A02YYUW Ultrasonic Sensor – Transducer Face Material and Additional Protective Membrane

I am using the A02YYUW waterproof ultrasonic distance sensor (SEN0311) in a Smart Zamzam Tank monitoring project. The sensor will be installed in the tank lid to measure the water level without directly contacting the water.

I would appreciate your help with the following questions:

1-What material is used to cover the two ultrasonic transducer faces on the A02YYUW sensor?

2-If I need to add an additional protective layer between the sensor and the tank's internal air space to provide an extra barrier against moisture and contamination, what material would you recommend?

3-Can the sensor operate reliably through a thin plastic membrane, such as polypropylene (PP) or polyethylene (PE), without significantly affecting its measurement accuracy or echo detection?

4-If an additional membrane is possible, what material and thickness would you recommend for operation at approximately 40 kHz?

5-Does adding such a membrane affect the sensor's measurement range, accuracy, or waterproof rating?

The purpose of this design is to keep the sensor electronics protected while measuring the water level without introducing any components into the water. Hygiene is particularly important for this application.

Thank you for your time and technical support. I look forward to your recommendations.