Electrical impedance

About: Electrical impedance is a research topic. Over the lifetime, 36015 publications have been published within this topic receiving 371891 citations. The topic is also known as: electrical impedance & complex impedance.

Stimulation control apparatus for an ink jet recorder

Abstract: A drive circuit for a stimulation transducer suppresses generation of satellite drops in an ink jet recorder. The drive circuit is an oscillator which tracks the resonant frequency of the stimulation transducer. As the resonant frequency of the transducer changes during normal operation, the frequency of the driving signal also changes, so that the power output of the transducer remains essentially unchanged. This provides accurate regulation of the filament length for the jets being stimulated and unexpectedly also suppresses generation of satellite drops. The drive circuit comprises an amplifier, a load resistor and positive and negative feedback paths to the input terminals of the amplifier. The load resistor is incorporated within the negative feedback path as well as within the supply path for the stimulation transducer. In general the impedance of the stimulation transducer is minimum at the resonant frequency thereof, so that for any shifting of the resonant frequency there is an increase in the input impedence to the transducer. This produces a voltage variation across the load resister which in turn alters the negative feedback to the amplifier. Means are provided for adjusting the negative feedback signal so as to maintain the amplifier in a state of continuous oscillation. The frequency at which this oscillation occurs is the frequency at which the impedance of the transducer is minimum, and therefore the drive circuit tracks the resonant frequency of the stimulation transducer.

Disk-loaded monopoles with parallel strip elements

Abstract: Design considerations and experimental performance data are presented for disk-loaded folded monopoles in which the vertical elements consist of flat parallel strips separated by a dielectric. The presence of the dielectric and the flat strip geometry permit control of resonance frequency, susceptance slope, and impedance step-up ratio over ranges suitable for the design of electrically small antennas with a broad double-tuned response. Graphs are presented giving the impedance step-up ratio due to folding for various strip dimensions derived from static calculations. Experimental results are shown for antennas with heights in the range of one-eighth to one-tenth wavelength.

Improved system and method for determining tissue contact of an implantable medical device within a body

Abstract: An improved system for monitoring the status of an IMD such as medical electrical lead during an implant procedure is provided. The system includes a signal generator for supplying a first signal such as a constant current or voltage to the IMD. A resulting voltage or current signal is generated, respectively, and may be sensed as an indication of the impedance of a portion of the body that is proximal to one or more electrodes carried by the lead. This impedance indication is converted to an audible signal having a frequency that is proportional to the amplitude of the impedance indication. The pitch of the audible signal therefore rises when measured impedance increases, and drops as the impedance decreases. These pitch changes allow a user to determine positional information associated with the IMD, including the degree of lead tissue contact and extent of fixation of a device to tissue.

Negative-Impedance Converters

Abstract: The conditions under which an active device exhibits an input impedance at one terminal pair which is exactly the negative of the load impedance connected to the other terminal pair are discussed. There are an infinite number of ways by which such a device, which is called a negative-impedance converter (NIC), can be made. One of the limits of this set is represented by a transistor circuit which was discussed previously by Linvill; the other limit, by a new circuit introduced recently. Practical negative-impedance converters are not exact; however, they may be made so by the addition of a pair of compensating impedances. The parameters of the NIC which most affect circuit performance are indicated as a guide to NIC design. Two typical transistor NIC circuits are compared on this basis. Experimental results are given.