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Some aspects of the Large Current Radiator construction for subsurface sounding applications at the depths of up to some hundred meters are considered. The antenna has to operate in a wide frequency band and transmit power effectively under the ground surface. It is shown that the antenna designed as a small horizontal magnetic loop with specific shape located close to the earth surface transmits power quite effectively when one of the wires, situated close the surface, is flat and the second is shielded by an envelope with certain electrical constants.

This report results from a contract tasking Semiconductor Physics Institute as follows: To achieve the proposed goals, the modeling of the circular waveguide section containing semiconductor obstacle will be performed. To calculate the average electric field in the semiconductor obstacle the finite difference time domain method will be used. Although, the lowest critical frequency in the circular waveguide is characteristic to H11 mode higher modes such as E01 and H01 are also sometimes used. Depending on mode some components of electromagnetic field are suppressed, nevertheless in the vicinity of the obstacle all six components of electromagnetic field might be excited and they should be taken into account when determining averaged electric field in the semiconductor obstacle. Since the resistive sensor actually feels the amplitude of electric field, the distribution of electric field component within the waveguide should have a crucial influence on the performance of the sensor and this fact should be taken into account in sensors design. Therefore it is also planning to investigate the behavior of the averaged electric field in the semiconductor obstacle when different modes are excited in the waveguide. To perform investigation it is planned to use internal programs for the modeling of electromagnetic wave propagating in the circular waveguide with the obstacle. Such modeling has already been done in rectangular waveguide with semiconductor obstacle placed on a wide wall of the waveguide and in the obstacle under the thin metal diaphragm. In both cases all six components of electromagnetic field in Cartesian coordinate system has been determined. It is planned to modify the program so that it should be able to calculate the electromagnetic field components in cylindrical coordinate system., The original document contains color images.

Our long-term goal is to contribute to our understanding of processes in the upper ocean and lower atmosphere through the conception, development, and application of novel microwave, acoustic, and optical remote sensing techniques. The objectives of this effort are to determine the extent to which Doppler radar techniques are useful for nearshore remote sensing applications. Of particular interest are estimates of surf zone location and extent, surface currents, waves, and bathymetry. To date, optical (video) techniques have been the primary remote sensing technology used for these applications. A key advantage of the radar is its all weather day-night operability., The original document contains color images. All DTIC reproductions will be in black and white.

Strontium sodium niobate ceramics are prepared by solid state reaction method. The crystal structures of these ceramics are studied by X-ray powder diffraction method. These materials are found to crystallize in the tetragonal tungsten bronze type structure and the unit cell parameters are calculated. The microstructural features were studied using scanning electron microscope. The real and imaginary part of complex Permittivity of the sample is determined by cavity perturbation technique. It is observed that the real and imaginary part of complex Permittivity varies with frequency. The temperature coefficient of dielectric constant and resonant frequency is found to be very small., See also ADM001697, ARO-44924.1-EG-CF, International Conference on Intelligent Materials (5th)(Smart Systems and Nanotechnology). Presented at the International Conference on Intelligent Materials (5th) (Smart Systems and Nanotechnology) (ICIM 2003) held at Pennsylvania State Univ., University Park, PA on 14-17 June 2003. The original document contains color images.

This report results from a contract tasking Semiconductor Physics Institute as follows: The contractor will investigate resistive sensors for measuring high power microwave pulses. At the end of this investigation, the contractor will develop a prototype unit of the coaxial-type resistive sensor and test it in a wide frequency and power range.

The University of Massachusetts operated a Cloud Profiling Radar System in Everglades City, Fla., for three weeks during September 1996. On-site calibration of the radar was performed with a trihedral comer reflector. Time-height measurements of reflectivity, Doppler mean velocity, Doppler velocity variance, and linear depolarization ratio were assembled into netCDF datafiles for further analysis and comparison with data from other sensors. The data were archived in the Phillips Laboratory Data Archive Center and were made available through the Worldwide Web on a university web site.

This report results from a contract tasking Semiconductor Physics Institute as follows: The contractor will investigate the development of a resistive sensor for HPM pulse measurement. Contractor will work on improving the rise time of the sensor and optimizing the frequency response and will design and manufacture sensors as described in the proposal.

