Energy Harvesting from Mechanical Vibrations
Human power-based energy harvesting strategies for mobile electronic devices a. Describe the application (10%)
1.2.3 Wearable or implantable medical devices
Implantable or wearable medical devices refer to any device that could help monitor metabolic parameters, assist defective physical function or cure diseases. Structural devices such as artificial joints, vascular grafts and artificial valves are called passive devices and their working does not need external power. But active devices can consume energy with different orders of magnitude from microwatts to several watts, as shown in Table 2.
b. Identify how the mechanical vibration is induced (20 %)
2.3.1 Characterization of vibration system for motion harvesting Displacement driven generators are typically inertial mechanism-based, second-order vibration systems excited by periodical human body movement of the legs, limbs or feet. Ideally, these systems can be described as spring-mass systems , as shown in Fig. 5. The frame is attached to the moving body. A proof mass (m) is suspended inside. A spring (with stiffness of k) and a damper (with damping coefficient of c) couple the relative movement (Z1) between these two parts. Z1 induces electricity by the transduction mechanism of the damper. Assuming that the mass of the vibration source is significantly larger than that of the seismic mass and therefore not affected by its presence, and that the external excitation is harmonic, then the differential equation of motion is described as
(5)
The standard steady-state solution for the mass displacement is given by
(6)
where f is the angle phase given by
: (7)
Maximum energy can be extracted when the excitation frequency matches the natural resonant frequency of the generator system ωn, given by
: (8)
The vibration structure for which resonant frequencies range from 10 kHz to 1 MHz is good at converting the high frequency energy of machine vibration with
1.2.3 Wearable or implantable medical devices
Implantable or wearable medical devices refer to any device that could help monitor metabolic parameters, assist defective physical function or cure diseases. Structural devices such as artificial joints, vascular grafts and artificial valves are called passive devices and their working does not need external power. But active devices can consume energy with different orders of magnitude from microwatts to several watts, as shown in Table 2.
b. Identify how the mechanical vibration is induced (20 %)
2.3.1 Characterization of vibration system for motion harvesting Displacement driven generators are typically inertial mechanism-based, second-order vibration systems excited by periodical human body movement of the legs, limbs or feet. Ideally, these systems can be described as spring-mass systems , as shown in Fig. 5. The frame is attached to the moving body. A proof mass (m) is suspended inside. A spring (with stiffness of k) and a damper (with damping coefficient of c) couple the relative movement (Z1) between these two parts. Z1 induces electricity by the transduction mechanism of the damper. Assuming that the mass of the vibration source is significantly larger than that of the seismic mass and therefore not affected by its presence, and that the external excitation is harmonic, then the differential equation of motion is described as
(5)
The standard steady-state solution for the mass displacement is given by
(6)
where f is the angle phase given by
: (7)
Maximum energy can be extracted when the excitation frequency matches the natural resonant frequency of the generator system ωn, given by
: (8)
The vibration structure for which resonant frequencies range from 10 kHz to 1 MHz is good at converting the high frequency energy of machine vibration with