1 Brief Description
This technical specification defines the requirements for the development, manufacturing, software, and commissioning of a laboratory test bench for remote non-contact control of magnetic microparticles in an aqueous medium.
The system shall provide generation of uniform and gradient magnetic fields in three orthogonal planes, continuous optical observation, and real-time telemetry collection. Delivery is carried out within the framework of an open tender for the needs of the FAPESP research project.
The conceptual design shown on the right illustrates the target configuration: a rigid aluminum cube frame, orthogonally arranged copper coils, a central glass reactor on a wooden support table, and an optical microscope mounted above the working zone.
2 Purpose and Operating Principle
2.1. Purpose
- Laboratory research in the field of microhydrodynamics and bioengineering.
- Precision control of orientation, rotation, and translation of magnetic microparticles.
- Continuous optical observation for at least 3 hours.
2.2. Operating Principle
Rotation (XY Plane)
Sinusoidal currents of equal amplitude with a 90° phase shift are applied to the X and Y coil pairs. The field vector describes a circle at a given frequency of 1–20 Hz.
Translation (Z Axis)
A DC or low-frequency current is applied to the gradient coils. A non-uniformity ∂Bz/∂z is created, providing attraction or repulsion of particles.
Drift Compensation
3-axis Hall sensors transmit data to the STM32. PID regulation corrects currents during coil heating in real time.
3 Technical Specifications
| Parameter | Value / Requirement |
|---|---|
| Operating frequency range | 1 – 20 Hz |
| Magnetic field amplitude | 1 – 5 mT |
| Phase shift (XY) | 0 – 360° |
| Diameter of Spherical Volume (DSV) | 80 – 100 mm |
| Coil radius (R) | 120 – 150 mm |
| Distance between coils in a pair (D) | D = R (strictly) |
| Number of independent channels | 4 (X, Y, Z_helmholtz, Z_gradient) |
| Output power per channel | 150 – 300 W |
| Power supply voltage | 36 V / 48 V (stabilized) |
| Winding wire | PEVT-2, cross-section 1.0 – 1.2 mm |
| PWM carrier frequency | 20 – 50 kHz |
| Bench dimensions (cube frame) | 500 × 500 × 500 mm |
| Reactor volume | 100 ml (optical glass) |
4 System Composition by Module
4.1. Load-Bearing Frame
- Cube frame made of 30×30 mm aluminum profile.
- Overall dimensions: 500 × 500 × 500 mm.
- Fasteners and adapter units — engineering plastic (PETG/ABS).
- Coil frames — high-density moisture-resistant plywood.
4.2. Inductive Coils
- 3 orthogonal axes (Helmholtz) + gradient pair (Maxwell).
- The upper Z coil has a central 40 mm window.
- The window is equipped with microscope mounting brackets.
4.3. Wooden Table for Reactor
- Reactor — cubic optical glass vessel with a volume of 100 ml.
- Fixation at the absolute center of the working zone.
- The table ensures rigid mounting and vibration isolation.
4.4. Electronic Unit
- Frequency, phase, and power control module.
- STM32-based microcontroller module.
- 4-channel Class D power amplifier (TPA3255 or equivalent).
- H-bridges on high-power MOSFET transistors.
4.5. Monitoring and Feedback System
- Digital 3-axis Hall sensors (MLX90393 or equivalent).
- Placement on a non-magnetic board outside the optical path.
- Polling every 5–10 ms, data transmission to STM32.
5 System Operation Examples
Rotation of Microparticles
Application of sinusoidal currents to the X and Y coils with a 90° phase shift. The field vector describes a circle at a frequency of 1–20 Hz, causing the particles to rotate in the XY plane.
Vertical Translation
Application of DC or low-frequency current to the Z gradient coils. A non-uniformity ∂Bz/∂z is created, providing attraction or repulsion of particles.
6 Software
Microcontroller (STM32)
- Direct Digital Synthesis (DDS) based on LUT.
- PWM generation with a carrier frequency of 20–50 kHz.
- Hall sensor polling every 5–10 ms.
- PID regulation for thermal drift compensation.
- Data exchange with PC via USB-UART protocol.
Desktop Software (GUI)
- Operator interface: frequency, phase, amplitude.
- Saving and loading of experiment presets.
- Real-time charts (based on GDI+).
- Automatic data recording to CSV.
- Logging of all parameters and events.
- Development environment: C++ Builder 6.0 (VCL).
7 Project Timeline and Phases
8 Bidder Requirements
- Proven experience in the development and manufacturing of laboratory benches with magnetic systems (at least 2 confirmed projects).
- Competence in power electronics (Class D amplifiers, H-bridges) and microcontroller programming (STM32).
- Competence in desktop software development on C++ Builder 6.0 (VCL) or provision of a subcontractor.
- Readiness to perform commissioning, calibration, and 3-hour stress tests.
- Provision of a complete set of design documentation and software source code upon project completion.