Pyroelectric sensor sensitivity enhanced by active hysteresis excitation

A pyroelectric sensor system comprising:

• an alternating voltage source generating an alternating voltage at a predetermined frequency;
• a pyroelectric sensor element responsive to the alternating voltage, said pyroelectric sensor generating a hysteresis loop charge output that follows a hysteresis loop of the element in response to the alternating voltage, said hysteresis loop of the sensor element changing shape when the sensor element changes temperature, said pyroelectric sensor element having a composition so that the alternating voltage causes a polarization reversal of dipoles in the element in response to positive and negative changes of the alternating voltage;
• a chopper alternately blocking and passing incident radiation directed towards the sensor element at a predetermined frequency, wherein a reference temperature is applied to the sensor element when the chopper is closed and blocks the incident radiation and a scene temperature is applied to the sensor element when the chopper is open and passes the incident radiation, said chopper having a frequency that is less than the frequency of the alternating voltage so that multiple positive and negative components of the alternating voltage are applied to the pyroelectric sensor element each time the chopper is either opened or closed;
• and
• a processing system responsive to the hysteresis loop charge output from the sensor and determining the area within the hysteresis loop of the hysteresis loop output, said signal processing system separately detecting and integrating the charge output each time the chopper is opened and closed to provide a comparison of the reference temperature and the scene temperature.

A method of determining a charge output from a pyroelectric element, said method comprising the steps of:

• applying an alternating voltage to the pyroelectric element, said pyroelectric element having a composition so that the alternating voltage causes a polarization reversal of dipoles in the element in response to positive and negative changes of the alternating voltage;
• detecting a hysteresis loop charge output of the pyroelectric element over a predetermined time period;
• determining the area within the hysteresis loop of the hysteresis loop output;
• and
• integrating the detected charge output over a plurality of cycles of the alternating voltage for the predetermined time period.

A method of determining a charge output from a pyroelectric element, said method comprising the steps of:

• driving the pyroelectric element with an alternating voltage so that the alternating voltage causes the pyroelectric element to cover at least a portion of a hysteresis loop output of the element to provide at least a partial polarization reversal of the element;
• detecting the hysteresis loop output of the pyroelectric element as a charge output over a predetermined time period;
• integrating the detected output over a plurality of hysteresis loop cycles of the hysteresis loop output from the element for the predetermined time period;
• and
• comparing the integrated charge output to the integrated charge output from a previous time period to provide increased signal averaging.

A system that exhibits a hysteresis loop output response to an input signal, said system comprising:

• an alternating voltage source generating an alternating voltage at a predetermined frequency;
• a system element responsive to the alternating voltage, said system element generating a hysteresis loop charge output in response to the alternating voltage, said alternating voltage driving the system element over at least a portion of the hysteresis loop output of the element, said system element having a composition so that the alternating voltage causes a polarization reversal of dipoles in the element in response to positive and negative changes of the alternating voltage;
• and
• a charge integration system responsive to the charge output from the system element, said charge integration system measuring multiple polarization reversals of the element for each positive and negative component of the alternating voltage, said integration system determining the area within the hysteresis loop of the hysteresis loop output and generating a signal indicative of the charge output from the sensor element.

A method of determining a charge output from a hysteresis loop element, said method comprising the steps of:

• applying an alternating voltage to the hysteresis loop element, said hysteresis loop element having a composition so that the alternating voltage causes a polarization reversal of the alignment of dipoles in the element in response to positive and negative changes of the alternating voltage;
• detecting a hysteresis loop charge output of the hysteresis loop element for multiple polarization reversals over a predetermined time period;
• determining the area within the hysteresis loop of the hysteresis loop output;
• and
• integrating the detected charge output over a plurality of cycles of the alternating voltage for the predetermined time period.

A pyroelectric sensor system comprising:

• an alternating voltage source generating an alternating voltage at a predetermined frequency;
• a pyroelectric sensor element responsive to the alternating voltage, said pyroelectric sensor element generating a hysteresis loop charge output in response to the alternating voltage, said alternating voltage driving the sensor element over at least a portion of the hysteresis loop output of the element;
• and
• a charge integration system responsive to the charge output from the pyroelectric sensor element, said integration system generating a signal indicative of the charge output from the sensor element, said charge integration system including a first detector responsive to the hysteresis loop charge output and a second detector responsive to the hysteresis loop charge output, said first detector generating a first voltage output from positive components of the alternating voltage and said second detector generating a second voltage output from negative components of the alternating voltage.