In this paper, we measure and analyze propagation characteristic of heating, ventilation, and air conditioning(HVAC) ducts within buildings for wireless networks. We analyze the duct structures, implement the feeders exciting propagating modes, and simulate the excitation characteristic. We measure the propagation characteristic of HAVC ducts at 2.45 GHz WiFi band and compare it with that of LOS and partitioned office environments. We propose the design method of wireless network using HVAC ducts based on our results.
Passivated 0.15 µm pseudomorphic high electron mobility
transistors (PHEMTs) were fabricated by combining a wide head T-shaped
gate, formed using a dose split method of electron beam lithography,
with a short source-gate separation, using formed an electron
cyclotron resonance dry recess etching process. The threshold voltage
of the devices showed 50 mV variation across three-inch wafers. The
extrinsic transconductance and cutoff frequency of the PHEMT devices
were 688 mS/mm and 82.6 GHz, respectively. The lowest minimum noise
figure, NF
min, of the PHEMT devices was observed
around 80% of the saturation drain current at 30 GHz and
V
ds = 2 V. The devices exhibited a
NF
min as low as 0.99 dB with an associated gain
of 9.1 dB at 30 GHz. This noise figure value is the lowest data ever
reported for a PHEMT device using a dry recess process.
Field emission from diamond-like-carbon (DLC) films grown on a silicon substrate has been investigated. The films were prepared using radio-frequency plasma-assisted chemical vapor deposition. A DLC film incorporated with nitrogen exhibited better emission characteristics. For both nitrogen-incorporated and pure DLC, electric arc between the film and anode drastically enhanced the emission current. Analysis showed that the arc induced the formation of silicon carbide and the change in the surface morphology. The possible mechanism of the enhanced emission is discussed.
An inverted double channel Al0.25Ga0.75As/In0.25Ga0.75As/GaAs pseudomorphic high electron mobility transistor (P-HEMT) grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) has been demonstrated for the first time. The inverted double channel heterostructure shows a high two-dimensional electron gas (2-DEG) concentration of 4.53×1012 cm-2 along with a large mobility of 5010 cm2/V·s at 300 K, respectively. The fabricated P-HEMT device with a gate dimension of 1.8×200 µm2 shows a maximum drain current of as high as 820 mA/mm and a maximum extrinsic transconductance of 320 mS/mm at 300 K. Also, extrinsic transconductance is sustained over a wide range of gate voltages from -2.0 V to 1.8 V. In addition, a high two-terminal gate-drain reverse breakdown voltage of -17 V is obtained. The results obtained show a great potential of the inverted double channel P-HEMT for power applications.
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