In recent years, several attempts have been made to develop instrumentation to aid in the measurement of soil water electrical conductivity. Each of the instruments have specific limitations. This dissertation discusses the available methods of measuring this parameter and indicates the limitations of the transducers which have been described in the literature. Also, discussed are the basic theories of operation of these transducers and definitions related to soil salinity in general. The major objective of this research was to develop a new transducer which would be a significant improvement over existing types of instrumentation. It is believed that this research has led to the development of two transducers of different geometries which can assess the soil water conductivity over a wider range of matric potential just as rapidly and accurately as the next best unit. At the same time the new transducers incorporate automatic temperature compensation which has not been done by any other field instrumentation of its type. Also presented, is the application of heat transfer theories to the diffusion of ions from the transducer to the surrounding environment, Application of this theory allows one to predict how the transducer will respond to a step change in ion concentration in an unsaturated soil system where the only process involved is diffusion. Good agreement between experimental measurements and predicted response indicates that the model may also be useful in further refinements of the transducer.

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Piezoelectric plate transducers are commonly used for the generation and detection of ultrasonic signals and have applications in, for example, non-destructive testing and medical imaging. A rigorous theoretical investigation of thermal noise in plate transducers has been undertaken with the aim of establishing the absolute limits of receiver sensitivity in terms of both Minimum Detectable Power (MDP) and Minimum Detectable Force (MDF). The central feature of the work has been the development of two independent theories which provide identical results. One theory is based on an electrical approach which makes use of an extensively modified version of Hayward's linear systems model of the piezoelectric plate transducer, along with the well known work of Johnson and Nyquist. The other theory is based on a mechanical approach which makes use of the less well known work of Callen and Welton. Both theories indicate that only two parameters are required in order to determine the MDP and MDF of an open circuit transducer. These parameters are the transducer's characteristic acoustic impedance and its mechanical quality factor. Significantly, the thermally limited sensitivity of an open circuit receiving transducer has been shown not to be related to its electromechanical coupling efficiency or any of its electrical properties. By applying the new theories it has been possible to design an ultra low noise ultrasonic receiver with wide ranging applications. Among other things, this receiver has been used to demonstrate the viability of a robust and truly practical air-coupled Lamb wave scanner suitable for detecting defects in thin plates which can be made from almost any type of material. The complete system has sufficient sensitivity to allow rapid scanning without the requirement for transducer matching layers or electronic signal averaging.

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Modern satellite, wireless communication, and radar systems often demand wideband performance for multi-channel operation and the ability to steer multiple beams for multiple moving targets. This dissertation covers a variety of topics to design low-cost and wideband antenna systems. The main areas of study are microwave devices controlled piezoelectric transducers (PETs) and wideband baluns and balanced microwave circuits using parallel-strip lines. Some focus has also been given to the design of Rotman lens for multiple beam generation and Vivaldi antenna arrays for wideband two-dimensional scanning. The dielectric perturbation technique controlled by PET is introduced to design a wideband phase shifter and a QPSK modulator, and to tune the resonant frequency of a slot dipole. The designed PET-controlled phase shifters are used for beam steering in a dual beam phased array using a bidirectional feeding scheme and a five-beam phased array using a microstrip Rotman lens. Vivaldi-type antennas are commonly used to achieve wideband performance. Very wideband performance can be achieved using an antipodal tapered slot antenna because of its inherent simple wideband transition from microstrip line to parallel-strip line. An antipodal tapered slot antenna and a phased array are designed to span 10 to 35 GHz. In addition, a 4??4 two-dimensional antenna array is designed using wideband antipodal tapered slot antennas, and two sets of PET-controlled phase shifters for E- and H-plane scanning are fabricated to steer the beam. As a microwave system using wideband antenna array, a new low-cost and wideband phased array radar is developed using a modulated pulse over 8 to 20 GHz band. The double-sided parallel-strip line as a balanced line is presented. The parallelstrip line offers much flexibility for microwave circuit designs. This transmission line makes it possible to realize a low impedance line and allows the design of a compact wideband balun and junction. Wideband transitions (or baluns) from parallel-strip line to microstrip line, a typical unbalanced transmission line, are realized to cover several octave bandwidth. Balanced microwave filters and a hybrid coupler are developed using the parallel-strip line.

In this thesis, piezoelectric transducers were fabricated by depositing ZnO films on PET substrates. The optimal deposition parameters for ZnO films are sputtering pressure of 15 mTorr, RF power of 75 W and oxygen concentration of 60 %, which are determined by scanning electron microscopy and X-ray diffraction analysis. PET substrates of Young¡¦s modulus of 6.62 GPa are obtained by Nano Indenter. To fabricate a transducer with resonance frequency of 100 Hz, the cantilever length of 0.979 cm and vibration area of 1.4835 cm2 are calculated by Cantilever Vibration Theory. Copper layer was attached to ZnO/ITO/PET structure to form piezoelectric transducers. A mass of 0.57 g was attached to the transducer to increase the vibration amplitude. A vibration source of 100 Hz was provided to the piezoelectric transducer and then the experimental results were obtained by oscilloscope. The optimal thickness of ZnO films is 964.65 nm, at which the open circuit voltage is 1.87 V. A bridge rectifier was constructed by Shottky diode with product number 1N5711 along with a capacitor of 37 nF. After rectifying and filtering of device output, the maximum power of 0.0697£gW/cm2 was generated with the load resistance of 5 M£[ and the internal resistance of 4.3185 M£[.

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