Energy transmission efficiency and working bandwidth are the two major factors limiting the application of current acoustic diodes (ADs). This letter presents a design of high efficiency and broadband acoustic diodes composed of a nonlinear frequency converter and a linear wave filter. The converter consists of two masses connected by a bilinear spring with asymmetric tension and compression stiffness. The wave filter is a linear mass-spring lattice (sonic crystal). Both numerical simulation and experiment show that the energy transmission efficiency of the acoustic diode can be improved by as much as two orders of magnitude, reaching about 61%. Moreover, the primary working band width of the AD is about two times of the cut-off frequency of the sonic crystal filter. The cut-off frequency dependent working band of the AD implies that the developed AD can be scaled up or down from macro-scale to micro- and nano-scale.

Stretchable electronics-based surface electromyography (sEMG) evaluation devices are expected to play a big role in clinical diagnosis. However, the stability and quality of the signals collected by existing stretchable electronics are too poor, especially when muscle movement is involved, making them inappropriate for high standard clinical diagnosis. Here, a physiology-based design method for stretchable electronics and a novel airbag-type stretchable electrode array (ASEA) device for assessment of the complex female pelvic floor muscle (PFM) is proposed. Clinical trials show that the ASEA device is able to provide stable contact interface and multi-channel accurate data acquisition. The stability and quality of the sEMG signal are much better than those obtained by the existing stretchable electronics-based PFM electrode devices. Furthermore, a muscle-unit evaluation method (MUEM) to assess the PFM complex state is proposed, especially its cross-interaction between muscles. Clinical trials show that MUEM can accurately and comprehensively assess PFM state and the correlations between main muscles, which unveils the mechanisms of some special muscle states that are not possible using traditional methods. This proof of concept research holds the promise for the development of new diagnostic strategies for muscle pathological research, and has the potential for clinical application and general implication.

Various acoustic and mechanical wave components have been developed. Most of them focused on the control of energy flow. However, these waves are not only energy flow but also wave signals with a frequency dependence. In this Letter, we propose a mechanical wave switch (MWS) capable of controlling energy flow and output frequency simultaneously. It consists of a difference frequency generation (DFG) unit and a wave filter. The DFG unit consists of two mass blocks and a tension/compression asymmetrical bilinear spring, and the wave filter is a one-dimensional mass-spring lattice. Systematical calculations were carried out to identify the critical condition for the design of MWSs. Both numerical and experimental results demonstrate the capability of the proposed MWS to tune the energy flow and the output frequency of acoustic waves via a small amplitude control wave signal. The scale-independent MWS can be implemented at micro- and nanoscales.

No abstract

No abstract