Magnetic Position Sensor Research Articles

Dynamic three-dimensional freehand echocardiography using raw digital ultrasound data

In this paper, we present a new method for simple acquisition of dynamic three-dimensional (3-D) ultrasound data. We used a magnetic position sensor device attached to the ultrasound probe for spatial location of the probe, which was slowly tilted in the transthoracic scanning position. The 3-D data were recorded in 10–20 s, and the analysis was performed on an external PC within 2 min after transferring the raw digital ultrasound data directly from the scanner. The spatial and temporal resolutions of the reconstruction were evaluated, and were superior to video-based 3-D systems. Examples of volume reconstructions with better than 7 ms temporal resolution are given. The raw data with Doppler measurements were used to reconstruct both blood and tissue velocity volumes. The velocity estimates were available for optimal visualization and for quantitative analysis. The freehand data reconstruction accuracy was tested by volume estimation of balloon phantoms, giving high correlation with true volumes. Results show in vivo 3-D reconstruction and visualization of mitral and aortic valve morphology and blood flow, and myocardial tissue velocity. We conclude that it was possible to construct multimodality 3-D data in a limited region of the human heart within one respiration cycle, with reconstruction errors smaller than the resolution of the original ultrasound beam, and with a temporal resolution of up to 150 frames per second.

Effect of an In1−xAlxSb buffer layer on InSb thin film mobility

Indium antimonide magnetoresistors are used for magnetic position sensors in very demanding automotive environments such as crankshaft and camshaft angular position sensors for engine control. Growth of very thin InSb layers is desirable to increase the sheet resistance, which makes it possible to reduce the size of a magnetoresistor. However, the minimum thickness of indium antimonide used in production devices is typically limited to at least 1.5 μm by crystallographic defects arising from growth on lattice mismatched substrates and by the device requirement of very large electron mobilities. The use of a highly resistive In1−x AlxSb buffer layer was studied to determine its effects on the electron mobility of the InSb active layer. With optimized buffer layers, InSb active layers with 0.55 μm thickness could be grown with electron mobilities of approximately 40 000 cm2 V−1 s−1 at room temperature and 30 000 cm2 V−1 s−1 at 200 °C.

Interactive 3-D registration of ultrasound and magnetic resonance images based on a magnetic position sensor.

The use of stereotactic systems has been one of the main approaches for image-based guidance of the surgical tool within the brain. The main limitation of stereotactic systems is that they are based on preoperative images that might become outdated and invalid during the course of surgery. Ultrasound (US) is considered the most practical and cost-effective intraoperative imaging modality, but US images inherently have a low signal-to-noise ratio. Integrating intraoperative US with stereotactic systems has recently been attempted. In this paper, we present a new system for interactively registering two-dimensional US and three-dimensional magnetic resonance (MR) images. This registration is based on tracking the US probe with a dc magnetic position sensor. We have performed an extensive analysis of the errors of our system by using a custom-built phantom. The registration error between the MR and the position sensor space was found to have a mean value of 1.78 mm and a standard deviation of 0.18 mm. The registration error between US and MR space was dependent on the distance of the target point from the US probe face. For a 3.5-MHz phased one-dimensional array transducer and a depth of 6 cm, the mean value of the registration error was 2.00 mm and the standard deviation was 0.75 mm. The registered MR images were reconstructed using either zeroth-order or first-order interpolation. The ease of use and the interactive nature of our system (approximately 6.5 frames/s for 344 x 310 images and first-order interpolation on a Pentium II 450 MHz) demonstrates its potential to be used in the operating room.

Compound Semiconductor Applications for Automotive Sensors

AbstractCompound semiconductors find extensive application as magnetic position sensors in the automotive environment. Typical applications involve the sensor element, a permanent magnet attached to the sensor, and a moving magnetic circuit -a target wheel. Wider mechanical gaps in the magnetic circuit can be utilized with a sensor of higher sensitivity, and thus high sensitivity is valuable. Further limitations on the choice of materials are imposed by temperature sensitivity, as the automotive environment is characterized by wide temperature operating ranges (-40°C up to 200°C). The magnetic signal may be hidden by the temperature drift in the sensor output, andthus temperature stability limits the sensor's resolution. Automotive position sensors find use in ignition timing and misfire detection (cam and crank sensors), as wheel speed sensors (anti-lock brakes and other types of active wheel-control), in brushless electric motors and several other applications. This work reviews progress achieved to refine the use of InSb for automotive sensing applications.

