A comparison of modified Howland circuits as current generators with current mirror type circuits

Bertemes-Filho, Pedro; Brown, Brian; Wilson, Adrian

doi:10.1088/0967-3334/21/1/301

Cited by 96 publications

(52 citation statements)

References 13 publications

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“…The output impedance of the implemented current sources has been measured with the impedance analyzer LCR HP4192A in Gain/Phase measurement mode, applying the technique used by Bertemes-Filho in (P. Bertemes-Filho et al 2000). The obtained measurement results have been compared with the calculated values resulting from the output impedance analysis.…”

Section: Output Impedance Measurementsmentioning

confidence: 99%

Electrical Bioimpedance Cerebral Monitoring

Martinez¹,

Lindecrantz²

Encyclopedia of Healthcare Information Systems

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-i - A B S T R A C TNeurologically related injuries cause a similar number of deaths as cancer, and brain damage is the second commonest cause of death in the world and probably the leading cause of permanent disability. The devastating effects of most cases of brain damage could be avoided if it were detected and medical treatment initiated in time. The passive electrical properties of biological tissue have been investigated for almost a century and electrical bioimpedance studies in neurology have been performed for more than 50 years. Even considering the extensive efforts dedicated to investigating potential applications of electrical bioimpedance for brain monitoring, especially in the last 20 years, and the specifically acute need for such non-invasive and efficient diagnosis support tools, Electrical Bioimpedance technology has not made the expected breakthrough into clinical application yet. In order to reach this stage in the age of evidence-based medicine, the first essential step is to demonstrate the biophysical basis of the method under study. The present research work confirms that the cell swelling accompanying the hypoxic/ischemic injury mechanism modifies the electrical properties of brain tissue, and shows that by measuring the complex electrical bioimpedance it is possible to detect the changes resulting from brain damage. For the development of a successful monitoring method, after the vital biophysical validation it is critical to have available the proper electrical bioimpedance technology and to implement an efficient protocol of use. Electronic instrumentation is needed for broadband spectroscopy measurements of complex electrical bioimpedance; the selection of the electrode setup is crucial to obtain clinically relevant measurements, and the proper biosignal analysis and processing is the core of the diagnosis support system. This work has focused on all these aspects since they are fundamental for providing the solid medico-technological background necessary to enable the clinical usage of Electrical Bioimpedance for cerebral monitoring.Keywords: Electrical Bioimpedance Spectroscopy, Hypoxia, Ischemia, Stroke, Brain Monitoring, Impedance Measurements, Biomedical Instrumentation, Non-invasive Monitoring.-iiPreface -iii - P R E F A C EThis research work has been performed mainly in collaboration between the following research and academic institutions: the School of Engineering at University College of Borås, the Department of Signals and Systems at Chalmers University of Technology, the Sahlgrenska University Hospital, and the Sahlgrenska Academy at Göteborg University.Specific activities of this research work have been carried out in collaboration with the Department of Electronic Engineering at the Polytechnic University of Catalonia, Spain.This research work has been mainly funded by the Swedish Research Council (Vetenskapsrådet) through a research grant (No. 2002-5487). The research activity performed has also been part of the following European Network of Excellence: "Comp...

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Section: Output Impedance Measurementsmentioning

confidence: 99%

Electrical Bioimpedance Cerebral Monitoring

Martinez¹,

Lindecrantz²

Encyclopedia of Healthcare Information Systems

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“…It can be concluded that small Z out has a phase near zero or −180 degrees, as the resistors are combined to give a higher Z out and then the phase tends to −90 degrees, as shown in Equation (16) by assuming that the Equation (17) is satisfied.…”

Section: Model 2: Finite Open-loop Gainmentioning

confidence: 99%

“…In most publications, the analysis of the circuit is based on either simplified ideal opamp circuits or using simulation tools, e.g. PSpice or Multisim from NI [12,16]. In many cases, however, the formulas they used are not suitable because the calculation errors are too large with a high-frequency current source [16].…”

Section: Introductionmentioning

confidence: 99%

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High Accurate Howland Current Source: Output Constraints Analysis

Bertemes-Filho¹,

Felipe²,

Vincence³

2013

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Howland circuits have been widely used as powerful source for exciting tissue over a wide frequency range. When a Howland source is designed, the components are chosen so that the designed source has the desired characteristics. However, the operational amplifier limitations and resistor tolerances cause undesired behaviors. This work proposes to take into account the influence of the random distribution of the resistors in the modified Howland circuit over the frequency range of 10 Hz to 10 MHz. Both output current and impedance of the circuit are deduced either considering or the operational amplifiers parameters. The probability density function due to small changes in the resistors of the circuit was calculated by using the analytical modeling. Results showed that both output current and impedance are very sensitive to the resistors variations. In order to get higher output impedances, high operational amplifier gains are required. The operational amplifier open-loop gain increases as increasing the sensitivity of the output impedance. The analysis done in this work can be used as a powerful co-adjuvant tool when projecting this type of circuit in Spice simulators. This might improve the implementations of practical current sources used in electrical bioimpedance.

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“…As current source, the well-known modified Howland circuit was employed [17]. This is a typical circuit to apply in bio-impedance measurements, such as impedance spectroscopy, and multi-frequency electrical impedance tomography [18].…”

Section: A Sinusoidal Oscillatormentioning

confidence: 99%

Contactless Impedance Cardiography Using Embedded Sensors

Pinheiro¹,

Postolache²,

Girão³

2013

Measurement Science Review

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Impedance cardiography is a technique developed with the intent of monitoring cardiac output. By inspecting a few properties of the obtained signal (impedance cardiogram (ICG), the left ventricular ejection time can be derived with certainty, and an estimate of cardiac output is available. This signal is nowadays used in non-invasive monitoring, requiring the placement of electrodes over the subject's skin, either ECG-type or in the form of encircling bands. The work here reported describes the implementation steps and the results obtained when embedding the ICG circuitry in a wheelchair's backrest. The subject is seated normally, is normally dressed, and is completely unaware that monitoring is taking place. That means that the variation of tenths of ohm produced due to the cardiac cycle has to be detected with electrodes having substantial coupling impedance. Contactless ICG with embedded sensors was developed and tested on fourteen healthy subjects. The signal was always acquired, although respiratory activity is also important, constituting a noteworthy innovation in the area.

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A comparison of modified Howland circuits as current generators with current mirror type circuits

Cited by 96 publications

References 13 publications

Electrical Bioimpedance Cerebral Monitoring

Electrical Bioimpedance Cerebral Monitoring

High Accurate Howland Current Source: Output Constraints Analysis

Contactless Impedance Cardiography Using Embedded Sensors

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