Sam Behrens

Energy Options for Wireless Sensor Nodes

Reduction in size and power consumption of consumer electronics has opened up many opportunities for low power wireless sensor networks. One of the major challenges is in supporting battery operated devices as the number of nodes in a network grows. The two main alternatives are to utilize higher energy density sources of stored energy, or to generate power at the node from local forms of energy. This paper reviews the state-of-the art technology in the field of both energy storage and energy harvesting for sensor nodes. The options discussed for energy storage include batteries, capacitors, fuel cells, heat engines and betavoltaic systems. The field of energy harvesting is discussed with reference to photovoltaics, temperature gradients, fluid flow, pressure variations and vibration harvesting.

Multiple mode current flowing passive piezoelectric shunt controller

Abstract A method for multiple mode piezoelectric shunt damping will be presented in this paper. The proposed “current flowing” shunt controller has a number of benefits compared to previous shunt damping schemes; it is simpler to implement and requires small number of passive circuit elements. The passive control strategy is validated through experimentation on two piezoelectric laminated structures.

Optimization and implementation of multimode piezoelectric shunt damping systems

Piezoelectric transducer (PZT) patches can be attached to a structure in order to reduce vibration. The PZT patches essentially convert vibrational mechanical energy into electrical energy. The electrical energy can be dissipated via an electrical impedance. Currently, impedance designs require experimental tuning of resistive circuit elements to provide optimal performance. A systematic method is presented for determining the resistance values by minimizing the H/sub 2/ norm of the damped system. After the design process, shunt circuits are normally implemented using discrete resistors, virtual inductors and Riordian gyrators. The difficulty in constructing the shunt circuits and achieving reasonable performance has been an ongoing and unaddressed problem in shunt damping. A new approach to implementing piezoelectric shunt circuits is presented. A synthetic impedance, consisting of a voltage controlled current source and a digital signal processor system, is used to synthesize the terminal impedance of a shunt network. A two-mode shunt circuit is designed and implemented for an experimental simply supported beam. The second and third structural modes of the beam are reduced in magnitude by 22 and 18 dB.

Design and experimental characterization of an electromagnetic transducer for large-scale vibratory energy harvesting applications

This article reports on the design and experimental characterization of an electromagnetic transducer for energy harvesting from large structures (e.g., multistory buildings and bridges), for which the power levels can be above 100 W and disturbance frequencies below 1 Hz. The transducer consists of a back-driven ballscrew coupled to a permanent-magnet synchronous machine with power harvesting regulated via control of a four-quadrant power electronic drive. Design considerations between various subsystems are illustrated and recommendations in terms of minimal values are made for each design metric. Developing control algorithms to take full advantage of the unique features of this type of transducer requires a mechanical model that can adequately characterize the device’s intrinsic nonlinear behavior. A new model is proposed that can effectively capture this behavior. Comparison with experimental results verifies that the model is accurate over a wide range of operating conditions. As such, the model can be used to assess the viability of the technology and to correctly design controllers to maximize power generation. To demonstrate the device’s energy harvesting capability, impedance matching theory is used to optimize the power generated from a base-excited tuned mass damper. Both theoretical and experimental investigations are compared and the results are shown to match closely.

Passive vibration control via electromagnetic shunt damping

This work will present a new type of passive vibration control technique based on the concept of electromagnetic shunt damping. The proposed technique is similar to piezoelectric shunt damping, as an appropriately designed impedance is shunted across the terminals of the transducer. Theoretical and experimental results are presented for a simple electromagnetic mass spring damper system.

Reducing the inductance requirements of piezoelectric shunt damping systems

Structural vibration can be reduced by shunting an attached piezoelectric transducer (PZT) with an electrical impedance. Current shunt circuit designs, e.g. a single-mode inductor–resistor network, typically require large inductance values of up to thousands of henries. In practice, discrete inductors are limited in size to around 1 H. By placing an additional capacitance across the terminals of the PZT, shunt circuit inductances can be drastically reduced. To justify our claims, we present a theoretical analysis of the damped system and identify the influence of the additional capacitance. Two modes of a simply supported beam are successfully damped using a capacitance modified shunt circuit. A low inductance multi-mode circuit is also studied and experimentally verified.

On the feedback structure of wideband piezoelectric shunt damping systems

This paper studies the feedback structure associated with piezoelectric shunt damping systems and introduces a new impedance structure for multi-mode piezoelectric shunt damping. The impedance is shown to be realizable using passive circuit components and digital implementation of the associated admittance transfer function is discussed.

Current flowing multiple-mode piezoelectric shunt dampener

This paper introduces a new type of passive piezoelectric shunt controller which is capable of damping multiple modes of a flexible structure using one piezoelectric transducer. The current flowing shunt technique has a number of advantages over comparable techniques; it is simpler to implement and requires less discrete circuit elements. The passive control strategy is validated through experimental work on a piezoelectric laminated simply supported beam.

Adaptive electromagnetic shunt damping

This paper presents a new type of passive vibration control: adaptive electromagnetic shunt damping. We propose a single-mode resonant shunt controller that adapts to environmental conditions using two different adaptation strategies. The first technique is based on minimizing the root mean square (RMS) vibration, while the second minimizes the phase difference between two measurable signals. An experimental comparison shows that relative phase adaptation performs better than the RMS technique.

Design of electromagnetic energy harvesters for large-scale structural vibration applications

This paper reports on the design and experimental validation of transducers for energy harvesting from largescale civil structures, for which the power levels can be above 100W, and disturbance frequencies below 1Hz. The transducer consists of a back-driven ballscrew, coupled to a permanent-magnet synchronous machine, and power harvesting is regulated via control of a four-quadrant power electronic drive. Design tradeoffs between the various subsystems (including the controller, electronics, machine, mechanical conversion, and structural system) are illustrated, and an approach to device optimization is presented. Additionally, it is shown that nonlinear dissipative behavior of the electromechanical system must be properly characterized in order to assess the viability of the technology, and also to correctly design the matched impedance to maximize harvested power. An analytical expression for the average power generated across a resistive load is presented, which takes the nonlinear dissipative behavior of the device into account. From this expression the optimal resistance is determined to maximize power for an example in which the transducer is coupled to base excited tuned mass damper (TMD). Finally, the results from the analytical model are compared to an experimental system that uses hybrid testing to simulated the dynamics of the TMD.