Acoustic Sensor System Research Articles

Acoustic sensing for urban battlefield applications.

For years, acoustic sensor systems have been used effectively in a variety of battlefield applications due to its low-cost, low-power, non-line-of-sight and 360 deg coverage capabilities. Acoustic (only) systems can autonomously detect, track, and classify a variety of targets: personnel, ground vehicles, airborne targets, and transient events. In recent years, acoustics has become an important sensing technology due to its complementary sensing capability within multi-modal sensor systems, and its wide-area coverage capability to alert and point other hi-resolution sensors within a network of sensor systems for intelligent-surveillance-reconnaissance (ISR). For example, in a multi-modal sensor system, acoustic can provide enhanced detection and discrimination of targets and activities, and cue imaging sensors to capture the events of interest. Similarly, in a network of ISR sensor systems, acoustic can reduce the search space for other ISR sensors to autonomously track and locate events of interest in real time. In this discussion, we will present an overview of battlefield acoustic applications that are of current interest to military operations: (i) detection and localization of transients, (ii) sensing from mobile and aerial platforms, and (iii) sensing within a network of ISR sensor systems. We will then discuss the signal processing strategies and challenges associated with the applications.

Development of a combined surface plasmon resonance/surface acoustic wave device for the characterization of biomolecules

It is known that acoustic sensor devices, if operated in liquid phase, are sensitive not just to the mass of the analyte but also to various other parameters, such as size, shape, charge and elastic constants of the analyte as well as bound and viscously entrained water. This can be used to extract valuable information about a biomolecule, particularly if the acoustic device is combined with another sensor element which is sensitive to the mass or amount of analyte only. The latter is true in good approximation for various optical sensor techniques. This work reports on the development of a combined surface plasmon resonance/surface acoustic wave sensor system which is designed for the investigation of biomolecules such as proteins or DNA. Results for the deposition of neutravidin and DNA are reported.

The deep sea Acoustic Detection system AMADEUS

As a part of the ANTARES neutrino telescope, the AMADEUS (ANTARES Modules for Acoustic Detection Under the Sea) system is an array of acoustical sensors designed to investigate the possibilities of acoustic detection of ultra-high energy neutrinos in the deep sea.The complete system will comprise a total of 36 acoustic sensors in six clusters on two of the ANTARES detector lines. With an inter-sensor spacing of about one metre inside the clusters and between 15 and 340 metres between the different clusters, it will cover a wide range of distances as will as provide a considerable lever arm for point source triangulation. Three of these clusters have already been deployed in 2007 and have been in operation since, currently yielding around 2GB of acoustic data per day. The remaining three clusters are scheduled to be deployed in May 2008 together with the final ANTARES detector line.Apart from proving the feasibility of operating an acoustic detection system in the deep sea, the main aim of this project is an in-depth survey of both the acoustic properties of the sea water and the acoustic background present at the detector site. It will also serve as a platform for the development and refinement of triggering, filtering and reconstruction algorithms for acoustic particle detection.In this presentation, a description of the acoustic sensor and read-out system is given, together with examples for the reconstruction and evaluation of the acoustic data.

Selection process generating peptide aptamers and analysis of their binding to the TiO2 surface of a surface acoustic wave sensor

The set-up presented in this article is intended for the selection of peptides which serve as specific binders to suitable materials. Additionally, the interaction of such binders with material surfaces can be characterized. Using this approach, a subset of peptides which adhere to the mineral TiO2 was generated by means of a cell surface display library. The peptides are constrained by a thioredoxin scaffold. Selection of proteins was carried out on a silicium wafer sputtered with TiO2 in anatase conformation. To verify binders and to analyze the binding kinetics of the diluted suspension of the purified proteins, the chip-based S-sens® K5 surface acoustic wave sensor system was used. The surface of the sensor chips was also TiO2, resembling the material of the Si wafer selection target retaining the peptides. Several peptides were identified. The respective binding behavior differed. The data derived from real-time interaction analysis were evaluated to select for strong and specific binders. For one of these peptides, the binding kinetics was analyzed. On- and off-rate binding constants were extracted from the fitted curves. With the resulting association rate constant kon and the dissociation constant koff, the affinity of the peptide for the TiO2 surface was calculated, represented by the equilibrium dissociation constant KD=81nM.

