Experimental Facilities and
Associated Experimental Laboratories
Students in the Acoustics Program can use equipment and facilities in a number of Penn
State laboratories and participate with the faculty in ongoing research programs. The
cooperating facilities and laboratories are housed within the College of Engineering, the
Physics department, the Communication Disorders department and the Applied Research Laboratory (ARL).
Some specialized laboratories are described more in detail and the contact faculty are
indicated.
- Acoustic Intensity Laboratory (J. Tichy)
- The intensity measurement system consists of a computer-controlled robot with
three-dimensional motion capability. The actual sensors consist of four pressure
microphones for simultaneous measurement of two components of the intensity vector. The
signal processing is based on measurement of the sound pressure autospectra and
cross-spectra by a MASSCOMP computer. The system generates two- or three-dimensional sound
field maps of a real or imaginary component of the complex intensity vector, sound
pressure, particle velocity vector, acoustic impedance and both potential and kinetic
energy densities.
This system has been used for research on sound field radiation and
nearfield studies of discrete source configuration; sound power radiation and modal
behavior of thin steel plates; sound field mapping for sound interference in ducts;
mapping of diffracted sound field behind noise barriers; detailed studies of the sound
radiator coupling on loudspeaker enclosures; and noise radiation from an impact excited
printing wheel.
- Flow-through Anechoic Chamber (G. C. Lauchle)
- The Applied Research Laboratory has a 22,800 cu.ft. anechoic chamber with the capability
to study the acoustic noise of air-moving machinery. One wall is not only anechoic but
permeable to flow. Air can pass through this wall without turbulent flu ctuations at a
rate in excess of 300 cu.ft./s. Behind this wall is a large plenum that connects to low
resistance ducting that passes over the roof of the chamber. This ducting can then connect
to a control room where the air moving device under test is located. One such device is a
moving-wall wind tunnel that is used to simulate the flow field under automobiles, while
another is a large axial-flow turbomachine. The cut-off frequency of the anechoic chamber
is 70 Hz. Wire mesh platforms can be mount ed on the floor above the wedges, or the floor
wedges can be removed completely to make the chamber into a hemi-anechoic chamber.
- Large Water Tank (W.J.
Hughes)
- The Applied Research Laboratory has a 9,000 cu.ft. water tank, with mobile experimental
platforms and mid-depth window portals, for use with laser based experiments and for
viewing of submerged equipment. The tank is equipped with a measurement positioning system
that is automated in two dimensions and can be manually positioned in the third.
- Moving-Wall Wind Tunnel (G. C. Lauchle)
- An open-circuit moving-wall wind tunnel is in operation at the Applied Research
Laboratory Flow-Through Anechoic Chamber. It was developed to study the fluid mechanics
and acoustics of the complex flow field beneath a moving automobile (or any other ground
effects vehicle). One wall of the rectangular test section is a mylar belt that is
supported by large rollers at the up and downstream ends of the tunnel. Air is supplied by
a large centrifugal blower located in a sound isolation enclosure. Flow from the blower is
conditioned by passing it through an expansion section, turbulence suppressing screens,
and then a 9:1 contraction section. Maximum flow and wall speed achieved in this facility
is 70 ft/s. Hot-wire anemometry and microphone systems are available to measure the flow
and acoustic parameters of interest.
- HVAC Flow Simulation Facility (G. C. Lauchle)
- Located on the ground floor of the New ARL Building is an ad hoc facility designed to
simulate the flow field and acoustic modes found in industrial heating, ventilation, and
air conditioning (HVAC) ducts. The flow field in the long rectangular duct is driven by an
isolated centrifugal blower. The maximum flow speed is 25 ft/s, and turbulence levels vary
from as high as 50% to as low as 10% depending on location downstream from the blower. A
hot-wire anemometry system is available to measure the tu rbulence, and microphone systems
are available to map acoustic fields in the duct along with wall pressure statistics.
- Flow Noise Tow Tank Facility (G. C. Lauchle)
- Located on rubber bladders which rest upon a bedrock foundation in the basement of the
New ARL Building is a 30 foot long tow tank. This facility is equipped with a
precision-controlled tow carriage that permits small bodies to be towed in water (or other
liquids such as glycerine) in order to measure the flow-induced noise created by these
moving bodies. Typically, the test bodies are acoustic sensors such as pressure, or
pressure gradient hydrophones which may be exposed to ocean currents in real applications.
The ambient noise of this facility is equivalent to that sensed in the deep ocean under
sea state 1 conditions.
- Noise Control Laboratory (G.H. Koopmann)
- The Noise Control Laboratory occupies six laboratories with a combined area of
approximately 4500 sq.ft. The primary facilities of the laboratory are an anechoic
chamber, a hemi-anechoic chamber and a reverberant chamber, with a common control room for
housing of instrumentation. Several other rooms are available for special projects, data
reduction, and electronic maintenance and instrumentation development, and for graduate
student offices.
