Shaking Patterns: How to Get the Most out of Your Shaker

A shaker can look like the simplest device on the bench: set a plate on it, press start, watch it go round. But “round” is one of several shapes a plate can trace, and which one you get (a line, a circle, an ellipse, a figure-eight) follows from a small handful of numbers. What follows is a lens for reading any shaker by how much of that shape-space it lets you reach.

Two sines, one plate

Underneath, a shaker moves its platform in two directions at once, call them x and y. Each direction follows a sine wave: the platform eases out to one side, back through the middle, out to the other, and repeats. Its position at time t is x(t) = Aₓ · sin(2π fₓ t) across one axis and y(t) = Aᵧ · sin(2π fᵧ t + φ) along the other.

Five numbers set the motion: how far it travels in x and in y (the two amplitudes, Aₓ and Aᵧ), how fast each axis oscillates (the two frequencies, fₓ and fᵧ), and how far the two axes are out of step (the phase, φ). The amplitudes stretch the picture; the shape itself comes from the frequency ratio and the phase.

The shapes

A handful of combinations cover most of what you will meet:

• Line. Turn one axis off (zero amplitude) and the platform slides back and forth along the other.
• Circle. Equal travel on both axes, matched frequencies, a quarter-turn of phase between them. This is what a plate reader’s menu tends to label orbital (there is a note in the glossary on why orbital and circular are not quite the same word).
• Ellipse. The circle with unequal amplitudes, squashed along one axis.
• Figure-eight. Run one axis at twice the frequency of the other and the path crosses itself into an infinity.

These are easier to move than to describe. Pick a preset, or drag any single parameter and watch the path redraw:

Two things reward a moment of play: hold the frequencies equal and sweep the phase, to watch a line fill out into an ellipse and flatten back again; then set a 1:2 ratio and notice how sharply the figure-eight depends on the phase. The oblique view tilts the plane into the plate’s own perspective.

What the firmware sets

Those sliders are not only a diagram. On an Inheco incubator shaker the same five numbers travel in one command, SSP, and the explorer prints the exact string as you go. A few practical limits shape how freely they combine:

• The phase can be set on its own, but the firmware accepts it when the two frequencies already sit at an integer ratio (1:1, 1:2, 1:3), with x no faster than y. The explorer marks any combination the device would refuse.
• The chamber is enclosed, so the pattern is not something you can watch by eye. The device reports the phase value back to you, though not the shape it produced, so confirming a figure-eight on the hardware means instrumenting the platform rather than looking at it.
• One point is still open. The firmware describes the phase as referenced to the x-axis, and it is not yet settled whether a true figure-eight lands at the textbook 0° / 180° or at some other value. The explorer draws the textbook convention; the device’s own is being checked on the bench.

Most shakers are simpler than this

The Inheco is unusually forthcoming about its motion. A more typical device, such as a QInstruments BioShake, narrows the whole shape-space to a single point. Its orbit is a fixed 2 mm circle built into the hardware; the parameter you set is the speed, in rpm (setShakeTargetSpeed, then shakeOn). With no amplitude, no phase and no second frequency to change, it offers one circle, faster or slower, rather than a family of shapes. In return it exposes two controls the Inheco command keeps to itself: the direction of rotation, and how sharply it ramps up to speed.

So the useful question about a shaker is less “does it shake” than how much of this motion it hands you. Most sit where the BioShake does, one circle at an adjustable speed, which is what a great many protocols ask for. A few, like the Inheco, open the whole family. The explorer above is a way to see what that family holds, and to read a datasheet knowing which of these numbers a given device will let you set.