RU1130158C - Surface acoustic wave device - Google Patents

Description

 The invention relates to the field of electronics, in particular to signal processing devices for surface acoustic waves (SAW).

 Known devices for surfactants containing located in the common acoustic stream of the input and output interdigital transducers (IDT). A disadvantage of the known devices is the distortion of the electrical characteristics of the device, due to the large amount of direct passage (pickup) of the input signal due to electrostatic induction directly to the output converter.

 The closest in technical essence to the invention is a device for a surfactant, containing broadband and apodized with variable overlapping bandpass transducers of the surfactant placed in a common acoustic stream and a conductive screen located between them. Using a conductive screen, the magnitude of the direct signal passage is significantly reduced.

 A disadvantage of the known device is the distortion of a given amplitude-frequency characteristic (AFC) associated with diffraction of a surfactant emitted or received by portions of an apodized converter with a small coating of pins, which leads to a reduction in the level of signal suppression outside the passband and an increase in the squareness coefficient in filters with arbitrary frequency response - also to the distortion of their phase-frequency characteristics (phase response).

 The aim of the invention is to increase the accuracy of reproduction of the frequency response by reducing diffraction distortion.

The goal is achieved by the fact that in a device on a SAW containing a sound duct and a broadband IDT and a conductive screen located between them and alternating between the electrodes placed on it in a common acoustic channel and a conductive screen located between them, slots are made in the conductive screen from the side of the apodized transducer along the acoustic wave propagation direction whose spatial step monotonically increases from the center of the conductive screen to its periphery, and
and _i / L ≅ 1, a _c / W ≅ 0.02-0.08, where a _i is the width of the slot;
L is the spatial period of the apodized transducer;
and _c is the total width of the slots;
W is the maximum aperture of the apodized surfactant converter.

The drawing shows a structural diagram of a device for a surfactant. The device on the surfactant contains stripe IDT 1, apodized by a change in overlap. A broadband IDT 2 is located in common with it. A conductive screen 3 is located between the IDT 3. In the conductive screen 3, slots 4 of width a _{i are} made along the SAW propagation direction along the direction of SAW propagation at a distance between them of b _i . The width of each of the slots is not more than one spatial period L of the transducers at the center frequency. The total width of the slots a _with at least 12-50 times less than the maximum aperture W of the converters 1, 2. The spatial step of the slots 4 monotonically increases from the center of the conductive screen 3 to its periphery.

 The device operates as follows.

 When a signal is applied to one of the converters (1, 2) of the device, the surfactants excited by it propagate in the zone of the sound duct, in which a conductive screen 3 is located between the IDTs. Due to the presence of slots 4, the surfactant is canalized and, as a result, the diffraction distortion is reduced. The location of the slots 4 in the conductive screen 3 from the side of the apodized transducer 1 brings the zone of localization of the wave to the apodized transducer 1.

The ratio of the total width of the slots 4 to the aperture of the IDTs is chosen from the condition of phase distortion at the level of ^about 5-10 and amplitude distortions at the level of 1-4%, which practically does not affect the frequency response fidelity. This level of distortion is provided when the total width of the slots does not exceed 2-8% of the maximum aperture of the converter.

 The law of changing the pitch of the slots 4 is selected from the condition of increasing the channeling properties in the region of the acoustic flow formed by electrodes with a minimum aperture of overlap. A reduction in diffraction distortion is achieved with a monotonic increase in the step of the slits along the wave front from the screen sections 3 lying in the center of the acoustic stream to its periphery, since in the most common constructions of the apodized transducer 1, sections with a small overlap lie in the central part of the acoustic stream.

 Thus, the use of slots in the conductive screen in this device for a surfactant allows for the directed propagation of the wave by correcting its trajectory with the help of these slots and thereby allows to increase attenuation outside the passband, reduce the squareness coefficient, i.e., increase the accuracy of the reproduction of the given frequency response. (56) Rechitsky V.I. Acoustoelectronic radio components. M.: Soviet Radio, 1980, p. 113.

 TIIER, N 5, 1976, p. 130, fig. 4.

Claims (1)

SURFACE ACOUSTIC WAVES DEVICE, comprising a sound guide and broadband and apodized with variable overlapping of electrodes placed on it in a common acoustic channel, alternating interdigital transducers and conductive screen located between them, characterized in that, in order to improve the accuracy of reproducing the amplitude-frequency characteristics by reduction of diffraction distortions in the conductive screen from the apodized transducer along the propagation direction a slots, the spatial step L of which monotonically increases from the center of the conductive screen to its periphery,
a _i / L ≅ 1; a _s / W ≅ 0.02 - 0.08,
where a _i is the width of the slot;
a _with - the total width of the slots;
W is the maximum aperture of the apodized transducer.

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