Precision Alignment Techniques for Affordable Manufacture of Millimeter Wave Vacuum Devices
Navy STTR 2020.A - Topic N20A-T013
NAVSEA - Mr. Dean Putnam [email protected]
Opens: January 14, 2020 - Closes: February 26, 2020 (8:00 PM ET)
TITLE: Precision Alignment Techniques for Affordable Manufacture of Millimeter Wave Vacuum Devices
ACQUISITION PROGRAM: PEO
IWS 2: Advanced Offboard Electronic Warfare Program
OBJECTIVE: Develop a
high precision alignment technology for affordable manufacture of high power
millimeter wave vacuum electron devices.
generation of high power at millimeter wave (mm-wave) frequencies is expensive
and the concurrent need for wide bandwidths at these frequencies creates an
extremely challenging problem. The most stringent requirements for mm-wave
power and bandwidth can only be practically met by vacuum electronics (VE)
technology. This is especially true for applications constrained by
considerations of size, weight, and power (SWaP). Design of such devices is no
longer the primary roadblock to their development as both theory and analysis
tools (for example, modelling and simulation codes) have advanced dramatically
over the past two decades. It is now possible to design, model and simulate a
mm-wave VE device and predict its performance to a high level of confidence –
if the device can be built to the tolerances required.
At present, vacuum amplifiers with the required performance are prohibitively
expensive due to the high precision machining and assembly processes involved.
Specifically, the devices are constructed of metal and ceramic parts that
require extremely tight tolerances be maintained across proportionally large
dimensions of assembled piece parts. Therefore, mm-wave device development and
deployment are severely impacted by limitations in manufacturing techniques and
processes, and devices providing state-of-the-art performance are expensive due
to complex manufacturing steps with relatively low yields. Systems applications
must therefore accept high component costs or compensate with less than ideal
system trade-offs that result in larger, heavier, and lower efficiency systems.
Either way, lack of suitable manufacturing techniques manifests itself in
greatly increased system cost. This situation will be most severe for future
mm-wave electronic warfare (EW) applications where system performance simply
cannot be compromised.
Vacuum electronic amplifiers are a critical technology for high power, broad
bandwidth, high efficiency mm-wave EW and countermeasures applications where platform
volume and weight are highly constrained. In such devices, critical dimensions
must scale with the operating wavelength. Thus, as the frequency of operation
increases, physical dimensions and mechanical tolerances decrease
proportionally. Precision alignment is therefore crucial to future mm-wave
device development as the higher frequencies demand tight alignment tolerances
to achieve peak performance (i.e., power, bandwidth, efficiency) while
maximizing manufacturing yields and minimizing cost and production time.
Complicating this problem are the large aspect ratios involved. For example,
the beam tunnel in a typical W-band traveling-wave tube is approximately 230
microns in diameter and may have a length of 5 cm or more.
Typically, the electron beam fills 50-80% of the tunnel diameter and must
propagate without interception over the full longitudinal distance with less
than 0.15 degrees of angular misalignment off the axis. The problem is
exacerbated when the assembly is non-axisymmetric as in the case of multiple
electron beams or sheet electron beams. Alignment of the component parts for
machining and joining is therefore the most critical step in the manufacturing
Traditional methods of precision assembly such as alignment pins and in-process
machining have accuracies limited to the 10-micron range or above. Furthermore,
there are other issues associated with these methods. For example, in-process
machining is both labor- and time-intensive, and alignment pins add additional
constraints to the assembly process, introducing yet more high tolerance
features in the course of achieving the desired overall precision. Recent
advances have demonstrated sub-micron level machining of individual parts but
the assembly of multiple parts into complete devices, while maintaining the
tolerances required, still presents a choke point in the manufacturing process.
If a completed assembly is found to be out of tolerance, all the precision
machining invested up to that point on the individual parts is lost.
The Navy needs advanced sources of mm-wave power that are affordable. While the
cost of individual devices depends on their design and performance, elimination
of low manufacturing yields and high rework rates could lower device cost by as
much as 50% across all types of mm-wave vacuum amplifiers. In order to achieve
this, new approaches to the mechanical design and assembly of critical
components must be developed. Specifically, a technology for the high precision
assembly of the extremely high tolerance, large aspect ratio components
required by modern mm-wave vacuum electronics is desired. The solution should
consider (but not be limited to) methods including elastic averaging (EA),
kinematic couplings (KC), and quasi-kinematic couplings (QKC). For example, EA
techniques offer precision down to approximately 1 micron and work by averaging
out errors through controlled compliance between precision surfaces. KC can
achieve better than 0.1-micron precision and work on exact constraints where
the number of constraint points is equal to the degrees of freedom to be
constrained. The process is deterministic and can provide high accuracy and
high repeatability. QKC rely on an arc contact as opposed to the point contacts
required by KC and can achieve sub-micron precision. Compared with KC, QKC has
reduced contact stresses, reduced cost and complexity, and (pertinent to VE
applications) has the ability to make a vacuum-tight seal. Other techniques,
not anticipated herein, and hybrid techniques combining the best qualities of
these techniques are equally of interest. The goal is to develop an innovative
manufacturing technology that exceeds the state-of-the-art presented by each of
these techniques individually.
