Identification of Frequency Ranges for Subharmonic Oscillations in a Relay Feedback System

This paper examines the behaviour of a single loop relay feedback system (RFS) which is driven by an external signal. It is well known that such a RFS exhibits a variety of oscillation patterns including forced and subharmonic oscillations (SO). This paper focuses on the conditions for SO. It will be shown that for an external signal with a fixed amplitude, it is possible for SO with different orders to occur simply by changing the frequency of the external signal. Similarly, for an external signal with a fixed frequency, it is possible for SO with different orders to occur when the amplitude of the external signal is varied. The conditions under which these different scenarios will occur are explored. An analysis of these conditions identifies the frequency ranges where certain orders of SO are possible for a given amplitude of the external signal. The effects of the initial conditions on the SO are illustrated and discussed. Simulation studies are presented to illustrate the result

Formation And Characterization Of Pbxcd1-Xs Interlayer For PbSCdSZnS Quantum Dot Sensitized Solar Cells

Sel suria sensitif titik kuantum (QDSSCs) mempunyai kecekapan yang rendah disebabkan oleh penggabungan semula antara muka elektrolit-elektrod. Titik kuantum plumbum sulfida (PbS), titik kuantum plumbum cadmium sulfida (PbxCd1-xS), titik kuantum kadmium sulfida (CdS) dan diikuti oleh salutan zink sulfida (ZnS) telah berjaya dimendapkan ke atas elektrod TiO2 melalui kaedah penjerapan dan tindakbalas lapisan berturut-ion (SILAR) sebagai fotoanod bagi QDSSCs. Pemendapan PbxCd1-xS di antara lapisan teras PbS dan lapisan luar CdS akan mengurangkan penggabungan semula dan meningkatkan kecekapan bagi QDSSCs. Elektrod TiO2 akan dibentukan dengan memendapkan TiO2 berliang meso di atas kaca oksida timah berdopkan florin (FTO) setelah pengkalsinan pada suhu 450 °C. Sel suria disediakan dengan mengapitkan fotoanod TiO2 berliang meso dengan fotokatod Cu2S. Enam kitaran SILAR PbS, CdS, ZnS dan PbxCd1-xS serta lapisan Bagi lapisan pelbagai PbS/PbxCd1-xS/CdS/ZnS sampel, kesan kitaran SILAR bagi PbxCd1-xS dikaji dengan empat jenis pecahan molar, x iaitu 0.05, 0.1, 0.15 and 0.2. Pengukuran ketumpatan arus-voltan (J-V) mengesahkan kecekapan sel suria untuk empat kitaran SILAR lapisan PbxCd1-xS dengan pecahan molar, x dalam 0.05 bagi lapisan pelbagai PbS/PbxCd1-xS/CdS/ZnS sampel akan meningkatkan sebanyak 38.2 % apabila berbanding dengan lapisan pelbagai PbS/CdS/ZnS sampel. In adalah kerana jurang jalur diperolehi bagi empat kitaran SILAR lapisan PbxCd1-xS dengan pecahan molar, x dalam 0.05adalah antara jurang jalur diperolehi bagi lapisan teras PbS dan lapisan luar CdS dengan pengukuran UV-Vis spektra penyerapan. Selain itu, perangkap keadaan di antara lapisan teras PbS dan lapisan luar CdS dapat diturunkan dengan pemendapan lapisan PbxCd1-xS dalam sampel lapisan pelbagai PbS/PbxCd1-xS/CdS/ZnS. Antara sampel lapisan pelbagai PbS/PbxCd1-xS/CdS/ZnS, empat kitaran SILAR bagi lapisan PbxCd1-xS dengan pecahan molar, x dalam 0.05 menunjukkan kecekapan sel suria yang paling tinggi iaitu 0.34 % apabila berbanding dengan empat kitaran SILAR bagi lapisan PbxCd1-xS dengan pecahan molar, x dalam 0.1, 0.15 and 0.2. Ini adalah disebabkan oleh empat kitaran SILAR bagi lapisan PbxCd1-xS dengan x dalam 0.05 mempunyai jalur konduksi yang tinggi akan membawa kepada suntikan electron yang