Abstract: A filtering assembly with an air filtering function includes a covering component for at least partially covering a covered body, an opening structure formed on the covering component, and a filtering device removably disposed on the covering component and covering the opening structure. The present invention solves a problem of discomfort of ears or skin and hard breathing caused by wearing a mask in the prior art and allows a user to replace the filtering device according to practical demands. The filtering assembly can be worn by a user directly or used together with a mattress, a bed frame, a child carrier, one of an inlet, an outlet and a built-in filtering element of an air treatment apparatus, a window frame, a door frame, or a head mounted accessory, such as a helmet, a hood, a hat or a cap. Therefore, the present invention has a wide range of applications.

Abstract: An interdigital electrode transducer mounted on an acoustic surface wave propagating medium having an output proportional to an Nth order derivative of the surface acoustic waves propagating in the medium. The Nth order derivative, where N is any real, positive number, is obtained by using a finite difference approximation. The transducer finger pairs are biphase coded and amplitude weighted in order to detect the proper combination of signal differences for the approximation and thereby indicate the desired derivative.