Is it about silicate glass or also other glases or even polymers, that also can be considered?

The lower he density of the glass (plastics for instance), the lower its transmission loss for sound impinging on it, from outdoors,for instance. For a composite window (two or more panes with airspace between) the reduced TL for each pane can be compensated by increasing the airspace distance ("gap"), space permitting.

Dear Mr. Campanella,

thanks a lot for the information. However, I am more interested in the impedance of a single layer of glass material which will be glued to a transducer element in a device we are currently developing. The idea is to have minimal sound energy losses and maximum protection for the transducer (chemical and mechanical). Therefore, I am more interested in the lowest transmission loss then in creating sound insulation and in the exact impedance values of the materials. Could you please let me know if you know of a reliable database?

With Respect,

Todor Hikov

That's a complex question. But I can relate some classical information. Like radio antennas, in days gone by we thought in terms of a single high frequency "carrier", even in ultrasound. In that case only one frequency was in question, viz 100 kHz. The transferred information was in the form of modulation at some much lower frequency (viz 500 Hz). I do NOT  know the M.O. of the sound transmission you require. If it is as described above, the impedance value you seek is for sound of 100 kHz, and we can proceed from there, attaching the"window" facing material that you reference. Typically that facing material has an impedance chosen midway between ("geometric mean") the material of the transducer (steel, aluminum or ceramic) and air (or water) and it might be a quarter wavelength thick.. On the other hand, if broadband (base-band?) audible audio is the influence to be transmitted, the the impedance is largely determined by the density of the window material, about 3 for glass and aluminum, or 1.3 to 1.5 for most plastic materials. But impedance to sound also depends on modal resonances when the window is large or very thick. So, elucidate a bit on your set-up..... As far as a "database" for materials is concerned, I always start by looking up the material density as found in the handbook of Chemistry and Physics, and/or the Mechanical Engineering Handbook. These days, Googling the internet with appropriate key words offers a jump start for any project...