Consistent with the Navy’s objective of producing affordable mm-wave vacuum
electronic devices, the solution should specifically demonstrate its utility in
the manufacture of mm-wave circuit stack assemblies, electron gun assemblies
(cathode to focus electrode positioning), and alignment of the electron gun to
the circuit assembly. Successful technologies should demonstrate at least a 10X
improvement in precision over existing techniques (better than 1.0 micron
tolerance over 5 cm total assembly length), repeatability, vacuum
compatibility, and compatibility with other processes common to the manufacture
of vacuum devices such as brazing, bakeout (at temperatures up to 500° C), and
steady-state operation at temperatures up to 200° C without distortion. The
technique should be experimentally demonstrated in at least one of the
following areas of relevant W-band vacuum device structure manufacturing:
circuit stack assembly; electron gun assembly; or electron gun to circuit
The prototype solution is expected to produce fixtures, tooling, instrumentation,
and the associated process steps (documented by drawings, procedures,
specifications, and protocols, etc.), as validated by the prototype device
structure. Testing shall include mechanical inspection to validate the
precision of the prototype processes and device performance testing, as
required to validate the manufacturing techniques. These items, including the
prototype structure, will be delivered to the Naval Research Laboratory upon
completion of the effort.
PHASE I: Propose a
concept for a precision alignment technology for the affordable manufacture of
high power mm-wave vacuum electron devices as described above. Propose a
specific prototype assembly, on which the technology will be demonstrated.
Demonstrate the feasibility of the approach by some combination of analysis,
modelling, and simulation. Predict the ability of the concept to achieve the
tolerances required according to the parameters of the Description. The Phase I
Option, if exercised, will include a device specification and test plan in
preparation for prototype development and demonstration in Phase II.
PHASE II: Develop and
deliver a prototype precision alignment technology that meets the requirements
in the Description. Ensure that the prototype processes and techniques
(including fixtures, tooling, and instrumentation) will demonstrate that the
requirements of the Description are met by validation of the proposed prototype
assembly. Perform testing and validation in the proposer’s facility or in a
qualified facility chosen by the company and approved by Naval Research
Laboratory (NRL) personnel. Include, in the testing, mechanical inspection to
validate the precision of the prototype processes and device performance
testing, as required to validate the manufacturing techniques. After testing
and validation, deliver to the NRL the process documentation, equipment,
hardware, test data, and prototype assembly.
PHASE III DUAL USE
APPLICATIONS: Support the Navy in transitioning the technology for Government
use. Since the prototype techniques, processes, and hardware resulting from
Phase II are a generic demonstration of the technology, assist in applying the
technology for the manufacture of specific VE devices.
Since active mm-wave VE devices require the most stringent manufacturing and
assembly tolerances, the technology should be readily applicable to the
manufacture of other precision passive mm-wave components such as couplers,
diplexers, mode convertors, and circulators. The technology should also prove
applicable to other industries requiring precision alignment, such as the laser
and electro-optics industry where the precise alignment of optical components
over long optical paths is costly and time consuming. The technology resulting
from this effort should therefore find a ready commercial market.
1. Gamzina, Diana, et
al. “Nano-CNC Machining of Sub-THz Vacuum Electron Devices.” IEEE Transactions
on Electron Devices 63, October 2016, pp. 4067-4073. https://ieeexplore.ieee.org/document/7536122
2. Culpeper, Martin L.
“Design of Quasi-Kinematic Couplings.” Precision Engineering 28, 2004, pp.
3. Slocum, Alexander.
“Kinematic Couplings: A Review of Design Principles and Applications.”
International Journal of Machine Tools and Manufacture, 50, 2010, pp. 310-327. https://www.sciencedirect.com/science/article/pii/S0890695509002090
4. Slocum, Alexander H.,
et al. “Kinematic and Elastically Averaged Joints: Connecting the Past,
Present, and Future.” International Symposium on Ultraprecision Engineering and
Nanotechnology, Tokyo, Japan, March 13, 2013. http://www.jspe.or.jp/wp_e/wp-content/uploads/isupen/2013s/2013s-1-1.pdf
KEYWORDS: Vacuum Electronics;
Manufacturing Techniques; Precision Alignment; Elastic Averaging; Kinematic
Couplings; Quasi-Kinematic Couplings