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A quadrature modulation method is used for studying the ultrasonic communications methods in air. The results have shown the system is feasible in principle for communications over distances of several meters by using frequencies in the 200 to 400 kHz range.

The use of ultrasound in air as a means of communicating digital signals is discussed. Findings reveal the capability of binary phase shift keying (BPSK) in transmitting signals with a low bit error rate.

The signal-to-signal ratio (SMR), which can be greatly improved, using two signal recovery techniques, namely pulse compression and swept frequency multiplication (SFM) is shown. A simulation of both techniques is presented and compared to experimental data.

A new technique is investigated for improving the signals that can be obtained in air-coupled nondestruction evaluation (NDE). The technique relies on a swept-frequency 'chirp' signal, which is transmitted from a transducer in air. It is found that the new technique differs from existing time-domain correlation techniques, such as pulse compression, in that a single multiplication process is performed in the time domain to give a difference frequency signal.

Intraocular light scatter is modeled through a stratified medium. It is shown that the eye lens possesses properties of an interference filter. In conditions that may mimic opacification, as found with cataract formation, such a filter may have stop zones with reflectance up to 1 in the band of visible light. OCIS codes: 170.4470, 170.4730, 330.5020, 330.3790, 310.6860, 290.1350.

A model demonstrating the effects of quantum capture and escape processes and carrier diffusion to nonlinear quantum-well laser diodes is presented. The proposed model was developed using laser rate equations, the Volterra nonlinear theory and the parameter transform. The proposed model shows that all three processes negatively affect the laser relaxation frequency, resulting to various distortions.

Analogue video cavalcade services in cable access television (CATV) networks usually require a very high carrier-to-noise ratio (CNR) in order to provide a good quality picture. In consequence, practical lightwave hybrid amplitude modulation (AM)/M-ary quadrature amplitude modulation (M-QAM) systems are found to suffer only infrequent clipping impulse noise, which can be provably modeled as a Poisson arriving pulse train. Based on this knowledge, a new expression for the probability density function (pdf) of the clipping noise at the output of a QAM demodulation matched filter is given which can be numerically evaluated with high accuracy. Bit-error rate (BER) performance prediction is then carried out for M-QAM signals within the hybrid system in the presence of an additive mixture of Gaussian and clipping impulse noise. Agreement between the analytical results and the experimental data is quite good.

This paper presents a new approach to the design of lightwave multichannel CATV transmission systems using broadband digital coding to convert an all-analog multiplexed video signal to a string of pulses suitable for digital transmission. Four broadband coding methods have been discussed and compared, which are: uniform and optimal companding PCM, as well as uniform and adaptive DM. The principle advantages of this approach include the benefits obtainable from digital transmission and also direct compatibility with current CATV networks. CNR limits have been investigated for all of these methods.

A study on the general theory of switches in three-terminal silicon heterostructures under avalanche breakdown conditions lead to modified three-terminal switching devices. The device functions properly in avalanche and punch-through modes. Epilayer doping and thickness are the device fabrication parameters which affect the characteristics. The devices with lower doping concentrations show the presence of a punch-through mechanism. The third terminal controls the carriers in the polysilicon-silicon interface.

Measurements of the transient effects seen in a silicon heterostructure switch due to optical and electrical stimuli show that the optical switching output differs from that of electrical switching. Analysis of input pulse width and external load conditions indicates that the turn-on time of the electrical drive pulses has three components, turn-on-delay time, capacitive rise time and feedback regenerative time. The measured data indicates the validity of the heterostructure switch.