FIToolbox - PWM transmit 29/10/2016 FIToolbox - PWM transmit FIToolbox - PWM transmit Diagnostic Sonar Ltd. Dave Lines

FIToolbox - PWM transmit 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

Experimental verification 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

PWM – 5MHz 1 cycle – No Window 29/10/2016 FIToolbox - PWM transmit PWM – 5MHz 1 cycle – No Window

Tx/Rx: 1 cycle 5MHz – No Window 29/10/2016 FIToolbox - PWM transmit Tx/Rx: 1 cycle 5MHz – No Window

FIToolbox - PWM transmit 29/10/2016 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

PWM – 5MHz 10 cycle – No Window 29/10/2016 FIToolbox - PWM transmit PWM – 5MHz 10 cycle – No Window

Tx/Rx: 10 cycle 5MHz – No Window 29/10/2016 FIToolbox - PWM transmit Tx/Rx: 10 cycle 5MHz – No Window

PWM – 5MHz – Hanning Window 29/10/2016 FIToolbox - PWM transmit PWM – 5MHz – Hanning Window

Tx/Rx: 5MHz – Hanning Window 29/10/2016 FIToolbox - PWM transmit Tx/Rx: 5MHz – Hanning Window

PWM – 5MHz – Twin Hanning Window 29/10/2016 FIToolbox - PWM transmit PWM – 5MHz – Twin Hanning Window

Tx/Rx: 5MHz – Twin Hanning Window 29/10/2016 FIToolbox - PWM transmit Tx/Rx: 5MHz – Twin Hanning Window

FIToolbox - PWM transmit 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