UCB Ultrasound Personal Locator System - Overview
We have developed a personal locator system to detect the presence or absence of persons in an enclosed space. The system consists of one to five small ultrasound emitting devices (“locators”) and one ultrasound receiving device. Each locator is worn on an individual’s clothing and produces a distinct pattern that is emitted every few seconds. The ultrasound receiver, mounted on the wall of a room, detects the pattern from the ultrasound emitting locator. If the identifying signal pattern emitted from a particular locator is received a certain number of times during a minute, that locator, and presumably the person wearing it, is recorded as being present in the room during that minute. Preliminary tests show good results, with a 93% accuracy rate in field trials as measured against direct observation. Future improvements include a stand-alone feature for the receiver, better current consumption, reduction of sensitivity, and more field testing.

Development Team
Gian Allen-Piccolo, Rufus D. Edwards, Kirk R Smith, Tracy Allen, Jamisine Rogers, Eduardo Castro, Fredy Agustin, Anaite Diaz.

Collaborating Institutions
University of California at Berkeley, EME Systems, University of California at Irvine, MERTU/Universidad del Valle de Guatemala

Why use the UCB Locator?
Measurement of exposure to pollutants and other hazards is of vital importance in the field of environmental health. The significance of a hazard depends greatly on the amount of time a person is in contact with it. For instance, high indoor air pollution levels have been found in many households around the world. The risk for respiratory disease, however, depends also on the amount of time people spend indoors in the presence of this pollution. A number of ways have been used to determine people’s time activity patterns in a way that can be use to combine with pollution levels to determine actual exposure. Among these methods, two that are most often used in third-world household settings where our research is focused are participant recollection and direct observation.

Participant recall requires that a study participant answer questions about her/his actions at a prior time. Such time/activity assessment is relatively cheap and easy, as a researcher only needs to have the participant fill out a questionnaire describing her/his whereabouts and actions during the period in question (e.g. the day before). A serious drawback to this method is that people’s memories are far from perfect. As such, the results of personal recollection cannot always be trusted to be very accurate, especially when the time period in question is relatively long. In addition, this method requires an excellent sense of time, both absolute time of day and duration, and such questionnaires tend to be tedious to administer and answer.

The “gold-standard” in time/activity assessment is direct observation of a participant’s actions during a defined time period. For example, a researcher may observe a family for three hours during the morning while breakfast is being cooked and served. The location and actions of one or more of the family members is recorded so as to ascertain the amount of time he/she/they are exposed to the cooking smoke. Although very accurate, direct observation does have drawbacks. One is the cost and time involved with researchers spending prolonged periods recording the direct observation results. Another is the question of whether a researcher’s presence in the study area influences the actions of the participants. Furthermore, the direct observation method is rather invasive.

How does the UCB Locator work?
We have developed a system as an alternative to these methods. The system makes use of electronics and ultrasound to determine if and when particular study participant is in a room. The system is comprised of two parts: one to several locators and one receiver. Locators are small, portable devices carried by participants whose location (and hence exposure) is in question. The locators emit an ultrasound pulse once every few seconds. Each locator emits a distinct sound pattern that defines its identity. The receiver, statically mounted in the room in question, listens constantly for ultrasound pulses from locators. If it hears a pulse, it records the time of the transmission (to the minute) and the identity of the locator. In this manner, the times a study participant spends in a room in question can be determined. When coupled with air pollution data from that room, the two can determine the participant’s exposure.