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- 3D sensor (2)
- Air-coupled (2)
- BLE (2)
- Bluetooth Low Energy (2)
- Ferroelectret (2)
- Fiber Bragg grating (2)
- Inertial navigation system (2)
- Magnetic field (2)
- Magnetostriction (2)
- Non-destructive evaluation (2)
Sensor based person tracking is a challenging
topic. The main objective is positioning in areas without
GPS connection, i.e. indoors. A research project is carried
out at BAM, Federal Institute for Materials Research and
Testing, to develop and to validate a multi-sensor system for
3D localization. It combines body motion sensing and a
guard system for the tracking and recording of the status of
persons. The so named BodyGuard system was designed for
sensor-based monitoring and radio-based transmission of
the movement of a person. Algorithms were developed to
transform the sensor data into a spatial coordinate. This
paper describes how the BodyGuard system operates, which
main components were used in the system, how the
individual sensor data are converted into 3D motion data,
with which algorithms the individual sensors are processed,
how individual errors are compensated and how the sensor
data are merged into a 3D Model. Final objective of the
BodyGuard system is to determine the exact location of a
person in a building, e.g. during fire-fighting operations.
Der Einsatz geführter Wellen für die
zerstörungsfreie Prüfung mit Ultraschall eröffnet neue Möglichkeiten,
räumlich ausgedehnte Bauteile mit begrenzter Zugänglichkeit
auf ihre Integrität zu prüfen und gewinnt daher
zunehmend an Bedeutung. Dieser Artikel behandelt die
physikalischen Grundlagen der Schallausbreitung. Deren Verständnis
bildet die Grundlage für die Entwicklung geeigneter
Prüfsysteme. An Beispielen werden verschiedene Möglichkeiten
zur Simulation der Schallausbereitung vorgestellt. Aktuelle
Lösungsansätze zur Prüfung von plattenförmigen Strukturen
und von Rohrleitungen werden beschrieben, wobei besonders
auf die Sensortechnik und die speziellen Anforderungen
an die Prüfhardware eingegangen wird. -----------------------------------------------------------------------------------------------------------------------------------
Guided waves are widely used for non-destructive
testing using ultrasound. Recently, the method has become increasingly
important for integrity tests of spatially extended
components with limited accessibility. This article discusses the
basic physics of the sound propagation of guided waves. Their
understanding forms the basis for the successful development
of adapted inspection systems. Examples for simulating the
wave propagation using different methods are presented. Current
approaches for the inspection of plate-like structures and
pipelines are described with focus on sensor technology and the
specific requirement on the test hardware.
In this study a method for early damage detection is investigated based on the directed excitation and measuring of Lamb waves (guided waves). The objective is to make a statement about the practicability of a Lamb wave generator (LWG) and about the application relevant parameters (specimen materials and dimensions, wave characteristics, excitation, transmission und reflection). Guided waves enable an effective differentiation of structural and defective indications as well as a classification of different defect types. For the investigations, a LWG was developed which combines the advantages of the single excitation of a piezoelectric actuator and the possibility of a group excitation. Algorithms were developed to identify and analyze damage patterns (cracks, wholes, weakening).
Limited access to the object of relevance is often an essential problem in testing routines, e.g. for non-destructive testing of industry facilities or components of means of transportation. The presented project is about the development of a non-destructive testing method for application over great distances (up to 100 m). The method is based on directed excitation and measuring of Lamb waves (guided waves). It enables an effective differentiation of structural and defective indications as well as a classification of different defect types.
The advantage of guided waves is the ability of propagation over great distances. This offers innovative possibilities for the investigation of large or difficult to access constructions. The testing method can be helpful in a broad variety of applications. It is useable for the characterization of plane or cylindrical, thin-walled surfaces of metal or fiber laminated materials. Particularly the investigation of aircraft wings and other aerospace components as well as the investigation of pipelines are addressed fields of application.
Fiber optic sensors have gained increasing importance in recent years and are well established in many areas of industrial applications. In this paper, we introduce a concept of a self-diagnostic fiber optic sensor. The presented sensor is to resolve the problems of embedded fiber optic sensors in complex structures and to enable the validation under operational conditions. For this purpose, different magnetostrictive coated fiber optic sensors were developed and various experiments were performed to verify their mode of Operation and to determine the respective reproducibility. The measuring principle is illustrated by obtained experimental results, which showed a change in wavelength from 1 pm at a magnetic field strength change of 0.25 mT.
In addition, the temperature characteristics of the implemented magnetostrictive sensor were analyzed and an experimental factor of 1.5 compared to a reference fiber optic sensor was determined.
Air-coupled ultrasound has been applied increasingly as a non-destructive testing method for lightweight construction in recent years. It is particularly appropriate for composite materials being used in automotive and aviation industry. Air-coupled ultrasound transducers mostly consist of piezoelectric materials and matching layers. However, their fabrication is challenging and their signal-to-noise ratio often not sufficient for many testing requirements. To enhance the efficiency, air-coupled ultrasound transducers made of cellular polypropylene have been developed. Because of its small density and sound velocity, this piezoelectric ferroelectret matches the small acoustic impedance of air much better than matching layers applied in conventional transducers. In our contribution, we present two different methods of spherical focusing of ferroelectret transducers for the further enhancement of their performance in NDT applications. Measurements on carbon-fiber-reinforced polymer (CFRP) samples and on metal adhesive joints performed with commercially available focused air-coupled ultrasound transducers are compared to measurements executed with self-developed focused ferroelectret transducers.
