Integrated Silicon Photonics has emerged as a powerful platform in the last two decades amongst high-bandwidth technologies, particularly since the adop- tion of CMOS compatible silicon-on-insulator(SOI) substrates. Microring res- onators are one of the fundamental blocks on a photonic integrated circuit chip o ering versatility in varied applications like sensing, optical bu ering, ltering, loss measurements, lasing, nonlinear e ects, understanding cavity optomechanics etc. This thesis covers the design and modeling of microring resonators for biosensing applications. The two applications considered are : homogeneous biosensing and wrist pulse pressure monitoring. Also, the designs have been used to fabricate ring resonator device using three different techniques. The results obtained through characterization of these devices are presented. Following are the observations made in lieu of this: 1) Design modeling and analysis - The analysis of ring resonator requires the study of both the straight and bent waveguide sections. Both rib and strip waveguide geometries have been considered for constructing the device as a building block by computing their respective eigen modes for both quasi-TE and quasi-TM polarizations. The non-uniform evanescent coupling between the straight and curved waveguide has been estimated using coupled mode theory. This method provided in estimating the quality-factor and free spec- tral range (FSR) of the ring-resonator. A case for optimizing the waveguide gap in the directional coupler section of a ring resonator has been presented for homogeneous biosensing application. On similar lines, a model of applying ring resonator for arterial pulse-pressure measurement has been analyzed. The results have been obtained by employing FD-BPM and FDTD including semi- vectorial eigen mode solutions to evaluate the spectral characteristics of ring resonator. The modeling and analytical results are supported by commercial software tools (RSoft). 2) Fabrication and Characterization - For the fabrication, we employ the design of ring resonator of radius 20 m on SOI substrate with two different waveguide gaps of 350 and 700 nm. Three different process sows have been used for fabricating the same device. The rst technique involved using negative e-beam resist HSQ which after exposure becomes SiO2, acts as a mask for Reactive-Ion Etching (RIE); helping in eliminating an additional step. The second technique involved the use of positive e-beam resist, PMMA for device patterning followed by metal deposition with lift-o . The third tech- nique employed was Focussed Ion-beam (FIB) which is resist-less patterning by bombarding Ga+ ions directly onto the top surface of the wafer with the help of a GDS le. The characterization process involved estimation of loss and observing the be- havior of optical elds in the device around the wavelength of 1550 nm using near-field scanning optical microscopy (NSOM) measurement. The estimation of roughness-induced losses has been made by performing Atomic Force Microscopy (AFM) measurements. In summary, the thesis presents novel design and analysis of SOI based microring resonators for homogeneous biosensing and wrist pulse pressure sensing applications. Also, the fabrication and characterization of 20 m radius ring- resonator with 500 500 nm rib cross-section is presented. Hence, this study brings forth several practical issues concerning application of ring resonators to biosensing applications.

The performance of an acoustic filter (or muffler) is measured in terms of one of the following parameters: Insertion Loss (IL), Level difference (LD) and Transmission loss (TL). All these three parameters may be evaluated in terms of the four-pole or transfer matrix parameters. Appropriate experimental setups have been designed and developed and practical considerations are described. Measured values of TL are compared with the analytically predicted values. It is shown that the Two-Source-Location method is relatively the best. To start with, the matrizant analysis of conical concentric tube resonators is validated experimentally. The effect of mean flow is investigated. The experimental setup is specially designed to measure the pressure transfer function across the test muffler. It is shown that there is reasonably good agreement between the predicted values of the transfer function and the measured ones for incompressible mean flow as well as stationary medium. To measure insertion loss of muffler, one needs to calculate the source impedance. The internal impedance of a sound source can be measured using direct or indirect methods. The four-load SPL measurement method is one such indirect method wherein there are three nonlinear equations in terms of two unknowns which makes one of the equations redundant. This leads to erroneous results. To overcome this inherent weakness, two alternatives multi-load methods have been offered in the literature; namely, the least squares and the direct least squares method, to analyze the measured data used for four (or more) different loads. These two methods produce better results than the four-load SPL measurement method used earlier. These measurement methods have been tested on a loudspeaker to measure its source impedance and the results are validated with a known additional acoustic load. Simple expansion chambers, the simplest of the muffler configurations, have very limited practical application due to the presence of periodic