Many advanced physical properties can be realized by using well-designed acoustic metamaterial (AM) structures, which have significant application value in engineering. In particular, thin-walled membrane, plate, and shell-type structures with deep subwavelength thicknesses that can meet light weight requirements have attracted the attention of many researchers and engineers from various specialized fields. This Tutorial systematically introduced the structural design methods, acoustic/elastic wave attenuation and regulation principles, and engineering applications of thin-walled AMs for low-frequency sound insulation, sound absorption, and vibration reduction. In particular, the design methods and sound insulation/absorption properties of thin-walled AMs for realizing narrow-band and broadband sound attenuation were explored. Furthermore, the local resonance bandgap characteristics, quantitative extraction method for the bending wave bandgap, vibration suppression properties, and the design method for local resonance vibration dampers for elastic wave regulation by thin-walled elastic metamaterials were summarized successively. Moreover, other thin-walled AM applications, such as the wavefront steering performance of thin-walled acoustic/elastic metasurfaces, and the active thin-walled AMs, were introduced as well.

The effective operation of certain electronic, medical, industrial, and testing equipment relies on high-quality focusing and imaging capability, which also plays a vital role in the field of wave physics. Therefore, continuously improving the resolution capacity is essential. However, in a homogeneous medium dominated by the diffraction limit, the best resolution for wave focusing and imaging could only reach half the wavelength corresponding to the lowest operating frequency, significantly hindering the relevant application value. The development of phononic crystals (PCs) and acoustic metamaterials (AMMs) has realized sub-wavelength focusing and super-resolution imaging and attracted increasing research attention in physics, mechanics, engineering, and biomedical science. This Tutorial explained the basic principles and traditional methods of acoustic focusing and imaging. Then, the implementation principles and related research progress of sub-wavelength focusing and super-resolution imaging based on artificial acoustic devices, including but not limited to PCs and AMMs, were systematically discussed. Moreover, a method was introduced to realize sub-wavelength or sub-diffraction focusing by integrating these artificial devices into the time-reversal procedure. Finally, the potential development trends and practical application prospects were presented.

No abstract

PurposeRelying on a multilevel approach, this paper investigates the day-to-day variations in family-supportive supervisor behaviors influencing subordinates' job stress, as well as the mediating role of positive emotions and the moderating role of ethical leadership.Design/methodology/approachUsing the experience-sampling methodology, the study collected the data from 137 civil servants in China who responded to one daily survey for 10 working days.FindingsWith a total of 1,370 surveys, results supported the hypothesized model linking daily family-supportive supervisor behaviors to daily job stress via subordinates' daily positive emotions. In addition, the study found a moderating effect for ethical leadership positively in the indirect relationship between family-supportive supervisor behaviors and job stress.Practical implicationsThe findings in this study serve practitioners in organizational and leadership development. On the one hand, this study contributes to raising awareness about the importance of improving family-related support in the workplace, in generating subordinates' positive emotions and relieving their job stress. On other hand, the findings highlight the necessity of cultivating ethical leadership for leaders.Originality/valueThis study fulfills an identified need to clarify how and when daily family supportive supervisor behaviors influence subordinates' daily job stress. This study moves beyond previous research by adopting the experience sampling method and demonstrating important cross-level effects of ethical leadership on the within-individual relationship between family supportive supervisor behaviors and job stress.

PurposeAlthough a plethora of literature has developed person–job fit theory, how leaders' emotions affect followers' person–job fit has received insufficient attention. Drawing on emotions as social information (EASI) theory, the present research study investigated the impact of leaders' positive emotions on person–job fit and further explained the mediating role of psychological safety and the moderating effect of organizational identification.Design/methodology/approachData were collected from 319 Chinese employees nested in 67 teams, and a cross-level design was adopted to examine the research hypotheses.FindingsThe results indicated that individual-level psychological safety played a mediating role in the cross-level relationship between team-directed leaders' positive emotions and individual-level person–job fit. Moreover, the authors found a cross-level moderating effect of team-level organizational identification.Practical implicationsThis present research empirically showed that leaders displaying positive emotions in the workplace benefited followers' perceptions of psychological safety, which in turn improved followers' attitudes towards their job in management practice. In addition, organizational identification could positively advance this process.Originality/valueThis study is the first to evaluate the operational mechanism of leaders' emotion on followers' perceived person–job fit in the Chinese context. Person–job fit has primarily been investigated as a driver of employee outcomes in the previous research studies. These studies focussed on whether and how leaders' emotions improve followers' person–job fit.