Environmental effects on short-range acoustic propagation and sensor performance.

Autonomous passive acoustic sensor systems can potentially detect, identify, and locate sound emissions from gunfire, explosions, vehicles, and animals. However, since sound propagation through the atmosphere is influenced by many environmental conditions including meteorology, ground impedance, and barriers or obstacles, these effects need to be understood and included in sensor system design to achieve accurate performance. Low-frequency short-range measurements using impulsive sources will be presented to quantify these effects on acoustic wave form shape and amplitude attenuation. In urban areas, multiple reflections and diffractions can add enough complexity to explosion wave forms that it becomes difficult for a human listener to identify them as explosions. In these areas, classical methods to determine source locations such as beam-forming or direction-of-arrival bearing estimates from time delays can fail completely. Novel signal processing methods that incorporate the complexity of propagation in these environments can produce accurate localizations. [Work funded by U.S. Army.]

Estimation of the lactate threshold using an electro acoustic sensor system analysing the respiratory air

The lactate threshold is used by athletes to optimise the intensity during exercise. It is of interest to measure the threshold on the very day and during the present sport activity. Steady state ergometer tests have been performed on 40 individuals to compare the threshold found by an electro acoustic sensor system to the lactate threshold established by blood analyses evaluated with the Dmax method. The correlation coefficient between the threshold found by the sensor system and the one established by blood analyses regarding workload (Watt), heart rate (beats/min), and lactate level (mmol lactate/l blood) at the thresholds were 0.87 (p < 0.001), 0.74 (p < 0.001), and 0.65 (p < 0.001), respectively. The findings in this study indicates that the thresholds of individuals measured by the sensor system show good correlations to the threshold established with the Dmax method from lactate levels in blood samples.

Acoustic sensor systems on a flying wing underwater glider and two prop‐driven autonomous underwater vehicles

The Marine Physical Laboratory, Scripps Institution of Oceanography operates several underwater vehicles including an autonomous underwater glider based on a flying wing design and two prop‐driven autonomous underwater vehicles (AUV) manufactured by Bluefin Robotics. The objective of this presentation is to describe the acoustic sensor systems on these platforms and provide sample results from the at‐sea data. The glider, with a 6.1‐m wing span, was developed jointly by the Marine Physical Lab and the Applied Physics Laboratory, University of Washington. It is designed to maximize the horizontal distance traveled between changes in buoyancy (i.e., maximize its "finesse") while quietly listening to sounds in the ocean. A 27‐element hydrophone array with 5 kHz per channel bandwidth is located in the sonar dome all along the wing's leading edge. In addition, it has a four‐component acoustic vector sensor in its nose. The two prop‐driven AUVs have been equipped with hull‐mounted hydrophone arrays with 10 kHz bandwidth for passive synthetic aperture studies, an acoustic vector sensor, and active acoustic imaging systems for ocean bottom/subbottom mapping. Results from the data processing illustrate the tight coupling between acoustic sensor systems, signal/array processing methods, and vehicle behavior. [Work supported by the Office of Naval Research.]

Networking and Fusion of Disparate Acoustic Sensors for Battlespace Applications

A network of distributed acoustic sensor systems on the ground and/or in the air can be used effectively for autonomous and remote intelligence, surveillance, and reconnaissance (ISR) applications. However interoperability of disparate sensor systems is a major challenge for current coalition force applications. Specifically, a network of acoustic sensor nodes can exhibit heterogeneity in a variety of dimensions. At the sensor‐level, the acoustic sensors can vary in their types (e.g., cardioid vs. omni‐direction) and in their responsiveness to transient and continuous sources. At the node‐level, the acoustic systems can vary in their array configuration, platform mobility, node reactiveness (e.g., timeliness of response), and information processing and output. At the network‐level, the acoustic systems can vary in their communication protocols and access mediums. Current R&D efforts within the US‐UK International Technology Alliance seek to develop a "sensor fabric" technology to seamlessly connect disparate systems for networked sensing applications. Results from a recent field experiment to detect and locate moving ground targets, weapon firings, and explosions via a network of disparate acoustic sensor systems and sensing platforms (e.g., PDA's, workstations, motes and unattended ground sensor systems) are presented.