troughs in the transmission loss (TL) spectrum which drastically lower the overall TL of the muffler. Many of the present days automobile exhaust systems make use of the extended tube mufflers, often with perforated ducts because of their low back pressure and good acoustic performance. Tuned extended inlet and outlet can be designed to nullify three-fourths of these troughs, making use of the plane wave theory. However, these cancellations would not occur unless one altered the geometric lengths for the extended tube and perforated tube resonators in order to incorporate the effect of the evanescent higher-order modes (multidimensional effect) through end corrections or lumped inertance approximation at the area discontinuities or junctions. This is investigated here experimentally as well as numerically (through use of 3-D FEM software) for a moving medium as well as stationary medium. The effect of temperature on the end corrections is also investigated. These tuned extended-tube chambers, however, suffer from the disadvantages of high back pressure and aerodynamic noise generation at the area discontinuities. These two disadvantages can be overcome by means of a perforated bridge between the extended inlet and the extended outlet. One dimensional control volume approach is used to analyze this muffler configuration. It is validated experimentally making use of the two source-location method, which is proven to be the best method available to us. It is thus shown that the inertance of holes plays a role similar to the lumped inertance generated by evanescent 3-D modes at the terminations of the quarter wave resonators in the case of the double-tuned extended tube chambers. The effect of mean flow is also investigated. The resultant transfer matrix is then used to carry out a systematic parametric study in order to arrive at empirical expressions for the differential lengths as well as the end corrections. Thus, an extended concentric tube resonator can be tuned such that the first three troughs that characterize the corresponding simple chamber transmission loss (TL) curve may be eliminated making use of the proposed procedure. In fact, the entire TL curve at low and medium frequencies may be substantially lifted, making the tuned extended concentric tube resonator a viable design option.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This paper briefly reports on concepts for hardening (physically toughening) crystal reference oscillators for the highly integrated program known as HSTSS. Within the HSTSS program is the L & S band transmitter development contract. The harshest requirements for this contract are surviving and functioning, to within 20 ppm of its center frequency, 30 ms after sustaining a shock pulse of 100,000 (g) for 0.5 ms on any axis. Additional requirements call for the transmitter to be no larger than 0.2 in3, and to operate within a 20 ppm frequency stability throughout the temperature range of -400 to +850 centigrade and during centrifugal spins of up to 300 Hz or 25,000 (g). Fundamentally the question is, is it feasible for any telemetry system to be capable of withstanding such harsh conditions and, to be practical on all DoD Test Ranges, still adhere to the stability tolerance guidelines set forth by the Range Commanders Council on Telemetry Standards - IRIG 106-96? Under "normal" conditions, stability requirements for "Range" transmitters are easily satisfied through the use of off-the-shelf crystal reference oscillators which provide the reference frequencies required within a transmitter’s phase lock loop circuitry. Unfortunately, the oscillator is also the most vulnerable part of a transmitter to the conditions listed and is the key to this problem. The oscillator’s weak points are in its resonator’s fragile quartz structure (the blank) and support mechanism. The challenge is to invent and adapt this area to these newer harsher conditions and to do it in the smallest space ever required.

Resonators are one of the most important parts of electronic products. They provide a stable reference frequency to ensure the operation of these products. Recently, the electronic products have the trend of miniaturization, which rendered the size reduction of the resonators as well [1]. Better design of the resonators relies on a better understanding of the crystals' nonlinear behavior [2]. The nonlinearities affect the quality factor and acoustic behavior of MEMS (Micro-Electro-Mechanical-System) and nano-structured resonators and filters [3]. Among these nonlinear effects, Drivel Level Dependence (DLD), which describes the instability of the resonator frequency due to voltage level and/or power density, is an urgent problem for miniaturized resonators [2]. Langasite and GaPO4 are new promising piezoelectric material. Resonators made from these new materials have superior performance such as good frequency-temperature characteristics, and low acoustic loss [2]. In this thesis, experimental measurements of drive level dependence of langasite resonators with different configurations (plano-plano, single bevel, and double bevel) are reported. The drive level dependence of GaPO4 resonators are reported as well for the purpose of comparison. The results show that the resonator configuration affects the DLD of the langasite resonator. Experiments for DLD at elevated temperature are also performed, and it was found that the temperature also affects the DLD of the langasite resonator.

