Final Design

Bio-mimicry is a new field in mechanical engineering, nanoengineering, and materials science with great potential to develop multifunctional, high-performance materials and devices inspired by nature. Many natural biological materials, such as bone, abalone shell, porcupine quill and elk antler are lightweight composites that exhibit exceptional mechanical properties tailored to specific functions. The unique properties found in these materials are due to complex architectural features found on multiple length scales, from nano- to macro- levels. With a goal to develop new materials that mimic the structure and match the mechanical properties of various biological materials, MSE graduate students at UCSD have built a freeze casting apparatus to fabricate ceramic scaffolds with highly-ordered, porous microstructures. Freeze casting is a physical process in which an aqueous slurry, typically composed of a solid phase and liquid phase, is directionally frozen, then sublimated to remove the frozen liquid phase and then sintered at high temperatures to densify the porous ceramics. During the freezing process, ceramic particles are pushed between and trapped within the growing ice crystals leading to well-ordered micro-structures. Intricate microstructural features may be controlled by altering the slurry properties or changing the freezing direction and solidification kinetics. To further control the microstructural features of freeze-casting ceramics, new additions to conventional freeze-casting techniques are of great interest, such as applying magnetism during the freezing process. By creating an external rotating magnetic field, UCSD researchers plan to use this to align magnetic particles or create concentration gradients within a slurry during the freeze-casting process. With this researchers hope to use the magnetic fields to mimic the spiraling biological structure of a narwhal tusk. To accomplish this, our team created a large iron horseshoe magnet with one large high power permanent magnet. This magnet is mounted to a stepper motor which rotates the entire magnet about the z- axis. The freeze-cast mold is placed in the open gap of the horseshoe magnet where it can be manipulated by the magnetic field of the magnet. Success of this magnet magnetic apparatus will be evaluated once it is built.

Presented here is our final design. We used a permanent magnet and funneled the magnetic field to a small gap where the freeze-casting sample will be. The magnet will be rotated by a stepper motor coupled to the magnet.

Caption: High Resolution Render of the Final Design of the Magnetic Field Apparatus

This design utilizes one permanent magnet one large 4in X 4in X 1in magnet which is rated at 1.32 Tesla, a pull force of over 700 lbs. Using the concept of flux funneling the magetic field , we will apply about a magnetic field strength of 2.3 Tesla at the surface of the magnet closest to the sample in the PVC tube. The magnetic field strength at the location of the sample can be adjusted simply by rotating the threaded blocks on the cylindrical screw on the magnet.

Caption: High Resolution Render Displaying Stepper Motor Setup

One large issue was supporting the weight of the magnet due to the weight of it. The stepper motor could not support the 12 kg magnet. In order to work around this, our magnet is held by a coupler resting on a thrust bearing. The coupler then connects to the motor on the other side which can now rotate the magnet without any weight on the motor. As a safety if the magnet slips out of the coupler, we have a safety clip which runs around a notched out area of the aluminum rod attached to the magnet.

Caption: High Resolution Render of Thrust-Load Mechanism and Safety Clip Cross Section

Control Interface

In order to have the magnet rotate we have a stepper motor that is controlled by an arduino and driven by a stepper motor driver. With the given potentiometer, one controls the rotation speed on an arbitrary scale from 1 to 49 that is displayed on an LED on the interface.

This can all be conveniently seen on the built-in controls on the magnetic freeze casting device. By simply plugging in the DC power to the arduino, one can control the the speed of the motor.

At the bottom of the page we have all the coding for arduino that works in the arduino-0022 compiler and a downloadable sketch with the NewSerialSoft library to load onto your computer.

Construction of Device

The building of the magnetic device includes several different components. The first part is building the magnet, second the frame, and the third consructing the controls to control the stepper motor ,interact with the potiometer, and display information on the serial LCD. Here is a build of materials for the final design which has a list of all the necessary components to build the device. Additionally, her is a list with all the CAD for Machining and Cutting Acrylic for the device. After machining the magnets themselves, we used this method to assemble them. To build the frame, we simply cut all the frame pieces to length and drilled several holes on a mill. We then pressed each of the members to the ordered joints. After this we soldered together all the controls according to the wiring diagram below:

After soldering together all the electronics, we had to assemble everything and now we have a working magnetic field generator.

Project Performance

Using a Gaussmeter, we were able to attain a tesla value of the magnet of .22 Tesla at the center of the gap. Though this is not the intended strength our sponsor asked for and it was not the what our simulations stated would be the case, it was strong enough to adjust the magnetic fields. We suspect the cause of this to be our iron reaching its magnetic flux saturation. Iron's flux saturation shown in this table here was not the best material to use. If we want to further improve our data, we recommend rebuilding the magnet with cast steel which is shown from the table to be much more effective. As for the rotations. We were able to hit the goal of one revolution every 20 minutes. With this, we can now effectively control the magnetic field. Below is a graph of the magnetic field strength vs.distance.

Instruction Manual

At the bottom of this page one can download the full instruction manual.

Here is a general overview of how the device works:

Operation:

1.       To turn on magnetic field generator,  plug DC power supply into DC power jack on the arduino which is located at the side of the black control interface sheet.

2.       After viewing the opening screens, the display will show the rotation speed on a scale from 1 to 49.

3.       To control the rotation speed, rotate the potentiometer to adjust the value on the LCD screen.

4.       Device is now ready to operate.

Video of Device Working:

Below is the Code we used to control the stepper motor, LCD screen, and potentiometer. Attached at the bottom is a sketch of all this code with the NewSoftSerial library also attached.