An acoustic sensor system for localizing RF breakdown in warm copper accelerating structures

X-band accelerator structures meeting the Next Linear Collider (NLC) design requirements have been found to suffer damage due to Radio Frequency (RF) breakdown when processed to high gradients [F. Le Pimpec, et al., in: LINAC 2002, Korea, SLAC-PUB-9526, 2002 [1]]. Improved understanding of these breakdown events is desirable for the development of structure designs, fabrication procedures, and processing techniques that minimize structure damage. Acoustic sensors attached to an accelerator structure can detect both normal and breakdown RF pulses [M. Gangeluk, et al., Acoustic monitoring system of RF breakdowns inside the electrodynamics structure at Kurchatov SR source accelerator, in: EPAC, P.1986, 1994 [2]]. Using an array of acoustic sensors, we have been able to pinpoint both the cell and azimuth location of individual breakdown events. This permits studies of breakdown in time and in space, so that underlying causes can be determined. This technique provided a significant understanding of breakdown in the structure input coupler.

Investigations of thin film structures of WO 3 and WO 3 with Pd for hydrogen detection in a surface acoustic wave sensor system

A single thin film sensor structure of WO 3 (∼ 50 nm) and bilayer sensor structure of WO 3 (∼ 50 nm) with a very thin film of palladium (Pd ∼ 18 nm) on the top, have been studied for hydrogen gas-sensing application at ∼ 30 °C and ∼ 50 °C. The structures were obtained by vacuum deposition (first the WO 3 and than the Pd film) onto a LiNbO 3 Y-cut Z-propagating substrate making use of the surface acoustic wave method and additionally (in this same technological processes) onto a glass substrate with a planar microelectrode array for simultaneously monitoring of the planar resistance of the structure. In the case of a bilayer structure a very good correlation has been observed between these two methods — frequency changes in SAW method correlate very well with decreases of the bilayer structure resistance. These frequency changes are on the level of 2.4 kHz to 4% of hydrogen concentration in dry air, whereas in the case of a single WO 3 structure almost no frequency shift is observed.

Surface acoustic wave sensor methods and systems

Sensor systems and methods are disclosed herein, including a sensor chip, upon which at least two surface acoustic wave (SAW) sensing elements are centrally located on a first side (e.g., front side) of the sensor chip. The SAW sensing elements occupy a common area on the first side of the sensor chip. An etched diaphragm is located centrally on the second side (i.e., back side) of the sensor chip opposite the first side in association with the two SAW sensing elements in order to concentrate the mechanical strain of the sensor system or sensor device in the etched diagram, thereby providing high strength, high sensitivity and ease of manufacturing thereof.

Laser pumped compact acoustic sensor system

An acoustic transducer system for acoustic signals in water has at least one hollow spherically-shaped shell for vibrating in response to acoustic signals impinging from the water. The hollow spherically-shaped shell has one or more portions that are reflective of impinging radiation, and a resilient matrix in contact with the water resiliently supports the responsive hollow shell. A laser Doppler velocimeter transmits radiation onto the reflective portion (portions) and receives reflected radiation from the reflective portion (portions). The reflected radiation generates signals in the laser Doppler velocimeter that are representative of the acoustic signals from the water medium. A computer receives the representative signals from the laser Doppler velocimeter and displays them on an interconnected display to determine direction and range to a target. The acoustic signals can originate from the target or can be reflected portions of acoustic energy transmitted from an acoustic projector.

