Low-frequency Sinusoidal Oscillator Research Articles

Single CDBA-based grounded parallel lossy inductor simulator circuits

Two new configurations for the realization of lossy grounded inductor each employing one current differencing buffered amplifier (CDBA), three resistors, a voltage follower and one grounded capacitor are presented. The realized inductances from the proposed configurations have independent tunability through a single resistor. The proposed circuits make use of the intrinsic current differencing property of CDBAs by not leaving any of its input terminals open or connected to ground. Both the presented circuits use grounded capacitor (which is particularly attractive for integrated circuit implementation) connected at the Z-terminal of CDBA which may also absorb the parasitic capacitance. The proposed lossy inductors can be used in applications such as low frequency sinusoidal oscillator, low pass filter (LPF) and band pass filter (BPF). Such examples may be suitable from the viewpoint of biomedical instrumentation and geo-physical applications. Non-ideal analysis has been carried out to support the theoretical propositions for both the proposed circuits. PSPICE simulation results with CMOS CDBA have been presented to establish the workability of the proposed lossy inductor structures. Experimental results using commercially available AD844 ICs have also been included to demonstrate the viability of the proposed lossy inductors based on CDBAs.

A rigid body model of the dynamic posteroanterior motion response of the human lumbar spine

Background: Clinicians apply posteroanterior (PA) forces to the spine for both mobility assessment and certain spinal mobilization and manipulation treatments. Commonly applied forces include low-frequency sinusoidal oscillations (<2 Hz) as used in mobilization, single haversine thrusts (<0.5 seconds) as imparted in high-velocity, low-amplitude (HVLA) manipulation, or very rapid impulsive thrusts (<5 ms) such as those delivered in mechanical-force, manually-assisted (MFMA) manipulation. Little is known about the mechanics of these procedures. Reliable methods are sought to obtain an adequate understanding of the force-induced displacement response of the lumbar spine to PA forces. Objective: The objective of this study was to investigate the kinematic response of the lumbar spine to static and dynamic PA forces. Design: A 2-dimensional modal analysis was performed to predict the dynamic motion response of the lumbar spine. Methods: A 5-degree-of-freedom, lumped equivalent model was developed to predict the PA motion of the lumbar spine. Lumbar vertebrae were modeled as masses, massless-spring, and dampers, and the resulting equations of motion were solved by using a modal analysis approach. The sensitivity of the model to variations in the spring stiffness and damping coefficients was examined, and the model validity was determined by comparing the results to oscillatory and impulsive force measurements of vertebral motion associated with spine mobilization and 2 forms of spinal manipulation. Results: Model predictions, based on a damping ratio of 0.15 (moderate damping) and PA spring stiffness coefficient ranging from 25 to 60 kN/m, showed good agreement with in vivo human studies. Quasi-static and low-frequency (<2.0 Hz) forces at L3 produced L3 segmental and L3-L4 intersegmental displacements up to 8.1 mm and 3.0 mm, respectively. PA oscillatory motions were over 2.5-fold greater for oscillatory forces applied at the natural frequency. Impulsive forces produced much lower segmental displacements in comparison to static and oscillatory forces. Differences in intersegmental displacements resulting from impulsive, static, and oscillatory forces were much less remarkable. The latter suggests that intersegmental motions produced by spinal manipulation may play a prominent role in eliciting therapeutic responses. Conclusions: The simple analytical model presented in this study can be used to predict the static, cyclic, and impulsive force PA displacement response of the lumbar spine. The model provides data on lumbar segmental and intersegmental motion patterns that are otherwise difficult to obtain experimentally. Modeling of the PA motion response of the lumbar spine to PA forces assists in the understanding the biomechanics of therapeutic PA forces applied to the lumbar spine and may ultimately be used to validate chiropractic technique procedures and minimize risk to patients receiving spinal manipulative therapy. (J Manipulative Physiol Ther 2002;25:485-96)

Three-dimensional organization of otolith-ocular reflexes in rhesus monkeys. II. Inertial detection of angular velocity.

