Android : What is a good speaker module that can operate in the inaudible range and is it possible for mobile phone to detect inaudible frequencies?

I would like to generate an inaudible sound using Arduino. Currently, I am using PKM34EW piezo speaker. It can generate 19kHz - 22kHz. However, my android phone can only detect this frequency if I place the phone very near to the piezo speaker.

As such, I would like to know whether is there any inaudible speaker module that I can integrate with Arduino?

Secondly, I would like to know whether would your mobile phone be able to pick up sound frequencies higher than 22kHz, and how to achieve that?

Thank you in advance.