Download SUPPLEMENTARY INFORMATION 6

SUPPLEMENTARY INFORMATION
To measure the magnetic field amplitude and orientation, a 3-axis magnetic field probe
(GMW, DMFS-3A)connected to a digital storage oscilloscope (Agilent Technologies,
DSO3102A) was used. Digital data was also acquired by using the sound card of a computer
(Dell Optiplex 9010), which can be used to acquire analog signal with up to 44 kHz
frequency. Table 1: List of major parts
Part #
SA-S3
266-580
DMFS-3A
50 W amplifier
10 mH inductors
Magnetic field probe
Manuf.
SMSL
Erse Audio
GMW
Supplier
Nettikama
Parts Express
GMW Associates
10
Dynamic viscosity
(Pa*s)
Sensor frequency (Hz)
As macroscopic application for the presented programmable magnetic field setup, the
dynamic viscosity of a four samples of glycerol-water mixtures were measured
simultaneously using asynchronous magnetic bead rotation sensors (Figure 3). A 5 Hz
rotating magnetic field was generated using the rotating magnetic field configuration, and a
cell phone audio output for signal generation. The asynchronous rotation rates of the
submerged micro-stir-bars were analyzed by video analysis, and the viscosities were
calculated with equations published in the literature.23
a)
1
0.1
0.01
c)
1.5
b)
1
0.5
0
1
2
3
Sensor #
4
1
2
3
Sensor #
4
Figure SI1: Dynamic viscosity measurement using a macroscopic AMBR sensor. a) Frequencies of four AMBR
sensors submerged in different viscosities (shown in part c), in a 96-microwell plate. b) Calculated dynamic
viscosities of the sensors, where sensor 1 is calibrated to the value of 100% glycerol. c) Image of the 96 well
plate, where every other well contains a fluid sample and a micro stir bar, used to measure the fluid viscosity.
The scale bar is 10 mm.
The authors would like to urge to use caution when designing alternating magnetic fields,
more information can be found in the ICNIRP safety guidelines for limiting exposure to timevarying magnetic fields.1
Figure SI 2: Connection diagram for generating an array of local rotating magnetic fields, where one repeating
unit is shown. The field amplitude within circle A is roughly half of the value in B. The signals for each phase
is again sinusoidal, with 90 degree difference.
a)
b)
A1
A3
A2
A4
c)
B2
B1
A
B4
A
B
B
B
B
B3
Phase A
Phase B
A
A
Figure SI3 a)-b) Inductor configuration for rotating magnetic field generation. Each phase consists of a
sinusoidal signal, 90 degrees out-of-phase with each other. c) Physical inductor configuration, used to generate
rotating magnetic field. The inner dimensions of the configuration are 105 mm by 128mm. To compensate for
the asymmetry of the inductor configuration, phase B signal amplitude was 80% of the phase B signal.
One of the potential limitations of this configuration is the inability to produce frequencies
below 0.5 Hz (depending on the sound card and amplifier). If such frequencies are needed, a
low cost setup can be constructed using a digital waveform generator such as USBwave12
(Elan Digital Systems Ltd., Fareham, UK), which can produce the usual waveforms from DC
to 1 MHz. The signal can then be amplified using a power op-amp instead of an audio
amplifier, which can supply 5A per channel with 19V voltage, (PA02, APEX
Microtechnology, Arizona, US).26
The original 20 Hz signals generated using a computer audio card (referred to in 2d-f in the
main article) can be seen in Fig SI4. While the sine and triangle signals are close to ideal, the
square wave is quite distorted. This may be due to low frequency filters sometimes present in
audio equipment.
Figure SI4: Square-, triangle- and sine waves generated using a computer soundcard (Dell Latitude E6430) at
20Hz. The distortion in the square wave is close to the distortion seen in Figure 2f in the main article.
The quality of the signal generated by a computer audio card was compared to the quality of
the magnetic field generated by the setup to identify the bottleneck of the system. This was
done by measuring the transfer functions (Fig SI5) for both, and clearly at higher frequencies
the limiting factor is the inductor setup, not the audio card. The transfer functions suggest that
the audio card can be used as a signal generator up to frequencies of 15 kHz, while the
magnetic field quality starts falling already after 10 Hz. However, at frequencies below 0.5
Hz the bottleneck is the audio in our system.
The transfer functions were measured by generating white noise using the soundcard and
measuring the signal in the frequency domain with “peak-hold” setting.
Figure SI5: Transfer function of the laptop computer soundcard system itself (left) and the magnetic field
generation system (right). The results clearly show that the limiting factor in the higher frequencies is the
inductor setup, not the audio card. However the reverse is true at low frequency end, since the audio card was
unable to generate frequencies below 0.5 Hz.
References
1
International Commission on Non-Ionizing Radiation Protection, Health Phys 99, (2010).
A. Tokarev, A. Aprelev, M.N. Zakharov, G. Korneva, Y. Gogotsi, and K.G. Kornev,
Review of Scientific Instruments 83, 065110 (2012).
2