Automatic Gain Compensation Research Articles

High-Resolution Imaging of Radiation Brightness Temperature Obtained by Drone-Borne Microwave Radiometer

A digital automatic gain compensation (AGC) drone-borne K-band microwave radiometer with continuous high-speed acquisition and fast storage functions is designed and applied to obtain high-resolution radiation brightness temperature (TB) images. In this paper, the composition of the drone-borne passive microwave observation system is introduced, a data processing method considering the topography and angle correction is proposed, the error analysis of the projection process is carried out, and finally, a high-resolution microwave radiation TB image is obtained by a demonstration area experiment. The characteristics of the radiometer are tested by experiments, and the standard deviation of the TB is 1K. The data processing method proposed is verified using a demonstration case. The corrected data have a good correlation with the theoretical values, of which the R2 is 0.87. A high-resolution radiation TB image is obtained, and the results show the TB characteristics of different objects well. The boundary of the ground object is closer to the real value after correction.

Dual-Frequency Retrodirective Antenna Array With Wide Dynamic Range for Wireless Power Transfer

This letter presents a dual-frequency heterodyne retrodirective antenna (RDA) array with relatively large frequency ratio between receiving and transmitting for adaptive tracking in far-field wireless power transfer systems. The proposed RDA consists of an eight-channel radio frequency mixing, amplify chain and two 1 × 8 circularly polarized arrays with different operation frequency and orthogonal polarizations, receiving at 3.8 GHz with right-hand circular polarization and transmitting at 5.8 GHz with left-hand circular polarization, respectively. For received power levels from −80 to −40 dBm, each chain outputs with consistent phase and stable power about 29 dBm brought by automatic gain control and compensation phase shifter. It can transmit reversely along the direction of beacon signal from near to far distance. High system isolation is achieved through inherent isolation of different frequencies and orthogonal polarizations of the T/R arrays. Monostatic and bistatic measurements are taken, and measured results verify that the proposed RDA is of far-field tracking capability to receive and transmit from −40° to 40°.

Products of Interest

Products of Interest

Effect of Cross-slot Defect in welded joint on Ultrasonic Test

This paper focuses on the influence of vertical hole defects on the ultrasonic propagation characteristics, which are studied from two aspects of the propagation characteristics of the base metal and the ultrasonic waves of the weld, respectively. The acoustic reflection characteristics of the reflector are compared with the acoustic reflection characteristics of the two different welding processes, manual welding and automatic welding, and the properties of the base material. It is shown that the cross-slot of the weld is different from the cross-slot in the base metal, and the attenuation of the ultrasonic wave in the base metal and the weld is different. The gain compensation is too large, and the automatic welding gain compensation ratio of the upper groove of the weld is lower. The automatic welding gain compensation of the cross-slot is large, and the manual welding gain compensation of the lower cross-slot is higher than that of the automatic welding, and the cross-slot gain compensation of the automatic welding upper surface weld is higher than that of the manual welding.

The effects of isometric resistance training on stretch reflex induced tremor in the knee extensor muscles

This study examines the effect of 4 wk of high-intensity isometric resistance training on induced tremor in knee extensor muscles. Fourteen healthy volunteers were assigned to either the training group (n = 7) or the nontraining control group (n = 7). Induced tremor was assessed by measuring force fluctuations during anisometric contractions against spring loading, whose compliance was varied to allow for preferential activation of the short or long latency stretch reflex components. Effects of high-intensity isometric resistance training on induced tremor was assessed under two contraction conditions: relative force matching, where the relative level of activity was equal for both pre- and post-training sessions, set at 30% maximum voluntary contraction (MVC), and absolute force matching, where the level of activity was set to 30% pretrained MVC. The training group experienced a 26.5% increase in MVC in contrast to the 0.8% for the control group. For relative force-matching contractions, induced tremor amplitude and frequency did not change in either the training or control group. During absolute force-matching contractions, induced tremor amplitude was decreased by 37.5% and 31.6% for the short and long components, respectively, with no accompanying change in frequency, for the training group. No change in either measure was observed in the control group for absolute force-matching contractions. The results are consistent with high-intensity isometric resistance training induced neural changes leading to increased strength, coupled with realignment of stretch reflex automatic gain compensation to the new maximal force output. Also, previous reported reductions in anisometric tremor following strength training may partly be due to changed stretch reflex behavior.