The University of Massachusetts Microwave Remote Sensing Laboratory (MIRSL) gathered coincident active and passive measurements of the ocean surface from the NASA Wallops P3 during the Ocean Wind Imaging (OWI) Experiment. The experiment consisted of five missions flown over the Labrador Sea. Surface winds from 8 to 16 m/s were sampled, and approximately thirty hours of data were collected. The passive measurements were obtained with a novel Ka-band conically scanning passive polarimeter (KASPR) that simultaneously measures the four brightness temperature Stokes parameters by using a correlation receiver. The active measurements were collected by a conically scanning C-band scatterometer (CSCAT) that simultaneously measures the backscatter at four separate incidence angles. Analysis of the passive data shows a wind directional signature in the vertically and horizontally polarized brightness temperature measurements at the high winds. For vertical polarization, the wind direction signature is best described by a two-term Fourier cosine series, while for horizontal polarization, the wind direction signature is described by a three-term Fourier cosine series. This report presents these results as well as summarizes the data obtained and the future analysis plans.

During the three years covered by this contract, we achieved a number of important results in millimeter wave radar hardware development, measurements, and data analysis. Important results include demonstrating the equivalence of coherent and noncoherent polarimetric measurement techniques; the development of a Kalman filter to improve the convergence of noncoherent polarimetric measurements; the development of a single antenna 95 GHz polarimetric radar; measurement of the polarimetric response of deciduous and coniferous trees at 35, 95 and 225 GHz; and development of polarimetric scattering models for anisotropic scattering volumes. Among the most significant accomplishments of the last three years were the snow measurement campaigns of 1992-1994 which resulted in a large volume of fully polarimetric data at 35, 95 and 225 GHz. In addition to yielding long records of the diurnal variation in radar cross section, these data showed for the first time that anisotropy in the snow pack has a major impact on the polarimetric response throughout the millimeter head. Finally, we have initiated a significant effort to archive all polarimetric data gathered during this project in the FINRACS database.

A high power 95 GHz radar system, developed at the University of Massachusetts, was used to make polarimetric measurements of natural surfaces. Over the two year period of this grant the following items were accomplished: (1) The 95 GHz radar was configured into a unique system capable of simultaneously making coherent and incoherent Mueller matrix measurements. (2) The equivalence of the coherent and noncoherent measurement technique was demonstrated. (3) The polarimetric properties of various foliage targets were characterized. These included the weeping willow, the sugar maple, and the white pine tree species. (4) The polarimetric properties of various snowcover types were characterized. (5) Mueller matrix models for wet and dry snow were developed.

We have developed a technique for the computation of the radar cross- section(RCS) of loaded and unloaded microstrip patch antennas of arbitrary shape. (I will present a paper on this research in a joint AP-S/URSI session during the upcoming AP-S Symposium in Chicago.) We continued research into a related problem of an arbitrarily shaped microstrip patch antenna excited through an iris in a rectangular waveguide. We also continued to make progress in the analysis of three-dimensional microstrip discontinuities and in the analysis of single and coupled integrated dielectric waveguides.

The University of Massachusetts has developed two high-power portable polarimetric radars operating at 95 and 225 GHz. The 95 GHz coherent polarimeter is configured to measure the complex scattering matrix of a target by transmitting a pair of orthogonally polarized pulses in rapid succession. We have also developed a noncoherent 225 GHz polarimetric radar which directly characterizes the target Mueller matrix by transmitting a sequence of four or six polarization states. In addition to reviewing the radar design and calibration, this paper summarizes measurements of natural and man-made objects made to date. These measurements include several varieties of trees, terrain, and snowcover. A model which approximates the Mueller matrix with a single parameter is introduced for a restricted class of clutter and is found to accurately predict the polarimetric behavior of vegetation and terrain at low incidence angles. We also present a two parameter approximation of the Mueller matrix that accurately models scattering from snowcover at large incidence angles., This article is from Target and Clutter Scattering and Their Effects on Military Radar Performance (Diffraction par les Cibles et le Fouillis et ses Effets sur les Performances des Radars Militaires ), AD-A244 893, p29-1 thru 29-10.

