Power transmission monitoring devices

In Fig. 6.32, monitoring devices are shown on the RF input and output of the device. These monitors protect the tube should a failure occur in the RF output circuit. Two directional couplers and a photodetector are attached to the output. These components and an RF switching device on the input form a protective network against output transmission line mismatch. The RF switch is activated by the photodetector or the reflected power monitor and must be capable of removing RF drive power from the klystron in less than 10 ms (typically). 

In vivo analytical devices ideally should be capable of monitoring several different physiological parameters simultaneously without interfering with an ongoing medical procedure, such as surgery. The devices should be biocompatible, simple to implement and operate, and highly reliable and safe. Fiber-optic chemical sensors can meet most of these requirements since the optical fibers are small (few hundred micrometers in diameter), flexible, nontoxic, and chemically inert. Optical fibers have already proven to be valuable for in vivo clinical applications such as endoscopic procedures and laser power transmission for surgical applications. 

Increasingly, biopotentials have to be measured within implanted devices and need to be transmitted to an external monitor or controller. Such applications include cardiac pacemakers transmitting the intracardiac ECG and functional electrical stimulation where, for example, action potentials measured at one eyelid serve to stimulate the other lid to restore the physiological function of a damaged lid at least to some degree. In these applications, the power consumption of the implanted biopotential amplifier hmits the life span of the implanted device. The usual solution to this problem is an inductive transmission of power into the implanted device that serves to recharge an implanted battery. In applications where the size of the implant is of concern, it is desirable to eliminate the need for the battery and the related circuitry by using a quasi-passive biopotential amplifier, that is, an amplifier that does not need a power supply. 

---