Moving Coil Transducers Research Articles

Ballistocardiography monitoring system based on optical fiber interferometer aided with heartbeat segmentation algorithm.

An optical fiber interferometer-based ballistocardiography (BCG) monitoring system aided with the IJK complex detection algorithm is proposed in this paper. A new phase modulation method based on a moving-coil transducer is developed to address the problem of signal fading in the optical fiber interferometer and keep the system in quadrature by the closed loop controller. As a result, a stable BCG signal without baseline drift can be obtained. This BCG monitor based on optical fiber interferometer using phase modulation method owns the advantages of compact, low-cost, portable, and user-friendly. In addition, an end-to-end modified U-net is developed to conduct pixel-wise classification in the BCG signal. This network can achieve high accuracy and shows its capability to segment IJK complex and body movement in the BCG signal. In conclusion, the proposed BCG monitoring system with IJK complex segmentation algorithm is potential and promising in healthcare applications.

Reduction of vibration by using mechatronical subsystem

The primary aim introduced in this paper is synthesis of mechatronical system understand as planning of this type of systems. Mechatronical system is consisted of fundamental mechanical system and subsystem reducing vibration including electric elements. Fundamental system is received applying reverse task of dynamic (synthesis) and it's including inertial and elastic elements. The subsystem includes electric elements by means moving-coil transducer. The synthesis can also be used to change the already existing systems. Due to the method, introduced in this work, may be performed as early as whilst the designing of future functions. Using this way of designing is support for designers of mechanical systems with active reducing of vibrations.

Toward broadband electroacoustic resonators through optimized feedback control strategies

This paper presents a methodology for the design of broadband electroacoustic resonators for low-frequency room equalization. An electroacoustic resonator denotes a loudspeaker used as a membrane resonator, the acoustic impedance of which can be modified through proportional feedback control, to match a target impedance. However, such impedance matching only occurs over a limited bandwidth around resonance, which can limit its use for the low-frequency equalization of rooms, requiring an effective control at least up to the Schroeder frequency. Previous experiments have shown that impedance matching can be achieved over a range of a few octaves using a simple proportional control law. But there is still a limit to the feedback gain, beyond which the feedback-controlled loudspeaker becomes non-dissipative. This paper evaluates the benefits of using PID control and phase compensation techniques to improve the overall performance of the electroacoustic resonator. More specifically, it is shown that some adverse effects due to high-order dynamics in the moving-coil transducer can be mitigated. The corresponding control settings are also identified with equivalent electroacoustic resonator parameters, allowing a straightforward design of the controller. Experimental results using PID control and phase compensation are finally compared in terms of sound absorption performances. As a conclusion the overall performances of electroacoustic resonators for damping the modal resonances inside a duct are presented, along with general discussions on practical implementation and the extension to actual room modes damping.

Comparison and verification of analogous circuit models for dynamic moving-coil transducers

For decades, analogous circuits have been used to model the electro-mechano-acoustical properties of moving-coil transducers. In recent years, many enhanced models have been proposed to improve the accuracy of their estimated voice-coil impedances. In this work, an iterative complex curve-fitting routine has been used to best fit and compare the various models to the measured complex input impedance data of several loudspeaker drivers in free air. The estimated blocked electrical impedance of each driver was extracted and used to predict its frequency-dependent cone velocity while under operation. Actual driver cone velocities were measured experimentally using a scanning laser Doppler vibrometer, and the predictions were compared to further substantiate the accuracy of each model. The results highlight those models with the greatest predictive capabilities and reliability.

Characteristics of chemo-mechanically driven polyacrylonitrile fiber gel actuators

Pure polyacrylonitrile (PAN) fiber gels, exhibiting effective actuation forces and displacements through muscle-like contractile behavior during the volume change when subjected to environmental stimuli, are prepared by electrospinning, twisting (strand creation) and activation process to investigate performance characteristics of chemo-mechanically driven PAN gel actuators. Single PAN strand (yarn) having a dimension of 210 μm in diameter is used. A typical hysteresis loop is observed for the length change (∼ 38%) of PAN gels with respect to pH variation. Diameter and volume changes are observed as greater than 100% and greater than 720%, respectively, for pH activated systems. Chemically induced force generation of pure PAN fiber gel is completed within a few seconds. The average maximum force is 0.002 N, implying that the force generation of a single PAN filament is 6.7 × 10 − 6 N. A linear relation between force and strain is observed. It is found that PAN fiber gels in contracted state have stronger force and strain (0.043 N/0.112) than those (0.015 N/0.002) in elongated state. The actuation stress of pure PAN is in the range of moving coil transducer and commercial PAN but the actuation strain is better than moving coil transducer and similar to natural muscle.