lebih cepat dari PbS/PbxCd1-xS jalur konduksi ke elektrod TiO2. Oleh itu, penggabungan semula yang rendah akan diperolehi dan kecekapan sel suria akan meningkatkan. Di samping itu, empat kitaran SILAR bagi lapisan PbxCd1-xS memberikan kecekapan sel suria yang tinggi daripada enam kitaran SILAR bagi lapisan PbxCd1-xS dalam lapisan pelbagai PbS/PbxCd1-xS/CdS/ZnS sampel. Ini adalah disebabkan oleh pemendapan titk kuantum yang tinggi bagi PbxCd1-xS dengan enam kitaran SILAR lapisan PbxCd1-xS mengelakkan penusukan elektrolit dan menurunkan kecekapan sel suria dalam pengukuran J-V. _______________________________________________________________________________________________________ Quantum dot sensitized solar cells (QDSSCs) have low efficiency due to the recombinations at electrolyte-electrode interfaces. Lead sulphide (PbS) quantum dots (QDs), lead cadmium sulphide (PbxCd1-xS) QDs, cadmium sulphide (CdS) QDs and followed by coating with zinc sulphide (ZnS) were deposited on TiO2 electrode as TiO2 mesoporous photoanode using successive ionic layer adsorption and reaction (SILAR) method for QDSSCs. PbxCd1-xS QDs deposited between PbS core and CdS shell layer could reduce the recombination and improve the efficiency. TiO2 electrode was formed with the deposition of TiO2 mesoporous film on fluorine doped tin oxide glass (FTO) after calcination at 450 °C. The PbS QDs, PbxCd1-xS QDs, CdS QDs and coating with ZnS were formed on TiO2 electrode with SILAR method. Solar cells were prepared by sandwiching the TiO2 mesoporous photoanode with Cu2S counter electrode. Six SILAR cycles of PbS, CdS, ZnS and PbxCd1-xS as well as multilayer of PbS/CdS/ZnS and PbS/PbxCd1-xS/CdS/ZnS were prepared for characterizations. In multilayer of PbS/PbxCd1-xS/CdS/ZnS, the effects of number of SILAR cycles of PbxCd1-xS were studied with four different molar fraction, x of 0.05, 0.1, 0.15 and 0.2. From current-density voltage (J-V) measurement, four SILAR cycles of PbxCd1-xS interlayer with molar fraction, x of 0.05 in multilayer PbS/PbxCd1-xS/CdS/ZnS samples showed 38.2 % improvement in the efficiency when compared to the multilayer PbS/CdS/ZnS sample. This was because the band gap value obtained for four SILAR cycles of PbxCd1-xS interlayer with molar fraction, x of 0.05 were between band gap value of PbS core and CdS shell layer during UV-Vis spectrometer analysis. Moreover, the traps states were reduced between the PbS core and CdS shell layers with the deposition of PbxCd1-xS interlayer in multilayer of PbS/PbxCd1-xS/CdS/ZnS sample. Among the multilayer PbS/PbxCd1-xS/CdS/ZnS samples, four SILAR cycles of PbxCd1-xS interlayer with molar fraction, x of 0.05 provided the highest efficiency of 0.34 % when compared with four SILAR cycles of PbxCd1-xS interlayer with molar fraction, x of 0.1, 0.15 and 0.2. This is due to the conduction band of four SILAR cycles of PbxCd1-xS interlayer with molar fraction, x of 0.05 was higher and lead to faster electron injection from the conduction band of PbS/PbxCd1-xS to the TiO2 electrode. Thus, lower recombination was obtained and the efficiency was improved. Besides that, four SILAR cycles PbxCd1-xS interlayer showed higher efficiency than six SILAR cycles of PbxCd1-xS interlayer in samples with multilayer PbS/PbxCd1-xS/CdS/ZnS. This was owing to the high loading of PbxCd1-xS QDs with six SILAR cycles of PbxCd1-xS interlayer would prevent the penetration of electrolyte and decreased the efficiency in J-V measurement