Quantum well (QW) diode oscillators have recently been shown to have the potential to generate power in the millimeter (mm) and sub-mm wave region. The small signal microwave impedance of a modified QW device called the quantum well injection transmit time (QWITT) diode is measured and compared with theoretical predictions. Based on the small signal impedance of the device, several QWITT oscillators were designed and fabricated. The highest power ever reported for a QW diode oscillator was obtained at about 8 GHz. Keywords: Quantum well oscillators, QWITT diode, Power combining, Quasi optical power combining.

Modeling and testing of monolithic coplanar waveguide (CPW) phase shifters using both optical and Schottky-contact control techniques have been performed. Simulation work on a periodically illuminated structure has been completed, showing that some improvement in performance may be possible, although with a reduction in frequency bandwidth. CPW transmission lines have been fabricated on semi-insulating GaAs, on lightly and heavily doped epi GaAs, and on AlGaAs/GaAs heterostructure, and electrical characterization has been performed. Both Schottky-bias controlled mechanism, using constant D.C. bias while using optical control has also been developed, which has yielded the best experimental performance to date for a distributed CPW phase shifter.

The crosstie-overlay slow-wave structure is proposed as a passive circuit element in monolithic microwave integrated circuits. The propagation characteristics of the crosstie-overlay slow-wave structure are analyzed both analytically and experimentally. In analysis, a method suitable for design as well as a rigorous two-dimensional spectral domain method for accurate results are developed. The results obtained in analysis are checked with experimental results. They are in good agreement. A modified structure is proposed to reduce the conductor loss. Distributed Chebychev bandstop filters utilizing the slow- wave structure are designed. Another circuit application of the slow-wave structure, frequency scanning antenna, is also investigated. (rrh)

The mixed potential electric field integral equation (MPIE) method is a widely used numerical method in wave scattering analysis. The MPIE and all other classical Maxwell equation scattering methods involving the scalar and vector potentials are based on the Lorentz gauge. In this report we analyze a series of waveguiding and scattering problems formulated by enforcing the Coulomb gauge. Coulomb gauge Green's functions are derived for a rectangular waveguide, free space, a cylinder and a wedge. With the MPIE method the currents on a scatterer are shown to be gauge independent. Comparisons are therefore made between the computation times necessary for calculating the current on a straight thin wire and arbitrary scatterers in the presence of a circular conducting cylinder and conducting wedge. Conclusions are drawn concerning the utility of the Coulomb gauge as compared to the Lorentz and other gauges.

A deterministic formulation of the method of moments carried out in the spectral domain is extended to include the effects of two-dimensional, two- component current flow in planar transmission line discontinuities on open substrates. The method includes the effects of space-wave and surface-wave and surface-wave radiation through the use of the exact spectral domain Green's function. The procedure and formulation of the method are described in detail. Also, techniques used to increase the numerical efficiency are described in detail. The method is used to determine accurate circuit models of three types of planar circuit discontinuities on open substrates: microstrip open-end discontinuities, slotline short-circuit discontinuities, and microstrip gap discontinuities. The analysis is then applied to gap-coupled resonators. The coupling between cascaded gap discontinuities is shown to be significant when the substrate is electrically thick since surface wave excitation is strong. Possibilities for further applications of the method to more complicated discontinuities are discussed.

The objective of research under this grant is to achieve fundamental understanding of the dynamics of coherent and incoherent image formation and inverse scattering employing spectral, angular (aspect dependent) and polarization diversity as means for realizing cost-effective imaging of 3-D objects with near optical resolution. Special attention is to be given to 3-D microwave diversity radar imaging. The approach is Theoretical - through development of a unified theory of microwave diversity imaging for both stationary and non-stationary objects which has been reported on extensively in preceeding reports and, Experimental - through development and verification of methodologies for efficient microwave diversity imaging that can be employed in future broad-band imaging radar networks capable of providing 3-D projective or tomographic images of remote aerospace targets with near optical resolution.

Extensive simulation and preliminary testing of a monolithic coplanar waveguide (CPW) phase shifter using an optical control technique has been performed. Improvements in numerical techniques has allowed the simulation of non-uniform lossy layers within the substrate supporting the CPW. In addition, a periodically illuminated structure has been proposed, and analysis begun on the slow wave effects expected in such a structure. A CPW transmission line has been fabricated on a AlGaAs/GaAs heterostructure, and initial electrical characterization has begun.

