MExpSimu

A microscopy experiment simulator. MExpSimu plays back recorded scanning-probe microscopy datasets through the same three operations a real acquisition control loop uses:

• image scan -- perform a full-frame scan and get back a recorded image channel
• move tip -- move the probe tip to a coordinate on the sample
• spectroscopy -- take a local spectroscopy measurement at the tip's position

It's meant as a stand-in for real instrument hardware when developing or testing acquisition logic, agents, or analysis pipelines that need something to talk to.

Installation

pip install -e ".[dev]"   # editable install, with pytest for the test suite

Requires Python >= 3.10 and numpy.

Quick start

import mexpsimu

mexpsimu.list_presets()
# ['PTO_BEPS_1d3um', 'PTO_BEPS_1d7um', 'PTO_BEPS_3um']

scope = mexpsimu.Microscope("PTO_BEPS_1d3um")

# 1. Image scan -- pick a channel by name (defaults to the first one)
scope.list_channels()                    # ['image', 'image2']
image = scope.scan_image("image")        # -> (65, 65) array, at that channel's own resolution

# 2. Move the tip to a physical coordinate, in microns
scope.move_tip(0.6, 0.6)
scope.position                            # TipPosition(row=28, col=28, x_um=..., y_um=...)

# 3. Local spectroscopy at the current tip position
voltage, response = scope.spectroscopy()
scope.voltage_source                      # "recorded" if the file had a vstep array, else "synthesized"

# ...or move-and-measure in one call
voltage, response = scope.spectroscopy(0.2, 1.0)

Run examples/quickstart.py for a plain-script tour (optionally plots with matplotlib if it's installed), or open notebooks/quickstart.ipynb for the same tour as an executed Jupyter notebook with plots inline.

Sample data

Three Band Excitation Piezoresponse Spectroscopy (BEPS) datasets on a PbTiO3 (PTO) sample are bundled in mexpsimu/data/, named by their physical scan size:

Each .npz file holds one or more 2-D image channels (image is topography; image2 is a derived response map -- it equals the recorded spectra averaged over its last axis), a spectra array of shape (rows, cols, n_steps) (the local piezoresponse loop recorded at every pixel), and a vstep array of length n_steps (the DC bias actually applied at each step).

Microscope addresses the tip on the dataset's spectroscopy grid (ScanDataset.measurement_shape), which is the same grid as the image channels in all three bundled datasets, but doesn't have to be -- spectroscopy is slower to acquire than an image scan, so a dataset with a coarser spectroscopy grid than its image channels is handled correctly too; scan_image() always returns a channel at its own native resolution regardless of where the tip currently is.

Drop additional .npz files with the same layout into mexpsimu/data/ (or point Microscope(..., data_dir=...) at your own folder) and they become available as presets automatically, using their filename's stem as the preset name.

A note on voltage and coordinates

• Coordinates are the pixel grid itself (the spectroscopy grid, when present). Physical coordinates (microns) are computed from the scan size parsed out of the filename, assuming a square scan with the origin at the top-left pixel.
• Excitation voltage: all three bundled datasets include a vstep array (the DC bias actually applied at each spectroscopy step, a +-12V bipolar triangular sweep over three cycles), which Microscope uses verbatim. For a dataset that lacks one, Microscope instead synthesizes a representative bias waveform (default: a bipolar triangular sweep, 0 -> +10V -> 0 -> -10V -> 0, the same shape typically used in switching-spectroscopy PFM / BEPS) sized to match the spectrum's length. Check Microscope.voltage_source ("recorded" or "synthesized") to tell which case you're in. The synthesized waveform's shape and amplitude can be changed via waveform_kind, waveform_v_max, and waveform_cycles when constructing a Microscope (see mexpsimu/waveform.py) -- these are ignored when a real vstep is present.

Package layout

mexpsimu/
├── __init__.py       Public API
├── registry.py        Discovers .npz presets, parses scan size from filenames
├── dataset.py          ScanDataset: loads a .npz file into channels + spectra
├── waveform.py         Synthetic excitation waveforms (bipolar/unipolar triangle, sine)
├── microscope.py       Microscope: scan_image / move_tip / spectroscopy
├── exceptions.py
└── data/                Bundled sample datasets
tests/                   pytest suite exercising the bundled datasets directly
examples/quickstart.py
notebooks/quickstart.ipynb

Running tests

pip install -e ".[dev]"
pytest

Acknowledgment

The domain concepts here (band-excitation PFM, image scan / tip motion / spectroscopy as the basic building blocks of a probe microscopy experiment) were informed by the AEcroscopyWave project, which drives real AFM hardware. MExpSimu is an independent implementation aimed at simulating that experience against recorded data rather than live instruments, and shares no code with it.

License

MIT