Academic literature on the topic 'Microwave sensing'

New types of stress sensitive and magnetic field tunable microwave composite materials are discussed where embedded short ferromagnetic microwire inclusions are used as controllable radiative elements. The dc external magnetic field is applied to the whole composite structure. And, the local stress is transferred to the individual microwires through the accommodating composite matrix. The spatial and angular distributions of microwires can be random, partly ordered, or completely ordered. For a wide frequency range, the free-space microwave response of a wire-filled composite can be characterized by a complex effective permittivity with resonance frequency dispersion. The latter depends on the conductive and magnetic properties of the microwire inclusions that contribute to the ac microwire magnetoimpedance (MI). In the vicinity of the so-called antenna resonance frequency, which is defined by the length of microwires and matrix dielectric constant, any variations in the MI of the microwires will result in large changes of the effective permittivity, and hence the reflection and transmission coefficients for an incident microwave. The field or stress dependence of the effective permittivity arises from the corresponding field or stress sensitivity of the MI in the ferromagnetic microwires with induced circumferential or helical magnetic anisotropy, respectively. The strong field tunable effect in the proposed composite materials can be utilized to introduce reconfigurable microwave properties in coatings, absorbers, and randomizers, and also in new media such as microwave metamaterials and bandgap wire structures. A maximum field tunability of 30 dB was achieved for free-space transmission measurements when the external magnetic field changed from zero to ~40 Oe. The stress sensitivity of reflection and transmission coefficients opens up new possibilities for the distant non-destructive testing and evaluation of composite materials both in the laboratory environment and large scale applications. The stress tunability of transmission coefficient may reach up to 5-8 dB within the elastic limit. The reflection coefficient usually demonstrates less tunability in both cases (field and stress dependent) and may require a multilayer structure to achieve better results, but it is always strong enough for the stress sensing applications.

In this paper, we present a form of food security sensing using a waveguide antenna microwave imaging system through an example of an egg. A waveguide antenna system with a frequency range of 7–13 GHz and a maximum gain of 17.37 dBi was proposed. The maximum scanning area of the waveguide antenna microwave imaging sensing system is 30 × 30 cm2. In order to study the resolution and sensitivity of the waveguide antenna microwave imaging sensing system, the circular and triangular high-k materials (with the same thickness but with different dielectric constants of the materials) were used as the testing sample for observing the microwave images. By using the proposed waveguide antenna microwave imaging sensing system, the high-k materials with different dielectric constants and shapes could be easily sensed. Therefore, the waveguide antenna microwave imaging sensing system could be potentially used for applications in rapid, non-destructive food security sensing. Regarding the example of an egg, the proposed waveguide antenna microwave imaging sensing system could effectively identify the health status of many eggs very quickly. The proposed waveguide antenna microwave imaging sensing system provides a simple, non-destructive, effective, and rapid method for food security applications.

Individual nitrogen vacancy (NV) color centers in diamond are versatile, spin-based quantum sensors. Coherently controlling the spin of NV centers using microwaves in a typical frequency range between 2.5 and 3.5 GHz is necessary for sensing applications. In this work, we present a stripline-based, planar, Ω-shaped microwave antenna that enables one to reliably manipulate NV spins. We found an optimal antenna design using finite integral simulations. We fabricated our antennas on low-cost, transparent glass substrate. We created highly uniform microwave fields in areas of roughly 400 × 400 μm2 while realizing high Rabi frequencies of up to 10 MHz in an ensemble of NV centers.