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IMPATT DIODE
AND
TRAPATT DIODE
IMPATT DIODE
IMPATT Stands for IMPact ionization Avalanche Transit-Time
Pn junction diode is
reverse
biased
Avalanche multiplication
of electrons and holes
occur
Negative resistance is
based upon avalanche
multiplication and
transit-time effect of
carriers
This exhibits negative
resistance
characteristics in
microwave frequency
range.
Device based on this
principal is called the
IMPATT DIODE
CONSTRUCTION OF IMPATT DIODE:
EQUIVALENT CIRCUIT FOR IMPATT DIODE:
Where,
Where,
OPERATION OF IMPATT DIODE:
Voltage and Current Vs Time:
COMPARISION
IMPATT is designed for high power applications
whereas, a diode burns (heat-up) at high power.
IMPATT is operated at reverse bias whereas a diode
is normally operated at forward bias because at
reverse bias there is high voltage drop.
ADVANTAGES OF IMPATT DIODE:
1. Operate at frequencies between about 3 and 100 GHz or more.
2. High power capability.
DISADVANTAGES OF IMPATT DIODE :
1. Major drawback of using IMPATT diodes is the high level of phase
noise they generate.
2. The noise figure for IMPATT is 30dB .
3. Tuning range is not as good as Gunn diodes.
APPLICATION OF IMPATT DIODE:
1. MICROWAVE GENERATOR
2. MODULATED OUTPUT OSCILLATOR
3. RECEIVER LOCAL OSCILLATOR
4. PARAMETRIC AMPLIFIER (par amps)
5. INTRUSION ALARM NETWORK
6. FM TELECOMMMUNICATION TRANSMITTERS
7. CW DOPPLER RADAR TRANSMITTER.
IMPATT DIODE OSCILLATOR:
•Very high frequency stability
•High output power
•Low phase noise
•Fine spectrum
•Precision frequency adjustment
•Weak temperature dependence
•Compact, low cost
TRAPATT DIODE
TRApped-Plasma Avalanche Trigged Transit Diode
Construction of TRAPATT Diode:

It is derived from IMPATT Diode.

Silicon or Gallium Arsenide is used for fabricating TRAPATT Diode.
 TRAPATT Diode can be constructed either by p+ -n-n+ or n+-p-p+.
OPERATION OF TRAPATT DIODE:
A square pulse is used to excite TRAPATT diode.
TRAPATT DIODE WAVEFORM:
AB – Charging of junction capacitance
BC – Electron and hole plasma formation by depressed field
DE – Plasma extraction
EF – Residual extraction
FG – Charging of diode
GA – Constant voltage after full charging
ANALYSIS OF TRAPATT DIODE:
1. The current density is given by,
Where,
3. Avalanche zone velocity is given by,
2. Electric field is given by,
Where,
SALIENT FEATURES OF TRPATT DIODE
1. It is a high efficiency diode oscillator .
2. Its oscillations depend on delay in current caused by avalanche
process.
3. The diode diameter is about 50 mm for CW operations and is
about 750 mm at lower frequency for high peak power
application.
4. It can be operated over a range of 400MHz to 12GHz.
5. Its has an efficiency of 20% - 40%.
ADVANTAGES OF TRAPATT DIODE:
1. Its efficiency is relatively high.
2. It can be used over a frequency range of a few hundred MHz
to several GHz.
DISAVANTAGE OF TRAPATT DIODE:
1. It has high noise figure.
2. Its use at upper microwave frequencies is limited .
3. It generate strong harmonics due to the short duration of
current pulse.
APPLICATION OF TRAPATT DIODE :
It is used in
•
•
•
•
in pulse radar as local oscillator.
in radio altimeter.
air borne and marine radars.
in microwave beacons and landing
system.
• in low power Doppler radars.
APPLICATION OF
MICROWAVE ENGINEERING
IN
BIOMEDICAL INSTRUMENTS
BIOMEDICAL INSTRUMENTS
The Signal Processing and Instrumentation Section (SPIS) provides electrical,
electronic, electro-optical, and computer engineering support to clinical and biomedical
research projects involving advanced real-time signal transduction, signal processing,
and control.
FIG: A JARVIK-7 artificial heart, an example of a biomedical engineering
1. APPLICATION IN STERILIZING MEDICAL EQUIPMENTS
• Sterilization (or sterilisation) is a term referring to any process that eliminates
(removes) or kills all forms of life, including transmissible agents (such
as fungi, bacteria, viruses, spore forms, etc.) present on a surface, contained in a
fluid, in medication, or in a compound such as biological culture media.
• Sterilization can be achieved by applying the proper combinations of heat,
chemicals, irradiation, high pressure, and filtration.
FIG: Sterilizing surgical instruments
HOW MICROWAVES ARE USED FOR
STERILIZING PROCESS?
• Low-cost technology to kill harmful bacteria has been developed at
Glyndŵr University in Wrexham.
• Researchers found that by attaching a vacuum vessel to a microwave
oven, atomic oxygen and ozone - both aggressive gases - can be generated.
• The modified microwave used by the team cost less than £2,000,
compared to £70,000 for conventional systems.
• The new method, developed by a team led by senior research scientist Dr
Andy Wright, provides a chemical-free solution to killing harmful bacteria
on medical tools used in GP, dentist and veterinary surgeries.
2. APPLICATION IN HISTOPATHOLOGY
• Refers to the microscopic examination of tissue in order to study the
manifestations of disease.
• Specifically, in clinical medicine, histopathology refers to the examination of
a biopsy or surgical specimen by a pathologist, after the specimen has been
processed and histological sections have been placed onto glass slides.
FIG: Micrograph showing contraction band necrosis, a histopathologic finding
of myocardial infarction (heart attack)
HOW MICROWAVES ARE USED IN
HISTOPATHALOGY ?
• Microwave accelerated procedures are useful at every step of sample
preparation for microscopy by speeding up reaction process and saving
time.
• Even more important , microwave procedures improves the retention
of soluble Antigen immuno reactivity better than conventional methods.
• In short, microwave accelerated techniques can be used to improve the
efficiency of variety of histopathology laboratory procedures, such as
fixation, decalcification , processing of specimens for paraffin wax or
resin embedding and staining.
• Two types of microwave devices are being used in histopathology
laboratory setting :
1. Microwave instruments specifically designed
and certified as medical devices
2. Commercial grade microwave units modified
for lab/clinics
• Laboratory microwave devices are designed with exhaust fans
and safety features to protect microwave devices.
Presented By:
GROUP 4
Roll No:
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