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Digital auscultation is a well-known method for assessing lung sounds, but remains a subjective process in typical practice, relying on the human interpretation. Several methods have been presented for detecting or analyzing crackles but are limited in their real-world application because few have been integrated into comprehensive systems or validated on non-ideal data. This work details a complete signal analysis methodology for analyzing crackles in challenging recordings. The procedure comprises five sequential processing blocks: (1) motion artifact detection, (2) deep learning denoising network, (3) respiratory cycle segmentation, (4) separation of discontinuous adventitious sounds from vesicular sounds, and (5) crackle peak detection. This system uses a collection of new methods and robustness-focused improvements on previous methods to analyze respiratory cycles and crackles therein. To validate the accuracy, the system is tested on a database of 1000 simulated lung sounds with varying levels of motion artifacts, ambient noise, cycle lengths and crackle intensities, in which ground truths are exactly known. The system performs with average F-score of 91.07% for detecting motion artifacts and 94.43% for respiratory cycle extraction, and an overall F-score of 94.08% for detecting the locations of individual crackles. The process also successfully detects healthy recordings. Preliminary validation is also presented on a small set of 20 patient recordings, for which the system performs comparably. These methods provide quantifiable analysis of respiratory sounds to enable clinicians to distinguish between types of crackles, their timing within the respiratory cycle, and the level of occurrence. Crackles are one of the most common abnormal lung sounds, presenting in multiple cardiorespiratory diseases. These features will contribute to a better understanding of disease severity and progression in an objective, simple and non-invasive way.

In the last 20 years, attention has been paid to characterize and improve the acoustic environment of hospitals, but much remains to be done. For instance, hospital operations often prevent patients from sleeping well. When the HCAHPS survey of hospital patients included a question about noise preventing sleep, it was routinely the lowest score patients awarded to hospitals. A few preliminary studies also have shown hospitals to be poor to fair spaces for speech intelligibility. The delicate balance between maintaining privacy and establishing good communication is particularly challenging for hospital patients because they often have hearing impairments or are medicated and potentially less able to focus. Noise in hospitals has also prompted the shift to written orders for lab work and pharmaceuticals to avoid errors. A relatively new area of research interest is the stress impact of hospital soundscapes. Hospital patients are a vulnerable population, suffering from anxiety about their medical condition, and the sounds to which they are exposed (such as moans) can exacerbate the problem. Hospital staff as well show the impacts of noise-related stress. This talk summarizes the current state of hospital acoustics.

The Reflections series takes a look back on historical articles from The Journal of the Acoustical Society of America that have had a significant impact on the science and practice of acoustics.

In the course of his career, Dick Lyon considered a large number of noise topics, including transportation noise, noise propagation in urban environments, statistical energy analysis, machinery diagnostics, product sound quality, and the importance of phase in acoustic transfer functions. What ties the body of Dick's work in these areas together are two features: the sheer inventiveness displayed both in theoretical and experimental approaches, and the focus on applied acoustics problems. For instance, Dick and collaborator Richard Cann designed a novel spark sound source to use for scale modeling. Dick's work on SEA similarly reflected a willingness to plow new ground in order to find the tools able to provide answers to vexing acoustical challenges. The majority of Dick's work can be traced to his desire to improve products by modifying the sound produced or to use the sound to identify functioning issues within the product. Dick leaves behind a legacy of accomplishments in the product acoustics arena. On a personal note, Dick was fond of pushing himself to the limit, whether in academic endeavors or in personal accomplishments, such as his rowing. He loved cars and was a great mentor to a large number of accomplished acousticians.