Performance Characteristics of Electro–chemically Driven Polyacrylonitrile Fiber Bundle Actuators

Polyacrylonitrile (PAN) gel is known for its large volume change when subjected to environmental stimuli. In particular, PAN fiber contracts when exposed to a low pH environment and expands when exposed to a high pH environment. Due to this phenomenon, PAN fibers can create effective actuation forces and displacements through muscle–like contractile behavior during the volume change. An alternative way to manage contraction/elongation is to generate a local pH gradient, which can be achieved through an electrochemical cell and is more convenient than using a pH changing solution. The main objective of this study is to investigate the chemo–mechanical (i.e., pH response) and electro–chemo–mechanical behavior of PAN bundle actuators in order to characterize the performance capability of PAN fiber gel as an effective soft actuator for new engineering applications. In order to do this, the shrinking and swelling properties of PAN gel fiber bundles under the influence of various stimuli, such as pH difference and electric field, are investigated and characterized, while a capability map has been suggested and compared with other conventional actuators. Pre–oxidized PAN fibers are annealed for 5 h at 220 C and then placed in a bundle configuration. Fibers of 30 strands, 150 mm in length, are bound as a soft actuator, with a ring gripper epoxied to each end of the bundle. After significant efforts were made to properly address the corrosive behavior of the electrode, performance characteristics of PAN actuators have been experimentally obtained and compared to other conventional actuator technologies. It was found that the actuation stress of PAN bundle actuators is in the range of a moving coil transducer, and the actuation strain is also better than a solenoid, as well as similar to natural muscle. The power, density, and frequency of a PAN actuator are within the range of other polymer gel actuators. The obtained maximum actuation stress and linear actuation strain are generally in the range of 2 10 3 –1 100 MPa and 20–100% for both chemically induced and electro–chemically induced PAN bundle actuators, respectively. Finally, suggestions for the practical application ranges of PAN actuation systems are given.

Introduction to distributed mode loudspeakers (DML) with first-order behavioural modelling

A simple equivalent circuit of a distributed mode loudspeaker (DML) is described, which is accessible to engineers not specialised in acoustics. The DML is an acoustic radiator, the electrical, mechanical and acoustical properties of which differ radically from conventional moving coil transducers. DML radiation results from uniformly distributed, free vibration in a stiff, light panel and not pistonic motion. To enable acoustic engineers to use existing software programs to model their application of DML technology, an efficient equivalent circuit is developed. Within the constraints of the model, velocities and displacements of the various elements can be calculated, and the radiated acoustic power and pressure predicted.

Harmonic distortion in moving coil transducers caused by generalized Coulomb damping

A generalized Coulomb damping model for transducer friction is presented and applied to an underwater sound moving coil transducer. Measured harmonic amplitudes in the acoustic output of a certain moving coil transducer showed characteristics that indicated they were caused by friction. However, calculations based on the usual definition of Coulomb damping predicted only odd harmonics while the measurements contained both odd and even harmonics. A generalization of Coulomb damping was developed in which the friction force depends on position and direction of motion. This damping model predicts both even and odd harmonics and gives satisfactory agreement with the data. This friction-generated distortion is independent of drive level and can be important since it puts a lower bound on the distortion-free dynamic range.

Nonlinear behavior of electroacoustic transducers

An important goal of electroacoustic transducer development has long been maximization of the acoustic output power for a given transducer size. This goal always encounters familiar material mechanical, electrical, magnetic or thermal limitations—all the ultimate effects of nonlinear behavior. However, other nonlinear effects, such as harmonic distortion and instability, are the practical operational limitation in some applications, making nonlinear analysis an essential part of the process. Most basic transduction mechanisms are strongly nonlinear and all have some nonlinearities. Fortunately, the nonlinearities in all transducers have similar features and can often be represented in identical mathematical forms even when physically different. This study identifies the nonlinear features which are common to all major types of transducers (electrostatic, variable reluctance, piezoelectric, electrostrictive, magnetostrictive, and moving coil). Recognizing these common features makes it possible to develop nonlinear solutions which apply to all types of transducers and facilitates comparison of transducer types for susceptibility to nonlinear effects. Recently published perturbation solutions obtained for moving coil transducers [J. Acoust. Soc. Am. 94, 2485–2496 (1993)] will be generalized and used to illustrate evaluation of harmonic distortion in other transducers.

