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This study aimed to estimate the radiofrequency exposure levels in the vicinity of nursery and primary schools at the northwest part of Crete island in Greece. Moreover, the compliance with the exposure limits, according to Greek legislation, was investigated. A total of 396 in situ frequency-selective and broadband measurements were conducted around 69 schools, classified in urban and suburban environments, in the range of 27–3000 MHz (subdivided in seven frequency bands). The measured value of the electric field strength (V/m) was recorded and, subsequently, the exposure ratio was calculated. Statistical analysis was performed in order to analyze and evaluate the data. In addition, a worst-case scenario was examined by considering the highest measured exposure level around each school. The statistical tests indicated that the mean and median values of the exposure ratio, even in the worst-case scenario, were found well below 1 for all frequency bands. The calculated distributions of the electric field measurements demonstrated that almost 90% of the latter were below 1 V/m, with the majority of values lying in the range of 0.5–1 V/m. The main contributors to the total exposure were the mobile communication frequencies and broadcasting, while the exposure was greater in urban than in suburban environments.

Abstract-The objective of this paper is to give an insight about the development of a fuzzy logic efficiency control system which is incorporated to a standard adjustable speed drive control (i.e. Indirect Vector Control) in order to improve the online efficiency in Permanent Magnet Synchronous Motor (PMSM) drives for both transient and steady state operation. The search criterion in steady state is the minimization of the drive power losses by reducing the stator flux while meeting the speed and load torque demands. The power losses are calculated as the difference between the measured input DC-link power and drive's output power. The power losses are calculated at every sampling step and the change of power losses are calculated over a constant time interval as it is needed by the efficiency control algorithm. Variables in the operating characteristics of the PMSM, such as DC input voltage/current and actuaI speed are inputs to the fuzzy control system, making the control system independent of any specific load. Our system combines two fuzzy logic designed efficiency controUen which are introduced as Fu~(l) and Fu~(2) controUers in order to generate the magnetizing current (d-axis component of the stator current). They are separately activated during the steady and transient state respectively. The Fu~l) controUer is a search controUer (SC) operating in steady state, so to decrease the stator flux for higher efficiency. The Fu~(2) controUer is a SC operating in transient state, so to increase at minimum the magnetizing current, to achieve fast tracking capability, less steady state error and robust to load disturbance during transient state. The torque component of the stator current is generated by the vector controUer in order to achieve higher motor performance. The fuzzy logic controllen (FLCs) prototypes were created and tested using Simulink@ simulations. Simulations are accomplished in SimuHnk@ in order to validate our method (i.e. emciency improvement, less torque ripple with flux changes and the less speed sensitivity to load disturbances). Experimental results will be available upon conclusion of the laboratory testings. Future experimental deployments will include a DSP board which will be directly programmed in assembler language via Simulink@.

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