Very little reliable information exists on the sound levels present in an operating room environment. To remedy this situation, sound pressure levels of the operating rooms in Johns Hopkins Hospital were monitored before, during, and after operations. The data were analyzed to determine background sound levels, average equivalent sound levels L(eq), frequency distribution, and peak sound pressure levels L(peak). Each surgery was matched to the period of noise it produced permitting the association of sound levels with particular types of surgeries and the determination of various sound measures for classes of surgery (e.g., orthopedic, neurological, etc.). Averaging over many surgeries, orthopedic surgery was found to have the highest L(eq) at approximately 66 dB(A). Neurosurgery, urology, cardiology, and gastrointestinal surgery followed closely, ranging from 62 to 65 dB(A). By considering the L(peak) along with the L(eq) values, a pattern emerges for the various surgical divisions. Gastrointestinal and thoracic surgery are relatively quiet among the surgical divisions. Neurosurgery and orthopedics have sustained high sound levels. Cardiology surgery has a more moderate average sound level but includes brief periods of extremely high peak sound levels. For neurosurgery and orthopedic surgery, peak levels exceeded 100 dB over 40% of the time. The highest peak levels routinely seen during surgery were well in excess of 120 dB.

This study has dissected the current curriculum in mechanical engineering into a list of required topics. The list indicates what material is currently considered to be the essential body of knowledge for graduating mechanical engineering students. It also provides a measure of the extent to which curricula differ from institution to institution. There is similarity in core material required among the institutions which we considered, but each one adds distinct requirements which give it an individual flavor or emphasis. The list reveals some of the differences among degree programs. While institutions have adjusted curricula to conform to the ABET engineering criteria, how they fulfill the “technical skill” outcomes is clearer than how they fulfill the “professional skill” outcomes. This survey shows that dissecting a degree program into required topics is useful for curriculum reform, as it provides a baseline to study the curriculum at a level more finely grained than a course.

The noise in hospitals has been growing monotonically since at least 1960, and noise is now a top complaint of patients, staff, and visitors. Hospital noise sources are of many types, including HVAC noise from required high air flows, equipment noise from machines such as MRI units, alarms from equipment at patient bedsides, pneumatic tube lab transport systems, PA systems, and speech absolutely everywhere. In 2006, the federal government introduced the Hospital Consumer Assessment of Healthcare Providers and Systems (HCAHPS) as a standardized survey to measure patient perception of the quality of care received. Results of the survey are publicly available for each of the over 5500 hospitals in the United States. The first analysis of results showed that the lowest score received by U.S. hospitals in aggregate was the single acoustics question which asks whether patients found their room sufficiently quiet to allow for sleep at night. With the threat of decrease of federal compensation unless they show im...

Monitoring the condition of signals during manufacturing can provide valuable information about the status of the parts being produced, as well as that of the components of the manufacturing machine. To this end, we introduce a monitoring technique based on the Karhunen–Loeve transform, which decomposes measured manufacturing signals into decorrelated components in the form of fundamental eigenfunctions. The isolated eigenfunctions are monitored by means of the corresponding coefficient vectors, which indicate stationary and non-stationary changes in the deterministic and stochastic fundamental patterns. In this paper, the mathematical foundations of the technique are explored to form a good understanding of the mechanics of the transformation. This understanding is achieved with simple illustrative examples in the discrete and continuous domains, followed by an example of multicomponent signal decomposition by means of numerical simulations. The monitoring potential of the technique is illustrated with an example from a milling process, where the main modes are extracted by means of the eigenvectors and coefficient vectors.

A novel design of traffic noise barriers is presented: barriers that have a jagged instead of the conventional straight top edge. Experimental, numerical, and analytical investigations show that noise barrier performance can be improved by making the top edge jagged. In many, but not all, cases the jagged edge improves insertion loss, by up to 6 dB. The most promising theoretical approach is to model the edge as a directive line source. Besides yielding predictions that agree favourably with measurements, the line source model reveals that the diffracted field behind a jagged edge barrier depends strongly on the receiver location, the portion of the edge on the most direct path between source and receiver, and the inclination of the straight barrier edge segments. Further, because the model is easy to apply, it is a promising and powerful tool for design of optimum edge profiles.

