Impedance Matching Transformer Research Articles

The auditory region of dermoptera: Morphology and function relative to other living mammals.

The dermopteran basicranium combines a primitively constructed and oriented auditory bulla formed by ectotympanic, rostral entotympanic, and tubal cartilage with derived features of the middle ear transformer and internal carotid circulation. Living dermopterans possess a primitive eutherian auditory region that has been structurally modified to perceive a lower frequency sound spectrum than probably was utilized by ancestral Mesozoic therians. Perception of the low to midfrequency range is enhanced in Dermoptera by reducing stiffness in the mechanical transformer while maintaining low mass of the component parts. Stiffness has been reduced by (1) development of an epitympanic sinus about four times the volume of the middle ear cavity proper, (2) detachment of the anterior process of the malleus from the ectotympanic, and (3) by delicate suspension of the ear ossicles within the middle ear. We apply to dermopterans a measure of hearing efficiency derived from recent functional studies of the mammalian middle ear that regards the middle ear mechanism as an impedance matching transformer. Calculation of the impedance transformer ratio for Dermoptera suggests that these mammals are relatively efficient in comparison to other eutherians in their ability to match the impedance of cochlear fluids to that of air at the eardrum. Dermopterans theoretically are capable of using over 90% of incident sound energy striking the eardrum at the resonant or natural frequency. Mechanical impedance of the middle ear transformer exerts a minimal influence on hearing efficiency due to low mass, little stiffness, and little frictional resistance. Analysis of measurements of the middle ear transformer published by Gerald Fleischer and integration of these data with current theory on the peripheral hearing mechanism in mammals allow us to propose a model that describes the structural and functional evolution of the mammalian middle ear transformer. Structural changes appear to be correlated with alteration in function from primitive small mammals with stiff middle ear transformers and high frequency dominated hearing to mammals with a wider range in body size with more mobile middle ear transformers and a greater range of frequency perception, often including improved sensitivity to lower frequencies. Mammals employ different anatomical strategies in attainment of increased hearing efficiency and sensitivity. Efficiency is improved by adjustment of lever and areal ratios of the middle ear transformer to achieve an optimum impedance match of external air and cochlear fluids. Sensitivity over a broad frequency spectrum is attained by minimizing mass, stiffness, and frictional resistance of the transformer. The morphology of the auditory region of both living and fossil mammals seems explicable in terms of selection pressure directed toward these ends.

Wide-Bandwidth Millimeter-Wave Gunn Amplifer in Reduced-Height Waveguide (Short Papers)

A Ka-band millimeter-wave Gunn-amplifier structure with 15-GHz gain1/2-bandwidth product has been fabricated in reduced-height waveguide. Measurements were taken of the terminal admittance of the diode and its mount and used in the computer optimization of impedance matching transformer sections.

Monolithic acoustic imaging transducer structures with high spatial resolution

A method is described for simplifying the construction of high-resolution imaging transducers by using impedance matching transformers on a monolithic plate structure. Simple physical arguments are used to establish the general design criterion that a broad frequency response leads to a wide angular response and high resolution. This conclusion is verified by numerically computed performance curves for a particular air-backed transducer structure.

An ultra-low-noise preamplifier using superconducting quantum devices

The application of superconducting (SQUID) galvanometers as low-noise preamplifiers with considerable bandwidth is explored. The important role of negative feedback in maximizing the bandwidth of these preamplifiers is carefully analyzed. Also discussed is the design and construction of superconducting impedance matching transformers suitable for making the unexcelled noise characteristics of these amplifiers available over a wide range of source impedances. A working preamplifier is described which has exhibited a maximum bandwidth of 10 kHz and noise temperatures in the liquid helium temperature range or below for all source impedances up to a few ohms. The operating characteristics of this preamplifier are compared to the best conventional room temperature amplifiers and are found to be superior for source impedances less than ∼10 Ω.

Partially Dielectric-Slab-Filled Waveguide Phase Shifter

An equivalent circuit of a waveguide junction between two asymmetrically filled waveguides is obtained. This equivalent circuit is applied to the design of single-section impedance-matching transformers for a dielectric-slab-filled waveguide phase shifter. Calculation and measurement indicated that when a thin alumina slab is employed, a 360/spl deg/ phase shift can be accomplished in a section approximately 1.1 times the unloaded waveguide wavelength at 2.7 GHz, and that the VSWR between 2.7 and 3.0 GHz is kept to less than 1.15.

A Wide Band Current Monitor Based on Pulsed Transformer Techniques

A charged-particle beam current monitor has been designed using a coaxial cable transmission line in a configuration similar to that employed in building toroidal-wound wide band impedance matching and balun transformers. Several sizes of the coax-wound monitors have been constructed and compared with units of similar ferrite core material and geometry that were wound with ordinary magnet wire. One of the transformers has been used by experimenters at the NAL Internal Tarqet area since August of 1972. In order to simplify electronic signal processing, only average circulating charge is measured. This is done by measuring the "zero"signal" base-line shift due to the natural L/R response of the transformer.

Impedance matching with a series transmission line section

A generalization of the transmission line quarter-wave impedance matching transformer is presented. The resultant series-section transformer can match complex as well as pure resistance loads to a transmission line, and the choice of the characteristic impedance of the matching section is not restricted to a single value.