Relative positioning for team robot navigation

The research presented in this paper approaches the issue of robot team navigation using relative positioning. With this approach each robot is equipped with sensors that allow it to independently estimate the relative direction of an assigned leader. Acoustic sensor systems are used and were seen to work very effectively in environments where datum relative positioning systems (such as GPS or acoustic transponders) are typically ineffective. While acoustic sensors provide distinct advantages, the variability of the acoustic environment presents significant control challenges. To address this challenge, directional control of the robot was accomplished with a feed forward neural network trained using a genetic algorithm, and a new approach to training using recent memories was successfully implemented. The design of this controller is presented and its performance is compared with more traditional classic logic and behavior controllers.

Power consumption analysis of surface acoustic wave sensor systems using ANSYS and PSPICE

The power consumption of a surface acoustic wave (SAW) sensor system was investigated using ANSYS and PSPICE. Simulation results show that several design parameters of the surface acoustic wave sensor, such as the center distance between two interdigital transducers (IDT), the thickness of the piezoelectric substrate, the finger space of the IDT, etc., can greatly affect the power consumption of the whole system. The results of this study will be helpful to optimum design and fabricate the SAW sensor systems with very low-power consumption.

Photocoupling of fibronectin to titanium surfaces influences keratinocyte adhesion, pellicle formation and thrombogenicity

Objectives Coating of implant surfaces with biomolecules can influence basic host responses and enhance subsequent tissue integration. The biological factors have to be immobilized on the implant material. Human fibronectin (Fn) was used as a model protein and covalently coupled to titanium (Ti) surfaces via silanization and an anthraquinone linker. The impact on several aspects of initial host/biomaterial interactions (keratinocyte adhesion, platelet interactions and pellicle formation) was studied. Methods Coupling efficiency was characterized by immunological techniques. The effects of coupled Fn on initial host/biomaterial interactions were assessed. Cell adhesion and spreading were investigated by fluorescent staining, pellicle formation by an acoustic sensor system (quartz crystal microbalance with dissipation, QCM-D), and platelet adhesion as one parameter mediating the inflammatory response by scanning electron microscopy (SEM) and immunological assays. Results Coupling efficiency was related to irradiation time used for photochemical coupling of the UV-activated anthraquinone to the silanized Ti surface. With an optimized protocol, the amount of Fn coupled to the surface could be almost doubled compared to standard dip-coating methods. On the anthraquinone-coupled Fn coatings, cell adhesion and spreading of human keratinocytes was significantly enhanced. Online detection of pellicle formation revealed strong reversibility of saliva protein adhesion on Fn coated surfaces compared to the pure Ti surface. Furthermore, the Fn coated Ti showed a low thrombogenicity. Significance This study suggests that anthraquinone-coupled biological coatings may be useful for biofunctionalization of Ti dental implants by enhancement of soft tissue re-integration (restoration of the epithelial seal) combined with diminished pellicle formation.

Autonomous acoustic sensing on mobile ground and aerial platforms

Acoustic sensor systems on the ground and/or in the air can be used effectively for autonomous and remote intelligence surveillance and reconnaissance (ISR) applications. Acoustic sensors can be used as primary sensors and/or secondary sensors to cue other higher-resolution sensors for detection, tracking and classification of continuous and transient battlefield acoustic events such as ground vehicles, airborne aircraft, personnel, indirect fire, and direct fire. Current collaborative research activities at ARL in acoustic sensing from mobile ground platforms such as HMMWVs and small robotic vehicles [P. Martin and S. Young, Proc. of SPIE Defense &amp; Security Symposium, 2004] and from aerial platforms such as UAVs and balloons [Reiff, Pham et al, Proc. of the 24th Army Science Conference, 2004] demonstrate practical performance enhancements over fixed ground-based platforms for a number of ISR applications. For both mobile ground and aerial platforms, self-generated noise (flow noise and platform noise) is problematic but they can be suppressed with specialized windscreens, sensor placement, and noise cancellation technology. Typical acoustic detection and processing results for mobile platforms are compared and contrasted against fixed ground-based platforms.

