Revised_Statement_of_Work.doc

Statement of Work

Title: NIST Microwave Blackbody Standard Purpose:

Two high-performance broadband passive microwave calibration sources will be constructed to act as the National Institute of Standards and Technology (NIST) primary standard for free-space microwave brightness temperature calibration.

Background:

Lack of a national microwave brightness temperature standard has consequences in long-term data records for climate-related remote sensing instruments. NIST maintains national radiance standards for infrared, visible, and ultraviolet parts of the spectrum but not for microwave.

Use of a standard source reduces the resulting calibration uncertainty compared to using the existing NIST standard radiometers. Many space-borne calibration sources employ a square pyramidal array geometry to achieve high emissivity. This geometry exhibits large surface temperature gradients because of the large distance between heater and pyramidal tips. The pyramidal array design also has a narrow frequency range of optimal performance dependent on the dimensions of the pyramids. A large circular cone structure is proposed as the optimal geometry for a lab-based, non-polarization-dependent, variable temperature microwave calibration source. The optimal cone angle and absorber material layering design were studied in detail. The temperature gradients on the proposed design geometry were also computationally simulated.

By simulating the microwave emissivity and physical temperature of the design, we have calculated the brightness temperature that is expected to be measured by a specific horn antenna. Similar to other microwave calibration sources, the main goals and tradeoff of this design were minimization of temperature gradients and maximization of microwave emissivity.

Requirements (including Minimum Specifications):

General Requirements

1. The two targets to be manufactured will be hollow right circular cone shapes. The smaller will have an inner radius of 6.56 cm and an internal length of 37.2 cm. The larger will have an inner radius of 10.85 cm and an internal length of 61.5 cm. These dimensions correspond to a half-cone-angle of 10 degrees. The base material shall be copper or Aluminum and the base structure shall be lined with layers of Emerson & Cuming Eccosorb CR1 castable microwave absorber material.

1Eccosorb is a registered trademark of Emerson & Cuming Microwave Products. NIST does not endorse this company or brand. Due to the available data, specific design requirements, and investment in design simulation work, this specific product has been chosen for the application.

2. The base structure shall be affixed with thermally conducting tubing coiled around the exterior of the cone for the purpose of circulating fluid or gas temperature control.

3. The supplier must have a proven record of reliability and experience in microwave blackbody technology. To allow assessment, each proposal must include appropriate documentation.

4. Documentation should include contact information for at least three prior clients.

5. Documentation must include schedule of prior clients, including contracted delivery date and actual delivery date.

6. The U.S. government reserves the right to identify and evaluate its own past-performance information.

Specific Requirements

1. The Emerson & Cuming microwave absorber formulations shall be applied in two or three layers, depending on manufacturer capabilities, resulting in a total thickness of 3 mm. Our simulations suggest that the following three layer configuration is optimal for electromagnetic performance but may not be practically achievable; CR-117 closest to the cone base with a thickness of 1.37 mm, CR-114 in the middle with a thickness of 0.45 mm, and CR-110 as the outermost layer with a thickness of 1.18 mm.

2. When viewing directly (normal incidence) into the cone, none of the base or cooling channel metal shall be visible, only absorber material. In other words, the absorber shall be “sharp” at the edge of the cone’s aperture, and only absorber under the insulation layer is visible looking into the cone aperture.

Note: Illustrations are not to scale. Above figures are for explanatory purpose only.

3. The absorber layers shall be uniform to within a provided non-uniformity and thickness uncertainty tolerance. Manufacturer shall state their achievable thickness uncertainty along with method and means for verification. All related data will be included as part of the deliverables.

4. The iron doping particles in the castable absorber materials should be homogeneous and randomly distributed such that the properties of the absorbers remain constant throughout the thickness of each layer.

5. The absorber and the interfaces between absorber layers shall be free of air bubbles and other inconsistencies that would influence the electromagnetic or heat transfer characteristics of the materials.

6. The system shall withstand repeated temperature cycling down to 77 K in vacuum and up to 350 K in vacuum and air.

7. The contractor shall also cast each absorber material into a set of waveguide shims to be provided. The shims to be cast include one in each absorber type, CR-110, CR-114, and CR-117, in each of the following waveguide bands, WR-42, WR-28, WR-22, WR-15, WR-10, WR-08, and WR-05. This sums to a total of 21 shim samples. The shims shall be machined to eliminate any surface non-uniformity from the absorbing curing process. The absorber shall be cast from the same batch that is used in the blackbody itself.

8. The cone base shall contain 16 drilled locations for placement of temperature sensors. 4 holes will be drilled along the cone axis at 4 equally spaced radial positions (will look like a + when viewed along cone axis). The 4 sensors along the cone surface shall span from the aperture to the tip, with one embedded at the tip of the conductive base, and at least one sensor in between tubing coils. The holes shall be 1 mm from the inner surface of the cone base material and 1.9 mm in diameter.

