AC Amplifier Research Articles

Combining Imaging and Electrophysiology to Visualize and Record Spreading Depolarizations in Mice.

Spreading Depolarizations (SDs) are massive events in the brain that often go undetected due to their slow propagation through gray matter. Because SD detection can be elusive, it is optimally confirmed using multiple methods. This protocol describes methods for combining imaging and electrophysiology to detect SDs in a manner that most laboratories can reliably and easily adopt. SDs occur following traumatic brain injuries, stroke, subarachnoid hemorrhages, ischemia, and migraine aura. Historically, SDs have been recorded using DC amplifiers, which can resolve the slow extracellular shift and the depression in high-frequency activity. However, DC amplifiers are nearly impossible to use for chronic in vivo recordings. This protocol employs a common AC amplifier for in vivo electrophysiology recordings to confirm high-frequency depression, along with non-invasive imaging necessary to detect the propagating wave of SD. These methods can be reliably adopted and/or modified for most experimental approaches to confirm the presence or absence of SDs following brain injury.

The use of low-frequency current fluctuations in measuring the mobility of holes in the MEH-PPV polymer

A diagnostic method based on the evaluation of low-frequency current fluctuation spectra is presented. When measuring the current through a p-type MEH-PPV sample, the occurrence of fluctuation is observable which can be measured with an AC amplifier. A model has been proposed that proves that the fluctuations originate from the interaction between the valence band and the band gap traps. The mean value of the amplitudes of these fluctuations increases linearly with decreasing frequency with a slope from which the product of mobility and lifetime of current carriers µpτp= (9 ± 3) × 10−15 cm2V−1 was obtained. The hole lifetime of (0.27 ± 0.01) ns was evaluated from the luminescence relaxation using the time-correlated single photon counting (TCSPC) technique. The mobility value (3 ± 1) × 10−5 cm2 V−1s−1 calculated using the above methods was compared with the mobility 1.8 × 10−5 cm2 V−1s−1 determined by the CELIV method (Charge extraction by linearly increasing voltage) and good agreement was obtained.

Ultralow-Noise Chopper Amplifier for Seafloor E-Field Measurement.

The seafloor E-field signal is extremely weak and difficult to measured, even with a high signal-to-noise ratio. The preamplifier for electrodes is a key technology for ocean-bottom electromagnetic receivers. In this study, a chopper amplifier was proposed and developed to measure the seafloor E-field signal in the nanovolt to millivolt range at significantly low frequencies. It included a modulator, transformer, AC amplifier, high-impedance (hi-Z) module, demodulator, low-pass filter, and chopper clock generator. The injected charge in complementary metal-oxide semiconductor (CMOS) switches that form the modulator is the main source of 1/f noise. Combined with the principles of peak filtering and dead bands, a hi-Z module was designed to effectively reduce low-frequency noise. The chopper amplifier achieved an ultralow voltage noise of 0.6 nV/rt (Hz) at 1 Hz and 1.2 nV/rt (Hz) at 0.001 Hz. The corner frequency was less than 100 mHz, and there were few 1/f noises in the effective observation frequency band used for detecting electric fields. Each component is described with relevant tradeoffs that realize low noise in the low-frequency range. The amplifier was compact, measuring Ø 68 mm × H 12 mm, and had a low power consumption of approximately 23 mW (two channels). The fixed gain was 1500 with an input voltage range of 2.7 mVPP. The chopper amplifiers demonstrated stable performance in offshore geophysical prospecting applications.

Low-Power Capacitively Coupled AC Amplifiers With Tunable Ultra Low-Frequency Operation

Low-Power Capacitively Coupled AC Amplifiers With Tunable Ultra Low-Frequency Operation

Bulk-driven CMOS linear transconductance-cell for AC amplifiers with very low cut-off frequency

This manuscript proposes a novel linearized transconductor for AC amplifiers with a very low cut-off frequency. The cell uses an alternative solution that is based on a modified source-degeneration OTA, using two bulk-driven buffers, incorporating bootstrapping techniques to a buffer and a degenerated resistor. In the buffer, the bootstrapping effect is implemented by using a pseudo-resistor and a linear capacitor properly configured, whereas in the resistor the output voltages of the buffers are used with this goal. Thus, the proposed solution allows realizing a very large time constant, avoiding the use of very large size resistors and capacitors, thus saving chip area. The technique is demonstrated in an 0.18μm CMOS technology by designing an OTA operating with a supply voltage of 0.6 V and achieving a low cut-off frequency of around 2Hz with a power consumption of 462 nW.

