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Methods of frequency tuning vibration based micro-generator

Methods of frequency tuning vibration based micro-generator
Methods of frequency tuning vibration based micro-generator
A vibration based micro-generator is an energy harvesting device that couples a certain transduction mechanism to the ambient vibration and converts mechanical energy to electrical energy. In order to maximize available power, micro-generators are typically inertial devices that operate at a single resonant frequency. The maximum output power is generated when the resonant frequency of the generator matches the ambient vibration frequency. The output power drops significantly if these two frequencies do not match due to the high Q-factor of the generator. This thesis addresses possible methods to overcome this limit of vibration based micro-generators, in particular, method of tuning the resonant frequency of the generator to match the ambient vibration frequency.
This thesis highlights mechanical and electrical methods of resonant frequency tuning of a vibration based micro-generator. The mechanical frequency tuning is realized by applying an axial tensile force to strain the cantilever structure of the generator. A tunable micro-generator with a tuning range from 67.6 Hz to 98Hz and a maximum output power of 156.6µW at a constant low vibration acceleration level of 0.59m·s-2 was designed and tested. The tuning mechanism was found not to affect the damping of the generator. A closed loop frequency tuning system as well as the frequency searching algorithms has been developed to realize automatic frequency tuning using the proposed mechanical tuning method. The model of duty cycle of the system was established and it was proved theoretically that a reasonable duty cycle can be achieved if the generator and tuning system is designed properly.
The electrical tuning method is realized by changing the load capacitance of the generator. Models of piezoelectric and electromagnetic generators using electrical tuning methods were derived. The model of the electromagnetic generator has also been experimentally verified. The electrically tunable generator tested has a maximum 3dB bandwidth of 4.2Hz.
In conclusion, resonant frequency tuning using mechanical methods presented in the thesis have larger tuning range than that using electrical methods. However, frequency tuning using electrical tuning methods consumes less power than that using mechanical methods for the same amount of tuning range.
Zhu, Dibin
ec52eae1-39fa-427c-968b-e76089a464a6
Zhu, Dibin
ec52eae1-39fa-427c-968b-e76089a464a6
Beeby, Steve
ba565001-2812-4300-89f1-fe5a437ecb0d
White, Neil
c7be4c26-e419-4e5c-9420-09fc02e2ac9c

Zhu, Dibin (2009) Methods of frequency tuning vibration based micro-generator. University of Southampton, School of Electronics and Computer Science, Doctoral Thesis, 264pp.

Record type: Thesis (Doctoral)

Abstract

A vibration based micro-generator is an energy harvesting device that couples a certain transduction mechanism to the ambient vibration and converts mechanical energy to electrical energy. In order to maximize available power, micro-generators are typically inertial devices that operate at a single resonant frequency. The maximum output power is generated when the resonant frequency of the generator matches the ambient vibration frequency. The output power drops significantly if these two frequencies do not match due to the high Q-factor of the generator. This thesis addresses possible methods to overcome this limit of vibration based micro-generators, in particular, method of tuning the resonant frequency of the generator to match the ambient vibration frequency.
This thesis highlights mechanical and electrical methods of resonant frequency tuning of a vibration based micro-generator. The mechanical frequency tuning is realized by applying an axial tensile force to strain the cantilever structure of the generator. A tunable micro-generator with a tuning range from 67.6 Hz to 98Hz and a maximum output power of 156.6µW at a constant low vibration acceleration level of 0.59m·s-2 was designed and tested. The tuning mechanism was found not to affect the damping of the generator. A closed loop frequency tuning system as well as the frequency searching algorithms has been developed to realize automatic frequency tuning using the proposed mechanical tuning method. The model of duty cycle of the system was established and it was proved theoretically that a reasonable duty cycle can be achieved if the generator and tuning system is designed properly.
The electrical tuning method is realized by changing the load capacitance of the generator. Models of piezoelectric and electromagnetic generators using electrical tuning methods were derived. The model of the electromagnetic generator has also been experimentally verified. The electrically tunable generator tested has a maximum 3dB bandwidth of 4.2Hz.
In conclusion, resonant frequency tuning using mechanical methods presented in the thesis have larger tuning range than that using electrical methods. However, frequency tuning using electrical tuning methods consumes less power than that using mechanical methods for the same amount of tuning range.

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Published date: October 2009
Organisations: University of Southampton

Identifiers

Local EPrints ID: 69323
URI: http://eprints.soton.ac.uk/id/eprint/69323
PURE UUID: 227996dd-087f-4705-94d6-5eb111f6fb85
ORCID for Dibin Zhu: ORCID iD orcid.org/0000-0003-0517-3974
ORCID for Steve Beeby: ORCID iD orcid.org/0000-0002-0800-1759
ORCID for Neil White: ORCID iD orcid.org/0000-0003-1532-6452

Catalogue record

Date deposited: 05 Nov 2009
Last modified: 14 Mar 2024 02:37

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Contributors

Author: Dibin Zhu ORCID iD
Thesis advisor: Steve Beeby ORCID iD
Thesis advisor: Neil White ORCID iD

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