Capacitive micromachined ultrasonic transducers (CMUTs) with a built-in charge layer are known as a pre-charged CMUT. In our prior work, we have shown how to model and characterize the charges inside the pre-charged collapse-mode CMUT and conducted life-time test that showed that the charges trapped inside the dielectric were stable in the order of years [1]. However, our prior work focused on the use of pre-charged collapse-mode CMUTs as a way to achieve ultrasound power reception, which does not require the CMUT to be actively driven. In this work, for the first time we use pre-charged collapse-mode CMUTs with an Al2O3 charge-trapping layer to create a B-mode ultrasound image. Thus, this work shows the first example that pre-charged collapse-mode CMUTs can fully operate with only an AC voltage.

Surfaces which can accurately distinguish spatial and temporal changes in temperature are critical for not only flow sensors, microbolometers, process control, but also future applications like electronic skins and soft robotics. Realizing such surfaces requires the deposition of thousands of thermal sensors over large areas, a task ideally suited for printing technologies. Negative temperature coefficient (NTC) ceramics represent the industry standard in temperature sensing due to their high thermal coefficient and excellent stability. A drawback is their complex and high temperature fabrication process and high stiffness, prohibiting their monolithic integration in large area or flexible applications. As a remedy, a printable NTC composite that combines a rapid and scalable all-printed fabrication process with performances that are on par with conventional NTC ceramics is demonstrated. The composite consists of micrometer-sized manganese spinel oxide particles dispersed in a benzocyclobutene matrix. The sensor has a B coefficient of 3500 K, with a 4.0% change in resistance at 25 °C, comparable to bulk ceramics. The selected polymer binder yields a composite exhibiting less than a 1 °C change in resistance to changes in humidity. The sensor's scalability is validated by demonstration of a Q4 A4-sized temperature sensing sheet consisting of over 400 sensors.