Very‐low frequency capacitively coupled AC amplifier with a current feedback operational amplifier

SummaryIn this paper, we propose the idea of using transimpedance amplifiers, in lieu of operational amplifiers (OAs) or transconductance amplifiers (OTAs) to design capacitively coupled AC amplifiers. The idea is demonstrated with a current feedback operational amplifier (CFOA) as an active element, which is actually an architecture consisting of voltage buffers and current copiers (mirrors). This last characteristic is further exploited to make the corner frequency of the AC amplifier tunable by means of bootstrapping low‐valued resistors with the output buffer. It is particularly suited to achieve very‐low corner frequencies as needed in applications such as bio‐ or seismic signals. The idea is demonstrated with simulations and experimental results with a discrete implementation.

Two types of clinical ictal direct current shifts in invasive EEG of intractable focal epilepsy identified by waveform cluster analysis

ObjectiveTo determine clinically ictal direct current (DC) shifts that can be identified by a time constant (TC) of 2 s and to delineate different types of DC shifts by different attenuation patterns between TC of 10 s and 2 s. MethodsTwenty-one patients who underwent subdural electrode implantation for epilepsy surgery were investigated. For habitual seizures, we compared (1) the peak amplitude and (2) peak latency of the earliest ictal DC shifts between TC of 10 s and 2 s. Cluster and logistic regression analyses were performed based on the attenuation rate of amplitude and peak latency with TC 10 s. ResultsIctal DC shifts in 120 seizures were analyzed; 89.1% of which were appropriately depicted even by a TC of 2 s. Cluster and logistic regression analyses revealed two types of ictal DC shift. Namely, a rapid development pattern was defined as the ictal DC shifts with a shorter peak latency and they also showed smaller attenuation rate of amplitude (73/120 seizures). Slow development pattern was defined as the ictal DC shifts with crosscurrent of a rapid development pattern, i.e., a longer peak latency and larger attenuation rate of amplitude (47/120 seizures). Focal cortical dysplasia (FCD) 1A tended to show a rapid development pattern (22/29 seizures) and FCD2A tended to show a slow development pattern (13 /18 seizures), indicating there might be some correlations between two types of ictal DC shift and certain pathologies. ConclusionsIctal DC shifts, especially rapid development pattern, can be recorded and identified by the AC amplifiers of TC of 2 s which is widely used in many institutes compared to that of TC of 10 s. Two types of ictal DC shifts were identified with possibility of corresponding pathology. SignificanceIctal DC shifts can be distinguished by their attenuation patterns.

Study of the Influence of the Different Parameters of the Atmospheric DBD Treatment on the Surface Roughness and the Electric Potential Distribution Generated After the Tribocharging of Polypropylene

Square plates of polypropylene (PP), dimensions 100 mm × 100 mm × 4.5 mm, were treated by atmospheric dielectric barrier discharge (DBD) generated between two disk-type electrodes (Ø 75 mm), energized from an ac amplifier 30 kV, 20 mA. The study aimed at evaluating the factors that affect the roughness and the triboelectric behavior of the plasma-treated samples. The alteration of surface aspect after each treatment was clearly visible with the naked eye and the changes were confirmed by measurements carried out with a portable roughness meter (Surftest SJ-210) and a digital microscope (Keyence VHX-7000). The roughness of the PP samples increased from an initial arithmetic mean Ra = 0.06 μm (±0.01 μm) and standard deviation Rq = 0.08 μm (±0.01 μm) to Ra = 0.22 μm (±0.03 μm) and Rq = 0.25 μm (±0.03 μm), respectively. These increases were highly dependent on the air gap distance (10.5-13.5 mm), the treatment time (5-20 min), and the configuration of the DBD cell, i.e., the number (one or two) and the thickness (4-5 mm) of the glass dielectric barriers. Untreated and DBD-treated samples were tribocharged in a linear tribometer, to evaluate the effect of the cold plasma treatment on the electric potential generated on the polymer surface by the triboelectric effect. The electric potential measured by a noncontact electrostatic voltmeter (Trek, 341B) was higher and better distributed over the surface of the plasma-treated samples.

