Abstract: The invention concerns a fabrication process for a selective absorber of a solar collector to achieve a solar-radiation collection-surface with high absorptivity and low emissivity.The collector surface is made of an iron alloy containing chrome and is immersed in an acid bath containing oxygen atoms and at least one metalloid substance based on sulfur, selenium and/or tellurium; beforehand, the state of the collector surface is adjusted for activation.

Abstract: A battery powered external pacer operable in fixed-rate and demand modes includes a sense amplifier having an active notch filter system for attenuating power line interference. The filter system comprises four separate data channels each including a transmission gate synchronously driven by pacer clock pulses for frequency stability. Charges developed on capacitors in each data channel are summed by an output capacitor to avoid the need for amplifiers in each channel. A detector having two comparators for detecting positive and negative directed R-wave components derives heart pulses from the amplified signal. A pulse-driven reference supply having very low power consumption provides operating bias required by the detector. A battery monitor having a single comparator simultaneously monitors supply voltage for low and unusable voltage levels.

Abstract: An interference filter for the removal of power line interference from amplifying systems, such as electrocardiographs, which includes a band-rejection filter tuned to reject the power line frequency interference, a differential amplifier to which the signal being amplified and the output of the notch filter are applied to produce an output consisting of only the interference signal. The interference signal is fed to and stored in a memory which is constantly updated and the output of the memory is then summed with the original signal. Since the phase of the output of the memory is reversed from the interference in the original signal, only the original signal will result. An electronic switch is connected between the output of the differential amplifier and the memory and is operated by a velocity detector connected with the output of the band-rejection filter.

Abstract: Apparatus for discriminating between heartbeat and artifact information contained in an ECG signal includes a pair of difference amplifiers, level-detecting circuitry and a coincidence detector. ECG waveforms are obtained from a number of heartbeat-sensing transducers attached to a person. The waveforms are individually applied to a pair of difference amplifiers to produce difference signals containing heartbeat information. The difference signals are applied to level-detecting circuits and compared to predetermined voltage levels to identify particular peaks indicative of a heartbeat. The result of the level-detecting circuits are compared for time coincidence to produce an output pulse indicative of a heartbeat.

Abstract: Apparatus for monitoring the heartbeat of a person by screening the occurrence of a heartbeat from artifact to produce a signal indicative of the heartbeat occurrence. Screening circuitry detects the R-wave and S-wave peaks of an ECG signal, delays the R-wave peak detection and compares the delayed R-wave peak detection to the S-wave peak detection for coincidence to determine a heartbeat occurrence. Binary counting circuits compare the elapsed time between any two immediately successive heartbeat occurrence indications to determine heartbeat rate. Display apparatus, operably coupled to the counting circuits, provides indicia of the relative heartbeat rate.

Abstract: Steady-state evoked potentials from the nervous system, measured on the scalp and elsewhere on the body in response to specific periodic sensory stimuli, contain the fundamental frequency of the stimulus and other waves, and are of the order of 40 dB below potentials due to general electrical activity of the nervous system which may be considered as noise. Medical information revealed by evoked potentials is extremely valuable but is limited by measuring methods of the prior art and by the background noise. In this disclosure the periodic steady-state evoked potential from a periodic stimulus, shifted to a suitable frequency band, is sampled at instants of zero-crossings of the shifted evoked potential, at the Nyquist frequency or greater for the noise frequency band, and the resultant samples of noise are reconstructed in a filter and subtracted from the entire evoked potential, to produce as a resultant the evoked potential substantially free from background noise.

Abstract: In an exemplary embodiment, the interference signals can occur as a mixture consisting of narrow interference pulse peaks of high amplitude and interference hum. It is desirable that such interference peaks and interference hum in a useful signal be suppressed without mutual influencing. To this end, an occurring useful signal having possibly superimposed interference signals is supplied to an interference hum filter. The filtered-out interference hum component is opposingly superimposed on the original signal for the purpose of compensation of the interference hum. This applies only for such a length of time as there are no interference pulse peaks recognized by a recognition installation. If such an interference pulse peak is recognized, the filter is disconnected from the input signal and switched over to self-oscillation operation.

Abstract: An electronic interface module for use with patient monitoring equipment which allows use of the monitoring equipment at the same time that the patient is being treated through the application to his body of electrical stimulating pulses or the like. Body contacting leads used to pick up physiologically generated impulses from the body of the patient are coupled through a suitable amplifier to a sample and hold circuit. The interface module also includes means for generating a control pulse at the onset of a body stimulating impulse which control pulse persists for a predetermined time greater than the period of the stimulating impulse. This control pulse is also applied to the sample and hold circuit. The output from the sample and hold circuit (which may be analog or digital in nature) is, in turn, coupled through suitable matching circuitry to the patient monitoring equipment.

Abstract: Filtering means for biophysical recording apparatus for removing interference from a signal source which includes a band rejection or notch filter and means for inserting the filter into the signal circuit when the signals have a certain characteristic and for removing the filter when the signals have another characteristic.