Invisibility Rays

In the 1930s the Austrian press was excited about the invention of "invisibility rays" by an Austrian inventor. The invention was licensed by the company Semperit (the largest car and bicycle tire manufacturer in Austria) and exhibited at a trade show where it became a sensation and was viewed by hundreds of thousands of visitors. During that trade show, the inventor made for the first time also people invisible. He applied and received a patent in Great Britain for his invention. What was behind that sensation? How did it work? Who was the inventor?