A new method termed Directive Line Source Model (DLSM) is presented for predicting the diffracted field produced by a sound wave incident on a rigid or pressure release half plane. In the new method the edge of the half plane is modeled as an infinite set of directive point sources continuously distributed along the edge. Because DLSM is fast, simple and intuitive, it is a promising tool for the study of diffraction. It can be applied for several types of incident radiation: omnidirectional cylindrical and spherical waves, plane waves, as well as waves from directional sources. Wedges may also be treated. Finally, DLSM can handle diffraction by an arbitrarily shaped edge profile, for example, a half plane having an edge that is jagged instead of straight. Results for plane, cylindrical and spherical incident waves, as well as for arrays of line and point sources, are presented and their agreement with known analytical solutions is demonstrated. Predictions based on DLSM compare favorably with experimental data.

Nonlinear programming is used to design a non-contact high resolution optical system capable of sensing all six degrees of freedom of an object. This system uses two wide-beam lasers to illuminate two reflective fiducial markers placed on the object's surface. Light rays reflected from these markers are incident on three position sensitive detectors, which measure the x-y coordinates of the ccntroids of the incident light spots. The mathematical model of the system, which maps object coordinates into light spot coordinates, is very complex and highly nonlinear. The purpose of the study is to find designs that optimize three objectives: linearity error, range, and sensitivity, both singly and in combination, and to gain insight into the design tradeoffs among them. The design variables include the angular orientation of the laser beams, the positions of each of the fiducial markers, and the distance between sensor and object planes. Analysis of the model shows how these variables must be changed to improve...

Fluid-structure interactions in hydrodynamic bearings result in load carrying and drag forces which give the bearing its characteristics. While these bearings offer many benefits as machine components, one of their shortcomings is their limited efficient range. In this paper, we demonstrate the use of micron-scale actuators to actively control the thrust and drag forces on a slider bearing. We show that for a set of control parameters, we are able to affect the performance of a bearing by more than 100 percent during operation, increasing the bearing’s range of operation. [S0742-4787(00)01602-7]

The status of fault patterns on part surfaces can provide valuable information about the condition of a manufacturing system. Accurate detection of the part surface condition in manufacturing ensures the fault-free manufacturing of high-quality parts, as well as helping in the accurate design/redesign of machine components and manufacturing parameters. To address this problem, we introduce an alternative mathematical transform that has the potential to detect faults in manufacturing machines by decomposing signals into individual components. Specifically, the paper focuses on the decomposition of numerically generated data using the Karhunen-Loe`ve transform to study a variety of signals from manufacturing. The potential utility of the proposed technique is then discussed in the context of understanding a manufacturing process under constant development. [S1087-1357(00)01801-3]

In conventional rotordynamic modeling, hydrodynamic bearings are often characterized by a set of linear stiffness and damping coefficients obtained from a first-order Taylor series expansion of bearing reactions. Theoretically, these coefficients are only valid for small amplitude motion about an equilibrium position. In this paper, a nonlinear dynamic model that overcomes the small amplitude assumption in the conventional linear analysis is described. By including higher-order terms in the bearing reaction expansion, nonlinearity in the oil film forces for large amplitude motion can be captured and represented by a set of nonlinear stiffness and damping coefficients. These coefficients are functions of static bearing displacement. A finite difference approach is described and is used to solve for these coefficients. The stated model is applied to a conventional slider bearing and a mechanical smart slider bearing that experiences large variations in load. Error assessment is performed numerically on the higher-order solutions to determine an acceptable displacement bound for the higher order coefficients.

Microdynamic systems have been studied for a number of years. Only limited work, however, has been completed on integrating microdynamic components into systems that satisfy mechanical tasks on macroscopic scales. In this paper, we describe microdynamic components needed to produce a surface which is actively deformable on local scales. In particular, we consider the design and demonstration of smart journal and thrust bearings capable of using embedded sensors and actuators to change dynamically the surface geometry. The ability actively to deform bearing surfaces allows for the design of bearings which are less prone to failure, the design of bearings with greater load-carrying abilities, and a fundamental study of the effect of surface geometries and fluid conditions on bearing performance, such as start-up and shut-down conditions. Some results of our new bearing designs are presented, focusing on numerical bearing models, sensor and actuator design and fabrication, and physical experimentation.