Acoustic methods for tactical surveillance

Smart acoustic sensor systems can be deployed for the automatic detection, localization, classification and tracking of military activities, which are inherently noisy. Acoustic sensors are appealing because they are passive, affordable, robust, and compact. Also, the propagation of sound energy is not limited by obstacles that block or obscure the clear line of sight that is required for the effective operation of electromagnetic systems. Methods, with examples, for extracting tactical information from acoustic signals emitted by moving sources (air and ground vehicles) are provided for both single sensor and multiple sensor configurations. The methods are based on processing either the narrowband or broadband spectral components of the sources’ acoustic signature. Weapon firings generate acoustic impulses and supersonic projectiles generate shock waves enabling source localization and classification by processing the signals received by spatially-distributed sensors. The methods developed for land-based acoustic surveillance using microphone data are also applied to hydrophone data for passive acoustic surveillance of the underwater environment.

Multifunctional sensor system for high-throughput primary, secondary, and tertiary screening of combinatorial materials

A modular multifunctional acoustic wave thickness shear mode sensor system has been designed and implemented for the rapid characterization of materials. The sensors are arranged as a 6×4 array and are compatible with available 24-well plates for manipulation with standard robotic equipment. The sensor system has two types of sensor enclosures including a gas-flowthough cell for studies of vapor-sorption properties and weathering of materials and a platform for immersion of sensors into 24-well plate arrays for studies of materials solubility. In addition, the sensor array design can be operated remotely from the rest of electronic components to decouple the environment of sensor array exposure (e.g., high temperature, pressure, chemicals). This sensor system has been used to screen sensor materials to emphasize (1) the magnitude of sensor response to the parameter of interest; (2) sensor specificity against environmental interferences; and (3) long-term stability. This work for the first time addresses all three aspects in sensor material development with a dedicated three-level high-throughput screening approach. The primary screen is the discovery screen where materials are exposed to a single analyte concentration. The secondary screen is the focused evaluation where the best subset of these materials is exposed to analytes and interference. The tertiary screen involves evaluation of material performance under conditions that mimic the long-term application. This approach can efficiently screen sensor materials not only for immediate performance but also for long-term stability thus providing significant saving of time in sensor development.

New virtual sonar and wireless sensor system concepts

Recently, exciting new sensor array concepts have been proposed which, if realized, could revolutionize how we approach surface mounted acoustic sensor systems for underwater vehicles. Two such schemes are so-called ‘‘virtual sonar’’ which is formulated around Helmholtz integral processing and ‘‘wireless’’ systems which transfer sensor information through radiated RF signals. The ‘‘virtual sonar’’ concept provides an interesting framework through which to combat the dilatory effects of the structure on surface mounted sensor systems including structure-borne vibration and variations in structure-backing impedance. The ‘‘wireless’’ concept would eliminate the necessity of a complex wiring or fiber-optic external network while minimizing vehicle penetrations. Such systems, however, would require a number of advances in sensor and RF waveguide technologies. In this presentation, we will discuss those sensor and sensor-related developments which are desired or required in order to make practical such new sensor system concepts, and we will present several underwater applications from the perspective of exploiting these new sonar concepts. [Work supported by ONR.]

Multimode and multifrequency gigahertz surface acoustic wave sensors

A simple surface acoustic wave sensor system is presented that combines the advantages of multifrequency/multimode operation and GHz frequencies in a single acoustic device structure. Analyzing multiple frequencies and modes is the basis for the multicomponent analysis of gases and liquids. The sensor system is based on floating electrode unidirectional transducers that allow efficient excitation of two modes and up to 48 harmonics (or 5 GHz). It can be fabricated without the need of costly nanofabrication techniques. Higher sensor frequencies are advantageous as the sensitivity increases with the frequency. We tested the basic operation of our sensor system by applying it to humidity sensing without a sensitive layer.