This letter presents a series-fed two-dipole antenna fabricated on a flexible liquid crystal polymer (LCP) substrate by using inkjet printing technology. The proposed antenna consists of two modified dipole elements of distinct lengths, a director element, a modified ground plane, and a balun filter, yielding a wide bandwidth with bandpass responses. The proposed antenna can be used at a frequency band of 26-32 GHz. The bending behaviors of the antennas with and without director elements were analyzed. The bending effect of the antenna should be considered when calculating the gain loss and bandwidth reduction. Inkjet printing on LCP substrates provides a low-cost, compact, and flexible packaging application that can be used in probable and flexible communication technology.

A fully inkjet-printed strain sensor based on carbon nanotubes (CNTs) was fabricated in this study for microstrain and microcrack detection. Carbon nanotubes and silver films were used as the sensing layer and conductive layer, respectively. Inkjet-printed CNTs easily undergo agglomeration due to van der Waals forces between CNTs, resulting in uneven films. The uniformity of CNT film affects the electrical and mechanical properties. Multi-pass printing and pattern rotation provided precise quantities of sensing materials, enabling the realization of uniform CNT films and stable resistance. Three strain sensors printed eight-layer CNT film by unidirectional printing, rotated by 180° and 90° were compared. The low density on one side of eight-layer CNT film by unidirectional printing results in more disconnection and poor connectivity with the silver film, thereby, significantly increasing the resistance. For 180° rotation eight-layer strain sensors, lower sensitivity and smaller measured range were found because strain was applied to the uneven CNT film resulting in non-uniform strain distribution. Lower resistance and better strain sensitivity was obtained for eight-layer strain sensor with 90° rotation because of uniform film. Given the uniform surface morphology and saturated sheet resistance of the 20-layer CNT film, the strain performance of the 20-layer CNT strain sensor was also examined. Excluding the permanent destruction of the first strain, 0.76% and 1.05% responses were obtained for the 8- and 20-layer strain sensors under strain between 0% and 3128 µε, respectively, which demonstrates the high reproducibility and recoverability of the sensor. The gauge factor (GF) of 20-layer strain sensor was found to be 2.77 under strain from 71 to 3128 µε, which is higher than eight-layer strain sensor (GF = 1.93) due to the uniform surface morphology and stable resistance. The strain sensors exhibited a highly linear and reversible behavior under strain of 71 to 3128 µε, so that the microstrain level could be clearly distinguished. The technology of the fully inkjet-printed CNT-based microstrain sensor provides high reproducibility, stability, and rapid hardness detection.

This paper presents a series-fed two-dipole antenna, fabricated on a liquid crystal polymer (LCP) substrate using inkjet-printing technology. The radio frequency characteristics of inkjet-printing silver film onto an LCP substrate are studied using the microstrip line. The proposed antenna consists of two modified dipole elements of distinct lengths: a modified ground plane and a balun filter yielding a wide bandwidth with bandpass responses. The proposed antenna can be used at frequency band of 26-33 GHz. The bending behaviors of the microstrip line and antenna are also measured. Inkjet printing on LCP substrates provides a low-cost, compact, and flexible packaging solution that can be used in future communication technology.

This letter investigates inkjet-printed interdigital coupled line bandpass filters on liquid crystal polymer substrates. Silver nanoparticle colloidal solution was used as the printing ink. Various numbers of passes were used to print the samples to study the changes in conductivity and uniformity. Samples were then sintered in an oven to remove excess solvent and material impurities. The silver-film conductivity of the conductive ink was ~1×10⁷ S/m. The interdigital coupled line bandpass filter was printed with an inkjet printing system. The study achieved a minimal insertion loss and maximal return loss of -3.6 and -24 dB at 25.7 GHz, respectively.

This paper presents the fabrication of an inkjet-printed multilayer bandpass filter using the liquid crystal polymer (LCP) system-on-package (SOP) technology. The LCP-SOP technology adopted by lamination bonding process reduces the occupied area of a device and is suitable for radio frequency (RF) package applications. The surface morphologies and RF performance of the inkjet-printed silver film on an LCP substrate after the lamination bonding process, which entails applying high temperatures and pressures, were observed and analyzed. Acceptable performance of the inkjet-printed silver film of an optimal lamination bonding condition was 0.69 MPa at 270 °C. Using the inkjet-printing and LCP-SOP technologies, a miniature bandpass filter was created with a minimal S ₂₁ value and a maximal S ₁₁ value of -1.5 and -17.4 dB at 10.6-14.5-GHz passband, respectively. A strain effect of silver line and bandpass filter was also analyzed. The results demonstrated the effectiveness of the proposed design methodology and the fabrication technique.