Metamaterials offer the freedom to tune the rich electromagnetic coupling between the constituent meta-atoms to tailor their collective electromagnetic response. Therefore, a comprehensive understanding of the nature of electromagnetic interactions between meta-atoms is necessary for novel metamaterial design, which is provided in the first part of this thesis. The subsequent work in the thesis applies the understanding from the first part to design and demonstrate novel one-dimensional metamaterials that overcome the limitations of metamaterials proposed in literature or exhibit electromagnetic responses not previously observed. Split-ring Resonators (SRRs) are a fundamental building block of many electromagnetic metamaterials. In the first part of the work in this thesis, it is shown that bianisotropic SRRs (with magneto-electric cross-polarisation) when in close proximity to each other, exhibit a rich coupling that involves both electric and magnetic interactions. The strength and nature of the coupling between two identical SRRs are studied experimentally and computationally as a function of their separation and relative orientation. The electric and magnetic couplings are characterised and it is found that, when SRRs are close enough to be in each other's near-field, the electric and magnetic couplings may either reinforce each other or act in opposition. At larger separations retardation effects become important. The findings on the electromagnetic interactions between bianisotropic resonators are next applied to developing a one-dimensional ultra-wideband backward-wave metamaterial waveguide. The key concept on which the metamaterial waveguide is built is electro-inductive wave propagation, which has emerged as an attractive solution for designing backward-wave supporting metamaterials. Stacked metasurfaces etched with complementary SRRs (CSRRs) have also been shown to exhibit a broadband negative dispersion. It is demonstrated through experiment and numerical modeling, that the operational bandwidth of a CSRR metamaterial waveguide can be improved by restricting the cross-polarisation effects in the constituent meta-atoms. The metamaterial waveguide constructed using the modified non-bianisotropic CSRRs are found to have a fractional bandwidth of 56.3\% which, based on a thorough search of relevant literature, is the broadest reported value for an electro-inductive metamaterial. A traditional coupled-dipole toy-model is presented as a tool to understand the field interactions in CSRR based metamaterials, and to explain the origin of their negative dispersion response. This metamaterial waveguide should be of assistance in the design of broadband backward-wave metamaterial devices, with enhanced electro-inductive waveguiding effects. In the final part of the thesis, a one-dimensional metamaterial prototype that permits simultaneous forward- and backward-wave propagation is designed. Such a metamaterial waveguide could act as a microwave analogue of nanoparticle chains that support electromagnetic energy transfer with a positive or a negative dispersion due to the excitation of their longitudinal or transverse dipole modes. The symmetry of the designed hybrid meta-atom permits the co-existence of two non-interfering resonances closely separated in frequency. It is experimentally and computationally shown that the metamaterial waveguide supports simultaneous non-interacting forward- and backward-wave propagation in an overlapping frequency band. The proposed metamaterial design should be suitable for realising bidirectional wireless power transfer applications.

A reflective Tiered Fresnel Zone Plate, herein called a Tiered Fresnel Mirror TFM, with a focal length on the order of a meter is studied for use as the mirror(s) in a Fabry-Perot interferometer type of laser. The relative phase transition within the individual zones (ideally smooth from zero to pi ) is stair-stepped or tiered in the longitudinal direction of the mirror. Within an individual zone the step height is constrained to a constant whereas the width of the tiers are monotonically decreased when traversing radially outward so that the overall profile follows the ideal smooth curve. The effectiveness of the number of tiers per zone, measured by the loss per pass or round-trip, varies from a Plane Mirror (zero tiers per zone) to a Spherical Mirror (an infinite number of zones per tier). The Fox and Li iterative method of determining the E-Field as the beam propagates back and forth is applied to an empty cavity resonator to determine the diffraction loss. A computer program is written to investigate the diffraction loss of various mirror configurations. The performance of the TFM is found to be not as efficient as the Spherical Mirror (the number of tiers per zone is shown to be a major variable) but may be tolerable under applications of a moderately high gain laser medium. The Gaussian Fundamental mode is easier to maintain since the higher order modes have a higher loss per round trip. The manufacture of the TFM can be incorporated easily into an IC process thereby making the cost of the novel mirror relatively cheap when produced in quantities. A major cost variable is again the number of tiers per zone which is proportional to the number of processing steps. The TFM's performance with respect to the etch depth of the steps in the mirror's stair-stepped profile is simulated and found to be a very doable etch with the current plasma etch technology.

