Bliss G. Carkhuff

Multisite microprobes for neural recordings

Multisite, passive microprobes have been developed to allow simultaneous recording of action potential activity from multiple neurons at different locations in the brain. The microprobes were fabricated using standard integrated-circuit techniques. The probe is a planar structure that consists of gold electrodes sandwiched between two polyimide dielectric layers and bonded to a molybdenum structural support. Windows in the top dielectric layer expose the electrode sites and bonding pads. In two distinct versions of the probe, four or six recording sites of approximately 25 mu m/sup 2/ are arranged on a dagger-shaped structure which can penetrate the pia. The bonding pads and interconnect wires at the probe head are entirely encapsulated in a tubular fixture that is packed with silicone RTV and sealed with epoxy to protect the interconnections from contact with body fluids. The site impedances at 1 kHz are typically between 2 and 4 M Omega . Probe lifetimes for continuous immersion in physiological saline solution, as measured by impedance, have exceeded 750 h. The failure mechanism is believed to be due to moisture and ion absorption in the top dielectric layer.<<ETX>>

Corrosion sensors for concrete bridges

Corrosion of rebar in concrete bridges is a problem for the infrastructure and is difficult to detect. Engineers and scientists at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) have developed a device that is designed to be buried in the concrete when the bridge deck is poured. The device, known as a wireless embeddable sensor platform/smart aggregate (WESP/SA), can provide data about conditions within the bridge deck. This data will assist highway maintenance engineers in determining corrosive actions.

Packaging for a Sensor Platform Embedded in Concrete

The Johns Hopkins University Applied Physics Laboratory is developing packaging for a sensor platform to be embedded in the harsh environment of concrete structures. The sensors will monitor the corrosive environment of the structure over periods of several decades to aid in scheduling maintenance and repair. The United States has recognized the risks associated with its aging infrastructure and is actively replacing deteriorated/high risk structures as well as simultaneously developing the tools and techniques to monitor new infrastructure as it ages. JHU/APL has reviewed the sensing requirements for infrastructure monitoring, especially bridge decks, and developed a concept based on distributed, embedded sensors. The Wireless, Embedded Sensor Platform (WESP) will implement the concept of a low-cost, customizable sensor platform suitable for long-term field measurements. The WESP is designed to be powered and queried remotely as often as required and can be used to measure the evolution of the corrosive environment over time. The objective of this research and development is to design, implement, and demonstrate packaging techniques for embedded sensor suites commensurate with a 50-year lifetime when embedded in concrete having a pH greater than 13, and exposed to harsh environments of salt, and mechanical and thermal stress. To meet this objective, the WESP construction will use a commercial ceramic IC package and unique manufacturing and assembly techniques. The prototype is expected to provide sensor identification, temperature, pressure, and conductivity data within a package volume less than 2.5 cm 3 (0.15 in 3 ). Reliability test results will be reviewed and specialized tests will be performed to evaluate the performance of the packaging design. These include such tests as freeze/thaw cycling, thermal shock, thermal cycling, Highly Accelerated Stress Test (HAST), 85% relative humidity/85°C, and accelerated life testing. Future developments are expected to reduce size and implement additional sensor types to fully characterize the concrete environment.

An external sensor for instantaneous measurement of the internal temperature in lithium-ion rechargeable cells

Based on a four-probe electrical measurement, we have developed a Battery Internal Temperature Sensor. BITS, unlike a surface-mounted thermocouple, provides a direct measure of the internal temperature. We have demonstrate in several different rechargeable lithium-ion cells ranging in capacity from 2- to 50-Ah, the existence of an intrinsic relationship between a cells internal temperature and a readily measurable electrical parameter. Today, container rupture and fire are the most detrimental consequences of thermal runaway in rechargeable Li-ion cells. Although storing or operating Li-ion cells in high-temperature environments is not advisable, high internal temperature has a greater potential to initiate catastrophic events. Measuring the environmental temperature at any proximity to the surface of the cell is insufficient to know or intervene with fast-rising internal heat. For example, monitoring internal temperature in real time has direct relevance to the thermal runaway caused by external and internal short circuits that may have no relevance to the external temperature. Yet, until now, there has been no simple technique to monitor the internal temperature of a single cell or multiple cells in Li-ion batteries. BITS, developed by the Johns Hopkins University Applied Physics Laboratory, is a miniature instrument, with demonstrated capability to measure and report internal temperature of individual cells in a multi-cell battery pack at the rate of 200-ms/cell.

