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Design of CMOS Millimeter-Wave and Terahertz Integrated Circuits with Metamaterials by Yang Shang, Hao Yu

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CMOS THz Imaging 263
with on-chip integrated THz transceivers, which has b een constructed by a
differential heterodyne receiver the on-chip CRLH-TL leaky wave antenna
(LWA), and zero-phase CON-based signal source demonstrated in previous
sections.
12.2 135-GHz Narrow-Band Ima ger by DTL-
SRR-Based SRX
12.2.1 THz Imaging by SRA Detection
THz radiation is usually attenuated due to absorption and scattering during
the propagation [261], which can be modeled by
I
γ
1
= I
γ
0
e
R
γ
1
γ
0
α
e
(z)dz
(12.1)
where I
γ
0
and I
γ
1
are the incoming and outgoing radiance intensity along the
path (γ
0
, γ
1
); and α
e
(z) is the extinction coefficient, which is the summation of
absorption (α
a
) and scattering (α
s
) coefficients. For a homogeneous material
placed between (γ
0
, γ
1
), α
a
is a constant. The s cattering only happens at the
interface with scattering coefficients of α
s
(γ
0
) and α
s
(γ
1
). T he rec eived power
(P
R
) in a transmissive-type THz imaging system is [262]
P
R
(dBm) = P
T
(dBm) + G
R
(dBi) L(dB)
8.686[∆γα
a
+ α
s
(γ
0
) + α
s
(γ
1
)](dB)
(12.2)
where P
T
is the effective iso tropic radia ted power (EIRP) of the trans mitter ,
G
R
is the receiver antenna gain, and L is the path loss without any objects
placed in the pr opagation path, including both the free space path loss (FSPL)
and atmosphere a bsorption.
As shown in (10.5), the envelope of receiver output is proportional to
the injected current or the square root of input power. A DC output ca n be
obtained by averaging Env[v
o
(t)] in each periodic quenching cycle.
V
DC
=
ω
i
Z
0
|S(∆ω)|
P
R
2R(t
b
t
a
)
Z
t
b
0
1
s(t)
dt (12.3)
As such, the received p ower could be detected by measuring V
DC
from the
SRA output. As a result, the THz image of a n object c an be further obtained
by the 2D scanning of V
DC
with fixed P
T
, G
R
and L. Moreover, by analyzing
V
DC
as well as P
R
with various object thickness (∆γ), one can further find
the absorption coefficient of the o bject under test.
12.2.2 Narrow-Band Imaging Results
The SRX can be integrated with the THz imaging sys tem by replacing the
GSG probe with bonding wires connected to an 135-GHz antenna. It is demon-
264 Design of CMOS Millimeter-Wave and Terahertz Integrated Circuits
(a)
(b)
Figure 12.3: (a) PCB integration of CMOS 135-GHz SRX with an-
tenna; (b) THz imaging measurement setup with the proposed re-
ceiver chip integrated on PCB and object under test fixed on an X-Y
moving stage.
strated by wires bonding from the input of the proposed 135-GHz SRX to a
2 × 4 antenna array with hybrid series/parallel feeding network as shown in
Figure 12.3(a). The receiver and antenna must be well aligned to minimize the
connection loss, which is estimated to be 35dB according to the EM simula-
CMOS THz Imaging 265
Figure 12.4: Images captured by imaging system with the proposed
135-GHz SRX receiver: knife , perfume, and coin i n handbag.
tion in Ansoft HFSS. A 2x4 antenna array us ing hybrid series/parallel feed is
designed and fabricated in Roger RT5880 with s ize of 8 ×8 mm
2
. The antenna
has 15.4dB i simulated gain at 1 35 GHz. Its input is matched to 50ohm with
measured S11 below -1 0dB from 124 to 139GHz. Detailed informatio n of the
antenna array design is s hown in [26 3]. The entire THz imaging se tup is a lso
shown in Figure 12.3(b). The 13 5-GHz radiation from a VDI source (0-dBm
output power) is received by proposed SRX after propagating through the
objects under test, which is held by an X-Y moving stag e (STANDA) place d
in the middle. Although a substantial portion of the object is illuminated due
to the divergent beam from the source antenna, only the power propagating
in the direction of the receiver is detected. As such, a high-resolution image
can be obtained without a focus lens. The res ulting V
out
at each X-Y stage
position is r ecorded into a 2D matrix, which can be plotted in colored image
in MATLAB
R
with JET colormap.
Figure 12.18 shows the imaging results by the proposed CMOS THz image
system. Figure 12.4 demo nstrates the detection of a knife, perfume, and a coin
inside a hand-bag. These items can be clearly identified in the image, because
different material types like metal, plastic and liquid have different absorption
and reflection proper ties to the THz radiation. Figure 12.5 shows that one can
differentiate between a moisturize d Panadol pill and a dry one. Due to the
strong water absorption at THz frequencies, a moisturized Panadol has higher
absorption than the dry one. Figure 12.6 shows the imaging of various types
of food oil including sunflower, olive, fresh soybean and soybean that has be en
used once. Note that four petri dishes are used to ho ld the oil samples.
The imaging system can also be applied in transmiss ion analysis to char-
acterize the material in the propagation path. T he absorptio n ratio of each oil

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