Abstract
The principles of ultrasonic ranging system are
introduced first. The problems of the basic range
measurement system are discussed with methods to improve
the range precision. In addition the use of the beam
pattern of a single transducer is studied. The ultrasonic
imaging systems in mobile robot consist usually of
multiple ultrasonic transducers around the vehicle or
arrays of ultrasonic transducers. In a basic ultrasonic
imaging system consisting of a group of transducers the
map of the environment around the robot is built up from
distances along the acoustic axis of each transducer.
Because the transducers point in different directions, it
is possible to fire some transducers simultaneously which
increases the imaging rate. The most advanced imaging
system is an ultrasonic beamformer that yields the image
from the whole beam area at a single pulse making these
systems very attractive in mobile robots. However, there
are at least two drawbacks which restrict the widespread
use of ultrasonic arrays operating in air. First, the
beamforming algorithm needs high processing power and
second, the distance between array elements needs to be
less than about half of the wavelength making the
construction of such systems difficult. In this thesis
the principles of a transducer array Lepakko are
presented. This ultrasonic system is based on a
non-linear amplitude detection method and because the
phase is not used as in a conventional array, the element
interval can be large compared with the wavelength.
However, the operation of the beamforming and echo
detection algorithms in real time involves many
calculations requiring the use of signal processor
circuits. Because the beamformer uses the amplitude of
echoes, wide bandwidth, wide beam elements are needed to
get distance and direction at high precision across the
whole beam. The specifications of the transducers gave an
impetus to study transducer elements needed in the array
Lepakko, and this work resulted later a model for the
capacitive ultrasonic transducers.
In this thesis a new equivalent circuit for capacitive
ultrasonic transducers is introduced. The properties of
capacitive ultrasonic transducers were studied in
extensive measurement series. The resonant frequency, the
bandwidth and sensitivity of ultrasonic transducers were
measured and the results were published in many articles.
This experimental research combined with theory of
capacitive acoustic transducers gave a simple equivalent
model for capacitive ultrasonic transducers. The model
was used to improve the performance of the transducer
array Lepakko and in a simulator that includes
ultrasonic transducers, acoustic path and electronic
circuits.
Original language | English |
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Qualification | Doctor Degree |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 26 Jan 1996 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 951-38-4921-X |
Publication status | Published - 1996 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- detectors
- transducers
- signal processing
- ultrasonic frequencies
- image processing
- image analysis
- distance
- measurement
- distance measuring equipment
- models
- robots