Perturbation analysis of nonlinear effects in moving coil transducers

A perturbation expansion model is presented for the evaluation of the second and third harmonic distortion in moving coil transducers. The model is applied to a particular underwater sound piston transducer resulting in a favorable comparison with measurements. The model should be useful for analyzing transducer data to determine the cause of nonlinear effects. The model can also provide information regarding different nonlinear mechanisms and different driving conditions. It was found that constant current drive gives higher harmonic distortion at certain frequencies near and below resonance while constant voltage drive gives higher harmonic distortion above resonance.

Apparatus to determine the complex mass density of a viscous fluid contained in a rigid porous solid from acoustic pressure measurements

Two experimental techniques to determine the frequency‐dependent complex mass density of a viscous fluid contained in a rigid porous solid are being investigated. The fluid‐filled solid is contained within a small (≪λ) cylindrical cavity. In one technique the moving mass of the fluid is sensed by the effect it has on the measured input electrical impedance of a moving coil transducer. In the second technique the moving mass is extracted from the measured pressure required for the fluid to oscillate with a known amplitude through the porous solid. Preliminary results have been reported for the impedance method [Grant et al., J. Acoust. Soc. Am. Suppl. 1 84, S176 (1988)]. Preliminary results for the pressure technique and a comparison of the two methods will be presented. [Work sponsored by NRL‐USRD and the Naval Postgraduate School.]

Moving coil transducers using multiple‐stranded coils

A moving coil transducer such as a loudspeaker has its coil formed of multiple strand or litz wire. The structure includes a form having multiple turns of the stranded wire thereon, and the leads or ends of the stranded wire forming the coil extend continuously from the moving coil structure to attachment or terminal means carried on some portion of a fixed structure associated with the moving coil. The multiple strand wire is twisted to a predetermined lay throughout its length.

Measurement of fetal movements by moving-coil transducer.

A transducer for the detection of fetal movements is described. The transducer is based on a coil moving in a magnetic field. It produces a signal as a result of fetal movements which create changes on the matemal anterior abdomen. The transducer is not affected by slow movements, maternal respiration, and uterine contractions. The sensitivity of the transducer in comparison with other means of fetal movement assessment is discussed.

Dynamic properties of moving magnet transducers

The equation of motion, the force, and the equivalent circuit of a moving magnet transducer are derived. The system is shown to be a low pass device and the high-frequency cutoff depends only on the properties of the permanent magnet material and the specified maximum displacement. Experiments with two moving magnet designs are described. Problems due to large constant forces are discussed and the importance of adequate centering and spring design is stressed. The development of high coercivity materials is shown to make moving magnet devices more competitive compared to moving coil transducers. The advantages of the former are high efficiency and good low-frequency response. Their use is, however, limited by the existence of the high-frequency cutoff and the more involved mechanical construction required.

Low‐frequency underwater moving coil projector fluids

Castor oil (dB grade) has been used as a coupling fluid in underwater transducers for many years. There are several good reasons for this, but not all of the characteristics of castor oil are best suited for this purpose. The viscosity for instance changes widely in the temperature range 0°–30°C. Since viscous damping affects the output of the moving coil projectors, the output is reduced at low frequencies as the temperature is lowered. FS 1265 fluoro silicone fluid (300 centistokes) has replaced castor oil in USRD moving coil projectors when extreme low temperatures are expected. Another fluid, monoalkyl terminated poly (1,2‐propylcne oxide) (PAG) has been evaluated as a replacement for castor oil and FS 1265 in transducer application. PAG has an even lower viscosity than FS 1265 and changes less with temperature. However, the volume resistivity of PAG is lower than FS 1265 or castor oil. These three fluids were, simultaneously, tested and compared in a USRD J15‐3 projector at the USRD Leesburg Facility, and then at the NUSC Seneca Lake Facility. Each of the three fluids was also tested in a J13 moving coil projector in the USRD/ATF Faculty at two temperatures. The results of the measurement demonstrate that PAG can replace FS 1265 and castor oil in moving coil transducers if a lower volume resisitivity can be tolerated.