Tonal noise propagating in ducts and radiating from their outlets is a common problem in situations where a fan or a blower is used to drive exhaust gases through the exhaust duct out to the environment. It is also a problem in the exhausts of large diesel engines such as those used to power large marine vessels. One way of attenuating tonal noise propagating in ducts is to use one or more side branch resonators, each of which is specifically designed for optimal performance at a particular frequency. One of the major problems associated with the use of side branch resonators is that any slight change in excitation frequency decreases the effectiveness of the resonators. The change in excitation frequency can be caused by a change in the speed of the engine, fan or blower, or change in temperature in the duct, which changes the speed of sound, and hence the wavelength of the noise. Resonators incorporating a provision for altering their geometry in real - time in order to adapt to environmental or operating condition changes is one approach that has been used by previous researchers. In particular, adaptive Helmholtz resonators have received considerable attention in the literature. Previous work has involved the use of one or more pressure sensors located in the duct downstream of the resonator to provide a cost function to be minimised by an electronic control system which alters the geometry of the resonator. However, in many cases, especially where the duct serves as a passage for exhaust gases to be driven out to the environment, it is not desirable to mount microphones in the duct. Also, microphones located remote from the resonator introduce wiring problems as well as the need to mount the microphones at the correct location in the duct, which will change as the wavelength of the tonal noise in the duct changes as a result of changes in operating or environmental conditions. It is highly desirable to have a completely self - contained Helmholtz resonator ( HR ) which can be attached to the duct and for which the only external wiring needed is the power supply. The work described in this thesis is concerned with the development of a self - contained adaptive HR which can be optimally tuned by using signals from two microphones located in the cavity and neck of the resonator, respectively. The primary focus of the work is the development of a novel cost function, which can be used by an electronic controller to optimally tune the HR. The scope of the analysis has been restricted here to the ' no mean flow ' condition. The theoretical and numerical analysis of the duct - HR system is first conducted using the well known transfer matrix method and finite element analysis ( FEA ) software package ANSYS, respectively. The net acoustic power transmission in the duct downstream of the HR is estimated by using the two - microphone method. Analysing the duct - HR system with the transfer matrix method mandates the incorporation of three end - correction factors which are related to the unflanged open end of the duct, neck - cavity interface and neck - duct interface. However, because of the complexity in estimating the end - correction factor of the neck at the neck - duct interface due to the generation of a complex sound field in the vicinity of the neck opening, the transfer matrix method only approximates the in - duct net acoustic power transmission. This implies that changing the value of the neck - duct interface end - correction factor changes the calculated frequency at which the maximum reduction of in - duct net acoustic power transmission downstream of the HR occurs. On the other hand, ANSYS does not require the inclusion of any kind of end - correction factors apart from the actual physical dimensions of the system, and is thus much more accurate than the transfer matrix method. To minimise the in - duct net acoustic power transmission downstream of the HR, a number of different cost functions that were related to the net acoustic power transmission were investigated theoretically, numerically and experimentally. These all involved either the acoustic pressure at the top of the closed end of the cavity of the HR or at the neck wall of the HR close to the neck - duct interface or the amplitude of the pressure transfer function between two microphones located in the resonator. The two potential cost functions which were initially considered to be maximised for indicating the minimisation of the in - duct net acoustic power transmission downstream of the resonator were : ( a ) the pressure at the top of the closed end of the cavity, and ( b ) the amplitude of the pressure transfer function between the pressure at the top of the closed end of the cavity and the pressure at the neck wall close to the neck - duct interface. It was found that the location of the microphone in the neck was extremely important, with the best location being at the centre of the duct adjacent to the neck opening. However, this location was not considered practical because a microphone in the duct can obstruct the mean flow of gas in the duct. The best location for mounting the microphone in the neck was found to be at the neck wall as close as possible to the neck - duct interface. The results are shown in two different ways : ( 1 ) broadband analysis, whereby the in - duct net acoustic power transmission downstream of the HR, the pressure at the top of the closed end of the cavity and the pressure transfer function between the pressure at the top of the closed end of the cavity and at the neck wall close to the neckduct interface are plotted as a function of frequency, and ( 2 ) single frequency analysis, whereby all the aforementioned results are plotted as a function of