Sound generally reaches the shadow zone behind a noise barrier by diffraction, or scattering, from the edge at the top of the barrier. By redirecting the incident sound into the shadow zone, the edge acts as a line source. For the traditional straight-edge barrier, the line source is coherent. Since a crooked line source is less coherent, we propose to improve barrier performance by making the edge randomly jagged. Laboratory model experiments to compare insertion loss of straight- and jagged-edge barriers are reported here. A spark was used as a point source, the barriers were thin (compared to a wavelength), and ground and meteorological effects were not important. After preliminary measurements showed that a jagged edge can produce significantly more insertion loss at high frequency, a three level full factorial experiment was done. The results led to an empirical equation for insertion loss of a jagged-edge barrier. Improvement over the straight barrier was found to increase with jaggedness. An unexplained result was the poorer performance of the jagged-edge barrier at low frequency.

This article develops a model of the piezoelectric ceramic vibrator which includes thermal energy exchange on an equal footing with the electrical and mechanical energy. By use of an isentropically linear model for the material and the bond graph models for a piezoelectric thickness vibrator and heat conduction previously developed by the authors, a thermodynamically complete model is developed. For a simple case, the predicted results from the developed model are compared with the results from experiments. Predictions are found to compare very favorably with these measurements.

A new bond graph model for conduction heat transfer is developed, and applied to thermal energy balance in the piezoelectric thickness vibrator. In formulation of the heat conduction model, the mechanical and electrical effects are included. Hence, it can be directly applied to the temperature-dependent thickness vibrator. For the purpose of evaluation of the new method, one-dimensional heat conduction excluding other variable effects is compared with the results of the analytic solutions in simple cases. The simulation illustrates the validity and the accuracy of the model. Although the model is applied to the one-dimensional case only, the method can be easily used for general heat conduction problems.

Most microelectromechanical systems (MEMS) designed today use macroscopic power supplies, thereby placing limits on the functionality of MEMS in many applications. An alternative to this approach is to design MEMS with integral microscopic distributed power supplies. This paper examines the feasibility of creating micro power supplies by considering three functions common to MEMS power systems: (1) capture energy; (2) store energy; and (3) drive actuation, of these, only the capture energy function is highly dependent on the specific application. For each of the three functions, a table is presented which compares various means of performing the function. This information makes it possible to determine what design alternatives are feasible for the creation of a micro power supply for any specific application of MEMS. We use smart bearings with active surface features as an example application and develop a design for a micro power supply suitable for this work.

A study of the different noise sources in a position sensitive detector (PSD)-transimpedance amplifier (TIA) sensing system is presented and the dominant noise sources are identified. The effect of these noise sources on the position detection capability of the sensing system is analyzed. An expression derived for the position resolution of the phase method of position detection reveals the position resolution depends inversely on the modulation frequency of the light source and the square of the amplitude of the currents flowing through the metal electrodes, and is dependent on the position of the incident light beam. Simulation results show that the best achievable position resolution is at the center of the PSD and becomes worse as one moves away from the center toward the edges. Compared to the 4 nm//spl radic/Hz position resolution that is achievable using the amplitude method of position detection, the phase method of position detection provides a resolution of 9 nm//spl radic/Hz and 6 nm//spl radic/Hz corresponding to a modulation frequency of 50 kHz and 70 kHz respectively.