Development of a Human Head Physical Surrogate Model for Investigating Blast Injury

The objective of this effort was to develop a Human Surrogate Head Model (HSHM) and measure its response to pressure loading conditions representative of a blast environment. The HSHM consists of skin, face, skull, and brain fabricated using biosimulant materials and mounted to the neck of a Hybrid III Anthropomorphic Test Device to allow head motion during loading. The HSHM instrumentation includes pressure and displacement sensors embedded in the anterior and posterior areas of the brain along the saggital plane. The displacement sensors are a custom solution developed for this particular application. A series of shock tube tests at three varying load levels were conducted with the HSHM to simulate blast loading conditions. As pressure loading levels increased, the intracranial pressures and brain displacements increased as well. However, the spatial response of the displacement sensors varied with location in the brain. The results of this test series provide the first instance of intracranial pressure and directly measured brain displacements recorded from an anatomically correct head surrogate exposed to conditions representative of blast loading.Copyright

Heat generation in Li-ion cells during charge and discharge

The conventional dialogues on the reasons for thermal runaway, venting and fire of Li-ion cells point to temperature increase and gas formation. There is, however, no consensus on which of these events occurs first, thereby enabling research to correctly target the root cause. The recent work conducted at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) demonstrates that neither the temperature increase nor gas formation may be the primary reason for the venting or fire. Instead, the primary reason could potentially be a thermodynamic parameter that is often associated with both anode and cathode, namely entropy. Typically, a decrease in entropy, and a concomitant increase in the electrode temperature have been observed in the anode during charging, and in the cathode during discharging. We find that under ambient operating conditions (0 to 40 °C), entropy-driven thermal energy accounts for more than 2/3rd of the heat. More importantly, sudden changes in the entropy increases the electrode temperature by an order-of-magnitude that if left unchecked could drive the electrode temperatures sufficiently high to disrupt the SEI layer, bringing the active materials in the electrodes in direct contact with the electrolyte, enabling exothermic reactions. Battery internal temperature (BIT) sensor, a technique that we recently developed at JHU/APL enables one to follow the anode and cathode temperatures in real time, while the cell is under charge and discharge. We will discuss the application of BIT sensor in estimating the entropy changes that define the limits of safety in Li-ion cells.

Advanced QCM controller for NASA's plume impingement contamination-II

Currently, no accurate models or recent data exist for modeling contamination from spacecraft thrusters to meet the stringent requirements of the International Space Station (ISS). Few flight measurements of contaminant deposition from spacecraft thrusters have been made, and no measurements have been made for angles away from the plume centerline. The Plume Impingement Contamination-II (PIC-II)1 experiment is planned to provide such measurements using quartz crystal microbalances placed into the plume of a Shuttle Orbiter RCS thruster. To this end, the Johns Hopkins University Applied Physics Laboratory (APL) has supported NASA in the development of the PIC-II experiment Flight Electronics Unit known as the Remote Arm TQCM System (RATS), which will measure the contamination in the Shuttle Obiter RCS thruster. The development was based on an ongoing effort between the APL and QCM Research to develop an inexpensive, miniature TQCM controller based on a legacy of QCM controllers developed at the APL. PIC-II will provide substantial improvements over previous systems, including higher resolution, greater flexibility, intensive housekeeping, and in-situ operational control. Details of the experiment hardware and measurement technique are given. The importance of the experiment to the ISS and the general plume contamination community is discussed.