RF MEMS reference oscillators platform for wireless communications

A complete platform for RF MEMS reference oscillator is built to replace bulky quartz from mobile devices, thus reducing size and cost. The design targets LTE transceivers. A low phase noise 76.8 MHz reference oscillator is designed using material temperature compensated AlN-on-silicon resonator. The thesis proposes a system combining piezoelectric resonator with low loading CMOS cross coupled series resonance oscillator to reach state-of-the-art LTE phase noise specifications. The designed resonator is a two port fundamental width extensional mode resonator. The resonator characterized by high unloaded quality factor in vacuum is designed with low temperature coefficient of frequency (TCF) using as compensation material which enhances the TCF from - 3000 ppm to 105 ppm across temperature ranges of -40˚C to 85˚C. By using a series resonant CMOS oscillator, phase noise of -123 dBc/Hz at 1 kHz, and -162 dBc/Hz at 1MHz offset is achieved. The oscillator’s integrated RMS jitter is 106 fs (10 kHz–20 MHz), consuming 850 μA, with startup time is 250μs, achieving a Figure-of-merit (FOM) of 216 dB. Electronic frequency compensation is presented to further enhance the frequency stability of the oscillator. Initial frequency offset of 8000 ppm and temperature drift errors are combined and further addressed electronically. A simple digital compensation circuitry generates a compensation word as an input to 21 bit MASH 1 -1-1 sigma delta modulator incorporated in RF LTE fractional N-PLL for frequency compensation. Temperature is sensed using low power BJT band-gap front end circuitry with 12 bit temperature to digital converter characterized by a resolution of 0.075˚C. The smart temperature sensor consumes only 4.6 μA. 700 MHz band LTE signal proved to have the stringent phase noise and frequency resolution specifications among all LTE bands. For this band, the achieved jitter value is 1.29 ps and the output frequency stability is 0.5 ppm over temperature ranges from -40˚C to 85˚C. The system is built on 32nm CMOS technology using 1.8V IO device

HUMIDITY SENSOR CIRCUIT USING REAL TIME OPERATING SYSTEM (FREERTOS) KERNEL

A humidity sensor can be used to measure the moisture content of the environment. The physical change of the sensor expresses as the change of electrical property like capacitance, resistance, voltage, current, frequency, etc. In order to process these analog signals digitally, microprocessor is involved in the measurement. This thesis presents design of a circuit to measure low moisture levels. The 16-bit RISC mixed signal microcontroller MSP430F249 from Texas Instruments will be used. The circuit has good performance at extremely low humidity levels. Meanwhile, a small real time operating system kernel FreeRTOS, a market leading RTOS from Real Time Engineer Ltd is ported to the microcontroller. The basic concept about FreeRTOS and how to port this RTOS to MSP430F249 microcontrollers will be the topics of this thesis as well

Development of low-cost indoor air quality monitoring devices: Recent advancements

The use of low-cost sensor technology to monitor air pollution has made remarkable strides in the last decade. The development of low-cost devices to monitor air quality in indoor environments can be used to understand the behaviour of indoor air pollutants and potentially impact on the reduction of related health impacts. These user-friendly devices are portable, require low-maintenance, and can enable near real-time, continuous monitoring. They can also contribute to citizen science projects and community-driven science. However, low-cost sensors have often been associated with design compromises that hamper data reliability. Moreover, with the rapidly increasing number of studies, projects, and grey literature based on low-cost sensors, information got scattered. Intending to identify and review scientifically validated literature on this topic, this study critically summarizes the recent research pertinent to the development of indoor air quality monitoring devices using low-cost sensors. The method employed for this review was a thorough search of three scientific databases, namely: ScienceDirect, IEEE, and Scopus. A total of 891 titles published since 2012 were found and scanned for relevance. Finally, 41 research articles consisting of 35 unique device development projects were reviewed with a particular emphasis on device development: calibration and performance of sensors, the processor used, data storage and communication, and the availability of real-time remote access of sensor data. The most prominent finding of the study showed a lack of studies consisting of sensor performance as only 16 out of 35 projects performed calibration/validation of sensors. An even fewer number of studies conducted these tests with a reference instrument. Hence, a need for more studies with calibration, credible validation, and standardization of sensor performance and assessment is recommended for subsequent research

