Lessons Learned of NSPO’s Picosatellite Mission: Yamsat - 1A, 1B & 1C

The YamSat is the first developed picosatellite in National Space Program Office’s (NSPO), Taiwan, R.O.C. It is scheduled to flight in the CubeSat launch in 2003. The rapid-prototyping system engineering different from the past formal discipline opens a new satellite development model in NSPO. The YamSat Test Readiness Review Meeting was successfully held in January 2002 and the environmental tests were completed by end March 2002. Besides the breadboard model and engineering test bed to prove of operation concept are built, three YamSats (1A, 1B, & 1C) instead of one are manufactured with slightly different configurations and purposes. The YamSat- 1A is for flight with ambitious and novel R.O.C. made components, including 15 domestic organizations and companies’ participation. The YamSat-1B is basically for backup purpose and demonstration, whereas the YamSat-1C is for amateur communication experiment end-to-end field test, and for public education purpose. This new experience gives fruitful lessons learned and provides low cost space experimentation and education to the next built picosatellites in Taiwan’s universities. Detailed mission and lessons learned are addressed in this paper

Measuring 3D indoor air velocity via an inexpensive low-power ultrasonic anemometer

The ability to inexpensively monitor indoor air speed and direction on a continuous basis would transform the control of environmental quality and energy use in buildings. Air motion transports energy, ventilation air, and pollutants around building interiors and their occupants, and measured feedback about it could be used in numerous ways to improve building operation. However indoor air movement is rarely monitored because of the expense and fragility of sensors. This paper describes a unique anemometer developed by the authors, that measures 3-dimensional air velocity for indoor environmental applications, leveraging new microelectromechanical systems (MEMS) technology for ultrasonic range-finding. The anemometer uses a tetrahedral arrangement of four transceivers, the smallest number able to capture a 3-dimensional flow, that provides greater measurement redundancy than in existing anemometry. We describe the theory, hardware, and software of the anemometer, including algorithms that detect and eliminate shielding errors caused by the wakes from anemometer support struts. The anemometer has a resolution and starting threshold of 0.01 m/s, an absolute air speed error of 0.05 m/s at a given orientation with minimal filtering, 3.1° angle- and 0.11 m/s velocity errors over 360° azimuthal rotation, and 3.5° angle- and 0.07 m/s velocity errors over 135° vertical declination. It includes radio connection to internet and is able to operate standalone for multiple years on a standard battery. The anemometer also measures temperature and has a compass and tilt sensor so that flow direction is globally referenced regardless of anemometer orientation. The retail cost of parts is $100 USD, and all parts snap together for ease of assembly

Development of MEMS - based IMU for position estimation: comparison of sensor fusion solutions

With the surge of inexpensive, widely accessible, and precise Micro-Electro Mechanical Systems (MEMS) in recent years, inertial systems tracking move ment have become ubiquitous nowadays. Contrary to Global Positioning Sys tem (GPS)-based positioning, Inertial Navigation System (INS) are intrinsically unaffected by signal jamming, blockage susceptibilities, and spoofing. Measure ments from inertial sensors are also acquired at elevated sampling rates and may be numerically integrated to estimate position and orientation knowledge. These measurements are precise on a small-time scale but gradually accumulate errors over extended periods. Combining multiple inertial sensors in a method known as sensor fusion makes it possible to produce a more consistent and dependable un derstanding of the system, decreasing accumulative errors. Several sensor fusion algorithms occur in literature aimed at estimating the Attitude and Heading Reference System (AHRS) of a rigid body with respect to a reference frame. This work describes the development and implementation of a low-cost, multi purpose INS for position and orientation estimation. Additionally, it presents an experimental comparison of a series of sensor fusion solutions and benchmarking their performance on estimating the position of a moving object. Results show a correlation between what sensors are trusted by the algorithm and how well it performed at estimating position. Mahony, SAAM and Tilt algorithms had best general position estimate performance.Com o recente surgimento de sistemas micro-eletromecânico amplamente acessíveis e precisos nos últimos anos, o rastreio de movimento através de sistemas de in erciais tornou-se omnipresente nos dias de hoje. Contrariamente à localização baseada no Sistema de Posicionamento Global (GPS), os Sistemas de Naveg ação Inercial (SNI) não são afetados intrinsecamente pela interferência de sinal, suscetibilidades de bloqueio e falsificação. As medições dos sensores inerciais também são adquiridas a elevadas taxas de amostragem e podem ser integradas numericamente para estimar os conhecimentos de posição e orientação. Estas medições são precisas numa escala de pequena dimensão, mas acumulam grad ualmente erros durante longos períodos. Combinar múltiplos sensores inerci ais num método conhecido como fusão de sensores permite produzir uma mais consistente e confiável compreensão do sistema, diminuindo erros acumulativos. Vários algoritmos de fusão de sensores ocorrem na literatura com o objetivo de estimar os Sistemas de Referência de Atitude e Rumo (SRAR) de um corpo rígido no que diz respeito a uma estrutura de referência. Este trabalho descreve o desenvolvimento e implementação de um sistema multiusos de baixo custo para estimativa de posição e orientação. Além disso, apresenta uma comparação experimental de uma série de soluções de fusão de sensores e compara o seu de sempenho na estimativa da posição de um objeto em movimento. Os resultados mostram uma correlação entre os sensores que são confiados pelo algoritmo e o quão bem ele desempenhou na posição estimada. Os algoritmos Mahony, SAAM e Tilt tiveram o melhor desempenho da estimativa da posição geral

Contactless measurement of electric current using magnetic sensors

We review recent advances in magnetic sensors for DC/AC current transducers, especially novel AMR sensors and integrated fluxgates, and we make critical comparison of their properties. Most contactless electric current transducers use magnetic cores to concentrate the flux generated by the measured current and to shield the sensor against external magnetic fields. In order to achieve this, the magnetic core should be massive. We present coreless current transducers which are lightweight, linear and free of hysteresis and remanence. We also show how to suppress their weak point: crosstalk from external currents and magnetic fields

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

Portable single-beam cesium zero-field magnetometer for magnetocardiography

Optically pumped magnetometers (OPMs) are becoming common in the realm of biomagnetic measurements. We discuss the development of a prototype zero-field cesium portable OPM and its miniaturized components. Zero-field sensors operate in a very low static magnetic field environment and exploit physical effects in this regime. OPMs of this type are extremely sensitive to small magnetic fields, but they bring specific challenges to component design, material choice, and current routing. The miniaturized cesium atomic vapor cell within this sensor has been produced through integrated microfabrication techniques. The cell must be heated to 120°C for effective sensing, while the sensor external faces must be skin safe ≤40°C making it suitable for use in biomagnetic measurements. We demonstrate a heating system that results in a stable outer package temperature of 36°C after 1.5 h of 120°C cell heating. This relatively cool package temperature enables safe operation on human subjects which is particularly important in the use of multi-sensor arrays. Biplanar printed circuit board coils are presented that produce a reliable homogeneous field along three axes, compensating residual fields and occupying only a small volume within the sensor. The performance of the prototype portable sensor is characterized through a measured sensitivity of 90 fT / Hz in the 5 to 20 Hz frequency band and demonstrated through the measurement of a cardiac magnetic signal