1. The dynamic contribution of otolith signals to three-dimensional angular vestibuloocular reflex (VOR) was studied during off-vertical axis rotations in rhesus monkeys. In an attempt to separate response components to head velocity from those to head position relative to gravity during low-frequency sinusoidal oscillations, large oscillation amplitudes were chosen such that peak-to-peak head displacements exceeded 360 degrees. Because the waveforms of head position and velocity differed in shape and frequency content, the particular head position and angular velocity sensitivity of otolith-ocular responses could be independently assessed. 2. During both constant velocity rotation and low-frequency sinusoidal oscillations, the otolith system generated two different types of oculomotor responses: 1) modulation of three-dimensional eye position and/or eye velocity as a function of head position relative to gravity, as presented in the preceding paper, and 2) slow-phase eye velocity as a function of head angular velocity. These two types of otolith-ocular responses have been analyzed separately. In this paper we focus on the angular velocity responses of the otolith system. 3. During constant velocity off-vertical axis rotations, a steady-state nystagmus was elicited that was maintained throughout rotation. During low-frequency sinusoidal off-vertical axis oscillations, dynamic otolith stimulation resulted primarily in a reduction of phase leads that characterize low-frequency VOR during earth-vertical axis rotations. Both of these effects are the result of an internally generated head angular velocity signal of otolithic origin that is coupled through a low-pass filter to the VOR. No change in either VOR gain or phase was observed at stimulus frequencies larger than 0.1 Hz. 4. The dynamic otolith contribution to low-frequency angular VOR exhibited three-dimensional response characteristics with some quantitative differences in the different response components. For horizontal VOR, the amplitude of the steady-state slow-phase velocity during constant velocity rotation and the reduction of phase leads during sinusoidal oscillation were relatively independent of tilt angle (for angles larger than approximately 10 degrees). For vertical and torsional VOR, the amplitude of steady-state slow-phase eye velocity during constant velocity rotation increased, and the phase leads during sinusoidal oscillation decreased with increasing tilt angle. The largest steady-state response amplitudes and smallest phase leads were observed during vertical/torsional VOR about an earth-horizontal axis. 5. The dynamic range of otolith-borne head angular velocity information in the VOR was limited to velocities up to approximately 110 degrees/s. Higher head velocities resulted in saturation and a decrease in the amplitude of the steady-state response components during constant velocity rotation and in increased phase leads during sinusoidal oscillations. 6. The response characteristics of otolith-borne angular VORs were also studied in animals after selective semicircular canal inactivation. Otolith angular VORs exhibited clear low-pass filtered properties with a corner frequency of approximately 0.05-0.1 Hz. Vectorial summation of canal VOR alone (elicited during earth-vertical axis rotations) and otolith VOR alone (elicited during off-vertical axis oscillations after semicircular canal inactivation) could not predict VOR gain and phase during off-vertical axis rotations in intact animals. This suggests a more complex interaction of semicircular canal and otolith signals. 7. The results of this study show that the primate low-frequency enhancement of VOR dynamics during off-vertical axis rotation is independent of a simultaneous activation of the vertical and torsional "tilt" otolith-ocular reflexes that have been characterized in the preceding paper. (ABSTRACT TRUNCATED)

Lesion of the nodulus and ventral uvula abolish steady-state off-vertical axis otolith response.

1. During rotations that dynamically activate utricular and saccular primary afferents, the otolith system centrally detects the velocity and direction of rotation of the head in space. This property is experimentally manifested as a steady-state compensatory nystagmus during constant velocity off-vertical axis rotations. The computational, physiological, and anatomic details of this response remain presently unknown. Here we report that surgical inactivation of the cerebellar nodulus and ventral uvula abolished the ability of the otolith system to generate steady-state nystagmus during constant velocity rotation and to improve the dynamics of the vestibuloocular reflex (VOR) during low-frequency sinusoidal oscillations about off-vertical axes in rhesus monkeys. These results suggest that the cerebellar nodulus and/or ventral uvula comprise part of the neural substrate that is involved in these computations.

Amplitude stabilized low frequency oscillator†

Abstract The paper describes an amplitude stabilized very low frequency sinusoidal oscillator generating a frequency as low as 0.01 Hz. It uses a second-order all-pass network and an operational amplifier interconnected in a feedback loop to form a highly selective amplifier. A secondary loop consisting of a squaring network is used to stabilize the amplitude of oscillation. The oscillator is analysed and the experimental results are discussed.