Electret based energy scavenging devices utilize electro-static induction to convert mechanical energy into electrical energy. Uses for these devices include harvesting ambient energy in the environment and acting as sensors for a range of applications. These types of devices have been used in MEMS applications for over a decade. However, recently there is an interest in triboelectric generators/harvesters, i.e., electret based harvesters that utilize triboelectrification as well as electrostatic induction. The literature is filled with a variety of designs for the latter devices, constructed from materials ranging from paper and thin films; rendering the generators lightweight, flexible and inexpensive. However, most of the design of these devices is ad-hoc and not based on exploiting the underlying physics that govern their behavior; the few models that exist neglect the coupled electromechanical behavior of the devices. Motivated by the lack of a comprehensive dynamic model of these devices this manuscript presents a generalized framework based on a Lagrangian formulation to derive electromechanical equation for a lumped parameter dynamic model of an electret-based harvester. The framework is robust, capturing the effects of traditional MEMS devices as well as triboelectric generators. Exploiting numerical simulations the predictions are used to examine the behavior of electret based devices for a variety of loading conditions simulating real-world applications such as power scavengers under simple harmonic forcing and in pedestrian walking.

This paper presents Kinematics and Dynamics of a Shape-Shifting Surface, a robotic system able to take on the shape of arbitrary connected 3D surfaces. Such a surface, which we introduced and described in previous work, consists of piecewise controllable chains in turn composed of serially connected foldable “robotic particles”. Aiming at a high resolution rendering, where tiny particles need to be combined in a large number, a tendon-driven design is a lightweight and scalable solution. However, improper actuation strategies might expose the system to undesired forces, which can compromise its integrity and stability. To tackle this problem, optimal actuation and planning strategies are required to anticipate unacceptable situations. To this end, a dynamic model is derived to predict the reaction of the system subject to control actions. Being the system both tendon-driven and under-actuated, we have to overcome a number of challenges in deriving this model.

We present an MRI-compatible vibration energy harvester for powering implantable medical devices with heartbeat induced vibrations. The state of the art heartbeat-powered energy harvesters are magnetically bi-stable, rendering this devices MRI incompatible. A type of nonlinear harvester exhibiting purely elastic multi-stability based on bi-stable composite laminates is herein proposed for this purpose. The purely elastic nature of the exhibited bi-stability is crucial for powering medical devices as magnetic based multi-stable harvesters are not suitable for implantation. The energy harvester structure based on cantilevered bi-stable laminates used in this paper is inherently nonlinear and is thus MRI compatible. Harmonic frequency sweeps and previously measured signals simulating vibrations produced around the chest area of the human heart are used as vibration inputs to the harvesting device for experimental tests. The results show the capability of harvesting sufficient energy for powering conventional pacemakers with the exact vibration inputs expected during in vivo operation.

This paper presents design and testing of a haptic keypad system using an array of haptic actuators. The research goals are to construct a prototype haptic keypad system using haptic actuators and to evaluate the performance of the prototype keypad for haptic rendering. To this end, an MR haptic actuator was designed and fabricated such that it can convey realistic force feedback to users. To demonstrate haptic applications of the MR actuator, a haptic keypad system was constructed, which consists of following components: (1) 3 × 3 array of haptic actuators, (2) 3 × 3 array of force sensing resistors (FSR), (3) a controller including a micro-processor, a current amplifier and a wireless communication module, (4) a graphic display unit with PC. After constructing a prototype keypad system, a haptic rendering technology was employed to interface the hardware keypad system with test software (virtual environment). The prototype system enabled human operators to interact with the target contents in a virtual environment more intuitively. The evaluation results show a feasibility of applications of MR fluids-based haptic actuators in real-world mobile applications.