Inspired by the invention of electric diode capable of rectifying current flux, considerable efforts have been made to design and fabricate devices for yielding rectification effects on different forms of energy fluxes. So, thermal rectifiers have been realized both theoretically and experimentally to rectify heat flux. Electromagnetic one-way phenomenon, showing important promise in optical and rf communications, have also been discovered by constructing analogs of quantum Hall edge states in photonic crystals.
In the field of acoustics, a direct analogue still lacks what can transform acoustic signals in a way exactly identical as electric diode rectifying alternating current to direct current. Nevertheless, some one-way devices have been proposed to yield asymmetric transmission for acoustic waves. The first theoretical model of such device consists of a superlattice and a strongly nonlinear medium (NLM). In the existing nonlinear models, however, the transmission efficiency increases monotonically with the nonlinearity and thickness of NLM as well as the amplitude of incident wave. As a result, the resulting device has to be consisted of a strong NLM with large size and be driven by a signal with high amplitude to yield satisfying transmission efficiency. This will undoubtedly render the practical application extremely difficult.
As a result, researchers from the Nanjing University and the Institute of Acoustics, Chinese Academy of Sciences devise an acoustic one-way frequency up-converter with high transmission efficiency. It comprises a nonlinear cavity and two different superlattices for converting acoustic energy into the second harmonic wave with high transmission efficiency in only one particular direction. The resonance in the high-Q cavity significantly enhances the interaction between the acoustic waves and the nonlinear medium. It leads to abnormal dependences of efficiency on the incident wave amplitude and the nonlinearity parameters. And the performance of the proposed structure is verified by numerically solving the nonlinear acoustic partial-differential-equations for a full transient solution.
Numerical results show that the transmission efficiency can be promoted by three orders of magnitude as compared with previous devices of the same size. Moreover, the transmission efficiency can reach its maximum when both the incident wave and the nonlinearity are comparatively weak. As well, the parameter dependence of efficiency and the necessary condition under which the acoustic frequency multiplier works are investigated. It is proved that the proposed design helps to remarkably improve the sensitivity and reduce the size for similar acoustic one-way devices, which may benefit the potential application of the resulting devices.
This research was supported by the National Basic Research Program of China (973 Program) (Grant Nos. 2010CB327803 and 2012CB921504), National Natural Science Foundation of China (Grant Nos. 11174138, 11174139, 11222442, 81127901, and 11274168), NCET-12-0254, and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
The research with the title of "Acoustic One-way Frequency Up-converter with High Transmission Efficiency" has been released online: http://dx.doi.org/10.1063/1.4823858 and published in the journal of J. Appl. Phys. (114, 134508 (2013)).