the cylindrical cavity length ( for a fixed cavity diameter ) for a single, tonal frequency. For broadband analysis, the numerical ( ANSYS ) results showed that the frequency at which the maximum reduction of in - duct net acoustic power transmission downstream of the HR occurs differs from the frequencies which correspond to the maximum responses of cost functions ( a ) and ( b ) described above. For single frequency analysis, when trying to optimise the performance of a duct - mounted HR at a particular frequency by altering its volume, the optimal dimensions of the HR required to attain the maximum reduction of in - duct net acoustic power transmission at that frequency differ from the dimensions of the HR which correspond to the maximised responses of the cost functions ( a ) and ( b ). These results were validated experimentally using a 3 m long circular duct of 0.1555 m diameter with an attached cylindrical HR. During the experimental work, only plane waves were propagating down the duct and there was no mean flow in the duct. Instead of only focusing on the amplitude of the pressure transfer function between the pressures at the top of the closed end of the cavity and the pressure at the neck wall close to the neck - duct interface, the phase difference between the same locations in the HR was also considered. It was found that the phase difference depends on the quality factor ( or damping ) of the entire acoustic system. Experiments were conducted with varying dimensions of the HR and two novel cost functions were empirically derived. Both cost functions, which does not include any kind of measurement remote from the HR, are based on the damping ( or the quality factor ) of the duct - HR system and the phase difference between the pressure at the top of the closed end of the cavity and the pressure at the neck wall close to the neck - duct interface. The effectiveness and performance of both cost functions were found to be excellent for minimising the in - duct net acoustic power transmission downstream of the HR. However, the second cost function is preferred because the procedure involved for measuring the system damping is more convenient from the practical point of view than the procedure for the first one. The quality factor of the duct - mounted HR, at the frequency at which noise needs to be attenuated, was determined by tuning the length of the cavity of the HR so as to maximise the amplitude of the pressure transfer function of the HR. This estimated quality factor was found to be directly related to the transfer function phase which corresponds to the minimum in - duct net acoustic power transmission at the tonal frequency. Once this optimum transfer function phase is known, an active control system can be used to drive a motor to adjust the cavity length of the HR to achieve the optimum phase. / Thesis (M.Eng.Sc.)--School of Mechanical Engineering, 2006.

by R.A. Rapuano and J. Halpern. / "June 28, 1946." / Includes bibliographical references. / Army Signal Corps Contract No. W-36-039 sc-32037.

El gran impacto de la tecnología FBAR tanto en sistemas de radio frecuencia como más recientemente en sensores han motivado el desarrollo de aplicaciones integradas. Esto implica que los procesos de fabricación deberían lograr producir dispositivos resonadores con un alto factor de calidad, al tiempo que permitir la integración de los FBAR con tecnologías CMOS estándar. De tal manera, esta tesis doctoral aborda dichos requerimientos, contribuyendo con el diseño, fabricación y caracterización de resonadores FBAR; su integración con tecnologías CMOS estándar; y su aplicación a sistemas de sensores. El desarrollo de la tecnología de fabricación de los FBAR ha involucrado la puesta a punto de las técnicas de depósito y micro-mecanización de la estructura en capas del resonador, la cual está comprendida por una película de material acústico hecha de nitruro de aluminio (AlN). Se realizaron diversas pruebas para analizar la calidad del AlN depositado. También se probaron y pusieron a punto diferentes tecnologías de micro¬mecanización para liberar la estructura del FBAR, destacando entre ellas la técnica de ataque en seco por la cara de componentes, dados los altos factores de calidad obtenidos (superiores a 2.000 a 2,4 GHz). Sobre los dispositivos fabricados se realizaron caracterizaciones estructurales, modelos utilizando análisis de elementos finitos y la extracción de parámetros de circuito equivalente. Una variación del proceso que involucraba el diseño, modelado y fabricación de un dispositivo FBAR con compensación de temperatura fue igualmente desarrollada. En este ámbito vale la pena resaltar la concepción y realización de una novedosa técnica post-fabricación para el ajuste fino de la frecuencia de resonancia de los FBAR por medio de un haz de iones focalizados (FIB). Basado en la tecnología arriba mencionada, se desarrolló un método de integración heterogénea a nivel de oblea de los dispositivos FBAR en sustratos CMOS estándar. De acuerdo con este método, se logró fabricar por primera vez dispositivos FBAR flotando sobre sustratos CMOS estándar. Este método ha sido exitosamente demostrado por medio de la integración de los FBAR tanto con la tecnología comercial AMS035 como con la CNM25, desarrollada en el CNM-IMB (CSIC). En el terreno de las aplicaciones, se diseñaron y realizaron diferentes aplicaciones de sensores basadas en FBAR, siendo el detector de masas localizadas la más relevante de entre ellas. Es de anotar que esta aplicación fue demostrada por primera vez utilizando FBARs de alta frecuencia como elemento sensor. De tal forma, se contrastaron los resultados experimentales y de modelado del sensor. Por otra parte, se presenta también