The anechoic chamber has usable dimensions of 14' x 17' x 9' and a
cutoff frequency of 125 Hz. The hemi-anechoic chamber is a larger room measuring 20' x 25'
x 18' and has a cutoff frequency of 125 Hz. Both chambers are equipped with ventilation,
temperature, and humidity controls. The reverberant chamber has a volume of 5000 cu.ft.
and inside dimensions of 22' x 19' x 12'. The reverberation time of the chamber is
approximately five seconds at 1000 Hz.
The Noise Control Laboratory is equipped with a full complement of modern
instrumentation including a large variety of transducers, accelerometers, instrumentation
amplifiers, pressure and temperature transducers. A 14 channel FM analog tape recorder,
and several smaller 7, 4 and 2 channel recorders are available for laboratory or field
measurements. The electronic maintenance and instrumentation development facility is
staffed with a highly experienced electronic technician, whose duties include
instrumentation, calibration and the design and construction of specialized analog and
digital electronics.
Data acquisition and analysis systems in the laboratories include a DEC 5000
workstation, several modern modal analysis systems, and hardware and software for
performing acoustic intensity analysis. Computation needs are supported by numerous IBM
compatible and MacIntosh personal computers. Projects requiring more computing power
utilize the extensive facilities of the College of Engineering Computer Center. Access to
the Von Neumann Supercomputer Center at Princeton is also available.
The laboratory can support research on active noise and vibration control and
optimization of mechanical systems, methods for computing surface intensities and power of
vibrating structures, actively controlled, high transmission loss composite materials,
atmospheric propagation, and uses of high intensity sound to control industrial processes,
particularly air pollution caused by coal burning power plants.
- Acousto-Optic Imaging Laboratory (S. I. Hayek)
- The Acousto-Optic Imaging Laboratory is a facility for visualization and quantification
of acoustic fields. The facility can be used to visualize the acoustic field generated by
acoustic emission, radiation, and scattering. The facility can also be used to measure the
acoustic impedance of materials, pinpoint defects and faults inside bulk materials and
structural components, identify sources of noise emission and diffraction, and identify
paths of structural wave propagation. The laboratory includes a Schlieren system,
electronic imaging system, and a supporting computer facility.
The Schlieren facility
includes two Spectra Physics continuous 50 mW lasers, an Isomet diffraction system, a
collimator lens system, a Sony Video-camera, an automated scanner, optical benches, a
frequency generator, a pulse generator, a Dranitz time gate, amplifiers, and transducers
in 0.2-10MHz. range.
The imaging system consists of two GE 9505 electronic charged-coupled device cameras
and IRI-256 systems containing image storage buffers, digital pre-processors, a
co-processor, a host computer, and a monitor which can be used to store the visual images
produced by diffracted acoustic fields.
- Ultrasonic Diagnostics Laboratory (J. C. Conway, Jr.)
- The Ultrasonics Laboratory has equipment suitable for ultrasonic non-destructive
evaluation including contact and immersion C-Scan (pulse echo and through transmission),
specialized flaw detection devices, scanning confocal microscopy, scanning acoustic
microscopy, and speckle interferometry. Specimens can be insonated over a frequency range
of from 1 kHz to 1 GHz.
The laboratory can support a variety of research projects
including ultrasonic flaw detection in ceramic preforms and metal metal matrix composites,
damage evaluation in impacted polymeric composites, thin films characterization and bond
strength evaluation, and texture characterization in copper and bronze sheet material.
- Acoustic Microscopy/Spectroscopy Laboratory (B. Tittmann)
- The focal point of this laboratory is the scanning acoustic microscope (SAM) which
allows subsurface examinations of a variety of materials, especially thin coating sand
films, but also deep level examination of composites and other strategic structural
materials. The SAM operates in the frequency range from 30 MHz to 1000 MHz and so goes far
beyond the conventional ultrasonic C-Scan typically carried out between 1 MHz and 15 MHz.
At 1000 MHz the instrument offers nearly optical type of high resolution for sub-surface
nondestructive microscopy. Only a few laboratories in this country and around the world
possess such an instrument, giving Penn State a unique capability in acoustics. Current
in-house modifications will extend the range of operations to include acoustic
spectroscopy, the analysis of acoustic waveforms in the frequency domain.
The
laboratory can support projects including diamond thin film characterization, impact
damage evaluation in graphite fiber/epoxy composites, ceramic preforms and texture
evaluation.