AC amplifiers with ultra‐low corner frequency by using bootstrapping

A novel architecture for an AC (i.e. high-pass) amplifier is proposed allowing a drastic reduction of the cutoff frequency to the sub-Hertz range. It builds upon the classic AC configuration with a high gain amplifier and a parallel RC circuit in the feedback loop, by increasing the feedback resistance through bootstrapping. Resistance multiplying factors higher than four orders of magnitude are easily achievable. The basic principle can be applied to several practical implementations, though in this letter it is demonstrate with measurement results of an op-amp based discrete implementation.

Double-channel resistance-to-voltage converter for cable teraohmmeters

The paper considers a teraohmmeter resistance converter to monitor cable insulation with an additional input amplifier that emits a low-frequency interference signal. Adaptive algorithms for a double-channel converter circuit to compensate for low-frequency interference are proposed. There are considered algorithms using minimax criteria and linear approximation method for estimation of interference influence. It is shown classification of algorithms according to industrial frequency interference filtering method and signal observation interval. There were investigated two ways of interference application: step signal from a DC voltage source up to 300 V and fading harmonic signal from an AC voltage source and amplifier up to 300 V. A doublechannel circuit of the resistance-to-voltage converter is found to provide a 2-fold increase in the signal-tonoise ratio in comparison with a single-channel circuit. It is shown that the maximum deviation of readings for the single-channel circuit exceeds 20 % (up to 32 %) in short-term exposure to interference with amplitude of up to 300 V. At the same time, the maximum deviation for the double-channel circuit can attain 17 %, but it does not exceed 20 %. According to GOST 3345–76, the insulation resistance measuring error in therange of 10 GΩ to 100 TΩ should not exceed 20 %.The advantage of the proposed double-channel converter is the possibility to develop new algorithms to eliminate the dependence of readings on interference effects.

Vortex Express Method for Parameter Determination Thermoelectric Materials

The method is based on the possibility of determining the heat loss of electric power during the flow of Foucault eddy currents in the volume of a thermoelectric sample, placing in the field of action of the ferrite core an inductor through which electric currents that are symmetrical and asymmetric in nature flow sequentially in time.
 Mathematical expressions are obtained for the coefficients of electrical conductivity σ, thermal conductivity ϰ, thermo-emf α and thermoelectric figure of merit Z. Minimization of the error of the proposed method, carried out by computer simulation of the physical processes occurring in the sample using appropriate programs, showed that the operating frequency of the device measuring sensors should be located in the range of 36 ÷ 250 kHz, and the electric current flowing through it — taking into account the inequality qф/П/ qф/ qϰ > 10. The magnetic field induction ratio in terms of components is selected from the condition В0/В > 8.6, which corresponds to the conditions of minimal impact on the parameters of the sample by galvanic thermomagnetic phenomena.
 The block diagram of a device for non-contact measurement of symmetric σс and asymmetric σа components of the electrical conductivity of thermoelectric materials consists of: 1 — SV switch block; 2 — electronic switch; 3 — auto generator; 4 — AC amplifier; 5 — synchronous detector; 6 — DC amplifier; 7 — pulse generator; 8 — signal processing unit; 9 — indicator device; 10 — DC indicator; 11 — correction unit; FR1, FR2.
 Measurement of the parameters of the thermoelectric sample based on Bi-Te-Se-Sb crystals showed that the real error of the proposed method is 2 %. This indicates that the eddy current method can be successfully used to determine the main parameters of thermoelectric materials.
 The use of this method allows solving the relevant problem of avtomazation of the process of monitoring and sorting out thermoelectric ingots, billets and parts.

A Fully Differential Synchronous Demodulator for AC Signals

We describe a new analog differential synchronous demodulator for AC signals where (i) the signal is synchronously demodulated using the floating-capacitor technique after being amplified, if necessary, by an AC amplifier with differential input and differential output, thus yielding a very high CMRR; and (ii) the differential-to-single-ended signal conversion is performed after demodulation, that is, on a low-frequency signal that can be amplified by low-cost, high-performance circuits. The possible signal-to-noise ratio degradation because of synchronous sampling is prevented by using bandpass differential filters.