el concepto de sensores mecánicos basados en FBAR. Para ello se han desarrollado dos ejemplos: el acelerómetro basado en FBAR y el sensor de fuerza para aplicaciones de puntas de AFM. Se reporta también en esta tesis la fabricación y caracterización de un nuevo tipo de resonadores acústicos de AlN sin contacto entre electrodos. / The high impact of FBAR on radio-frequency and, most recently, on sensing systems has motivated the development of integrated applications. This means that the fabrication process should succeed in producing high-quality-factor resonators and, at the same time, in integrating FBARs with standard CMOS technologies. Hence, this Ph.D. thesis addresses these requirements by contributing with the design, fabrication and characterization of thin-film bulk acoustic wave resonators (FBAR); their integration with standard complementary-metal-oxide-semiconductor (CMOS) technologies; and their application to sensing systems. The development of the FBAR's fabrication technology has involved the set up of the deposition and micromachining techniques of the layered structure of the resonator, which comprises an acoustic layer made of aluminum nitride (AlN). Several tests on the deposition and characterization of the AlN quality were carried out. Also, different micro-machining technologies for FBAR releasing were tested, the front-side micro-machining technique having obtained the best quality-factor results (over 2,000 at 2.4 GHz). Structural and device experimental characterization; and equivalent-circuit parameter and finite-element modeling of the FBAR were carried out. A process variation involving the design, modeling and fabrication of a temperature-compensated (TC) FBAR device was also implemented. Another remarkable result is the implementation of a post-fabrication, focused-ion-beam assisted technique for tuning of the resonance frequency of the FBAR. Based on the foregoing-mentioned FBAR technology, a method for performing wafer-level heterogeneous integration of the FBAR with a CMOS substrate was developed. According to this method, the fabrication of a floating FBAR above standard CMOS substrates has been achieved for the first time. The method was demonstrated by integrating FBARs on the commercial AMS035 and the in-house CNM25 CMOS technologies. On the application side, different FBAR-based sensor applications were implemented, the localized-mass detector being the most relevant, which has been demonstrated for the first time for high-frequency bulk-acoustic resonators. Experimental and modeling results have been contrasted. Also, the concept of FBAR-based mechanical sensor has been introduced. Two examples are the embedded-FBAR accelerometer and the force sensor for AFM-cantilever applications. The fabrication and characterization results of an AlN-based contactless acoustic resonator are also reported in this thesis.

Many interesting ideas have emerged from research on electromagnetic eld interactions with di erent materials. Analyzing such interactions has extracted some essential proper- ties of the materials. For example, extracting constitutive parameters such as permittivity, permeability, and conductivity, clari es a material's behavior. In general, the electromag- netic eld interacts with materials either in the far- eld or near- eld of a source. This study focuses on the principle of near- eld microwave microscopy for detection purposes. Many studies have focused on the use of an electrically small resonator, such as a split-ring resonator (SRR) and a complementary split-ring resonator (CSRR), to act as a near- eld sensor for material characterization and detection. At the resonance frequency, the electric and magnetic energy densities are enhanced dramatically at certain locations in the resonator. Any disturbance of the eld around such a resonator with a material under test causes the resonance frequencies to exhibit a shift that is used as an indicator of the sensor sensitivity. In this thesis, a single CSRR is used as a sensing element for detecting cracks in metal surfaces. Many microwave techniques have been developed for crack detection. However, these techniques have at least one of the following drawbacks: working at high frequencies, measurement setup complexity and cost, and low sensitivity. The rst part of this thesis presents a new sensor based on the complementary split-ring resonator (CSRR) that is used to detect sub-millimeter surface cracks. The sensing mechanism is based on perturbing the electromagnetic eld around an electrically small resonator, thus initiating a shift in the resonance frequency. Investigation of the current distribution on a CSRR at the resonance frequency shows the critical location at which the enhanced energy is concentrated. In addition, the current distribution demonstrates the sensing element in the CSRR. The sensor is simple to fabricate and inexpensive, as it is etched-out in the ground plane of a microstrip-line using printed circuit board technology. The microstrip-line excites the CSRR by producing an electric eld perpendicular to the surface of the CSRR. The sensor exhibits a frequency shift of more than 240 MHz for a 200 m crack. In the second part of this thesis, the sensitivity of the sensor is increased by lling the same crack with a dielectric material such as silicon oil. While using CSRR to scan a block with 200 m wide and 2 mm depth dielectric lled crack, the resonance frequency of the sensor shifts 435 MHz more than a case scanning a solid aluminum. Finally, the total Inductance of a CSRR for miniaturizing purposes is increased using either lumped or distributed elements. In this thesis, the designs and the results are validated experimentally and numerically.