Abstract
Electromagnetic waves play a key role in contactless sensing and stimulations. In this thesis, new designs have been proposed and successfully validated and demonstrated to manipulate electromagnetic fields or static magnetic fields to enable contactless sensing to revolutionize the conventional in-circuit testing (ICT), and to tackle the bottleneck of traditional transcranial magnetic stimulation (TMS) in terms of how to achieve the high field focality at a deeper region. For ICT, to address the challenges brought by the shrinking size and increasing density of modern printed circuit board assemblies (PCBAs), various sensing techniques have been proposed in this thesis to enable contactless detections of defects, focusing mainly on shorts and opens. New capacitive and inductive sensors have been proposed to properly couple the electromagnetic field with the device under test (DUT) on PCBAs for defect detections. The challenges of defect detections for ball grid array (BGA) were taken up by further extending transformation optics (TO) techniques where a novel metasurface design which emulates the effects of static negative permeability (SNP) was proposed to control the magnetic field precisely at a remote region by creating a virtual current source. The newly proposed SNP metasurface was further applied to tackle the bottleneck of TMS coil designs, the limited penetration depth for high field focality, by proposing an SNP-metasurface TMS coil design. The proposed SNP-metasurface TMS coil can generate a virtual figure-8 inside the human brain at different depths by adjusting the value of the current flowing through the coil, which opens a new way to create high focality field at a deeper region inside human brain. iii In summary, this thesis provides effective field-based solutions to solve the existing challenging ICT and TMS problems. It offers three main contributions: a) designs of capacitive and inductive sensing probes that efficiently couple the electromagnetic field with the PCBA under test to accurately detect the defects; b) an SNP metasuface (and the design method) that enables a precise control of magnetic field in inaccessible regions by creating a virtual current source in these regions; and c) an SNP-metasuface based TMS coil that breaks the existing limitation on how to achieve high field focality for stimulation at a deeper region in human brain. The thesis demonstrates the possibility and flexibility of electromagnetic field manipulations for real industrial and medical applications, especially at the challenging part of the electromagnetic spectrum, DC and low frequencies, with corresponding new knowledge built