Conformal Printing of Electrically Small Antennas on Three‐Dimensional Surfaces

Abstract

Increasingly stringent design constraints imposed by compact wireless devices for telecommunications, defense, and aerospace systems require the miniaturization of antennas. Unlike most electronic components, which benefi t from decreased size, antennas suffer limitations in gain, effi ciency, system range, and bandwidth when their size is reduced below a quarter-wavelength. The electrical size of the antenna is measured by its ka value, where k is the wavenumber ( k = 2 π / λ , λ = wavelength at the operating frequency) and a is the radius of the smallest sphere that circumscribes the antenna. Antennas are considered to be electrically small when ka ≤ 0.5. Recent attention has been directed towards producing radiofrequency identifi cation (RFID) antennas by screen-printing, [ 1 ] inkjet printing, [ 2 ] and liquid metalfi lled microfl uidics [3][4][5] in simple motifs, such as dipoles and loops. However, these fabrication techniques are limited in both spatial resolution and dimensionality; yielding planar antennas that occupy a large area relative to the achieved performance.Omnidirectional printing of metallic nanoparticle inks offers an attractive alternative for meeting the demanding form factors of 3D electrically small antennas (ESAs). We have previously demonstrated that fl exible, stretchable, and spanning silver microelectrodes with features as small as ∼ 2 μ m can be patterned both in and out-of-plane (e.g., spanning arches) on fl at substrates by this approach. [ 6 ] Here, for the fi rst time, we demonstrate the conformal printing of silver nanoparticle inks on curvilinear surfaces to create electrically conductive meander lines. When interconnected with a feed line and ground plane, the resulting 3D ESAs exhibit performance properties that nearly match those predicted theoretically for these optimized designs.Antennas act as effective transducers between free space and guided waves over a range of frequencies, known as their impedance bandwidth. The impedance of most small antennas can be approximated by a single resistor-inductor-capacitor (RLC) circuit, and their bandwidth is inversely proportional to their radiation quality factor ( Q ), defi ned as the ratio of energy stored to energy radiated. [ 7 ] Because of this inverse relationship, a low Q serves to increase bandwidth, and therefore the data rate over a given wireless channel. However, a fundamental relation exists between the antenna size and Q . [ 8 , 9 ] As the maximum dimension decreases below a wavelength, the bound on the minimum attainable Q rapidly increases, a phenomenon commonly referred to as Chu's limit -an important fi gure of merit for antenna performance. While Thal recently derived a more accurate bounding limit, [ 10 ] both limits depend on the electrical size of the antenna. For decades, researchers have sought antenna designs that approach these fundamental lower limits. However, prior efforts, such as those based on genetic algorithms [ 11 , 12 ] lack fl exibility, since their output cannot be modifi ed in a straightfor...

Investigation of 3D Printed Electrically Small Folded Spherical Meander Wire Antenna

“…The quality factor Q of the designed antenna is 26.03, approaching the lower physical bound of electrically small electric antennas at a given electrical size [14]. It is found that the radiation efficiency is improved when compared with the antenna in [12], which is built by printing silver nanoparticle ink on a hemispherical dielectric surface. It shows 71% radiation efficiency at ka of 0.46.…”

“…The meander design is prevalent due to its intuitiveness in achieving a small form factor. It has been found that the 3D printed FSM antenna shows superior radiation efficiency when compared with the antenna in [12] due to the advantageous 3DP manufacturing technology. Some preliminary simulation results are shown in [13].…”

“…The FSM design itself is not new but has been reported in [12] as a printed form on a hemispherical dielectric surface. The meander design is prevalent due to its intuitiveness in achieving a small form factor.…”

Compact helical antenna for smart implant applications

“…20 However, keeping in mind the commercialization of the technology, manual fabrication of small-sized helixes is economically questionable. Therefore, advanced fabrication technologies, for example, conformal printing, 21 microcontact printing 22,23 and rolled-up strain engineering, [24][25][26][27][28] were suggested and applied to realize metallic and semiconducting helixes with linear dimensions in the tens of micrometer range. However, simple, precise, large-scale and high-yield fabrication of highperformance helical antennas that are compact but remain impedance matched to standard 50 Ω electronics is challenging and has not yet been achieved, thus preventing the commercial realization of smart implants.…”

Correlation Effects on the Mimo Capacity for Conformal Antennas on a Paraboloid

“…For complicated antenna geometries such as conformal arrays full wave analysis and rigorous electromagnetic analysis is indispensable [12]. Conformal antenna arrays are utilized in airborne and space vehicles and also find applications in situations where surface adaptation is required (e.g., environmentally friendly cellular base stations) or flexible substrates [13][14][15]. Several conformal antennas have been suggested for MIMO use focusing only on mutual coupling but without any capacity calculations [16][17][18][19][20].…”