Electromagnetic acoustic transducer (EMAT) proof-of-concept project.

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EMAT amplifier is based on AD830 IC and a cascode amplifier. I've taken the schematic from  this article . I also added a LC oscillator to measure the inductance of coils. The inductance of transducer coil is less than 1 uH and I don't have a LC meter capable to measure such a small value. Instead the oscillator frequency could be measured. The formula to calculate the LC oscillator frequency is the following: Where In my case CX1=47nF and CX2=10nF. A transducer coil has 10 turns of 0.16 mm wire glued with epoxy resin to 3D printed handle. After connecting to the LC oscillator it runs on frequency 1.83MHz. According to the given formula the coil inductance L is 0.91uH. Here is an assembled amplifier PCB with transducer coil attached to the LC oscillator. One can see three resistors placed on separate small PCB. These are R1, R2 and R3 resistors which should have had 2512 footprint (because they dissipate 1 W each) but I made a mistake and selected the default ...

Properly assembled circuit requires no fine tuning and works as expected after first run, providing  300V output. After assembling 2 more rectifiers we've got 924V output voltage.

We need a high voltage power supply. I am going to use DC/DC 12 to 300V boost converter schematic based on UC3843. Fig. 1. UC3843 based 12 to 300V  DC/DC  up-converter. To achieve even higher voltages I am going to use 3 identical secondary coils instead of one. This would give us 3 x 300 = 900V. Although it is less than 1200V used in original design I think we can start with this voltage. Special bobbin has been designed and 3D printed to incorporate 3 secondary coils. Coils are separated to avoid insulation breakdown. Fig. 2. 3D-printed bobbin for EFD25. Each secondary coil should be a accompanied by separate rectifier diode, RC snubber and output capacitors of course. The PCB has been designed in a way that all these elements are placed together inside a dashed rectangular area. So I don't have to order additional PCB from the factory, I can simply cut it from those PCBs that I already have.

I've made a high voltage bank. It consists of 5 WIMA FKP1 0.068 uF 1600V capacitors and six P600S diodes. Total capacity is 0.34 uF.

First I am going to copy  Experimental Demonstration and Circuitry for a Very Compact Coil-Only Pulse Echo EMAT