Showing papers on "Interdigital transducer published in 1980"

Low‐temperature growth of piezoelectric AlN film by rf reactive planar magnetron sputtering

Abstract: A single‐crystalline aluminum nitride film is grown on a basal‐plane sapphire substrate and the c‐axis‐oriented films are grown on glass and gold‐film substrates at substrate temperatures as low as from 50 to 500 °C by using reactive rf planar magnetron sputtering. Surface acoustic waves are generated in both structures where interdigital transducers are located on the top of an aluminum nitride film and at the interface between the film and the substrate sapphire. The effective surface acoustic wave coupling factor k2 is 0.09 and 0.12%, respectively, for these interdigital transducer configurations. The aluminum nitride films sputtered on a gold film on a glass rod and on a glass sheet itself are also piezoelectric and used as bulk and surface acoustic wave transducers, respectively. These piezoelectric aluminum nitride films on glass and metal‐film substrates have become available for the first time because film growth at low temperature has become possible in the present study.

Surface acoustic wave resonator device

Abstract: This disclosure concerns surface acoustic wave resonator devices having grating reflectors. The resonator comprises a substrate of piezoelectric material, an input interdigital transducer which converts electrical energy to surface acoustic wave energy, an output interdigital transducer which converts surface acoustic wave energy to electrical energy, first and second grating reflectors arranged in spaced aligned relationship on opposite ends of the substrate with the input transducer and the output transducer interposed therebetween the input transducer and the output transducer. The first grating reflector, whose aperture length is the same effective length as the input and output transducers, comprises a first group of interconnected parallel spaced conductors, a second group of interconnected parallel spaced conductors and at least one of isolated parallel conductors positioned between the first and second groups of conductors. Each conductor of the one group is aligned with a corresponding conductor of the first group and a corresponding conductor of the second group. Each conductor of the first and second group is parallel and electrically interconnected. The second grating reflector is identical with the first grating reflector.

Surface acoustic wave device having buried transducer

Abstract: An acoustic wave device wherein each electrode element of an interdigital transducer is buried or embedded between a pair of layers of piezoelectric material. The use of a multi-layer stack of layers of piezoelectric material enables each electrode element of the transducer to be sandwiched between a distinct pair of layers and thus to be insulated from the other electrode element or elements. Because of the insulation thus provided, the spacing between the fingers of each electrode element may be selected without fear of causing short circuits between electrode elements.

Planar acoustic microscope lens using Rayleigh to compressional conversion

Abstract: A planar acoustic lens is described in which Rayleigh waves generated by a circular interdigital transducer on LiNbO3 are converted to a focused hollow conical beam in the contiguous liquid. The focal spot is comparable to that of a standard diffraction-limited lens of similar aperture; the calculated sidelobes are higher but the measured ones are comparable.

Radar applications of s.a.w. dispersive filters

Abstract: Pulse-compression radars have been developed in several countries over a period in excess of twenty years. A great advance in the performance of such systems has been made possible with the development of the surface acoustic wave (s.a.w.) interdigital transducer (i.d.t.). In the paper, some recent advances in i.d.t. performance are presented against a background which demonstrates the basic consistency in design techniques for both linear-and nonlinear-chirp signals. Later Sections of the paper assess the range of performance now available and consider the ways in which ultimate system performance may be achieved in respect of Doppler shift, coherence, mismatch loss and dynamic range.

Microscope Lens Using Conversion of Rayleigh to Compressional Waves

Abstract: A planar a coustic microscope lens is demonstrated which produces an almost aberrationfree focal spot in a liquid mediuc. A circular interdigital transducer generates converging acoustic surface waves on the interface between the piezoelectric solid and the liquid and these Rayleigh waves convert to a hollow cone of compressional waves converging to a focus on the axis in the liquid. The measured amplitude distribution in the r egion of the focus agrees with calculations and the p rototype l ens has been used at 20 MHz with a mechanical sweep to produce acoustic images. The simplicity of the planar photolithographi c fabrication i nvites modified electrode shapes and excitation to change tho focal p attern.

Radiation Patterns of Bulk Modes from a Finite Interdigital Transducer on Y-Z LiNbO 3

Abstract: Radiation patterns of bulk acoustic modes from a finite in- terdigital transducer on Y-Z LiNb03 were found using moment method and then compared with the experimental results. The power density radiation patterns of shear and longitudinal bulk modes were computed as functionsof the radiation angle, the electrode metallization ratio, and the frequency. It was shown that a SAW transducer can be very effi- ciently used for shear bulk wave excitation. For instance, at the sec- ond harmonic of the Rayleigh wave the percentage power of the shear, longitudinal, and SAW is 67.2,26.4, and 6.4 percent, respectively. The bulk power density distribution versus radiation angle does not change in form with a change in the metallization ratio. The SAW power density increases with increasing values of the metallization ratio.

