The choice of substrate material in a chip that combines ultrasound with microfluidics for handling biological and synthetic microparticles can have a profound effect on the performance of the device. This is due to the high surface-to-volume ratio that exists within such small structures and acquires particular relevance in polymer-based resonators with 3D standing waves. This paper presents three chips developed to perform particle flow-through separation by ultrasound based on a polymeric SU-8 layer containing channelization over three different substrates: Polymethyl methacrylate (PMMA); Pyrex; and a cracked PMMA composite-like structure. Through direct observations of polystyrene microbeads inside the channel, the three checked chips exhibit their potential as disposable continuous concentration devices with different spatial pressure patterns at frequencies of resonance close to 1 Mhz. Chips with Pyrex and cracked PMMA substrates show restrictions on the number of pressure nodes established in the channel associated with the inhibition of 3D modes in the solid structure. The glass-substrate chip presents some advantages associated with lower energy requirements to collect particles. According to the results, the use of polymer-based chips with rigid substrates can be advantageous for applications that require short treatment times (clinical tests handling human samples) and low-cost fabrication.

An impedance model, based on transmission line theory, is introduced for common mode ferrite chokes. The proposed model takes into account the geometrical properties of the choke, the distribution of electromagnetic fields within the core material and the impact of the measurement setup. The validity of the model was tested through numerical simulations. As a practical application, the model was applied to estimate the complex permeability of manganese zinc (MnZn) and nickel zinc (NiZn) cores from impedance measurements, resulting in a range of values compatible with those reported in other works.

This paper presents a full-wave 3-D FEM simulation methodology for magnetic toroidal cores up to 100 MHz. 3-D FEM simulation of magnetic toroidal cores has gained significant relevance in recent years. However, the use of magnetic materials in simulation presents some difficulties. Complex permeability is typically the only electromagnetic property used in magnetic toroidal cores' simulation. Nonetheless, recent results suggest that other properties must also be considered in high-frequency simulations. The presented methodology is particularly practical as it accurately models commercial cores easily. Electromagnetic properties valid for simulation are directly extracted from the cores with two simple setups. No complex fixtures or sample modification are required. Two ferrites (MnZn and NiZn) and a nanocrystalline core are studied. Complex permeability is characterized with a largely used method, and complex permittivity is extracted directly from the cores using the parallel plate capacitor method. With this methodology, cores' electromagnetic models are achieved, which are validated by comparing 3-D FEM simulations of several inductors with their measurements. Results lead to a simple and practical methodology to perform small-signal cores simulation in linear zone up to 100 MHz, which had not been achieved so far.