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First conclusive tests using the probe

During our last session of work, some unfortunate events worked against us: our 0-500V power supply burned (it was a terrible thing to see…) and we were not able to find the right pins controlling the motor of the probe.

But, we still made great advances. We started the tests using the probe, here are the conditions of the experiment:

  • we bought a plastic tray to put some water in it;
  • we also put a piece of metal to try to detect it with the probe (at max 5 cm from it);
  • someone is keeping the probe in hand in the water;
  • we didn’t connect the oscilloscope at the OUT1, to avoid any influence of it;
  • we connected the oscilloscope at the LVOUT1 output to see the echo;
  • using the “+12V/-12V” power supply of the breadboard, we can get a pulse of 24V.

We can see, in the pictures below, that we finally get an echo.

Echos and power supply

Since we have a pulse visible on an oscilloscope, we can go to the next step: having an echo using the probe. Unfortunately, some problems remain.

The first ones are concerning the probe itself. We do not know which pin of the motor’s connectors should be connected, we must insert linseed oil in the probe, connect the BNC connector to the pulser and understand why the impedance of the probe measured with a multimeter is only 6 ohms. The last problem is concerning the power supply: we need a continuous 100V.

Concerning the linseed oil and the BNC connector, we easily found a way to solve these problems (we found the connector in the LISA and the linseed oil at home). For the impedance, our colleague Luc on the slack (the one who sold us the probe) explained that the impedance is a imaginary one, so it’s high only when a high frequency voltage is applied to it. We are still looking for the pins connections.

We can not use the probe for now, so we sent our pulse in the oscilloscope (too see it), regain the signal (the echo of the oscilloscope) with the same cable and then connect the output of the echo (the TLVout) to the oscilloscope again. Here is the result:

We found the power supply (0-500V continuous) in the electronics laboratories. Using it, we can obtain a scalable pulse visible on a oscilloscope.

The next step is to use the probe and do the firsts tests with it.

How to get a pulse

Now that we have our different components, we can begin our work. The first step aims to learn how to use the pulser and produce a visible pulse on an oscilloscope.  In that purpose, our professor Mr Debeir allowed us to work in the LISA research service and provided the needed equipment such as oscilloscope and wires.

Technical information about the pulser were obtained from a website given by the manufacturer. We rapidly found the “how to start” section, explaining the first steps to obtain a simple pulse.

Here is the menu that defines the parameters of the pulse:

We used a protoboard for the voltage source and the assembly. The final result and the obtained pulse are shown on the following picture.

Our first components

We finally received the components we ordered. These are a probe, a pulser+switch+command and an acquisition card.

Probe: We bought it via a contact in the echOpen Slack community at 120€. Here is the site of our contact where the probe is used: https://kelu124.gitbooks.io/echomods/content/ )

Pulser: We ordered the following kit (including the software): https://www.maximintegrated.com/en/products/analog/analog-switches-multiplexers/MAX14808EVKIT.html

Acquisition card: http://www.ti.com/tool/LAUNCHXL-F28377S?HQS=epd-mcu-c2x-launchxlf28377s-etxt-evm-null-wwe&dcm=yes

We will soon try to command a pulse with the pulser+command and see it on a oscilloscope.

Electronic components

f1x600

(source: http://m.eet.com/media/1179962/f1x600.jpg)

Echography is about emitting and receiving mechanical waves that we interpret in order to build an image of the environment which was sounded. The principle is simple, but the electronic behind to achieve that goal is more complex.

The central part of the components is the piezoelectric transducer. It’s the element which is able to convert electrical signal into mechanical wave and vice versa. Therefore, it can alternatively play the role of transmitter and receiver.

The electrical signal that we just mentionned above is a high voltage signal, around 100 V. We use a high voltage pulse generator to obtain it and send it to the transducer by order of an Arduino for instance.

The excited transducer will generate high frequency waves, which will be reflected by the different obstacles of their path. The converted electrical signal corresponding to the returned waves is at low voltage. To protect the circuit downstream from the high votage pulse and at the same time allow the low voltage signal to penetrate it, we use a switch. This eletronic component can manage the abrupt changes of high and low voltage signal. It can be intergrated or not into the pulser.

The low voltage and high frequency signal coming from the transducer has to be filtered in order to minimize noise and to be amplified to be able to handle it. That’s the signal conditionning. We use a Time Gain Compensation (TGC) to amplify the returned signal. Actually, the emitted signal is attenuated by the tissues it meets (function of the distance covered). This attenuation is exponentiel. In order to remedy to this phenomenon, we use a component that will give an exponentiel gain, the TGC.

To sample the high frequency signal obtained, we can use a Red Pitaya (acquisition card with ADC) or we can first use an envelop detector and sample the result of it. In fact, the initial frequency is around 5 Mhz. To sample that by respecting the Shannon criterium, we have to use a sampling frequency of at least 15 Mhz, which is important. The Red Pitaya can do it without any problem. Meanwhile, the envelop detector allows us to reduce the frequency and use a less efficient and expensive ADC.

Once the signal has been digitized, it can be treated by a computer to finally build an image.

Short-term objectives

The aim of our project, as a first step, is to determine and order the components of the acquisition chain. We have several choices in order to achieve that purpose. First, choosing the different elements (like the pulser, the switch, the TGC, etc.) according to the offer’s market. Our visit in Paris brought us a lot of information about the specific components they used to build their prototype. It will surely help us. The second way is to order an echOpen kit which will provide us all the different components. We’ll just have to combine each part with the others. It’s probably an easier way but a less creative solution and we want to build our own echograph with its Belgian specifications.

However, we have to buy a used probe to begin our great work. It’s the most urgent case and it will determine the rest of the development.

A visit to echOpen Paris !

In order to have more informations on the progress of the original echOpen project, we decided to visit them in Paris.

We first saw their prototype, guided by one of their engineer. It helped us a lot by knowing the difficulties the encountered and which equipment the used.

Then we moved in one of their meeting room and we worked on the project with Mr Debeir.  We made the first researches on the equipment needed, particularly concerning the probe.

Finally, we had the privilege to see a demonstration of their prototype. It was pretty impressive and motivated us for our project.