Unipolar recording

Figure 6.10 Moving current dipole ( ) with fixed position unipolar recording electrode.

All the bipolar recordings show higher discriminative power than the unipolar recordings. The bipolar waveforms therefore have higher frequency components. 

Currem field characteristics measured wiih conjugated polymers sandwiched between an indium-tin oxide (ITO) anode and an aluminum cathode are usually hole dominated and are, consequently, appropriate for testing injection/lransport models for the case of unipolar current How. Data shown in Figure 12-1 refer to injection-limited currents recorded on typically 100 nm thick spin-coated films of derivatives of poly(y d/"fi-phenylenevinylene) (PPV) and a planarized poly(/ /" -pheny-leue) employing a Keilhley source measure unit. The polymers were ... 

Very high a values have been recorded for m- and p-NMe3+, about 1.0 and 0.9 respectively. However, as already remarked, the significance of the substituent constants of unipolar groups is a matter of debate234. 

In addition to epilepsy, reduced GABA has been recorded in patients with unipolar depression, following alcohol withdrawal and in hepatic encephalopathy. The finding that the concentration of GABA is reduced in depression is unexpected as there is no evidence that the disorder is associated with an increased cortical excitability. One possibility is that the reduction in GABA is a reflection of a decreased availability in its excitatory amino acid precursor glutamate. 

The conventional limb leads record potentials between two apices of the triangle. Lead 1 records potentials between the right arm and left arm, lead 2 records potentials between the right arm and left leg and lead 3 records potentials between the left arm and left leg. These are known as bipolar leads. In addition there are three unipolar leads attached to the limbs, which record potentials between the limb and a reference zero. 

Sodi Pallares D, Rodriguez H. Morphology of the unipolar leads recorded at the septal surface its application to diagnosis of left bundle branch block complicated by myocardial infarction. Am Heart J 1952 43 27. 

The developed specimens (f) and (g) are n-type in nature, whereas specimen (h) is p-type. The prototype solar cells developed and discussed here are (i) p-n type heterojunction (ii) unipolar with redox pair of electrodes. I-V characteristics of the developed biopolymeric solar cell are shown in Figure 12.47. Figures 12.47a, 12.47b, and 12.47c show the I-V characteristics of the developed solar cells, namely HJl, HJ2, and HJ3 respectively. In all cases, the recorded current density was found to be high along with the scope for further modification. The short circuited current and open circuit voltages of all the cells are given in their respective figure captions. It appears that all the developed cells are competitive. 

For DC measurement, it is important that the two electrodes are reference electrodes. If the electrodes are made of different metals or surfaces, then a large exogenic DC voltage (possibly > 1 V) may be generated. Often the best choice is two silver chloride reference electrodes. They can be coupled to the skin or tissue via electrode gel, as shown in Figure 7.1, or via a salt bridge to reduce the DC offset from liquid junction potentials. An invasive electrode as a neutral electrode is the most stable DC reference with a unipolar skin potential recording system. 

Figure 6.11 Unipolar potentials from a current dipole moving along the horizontal x-axis. Dipole length is L c) the unit of the x-axis is L c- The recording electrode is at distance SL c and lOLcc (a) horizontal dipole orientation, biphasic waveforms, and high spatial resolution (b) vertical dipole orientation, monophasic waveforms, and largest signal amplitude of...

However, as long as we are inside the symmetrical zone of reciprocal current density, the contribution from the left and right side volumes with respect to the PU electrode position are equal but with opposite signs. The volume of the symmetrical zone is dependent on the reciprocal current path (e.g., whether it is a bipolar or unipolar PU electrode system). The paradox is that the symmetrical very high sensitivity region has zero net sensitivity all contributions cancel. In conclusion, such an electrode configuration will be very sensitive to asymmetry in the tissue near the PU electrode, and the recording may easily be unstable and noisy. Increased PU electrode contact area will reduce the problem, but this implies current disturbance of the J field. 

An electrode pair and their two wires are called a bipolar lead. A unipolar/monopolar lead is with one PU and an indifferent electrode or a wire from Wilson s terminal. A lead may be defined physically as two signal wires with an associated recording electrode system. 

EEG is recorded with three types of electrodes scalp, cortical, and depth. The electrical activity of 10 brain cells can be recorded on the skin of the scalp with a standardized electrode network of 21 electrodes. The leads may be bipolar or unipolar. The signal amplitude is only of the order of 50 pV, and the frequency content 1—50 Hz, so DC... 

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