Transcutaneous vs. Intraoperative Quantitative Ultrasound for Staging Bovine Hepatic Steatosis

The aim of this study was to test the hypothesis that quantitative analysis of transcutaneous (Transc) ultrasound (US) images can predict the liver fat content with similar accuracy and precision as using intraoperative (Intraop) US. The second goal was to investigate if a tissue mimicking phantom (TMP) might be used as reference for automatic gain compensation (AGC) vs. depth instead of using the data of a set of cows without hepatic alterations. A study was performed in post partum dairy cows (N = 151), as an animal model of human nonalcoholic fatty liver disease (NAFLD), to test these hypotheses. Five Transc and five Intraop US liver images were acquired in each animal and a liver biopsy was taken. In liver tissue samples, triacylglycerol (TAG) content was measured by biochemical analysis and hepatic alterations, other than hepatic steatosis, were excluded by clinical examination. Several preprocessing steps were performed before the ultrasound tissue characteristics (UTC) parameters of B-mode images were derived. Stepwise multiple linear regression analysis was performed on a training set (N = 76) and the results were used on the test group (N = 75) to predict the TAG content in the liver. In all cases, the residual attenuation coefficient (ResAtt) was the only selected parameter. Receiver operating characteristics (ROC) analysis was applied to assess the performance and area under the curve (AUC) of predicting TAG and to compare the sensitivity and specificity of the methods used. High ROC values for AUC (95%), sensitivity (87%) and specificity (83%) for both Intraop and Transc applications with control group as well as with phantom-based AGC were obtained. Consequently, it can be concluded that Transc results are equivalent to Intraop results. Furthermore, equivalent ROC values, when using TMP AGC, indicates the potential use of TMP-based corrections instead of normal group-based corrections. The high predictive values indicate that noninvasive quantitative US has a great potential for staging and screening on hepatic steatosis in cows.

용량형 마이크로 공진기의 주파수 응답 보상 기법

This paper presents frequency response compensation technique, and a self-oscillation circuit for capacitive microresonator with the compensation technique using programmable capacitor array, to compensate for the frequency response distorted by parasitic capacitances, and to obtain stable oscillation condition. The parasitic capacitances between the actuation input port and capacitive output port distort the frequency response of the microresonator. The distorted non-ideal frequency response can be compensated using two programmable capacitor arrays, which are connected between anti-phased actuation input port and capacitive output port. The simulation model includes the whole microresonator system, which consists of mechanical structure, transimpedance amplifier with automatic gain control, actuation driver and compensation circuit. The compensation operation and oscillation output of the system is verified with the simulation results.

Automatic Hardware Reconfiguration for Current Reduction at Low Power in RFIC PAs

This paper presents a novel hardware reconfiguration technique implemented in a dual integrated-circuit (IC) GaAs HBT power amplifier (PA) design and demonstrates reduced current and improved efficiency at low power. The method automatically reconfigures the hardware of an RF IC PA over a given power transmission. Hardware interfacing and synchronization from outside the PA is minimized, and automatic gain compensation upon hardware reconfiguration is achieved with minimal temperature-dependant calibration. The challenge of integrating such complex on-chip hardware functions in a GaAs HBT technology was circumvented by the introduction of a gating concept used in conjunction with envelope feedback, and careful tradeoffs between circuit complexity and performance. Designs that suit the on-chip integration of the technique in GaAs HBT or Si bipolar junction transistor technologies are described. Experimental data are reported to support the proposed method.

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Automatic gain compensation in an ultrasound imaging system

The invention includes a method and system for automatic gain compensation in an ultrasound imaging system. The method and system may be used in place of, or in addition to, gain compensation selected by an operator. Gain compensation may be in response to range, in response to cross-range, or in response to both. Ultrasound imaging data is partitioned into relatively small zones (such as regions selected in response to range and cross-range), and a zone intensity value representative of each zone is used to determine information, such as an average image intensity, about ultrasound signals reflected from objects being imaged in each zone. The zone intensity value can be determined during real-time image acquisition by special-purpose averaging hardware, so that a commercial programmable microprocessor may operate on the zone intensity values to generate a gain compensation curve, also in real-time. Only those zones whose intensity is determined to be from tissue reflection are used to determine gain variations with range. A set of row mean values and a set of attenuation estimates for each row of zones having like range is determined, allowing for lateral gain rolloff at image edges, and from which a global gain to be applied, and a gain curve to be applied, are determined.

Reduced servo-control of fatigued human finger extensor and flexor muscles.