Temperature Dependence of the Heart Rates in the Blue Swimming Crab Portunus segnis (Forskal, 1775)

Portunus segnis (Forskal, 1775) has been referred to as Portunus pelagicus for very long time until Portunus species complex have been recognized based on their molecular distinction (Lai in Raffles Bull Zool 58(2):199–237, 2010). P. segnis are native species in the Arabian Gulf. Inter-moult stage adults were caught during February–November 2016 along the Northern coastal areas of Bahrain to investigate responses of cardiac activity to changes in water temperature normally encountered in their natural environment. Similar body sized individuals of both males and non-ovigerous females were maintained initially at $$20\,^{\circ }\hbox {C}$$ in a re-circulating artificial seawater for 2 days prior to recordings of their heartbeats. Recordings were continued over 24–48 h for 39 crabs. Power lab-Ad-Instrument coupled with Impedance Technique adjoined by AC amplifier, Bio-Amp and LabChart-6 were used. The heart rates of P. segnis acutely followed rising or falling temperatures and a stable heart rate at a particular temperature indicated an acclimatization. Temperature coefficient values ( $${Q}_{10})$$ were between 0.1 and 8.6. At a temperature range of (20–30 $$\,^{\circ }\hbox {C}$$ ), $${Q}_{10}$$ between 0.4 and 4 were significantly higher ( $${p}< 0.05$$ ) compared to $${Q}_{10 }$$ of 2–3 calculated at the lower temperature range (10–20 $$\,^{\circ }\hbox {C}$$ ). The higher values were obtained during either very fast or very low rates at 5–10 $$\,^{\circ }\hbox {C}$$ and at $$\ge $$ 30–40 $$\,^{\circ }\hbox {C}$$ , respectively. The upper lethal limits were $$40\,^{\circ }\hbox {C}$$ and $$5\,^{\circ }\hbox {C}$$ as the survival becomes limited at these two ‘extreme’ temperatures. Overall, at stable rates, $${Q}_{10}$$ was between $$2.98\pm 2$$ and $$2.26\pm 1$$ for heart rates at thermal intervals of (20–30 $$\,^{\circ }\hbox {C}$$ ) and (10–20 $$\,^{\circ }\hbox {C}$$ ), respectively. Below $$5\,^{\circ }\hbox {C}$$ , the heart rate slows down progressively and the crabs become motionless and eventually die. The survival of these species was critical above $$40\,^{\circ }\hbox {C}$$ . Warm-adapted species such as P. segnis may be threatened by changes in temperatures as they may already be living at the upper limit of their thermal tolerance during the summer months. Understanding the thermal tolerance of P. segnis would help optimizing conditions for this valuable commercial species in aquaculture.

DESIGN IMPROVEMENT AND OPERATION MODELING OF EAF GAS EXHAUST SYSTEM OF A FOUNDRY SHOP

As a result of a survey of gas exhaust systems of low-tonnage electric arc furnaces (from 3 to 10 tons) operated in the foundries of machine-building enterprises, the bottlenecks were identified, due to which a large amount of gas-dust emissions gets into the production rooms and pollutes the air in the working areas. First of all, it occurs due to the design schemes imperfection of the evacuation systems of gas and dust ejected from the furnace cavity through the outlet channel, the working window, gaps between its body and the roof, between edges of the holes in its upper part and the electrodes lowered through them. In particular, joint units of the rotary collection hoods with the gas exhaust pipelines in these systems do not provide proper sealing of movable joints. In this regard, the authors have proposed an improved design of rotation mechanism of the furnace collection hood, which involves the use of two sand gates. These gates eliminate the possibility of harmful emissions release between movably connected elements of the system into the environment. To begin designing of the industrial sample of a modernized mechanism, a method for calculating the energy-power parameters of its drive has been developed. A preliminary validation of the correctness of the taken technical decisions and of the obtained calculating dependencies was performed on the operating model of the investigated system manufactured on a 1:10 scale relative to the industrial sample. For the model research an instrumentation complex that included strain gauge transducer, AC amplifier, analogto-digital converter and computer was used. During this research the load acting on the model drive of the collection hood rotation mechanism when it was transferred from the working position to the parking one and back was fixed. At the same time, the load was measured for two cases: in the absence and in the presence of sand in the gates which ensure sealing of the movably joint elements of the investigated mechanical system. It was established that the portion of resistance forces arising in two sand gates during relative rotation of the moving element is 20 – 26 % of total load on the mechanism drive depending on angular velocity of the cantilever with collection hood. Similarly, this indicator calculated from obtained theoretical dependences was in the range of 17 – 23 % for the rotation mechanisms of collection hood of arc furnaces with a tonnage of 3 to 10 tons. Video filming of the smoke movement patterns, which flows from the furnace model through the existing gaps between its body and roof during the steelmaking process imitating, confirmed the reliability of the sand gates that provide complete sealing at the joint units of the moving parts of the collection hood rotation mechanism. Practical use of the proposed technical solution allows increasing of efficiency of evacuation of the harmful gas and dust emissions from the working zone of smelting furnaces used in the foundry.

