Nominal Band Research Articles

An Implanted Telemetry Unit for Ambulatory Animals

An implanted physiological-signal telemetry unit for an ambulatory animal is described. It uses a single 1.35 V mercury cell, is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 \times 2.5 \times 4</tex> cm in size, and weighs 15 g. Transcutaneous RF turn-on and magnetic turn-off are used to conserve battery power. The battery can operate 175 h before replacement. An integrated circuit amplifier supplies a voltage gain of 250 over a nominal band from 0.2 Hz to over 4 kHz. With 2 mV peak input, it yields 75 kHz peak deviation of a 20 MHz carrier. Relations between frequency, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> , receiving antenna voltage, and implant coil diameter are derived. Circuits are also given for a "turn-on" device, a 20 MHz converter, and the sequential gating of three mutually perpendicular antennas to avoid dropouts as the animal moves within the cage.

Random Sound Field in Reverberation Chambers

A series of experiments were performed to compare the efficiency of different diffusing devices in producing a completely random sound field in a reverberation chamber and the effectiveness of some of the methods for judging whether a sound field is completely random. An additional experiment was performed to compare two types of test signals, viz., warble tone and the same nominal band width of random noise. Results of these measurements indicate the general superiority of the rotating vane over other diffusing devices and superiority of random noise over warble tone in producing a smooth decay curve. One of the significant conclusions is that even when the diffusion is reasonably adequate the measured absorption coefficient of a standard sample appears to vary with the chamber absorption especially at the high frequencies.

A Medium Resolution Replica Grating Spectrophotometer

Using the simplest optical parts a monochromator with a nominal band width of about 15A was constructed, covering the range of 3600 to 9000A. This monochromator, in combination with suitable photocells and a direct reading, linear, negative feedback amplifier, permits the determination of extinctions with an error of about 1.5 percent. The performance of the instrument was checked by measuring the absorption spectra of rare earth ions.