Abstract: A railway crossing guard includes a pivotable crossing gate and a set of retractable barriers on the same side of a set of railroad tracks. The pivotable crossing gate is mounted adjacent a first traffic lane to move between a lowered position and a raised position, and the retractable barriers are mounted in a line oriented parallel to the traffic lanes on a median strip between first and second traffic lanes. These retractable barriers move between a retracted position, in which the retractable barriers are substantially flush with the roadway, and an extended position, in which the retractable barriers are raised above the roadway. In the extended position, the retractable barriers are positioned to block a vehicle in front of the lowered crossing gate from crossing the median strip to drive around the lowered crossing gate.

Abstract: Two input transducers launch oppositely-propagating acoustic surface waves on a piezoelectric substrate. The waves are compressed to a smaller beamwidth and then laterally confined in a diffused channel waveguide where non-linear interaction occurs at increased energy densities due to the beam compression. In one embodiment the beam compression is accomplished in multistrip couplers. In another embodiment, diffused horn-shaped channels are provided for compressing the beamwidth. Both piezoelectric and semiconductor convolvers are disclosed.

Abstract: A tapped surface acoustic wave (SAW) delay line with time-resolved outputs sing piezoelectric leaky wave coupling and bulk wave amplification, and having low loss characteristics. A solid piezoelectric semiconductor is placed adjacent to a solid piezoelectric substrate. A pulsed rf input signal is applied to interdigital transducers (IDT) on the substrate. The applied signal launches a SAW in the substrate in a direction parallel to the interface between the substrate and the piezoelectric semiconductor solid. Upon reaching the interface, the SAW is piezoelectrically leaky-wave coupled across an air gap to a bulk acoustic wave in the piezoelectric semiconductor. Reflections of the bulk wave occur at both surfaces of the piezoelectric semiconductor, and piezoelectrically couples back across the air gap to excite a SAW on the piezoelectric substrate. The resultant rf output includes the normal delayed SAW pulse and additional delayed and time-resolved pulses.