215 ウエーブレット変換を用いた差動磁気センサーの可視化信号処理

This paper proposes a vectorized signal visualization method based on a multi-resolution analysis of the discrete wavelets. We apply our approach to a signal processing of a differential type magnetic position sensor for the metallic objects. At first, to derive a frequency domain information, we apply a conventional FFT analysis to the sensor output signals. Second, we apply a wavelet transform to the sensor output signals. After expanding the sensor output signals into a multi-resolution form, we comprise a series of the signal vectors by combining the low level on and off loaded signals. As a result, we have succeeded in visualizing the no-load and target reaction output signals. Thus, it is revealed that our vectorization methodology based on the wavelet analysis may becomes one of the distinguished methodologies for a signal processing technique.

The influence of stoichiometry on the growth of tellurium-doped indium antimonide for magnetic field sensors

Indium antimonide magnetoresistors are used as magnetic position sensors in very demanding automotive environments such as crankshaft and camshaft sensors for engine control. The use of tellurium as an n-type dopant was studied using Hall effect measurements up to 200°C, Hall depth profiling, and secondary ion mass spectroscopy. The films were grown by metal organic chemical vapor deposition using trimethyl indium, trisdimethylamino antimony, and diethyl telluride. It was found that the incorporation of tellurium strongly depends upon the V/III ratio during growth, implying that it is influenced by the availability of antimony vacancies. Thus, our results show that the reproducibility of tellurium doping is not limited by memory effects in a well-designed reactor, but by the control of stoichiometry. It is now possible to grow films with optimum doping profile and with good uniformity and reproducibility over hundreds of growth runs. These films can be used to make magnetoresistors that have good sensitivity to a magnetic field and good stability over a wide temperature range.

In vitro evaluation of three-dimensional ultrasonography based on magnetic scanhead tracking

The objective of this study was to evaluate the accuracy and precision of a magnetic position sensor system for acquisition of three-dimensional (3D) ultrasound images in volume estimation of phantoms in vitro. Installation of either 0.9% solution of saline at 37° C or distilled water at 20°C to a condom was performed. Scanning was performed either by a continuous or stepwise acquisition. This 3D ultrasound system demonstrated good correlation ( r = 0.99–1.0, n = 8) between estimated (EV) and true volumes (TV). The errors were in the range 1.3% ± 0.3% (SEM) to 1.9% ± 0.6%, independent of sound velocity. Scanning through a porcine abdominal wall positioned at the fluid surface yielded a systematic underestimation of the volume: mean (EV − TV) = −7.2 ± 0.8 ml. Eight repeated scans of the same volume yielded a coefficient of variation of 1.1%. Interobserver error of the tracing procedure was 2.6% ± 0.9%. This 3D ultrasound system gave high accuracy and precision in volume estimation in vitro, and yielded low interobserver error. A change in ultrasound velocity of approximately 60 m/s did not influence the accuracy significantly. Scanning through an abdominal wall underestimated volumes slightly.

Intragastric distribution and gastric emptying assessed by three- dimensional ultrasonography

BACKGROUND & AIMS: Three-dimensional (3D) ultrasound imaging of the total stomach volume has not yet been achieved. The aim of this study was to investigate whether a magnetic position sensor system for acquisition of 3D ultrasonograms could be used to determine gastric emptying rates and intragastric distribution. METHODS: A system for position and orientation measurement was interfaced to an ultrasound scanner. In vitro accuracy was evaluated by scanning a porcine stomach. Fourteen volunteers, with a median age of 35 years, were scanned fasting and postcibally by two-dimensional (2D) and 3D ultrasound after ingesting a 500-mL soup meal. RESULTS: This 3D system yielded a strong correlation (r = 0.997) between true and estimated volumes in vitro. The limits of agreement were -9.1:70.1 mL in the volume range 1200-1900 mL. The intersubject variability of the total gastric volumes ranged from 12.5% to 46.0%, less than for antral area variability. The average half-emptying time was 22.1 +/- 3.8 minutes. Intragastric distribution of the meal, expressed as proximal distal volume, varied on average from 3.6 +/- 2.1 (5 minutes postpradially) to 2.7 +/- 1.9 (30 minutes postprandially). CONCLUSIONS: This 3D ultrasound system using magnetic scanhead tracking showed excellent in vitro accuracy, calculated gastric emptying rates more precisely than by 2D ultrasound, and enabled estimation of intragastric distribution of a soup meal. (Gastroenterology 1997 Jul;113(1):38-49)

Industrialization of Microsystems

Abstract Microsystems involve many different scientific disciplines and technical fields. Even though microsystem technology is based on IC technology, there are many important differences such as to the number of product manufactured per technology, cost and development time. These aspects have to be taken into account in the design of a microsystem development and manufacturing environment. The CSEM approach to that challenge is based on a wafer fab focusing on 3 technology families, i) bulk silicon micormechanics for capacitive pressure and acceleration sensors, ii) galvanic technology for coils for magnetic actuators and position sensors and iii) a quartz technology for UV-beam shaping applications. The associated packaging line is based on a flexible manufacturing concept to handle many product each produced in relatively low numbers. This industrialization concept is intended to respond to a fast growing market need for customized microsystem products.