Moving-coil transducers : Standard Telephones & Cables Ltd, British Patent 1,219,918 (1971) Filed 8 August 1968

Moving-coil transducers : Standard Telephones & Cables Ltd, British Patent 1,219,918 (1971) Filed 8 August 1968

Seismic streamer cable : Western Geophysical Co of America, British Patent 1,230,701 (1971) Filed 21 March 1969

This paper presents a methodology for the design of broadband electroacoustic resonators for low-frequency room equalization. An electroacoustic resonator denotes a loudspeaker used as a membrane resonator, the acoustic impedance of which can be modified through proportional feedback control, to match a target impedance. However, such impedance matching only occurs over a limited bandwidth around resonance, which can limit its use for the low-frequency equalization of rooms, requiring an effective control at least up to the Schroeder frequency. Previous experiments have shown that impedance matching can be achieved over a range of a few octaves using a simple proportional control law. But there is still a limit to the feedback gain, beyond which the feedback-controlled loudspeaker becomes non-dissipative. This paper evaluates the benefits of using PID control and phase compensation techniques to improve the overall performance of the electroacoustic resonator. More specifically, it is shown that some adverse effects due to high-order dynamics in the moving-coil transducer can be mitigated. The corresponding control settings are also identified with equivalent electroacoustic resonator parameters, allowing a straightforward design of the controller. Experimental results using PID control and phase compensation are finally compared in terms of sound absorption performances. As a conclusion the overall performances of electroacoustic resonators for damping the modal resonances inside a duct are presented, along with general discussions on practical implementation and the extension to actual room modes damping.

Fluid flowmeters : R.B. Jacobs, British Patent 1,219,887 (1971) Filed 10 Feb 1969

This paper presents a methodology for the design of broadband electroacoustic resonators for low-frequency room equalization. An electroacoustic resonator denotes a loudspeaker used as a membrane resonator, the acoustic impedance of which can be modified through proportional feedback control, to match a target impedance. However, such impedance matching only occurs over a limited bandwidth around resonance, which can limit its use for the low-frequency equalization of rooms, requiring an effective control at least up to the Schroeder frequency. Previous experiments have shown that impedance matching can be achieved over a range of a few octaves using a simple proportional control law. But there is still a limit to the feedback gain, beyond which the feedback-controlled loudspeaker becomes non-dissipative. This paper evaluates the benefits of using PID control and phase compensation techniques to improve the overall performance of the electroacoustic resonator. More specifically, it is shown that some adverse effects due to high-order dynamics in the moving-coil transducer can be mitigated. The corresponding control settings are also identified with equivalent electroacoustic resonator parameters, allowing a straightforward design of the controller. Experimental results using PID control and phase compensation are finally compared in terms of sound absorption performances. As a conclusion the overall performances of electroacoustic resonators for damping the modal resonances inside a duct are presented, along with general discussions on practical implementation and the extension to actual room modes damping.

A high-sensitivity strain/inertial seismograph installation

Abstract A seismograph complex consisting of short-period (SP), long-period (LP), and extended long-period (XLP) inertial and strain seismographs has been installed. Recordings are made on magnetic tape and photographic film. Routine magnifications on the 20-trace, 16-mm film recorders for all three components are: SP inertial, 500 K; LP inertial, 100 K. The noise levels permit equivalent magnifications on the strain seismographs. The complex provides seismic wave discrimination by directional response, which is independent of period, and by detection of differences in phase velocities between P, S, Love, or Rayleigh arrivals. The strain seismographs use 40-m-long rods and moving coil transducers with generator constants of 32,000 v/m/sec. They sense waves of 5 × 10-13 strain at 30 sec and reject the 2 × 10-8 earth-tide strain. A low-noise preamplifier drives a filter assembly which provides SP, LP, and XLP strain outputs. The complex is installed in an abandoned mine 50 km southeast of Phoenix, Arizona. Environmental control is provided by burial at a depth of about 110 m in a quartz diorite, by sealing the mine, and by insulating the seismometers.

Vibration measurements in the middle frequency range by means of moving coil transducers

1. It is advisable to employ moving coil transducers having a resonant frequency no less than 15 to 25 Hz in the design of middle frequency (7 to 400 Hz) vibration measuring instruments. 2. The correction of the characteristics of such instruments that is necessary in order to operate over the entire frequency range cited can be accomplished both by passive electrical compensation and with positive displacement feedback. 3. Passive electrical compensation is a more universal method of transforming the characteristics but when it is used, it is difficult to make transducers interchangeable. The application of positive displacement feedback is advisable for the construction of multichannel vibration measuring instruments.