Ashok Jhunjhunwala

In planar bulk acoustic wave devices, an interdigital transducer (IDT) is generally used as the source of excitation. Grooves, which convert an incident SAW (surface acoustic wave) to bulk waves and vice versa, also have the potential to be used as an alternative (if secondary) source of excitation. A typical shallow rectangular groove etched into a crystalline substrate perpendicular to the propagation direction is considered. The groove is modeled as an interior perturbation to the substrate. Coupled-mode equations are developed and solved for the reflected SAW and the scattered bulk waves. The results are compared to those of the half-space geometry. The interior-perturbation approach produces a good match with earlier published results that used the boundary-perturbation method.

A recirculating, synchronous TDM (time division multiplexed) backbone loop operating at 1 Mbps that supports multiple 9600 baud point-to-point connections, and multiple low bit rate packet channels is described. Slots are deterministically allotted to groups of devices and any medium access protocol suitable for the ring topology can be used to regulate access to the transmission channel. Nodes on the backbone are interconnected through fiber optic or atmospheric optical links. The objective of the network is to satisfy the demands of a typical computing environment, viz., to offer a terminal distribution system and to simultaneously support multiple low bit rate packet channels. Devices communicate with the network through RS-232C serial lines.

The bulk acoustic waves launched in a piezoelectric crystal by an interdigital transducer, considered earlier as a spurious response in SAW devices, are now usefully employed in planar bulk acoustic wave (BAW) devices. This paper presents the results of a theoretical analysis of bulk wave response in a material. The analysis enables one to design BAW devices with a more desirable response than those obtained so far. Copyright © 1988, The Institution of Electrical Engineers. All rights reserved.

Normal communication link with submerged bodies in the VLF range has serious practical limitations besides providing limited bandwidth capabilities. Optical communication links are thus being studied as an alternative possibility. It is now known that a window exists in the blue/green region of the optical spectrum, where the ocean water attenuation factors are very low. The ground-submarine link via a satellite has to necessarily contend with propagation through the atmosphere, ocean and air-water interface. The vagaries of the air-water interface on the reliability of the optical communication link have been studied both theoretically and experimentally and the results presented. It is observed that as long as the diameter of the optical beam incident on the interface is comparable to the ocean wavelength, the attenuation of the received underwater optical intensity is never more than 50 percent of what it would have been without ocean waves.

The design of a high speed, broadband packet switch with two priority levels for application in integrated voice/data networks is presented. The packet switch can efficiently cope with 128 byte packets converging on it from eight 140 Mbit/s dynamic time division multiplexed fibre optic links. The packet switch throughput varies with the load and traffic composition, and the delay experienced by voice and data packets is within 300 μs and 3 ms, respectively. The design is implemented by task-sharing in a multi-processor configuration. The design of the packet switch, including its subsystems, is detailed here. © 1989.

Digital transmission through optical fibres and 'packet-switching' are two independent technologies that have gained wide acceptance during the past decade. This paper considers the possibility of a fusion between the two technologies. The network envisaged is a long-haul, packet-switched network, with optical fibre links between the nodes, for the integrated transmission of voice and data. The advantages of implementing packetswitching on an optical fibre network are brought out. The proposed network effectively utilizes the bandwidth of 140 Mbit/s fibre optic links to transport voice and data packets in a store-and-forward manner from the source node to the destination node. The issues involved in the selection of routes for voice and data packets are discussed. Some standards and timing constraints have been evolved for the transmission of speech in packets. This imposes a limitation on the allowable delay at each node. The design of an ultra-fast packet-switch with high throughput, which satisfies the timing constraints, is described in this paper. Protocols for call set-up, priority rules, traffic flow and congestion control procedures are proposed and discussed. A simulation model of the packet-switch is developed, and its performance is evaluated for varying traffic conditions. The results of the simulation are presented.

A versatile communication system in a ship with 120 stations, each having voice and data transmission is envisaged. The proposed fibre optic network has a bus topology ideally suited for distribution in ship-like environment. Use has been made of standard ETHERNET chip sets manufactured by INTEL. This makes the stations compact, easier to maintain and inexpensive. The ETHERNET proto-col is primarily designed for packet data transmission. The collision detection and backoff protocol makes the packet transmission probabilistic and is therefore not suitable for voice transmission. This problem is overcome in the present design by a scheme where the required number of voice slots are dynamically allocated. That is, having established a connection for voice communication between stations, fixed slots are assigned for voice transmission and reception. The data transmission continues to use CSMA/CD Protocol. A simple hardware addition to the ETHERNET chip set makes the scheme workable. Drops in the fiber optic bus network is through passive star couplers. Four to eight star couplers are used in the present scheme with repeaters between adjacent star couplers. The repeaters will not be usual repeaters, as ordinary repeaters would cause loops to be formed between adjacent stars, thereby causing data to recirculate. This recirculation is avoided by making the repeater intelligent and also performing the task of detecting collisions between signals originating from stations connected to different star couplers. © 1987, SPIE.