Dual-frequency piezoelectric micromachined ultrasound transducer based on polarization switching in ferroelectric thin films

Due to its additional frequency response,dual-frequency ultrasound has advantages over conventional ultrasound,which operates at a specific frequency band.Moreover,a tunable frequency from a single transducer enables sonographers to achieve ultrasound images with a large detection area and high resolution.This facilitates the availability of more advanced techniques that simultaneously require low-and high-frequency ultrasounds,such as harmonic imaging and image-guided therapy.In this study,we present a novel method for dual-frequency ultrasound generation from a ferroelectric piezoelectric micromachined ultrasound transducer(PMUT).Uniformly designed transducer arrays can be used for both deep low-resolution imaging and shallow high-resolution imaging.To switch the ultrasound frequency,the only requirement is to tune a DC bias to control the polarization state of the ferroelectric film.Flextensional vibration of the PMUT membrane strongly depends on the polarization state,producing low-and high-frequency ultrasounds from a single excitation frequency.This strategy for dual-frequency ultrasounds meets the requirement for either multielectrode configurations or heterodesigned elements,which are integrated into an array.Consequently,this technique significantly reduces the design complexity of transducer arrays and their associated driving circuits.

Cloning of heat shock protein genes from the brown planthopper, Nilaparvata lugens, and the small brown planthopper, Laodelphax striatellus, and their expression in relation to thermal stress

Three heat shock protein （HSP） genes （hsp70, hsc70, hsp90） were partially cloned from the brown planthopper Nilaparvata lugens and the small brown planthopper Laodelphax striatellus （Homoptera： Delphacidae）, which are serious pests of the rice plant. Sequence comparisons at the deduced amino acid level showed that the three HSPs of planthoppers were most homologous to corresponding HSPs of dipteran and lepidopteran species. Identities of both heat shock cognate 70 and HSP90 were higher than HSP70 in both species. Identity of the HSP70 between the two planthopper species was only 81%, a value much lower than seen among fly and moth groups. Effects of heat and cold shocks were demonstrated on expression of the three hsp genes in the two planthopper species. Heat shock （40 ℃） upregulated the hsp90 level but did not change the hsc70 level in either the nymph and adult stages of either species. On the other hand, the hsp70 level was only upregulated in L. striatellus. This heat shock response was prompt and lasted only for 1 h after treatment. In contrast, cold shock at 4℃ did not change the expression levels of any hsp in either species.