1. In healthy human subjects holding the index finger semi-extended at the metacarpophalangeal joint against a moderate load, electromyographic (EMG) activity was recorded from the finger extensor and flexor muscles during different stages of muscle fatigue. The aim was to study the effect of muscle fatigue on the level of background EMG activity and on the reflex responses to torque pulses causing sudden extensor unloadings. Paired comparisons were made between the averaged EMG and finger deflection responses under two conditions: (1) at a stage of fatigue (following a sustained co-contraction) when great effort was required to maintain the finger position, and (2) under non-fatigue conditions while the subject tried to produce similar background EMG levels to those in the corresponding fatigue trials. 2. Both the unloading reflex in the extensor and the concurrent stretch reflex in the flexor were significantly less pronounced and had a longer latency in the fatigue trials. Consequently, the finger deflections had a larger amplitude and were arrested later in the fatigue trials. 3. It is concluded that--with avoidance of 'automatic gain compensation', i.e. reflex modifications attributable to differences in background EMG levels--the servo-like action of the unloading and stretch reflexes is reduced in fatigued finger extensor and flexor muscles.

Excitability of the soleus H reflex during graded walking in humans

The excitability of the soleus Hoffmann (H) reflex was measured in five healthy male subjects during graded treadmill walking. Uphill and downhill walking at an 8% grade as well as level walking were used to vary the demands for lengthening and shortening contractions of the soleus muscle. These changes were assumed to cause differences in control of the afferent input in the spinal cord and the voluntary output to the soleus muscle. The H reflex was strongly modulated in all three walking conditions, high during the stance phase and low or absent during the swing phase. The shape of the modulations was, however, different. At uphill walking the reflex increased gradually during the whole stance phase and seemed to follow the soleus electromyogram (EMG) pattern closely. In the downhill condition the reflex excitability increased rapidly at heel strike like the soleus EMG and co-contraction of the anterior tibial muscle was observed. At level walking a fast rise in reflex excitability was seen just after heel strike with low or absent soleus EMG. Mean soleus EMG was lower during downhill than during uphill or level walking, but the mean H reflex amplitude was similar in all three conditions. However, when the H reflex was related directly to the EMG activity by linear regression the reflex gain was lower during uphill walking than in the two other conditions. Furthermore, the ratio between H reflex and EMG amplitude was high during the first half of the stance phase at level walking indicating an elevated reflex excitability independent of the voluntary motor output. It is therefore concluded that the modulation of reflexes during walking cannot be interpreted in terms of the idea of automatic gain compensation. The reflexes must be controlled specifically and independently during the different phases of the motor output to meet the mechanical requirements of the movement task. Most explicitly this was seen during downhill walking, where an elevated reflex excitability together with co-contraction at the ankle joint seem to provide increased joint stiffness and security, when the kinetic energy of the body has to be brought under control at heel strike.

Reflectance calibration of aerial video imagery with automatic gain compensation on and off

Abstract Video imaging systems are noi radiometrically calibrated, thus it is difficult to obtain quantitative remotely-sensed imagery for natural resource applications. Video camera automatic gain controls (AGC) present potential problems in calibrating video systems for quantitative analysis because they compensate for changing solar illumination conditions. In this experiment aerial video calibrations to ground reflectance standards were compared for AGC turned on and off, The calibrated aerial video was evaluated for guinea grass (Panicum maximum L.) biomass treatments on two dates. Results showed that there was more atmospheric light scattering in the red than in the NIR video band. Light scattering affects could be detected only when the AGC was ofT because when AGC was on light scattering affects were masked. These results also showed that video imagery produced significant correlations with guinea grass biomass that were comparable to ground reflectance measurements.

The Development of Airborne/ground-based 13mm Imaging Microwave Radiometer Using Two Reference Temperatures with Automatic Gain Compensation

The Development of Airborne/ground-based 13mm Imaging Microwave Radiometer Using Two Reference Temperatures with Automatic Gain Compensation

Mechanical and electromyographic responses to stretch of the human anterior tibial muscle at different levels of contraction.

