Hello from Hanna:
"When one design a circuit, it is always exciting to see how small you are able to make it. Our engineers have made a very small one! This little PCB can fit the whole circuit needed to recieve signals from the sensors, filter it, change it from a voltage to a modulated digital value, and ship it off to the transmitter. All of this fit on your fingertip!"
There are several reasons for engineers to minimize the size of their systems, and even more reasons when the system is going inside a living creature:
Limit weight
Fit in a limited area
Less materials needed
The PCB needs to be small and light, to cause the least amount of stress to the fish. The whole system has to be <2% of the fishes body weight. To reach that requirement our team has worked hard to optimize every piece of the system, from chioce of components and materials to placement within the capsule.
So:
To make a PCB small is no easy feat, and you will always want to make it smaller (Sometimes it's like a challange: Just to see if you are able to do it). As the size decreases, so does the level of freedom regarding components. E.g. both inductors and capasitors change their physical size depending on its value. They are measured in Henry[H] and Farad[F] respectively. Inductors and capasitors will to a great extent decide the frequency of the system, and the transmitter will respont optimally at just one frequency; its resonance frequency. The resonance frequency introduces another requirement and is met by the values of the inductors and capasitors.
The voltage input from the sensor is boosted so that the piezo transducer (transmitter) have enough energy to transmit an acoustic signal to a reciever. The signal has to be boosted as it moves through both fish and water. With a limited space for batteries, it's important to minimize the power consumption. The lifetime of the system is calculated to be 3 months with a current of 10 µA.
With the PCB optimized in size and weight, we have now moved on to decrease dimensions and mass of the wire sensor. More on the wire sensors in another post! Until next time,
Hanna T. Bråthen
Engineer at ZP
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