Two strategies or approaches to millimeter wave (MMW) microwave imaging and recognition are investigated. One approach seeks to produce cost-effective high resolution images of scattering targets and scenes that would resemble as closely as possible their more familiar visual and therefore can be readily recognized and interpreted by a minimally trained observer. In this approach we have extensively studied the principles and methodologies of a 3-D tomographic microwave /mmw diversity imaging where angular, spectral, and polarization degrees of freedom are combined for efficient imaging of remote scattering objects. This work has lead to images with unprecedented quality with near optical resolution employing a unique experimental microwave imaging facility. At such high resolution, image artifact produced by clutter and multiple reflections on the target can be detrimental as these and specially the latter can make the microwave/mmw image depart noticeably in appearance from the visual image in that ghost detail not corresponding to any physical detail on the target can emerge. For this purpose we have conducted a study of the effect of background clutter and multiple reflections on image quality. It was found that microwave/mmw images can be separated from ground or clutter provided that adequate range resolution is available.

A method of analysis is described for characterizing the discontinuities made of orthogonally crossed two striplines on a suspended structure. The method of analysis is based on generalized transverse resonant technique extended to 4-port configurations. The technique is used for determination of resonant structure at a given frequency and subsequently the equivalent circuit parameters of the discontinuities. Keywords: Transverse resonance method; Stripline crossing; and 4-port network.

A modal expansion technique is applied to a system of uniform waveguides interconnected by abrupt junctions. Computer codes developed for the asymmetrical modes on-axis transition and all modes off-axis transition have been tested and verified through two separate experimental verifications. The three main parts of this work are: (a) The tentative formulation for an abrupt transition from one waveguide to another, where each junction is restricted to having only one input and one output waveguide, while a conducting wall on each side of the junction is accounted for, (b) The development of convergence criteria for the selection of the important modes via symmetry used in each waveguide section, and (c) The numerical implementation of the evaluation of the coupling coefficients for the coupling cases: On-axis asymmetrical modes (circular to circular, circular to coaxial, and coaxial to coaxial waveguide transitions). Off-axis for all modes (circular to circular, circular to coaxial, and coaxial to coaxial waveguide transitions). The implementation of this formulation requires modification of the structure of the matrix equation of the existing code. To expand the capability and the versatility of the code, future work should include the implementation of ridged waveguide, dielectric loaded waveguide, and multiport junctions. (Author)

Very high-speed picosecond range pulse transmission along a coplanar wave guide (CPW) integrated in a monolithic microwave integrated circuit (MMIC) is analyzed in the time domain, changing the input excitations, conductivity of the epitaxial layer, and terminating conditions. The time domain waveform is obtained by inverse discrete Fourier transform (IDFT) of the frequency domain data, namely, complex characteristic impedance and propagation constant. The full wave mode-matching method (MMM) is employed to analyze the dispersion of the CPW. A simple wide band matching scheme is found to be effective to make the slow-wave CPW a viable circuit element in applications such as a delay line or an interconnection line. Knowing the device processing data and physical dimensions, a designer should benefit from the present analysis that simulates the transmission of a very high-speed pulse on an MMIC CPW under various terminations.

Extensive finite element analyses on MMIC (monolithic microwave integrated circuit) slow wave structures with both localized and layered models are presented. Good agreement is achieved for results obtained in this paper with other theoretical results and experiments. Higher order elements that improve accuracy are discussed. The comparative studies for the Schottky contact microstrip and the coplanar waveguide with localized and layered models are presented. Potential applications of the localized models to more general and practical slow wave circuits are also discussed.

