K. A. Jose

Resonant frequency of Hilbert curve fractal antennas

An approximate formulation for the resonant frequency of a dipole Hilbert curve fractal antenna (HCFA) is derived here. These can be used as small resonant antennas, useful in VHF/UHF communication. The formulas presented here can be appropriately inverted to obtain the design equations for the antenna, for a given resonant frequency.

Surface acoustic wave MEMS gyroscope

The design and performance evaluation of a surface acoustic wave (SAW) MEMS gyroscope is presented in this paper. This gyroscope is an integration of a SAW resonator and a SAW sensor. The SAW resonator is used to setup a stable reference vibration and SAW sensor is used for the detection of the secondary SAW generated by the Coriolis force. Further to this resonator, strategically positioned metallic dots that form an array along the standing wave anti-node locations are subjected to the reference vibratory motion. These vibrating dot arrays through the Coriolis effect will generate secondary SAW, which is picked up by the SAW sensor. The SAW resonator is designed and optimized using coupling-of-modes (COM) theory. In view of its one-layer planar configuration, this gyroscope can be implemented easily for applications requiring conformal mounting onto a surface of interest. This SAW gyroscope can be competitively priced inherently rugged, reliable and very sensitive. It is also capable of being wirelessly interrogated, without any sensor power source.

Hilbert curve fractal antennas with reconfigurable characteristics

Fractal Hilbert curve is one of the most recent geometries to be studied for antennas. This geometry results in an antenna with low resonant frequency compared to other configurations. The antenna consists of line segments arranged in a predictable fractal order, thus enabling easy generation and reproducible results compared to an arbitrary shrinkage of antenna size. This can be modeled using wire segments. An addition of few more interconnecting segments to the geometry is found to result in significant changes in its radiation pattern. With RF switches within these few selected additional segments and the necessary control units, radiation pattern of the antenna can be made adaptively reconfigurable. Similarly, switches connected in series along the length of the antenna result in frequency tuning characteristics.

Design and development of a smart wireless system for passive temperature sensors

The design and development of a smart wireless system for remote reading of a passive surface acoustic wave (SAW) sensor is presented in this paper. The SAW sensor is a lithium niobate wafer with an inter-digital transducer (IDT) with reflectors, which is inductively coupled to a microstrip meander antenna (ICMA). The reading system is a special FM radar, which transmits and receives FM electromagnetic signals. The transmitted FM signal is picked up by the ICMA which subsequently, converts into a SAW in the LiNbO3 wafer through the IDTs. These SAWs are reflected back to the IDTs by the reflectors, converted back to an electromagnetic wave and returned to the FM radar by the ICMA. The acoustic velocity varies as a function of the propagation characteristics of the SAW in the substrate and results in varying time delay of the echoes, which is detected by the system. The resolution and accuracy of such a system are investigated theoretically and experimentally. The operating principle is evaluated for a remote temperature measurement system. The salient feature of this system is that no power source is required at the sensor and thus is applicable for remote temperature sensing of propellant in barrel-launched adaptive munitions (BLAM), tank rounds and other munitions and missiles. This is also suitable for other remote reading SAW sensors such as indentity tags, wireless pressure sensors, wireless gas sensors, strain sensors, hospital sterilizer sensors, etc.

Multi-band characteristics and fractal dimension of dipole antennas with Koch curve geometry

Fractal geometries have been studied for antennas with special characteristics, both as antenna elements, and as spatial distribution functions for elements in antenna arrays. Koch dipole and monopole antennas have been studied recently as smaller sized antennas, and their multi-band characteristics have been reported (see Cohen, N., IEEE Professional Program Proc. of Electronics Industries Forum of New England, p.43-9, 1997; Puente-Baliarda, C., IEEE Trans. Antennas Propagat., vol.48, p.1773-81, 2000). We try to establish a link between the interval of multi-band characteristics of dipole Koch curve antennas with the dimension of the underlying fractal geometry.