Computer Assisted Knee Surgery: Diagnostics and Planning of Knee Surgery

Cruciate ligament rupture, a common injury among young active adults, disrupts the knee's complex movement and often leads to premature degenerative arthritis of the joint. Prosthetic cruciate ligaments can be used for replacement but often fail owing to incorrect surgical placement. To aid in die planning of cruciate prosthetic substitution, a computerized system has been developed to provide the surgeon with a virtual interface allowing accurate visualization of three-dimensional (3D) bone structure and movement normally hidden beneath layers of soft tissue.Preoperatively, precise in vivo kinematics are quantified with the help of 3D medical images. Three-dimensional imagery techniques based on computed tomography (CT) have been developed to obtain accurate 3D reconstruction of knee geometry preoperatively. The system allows the surgeon to know the real-time spatial position of the patient via magnetic position and orientation sensors attached noninvasively onto the femur and tibia via a new attachment system. An interactive computer program has been developed to allow the user to simulate different prosthetic ligament insertions and compute elongation, bending, and torsion values that will be imposed on the prosthesis. Through comparison with cadaver studies and a perturbation analysis, the system is shown to be sufficiently accurate to predict certain in vivo ligament bending and torsion deformations.

A state-based approach to the representation and recognition of gesture

A state-based technique for the representation and recognition of gesture is presented. We define a gesture to be a sequence of states in a measurement or configuration space. For a given gesture, these states are used to capture both the repeatability and variability evidenced in a training set of example trajectories. Using techniques for computing a prototype trajectory of an ensemble of trajectories, we develop methods for defining configuration states along the prototype and for recognizing gestures from an unsegmented, continuous stream of sensor data. The approach is illustrated by application to a range of gesture-related sensory data: the two-dimensional movements of a mouse input device, the movement of the hand measured by a magnetic spatial position and orientation sensor, and, lastly, the changing eigenvector projection coefficients computed from an image sequence.

Performance of a miniature magnetic position sensor for three-dimensional ultrasound imaging

A miniature magnetic position sensor used for three-dimensional ultrasound imaging was tested for precision and accuracy in vitro. The sensor alone was able to locate points with root-mean-square (rms) uncertainty of 1.7 mm and accuracy of 0.05 ± 0.62 mm over its specified operating range of 50 cm. With an ultrasound imaging system, a point was located from arbitrary viewing windows with 2.4-mm rms uncertainty and 0.06 ± 0.68 mm accuracy. If viewing windows were limited to those representative of a typical ultrasound examination, the system could achieve rms uncertainty in point location of < 1 mm. Performance was not affected by operation of the imaging system when the sensor was mounted on an ultrasound scanhead. Sensitivity to metals in the operating environment was also measured.

A Teaspoon Pump for Pumping Blood with High Hydraulic Efficiency and Low Hemolysis Potential.

Virtually all blood pumps contain some kind of rubbing, sliding, closely moving machinery surfaces that are exposed to the blood being pumped. These valves, internal bearings, magnetic bearing position sensors, and shaft seals cause most of the problems with blood pumps. The original teaspoon pump design prevented the rubbing, sliding machinery surfaces from contacting the blood. However, the hydraulic efficiency was low because the blood was able to "slip around" the rotating impeller so that the blood itself never rotated fast enough to develop adequate pressure. An improved teaspoon blood pump has been designed and tested and has shown acceptable hydraulic performance and low hemolysis potential. The new pump uses a nonrotating "swinging" hose as the pump impeller. The fluid enters the pump through the center of the swinging hose; therefore, there can be no fluid slip between the revolving blood and the revolving impeller. The new pump uses an impeller that is comparable to a flexible garden hose. If the free end of the hose were swung around in a circle like half of a jump rope, the fluid inside the hose would rotate and develop pressure even though the hose impeller itself did not "rotate"; therefore, no rotating shaft seal or internal bearings are required.

Arcsecond grating drive mechanism for operation at 4 K

A grating drive mechanism that achieves arcsecond positional control at both room temperature and 4 K is described. The mechanism accommodates eight equally spaced facets on a 360° drum, with each facet having arcsecond control over an angular range of ±3°. The cryogenic portion consists of dry lubricated angular contact bearings, a d.c. brushless torque motor and a compact magnetic position sensor capable of < 1 arcsec r.m.s. resolution. Test results demonstrate angular repeatability of < 2 arcsec r.m.s. at 4 K and static power dissipation to the helium bath of < 100 μW.

磁気式簡易位置センサの開発と人工心臓への応用

磁気式簡易位置センサの開発と人工心臓への応用