"Lost beams" from a dielectric covered phased-array aperture

Considerable attention has been devoted to the anomalies in the radiation pattern of a phased-array antenna aperture covered with a dielectric sheet. This phenomenon appears as a notch in the element radiation pattern at a scan angle smaller than that commensurate with the appearance of the grating lobes in real space. This communication discusses the observation of this phenomenon in a 96-element phased array of triangularspaced waveguide radiators utilizing a dielectric impedance matching transformer on the radiating aperture. The effect of the dielectric sheet on the aperture was observed both as a deep notch in the radiation pattern of the central element (with the remaining 95 elements terminated) and in "lost beams" as the 96-element phased-array beam was steered to the angles corresponding to the element pattern nulls. Further, these data are in good agreement with reflection coefficient maxima measured in waveguide array simulators.

Piezoelectric ceramic transformers and filters

The development of improved piezoelectric ceramics has enabled these materials to be used in the design of electronic components. Two new devices are described embodying piezoelectric principles of operation and relying on electromechanical resonance to obtain efficient energy transformation. The ceramic transformer provides a high voltage source without involving insulation problems or magnetic fields. The Transfilter is used as a miniature filter or an interstage impedance matching transformer suitable for radio receivers. Both are essentially solid-state in character and possess all the advantages of such systems. They represent an entirely new approach to component development and can be considered as forerunners of other devices using similar principles.

Photoetched Microwave Transmission Lines

Microwave transmission line and components of unusual light weight and compact construction can be made employing photoetching techniques to produce strip type transmission line. This report will be a general description of work done at Sanders Associates, Inc., to develop techniques for the design and manufacture of photoetched microwave transmission lines. Discussion will include measurements of attenuation and radiation leakage on parallel plate strip lines, as well as shielded type Tri-plate lines, the problem of mode purity and its relation to electrical parameters, various schemes of making transitions from standard waveguide to photoetched strip line. The basic design and performance of various components, as well as items of test equipment, such as slotted lines, matched loads, fixed attenuators, variable attenuators, directional couplers, crystal holders, phase shifters, hybrid rings, coax to Tri-plate transistors, etc., will also be treated. In addition, data will be presented showing impedance and susceptance values of simple discontinuities and impedance matching transformers. A simple technique for constructing gyrators and resonators will be presented, and the design and fabrication of an S-band signal generator employing photoetched microwave Tri-plate line will be shown, illustrating that practical microwave systems can be constructed far more economically than would be possible utilizing conventional waveguide techniques.

Analysis of a Single-Ended Push-Pull Audio Amplifier

This paper deals with a theoretical circuit analysis of a single-ended push-pull audio amplifier. Linear tube characteristics and small signals are assumed. The problem of impedance matching is first discussed. The properties and the requirements of a satisfactory driver stage are analyzed, and an output stage using an impedance matching output transformer is discussed. The effects of the plate-to-ground capacitance of the driver stage on the frequency-gain characteristic and of the choice of the tube and circuit parameters are analyzed. The paper concludes with some experimental results indicative of the inherant properties of the amplifier.

Analysis of a single-ended push-pull audio amplifier

This paper deals with a t h e o r e t i c a l c i r c u i t analysis of a single-ended push-pull audio amplifier. Linear tube characteristics and small signals are assumed. The problem of impedance matching is first discussed. The properties and the requirements of a s a t i s f a c t o r y d r i v e r s t a g e are analyzed, and an output stage using an impedance matching output transformer is discussed. The effects of the plate-to-ground capacitance of t h e d r i v e r stage on the frequency-gain characteristic and of the choice of the tube and circuit parameters are analyzed. The paper concludes with some experimental results indicative of the inherent properties of the amplifier. In a r e c e n t a r t i c l e by Peterson and Sinclair,l special c i r c u i t s have been suggested by which a high fidelity, low d i s t o r t i o n audio amplifier can be constructed without using output transformers or i n which the requimrnents of an output transformer can be greatly simplified, The present a r t i c l e will give a t h e o r e t i c a l analysis of the b a s i c c i r c u i t used by Peterson and Sinclair. It will be observed that many desirable characte r i s t i c s of t h i s a m p l i f i e r c i r c u i t can be deduced from this analysis.

"Cloverleaf" Antenna for F.M. Broadcasting

The radiation requirements and general design considerations for transmitting antennas suitable for f.m. broadcasting are briefly discussed, and an explanation of the design and operation of the arrangement of radiating elements and associated feed system employed in the "cloverleaf" antenna is given. Both calculated and measured data are included, showing field-intensity distribution, gain, impedance-frequency characteristics, etc. Design features which are discussed include a simple coaxial impedance-matching transformer developed initially for microwave application, and the method and facilities provided for the removal of sleet.

The Present Status of the Mechanics of Sound Conduction in Its Relation to the Possible Correction of Conduction Deafness

E. H. Weber in 1851 interpreted the middle ear apparatus as an impedance matching transformer which balanced the resistance differences between the medium of conduction (air) and the medium of reception (liquid). The interpretation implied that the apparatus must be effective for all audiofrequency levels. It was not accepted by otologists because it was known that in conduction deafness, greater functional disability is noted for the low than for the high frequencies. Recent developments support the Weber interpretation and indicate that this low pitch disability is not dependent on frequency limitations due to the pathology of the middle ear. Evidence will be submitted to show that where the sound conduction apparatus is nonfunctional the drum membrane damps the direct conduction through the air of the middle ear. A case will be reported on the replacement of the lost drum membrane and ossicles by a prosthesis patterned after the middle ear apparatus of the bird. The possibility of creating a soft spot in the otic capsule in cases where the stapes is “frozen” to the head so that a transformer prosthesis may be applied will be considered. The accepted idea of a mass shuttling in the labyrinth liquid as the mechanical factor essential to audition is opposed.