The EMG response and the mechanical response to 2 degree stretch of the human anterior tibial muscle was studied during contractions ranging from 0% to 80% of maximal voluntary contraction (MVC). The EMG response showed three distinct peaks M1, M2, and M3 with peak latencies of 59 ms, 86 ms, and 120 ms respectively. At low background torques M1 dominated while M2 and M3 were small or absent. M2 and M3 dominated above 40% of MVC and M2 in particular showed "automatic gain compensation", i.e. it constituted a - more or less - constant proportion of the background EMG for all contraction levels. The ratio between M1 amplitude and background EMG steadily decreased with contraction level. Even though the summed contributions of M1, M2, and M3 to some degree showed automatic gain compensation, this was not the case for the mechanical response to stretch. Between 0% and 30% of MVC the reflex mediated mechanical response increased approximately in proportion to the contraction level, but the reflex mediated mechanical response peaked at 40% of MVC and declined to zero at 80% of MVC. This discrepancy between EMG and mechanical response was explained by a simple model. The regression line between rectified and filtered tibialis anterior EMG and torque was used to predict the mechanical response from the EMG response. At increasing contraction levels the twitch elicited by supramaximal electrical stimulation decreases, and we reduced the predicted mechanical response by the same factor as the twitch.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative ultrasonic tissue characterization with real-time integrated backscatter imaging in normal human subjects and in patients with dilated cardiomyopathy.

We have shown previously that the physical properties of myocardium in dogs can be characterized with quantitative ultrasonic integrated backscatter and that interrogation of the tissue with ultrasound can delineate cardiac cycle-dependent changes in ultrasonic backscatter in normal tissue that disappear with ischemia and reappear with reperfusion if functional integrity is restorable. To determine whether this approach can be applied to man, we implemented an automatic gain compensation and continuous data acquisition system to characterize myocardium with quantitative ultrasonic backscatter and to detect cardiac cycle-dependent changes in real time. We developed a two-dimensional echocardiographic system with quantitative integrated backscatter imaging capabilities for use in human subjects that can automatically differentiate ultrasonic signals from blood as opposed to those obtained from tissue and adjust the slope of the gain compensation appropriately. Real-time images were formed from a continuous signal proportional to the logarithm of the integrated backscatter along each A-line. In our initial investigation, 15 normal volunteers (ages 17 to 40 years, heart rates 44 to 88 beats/min) and five patients with dilated cardiomyopathy (ages 22 to 52, heart rates 82 to 120 beats/min) were studied with conventional parasternal long-axis echocardiographic views. Diastolic-to-systolic variation of integrated backscatter in the interventricular septum and left ventricular posterior wall was seen in each of the normal subjects averaging 4.6 +/- 1.4 dB (SD) and 5.3 +/- 1.5 dB (n = 127 sites), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Observations on the automatic compensation of reflex gain on varying the pre-existing level of motor discharge in man.

The human stretch reflex is well known to show 'automatic gain compensation'; in other words, the electromyographic (e.m.g.) response evoked by a given disturbance increases progressively with the level of pre-existing voluntary activity, and so remains an approximately constant proportion of the background. Such behaviour has now been observed using vibration as the stimulus to Ia action and recording the reflexly developed force, in addition to the e.m.g. Inhibition was studied as well as excitation by vibrating the antagonist as well as the agonist, and found to be similarly regulated. The experiments were performed on the elbow flexors while they were contracting isometrically under voluntary drive. The vibration was either square-wave modulated at 5 Hz or delivered in bursts of one to five pulses. The latency of the e.m.g. responses produced by the latter was sufficiently short to show that gain compensation was a feature of spinal reflex action. In the Discussion, it is concluded that in principle 'automatic gain compensation' can be readily attributed to the known organization of the motoneurone pool. As the background force increases so does the number of active motoneurones available to be frequency-modulated by a given input, and the larger and stronger will be those motor units which are on the verge of recruitment or de-recruitment.

Equivalent Electrical Representation of the Sweat Layer and Gain Compensation of the EMG Amplifier

The sweat layer, formed on the surface of the skin, causes a partial short-circuit of the surface electrodes in an electromyographic (EMG) channel. As a result, the effective input impedance of the channel varies at random and, along with the impedance, the output voltage varies. In this note, the sweat layer has been represented as a variable resistance connected across the input stage of the EMG channel and the effect is analyzed. It has also been shown that the sweat layer's equivalent resistance can also be used for the continuous and automatic gain compensation of the EMG amplifier.

Servo action in human voluntary movement.

Muscular movements are under the control of a servo similar in many ways to those used in engineering control systems but with a subtlety of design not found in man-made servo mechanisms—including an automatic gain compensation for altered load which must be useful, for example, for adjusting to reduced g on the Moon.

Least Squares Gamma Spectrum Analysis with Automatic Gain and Baseline Compensation

The usual least squares fitting technique for gamma spectrum analysis has been expanded to include the computation of gain and baseline shifts. An iterative nonlinear technique is used. Since the shifting parameters are determined from the sample spectrum, no additional calibration data are needed. Implementation provided fitting up to 14 standards using an 8K PDP-8 with DECtape.