Abstract: An apparatus for detecting resonant frequency of bones has an electro-mechanical transducer arranged for application to the external skin surface covering a bone, the transducer being in a feed-back circuit with an amplifier and phase shifter having a unity gain and a loop phase of zero. The feed-back circuit is connected to a display comprising an A-D converter and a digital display. The apparatus displays the lowest order transverse mode set up in a bone.In a further embodiment the transducer is arranged to pierce the skin and to be in direct contact with a bone. The transducer has a coupling rod and a detector which may be both positioned at the same station on a bone or at spaced stations along a bone.

Abstract: A six-port reflectometer has first and second directional couplers, a first waveguide and a third directional coupler providing a series connection from a source to a test device. The first coupler is connected to two detectors. The second coupler is connected to a third detector and to a fourth waveguide having two ports connected via a waveguide and a further port connected to an absorber. The third coupler is connected to a detector and a reflector. The second waveguide and the reflector receive radiation coupled by the second and third couplers respectively. The third and fourth couplers provide equivalent transmission paths. Equal path lengths are traversed by signals leaving the second coupler and returning to it from the reflector and the fourth coupler respectively. With broad-band couplers and waveguides, this arrangement gives broad-band performance.