A surface acoustic wave filter has, on a piezoelectric substrate, surface acoustic wave resonators each composed of an interdigital transducer and reflectors disposed on both sides of the interdigital transducer. In one embodiment, a method for manufacturing a wellscreen for use in a wellbore is provided. GPS coordinates can also be pre-loaded into mobile devices awarded to particular geocachers. Since the heated fluid is not allowed to enter the refrigerant absorption cycle as its drive heating source, no additional hardware and control for dumping excess heat is necessary within the refrigerant absorption cycle.