Robust H∞ optimal control theory has proven to be one of the best techniques in linear control system design. The achievable robust stability and performance are high, but the resulting controllers are very complex and difficult to implement. As a result, few practical implementations of H∞ control can be found in the literature. This paper presents a robust H∞ controller for a two-degree-of-freedom magnetic micro-levitation positioner and its real time experimental implementation. The experimental device used in this study is designed for use in semiconductor manufacturing and consists of two U-shaped electromagnets and a manipulator. First, we describe the system dynamics in state space form. Second, the system which is unstable in nature is stabilized using the H∞ synthesis. The H∞ control design problem is described and formulated in the standard form with emphasis on the selection of weighting transfer functions that reflect robustness and performance goals. The interactive computing environment MATLAB is used to calculate the controller. Third, the controller is implemented digitally using a digital signal processor with 16 bit A/D and 12 bit D/A converters. Finally, some simulation and experimental results are presented. The results obtained show that robust stability against model uncertainties is achieved and the performance goals are satisfied.

The viability of using a nondestructive micro-shear test to resolve interfacial features in integrated circuits incorporating TAB (tape automated bonding) technology has been confirmed using finite element method (FEM) simulations. Both two- and three-dimensional finite element models were built to determine whether the size and location of interfacial features such as dead zones (nonbonded regions), delaminations and inclusions could be identified by applying one or more forces to the surfaces of a bond and monitoring the resulting deflections. By monitoring the localized Von Mises stress in the model, it was shown that the applied surface forces did not cause irreversible yield within the bond, and could therefore be considered nondestructive. The models, created in NASTRAN, consisted of two- or three-dimensional brick shaped elements (of length 12.5 /spl mu/m per side) whose material properties were set to either copper (representing the lead) or gold (representing the bump). Non-bonded regions within the bond were simulated by either removing elements adjacent to the lead/bump interface, or by implementing gap elements between interfacial nodes. Inclusions were modeled by setting the material parameters of elements adjacent to the interface to those of silicon dioxide. The input force was applied either directly through the surface nodes of the lead, or through a force tool which contacted the lead surface via gap elements. Other issues considered include the relationship between lead overhang length and the bond force deflection curve, as well as the surface force and displacement profiles generated on the bond under the force tool. >

The partial differential equations for a piezoelectric ceramic body are derived to describe thermal as well as mechanical and electrical responses. Those can include conduction heat transfer, mechanical and electrical dissipation, thermal expansion, and pyroelectricity. The derived differential equations are so complicated that it is almost impossible to reduce them into a minimum independent set of differential equations. A simple one‐dimensional case of the thickness vibrator with thermal effects is considered and an approximate model is proposed.

The problem caused by imbalance in rotating machinery can be solved using actively controlled magnetic bearing systems. There are two methods to solve this problem using feedback control: 1) compensate for the imbalance forces by generating opposing forces on the bearing surface; and 2) make the rotor rotate around its axis of inertia so no imbalance forces will be generated. The dynamics of the magnetic bearing are described in state-space form using airgap displacement, velocity, and airgap flux as state variables. The system which is unstable in nature is stabilized using the Q-parameterization theory. To compensate for the imbalance disturbance forces, the controller Q-parameter is chosen such that rejection of sinusoidal disturbances is achieved. To achieve automatic balancing, the imbalance is assumed as a sinusoidal noise in the measured signal, and the controller Q-parameter is chosen such that rejection of sinusoidal noise is achieved. Simulation results are presented and show the robustness of the proposed controllers and that the rejection of sinusoidal disturbances is achieved. The rotation of the rotor around its axis of inertia is also achieved. >

On any given day in the United States, there are about 480,000 patients in hospital for reasons other than psychiatric care or rehabilitation, each generating, on average, about 135 clinical alarms per day. Studies have shown that over 90% of these alarms result in no action being taken. Alarm errors, either alarms that sound and receive no response or alarms that fail to sound when they should, number roughly 8 million per day yet data on adverse alarm impacts indicate about 200 alarm-related deaths per year and a total of a little more than 500 adverse impacts per year. A compelling conclusion from this data is that clinical alarms in hospital are very inefficient and ineffective tools for monitoring medical emergencies. Much attention has been dedicated to alarms recently, with the general goal of improving response to alarms in order to ensure no medical emergency is missed. While this work is of immediate use and is vitally important to the operation of the modern hospital, it focuses on minor changes to the existing systems rather than on trying to design the optimum system for the future. It is future alarm systems that we consider here, with an aim of designing a more effective and efficient system for use in hospitals in roughly 20 years.

