A forcing function is required to run a model. For our model we'll add a time forcing function. Later, when adding our loads (which in our model will represent electrodes) we'll associate one of these loads with this function.

The time function is generally a short pulse that allows the system response to be extracted from a device or that can be used to analyse reflections from target. We provide a variety of time functions and you can also define your own.

**Note:** OnScale is based in the time domain. We work with analog signals (waveforms varying over time) that directly correlate with real-world signals. This lets you recreate experimental setups directly in the software to get like-for-like datasets out.

## Adding the Ricker Wavelet Function

Follow these steps:

- In the
**Model Tree**, expand**Forcing Functions**. - Beside
**Time**, click . The**Define Input Drive Function**window shows. -
In the dropdown, select

**Ricker Wavelet**. - Click
**Insert**.

Our time forcing function is added to the **Model Tree**.

**Note:** For the record, here's how the Ricker Wavelet input function looks in the frequency domain.

## What Next?

Next let's add the parameters we'll need.