We describe a technique for generating tunable narrow-band terahertz radiation via optical rectification in periodically-poled lithium niobate. Frequency tuning is accomplished by spatially chirping the domain width laterally to the beam propagation direction, and adjusting the temperature of the sample. We demonstrate tuning over a continuous range from 0.8 to 2.5 THz. The bandwidth of the ter...

Chirps arise in many signal processing applications. While chirps have been extensively studied both as functions over the real line and the integers, less attention has been paid to the study of chirps over finite groups. We study the existence and properties of chirps over finite cyclic groups of integers. In particular, we introduce a new definition of a finite chirp which is slightly more g...

During social interactions, apteronotid electric fish modulate their electric organ discharges (EODs) to produce transient communication signals known as chirps. Chirps vary widely across species and sex in both number and structure. In Apteronotus leptorhynchus, males chirp far more than females and their chirps have greater frequency modulation than those of females. High-frequency chirps are...

Acoustically interacting males of the tropical katydid Mecopoda elongata synchronize their chirps imperfectly, so that one male calls consistently earlier in time than the other. In choice situations, females prefer the leader signal, and it has been suggested that a neuronal mechanism based on directional hearing may be responsible for the asymmetric, stronger representation of the leader sign...

The most common way to define instantaneous amplitude, phase and frequency of a real signal is to use its analytic signal. One of the main advantages of this procedure is that it establishes a one-to-one relationship between any real signal and the pair of functions defining its instantaneous amplitude and phase. However, there are some problems in its physical interpretation but it is shown th...

Electro-mechanical impedance method is emerging as an important and powerful technique for structural health monitoring. The E/M impedance method utilizes as its main apparatus an impedance analyzer that reads the in-situ E/M impedance of the piezoelectric wafer active sensors (PWAS) attached to the monitored structure. Present-day impedance analyzer equipments (e.g. HP4194) are bulky, heavy an...

Traditional stepped frequency chirp pulse train methods suffer from high sidelobes and ambiguous peaks, known as grating lobes and difficulty in compensating Doppler effect caused by target motion. This paper investigates a class of non-linear stepped frequency chirp pulse train with low sidelobes and capability to cancel clutter and to compensate motion. We present analytic expression for its ...