In each case, the resulting image is focused by a clever arrangement of lenses on to a three-layer sandwich made of special materials.

ECONOMIST: Curtains for celluloid

The first layer of the sandwich is photoelectric.

ECONOMIST: Curtains for celluloid

The device that Dr Kirczenow and Dr Rego had in mind is called a semiconductor heterostructure a semiconductor sandwich made of a thin layer of aluminium gallium arsenide held between two thicker layers of gallium arsenide.

ECONOMIST: Microelectronics

OLETs rely on three layers of material, with the bottom layers carrying a charge, the middle layer (the meat in this high-tech sandwich) emitting photons when excited by the bottom, and the top layer selectively letting those photos through.

ENGADGET: Organic Light Emitting Transistors might make us forget all about OLED

To enable this material to store electrical energy, two layers of woven fibres are made into a sandwich, separated by a thin layer of a glass-based insulating material.

ECONOMIST: Carbon-composite batteries

And much to my delight, I discovered that I was able to see the city's past as well as its present: the London of my imagination superimposed upon the reality, a transparent city in which the old was encased in the new like an ancient layer cake wrapped in glistening sandwich-wrap.

WSJ: Alan Bradley on Writing About an England He'd Never Seen | Traveler's Tale

The Dutch Sandwich has been used for decades but involves another layer of complexity.

FORBES: Facebook Mirrors Google's Offshore Tax Scheme

The resin within the carbon layers is laced with lithium ions, so that each layer acts like an electrode, causing the positively charged lithium ions to collect in one layer when a voltage is applied, and a current to flow when the sandwich is placed in a circuit.

ECONOMIST: Carbon-composite batteries