Use Of Frequency Response Research Articles

3.2 Gigabit-per-second Visible Light Communication Link with InGaN/GaN MQW Micro-photodetector.

This paper presents the first demonstration of InGaN multiple quantum well (MQW) based micro-photodetectors (µPD) used as the optical receiver in orthogonal frequency-division multiplexing (OFDM) modulated visible communication system (VLC). The 80-µm diameter µPD exhibits a wavelength-selective responsivity in the near-UV to violet regime (374 nm - 408 nm) under a low reverse bias of -3 V. The modulation scheme of 16-quadrature amplitude modulation (16-QAM) OFDM enables the use of frequency response beyond -3 dB cutoff bandwidth of µPD. A record high data rate of 3.2 Gigabit per second (Gpbs) was achieved as a result, which provides the proof-of-concept verification of a viable high speed VLC link.

Evaluation of the use of frequency response in the diagnosis of pleural effusion on a phantom model of the human lungs.

Pleural effusion is one of the most widespread respiratory diseases in the world. Current diagnostic techniques include a combination of medical history and x-ray or CT scan imaging of the chest. However, these techniques are expensive and impractical in resource limited settings. We propose a new method based on sound transmission into the respiratory system through the chest wall. To evaluate this technique, a sine sweep signal with a frequency range between 100 Hz and 1000 Hz was transmitted into a phantom model of the human lungs capable of simulating healthy and effused conditions. The frequency response of the model under both conditions was computed and compared to evaluate the diagnostic performance of the new method. The results indicate that there is a significant difference between the frequency response of healthy and effused lungs, which suggests that the new technique may be suitable for the clinical diagnosis of pleural effusion.

Effect of cracking, corrosion and repair on the frequency response of RC beams

This paper presents a laboratory investigation to study the effect of cracking, corrosion and repair on the frequency response of simply-supported reinforced concrete beams. The beams were subjected to four-point bending at 70% of their theoretical ultimate loads. Corrosion was then induced using an electro-chemical acceleration technique. The beams were then repaired to restore their load-carrying and deflection capacities. Based on response time histories, the fundamental frequency characteristics of the beams were deduced using Fourier transform (FT) and Hilbert-Huang transform (HHT). Experimental results revealed significant changes in the normalized frequency, R f , with decrease in R f associated with load-induced cracking, an increase in R f associated with moderate reinforcement corrosion and a subsequent decrease in R f associated with repair. The results of this study support the use of frequency response, obtained with an appropriate signal processing technique such as HHT, to infer the health of monitored structures, taking into account environmental conditions, likelihood of corrosion occurrence, properties of repair material and interfacial bonding.

Assessing manufacturing system performance: Frequency response revisited

The use of continuous models, both mathematical and computer simulation package based, is currently being reappraised to evaluate the interaction between order and material flows in production environments. It is found that these models adequately replicate observed industrial behaviour. Furthermore, they are couched in terms, which permits the correlation between observed flow amplifications and various counterbalancing effects. The frequency response of these models can be directly interpreted as the needs of managers requiring smooth production flow in the face of periodic market trends. It is thus relevant to assessing system performance along with other standard tests found in classical control theory studies. In developing the use of general purpose models of manufacturing systems, the need for succinct and easily generated criteria has led to the authors favouring the use of frequency response as a general design tool. This paper explores the reasoning behind this choice via a comparison of two examples of inventory and order based production control systems.

The 12th Renwick Memorial Lecture Scientists’ Ways of Thinking About Definition

AbstractMost of the recent ideas for the quantitative estimation of definition are based on the possibility of analysis of the subject photographed into sine-curve components. This has led to the use of frequency response of the lens and film as a measure of the defining power of the system. The importance of granularity as a limitation of definition was first recognized in the case of resolving power and has been further emphasized by the application of information theory to photography.

A new chart relating open-loop and closed-loop frequency responses of linear control systems

CONTROL ENGINEERS generally adhere to the use of frequency response as the fundamental tool for feedback control systems. Through the use of the Nichols chart,1 the open-loop characteristics can be quickly converted to the closed-loop characteristics. The performance of control systems can be estimated according to the gain and phase margins and the magnitude of peak M. Although actual performance may be quite different from that predicted by a certain value of a particular specification, yet by means of Meerov's method2 it should not be difficult for engineers to determine the limits of applicability and to evaluate its effectiveness.