Note: Illustrations are not to scale. Above figures are for explanatory purpose only.

9. Two independent copper or aluminum tubing lines or alternative fluid transfer mechanism shall circulate around the cone base. There shall be one inlet and one outlet connection towards the tip of the cone. There shall be a split and an insulated line running to the outer (forward) edge of the cone. The two split independent pathways will then flow in opposite directions.

10. Fasteners and other hardware in system shall be vacuum compatible, down to a pressure of less than 10-6 Torr (1 μTorr) and compatible with water and liquid nitrogen.

11. The exact design for the fluid circulating heat exchanger will need to be simulated by NIST to confirm temperature uniformity. We have concluded that for a 0.5 inch diameter copper tube with a 0.8 inch wide welded thermal contact to the conical base, a maximum span of 80 mm between conic helix coils must be maintained.

12. Weld or hard-solder connection between tubing and conical substrate shall maximize surface contact between the two parts and minimize any thermal resistance at the interface. If manufacturer’s skill or experience suggests other appropriate means for providing liquid/gas circulation for base metal temperature control this shall be allowed and given appropriate consideration.

13. Interfacing and mounting points shall be attached to the cone base. These points will allow for appropriate packing and storage in addition to mounting for measurements. Any mounting structure must be thermally well isolated from the cone base to avoid conductive heat loss and heating of the mounting structure itself. The attachment points shall be located near the circular cross section of the cone containing the center-of-mass while keeping any large metallic surfaces out of line-of-sight when looking into the cone aperture.

14. Optional: If the manufacturer can show that they are capable then this item may be included as an optional addition to the quotation (i.e. priced separately). A 3 mm layer of Zotefoams2 HD-60 insulation shall be affixed directly to the absorber layer surface within the conical target. This may be done by inserting a flat conical section of insulation sheet into the cone. A peripheral, annular ring of Zotefoams HD-60 shall then also be attached around the exterior of the aperture to reduce thermal gradients near the edge of the absorber. This ring may be substantially thicker than 3 mm but must not occlude the target aperture. See Fig. 1 for reference locations of HD-60 liner and annular ring. The HD-60 must be homogenous with surface properties equivalent to the bulk volume. Some samples of this foam have been observed to have a glossy film-like surface which must be avoided for electromagnetic performance considerations.

Delivery (Period of Performance):

Delivery must be made to NIST within 6 months of award. The contractor shall provide a one-year warranty on all parts, beginning the day of equipment acceptance. The warranty will cover the mechanical integrity of the item and guarantee against changes in the electromagnetic characteristics over time.

Inspection and Acceptance Criteria

Contractor adherence to technical specifications 2Zotefoams plc is a registered company in the United Kingdom. NIST does not endorse this company or brand. Due to the available data, specific design requirements, and investment in design simulation work, this specific product has been specified.

The contractor shall provide evidence of absorber layer thickness and uniformity. Results of multiple thickness measurements on each layer will be provided along with photographs showing each layer throughout the manufacturing process.

The absorber material waveguide shims will be measured at NIST (at no cost to the manufacturer) to verify the electromagnetic material properties of the specific absorber batches used in the process.

Physical check at contractor facility

Contractor will allow visual inspection at the manufacturing facility prior to delivery. This will allow for education on the manufacturing process and provide clarity on how the requirements were achieved. This check will be at the expense of NIST.

Physical check at NIST laboratory for adherence to technical specifications Upon delivery of the item NIST will perform visual and performance testing. All welds, absorber casting, and connectors will be thoroughly inspected.

A technical manual shall be provided, including final drawings of all components and parts. The manual shall be provided in hard copy and electronic form.

If performance specifications as described under the requirements section are not demonstrated, the Contractor shall make all repairs/changes necessary to demonstrate specifications. All repairs/changes shall be performed at no additional charge to NIST. Repairs/changes shall be completed no later than 60 days from the date the Contractor receives notification (via telephone, or e-mail) of the problem.

Delivery/Payment Schedule:

Contractor shall provide progress reports every 2 months. The report will summarize the current status of the build process and confirm that the schedule is on time. Photographs and other details of the build procedure may be included.

Payment schedule is negotiable, but full payment will be made upon completion of delivery and confirmation of specifications.

In addition to information required in the Evaluation Criteria section of this document, all quoters shall submit ALL of the following:

1) One (1) copy of a quotation (including FOB Destination pricing);

2) Technical description and/or descriptive product literature;

3) Description of warranty;

4) One (1) copy of the most recent (relevant portions) of published price list(s) (if available);

5) Completed Representations and Certifications Fig. 1 Cross-section of upper edge of cone:

HD-60 annular ring fluid circulation tube/channel cone base

Looking into cone aperture

Eccosorb CR layers

HD-60 liner

Fig. 2b. Four holes along cone surface at each radial position:

Fig. 2a. Four equally spaced radial positions: