Ultrasonic drilling
The principle is very simple. An ultrasonic horn is used to vibrate a drillbit vertically. The drillbit can consist of nothing more than a piece of wire - I used standard household pins, which are steel and are around 0.7mm diameter. In the presence of an abrasive slurry, the pounding action of the drillbit tip causes the underlying material to chip away, gradually drilling a hole. It works best on brittle materials like glass and ceramics.