Picture of the setup. From left to right, the detection circuit, the coils assembly, and the excitation circuit. Dimensions: .
Block diagram of the system. (A) Electronics generating the rf excitation and AF modulation currents. (B) AF, excitation, and detection coils, and their mechanical assembly. (C) Detection electronics performing amplification and demodulation. (D) The software running on a PC that processes the signal of the beads, generates the AF signal, and displays the results. A National Instruments PCI-6052E multifunction board performs the AD/DA conversions.
Representation of the PCB coils. The layer in gray is on the opposite side of the PCB.
Schematic view of the coils mechanical assembly. (A) Ferrite E-cores, (B) wire-wound coils, (C) sample holder, (D) iron spacers, (E) coils PCB, (F) aluminum support, (G) adjustment screws, and (H) springs.
Schematics of the rf generation and amplification circuits.
Schematics of the AF amplifier.
Schematics of the detection electronics.
(a) Signal at the detection coils ends with the sample alternatively placed over each coil for . The integration time is , the modulation frequency is , the modulation amplitude is , and the excitation amplitude is about . The black line shows the signal obtained with the sample shown in (b), containing Dynabeads MyOne™. The gray dotted line is the result of the same procedure with an empty sample holder.
Characteristics of the printed coils. and are the values of the series resistance and inductance corresponding to the complex impedance at . When the coils are positioned inside the electromagnet, both inductance and resistance increase significantly (values in brackets).
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