Selective Bandpass Filter Research Articles

A modified canonic active-RC bandpass filter with reduced sensitivity to amplifier gain-bandwidth product

A new configuration for activating a passive-RC bandpass building block to realize an inverting selective bandpass filter is described. The proposed network has the advantages of being canonic, is always stable, and has reduced sensitivity to the amplifier gain-bandwidth product.

A computerized technique to record new components of the electrocardiogram

The His-Purkinje system (HPS) is a specialized conduction system in the heart that participates in the control of the ventricular contraction. However, the standard electrocagdiogram (ECG)does not provide direct information about this system. His bundle recordings that require cardiac catherization aid in the diagnosis of abnormalities within the HPS; these recordings have limitations that include discomfort, a slight morbidity risk, and limited recorded area within the heart. This report outlines a noninvasive technique that utilizes high-gain, selective bandpass filtering and signal averaging to extract the electrical activity of the major portions of intraventricular conduction time when the intracardiac procedure is compared to the noninvasive technique. Frequency analysis of nine HPS waveforms indicates that an average of 79 percent of the power spectrum is below 50 Hz. Although the technique is presently useful in selected cases, i.e., patients with long P-R segments, ongoing analysts of optimal filter settings and lead axes may provide insights that lead to more universal applications of this technique.

ATMOSPHERIC WATER VAPOR PROFILES DERIVED FROM REMOTE-SENSING RADIOMETER MEASUREMENTS

The feasibility and preliminary testing of a low cost, remote-sensing air-borne, double bolometer technique for inferring atmospheric water vapor is illustrated. To deduce the water vapor profile with commercially available equipment, the radiative transfer equation is solved for the water vapor transmissivity employing an input data remote radiometer-measured upward irradiances obtained at aircraft holding levels. Radiometers sensitive in two separate spectral bands are used. The primary radiometer covers the 4.39 to 20.83µ, broad atmospheric radiation band, and the second, for surface temperature deduction, covers the atmospheric window region, 7.35 to 13.16µ. The transfer solution results are acquired from computer programs developed specifically for this purpose. Results indicate an accuracy for inferred total tropospheric water vapor and mixing ratio profiles close to that of the standard sounding electrical hygrometer. The absolute accuracy of the radiosonde hygrometer, considering surface calibration procedures, and for a single ascent, is not better than ±12 percent. The absolute accuracy is greatest for “dry” soundings where the largest changes in irradiance occur for given changes in moisture. Specifically, tests for a vertical profile averaging 6.00 gm./kg. of water vapor produce an average error of 0.70 gm./kg. in the inferred mixing ratio. The average error in mixing ratio obtained by this technique for profiles averaging 2.3 gm./kg. is 0.05 gm./kg. The implications for use on high-flying aircraft or on rockets with highly sensitive radiometers are obvious. The primary purpose in reporting this research is to suggest a technique and illustrate its use. It is clear that with more sensitive bolometer radiometers with selective band pass filters a considerable increase in accuracy can be achieved.

Functional Circuits Through Acoustic Devices

In essence, the communication specialist in the field with his complex electronic gear and the native who beats a hollow log both perform the same function-communication over a distance. However, there is no gainsaying that the hollow log is undoubtedly the more reliable of the two communication equipments. The implication of this analogy is not as far fetched as it may appear. It has been found that considerable circuit simplification with a consequent increased reliability are attainable through the application to electronic circuits of the mechanical and acoustic properties of certain materials. Miniaturized, rugged, low cost, highly selective band-pass filters ranging from 100 cps to approximately 10 Mc are feasible. Power transformers without core or coil are definite possibilities. Stable delay media provide large delays in small simple packages. Hybrid structures of conventional parts and nonconventional resonators provide techniques for broadbanding and impedance transformation. A new element, it is expected, will soon be generated for use at low frequencies-a passive four-terminal nonreciprocal network.

An Alternative Approach to the Realization of Network Transfer Functions: TheN-Path Filter

A particular time-varying network consisting of several parallel transmission paths, each containing input and output modulators, is described and analyzed. It is shown that, under certain conditions, the network may be characterized by a transfer function. A particular form of this transfer function yields periodic filtering characteristics over a limited frequency band without employing distributed elements. Techniques are also presented for realizing highly selective band-pass filters without the use of magnetic elements. Some practical applications are discussed in detail and experimental verification is presented.

A Magnetostriction Filter

A rod of monel metal supported at its mid-point and fitted with two coils, one on each end, shielded from each other, and supplied with a polarizing magnetic field, resonates sharply at its natural longitudinal frequency to a voltage impressed on one coil, and induces a voltage in the other only while vibrating. It is thus a very selective band-pass filter. The attenuation is more than sixty decibels off resonance and about twenty at resonance. The band is about seventy cycles wide, thirty decibels up from the minimum, when the resonant frequency is 20,000 cycles. The effect of heat treatment and the design of the coils and shields are discussed. Actually two rods in series, coupled by a vacuum tube are used. This gives a curve only seventy cycles wide, as much as sixty decibels up from the minimum. The attentuation is found to be low at frequencies below about 8,000 cycles and there is a rather sharp minimum at 16,000 cycles due to some mode of vibration other than the longitudinal one. These defects, however, may easily be remedied by the use of a high-pass filter of conventional design.