A two-dimensional computer model, which takes into account the non- stationary conditions, is used to investigate several aspects of the GaAs submicron-gate MESFET. First, this model is used to evaluate the effects of carrier injection into the MESFET buffer-layer. It is shown that the carrier of injection reduces the transconductance and increases the output conductance. One of the ways to reduce the carrier injection is to introduce a potential-barrier between the active-layer and the substrate. Therefore, the MESFET grown on a P- substrate is studied. It is shown that a high acceptor concentration in the substrate depletes large part of the active-layer and greatly reduces the output current. A more flexible design can be obtained by introducing a thin P-layer between the active-layer and the semi-insulating substrate. This model is also used in investigating the traveling Gunn domain phenomenon in GaAs MESFET's. It is shown that traveling domains exist in MESFET's with relatively thick active- layers. The propagation characteristics of these domains are studied in detail. A new structure called Inverted-Gate FET (INGFET) is studied as well. This structure has equal input and output reactances. Hence, it relaxes the restriction on the device width which becomes very severe in the mm-wave range. Another structure that employs carrier injection over an N+i junction and possesses equal input and output reactances is analyzed. It is called Inverted- Gate-Injection FET (INGIFET). The potential characteristics of the INGIFET are compared with those of the INGFET as well as the coplanar MESFET.

The small and large signal analysis of QWITT diode oscillators is presented. The small signal analysis determines the oscillation frequency of a power combining periodic structure. The large signal analysis, by the harmonic balance method, determines the power and efficiency of a single diode oscillator. These analyses show that the QWITT diode is good candidate for signal generation in the millimeter wave region. The theoretical results predict that powers of about 1 mW can be obtained at frequencies up to 600 GHz. At the end, experimental results are presented that confirm microwave operation of the QWITT device. The experiments have demonstrated powers of 300 micro W through the X-band.

The main subject of this thesis is to develop a general purpose computer program for the analysis containing a planar microstrip circuit arbitrarily shaped. Based on the boundary-integral method (also called the contour-integral method), the analyses of circuits containing right - angled microstrip bend with or without a miter cut and circuits of a T-junctions with or without a V-shaped cut are presented in this thesis. Scattering parameters and other related.

In this project, mode matching was used to calculate the propagation constant and the characteristic impedance of a coplanar coupled microstrip line. The Striplines are considered to be perfect electric conductors of negligible thickness, and are separated from the ground plane by three layers of dielectric material. The layer with the higher dielectric constant is sandwiched between two layers of lower dielectric constants, such that the field is confined to this middle layer, which is called the 'conducting layer' of the microstrip line. By confining the field to this layer, losses at the metal conductor are minimized.

This technical report presents a simple and practical method for the conductor loss calculation over a wide range of field penetration which can be applied to both normal-state and superconducting transmission lines. The calculated results for microstrip lines and coplanar waveguides using normal conductors and superconductors agree very well with the data obtained using the finite element method, the Monte-Carlo method, and experimental measurements. Because of the calculation simplicity, this method is very suitable for computer-aided design of monolithic microwave and millimeter-wave integrated circuits. (RRH)

A new time domain method for the analysis of planar guided wave propagation and scattering is developed in which an analytical process is incorporated along one of the spatial dimensions. The method makes use of the Method of Lines which has been applied to microwave problems in the time- harmonic cases. The procedure and the formulation of the proposed method to calculate the time history of a pulse scattered in a partially filled waveguide and a finned waveguide are described in detail. The cutoff characteristics of the structures can be derived via the Fourier transform of the time-domain pulse scattering data. The results are compared with other available data. The method is extended to characterize three dimensional structures. The procedure and the formulation of the three dimensional analysis are explained. The propagation and scattering data of a pulse in a planar transmission line with its discontinuities can be obtained by using the three dimensional analysis. From the time domain data, the frequency-domain characteristics for a wide range of frequencies can be extracted by the Fourier transform. The important design parameters such as the characteristic impedance and the propagation constant of a uniform microstrip line and the scattering parameters of its discontinuities (step-in-width, open end and gap discontinuities) are presented and compared with available published data. (JHD)

The design and test of planar integrated circuits for the transmission and reception of microwave power are described. The circuits consist of MESFET transistor oscillators incorporating periodic microstrip antennas to form transmitters and transceivers. The nature of the periodic antennas allows their use as both resonant and radiating elements in the oscillator design, resulting in a simple and inexpensive circuit. The transmitter and transceiver circuits described here may be divided into two types; single device and dual device. The single device circuits use a single MESFET oscillating into a periodic microstrip patch antenna. The dual device circuits use two MESFETS which oscillate into a couple rampart line microstrip antenna. In the dual device circuit, the FETs may oscillate out of phase for power combining or in phase for frequency doubling. The transmitter circuits generate a beam of RF energy which radiates normal to the planar circuit surface. The transceiver circuits operate in a similar fashion, except that in this case, the antenna also acts to receive RF energy and direct it back to the oscillating MESFET. The MESFET then functions as a self-oscillating mixer for down-conversion of the received signal to the IF frequency. Planar integrated circuits; Microwave transmission.

