Degradation behavior of deep UV-LEDs studied by electro-optical methods and transmission electron microscopy

Degradation mechanism of 265-nm deep ultraviolet light emitting diodes (UV-LEDs) has been investigated by means of electroluminescence, current-voltage measurement, capacitance-voltage measurement, and transmission electron microscopy (TEM) equipped with energy dispersive X-ray spectrometer (EDAX). It is revealed that a major degradation mode of UV-LEDs may be the leakage current induced optical degradation. The current pathway is demonstrated by TEM with EDAX, indicating that the contact metals can partially interact with p-type materials, which accelerate the degradation of LEDs. The presented results can help to understand the degradation mechanisms and improve the reliability of deep UV-LEDs.     

Implementation of a Biometric Interface in Voice Controlled Wheelchairs

In order to assist physically handicapped persons in their movements, we developed an embedded isolated word speech recognition system (ASR) applied to voice control of smart wheelchairs. However, in spite of the existence in the industrial market of several kinds of electric wheelchairs, the problem remains the need to manually control this device by hand via joystick; which limits their use especially by people with severe disabilities. Thus, a significant number of disabled people cannot use a standard electric wheelchair or drive it with difficulty. The proposed solution is to use the voice to control and drive the wheelchair instead of classical joysticks. The intelligent chair is equipped with an obstacle detection system consisting of ultrasonic sensors, a moving navigation algorithm and a speech acquisition and recognition module for voice control embedded in a DSP card. The ASR architecture consists of two main modules. The first one is the speech parameterization module (features extraction) and the second module is the classifier which identifies the speech and generates the control word to motors power unit. The training and recognition phases are based on Hidden Markov Models (HMM), K-means, Baum-Welch and Viterbi algorithms. The database consists of 39 isolated speaker words (13 words pronounced 3 times under different environments and conditions). The simulations are tested under Matlab environment and the real-time implementation is performed by C language with code composer studio embedded in a TMS 320 C6416 DSP kit. The results and experiments obtained gave promising recognition ratio and accuracy around 99% in clean environment. However, the system accuracy decreases considerably in noisy environments, especially for SNR values below 5 dB (in street: 78%, in factory: 52%).     

Effect of Input Waveform to Vibration Speaker on Sound Quality of Electric Artificial Voice

A number of studies have been conducted on the improvement of the sound quality of electrical artificial laryngeal speech, the speech produced has been difficult to hear compared to a natural voice. For this reason, it is necessary to effectively improve the frequency characteristics of the input signal. In the present study, to improve the sound quality of vocalization using an electrical artifi- cial larynx, first, a comparison of the frequency characteristics between the real and artificial voices was conducted, and three filters that can make the frequency characteristics of the artificial voice closer to those of a real voice were generated. Then, the influence of these filters on the quality of the artificial voice was investigated via physical measurement and a subjective evaluation experiment targeted at Japanese five vowels. It was found that the intelligibility of artificial /a/ and /o/ sounds was improved, whereas little improvement was observed in the case of /i/, /u/, and /e/. The obtained results confirmed the effect of optimizing the input signal into the vibration speaker and indicated areas for further improvement.     

Degradation of polymeric bellows effecting life cycle of constant-velocity joint

One broken and three new polymeric constant-velocity boots (bellows) being a spare part of a constant-velocity joint in two military vehicles were analyzed to identify basic composition and to determine if composition or structure of broken bellows differ. Infrared spectroscopy, differential scanning calorimetry, and thermogravimetry were used for analyses. Bellows for both vehicles are produced from thermoplastic elastomer. Broken bellows is chemically degraded and material just from the fracture is deformed plastically. The life cycle of bellows depends especially on applied stress and temperature (that about ?20°C seems to be critical due to crystallization of soft segments).