Investigation of a Balanced-Armature Transducer for Vibrational Energy Harvesting

Open Access
Vitt, Nikolas Troy
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 08, 2011
Committee Members:
  • Stephen Thompson, Thesis Advisor
  • energy harvesting
  • Balanced-armature
  • transducer
<p style="text-indent: 1em;">There are countless portable devices that rely on batteries to operate. In some applications, replacing or recharging batteries is not feasible or is very costly. One promising solution for extending the life of low power portable devices that rely on stored energy is vibrational energy harvesting. <p style="text-indent: 1em;">This thesis investigates the potential of using a commercially available hearing aid loudspeaker as a vibrational energy harvesting device. The device under study is the Knowles CI-28409 balanced armature transducer. In addition to being commercially available, the CI-28409 is attractive because it has an overall device volume of just 0.28 cm3. Moreover, the use of balanced armature transducers for energy harvesting has yet to be explored in the literature. <p style="text-indent: 1em;">A primary contribution of this work is the development of an analog circuit model of the CI-28409, which captures the behavior of the device when subjected to vibration inputs. In addition, electrical input impedance measurements and vibration response measurements of the CI-28409 are made. These measurements are used to verify the validity of the model and to establish the baseline performance of the device as an energy harvester. <p style="text-indent: 1em;">The model and measurements show that using the CI-28409 as an energy harvesting device without any modifications is impractical. For an input acceleration of 9.8 m/s2 applied to the housing of the CI-28409, measurements showed that the device is only capable of producing a maximum of roughly 80 nW into an 825&#937; resistor at 1.7 kHz. However, the proposed model predicts that, by modifying the design so that the vibrations are applied to the armature while allowing the rest of the device to move freely, the Knowles CI-28409 may be able to produce as much as 57 &#956;W of power for an input acceleration of 8.8 m/s2 at 250 Hz.