This technical report describes traveling-wave optical modulators using cross-tie slow-wave electrodes on GaAs substrates as well as wideband feeding of a coplanar strip electrode. Periodic cross-tie conductors are overlaid on a modulated coplanar strip and a modulated coplanar waveguide electrode to make slow-wave electrodes. In these structures, phase velocity matching between modulation and optical waves is satisfied over a very wide bandwidth by reducing the phase velocity of the modulation wave using the slow- wave electrodes. Therefore, the modulation bandwidths are greatly increased while the dominant conductor losses are relatively high and limit the bandwidths. The coplanar strip slow-wave structure has been build on a semi- insulating GaAs substrate and measured using a microwave network analyzer. The measured phase velocity is much lower than those of conventional coplanar electrodes and agrees very well with the calculated one. Keywords: Optical communications; Optical signal processing.

Our research in high resolution microwave imaging has to date focused broadly on the study and development of efficient and cost-effective data acquisition and image reconstruction methods for use in lambda and polarization diversity 3-D tomographic imaging. The techniques developed, combine angular, spectral, and polarization diversity measurements with a unique target derived reference (TDR) technique to produce images of the scattering centers on complex-shaped bodies with unprecedented resolution and quality, as reported here, that exceed by far anything reported to this date. Analytical studies of information content, speckle suppression, and resolution show however that image quality can further be enhanced and made to approach and even exceed the resolution of optical systems when the imaging of remote objects specially through the earth's atmosphere is desired. Originator supplied keywords include: Radar imaging, coherent and incoherent 3-D imaging, microwave tomography, wavelength diversity, polarization diversity, image reconstruction, filtered back-projection, the Fourier camera, dielectric imaging, and measurement methodologies.

A millimeter-wave travelling-wave IMPATT diode is studied. This device has a simple configuration and is suitable for monolithic integration. The travelling-wave structure permits oscillation of the IMPATT diode at a desired frequency without any external resonant circuit, making the whole system extremely simple. The theoretical analysis determines the condition under which gain is produced in the IMPATT device. A reasonable agreement is obtained with the experimental results.

Nonreciprocal devices, such as circulators and isolators, are among the important devices for microwave and millimeter-wave communication systems. Two types of isolators which can be used at both microwave and millimeter-wave frequencies have been studied both theoretically and experimentally. One isolator uses a dielectric guide and a ferrite slab, while the other uses a hollow image guide with a dielectric overlay.

Three Surface Acoustic Wave (SAW) devices, the separated-medium convolver, the memory correlator and the chirp filter are analyzed for signal processing applications. Emphasis is placed on convolution/correlation and Fourier transformation processes. The chirp filter theory is more general and applied equally well to chirp filters fabricated by alternate techniques. In the SAW convolver there is a piezoelectric delay line. Two surface waves are introduced onto the delay line surface by interdigital transducers at its opposing ends. The two waves overlap beneath a semiconductor spaced above the surface and their fields interact with its charge carriers. A non-linear potential is produced and averaged over the semiconductor. From its back contact is obtained the time-compressed convolution of the two signals. The memory correlator is similar to the convolver except that the semiconductor possesses a charge-storage mechanism. Also additional transducers are required for recovery of stored information. (Author)

Contents: Acoustic Microscope, New Acoustic Imaging Techniques, Video Bandwidth Compression Using Surface Acoustic Waves, and Application of Acoustic Scanning to Non-Destructive Testing of Materials.