Design optimization and experimental verification of wireless IDT based micro temperature sensor

This paper presents the prediction and measurement of the phase response from a wireless surface acoustic wave (SAW) device for temperature sensing applications. This wireless sensor consists of two or more arrays of an interdigital transducer (IDT) and reflector pair with different IDT-reflector distances. Pulse modulated signals are transmitted from a remote reader system and their echoes are returned with different time delays due to the different IDT-reflector distances. Corresponding intermediate frequency signals are generated in a mixer and their phase differences are calibrated to temperature values. Using the coupled-mode theory of SAWs, the phase characteristic relative to temperature was examined. The effect of the relative distances between the two reflector arrays is demonstrated. The influence of the phase reversal location, which produces multiple temperature values for a given phase difference, is also discussed and a simple solution is illustrated. This sensor is coupled with a small planar antenna, which will be well suited for applications that require passive and conformal sensors.

Low voltage tunable capacitors for RF MEM filters and antenna applications

The design and experimental evaluation of a very low voltage tunable capacitor is presented in this paper. Interdigital capacitors are designed and fabricated on high resistance silicon substrate. Tunable ferroelectric thin film is deposited on to the device and its tunability is measured using an RF network analyzer. It is observed that the capacitor has 80% tunability at 6 volts. In conventional micro fabrication techniques, metal is deposited on the top of a ferroelectric thin film and then develops the device layout by photolithographic and etching technique. However, in this paper, the thin film is deposited on the top of IDT. This helps to reduce the bias voltage and to eliminate the device micro fabrication problems on ferroelectric films. High dielectric constant films can dramatically reduce the device size and it could be possible to achieve desired size of microsensors using these devices. These low voltage tunable ferroelectric films are also useful for the design of phase shifters for phased array antennas and tunable RF MEM filters.

Hybrid MEMS-IDT-based accelerometer and gyroscope in a single chip

In this paper, recent advances made on wireless MEMS-IDT (Interdigital Transducer) based accelerometers and gyroscopes at Penn State and HVS are presented. The concept and design principles are based on using surface acoustic waves (SAW) and polysilicon seismic mass for acceleration and proof mass for gyro. By designing the seismic mass of the accelerometer to float just above a high frequency Rayleigh Surface Acoustic Wave Sensor (SAWS), we are able to realize the accuracy and versatility required for the measurement of accelerations from 10-6 g to 100 g. The gyro design is based on the combination of Surface Acoustic Wave Resonator (SAWR) and Surface Acoustic Wave Sensor, which operates at the Rayleigh mode. The transmitter IDT creates SAW that propagates back and forth between the reflectors and forms a standing wave pattern within the cavity space between the IDTs. The particles at the anti-nodes of standing wave pattern experience large amplitude of vibration perpendicular to the plane of the substrate, which serves as the reference vibrating motion for the gyroscope. A number of metallic (proof) masses are strategically positioned at the anti-node locations so that the effect of the Coriolis force can be used to sense the gyroscopic motion.

FSS embedded microwave absorber with carbon fiber composite

The design and experimental evaluation of microwave absorbers with frequency selective surface (FSS) embedded in impedance-graded carbon fiber (CF) composite is presented. Samples with different FSS patterns embedded in CF composites are fabricated and experiments carried out to find out the effects of embedded FSSs. It is found that both the FSS pattern and its location in the composite are critical for the reflection property of the sample. The results were compared with that the theoretical predictions using a micro-genetic algorithm (MGA) and are in good agreement.

Highly sensitive and wide-dynamic-range navigation microsystem on a single chip

AbstractThe inertial navigation system uses both gyroscopes and accelerometers tomeasure the state of motion of a target or a missile by sensing the changes in that statecaused by accelerations. The required features in many of these applications are high precision, wide dynamic range and wide frequency range. In this paper, recent advances made on MEMS-IDT based accelerometers and gyroscopes at Penn State is presented.These devices possess typical advantages of MEMS sensors including the additionalbenefits of robustness, excellent sensitivity, surface conformability and durability. Thetransmitter IDT creates SAW (Surface Acoustic Wave) that propagates back and forth between the reflectors and forms a standing wave pattern within the cavity space between the IDTs. The particles at the anti-nodes of standing wave pattern experience largeamplitude of vibration perpendicular to the plane of the substrate, which serves as the reference vibrating motion for this gyroscope. A number of metallic masses are