In the wafer bumping process, metal bumps are deposited on aluminum pads and are later used to bond the silicon die to the I/O connections. The bump strength is important for the mechanical integrity and overall reliability of the interconnect. In this paper the effects of the following thermocompression bonding parameters on the bump-pad adhesion of TAB (tape automated bonding) bonds are experimentally determined and analytically explained: thermode temperature, base temperature, bonding pressure, and bonding duration. Experiments were performed on a 328-lead TAB device (gold bump on 4-mil pitch) and were based upon a 4-parameter, 3-level, Taguchi orthogonal array. The experimental results are compared with results obtained from finite element analyses. A consistent increase in the bump strength was observed after thermocompression bonding. Applied thermode pressure and bonding duration were found to be the most significant parameters that affect bump-pad adhesion. >

With the challenge of the shrinking dimensions in the fabrication process, demands are growing for higher precision and more powerful analytical probing stations to be used for characterization and failure analysis of integrated circuits. A magnetic levitation-based approach to analytical probing stations is proposed and investigated in this paper. This approach permits the process to be automated while maintaining better resolution and easier operation than is currently available. Further, force control can be implemented to ensure that the probe contact does not scratch the device under testing. Feedback controllers are designed and used in both the suspension and the XY positioning. The suspension motion controller is implemented in analog circuitry while the XY motion controller is implemented in a digital controller. An air gap sensor and optical position sensors are used for the position feedback. A simple open loop control method is derived for the force control. A positioning repeatability of 0.2 /spl mu/m and a force repeatability of 80 mgf are observed from the experimental results. >

To reduce the average accessing time of a magneto-optical (MO) disk drive, which is a severe drawback of current products, a newly developed moving-magnet type tracking actuator has been implemented and will be tested. The moving-magnet type actuator meets the following objectives which the known prior actuator designs have not been able to satisfy: providing sufficiently high magnetic force constants over essentially the whole stroke length of the actuator, achieving extremely rapid accessing time while providing a mechanically stiff carriage; eliminating the carriage thermal expansion which causes a head misalignment on disk tracks; eliminating flexible cable connections to the moving parts; providing a very compact design, and reducing the cost of manufacturing. Computer aided design using magnetic circuit theory is applied for determining optimal design parameters for the actuator.

This paper introduces a new repulsive magnetic levitation approach using permanent magnets and air-core electromagnets as primary actuating components. The permanent magnets, which are attached to the bottom of a carrier, are repulsively levitated above and by oblong shaped electromagnets, which constitute one part of the guide tracks. Due to the lateral unstable nature of repulsive levitation, the stability of the levitated permanent magnets is regulated by another part of the guide tracks, electromagnetic stabilizers, which are strands of straight wires running through the entire length of the guide tracks above the levitation coils. A state feedback controller with integral compensator is designed for the stability control. The entire levitation system is divided into three subsystems: levitation, stabilization and propulsion. All the control works with respect to each subsystem are executed extrinsic to the carrier, i.e., there is no electrical circuit on board the carrier. The feasibility of this new levitation approach is confirmed successfully by a small scale demonstration system designed to transport a single silicon wafer in a microelectronic fabrication line. The wafer carrier is stably levitated 1.5 mm above the track surface with lateral air-gaps of 0.5 mm. Its maximum velocity is 22.2 cm/sec and the traveling range is 1 m. >

Earlier work on lateral-effect position-sensitive detectors (PSD) has used an amplitude detection signal-processing scheme to determine the position of the centroid of the incident light beam on the PSD surface. In this work we introduce a phase detection method of position measurement which is based on detecting the phase difference between the sinusoidal currents flowing through the metal electrodes. A distributed transmission line model for the PSD and a one-pole model for the transimpedance preamplifier are used in the analysis of the sensor. Experimental results are presented and are found to be in close agreement with simulation results. It is seen that the spatial resolution is proportional to the modulation frequency. With a light modulation frequency of 50 kHz and the introduction of frequency multiplication (/spl times/8) after the transimpedance preamplifier, a spatial resolution of 2 /spl mu/m is demonstrated. For application in multi-degree-of-freedom position sensors, we demonstrate the simultaneous detection of centroids of multiple light beams using frequency division multiplexing. Application of the phase method of position detection to a two dimensional PSD shows a maximum deviation from linearity of 1% over the working range of the PSD. >

