... - 10:06 AM
Lò nấu visóng
Lò Visóng (Microwave oven - sóng cực ngắn) hiện nay đã ngự trị trong bếp của nhiều gia
đình cũng như tại công sở, trường học…. Dân giầu có thì sắm một lò gắn vào tường ... bình thường thì cũng cố mua một lò nấu vi sóng, nhỏ bé, giản dị. Bởi lẽ
công dụng của nó rất tiện lợi, đặc biệt người Vi t Nam có thói ăn nóng.
Nấu thực phẩm bằng lò này đã trở thành một nhu cầu ... học, lò cũng có những rủi
ro, bất lợi.
Xin cùng tìm hiểu thêm về bếp nấu hiện đại này.
KHCN Số 4 giới thiệu cùng bạn đọc về lịch sử ra đời lòvi sóng,
những ưu khuyết điểm của nó, cũng như cách...
... wavelengths between 1 m
(10
–6
m) and 1 mm. Beyond the infrared spectrum is the visible optical spectrum,
the ultraviolet spectrum, and x-rays. Below the microwave frequency spectrum is
the radio ... tuning. Here the costs for the design and tuning can be reduced greatly by using
CAD, which can provide more accurate design with less design iterations, leading to
first-pass or tuneless filters. ... developments in this area are cer-
tainly being stimulated by increasing computer power. Another driving force for the
developments is the requirement of CAD for low-cost and high-volume production.
In...
... ports of the network NЈЈ ; and all the S submatrices con-
tain the corresponding S parameters. Obviously, p + c = M
1
and q + c = M
2
. It is
[aЉ]
q
[aЉ]
c
[SЉ]
qc
[SЉ]
cc
[SЉ]
qq
[SЉ]
cq
[bЉ]
q
[bЉ]
c
[aЈ]
p
[aЈ]
c
[SЈ]
pc
[SЈ]
cc
[SЈ]
pp
[SЈ]
cp
[bЈ]
p
[bЈ]
c
b
i
ᎏ
a
j
a
1
a
2
Ӈ
a
M
S
1M
S
2M
Ӈ
S
MM
... at port 2 of the network NЈ and port 1 of the network N Љ
when SЈ
mn
and SЉ
mn
are evaluated individually.
2.8 NETWORK PARAMETER CONVERSIONS
From the above discussions it can be seen that for ... composite
network is given simply by the sum of the short-circuit admittance matrices of the
individual networks.
Analogously, the networks of Figure 2.3(b) are connected in series at both their
input...
... the same 3 pole
Butterworth lowpass prototype as that used previously in Section 3.3.1, Figure
3.15(b) illustrates a bandpass having a passband from 1 to 2 GHz obtained using the
element transformation.
3.3.4 ... = 1 to n (3.24)
g
n+1
= 1.0
For convenience, Table 3.1 gives element values for such filters having n = 1 to 9.
As can be seen, the two-port Butterworth filters considered here are always sym-
metrical ... be chosen.
3.2.2 Chebyshev Lowpass Prototype Filters
For Chebyshev lowpass prototype filters having a transfer function given in (3.9)
with a passband ripple L
Ar
dB and the cutoff frequency...
... previous expressions for
re
are
obtained based on the quasi-TEM or quasistatic approximation, and therefore are
rigorous only with DC. At low microwave frequencies, these expressions provide ... expressions also provide accuracy better than one percent. If more accurate
values are needed, an iterative or optimization process based on the more accurate
analysis models described previously can ... 4.10(h).
These microstrip patch resonators can be analyzed as waveguide cavities with mag-
netic walls on the sides. The fields within the cavities can be expanded by the
TM
Z
nm0
modes, where z is perpendicular...
... Semilumped Lowpass Filters Having Finite-Frequency
Attenuation Poles
The previous two types of microstrip lowpass filter realize the lowpass prototype
filters having their frequencies of infinite ... (b)
can only be electrically equivalent to the combline filter in the vicinity of the mid-
band frequency, and its stopband behavior is different from that of the combline fil-
ter.
Similar to the ... inductances L
1
, L
3
, and L
5
block transmission by
having infinite series reactance, whereas the capacitance C
6
shorts out transmission
by having infinite shunt susceptance.