The program 'Equivalence Principle As Applied To Conical Arrays' has been successfully completed. The equivalence principle pattern synthesis technique has been used to provide aperture distributions for an experimental conical array. The array consisted of thirty-seven crossed-slot elements on a cone of half-angle 10.25 degrees and was operated at 3.185 GHz. Radiation patterns were measured for two beam pointing directions, one 50 deg. from the cone tip and the second normal to the conical surface. Excellent agreement was obtained bewteen measured patterns and calculated patterns. It is concluded that the technique can be used successfully to synthesize radiation patterns from arrays on conical and other curved surfaces. (Author)

Progress on the development of piezoelectric transducer arrays for use in electronically focused acoustic imaging systems is reported. Design techniques and experimental results are described for two types of transducer arrays, one utilizing individual slotted array elements, and the other, array elements constructed by depositing electrodes on a monolithic slab of piezoelectric ceramic. Development of lossy, high impedance tungsten-epoxy matched backing material, necessary for broad bandwidth transducer arrays, is also described. (Author), Presented at the 1975 IEEE Ultrasonics Symposium, Los Angeles, CA 22-24 Sep 75.

A scanning acoustic microscope, using the design we have previously described, can now be routinely operated at a frequency of 1 GHz with a corresponding resolution of nearly 1 micron. Operating in transmission a number of biological samples have been imaged. With this high resolution, variations in the elastic properties within individual cells can be seen. Moreover, clear distinctions have been demonstrated between the acoustic images and corresponding optical micrographs. Several alternative imaging modes have also been demonstrated with this instrument. One of these is a phase contrast technique in which the phase of the output signal is compared directly to the phase of the input signal. Another mode is reflection imaging which allows specimens on thick substrates to be viewed. This technique has been applied profitably to an investigation of integrated circuits. (Author), Presented at the 1974 IEEE Ultrasonics Symposium, 11-14 Nov 74, Milwaukee, WI.

This work presents a study of the electrical properties of semiconductors using the interaction between surface acoustic waves and a semiconductor in the separated medium configuration (the SAW convolver). This study has been conducted towards developing a new technique for nondestructive evaluation of semiconductor surfaces using surface acoustic waves. The semiconductor is placed a small distance above the delay line, with a uniform airgap between the two media. Although there is no mechanical contact between the two media, the electric fields associated with the surface acoustic waves penetrate into the semiconductor and interact with the free carriers. As a result of this nonlinear interaction, the SAW is attenuated, there is a change in the SAW velocity, and dc acousto-electric voltages are developed across the semiconductor. In the case of two oppositely propagating surface waves, voltage proportional to the convolution of the two input voltages is also generated.

Excellent agreement has been shown between element patterns of circumferential and radial slots on a cone, computed with the normal mode series computer programs, and patterns measured with an experimental model with both types of slots. When the modal series is used for the computation of exact patterns, the number of modes required for convergence of the series increases as the distance of the slot location from the tip of the cone increases. Computational difficulties from accumulated round-off errors also affect the accuracy and limit the applicability of the modal series program to element positions not too far from the cone tip. The approximate asymptotic approach, on the other hand, allows the separation of the diffracted field and the geometrical optics field. More specifically, the asymptotic approach resulted in complete expressions for the E sub theta and E sub phi radiation fields in terms of optical, transition, and diffraction fields. The complete expressions for each of the two field components, in a form suitable for numerical computation, were included in the Final Report on Contract No. N00019-74-C-0127. An examination of these expressions indicates that the diffraction coefficients of both field components are only a function of the angular coordinates and not of the location of the radiating element.

With the development of the laser and its enormous bandwidth capabilities, the simultaneous development of the photosensing devices has proceeded. A photodiode is one of these devices and shows great promise due to its inherent sensitivity, ruggedness, and the ability to obtain large internal gain. Because of this, many photodiodes have been built with responses into the microwave region. These devices have extremely small active areas and low quantum efficiencies, as with a point contact photodiode. This paper discusses the problems of building a large area high frequency photodiode and how they were overcome. The theoretical considerations for using a free-running inhomogeneously broadened laser to obtain a millifrequency signal to test the photodiodes are discussed in some detail. These results have been used to obtain the frequency response of the photodiodes.

