Monthly Archives: November 2016

Electronic components

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(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.