- Medical Ultrasonics Laboratory (K. K. Shung)
- Major facilities include a Technicare 280S/L sector and linear real-time ultrasonic
scanner, a Unirad linear array real-time ultrasonic scanner, a Sonocaid Continuous Wave
Ultrasonic Doppler Flowmeter for transcutaneous blood-flow measurements, a DEC PDP 11/73
minicomputer, a DEC PDP 11/23 microcomputer, a Biomation 8100 100 MHz Digitizer, a
Tektronix 390AD 60 MHz digitizer, a Ramtek 6211 Color Graphics terminal, a Peritek
512x512x8 video generation board, and other computer peripherals. Electronic equipment
includes several high- energy Metrotek pulsers, function generators, 3 wideband
amplifiers, one KB-Aerotech pulser-receiver, a Hewlett-Packard RF spectrum analyzer, one
40-watt power amplifier, several oscilloscopes, and two scope monitors. The acoustical
apparatus includes ultrasonic transducers with resonant frequency ranging from 2.25 MHz to
20 MHz, 5 wideband hydrophones, and a water tank with positioning devices.
The
laboratory can support research on the ultrasonic transmission and scattering
characteristics of body tissue and organs.
- The Applied Research Laboratory (ARL) is the largest of eleven interdisciplinary
research units at Penn State. Sponsored almost exclusively by the U.S. Navy, ARL supports
more than fifty applied and basic research projects related to acoustics.
Researchers
at the Applied Research Laboratory have an excellent selection of equipment and facilities
with which to conduct their research including two underwater anechoic tanks, three high
pressure tanks, an underwater reverberation chamber, a noise analysis room, the largest
water tunnel in the world, two smaller water tunnels, a wind tunnel, a clean room for
transducer fabrication, a general acoustics laboratory, and specialized vibration and
materials laboratories as well as machine shops and electronic construction facilities.
These facilities are used to support research on radiated noise; gear noise generation;
vibration control using constrained layer damping and compound isolation mounts; materials
for acoustic absorption and transmission; flow and acoustic induced vibrations;
hydrodynamic flow noise; acoustic scattering and diffraction; structural acoustics;
underwater sound propagation, particularly reverberation and bottom loss effects; adaptive
signal and array processing; high resolution image processing; acoustic signal analysis;
sonar guidance and control; and electroacoustic transducers.
Other University Laboratories
- Nearfield Acoustic Holography Laboratory - Department of Physics (J. D. Maynard)
- The nearfield acoustic holography (NAH) facility for airborne sound consists of a large
microphone array in an anechoic chamber. The microphone array is constructed with a square
aluminum I-beam frame on which is attached a 16 x 16 latticework of 0.8mm steel wires. The
microphones are attached at the intersections of the wires, resulting in a 256 element
array. The microphones are small (1 cm) and spaced at 0.18m intervals, resulting in an
open array that minimizes the perturbation of the sound field of the source. The vibrating
structure to be studied is positioned only a few centimeters below the array so that the
evanescent wave components from the source may be measured. Signals from the microphones
are multiplexed to a 4-MHz analog-to-digital converter. Digitized data, consisting of 256
time sequences recorded simultaneously at the 256 microphone sites, are stored in a high
speed buffer memory. The contents of the buffer are passed through an on-line minicomputer
to a dedicated array processor that executes the temporal and spatial Fourier transforms,
performs other special data processing, and generates a variety of graphical displays. A
high-speed vector graphics system is used to obtain animated reconstructions of vibrating
surfaces, etc. Because the data throughout the entire array is recorded simultaneously,
wideband noise sources may be recorded with a single measurement in a fraction of a
second. Holographic reconstructions of such sources reveal the real-time interactions of
parts of the source that have different degrees of spatial and temporal correlation. While
other holographic reconstruction systems require that the measurement and reconstruction
surfaces be level surfaces of separable coordinate systems (i.e. planes, cylinders,
spheres, etc.), the Penn State NAH system incorporates unique algorithms using finite
element and singular value decomposition techniques that permit a numerical determination
of Green's functions and a complete reconstruction of sources that have arbitrarily shaped
surfaces.
The laboratory can support research on the vibration and sound radiation from
plates of different shapes and ribbing, including those that are used in musical
instruments; on nearfield acoustic holography techniques for analyzing sound sources; on
cryogenic studies of shear viscosity of fluids, in the frequency range of 100 kHz to 10
MHz; and on diffraction studies on three-dimensional bodies in which Keller's and
Freeman's echo theories are compared with experimental results.
- Hearing Research Laboratory - Communication Disorders Program (T. A.
Frank)
- Facilities include mechanically and electrically isolated quiet rooms, an anechoic
chamber, and instrumentation and test areas. Modern equipment includes general-purpose and
precision instrumentation, as well as portable instruments and accessories for measuring,
processing, recording and analyzing acoustical and audiological data. These facilities can
accommodate research on hearing protection, audiology, hearing science, effects of sound
and vibration on man, communication and communications systems, and general environmental
noise problems.
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