Controlled deposition of electrospun nanofibers by electrohydrodynamic deflection

Electrospinning is a technique often used for the production of nanofibers composed of various polymers and ceramics. For enhanced material performance, it is desirable to obtain nanofibrous structures with a pre-determined microscopic fiber orientation and macroscopic geometry. However, it is challenging to control or predict the final deposition structure of an electrospun nanofiber due to the inherent instabilities induced along the polymer jet during the electrospinning process. Historically, mitigating these instabilities has been attempted electrically, magnetically, and mechanically with limited levels of success. Here, a new technique to electrically control the trajectory of an electrospun jet by electrohydrodynamic deflection is introduced. This protocol is achieved using a set of linearly actuated intermediary electrodes and a rapidly oscillating electric potential, driven by home-built AC amplifiers and a switching algorithm to control the amplitude, frequency, duty cycle, and the relative phase of the external electric field. Predetermined nanofibrous geometries are printed along predetermined paths using a 10% polyethylene oxide polymer solution.

Improving the Gas-Exhaust System at Foundry Electrofurnaces

Abstract—Inspection of the gas-exhaust system at arc furnaces of capacity 3–10 t in the casting shops of manufacturing enterprises reveals problems responsible for copious gas and dust emissions in the production buildings, with degradation of the air quality. This is mainly associated with structural shortcomings of the systems for gas and dust evacuation from the furnace chamber through the exhaust channel, working window, and gaps between the housing and roof and also between the edges of the holes in the upper section and the electrodes within the holes. In particular, the moving joints between the rotary hoods and the gas-exhaust lines in such systems do not ensure reliable sealing. Accordingly, an improved design of the hood-rotation mechanisms has been proposed, with two sand barriers preventing the atmospheric emission of harmful emissions between the moving components. In the design of an industrial prototype, a method is developed for calculating the energy parameters of the drive in the improved system. A 1 : 10 scale model of the system is built to check the design and the theoretical equations. By means of a measuring system consisting of a tensoresistive converter, an ac amplifier, an analog–digital converter, and a computer, the load on the model’s drive on switching from the working position to the rest position and back is determined, for two cases: with and without sand barriers to seal the mobile components. The drag in the two sand barriers on rotation of the moving element amounts to 20–26% of the total load on the drive, depending on the angular velocity of the cantilever with the hood. According to the theoretical formulas, this figure is 17–23% for hood-rotation mechanisms in arc furnaces of capacity 3–10 t. Video recordings of the smoke fluxes from the model through the gaps between its housing and the roof during simulations of steel production confirm the reliability of the sand barriers, which ensure complete sealing of joints in the hood-rotation mechanism. Practical use of the proposed design improves gas–dust evacuation from the working zone of smelting furnaces used in the foundry.

A Self-Powered and Autonomous Fringing Field Capacitive Sensor Integrated into a Micro Sprinkler Spinner to Measure Soil Water Content.

We present here the design and fabrication of a self-powered and autonomous fringing field capacitive sensor to measure soil water content. The sensor is manufactured using a conventional printed circuit board and includes a porous ceramic. To read the sensor, we use a circuit that includes a 10 kHz triangle wave generator, an AC amplifier, a precision rectifier and a microcontroller. In terms of performance, the sensor’s capacitance (measured in a laboratory prototype) increases up to 5% when the volumetric water content of the porous ceramic changed from 3% to 36%, resulting in a sensitivity of pF per unity change. Repeatability tests for capacitance measurement showed that the sensor’s root mean square error is 0.13%. The average current consumption of the system (sensor and signal conditioning circuit) is less than 1.5 A, which demonstrates its suitability for being powered by energy harvesting systems. We developed a complete irrigation control system that integrates the sensor, an energy harvesting module composed of a microgenerator installed on the top of a micro sprinkler spinner, and a DC/DC converter circuit that charges a 1 F supercapacitor. The energy harvesting module operates only when the micro sprinkler spinner is irrigating the soil, and the supercapacitor is fully charged to 5 V in about 3 h during the first irrigation. After the first irrigation, with the supercap fully charged, the system can operate powered only by the supercapacitor for approximately 23 days, without any energy being harvested.