A bond graph modeling approach that is equivalent to a finite‐element method is formulated. This formulation leads to a new definition of the generalized displacements for a continuous system. The newly defined coordinates are easily interpreted physically and easily used in analysis of the system performance. The new bond graph modeling approach is applied to the piezoelectric thickness vibrator. Compared to the Mason equivalent circuit model, the bond graph model offers the primary advantage of physical realizability. Compared to circuit models based on standard discrete electrical elements, the main advantage of the bond graph model is a greater physical accuracy because of the use of multiport energic elements. While results are presented here for the thickness vibrator, the modeling method presented is general in scope and can be applied to arbitrary physical systems.

An automated loading and unloading system for placing silicon wafers on a carrier is discussed. Interest is particularly focused on the automated loading of wafers onto a carrier which is moved along a transport path using a magnetic levitation (maglev) drive mechanism. The system consists of a wafer carrier which can move along the path and is purely passive, and a loading and unloading device which uses vacuum and electrical power. A magnetic clamping mechanism presents the wafer from sliding when the carrier moves along the path. The electromagnetic loading and unloading device firmly holds the wafer using vacuum suction and may be carried out by a robot. Only the bottom surface and edge of the wafer are touched by the carrier and the loader-unloader. The loader-unloader described, when combined with a maglev transport path, is potentially useful for connecting the processing tools in a cluster or connecting the workstations along a semiconductor fabrication line. >

The measurement method described relies on using light sources, each of which is modulated at different frequencies and then demodulated in the sensor signal-processing circuit using a pulse amplitude modulation (PAM) scheme. The position of each light spot can be determined even if there are other beams irradiating the PSD at the same time. In a very simple experiment, the light beams from two LEDs were projected onto one PSD, with one LED modulated at 10 kHz and the other at 5 kHz. The PSD was calibrated by scanning the light beams across the PSD in equidistant grid lines over a 4-mm*7.2-mm area. It was found that the resolution, linearity, and accuracy of the measurement are not affected even if multiple light beams are continuously present. The number of light beams which can be used simultaneously is limited only by the bandwidth of the PSD and the sampling time of the sample/hold devices used in the DC restoration circuit. >

A model based on sinusoidal steady-state analysis is developed for the position-sensitive detector (PSD), which is approximated as a distributed RC transmission line. This model is used to study the output response of the lateral effect PSD (i) when only one pulse-modulated light beam is incident and (ii) when two light beams of different wavelengths, with one beam modulated at a frequency f and the other beam modulated at a frequency 2f, are incident at the same time. The simulation shows, and experiments confirm, that the transient response of the PSD consists of a position-dependent dead time (time for the output current to sense the change in the induced photocurrent) and a position-independent exponential rise decay time. For the application of resolving the positions of two or more pulsed-modulated light spots, it is shown that there is a position-dependent upper limit on the usable modulation frequency. With the per-unit-length values chosen for the sheet resistance as R=315 Omega /mm and the junction capacitance as C=330 pF/mm, the modulation frequency limit is determined to be 20 kHz. >

This paper describes the unique design, fabrication and control of a one-dimensional magnetic levitation micromachine with endpoint friction. The flat manipulator, which is driven by six air-core solenoids fixed in the workspace, supports three rare earth permanent magnets in the vertices of its equilateral triangular structure. The manipulator moves from one position to another by making contact with a solid surface under the solenoids after every step, but it does not contact the surface during a lateral step motion. Noncontact measurements of the manipulator movement were made using LED-phototransistor pairs. The 0.21 g manipulator was controlled with 0.5 μm position accuracy over a 100 μm range with a very simple monitored open-loop control strategy. The accuracy and motion range can be improved with large-range high-resolution linear optical sensors.

