Method and apparatus for sensing fluids using surface acoustic waves

A surface acoustic wave resonator, comprising:

• (a) a doubly supported beam in which surface acoustic waves can be propagated, said beam having two lateral sides each with a sufficient air gap to reflect said waves;
• (b) a transducer attached thereto for propagating surface waves laterally across the beam and for reflecting said waves off of said sides;
• and
• (c) means, connected to the transducer, for driving the transducer with a signal having a period equal to an integral multiple of the wavelength of a mode of wave propagation in the beam.

Apparatus for sensing the presence of a specific fluid, comprising:

• (a) a substrate having a thinned membrane portion, said membrane portion having a planar top surface and a planar bottom surface opposite thereto;
• (b) means attached to the top surface of said membrane for vibrating said membrane at mechanical resonance and with a generally drum-head like vibration;
• (c) a sensing member located on the bottom surface of said membrane and having a physical characteristic that varies the mechanical resonance of the membrane when in the presence of a specific fluid;
• and
• (d) means for sensing mechanical resonance of the membrane when vibrated.