 mJ stored energy for 14 seconds.

A study on the optical switch using magnetic behavior of magnetic fluids

This paper presents the development of the optical switch using magnetic behavior of magnetic fluids, which is expected to be used broadly in high-speed information communication. The magnetic fluids for switching an incident light, have the magnetic characteristics of magnetic materials and fluidity of liquids, simultaneously. The relations are derived between the intensity of magnetic field and the angle of optical fiber which is bent by a behavior of magnetic fluid when the magnetic field is applied. When optical switch is implemented by the movement of liquid using magnetic fluid, the existing problem of durability for optical switch will be improved. Thus, this study shows the feasibility of the application for the optical switches using magnetic fluids.

A Monolithically Packaged Cordless Sensor System Embedding MEMS A/D Converter and Saw Transponder

A monolithically packaged SAW (Surface Acoustic Wave) radio transponder and pressure sensor is developed for the application to a TPMS (Tire Pressure Monitoring System). The device contains the wireless transponder, which converts analog signal into digital one without any auxillary electronic circuits and then transmits the converted data wirelessly. No power sources are needed for wireless transponder and pressure sensor. The touch-mode pressure sensor converts externally applied pressure into a capacitance, and the SAW radio transponder radiates sensor values as pulse train to the interrogation (measurement) unit. The realization of the mechanical A/D conversion is possible since the SAW radio transponder has been connected to the touch-mode capacitive pressure sensor. The SAW radio transponder and touch-mode sensor have been fabricated using a surface micromachining and a bulk micromachining technologies, respectively. The performance of the integrated, passive and wireless pressure sensor meets the design specifications such as linearity, sensitivity and noise figure. Finally, experimental results on the radio transponder and sensor without power source are presented.

The Microfluidic Device using Viscosity Deviation of Magnetic Fluids Due to Temperature Changes

This study focused on the charateristic of magnetic fluids, the viscosity deviation of magnetic fluids due to temperature changes, and fabrication of a `purely` liquid type microvalve. The viscosity of magnetic fluids decreases sharply during increasing of temperature. The viscosity of magnetic fluids is rated 1,000 cP at the room temperature and 25 cP when the temperature reaches . Briefly, it is remarkable that the fluid flow can be controlled by the temperature and this characteristic can be adopted to the microfluidics as a microvalve. The fabrication of a liquid type microvalve is more easy than solid state microvalves and which can increase an efficiency of the controlability with respect to the thermo-pneumatic micropump which is studied broadly for many years. When the magnetic fluid used as a sealant for high level sealing, the pressure leakage is less than solid state microvalve. The experimental results show that the pressure drop in microchannel, filled with the magnetic fluid, is significant in the temperature range of and this result explains why the use of magnetic fluids is possible as a microvalve searcher uses this characteristics. Well known thermo-pnumatic.