PubMed · 1109149
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V N Zhigalkin, L A Brichkin, Machugin YuM, R B Kushnarev. 1975. Biomedical data-recording and storage system.. https://doi.org/10.1007/bf00561811
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The aim of this study was to investigate the mechanisms by which the radiated radiofrequency (RF) GSM (global system for mobile communication) signal may affect pacemaker (PM) function. We measured the signal at the output of the sensing amplifier of PMs with various configurations of low-pass filters. We used three versions of the same PM model: one with a block capacitor which short circuits high-frequency signals; one with a ceramic feedthrough capacitor, a hermetically sealed mechanism connecting the internal electronics to the external connection block, and one with both. The PMs had been modified to have an electrical shielded connection to the output of the sensing amplifier. For each PM, the output of the sensing amplifier was monitored under exposure to modulated and non-modulated RF signals, and to GSM signals (900 and 1800 MHz). Non-modulated RF signals did not alter the response of the PM sensing amplifier. Modulated RF signals showed that the block capacitor did not succeed in short circuiting the RF signal, which is somehow demodulated by the PM internal non-linear circuit elements. Such a demodulation phenomenon poses a critical problem because digital cellular phones use extremely low-frequency modulation (as low as 2 Hz). which can be mistaken for normal heartbeat.
Investigations of the properties of fast, transient potential changes (e.g. receptor potentials or synaptic potentials) in excitable cells by means of current-clamp recording techniques require the exact adjustment and control of membrane potentials. Usually, the desired membrane potential values are set by current injection via the recording electrode and are controlled manually by regulating the current strength necessary to maintain a constant potential. However, this technique is associated with a number of disadvantages. A single-electrode current- and voltage-clamp amplifier was therefore modified to compensate for slow membrane potential changes without affecting faster voltage responses. Basically, low-pass filters with selectable time constants were incorporated into the voltage-clamp feedback circuit to control the amplifier's response speed. In addition, the amplifier's electronic circuits were altered to enable current pulse injection into the cells. Thus, while recording at preset and controlled membrane potentials, it was possible to monitor the cell's input resistance or current/voltage relationship. This new recording technique has been designated "voltage-clamp-controlled current clamp" (VCcCC) and its performance was tested by intracellular recordings from neocortical and neostriatal neurons in vitro using either conventional microelectrodes or patch-clamp electrodes.
A flat panel distributed mode loudspeaker (DML) has many advantages over traditional cone speakers in terms of its weight, size, and durability. However, its frequency response is uneven and complex, thus bringing its suitability for active noise control (ANC) under question. This paper presents experimental results demonstrating the effective use of panel DML speakers in an ANC application. Both feedback and feedforward control techniques are considered. Effective feedback control with a flat panel speaker could open up a whole range of new noise control applications and has many advantages over feedforward control. The paper develops a new control algorithm to attenuate tonal noise of a known frequency by feedback control. However, due to the uneven response of the speakers, feedback control is found to be only moderately effective even for this narrow-band application. Feedforward control proves to be most capable for the flat panel speaker. Using feedforward control, the sound pressure level can be significantly reduced in close proximity to an error microphone. The paper demonstrates an interesting application of the flat panel in which the panel is placed in the path of sound and effectively used to block sound transmission using feedforward control. This is a new approach to active noise control enabled by the use of flat panels and can be used to prevent sound from entering into an enclosure in the first place rather than the traditional approach of attempting to cancel sound after it enters the enclosure.