Acousto-optic mode-locked laser

Abstract: An acousto-optic mode-locked laser comprises a piezo-electric, acousto-optic crystal disposed within the cavity of a laser in the path of the laser beam, and a radio-frequency energized interdigital transducer (IDT) array coupled to the crystal so as to launch bulk shear waves in the crystal for a limited number of interactions with the laser beam. The IDT is mounted on a first plane surface of the crystal opposite from a second plane surface thereof which is disposed at an acute angle θ to the first surface and which is nominally parallel to the laser beam. Bulk shear waves are launched in the crystal by the IDT at the first surface at the angle θ to a normal to that surface with the forward wave traversing the laser beam perpendicular to its axis and being reflected back through the beam by the opposite or second crystal surface to form standing waves which modulate the beam. This reflected wave thereafter is reflected by the first surface out of the interaction zone so as to be ineffective in establishing additional standing waves. Optimum efficiency of shear wave generation is achieved when df=v.sub.l ( 1) where d is the finger period of the IDT, f is the frequency of the microwave source, and v l is the velocity of the acoustic longitudinal wave.

Ultrasonic scanning and imaging appts. - has organic piezoelectric transducer detector, between sample and ceramic transducer transmitter, with matched acoustic impedance

Abstract: The appts. generates ultrasonic images of e.g. parts of the human body and has a transmitter transducer of a ceramic piezoelectric and a receiver transducer of organic piezoelectric. The ceramic is e.g. PZT and the organic material is e.g. a film polymer piezoelectric of an acoustic impedance near to that of the body to be examined. The receiver transducer is interposed between the transmitter and the body. The polymer is conveniently a vinylidene polyfluoride rendered piezoelectric by the single action of an electric field normal to the film principal faces while the organic material is a film of thickness determined as a function of the frequency of electric pulses applied to the transmitter transducer. The principal transducer faces are metallised with that of the receiver in body contact and at earth potential while that of the transmitter is secured to a backing which strongly attenuates reverse transmitted sound waves.

Two types of acoustic focusing devices

Abstract: Two types of Lamb wave devices for acoustic focusing are presented. These are a devive with a biphase interdigital transducer and a unidirectional device. The latter consists of a group of three electrodes. One of the electrodes is deposited on the substrate surface in contact with water, and the others are interdigital electrodes. In both devices, the compressional wave radiated into water from the surface without the interdigital electrodes interferes constructively at a focal point. Basic design considerations for two types of focusing devices and acoustic imaging results are given.

A Latent Failure Mechanism for Surface Acoustic Wave Components Utilizing Lithium Niobate

Abstract: A latent failure mechanism for surface acoustic wave components which utilize lithium niobate as the piezoelectric has been, identified. This failure mechanism involves the growth of aluminum oxide on the thin film aluminum metal which constitutes the interdigitated electrical/mechanical transducer structure. This failure mechanism has been successfully eliminated in high-reliability components by making certain that a necessary condition for the growth of the oxide does not exist. The necessary condition is the existence of a dc electric field within the transducer structure. The exact conditions necessary for the initiation of the oxide growth have not, as yet, been determined. It is known that electric field values of the order of 104 volts per centimeter with ambient temperature of 125°C for 168 hours can cause the growth. The effect of the growth is to reduce the effective electroacoustical coupling factor which results in the component exhibiting added insertion loss and a skewing of pass band RF characteristics as the growth progresses.

Resonant circuit with surface acoustic wave resonator - which is integrated onto same substrate as capacitor to form single component

Abstract: The resonant circuit e.g. for use in a TV receiver oscillator, has its capacitor (15,18) combined with a surface acoustic wave (SAW) resonator (12,17) to form a single component. The SAW resonator consists of a thin piezoelectric film (17) and a substrate and interdigital electrode pairs (13,14) formed on the surface of the piezoelectric film. The capacitor consists of a first conducting film (15), connected to one of the ele ctrode pairs and on the surface of the piezoelectric film, and a second conducting film (18) on the other surface of the piezoelectric film and opposite the first conducting film. A relatively large number of interdigital electrode pairs are present such that the SAW resonator consists solely of interdigital electrodes and the piezoelectric thin-film.

Surface wave component

Abstract: A surface wave component has a pair of interdigital transducer comb structures carried spaced apart on a surface of a substrate which is carried on a base plate. In one embodiment, signal leads extend beneath the substrate to areas adjacent the rear portions of the comb structures and are capacitively coupled thereto via the substrate which is a dielectric. In another embodiment, inductive coupling loops interconnect the rear portions of the comb structures of a respective transducer and another inductive loop is carried on the opposite side of the substrate for signal coupling. In both embodiments both symmetrical and asymmetrical signal coupling is provided by utilizing a grounding plate or layer as a signal lead.

Tuning of transducer elements in transducer array

Abstract: It is found that the resonance frequencies of various identical transducer elements used in a transducer array differ slightly. Due to this, relatively high power sources are required to radiate a certain amount of power. A possible solution to this problem which can be easily realised in practice for a ceramic transducer array is presented.

A Polyvinylidene Fluoride Differential Membrane Pressure Acoustical Array Transducer.

Abstract: : This work describes an ultrasonic acoustical transducer used to generate and receive ultrasonic waves. Transducer construction includes a membrane of polyvinylidene fluoride (PVDF), a piezoelectric polymer, which is deflected by liquid or gas pressure to form a concave or convex surface. When an RF signal is applied to the membrane transducer ultrasonic waves are generated. Calculations for the performance of the transducer are given along with the results of a series of ten tests. A 1.27 cm diameter transducer was constructed for this study. Results indicate that, although the acoustical power output of the device is lower than conventional transducers, the lower construction costs and variable focal length capability may make it ideal for fabrication into large transducer arrays. (Author)