A magnetic levitation transport path particularly suitable for moving objects in clean environments, such as for the transportation of wafers in clean rooms, is described. The present transport path is a demonstration system and is not designed for a specific application. It demonstrates the feasibility of applying a microcomputer-controlled magnetic field to generate linear motion of a carrier with permanent magnets. A simple path geometry is adopted for analysis, and it shows that the control task involved can be very straightforward. Completely free-floating levitation of the carrier has not yet been achieved, but reducing contact friction has been studied. Areas of discussion include controller design, carrier velocity, motion smoothness, and load-carrying ability for different versions of transport paths. >

The radiation characteristics of a magnetohydrodynamic (MHD) acoustic transmitter radiating into a free medium are examined. Two source mechanisms are associated with the transducer: an electromagnetic force associated with the MHD operation, and a density fluctuation associated with heating of the medium by an electrical current. The wave equation is derived and a solution is found for impedance boundary conditions using a Green's function approach. Measurements obtained in a large water tank are shown to compare favorably with the predictions.

Pure circuit models of transducers have been used for many years with varying degrees of success. However, pure circuit models impose restrictions not all of which are predicated on laws of physics. These restrictions can produce transducer models which are nonphysical. Bond graph models offer an alternative that is less restrictive and thus better able to provide clear physical insight. We discuss the problem of pure circuit models of transducers and the advantages of bond graph approaches by examination of the special case of a piezoelectric transducer.

The process of modeling transducers generally involves the use of a finite number of discrete lumped elements connected using circuit-like conventions. However, such models are difficult to use for transducers which implicitly depend upon variation of a physical parameter with location since they view the transducer as existing only at points or discrete intervals in space. In this article a general modeling procedure is developed which views a transducer as a spatially distributed device. The model introduced here uses the theory of connected two-ports to determine the overall transfer matrix and scattering matrix representations. This directly yields the transducer sensitivities and efficiencies. The model is limited to transducers which may be thought of as being comprised of an infinite number of infinitesimal twoport elements, each of which is mechanically independent of the others. Coupling between the elements occurs through the input and output ports. The modeling procedure is demonstrated using an acoustic antenna, and shown to accurately predict the directional behavior.

Transducer models are typically comprised of a finite number of discrete lumped elements connected using circuit conventions. Such models are inappropriate for transducers which explicitly depend upon the continuous nature of one or more system element. These transducers must be modeled as spatially distributed devices. In this article we present a class of models which is useful for spatially distributed transducers in which the response at one location is coupled to that at other locations. The models use a transmission line to describe the mechanical coupling between locations on the transducer, but have been augmented to include interaction with the environment and sources everywhere along the line. If only one element is used at every location to represent the interaction of the transducer and the environment, and only one type of source is present, then there are only four general models which need to be considered. These models are analyzed for the general case of spatially varying sources and physical parameters. It is shown that it is possible to prescribe up to four response characteristics of the transducer if the physical parameters are permitted to vary with space. Examples of spatially distributed transducers are presented and applications discussed.

It is pointed out that the demands for precision and speed in manufacturing processes in the semiconductor industry are not well suited to traditional, large-scale approaches to automation. Consideration of several microautomation approaches has led to the development of a magnetic levitation-based system capable of three-dimensional motions. Such systems are able to move quickly and precisely, and can deliver prescribed forces and moments. Several significant applications of magnetic levitation-based microautomation in semiconductor manufacturing have been identified. These include positioning operations at various scales, such as mask alignment, hybrid circuit assembly, and transport between process stations. Other applications are analytical probing, nondestructive tape automated bonding (TAB) bond testing, and optical system alignment. A prototype system capable of high-speed four-degree-of-freedom motions with 0.5- mu m accuracy over small workspaces has been demonstrated. >