Cortical spreading depression occurs during elective neurosurgical procedures.

OBJECTIVE Cortical spreading depression (CSD) has been observed with relatively high frequency in the period following human brain injury, including traumatic brain injury and ischemic/hemorrhagic stroke. These events are characterized by loss of ionic gradients through massive cellular depolarization, neuronal dysfunction (depression of electrocorticographic [ECoG] activity) and slow spread (2-5 mm/min) across the cortical surface. Previous data obtained in animals have suggested that even in the absence of underlying injury, neurosurgical manipulation can induce CSD and could potentially be a modifiable factor in neurosurgical injury. The authors report their initial experience with direct intraoperative ECoG monitoring for CSD. METHODS The authors prospectively enrolled patients undergoing elective craniotomy for supratentorial lesions in cases in which the surgical procedure was expected to last > 2 hours. These patients were monitored for CSD from the time of dural opening through the time of dural closure, using a standard 1 × 6 platinum electrode coupled with an AC or full-spectrum DC amplifier. The data were processed using standard techniques to evaluate for slow potential changes coupled with suppression of high-frequency ECoG propagating across the electrodes. Data were compared with CSD validated in previous intensive care unit (ICU) studies, to evaluate recording conditions most likely to permit CSD detection, and identify likely events during the course of neurosurgical procedures using standard criteria. RESULTS Eleven patients underwent ECoG monitoring during elective neurosurgical procedures. During the periods of monitoring, 2 definite CSDs were observed to occur in 1 patient and 8 suspicious events were detected in 4 patients. In other patients, either no events were observed or artifact limited interpretation of the data. The DC-coupled amplifier system represented an improvement in stability of data compared with AC-coupled systems. Compared with more widely used postoperative ICU monitoring, there were additional challenges with artifact from saturation during bipolar cautery as well as additional noise peaks detected. CONCLUSIONS CSD can occur during elective neurosurgical procedures even in brain regions distant from the immediate operative site. ECoG monitoring with a DC-coupled full-spectrum amplifier seemed to provide the most stable signal despite significant challenges to the operating room environment. CSD may be responsible for some cases of secondary surgical injury. Though further studies on outcome related to the occurrence of these events is needed, efforts to decrease the occurrence of CSD by modification of anesthetic regimen may represent a novel target for study to increase the safety of neurosurgical procedures.

High frequency oscillations and infraslow activity in epilepsy

In pre-surgical evaluation of epilepsy, there has been an increased interest in the study of electroencephalogram (EEG) activity outside the 1-70 Hz band of conventional frequency activity (CFA). Research over the last couple of decades has shown that EEG activity in the 70-600 Hz range, termed high frequency oscillations (HFOs), can be recorded intracranially from all brain regions both interictally and at seizure onset. In patients with epilepsy, HFOs are now considered as pathologic regardless of their frequency band although it may be difficult to distinguish them from the physiologic HFOs, which occur in a similar frequency range. Interictal HFOs are likely to be confined mostly to the seizure onset zone, thus providing a new measure for localizing it. More importantly, several studies have linked HFOs to underlying epileptogenicity, suggesting that HFOs can serve as potential biomarkers for the illness. Along with HFOs, analysis of ictal baseline shifts (IBS; or direct current shifts) and infraslow activity (ISA) (ISA: <0.1 Hz) has also attracted attention. Studies have shown that: IBSs can be recorded using the routine AC amplifiers with long time constants; IBSs occur at the time of conventional EEG onset, but in a restricted spatial distribution compared with conventional frequencies; and inclusion of IBS contacts in the resection can be associated with favorable seizure outcome. Only a handful of studies have evaluated all the EEG frequencies together in the same patient group. The latter studies suggest that the seizure onset is best localized by the ictal HFOs, the IBSs tend to provide a broader localization and the conventional frequencies could be non-localizing. However, small number of patients included in these studies precludes definitive conclusions regarding post-operative seizure outcome based on selective or combined resection of HFO, IBS and CFA contacts. Large, preferably prospective, studies are needed to further evaluate the implications of different EEG frequencies in epilepsy.

An amplifier of the signal from a converter of the temperature oscillations of the surface of an object

The operating principle and circuit of a low-frequency ac amplifier with a program-controlled transfer constant and a comparatively short regulation time are considered.