Wildlife Biotelemetry

The electronics and circuitry used in telemetry systems for wildlife studies have probably reached a mature state, with modifications mostly being the results of new technologies rather than bringing new fundamental ideas to the design. Thus, the improvement of telemetry systems will likely depend on improvements in sensors, in packaging, and in overall system reliability. Sensor development has been the focus of continuing effort since telemetry began and will continue to present interesting challenges as only a few measurements can be made with reasonable ease today. Packaging and system reliability, problems for nearly all systems, have become the subjects of more intensive investigations recenty, particularly as some of the laboratory systems have become production products. Packaging in general has progressed a long way from the early designs and is discussed elsewhere in this issue. Perhaps the most important advance for implanted circuits using hybrid fabrication is the development of good moisture barrier encapsulation materials with temperature coefficients of expansion and curing dimension changes that are compatible with direct encapsulation of bare chips and wire bonds. These provide satisfactory protection from body fluids for several months while at the same time being non-toxic, non-irritant, and essentially inert within the body even after penetration by fluids. For implants with desired lifetimes approaching a year or more, hermetic packages are still recommended. The added size and weight of hermetically sealed packages is often undesirable, but at present there are no alternatives. A few examples of recent physiological telemetry are interesting.