Photonics from Al-Haitham to Optoelectronics of AMTEC
Open Access JCC
cation of optics more in practical aspect, and an analogy
to electronics.
The term quantum electronics was used for the area of
physics dealing with the effects of quantum mechanics
on the behavior of electrons in matter, and their interac-
tions with photons. It is today rarely considered a sub-
field in its own right, as it has been absorbed by other
fields. The term was mainly used between the 1950s and
the 1970s. Today, the research output of this field is
mainly used in quantum optics, especially for the part of
it that draws not from atomic physics but from solid-state
physics.
Electro-optics, not to be confused with optoelectronics,
involves components, devices and systems which operate
by modification of the optical properties of a material by
an electric field. This branch of technology deals with the
interaction between the electromagnetic and the electrical
or in modern terminology electronic and optical states of
material.
Optomechanics can be referred to as the study of the
interaction of photons (electromagnetic radiation) with
mechanical systems via radiation pressure, and also the
manufacture and maintenance of optical devic es and parts,
such as fiber aligners, mirror mounts, optical mounts,
translation stages, rotary and kinematic stages, pedestals
and posts, rails, micrometers, screws and screw sets. It
may also include optomechanical design and integration
with exterior package, manufacture and maintenance of
fiber optic materials, and design and packaging of rugged
optical trains in compact form.
The term optoelectronics connotes devices or circuits
comprise both electrical and optical functions, i.e., a thin-
film semiconductor device. The term electro-optics came
into earlier use and sp e c ifically encompasses nonlinear
electrical-optical interactions applied, e.g., as bulk crystal
modulators. It also includes advanced imaging sensors
used typically for surveillance. It is the design, manufac-
ture and working of AMTEC as a whole, which p er tains
to the device domain of optoelectronics.
AMTEC is an infrared regenerative electrochemical
device for the direct conversion of heat into electricity.
While AMTEC technology development is primarily fo-
cused for deep space missions because of its longevity
and high efficiency under static conversion, it is also
expected to have many terrestrial uses. Its simulated de-
sign has shown its longevity as much as fifteen years.
Some of its laboratory devices have achieved efficiencies
as high as 19%. Small system designs using AMTEC
have shown 27% cell and 23% system efficiencies. An
Optimized AMTEC can, however, potentially provide a
theoretical efficiency close to Carnot efficiency almost
up to 40% [2]. It has no moving part thus creating no
noise with the potential for low maintenance, high dura-
bility and reliability. As it has no moving parts it is not
subjected to any material wear and tear. There is no vi-
bration or uncompensated momentum present in AM-
TEC, which reduces the chances of corrosion. It has the
ability to use infrared energy as an input from high tem-
perature combustion, nuclear, radioisotope, solar or heat
rejected from other devices [3-6]. A number of research
programs on AMTEC have been focusing on improving
its performance characteristics and technology improve-
ment. Of course, these efforts have successfully resolved
many of the important technological issues pertaining to
its design and fabrication. The performance level, how-
ever, achieved until today is still below the expected po-
tential of AMTEC. During an extended testing of an
AMTEC model the maximum power of its output was
observed (Figure 1) to be decreasing from 2.49 W to
1.27 W over a period of 18,000 hours of operation [7].
The degradation is primarily due to its solid electrolyte,
called bête alumina solid electrolyte (BASE). The role of
electrodes is insignificantly small compared to BASE
[8].
Before we discuss their respective contributions to the
power out and efficiency it may be in order to give a
brief description and working princ iple of AMTEC. Th is
is mostly borrowed from an encyclopedic article of the
author [9].
2. Physical Description of AMTEC
Initially AMTEC was developed as liquid-anode cycle
but soon the vapor-anode cycle system took over. The
use of the vapor-fed AMTEC cycle system has presently
been in the vogue and being investigated. A typical AM-
TEC unit is sealed, housed in a sealed container. The
working fluid should be so selected that it should have a
high negative potential, lightweight and abundantly avail-
able for cost effectiveness. An alkali metal with relative-
ly low melting point would satisfy these qualities. Out of
number of possible samples sodium (Na) is chosen for
this task. At the heart of AMTEC lies a solid electrolyte
made of a dense micro-crystalline sintered ceramic ma-
terial beta” aluminum solid electrolyte (BASE)
(Na5/3Li1/3Al32/3O17) in the form of individual tubes con-
nected in series as shown in Figure 2.
The BASE separates two regions of alkali (sodium in
this case) vapor introduced; a high-temperature (900 K –
1300 K) high-pressure (20 - 100 kPa) region and a low-
temperature (400 - 700 K), low-pressure (<100 Pa) re-
gion, see Figure 2. From the physical dimensions of this
type of AMTEC cell it looks about a D-size dry cell.
Two thin, porous electrodes are placed on inside and
outside walls of the BASE, as shown schematically in
Figure 3.
The electrode mounted on the inner side of the BASE
acts as anode and the one on the outer side of the BASE
is treated as cathode. The inner and outer electrodes are