A study to identify and compare airborne systems for in-situ measurements of launch vehicle effluents

An in-situ system for monitoring the concentration of HCl, CO, CO2, and Al2O3 in the cloud of reaction products that form as a result of a launch of solid propellant launch vehicle is studied. A wide array of instrumentation and platforms are reviewed to yield the recommended system. An airborne system suited to monitoring pollution concentrations over urban areas for the purpose of calibrating remote sensors is then selected using a similar methodology to yield the optimal configuration

Description of a Portable Wireless Device for High-Frequency Body Temperature Acquisition and Analysis

We describe a device for dual channel body temperature monitoring. The device can operate as a real time monitor or as a data logger, and has Bluetooth capabilities to enable for wireless data download to the computer used for data analysis. The proposed device is capable of sampling temperature at a rate of 1 sample per minute with a resolution of 0.01 °C . The internal memory allows for stand-alone data logging of up to 10 days. The device has a battery life of 50 hours in continuous real-time mode. In addition to describing the proposed device in detail, we report the results of a statistical analysis conducted to assess its accuracy and reproducibility

A WIRELESS SENSOR SYSTEM WITH DIGITALLY CONTROLLED SIGNAL CONDITIONING CIRCUIT FOR FORCE MONITORING AT BONE FIXATION PLATES

Post-rehabilitation of orthopedic surgery is critical for bone fracture treatments. Current protocols are not based on quantitative assessments of the patient condition but they are conservative estimations mostly based on prior experience and physician’s opinions. While there are quantitative methods for assessing the recovery of orthopedic surgery, they are typically very expensive and provide only snapshots during the healing process. A standalone, reconfigurable, embedded wireless sensor system with digitally controlled signal conditioning system capable of providing continuous monitoring of bone healing is developed. Strain sensor measurements were validated against a commercial mechanical loading instrument for relevant loads that an animal (ovine) would experience during in vivo testing (up to 250 N). The loader was configured to apply a maximum force of 250 N to the bone fixation plate at a rate of 1000 N/min. Cyclic testing of the system showed optimal stability and no observable drift in the sensor. The sensor was also implemented in a rodent model for monitoring force loading at an internal bone fixation plate. The platform’s small, robust, and low power nature is usefulness for continuous wireless monitoring and actuation in many biomedical applications

Results of the 1992 NASA/JPL Balloon Flight Solar Cell Calibration Program

The 1992 solar cell calibration balloon flight was completed on August 1, 1992. All objectives of the flight program were met. Forty-one modules were carried to an altitude of 119,000 ft (36.3 km). Data telemetered from the modules was corrected to 28 C and 1 AU. The calibrated cells have been returned to 39 participants and can now be used as reference standards in simulator testing of cells and arrays

A Wireless Electronic Nose System Using a Fe2O3 Gas Sensing Array and Least Squares Support Vector Regression

This paper describes the design and implementation of a wireless electronic nose (WEN) system which can online detect the combustible gases methane and hydrogen (CH4/H2) and estimate their concentrations, either singly or in mixtures. The system is composed of two wireless sensor nodes—a slave node and a master node. The former comprises a Fe2O3 gas sensing array for the combustible gas detection, a digital signal processor (DSP) system for real-time sampling and processing the sensor array data and a wireless transceiver unit (WTU) by which the detection results can be transmitted to the master node connected with a computer. A type of Fe2O3 gas sensor insensitive to humidity is developed for resistance to environmental influences. A threshold-based least square support vector regression (LS-SVR)estimator is implemented on a DSP for classification and concentration measurements. Experimental results confirm that LS-SVR produces higher accuracy compared with artificial neural networks (ANNs) and a faster convergence rate than the standard support vector regression (SVR). The designed WEN system effectively achieves gas mixture analysis in a real-time process