29/10/2016
FIToolbox - PWM transmit
FIToolbox - PWM transmit
Diagnostic Sonar Ltd.
Dave Lines
29/10/2016
FIToolbox - PWM transmit
Background
Requirement is to demonstrate the ability of the FIToolbox
to produced shaped excitation on each transmit channel
by means of Pulse Width Modulation (PWM)
A utility has been implemented that converts a desired
waveform into a 3-level PWM signal
 It produces a graph showing the filtered PWM output and the
filtered version of the desired waveform, allowing comparison
 The filter is Band Pass and attempts to mimic the combined effect
of the transducer response and any system filtering
 The utility can export the PWM output as a Pulse definition file
(.pul) for import into the FIToolbox applications
29/10/2016
FIToolbox - PWM transmit
Experimental verification
A wideband 5MHz 0.5inch single element unfocused
transducer was used
The echo signal from the air interface at the end of an
acoustic delay line was recorded for different PWM
excitations
The band pass filter (BPF) in the PWM utility was set from
3MHz to 7MHz to try to match the transducer response
Minimum pulse width was set to 4 samples = 20ns and
this will limit the rendition of low amplitude parts of the
signal at 5MHz
A single cycle at 5MHz was used as a reference to see
how well the utility output matched the measured echo
29/10/2016
FIToolbox - PWM transmit
PWM – 5MHz 1 cycle – No Window
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FIToolbox - PWM transmit
Tx/Rx: 1 cycle 5MHz – No Window
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FIToolbox - PWM transmit
Shaped waveforms
The following waveforms were generated in the utility and
the matching pulse-echo responses are shown:
5MHz 10 cycles without amplitude shading
5MHz 1000 samples at 5ns with Hanning envelope
shading
5MHz 1600 samples at 5ns with amplitude shading as
two concatenated Hanning windows
29/10/2016
FIToolbox - PWM transmit
PWM – 5MHz 10 cycle – No Window
29/10/2016
FIToolbox - PWM transmit
Tx/Rx: 10 cycle 5MHz – No Window
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FIToolbox - PWM transmit
PWM – 5MHz – Hanning Window
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FIToolbox - PWM transmit
Tx/Rx: 5MHz – Hanning Window
29/10/2016
FIToolbox - PWM transmit
PWM – 5MHz – Twin Hanning Window
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FIToolbox - PWM transmit
Tx/Rx: 5MHz – Twin Hanning Window
29/10/2016
FIToolbox - PWM transmit
Conclusions
A utility has been created for converting a desired excitation
signal into a 3 level pulse file that can then be loaded into the
FIToolbox applications
A range of excitation amplitude shapes have been generated
and the utility screenshots show:
 Pulse shape generated
 Expected result after filter matching transducer & system
A 5MHz transducer was used to produce matching pulse echo
responses for each excitation and verifies the approach
Control of low amplitude parts of the envelope is constrained
by the minimum pulse width (20ns) but this limitation is reduced
at lower frequencies
The FIToolbox supports different excitation waveforms for each
transmit channel and each transmission and so can be used in
place of multiple arbitrary waveform generators