MEMS Technology for Biomedical Imaging Applications

Biomedical imaging is the key technique and process to create informative images of the human body or other organic structures for clinical purposes or medical science. Micro-electro-mechanical systems (MEMS) technology has demonstrated enormous potential in biomedical imaging applications due to its outstanding advantages of, for instance, miniaturization, high speed, higher resolution, and convenience of batch fabrication. There are many advancements and breakthroughs developing in the academic community, and there are a few challenges raised accordingly upon the designs, structures, fabrication, integration, and applications of MEMS for all kinds of biomedical imaging. This Special Issue aims to collate and showcase research papers, short commutations, perspectives, and insightful review articles from esteemed colleagues that demonstrate: (1) original works on the topic of MEMS components or devices based on various kinds of mechanisms for biomedical imaging; and (2) new developments and potentials of applying MEMS technology of any kind in biomedical imaging. The objective of this special session is to provide insightful information regarding the technological advancements for the researchers in the community

MEMS Cantilever Sensor for THz Photoacoustic Chemical Sensing and Spectroscopy

Sensitive Microelectromechanical System (MEMS) cantilever designs were modeled, fabricated, and tested to measure the photoacoustic (PA) response of gasses to terahertz (THz) radiation. Surface and bulk micromachining technologies were employed to create the extremely sensitive devices that could detect very small changes in pressure. Fabricated devices were then tested in a custom made THz PA vacuum test chamber where the cantilever deflections caused by the photoacoustic effect were measured with a laser interferometer and iris beam clipped methods. The sensitive cantilever designs achieved a normalized noise equivalent absorption coefficient of 2.83x10-10 cm-1 W Hz-1/2 using a 25 µW radiation source power and a 1 s sampling time. Traditional gas phase molecular spectroscopy absorption cells are large and bulky. The outcome of this research resulted was a photoacoustic detection method that was virtually independent of the absorption path-length, which allowed the chamber dimensions to be greatly reduced, leading to the possibility of a compact, portable chemical detection and spectroscopy system

Semiconductor Infrared Devices and Applications

Infrared (IR) technologies—from Herschel’s initial experiment in the 1800s to thermal detector development in the 1900s, followed by defense-focused developments using HgCdTe—have now incorporated a myriad of novel materials for a wide variety of applications in numerous high-impact fields. These include astronomy applications; composition identifications; toxic gas and explosive detection; medical diagnostics; and industrial, commercial, imaging, and security applications. Various types of semiconductor-based (including quantum well, dot, ring, wire, dot in well, hetero and/or homo junction, Type II super lattice, and Schottky) IR (photon) detectors, based on various materials (type IV, III-V, and II-VI), have been developed to satisfy these needs. Currently, room temperature detectors operating over a wide wavelength range from near IR to terahertz are available in various forms, including focal plane array cameras. Recent advances include performance enhancements by using surface Plasmon and ultrafast, high-sensitivity 2D materials for infrared sensing. Specialized detectors with features such as multiband, selectable wavelength, polarization sensitive, high operating temperature, and high performance (including but not limited to very low dark currents) are also being developed. This Special Issue highlights advances in these various types of infrared detectors based on various material systems

Review of photoacoustic imaging plus X

Photoacoustic imaging (PAI) is a novel modality in biomedical imaging technology that combines the rich optical contrast with the deep penetration of ultrasound. To date, PAI technology has found applications in various biomedical fields. In this review, we present an overview of the emerging research frontiers on PAI plus other advanced technologies, named as PAI plus X, which includes but not limited to PAI plus treatment, PAI plus new circuits design, PAI plus accurate positioning system, PAI plus fast scanning systems, PAI plus novel ultrasound sensors, PAI plus advanced laser sources, PAI plus deep learning, and PAI plus other imaging modalities. We will discuss each technology's current state, technical advantages, and prospects for application, reported mostly in recent three years. Lastly, we discuss and summarize the challenges and potential future work in PAI plus X area

Diagnostic ultrasound probes: a typology and overview of technologies

AbstractThe routine clinical use of diagnostic ultrasound (US) has spread considerably worldwide in recent decades. This is due in large part to the availability of US probes that enable a wide range of clinical applications as well as provide performance benefits arising from technological improvements. This paper describes the current commercially available US probe types, lists some of their clinical applications and briefly explains the technologies that are responsible for recent enhancements in image quality and ergonomics. Our intention is to summarize information that will allow healthcare professionals to select the appropriate probe for the intended use and the desired performance-price ratio.</jats:p

Multielement Ring Array Based on Minute Size PMUTs for High Acoustic Pressure and Tunable Focus Depth

This paper presents a multielement annular ring ultrasound transducer formed by individual high-frequency PMUTs (17.5 MHz in air and 8.7 MHz in liquid) intended for high-precision axial focalization and high-performance ultrasound imaging. The prototype has five independent multielement rings fabricated by a monolithic process over CMOS, allowing for a very compact and robust design. Crosstalk between rings is under 56 dB, which guarantees an efficient beam focusing on a range between 1.4 mm and 67 µm. The presented PMUT-on-CMOS annular array with an overall diameter down to 669 µm achieves an output pressure in liquid of 4.84 kPa/V/mm 2 at 1.5 mm away from the array when the five channels are excited together, which is the largest reported for PMUTs. Pulse-echo experiments towards high-resolution imaging are demonstrated using the central ring as a receiver. With an equivalent diameter of 149 µm, this central ring provides high receiving sensitivity, 441.6 nV/Pa, higher than that of commercial hydrophones with equivalent size. A 1D ultrasound image using two channels is demonstrated, with maximum received signals of 7 mVpp when a nonintegrated amplifier is used, demonstrating the ultrasound imaging capabilities

CMUT array design and fabrication for high frequency ultrasound imaging

High frequency ultrasound imaging is utilized in a broad range of applications from intravascular imaging to small animal imaging for preclinical studies. Capacitive micromachined ultrasonic transducers (CMUTs) possess multiple preferable characteristics for high frequency imaging systems, such as simpler fabrication methods, simpler integration to electronics, and greater variety of array geometries. Adequate performance and optimization of CMUT based systems require a comprehensive analysis of multiple design parameters. This research utilizes a nonlinear lumped model, capable of simulating the pressure output, electrical input-output, and echo response to a planar reflector of CMUT arrays with arbitrary membrane shape and array geometry, to determine the performance limitations of high frequency CMUT arrays and the effect of different design parameters on its performance. Receiver performance is analyzed through parameters extracted from simulations, namely, thermal mechanical current noise, plane wave pressure sensitivity, and pressure noise spectrum. Transmitter performance is analyzed through pressure output simulation, and the overall performance is analyzed through the simulated pulse-echo response from a perfect planar reflector and the thermal mechanical current noise limited SNR. It is observed that the frequency response is dominated by two vibroacoustic limiting mechanisms: Bragg’s scattering, determined by array lateral dimensions, and crosstalk actuated fundamental and antisymmetric array modes, determined by individual membrane dynamics. Based on the limiting mechanism frequencies, a simplified design methodology is developed and used to design two CMUT array sets covering a broad frequency range of 1-80MHz. These CMUT arrays are fabricated and their limiting mechanisms are experimentally verified through pressure and admittance measurement and simulation comparison. CMUT arrays for guidewire IVUS application are implemented and successfully interfaced with ASICs to demonstrate imaging at 40MHz. Considering that CMUT array performance is also susceptible to the electrical termination conditions, the simulation model is utilized to investigate the effect of different impedance matching scenarios. Receiver performance of the integrated CMUT array and termination circuitry is analyzed through the system’s SNR and acoustic reflectivity.Ph.D