1. Low frequency acoustic energy harvester and the interface circuit
Bin Li and Jeong Ho You
Energy Harvesting Materials Lab
Department of Mechanical Engineering
Southern Methodist University

2. Objective: harvesting wasted acoustic energy
(1)Abundant, clean and renewable (2)Intensive in urban life (2)Currently wasted (3)Low energy density
Various sound sources

3. Vibration to electricity
Approach
Develop an acoustic energy harvester:
Low audible operating frequency(about 100~200Hz)
High efficiency
AC/DC conversion
Accumulated
acoustic energy
Vibration to electricity
Quarter wavelength resonator
Piezoelectric cantilevered plate
External circuit

4. Total output voltage and power as a function of incident SPL
Multiple piezo plates placed along the resonator
Total output voltage and power as a function of incident SPL
The number of plates to generate the maximum voltage and power is limited by the interruption of air particle motion.
SPL: 100dB
The summation of power:

5. Interface AC/DC conversion circuit design
Piezo plates
Electric power Pe flowing
into the circuit
Pe=Ieq×Vp
Standard
circuit
Time
Pe=Ieq×Vp
Self-powered
P- SSHI circuit
Time
Self-powered SSHI allow more electric power flowing into the circuit and improve AC/DC conversion efficiency by switching technology.

6. Harvested powers in our acoustic energy harvester
Incident SPL: 112 dB
Conclusions:
Acoustic energy harvesting mechanism is developed at low operating frequency (100~200 Hz) using quarter-wavelength straight-tube resonator with multiple piezoelectric cantilever plates;
The number of plates to generate the maximum voltage and power are limited by the interruption of acoustic air particle motion caused by the presence of plates;
When the incident SPL is 112 dB, the simulated output power of the acoustic energy harvester is mW using self-powered P-SSHI circuit.