Sensors

Introduction

KiSSAM can simulate the readings for the two type of detectors: radiation detectors to measure emitted and reflected electromagnetics waves, as well as detectors of back-scattered electrons.

General setup

The Sensors section can contain the two fields: Default and Array.

Default is a default setting for every sensor that is added to the simulation.

Array is an array. For every element of an array, a sensor is added to the simulation. Every element should be represented by JSON data with the same fields that are present in the default sensor. If any field is not specified, the default value is taken.

If the sensor readings are not required, an empty array should be specified to save the computational cost.

Backscattered Electrons

In KiSSAM, each simulated electron from the source are traced inside the material, reducing its kinetic energy along the path. Both elastic and inelastic scattering processes are taken into account. In the Monte-Carlo model, the electron trajectory in the material is approximated by a series of straight line segments with a randomly chosen length. The energy loss is modelled by reducing the electron energy at each line segment between two collisions. In the scattering events, the energy is deposited as a volume heat source at the corresponding cells for the LBM temperature model. The electrons can be fully absorbed in the material, if all energy is deposited, or leave the material otherwise.

The electrons that leave the material can be measured by the detectors.

Obviously, the number of the model electrons is small relative to the number of real electron. By default, one electron ray falls on each cell on the surface, which proves to be enough for accurate energy deposition. The parameter can, and should be increased for simulating backscattered electron voltage.

Warning

For low noise in the detector measurements, increase the Beam.RaysPerCell parameter. The defaul value is too low. Set it to a perfect square number, such as 100.

Input

To measure backscattered electron voltage, set the deterctor type to Electrons.

The two other fields are relevant for the detector setting: Origin and Size.

Origin are the three coordinates of the detector, which are specified in meters relative to the origin of the simulation domain.

Note

The detection works outside the simulation domain. The coordinates of the origin should be outside the simulation area, specified in sizes.FullXapprox, sizes.FullYapprox, sizes.FullZapprox

The electrons which approach the origin closer than Size/2 (meters) are counted by the detector.

Size can take a special value -1. A detector with Size equal to -1 will count all electrons which are not absorbed by the solid or liquid material.

Here is an example:

 "Sensors":{
    "Default":{
       "DetectType":"Electrons",
       "Size":0.05
    },
    "Array":[
       { "Origin":[ 0.006, 0.006, 0.3006 ]},
       { "Origin":[ 0.2302, 0.006, 0.1933 ]},
       { "Origin":[ 0.2902, 0.006, 0.0782 ]},
       { "Size":-1, "Origin":[ 0, 0, 0 ] }
    ]
 },
 "sizes":{
    "FullZapprox":0.001,
    "FullYapprox":0.0012,
    "FullXapprox":0.0012,
    "substrate":0.0006
    },
"ScanStrategy": {
  "Beam": {
    "type"     : "Ebeam",
    "SuppressBackScattering": 0,
    "RaysPerCell": 100
    }
 }

Here, all sensors detect backscattered electrons. The first sensor is directly above the center of the simulation area, 30 cm above the surface. The next two sensors measure electrons scattered at an angle. The size of the first three sensors is 5 cm. This means, that any electron that enters a sphere (5 cm in diameter) located at the origin coordinates, is counted.

The size of the last sensor is -1. It will count every electron that leaves the material.

Output

When the sensors exist in a simulation, the sensors.dat file in the output directory is not empty. It contains a table. Each column represents a sensor from the Sensors.Array. Each row is the reading of the sensor: the power (W) measured during the config.IterationSubstepsRate time steps, multiplied by the value of config.IterationSubstepsRate.

In the example above, the file will contain four columns.