A microstrip filter...
... design this type of filter, let us consider the design of an op-
timum distributed highpass filter having a cutoff frequency f
c
= 1.5 GHz and a 0.1
dB ripple passband up to 6.5 GHz. Referring to Figure ... = 1 to n
where b
i
are the susceptance slope parameters of series parallel resonators.
It is obvious that for a chosen lowpass prototype, with known element values, the
desired reactance/susceptance ... relative dielectric constant of 10.8 and a thickness of 1.27
mm. The bandstop filter is designed to provide an RF rejection better than 40 dB
over an operating frequency band from 3.5 GHz to 5.5 GHz....
... (MEMS) provide a class of new devices and com-
ponents which display superior high-frequency performance and enable new system
capabilities. For a general definition, a MEMS is a miniature device ... ability to effectively improve filter selectivity. Therefore, it does not
constitute a particularly attractive choice for achieving frequency selectivity. Never-
theless, it may be of interest ... production. The change in permittivity as a func-
tion of electric field is the key to a wide range of applications.
Frequency-agile filters are among many other device applications of ferro-
electrics....
... of S
11
in (8.76)
is always equal to 1. This is because in the vicinity of resonance, the parallel res-
onator of Figure 8.11 behavior likes an open circuit. However, the phase response of
S
11
changes ... of
Kirchhoff’s two circuit laws and states that the algebraic sum of the currents leaving
a node in a network is zero, with a driving or external current of i
s
the node equa-
tions for the circuit of Figure ... resonator
Y
in
= j
C + = j
0
C
–
(8.74)
Note that
0
= 1/͙L
ෆ
C
ෆ
is the resonant frequency. In the vicinity of resonance, say,
=
0
+ ⌬
, (8.74) may be simplified as
Y
in
= j
0
C· (8.75)
where...
... filter synthesis by optimization is a three-pole cross-cou-
pled resonator filter having asymmetrical frequency selectivity. The desired filter
response will exhibit a single finite frequency attenuation ... are violated.
9.3 OPTIMIZATION
287
minimize
⌬⌽,⌬⌰
Ή R
b
(⌽ + ⌬⌽, ⌬⌰) – R
a
(⌽)Ή
where ⌬⌽
denotes the modifications to the physical design parameters
for compensating the characteristic deviation ... the initial decomposition design, the filter is decomposed into individual
cascaded sections, where reference planes of each individual section are represented
by circuit nodes and the discontinuities...
... the
improvement in selectivity over the Chebyshev filter is evident. The closer the atten-
uation poles to the cut-off frequency (⍀ = 1), the sharper the filter skirt and the
higher the selectivity.
⍀
a
FBW ... rejection bandwidths are 100 MHz
and 120 MHz, respectively, which obviously does not meet the rejection require-
ments.
Having determined the design parameters, the nest step is to find the physical ... communications systems, flat group delay of a bandpass fil-
ter is demanded in addition to its selectivity. In order to achieve a flat group delay
characteristic, two approaches are commonly used. The...
... even without the via hole grounding. Thus, it would seem that the voltage
and current distributions would not change much in the vicinity of the midband fre-
quency, even though the via holes are ... “New
high temperature superconductive microstrip lines and resonators,” Applied Supercon-
ductivity, Inst. Phys. Conf. Ser. 148, 1995, 1995, 1195–1198.
[7] J S. Hong and M. J. Lancaster, “Novel ... is associated with the
necessity of using low-value characteristic impedance lines
ț High sensitivity to small variations in physical dimensions
ț Excitation of higher-order modes
ț Difficulty...
... stations
vary but may focus on increasing sensitivity and selectivity:
ț Sensitivity—The benefits of increasing sensitivity in rural areas is obvious
since the number of mobile base stations and ... Nevertheless, the full-wave simulated re-
sponse did verify the design approach.
12.3.3 Sensitivity Analysis
Sensitivity analysis is very important for filter design, particularly for filter tuning,
mainly ... specification. It is estimated the Q that can be attained is 50,000.
Therefore, provided the required rejection and selectivity can be met, a filter
with as low a number of poles as possible should be...