Specifications.docx

BACKGROUND:

NASA is performing research involving the scattering of ultrasound from fiber-reinforced composite materials. Figure 1A depicts a general ultrasonic scattering event, in which an ultrasonic source impinges upon a target object, resulting in ultrasound scattering in many directions in the surrounding medium. In practice, ultrasonic interrogation has concentrated upon measuring the scattered (or reflected) ultrasound returning along the original input direction, otherwise known as backscattered ultrasound. The current research is broader in scope, involving the measurement of the scattered field over a range of angles, including, but not limited to, the incoming direction.

Furthermore, the class of scattering targets of interest are the fibers and potential flaws or damage contained within fiber-reinforced composite laminates, measured in a water immersion system, as depicted in Figure 1B. Refraction of the ultrasound at the water-composite interface will limit the range of incident angles.

The method selected to measure the scattering described is to employ a sparsely-sampled array, with transducer elements distributed in angle over the face of a spherical surface of constant radius. The government seeks to procure such an array to be interfaced with a government-owned Verasonics Vantage 256 measurement system, as depicted in Figure 2.

SPECIFICATIONS:

The government requires a two-dimensional ultrasonic array probe with the following characteristics:

Mechanical

· Immersion: The probe shall be designed to operate in water.

· Housing: The probe shall have a housing made of stainless steel or other water-resistant materials which can provide adequate electrical shielding and mechanical stability. Any non-metallic materials shall be rot-resistant and geometrically stable under conditions of extended immersion in water (1 meter or less).

· Mechanical mounting: The probe shall have, as a method of mounting, a 5/8-inch 24 tpi threaded rod with a central opening compatible with standard UHF male connectors, enabling the array probe to be mechanically substituted for a conventional immersion transducer in a conventional scanning system. This mounting rod shall be coaxial with the geometrical axis of the probe, and shall allow rigid movement and positioning of the probe at any angle.

· Cable: The probe shall have an integral cable, which is a minimum of 3 meters in length, terminating in a pair of Hypertronics 160-pin male plug connectors, one holding 128 elements and the other holding the remainder of elements. The probe is to be used with a Verasonics Vantage 256 array system fitted with a UTA 160-DH/32 Lemo adapter, depicted in Figure 2. If the offeror does not already have a nondisclosure agreement (NDA) in place with Verasonics, then a signed NDA will have to be executed before disclosure of the connector pin-outs can be obtained.

Array

· Spherically contoured aperture: The active face of the probe shall be concave, in the shape of a portion of a spherical surface, with a radius of curvature of between 2.0 inches and 3.0 inches.

· Number of elements: The active aperture of the probe shall be populated by no more than 256 independent array elements. If less than 256, the number of elements shall be as close to 256 as is practical within the constraints of the design. (See Note 1.)

· Ultrasonic frequency characteristics: Each array element shall have center frequency at or near 10 MHz, with 6 dB bandwidth of 50% or greater. (See Notes 2 and 3.)

· Element distribution: The circular elements shall be uniformly distributed over the angular face of the probe, and shall be of such size as to cover as much of the area of the aperture as possible. The nominal distribution shall be hexagonally arranged in angle, as shown in Figure 4.

· Similarity: The individual elements shall be nominally identical, except for position. (See Note 4.) The intent is to mimic a single transducer element being moved to all the different positions for measurement.

· Ultrasonic sensitivity: It is anticipated that the signals to be measured using this probe will be low in magnitude. Consequently, each element shall have excellent transmit efficiency and receive sensitivity. (See Note 3.)

· Central element: One array element shall be located at the geometrical center of the active aperture and oriented along the mechanical axis of the probe. This location shall define the polar angle of zero degrees.

· Subtended angle: The active area of the spherically-contoured probe face shall subtend a polar angle of 45° from the geometrical axis of the probe. This means that the elements located at the most extreme angle shall be located at 45° relative to the axis, as illustrated in Figure 3.

Notes:

1. The government recognizes that small immersion transducers are commercially available, and could be purchased and mounted in-house. An independent assessment is being performed to inform the government’s make-or-buy decision. The government anticipates that transducer OEMs can potentially achieve economies to reduce the cost-per-element relative to this approach.

2. Lower ultrasonic center frequency may be acceptable, if that reduces the cost per element while meeting the other specifications. A lower limit of 5 MHz is established for the center frequency.

3. It is understood that there may be a tradeoff between sensitivities and ultrasonic bandwidth. A lower fractional bandwidth may be acceptable in order to increase the sensitivity of the elements. A lower limit of 40% fractional bandwidth is established. (E.g., 6 dB bandwidth from 8 MHz to 12 MHz for center frequency 10 MHz.)

4. The offeror may have at its disposal specific manufacturing methods which would lend themselves better to array layouts different from a hexagonal grid of circular elements (Figure 4). The government may consider such alternatives, if these reduce the cost/element significantly while still meeting the spirit of the remaining requirements. The increased complexity of interpreting an array with non-identical elements will play a major role in the evaluation of such alternative layouts.

Incoming Sound ScatteredSound Scatterer ScatteredSound (A)

(B) Composite Array Probe

Figure 1. A. Schematic of a general ultrasonic scattering event. Ultrasound propagates along one direction and impinges upon a discontinuity in the medium, i.e., a scatterer. Ultrasound scatters from the discontinuity in many directions, depending upon the characteristics of the scatterer, the surrounding medium, and the ultrasound. B. The current procurement seeks an array probe which permits the measurement of ultrasonic scattering from an immersed specimen of composite material over a wide range of angles.

UTA 160-DH/32 LEMO

For research and development in materials science and NDT applications, using phased arrays and/or single element transducers, the UTA 160-DH/32 LEMO adapter provides 2 Hypertronics 160-pin connectors in addition to 32 single-channel LEMO connectors. This UTA is available on all Vantage systems.

Figure 2. The subject array probe will be interfaced with a government-owned array system: Vantage 256 by Verasonics, Inc., 11335 NE 122nd Way, Suite 100, Kirkland, WA 98034. Telephone: 425-998-9836.

45° Center Element Widest-Angle Element UHF Threaded Mount (5/8-24) Cable

Figure 3. The subject probe is intended to be mechanically substituted for a standard immersion transducer in a conventional scanning system. The mounting device shall be collinear with the axis of the array, and shall mechanically mate with a UHF female socket. There shall be one element, called the center element, which is also collinear with the probe axis. Those elements which are at the most extreme polar angle in the probe shall be located at 45° ± 2°.

Radius

Figure 4. Sketch of the angular layout of elements on the face of the probe. The center element (darkened for clarity) defines 0° polar angle. Here, 251 elements are hexagonally distributed over the area of the probe face.

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