H. SANDLER, T. B. FRYER AND H. L. STONE 
1203 
FLOW. ^ 
ml/sec ®° 
FLOW. 
ml /sec -J 
FLOW, 
ml /sec 
FLOW, 
ml/sec 
PRESSURE, 
mm Hg -j 
Figure 5. — A typical recording of flow from backpack electromagnetic flow telemetry system. 
concerning location. Studies are being con- 
ducted to determine the feasibility of operating 
these units as passive transmitters (energy is 
received from an external source), rather than 
using an implanted pov^er source. This source 
may be a backpack w^orn by the animal. Work is 
already in progress, as mentioned above, to re- 
place conventional poM^er sources v^^ith more re- 
liable and long-term sources of pow^er such as 
radioactive materials. Tests need to be con- 
ducted and evaluated in using small retransmit- 
ters or transponders which receive the signals 