Ultrasonic testing of adhesively bonded joints using air-coupled cellular polypropylene transducers
(2014)
In air-coupled ultrasonic testing, the impedance mismatch between the transducer and the air is commonly being solved by adding matching layers to composite transducers. To avoid the difficult technological procedure regarding matching layers, some new piezoelectric materials have been proposed. Most promising are ferroelectrets, which are charged cellular polymers, having ferroelectric and consequently piezoelectric properties. In particular, the extreme softness of cellular polypropylene (cPP) leads to a high piezoelectric constant and to a good impedance match with the air, making matching layers redundant. Its elasticity modulus below 1 MPa causes an additional effect not observed with common piezoelectric materials: that is the electrostrictive effect, here defined as the thickness change due to the attractive force between the transducer electrodes. This effect exceeds the piezoelectric effect at excitation voltages over 1 kV. The extreme softness of cPP leads also to high flexibility, enabling easy focusing by bending the transducer.
We have developed air-coupled ultrasonic transducers based on cPP. This includes the electrical matching networks for the transmitter and for the receiver. The transmitter is excited with voltages up to 2.5 kV, so that the electrostrictive effect dominates, leading to sound pressure around 145dB at the transducer surface. These transducers have been applied for testing carbon-fiber-reinforced polymer plates, adhesive joints and other composite structures. Here we report about ultrasonic transmission of two types of adhesive joints. The first one is multi-layer aluminium components with some artificial disbonds, which are common in aerospace industry, and the second one is an aluminium-steel joint with polyurethane adhesive, which is used in automotive industry.
Zur Untersuchung der Sicherheit von Behältern für den Transport und die Lagerung von Gefahrstoffen und -gütern werden Fallprüfungen durchgeführt. Die Aufpralldynamik und die strukturmechanischen Einwirkungen auf den Behälter werden mittels Beschleunigungsaufnehmern und Dehnungsmessstreifen erfasst. Dabei kommen derzeit Vielkanalmesssysteme zum Einsatz, die eine Verkabelung jeder einzelnen Messstelle und somit das Mitfallen eines Kabelbaums erfordern, wodurch Probleme bei der Versuchsvorbereitung und Durchführung entstehen. Die Verwendung eines Messsystems mit Datenbus und dezentraler Datenspeicherung bietet diesbezüglich einen vielversprechenden Lösungsansatz.
A high-performance fiber Bragg grating-based (FBG) sensor device has been developed for the detection of small magnetic fields. Based on a smart multilayer jacket around the fibre over the physical length of the FBG, magnetic fields generated by rotating machine parts, power generators or power cable can be easily detected, analysed and evaluated. Consequently, this innovative, on-line and non-contact inspection method results in an increase in quality and reliability of high-performing machine parts, devices and cables. The basic physical principle is based on a magnetostrictive multilayer system that strains the high-resolution FBG element in presence of magnetic fields. Subsequently, a fixed relationship between induced magnetic field and wavelength change of the FBG element describes the characteristic sensitivity curve. Intensive tests regarding characterisation of this magnetic field FBG sensor have been carried out and its performance has been evaluated.
Die Langzeitüberwachung von Bauteilen (Structural Health Monitoring, SHM) ging in den letzten Jahren zunehmend von verkabelten Sensoren zu kabellosen Sensornetzwerken (WSN) über. Frühwarnsysteme sollen rechtzeitige Signale senden, wenn Schädigungsprozesse einsetzen, wenn ein Bauteil z. B. zu feucht wird (Deiche, Staumauern), oder wenn Feuchteprozesse in Bauteilen auftreten, die den Transport von schädlichen Stoffen ermöglichen. Mittels handelsüblicher multifunktionaler Sensoren wie einem Bluetooth Low Energy (BLE) wurden erste Machbarkeitsuntersuchungen zur Massenfeuchtemessung durchgeführt. Die untersuchten Parameter sind der sogenannte Received Signal Strength Indicator (RSSI) eines Bluetooth-Low-Energy(BLE)-Signals und die abgestrahlte Sendeleistung eines eingebetteten BLE-Moduls. Das BLE-Modul kommuniziert mit einem mobilen smarten Empfänger wie einem Tablet oder einem Smartphone als SmartHub. Die Veränderung des RSS-Indikators ist ein Maß für die Veränderung der Feuchte im Bauteil, während die ausgesandte Signalstärke konstant bleibt. Wenn das BLE-Signal einen feuchten Bereich im Baumaterial durchläuft, verändert sich der RSS-Indikator. Nach erfolgreicher Machbarkeitsstudie wurde nun ein aus dem Netzwerk MI4G (Modern Industry for Germany) zwischen der Bundesanstalt für Materialprüfung und dem Klein- und mittelständigen Unternehmen LinTech GmbH heraus beantragtes ZIM-Projekt bewilligt. Der Bericht zeigt erste Ergebnisse von Voruntersuchungen und gibt einen Ausblick auf weitere Forschungsaktivitäten.