Design procedures for wrap-around, helical SAW delay lines of large time delay together with large bandwidth are developed. The frequency dependence of the various loss mechanisms, i.e., crystal loss, air loading loss, and diffraction loss, are studied. This includes an analytical treatment of diffraction loss in unguided SAW delay lines. Loss balancing procedures are developed, for designing interdigital transducers to equalize the frequency tilt due to frequency dependence of the loss factors and produce a level passband, and procedures for removing the residual passband curvature are developed. These are applied to graded, phase weighted interdigital transducers. Summaries are given of time delay and bandwidth values available in delay lines on BGO, for typical values of delay line parameters and dynamic range. Delay line designs are presented for time delays of 0.1, 0.5, and 1 millisecond time delay. Experimental delay lines for these time delay values are described, one having time delay of .91 milliseconds and bandwidth of 65 MHz, for a time bandwidth product of 60,000, with center frequency of 83 MHz. (Author)

The aim of the work on this contract during the last six months has been to improve the technology of the optical imaging devices so that we can carry out more sophisticated studies of optical transform methods; and can made reproducible devices with reasonably uniform characteristics, so we need not spend a large amount of time with difficult problems of mechanical alignment. In addition, we have been concerned to eliminate the trapping problem in zinc oxide, to eliminate sideways diffusion of carriers generated by light, so as to keep a constant modulation transfer factor, and to eliminate problems with surface states in both airgap and ZnO devices., Sponsored in part by DARPA.

The report describes work on a new type of optical scanning device which makes use of acoustic surface waves to scan an optical image. The device employs a silicon semiconductor as the photodector; the nonlinear interaction of two acoustic surface waves, whose electric fields interact with the silicon is employed in the basic mechanism of detection. Work on the airgap Si-LiNbO3 convolver configuration which is employed in this optical imaging device is described. Described is the theoretical development of the semiconductor convolver theory. Development of the technology of the ZnO on Si convolver configuration for use in the optical imaging device is discussed. A short description is given of a chirp generator, which was constructed for use in transform coding in these types of devices.

This report is the second Interim Technical Report on the contract. It covers research done on acoustic surface wave devices during the six month period 1 May to 31 October 1974. The objective of the research is the generation of new device concepts and the analytical and experimental verification as to their ultimate usefulness for signal processing applications. Improvements were made in acoustic surface wave convolver efficiency. The surface wave convolver can be used for performing convolution/correlation, time reversal and Fourier analysis of arbitrary signals. A new approach which may lead to low cost, simplified analog/digital conversion has been devised. This combines a surface acoustic wave delay line and external digital circuitry., See also report dated Sep 74, AD-787 869.

This work presents an experimental and theoretical study of the interactions between acoustic surface waves on a piezoelectric insulator and charge carriers in a neighboring semiconductor separated by a small airgap; and the application of these phenomena to signal processing and optical imaging. Although the two media are mechanically isolated, the electric field associated with the surface waves penetrate into the semiconductor and interact with its charge carriers. This interaction is nonlinear, and, in the case of two oppositely propagating surface waves, real time convolution is performed. A new theory of the convolution interaction, taking into account the possible presence of a depletion, inversion or accumulation layer at the surface of the semiconductor, resulting from a built-in or applied dc field is presented. Experimental measurements for both n- and p-type Silicon on Lithium Niobate systems are in very good agreement with this theory, and they lead to a novel technique of measurement of the surface state distribution on semiconductors. The silicon on lithium niobate structure used gives rise to one of the largest convolution efficiencies reported to date. Several signal processing applications are presented. They show the versatility of the device which can be employed as a programmable filter or a parametric processor. In addition, the first autocorrelation is demonstrated by cascading two convolvers. The acoustic convolver was adapted for the scanning of optical images., Sponsored in part by DARPA.

For missile seeker radars, the use of mechanically scanned antenna systems becomes increasingly difficult as the requirements for the aerodynamic and electrical performance of missiles become more demanding. One possible alternative to the use of mechanically scanned antennas lies in the application of flush-mounted slot antenna systems on metallic cones or ogival surfaces. These antenna systems would be inertialessly scanned in the required directions. The curvature of the particular conformal surfaces and the positional relationships of the radiating elements, however, introduce many problems which are different than those associated with planar electronically controlled arrays. As a consequence of these positional relationships, there may be no element that can be considered 'typical' so that impedances, patterns, and polarizations may vary significantly among the elements, in contrast to the conditions that are obtained in planar arrays for elements not too near the edge. In addition, since the radiating elements are not all similarly oriented, there may be a significant cross polarized component in the array pattern that could interfere with the desired system operation., Also available as Rept. no. HAC-REF-2753/1691. DDC Form 55 not necessary for document request.