Abstract-This paper presents a survey on the MAC and network layer of Wireless Sensor Networks. Performance requirements of the MAC layer are explored. MAC layer protocols for battery-powered networks and energy harvestingbased networks are discussed and compared. A detailed discussion on design constraints and classification of routing protocols is presented. Several routing protocols are compared in terms of such parameters as: energy consumption, scalability, network lifetime and mobility. Problems that require future research are presented. The cross-layer approach for WSNs is also surveyed.

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A novel technique is presented to maintain closed-loop performance of a smart piezo structure at an elevated temperature. Square cantilevered plate instrumented with a piezoelectric sensor and a piezoelectric actuator is taken as a test structure. Finite element model of the smart plate is developed using Hamilton's principle. Finite element model is reduced to first three modes using modal truncation and subsequently a model in state space is derived. First three modal displacements and velocities are observed by a Kalman observer. Negative first modal velocity feedback is employed to control structural vibrations. Performance of the smart structure in open loop as well as in closed-loop changes appreciably at elevated temperature because piezoelectric strain coefficient as well as permittivity increases with increase in temperature. This change in performance is successfully suppressed by application of suitable DC bias on piezoelectric patches. DC bias applied on sensor is blocked from entering signal conditioner by a DC blocker circuit. DC blocker circuit is simulated in LTspice Ò software to verify its performance.