Method for protecting a resonating sensor

A method for protecting an implantable, passive ultrasonically excitable resonating sensor from deposition of extraneous materials thereupon, the method comprising:

• providing a sensor having a passive ultrasonically excitable resonating sensor unit, said sensor unit including a substrate and a vibratable member, and a recess disposed between said vibratable member and said substrate to define a first chamber, said first chamber being a sensor unit chamber, said vibratable member having a resonance frequency that varies as a function of a physical variable in a measurement environment in which said sensor is disposed in response to an interrogating ultrasound beam;
• and
• forming a second chamber having walls to protect said vibratable member from the deposition of extraneous material thereupon, said second chamber defined between said vibratable member and a compliant member and filled with a substantially non-compressible medium, said compliant member having a first side and a second side and forming at least part of the walls of said second chamber, said vibratable member forming at least part of the walls of said second chamber;
• wherein said substantially non-compressible medium is in contact with said compliant member and said vibratable member;
• wherein said first side of said compliant member is in contact with a measurement environment to form a first interface when said sensor is disposed in said measurement environment and said second side of said compliant member is in contact with said substantially non-compressible medium to form a second interface;
• and wherein said compliant member comprises a structure that limits reflection of said interrogating ultrasound beam at said first interface and said second interface, said structure selected from the group consisting of a material, a thickness, and a material and thickness.